Biomedical Technology Dept. Fondazione Don Gnocchi via Capecelatro 66 20148 Milan. Italy
pcastiglioni@dongnocchi.it
Paolo Castiglioni (Varese, Italy, 1961) received the M. Sc. Degree in electronic engineering (1987) and the Ph. D. degree in biomedical engineering (1993), both from the Politecnico di Milano University (Milan, Italy). From 1989 to 2007 he was researcher at the Bioengineering Department of Fondazione Don Carlo Gnocchi in Milan (Italy). From 2007 he is research coordinator of the Biosignal Analysis Area at the Biomedical Technology Department of Fondazione Don Carlo Gnocchi in Milan (Italy). His research interests include the analysis of biological signals (mainly cardiovascular signals and EEG), physiological mechanisms for cardiovascular control and gravitational physiology.
Abstract: We read with interest the paper by Vernet et al. published on this journal [1] which describes the characteristics of residual excessive sleepiness (RES) in obstructive sleep apnea (OSA) patients treated with continuous positive airway pressure (CPAP). The authors studied two groups of OSA patients, with and without RES. The apnea/hypopnea index dramatically decreased in both groups testifying that CPAP was applied properly. Patients underwent cognitive, psychological, biological and clinical tests, and 24-h sleep analyses. Surprisingly, very few differences were found between patients with and without RES, despite the large disparity in the Epworth sleepiness score. In his editorial comment, Rodenstein notes that after such as “breathtaking effort... very little comes out†on what may cause RES [2]. In this scenario, even decidedly unorthodox hypotheses may appear as possible mechanisms for explaining RES, worth of future investigations. For instance, Rodenstein suggested to consider the effects of “catastrophising†in perceiving and reporting subjective sleepiness, or the hypothesis that diabetes plays a protective role in RES [2].
We want to suggest, however, two more orthodox explanations for RES in OSA patients properly treated by CPAP. The first explanation regards the presence of the Obesity Hypoventilation Syndrome (OHS), or of a comorbidity with chronic obstructive pulmonary disease, the so-called overlap syndrome (OS), in the OSA group with RES. In fact, both OHS and OS contribute to daytime sleepiness [3;4] through hypercapnia. Proper CPAP treatment in OSA patients with OHS may make the sleep architecture, the arousal index and the apnea/hypopnea index similar to those of CPAP-treated OSA patients without OHS, but nevertheless hypercapnia may remain significant [5]. Moreover, CPAP treatment does not reduce the high Epworth sleepiness score of OS patients [4]. Since PaCO2 was not measured, OHS or OS cannot be excluded in the obese OSA patients with RES studied by Vernet et al. Therefore RES could be in part explained by the ineffectiveness of CPAP to reduce hypercapnia in OHS or OS patients.
Another explanation for RES could be linked to the possible presence of cardiovascular autonomic dysregulations induced by autonomic or “subcortical†arousals. “Autonomic arousals†involve brain-stem neurons controlling both sleep/vigilance and cardiovascular regulation. They are not necessarily associated with detectable EEG changes, but are responsible for changes in cardiac autonomic regulation. Actually we found an association between excessive sleepiness during the day and impaired autonomic cardiac modulation at night comparing two groups of sleep disordered breathing patients, with and without excessive daytime sleepiness [6]. Both groups had a wide spectrum of disease severity, from simple snoring to OSA, had similar sleep architectures, similar apnea/hypopnea index and arousal index; but patients with excessive daytime somnolence showed lower baroreflex sensitivity and greater ratio of the low- to-high frequency heart rate powers at night, both indexes of increased sympatho/vagal balance [7]. Results were confirmed after having removed obese patients to exclude OHS [8]. Thus cardiovascular autonomic alterations during sleep may be associated to excessive daytime sleepiness, probably because markers of brainstem dysfunctions involving both alertness and cardiovascular control.
Abstract: Brain-computer interface (BCI) systems aim to enable interaction with other people and the environment without muscular activation by the exploitation of changes in brain signals due to the execution of cognitive tasks. In this context, the visual P300 potential appears suited to control smart homes through BCI spellers. The aim of this work is to evaluate whether the widely used character-speller is more sustainable than an icon-based one, designed to operate smart home environment or to communicate moods and needs. Nine subjects with neurodegenerative diseases and no BCI experience used both speller types in a real smart home environment. User experience during BCI tasks was evaluated recording concurrent physiological signals. Usability was assessed for each speller type immediately after use. Classification accuracy was lower for the icon-speller, which was also more attention demanding. However, in subjective evaluations, the effect of a real feedback partially counterbalanced the difficulty in BCI use. Practitioner Summary: Since inclusive BCIs require to consider interface sustainability, we evaluated different ergonomic aspects of the interaction of disabled users with a character-speller (goal: word spelling) and an icon-speller (goal: operating a real smart home). We found the first one as more sustainable in terms of accuracy and cognitive effort.
Abstract: How the autonomic nervous system influences the fractal dynamics of heart rate (HR) and blood pressure (BP) remains unclear. The purpose of our study was to separately assess cardiac vagal and sympathetic (cardiac vs. vascular) influences on fractal properties of HR and BP as described by scale exponents of detrended fluctuation analysis (DFA). R-R intervals, systolic and diastolic BP were measured in nine supine volunteers before and after administration of autonomic blocking agents (atropine, propranolol, atropine+propranolol, clonidine). Spectra of DFA scale exponents, α(t), were calculated for scales between 5 and 100 s. HR and BP scale structures differed at baseline, being α(t) of HR <1, with a minimum between 10 and 20 s followed by a higher plateau between 40 to 80 s, while α(t) of BP decreased with t from values >1. Comparison of atropine and propranolol with baseline and combined cardiac parasympathetic and sympathetic blockade (atropine+propranolol) indicated opposite influences of vagal and cardiac sympathetic outflows on HR exponents. The vagal outflow adds white-noise components, amplifying differences with BP exponents; the cardiac sympathetic outflow adds Brownian motion components at short scales and contributes to the plateau between 40 and 80 s. Overall sympathetic inhibition by clonidine decreased short- and long-term exponents of HR, and short-term exponents of BP, so that their α(t) spectra had different means but similar profiles. Therefore, cardiac vagal, cardiac sympathetic and vascular sympathetic outflows contribute differently to HR and BP fractal structures. Results are explained by different distribution and dynamics of acetylcholine receptors and of α- and β-adrenergic receptors between heart and vasculature.
Abstract: Detrended fluctuation analysis (DFA) is the most popular method for assessing the fractal characteristics of heart rate (HR). Traditionally, short-term and long-term scale coefficients, α(1) and α(2), are calculated from DFA. We recently showed that the traditional approach oversimplifies a more complex phenomenon better represented by a continuous spectrum of scale coefficients. In this paper we present a DFA based method for describing the HR fractal dynamics with a temporal spectrum of scale exponents, α(t), rather than by a model of lumped parameters, α(1) and α(2). Since α(t) is a function of the temporal scale, its interpretation is facilitated when conditions with different mean HR are compared. In this work, we reanalyze HR data, collected by our group in previous studies, by applying the proposed α(t) spectrum. We quantify the effects of gender, ageing, posture and activity level, and the alterations induced by exposure to high and very-high altitude hypoxia, on α(t). Most of the results may be interpreted in terms of changes of cardiac autonomic regulation, and indicate clearly that the new proposed DFA spectrum provides a more faithful and interpretable description of the HR fractal dynamics than traditional α(1) and α(2) scale coefficients.
Abstract: Sodium sensitivity is an important cardiovascular risk factor for which a diagnosis requires a time-consuming protocol, the implementation of which is often challenging for patients and physicians. Our aim was to assess the reliability of an easier approach based on data from 24-hour ambulatory blood pressure monitoring performed in hypertensive subjects during daily-life conditions and habitual diet. We enrolled 46 mild to moderate hypertensive subjects who underwent 24-hour ambulatory blood pressure monitoring during usual sodium intake. Patients were divided into 3 classes of sodium sensitivity risk on the basis of ambulatory blood pressure monitoring data: low risk if dippers and a 24-hour heart rate ≤ 70 bpm; high risk if nondippers and a 24-hour heart rate of > 70 bpm; intermediate risk with the remaining combinations (dippers with heart rate > 70 bpm or nondippers with heart rate ≤ 70 bpm). Then patients underwent a traditional sodium sensitivity test for the dichotomous classification as sodium sensitive or sodium resistant and for evaluating the sodium sensitivity index. Prevalence of sodium-sensitive patients and mean value of sodium sensitivity index were calculated in the 3 risk classes. The sodium sensitivity index markedly and significantly increased from the low-risk to the high-risk class, being equal to 19.9 ± 14.4, 37.8 ± 8.3, and 68.3 ± 17.0 mm Hg/(mol/day) in the low-risk, intermediate-risk, and high-risk classes, respectively (M ± SEM). Also, the prevalence of sodium-sensitive patients increased significantly from the low-risk class (25%) to the intermediate-risk (40%) and high-risk (70%) classes. Thus, performance of 24-hour ambulatory blood pressure monitoring in daily-life conditions and habitual diet may give useful information on the sodium sensitivity condition of hypertensive subjects in an easier manner than with the traditional sodium sensitivity test approach.
Abstract: Nutrition support is an important aspect of multidisciplinary approaches in cardiology rehabilitation. However, little is known about the impact of a patient's nutrition status on recovery after elective heart surgery. The authors assessed changes in nutrition markers in patients undergoing postsurgical rehabilitation, and tested their correlation with systemic inflammatory responses and clinical outcomes to determine the adequacy of the prescribed dietary regimen.
Abstract: This paper illustrates two extensive applications of a smart garment we previously developed for the monitoring of ECG, respiration, and movement. In the first application, the device, named Maglietta Interattiva Computerizzata (MagIC), was used for the home monitoring of cardiac patients. The used platform included MagIC for signals collection, a touchscreen computer with a dedicated software for data handling, and a universal mobile telecommunications system (UMTS) dongle for data transmission, via email, to three cardiologists. Three patients daily-performed 3-min telemonitoring sessions for 30 days by using the platform. The whole system behaved correctly in 85 out of 90 sessions. In five instances, a second session was required due to UMTS traffic congestion. Only in three sessions, cardiologists asked the patient to repeat the acquisition because of poor signal quality. In the second application, MagIC was used to evaluate the effects of high-altitude hypoxia on sleep and 24 h daily life in 30 healthy subjects at 3500 and 5400 m above sea level on Mount Everest slopes. The use of MagIC garment was reported to be simple and requiring short instrumentation time even in the demanding expedition environment. The signal quality was adequate in 111 out of 115 recordings and 90% of the subjects found the vest comfortable.
Abstract: To investigate the effects of hypoxia during sleep on linear and self-similar components of heart rate variability (HRV) in eight healthy subjects at high altitude on Mount Everest.
Abstract: It is known that baroreflex sensitivity (BRS) is impaired in cardiac patients with myocardial infarction (MI). Nevertheless, it is unknown whether factors other than a reduced ejection fraction play a role in the baroreflex impairment of these patients.
Abstract: The aim of this paper is to highlight the aspects of the baroreflex control of the cardiovascular system that could be relevant to the analysis and modelling of cardiovascular oscillations and regulation. In particular, complex and/or controversial issues of the baroreflex control are addressed on the basis of results obtained in previous studies by others as well as by our group. Attention has been focused on time-variant and nonlinear characteristics of the baroreflex function and on the influence of this physiological mechanism on different frequency regions of blood pressure and heart rate spectra.
Abstract: Heart rate self-affinity is often assessed by detrended fluctuations analysis, obtaining two coefficients only: a short-term (alpha(1)) exponent and a long-term (alpha(2)) exponent. Our aim is to show the limits of this approach and alternatively propose the estimation of the whole spectrum of local exponents alpha(n) for heart rate and blood pressure. To illustrate the advantages of this approach, we assess the effects of autonomic activations and age on alpha(n). We measured ECG and arterial pressure in 60 volunteers for 10 min, considering three conditions at increasing sympathetic activation: supine rest, sitting, and sitting during exercise. We computed alpha(n) of R-R intervals and systolic, mean, and diastolic blood pressures, as the slope of the detrended fluctuations function in a log-log plot. Volunteers were divided into age groups and compared. Results indicate that: 1) alpha(1) cannot be defined because short-term coefficients decrease with n, while alpha(2) cannot be defined only for blood pressure during supine rest; 2) heart rate and blood pressure scaling structures differ during supine rest but not during exercise; and 3) age effects appear mainly in supine rest, explaining discrepant results in literature. In conclusion, we recommend estimating the whole alpha(n) spectrum before possibly providing the "two-exponent" description only.
Abstract: A brain-computer interface (BCI) directly uses brain-activity signals to allow users to operate the environment without any muscular activation. Thanks to this feature, BCI systems can be employed not only as assistive devices, but also as neurorehabilitation tools in clinical settings. However, several critical issues need to be addressed before using BCI in neurorehabilitation, issues ranging from signal acquisition and selection of the proper BCI paradigm to the evaluation of the affective state, cognitive load and system acceptability of the users. Here we discuss these issues, illustrating how a rehabilitation program can benefit from BCI sessions, and summarize the results obtained so far in this field. Also provided are experimental data concerning two important topics related to BCI usability in rehabilitation: the possibility of using dry electrodes for EEG acquisition, and the monitoring of psychophysiological effects during BCI tasks.
Abstract: Sleep-related breathing disorders are common causes of excessive daytime sleepiness, a socially and clinically relevant problem. Mechanisms responsible for daytime sleepiness are still largely unknown. We investigated whether specific alterations in autonomic cardiac modulation during sleep, commonly associated with sleep-related breathing disorders, are related to excessive daytime sleepiness. Fifty-three patients with sleep-related breathing disorders underwent nocturnal polysomnography. Excessive daytime sleepiness was diagnosed as a Multiple Sleep Latency Test response less than or equal to 600 s. We explored the relation of excessive daytime sleepiness, objectively determined, with indices of autonomic cardiac regulation, such as baroreflex sensitivity and heart rate variability, with polysomnographic indices of the severity of sleep-related breathing disorders and with quality of sleep. Patients with excessive daytime sleepiness, when compared with patients without, had significantly lower baroreflex sensitivity and significantly higher low-to-high frequency power ratio of heart rate variability during the different stages of nocturnal sleep. By contrast, no differences were found in indices quantifying the severity of sleep-related breathing disorders or sleep quality. We demonstrated that excessive daytime sleepiness is accompanied by a deranged cardiac autonomic control at night, the latter probably reflecting autonomic arousals not detectable in the EEG. As abnormal autonomic regulation is also known to be associated with increased cardiovascular risk, a possible relation between excessive daytime sleepiness and cardiovascular events in patients with sleep-related breathing disorders deserves to be investigated in future studies.
Abstract: This study explored the process of arterial baroreflex adaptation to microgravity, starting from the first day of flight, during the 16-day STS-107 Columbia Space Shuttle mission. Continuous blood pressure (BP), ECG, and respiratory frequency were collected in four astronauts on ground (baseline) and during flight at days 0-1, 6-7, and 12-13, both at rest and during moderate exercise (75 W) on a cycle ergometer. Sensitivity of the baroreflex heart rate control (BRS) was assessed by sequence and spectral alpha methods. Baroreflex effectiveness index (BEI); low-frequency (LF) power and high-frequency (HF) power of systolic BP (SBP), diastolic BP (DBP), and R-R interval (RRI); the RRI LF/HF ratio; and the RRI root mean square of successive differences (RMSSD) index were also estimated. We found that, at rest, BRS increased in early flight phase, compared with baseline (means +/- SE: 18.3 +/- 3.4 vs. 10.4 +/- 1.2 ms/mmHg; P < 0.05), and it tended to return to baseline in subsequent days. During exercise, BRS was lower than at rest, without differences between preflight and in-flight values. At rest, in the early flight phase, RMSSD and RRI HF power increased (P < 0.05) compared with baseline, whereas LF powers of SBP and DBP decreased. No statistical difference was found in these parameters during exercise before vs. during flight. These findings demonstrate that heart rate baroreflex sensitivity and markers of cardiac vagal modulation are enhanced during early exposure to microgravity, likely because of the blood centralization, and return to baseline values in subsequent flight phases, possibly because of the fluid loss. No deconditioning seems to occur in the baroreflex control of the heart.
Abstract: In inflammatory bowel diseases, changes in autonomic enteric regulation may also affect neural cardiovascular control. However, while cardiac autonomic modulation has been shown to be impaired in active ulcerative colitis, the occurrence of cardiovascular autonomic alterations, also in the quiescent phase of inflammatory bowel diseases, is still a matter of debate. The aim of our study was thus to explore the features of cardiovascular autonomic regulation in ulcerative colitis and Crohn's disease during their remission phase.
Abstract: It is still unclear whether the low-frequency oscillation in heart rate is generated by an endogenous neural oscillator or by a baroreflex resonance. Our aim was to investigate this issue by analyzing blood pressure and heart rate variability and the baroreflex function in paraplegic subjects with spinal cord injury below the fourth thoracic vertebra. These subjects were selected because they represent a model of intact central neural drive to the heart, with a partially impaired autonomic control of the vessels. In our study, arterial blood pressure and ECG were recorded in 33 able-bodied controls and in 33 subjects with spinal cord lesions between the fifth thoracic and the fourth lumbar vertebra 1) during supine rest (lowest sympathetic activation), 2) sitting on a wheelchair (light sympathetic activation), and 3) during exercise (moderate sympathetic activation). Blood pressure and heart rate spectra, coherence, and baroreflex function (sequence technique) were estimated in each condition. Compared with controls, paraplegic subjects showed a reduction of the low-frequency power of blood pressure and heart rate, and, unlike controls, a 0.1-Hz peak did not appear in their spectra. Sympathetic activation increased the 0.1-Hz peak of blood pressure and heart rate and the coherence at 0.1 Hz in controls only. Paraplegic subjects also had significantly lower baroreflex effectiveness and greater blood pressure variability. In conclusion, the disappearance of the 10-s oscillation of heart rate and blood pressure in subjects with spinal cord lesion supports the hypothesis of the baroreflex nature of this phenomenon.
Abstract: One of the most important features of prolonged weightlessness is a progressive impairment of muscular function with a consequent decrease in exercise capacity. We tested the hypothesis that the impairment in musculo-skeletal function that occurs in microgravity results in a potentiation of the muscle metaboreflex mechanism and also affects baroreflex modulation of heart rate (HR) during exercise. Four astronauts participating in the 16 day Columbia shuttle mission (STS-107) were studied 72-71 days before launch and on days 12-13 in-flight. The protocol consisted of 6 min bicycle exercise at 50% of individual V(o2,max) followed by 4 min of postexercise leg circulatory occlusion (PECO). At rest, systolic (S) and diastolic (D) blood pressure (BP), R-R interval and baroreflex sensitivity (BRS) did not differ significantly between pre- and in-flight measurements. Both pre- and in-flight, SBP increased and R-R interval and BRS decreased during exercise, whereas DBP did not change. During PECO preflight, SBP and DBP were higher than at rest, whereas R-R interval and BRS recovered to resting levels. During PECO in-flight, SBP and DBP were significantly higher whereas R-R interval and BRS remained significantly lower than at rest. The part of the SBP response (delta) that was maintained by PECO was significantly greater during spaceflight than before (34.5 +/- 8.8 versus 13.8 +/- 11.9 mmHg, P = 0.03). The tachycardic response to PECO was also significantly greater during spaceflight than preflight (-141.5 +/- 25.2 versus - 90.5 +/- 33.3 ms, P = 0.02). This study suggests that the muscle metaboreflex is enhanced during dynamic exercise in space and that the potentiation of the muscle metaboreflex affects the vagally mediated arterial baroreflex contribution to HR control.
Abstract: Baroreflex control of heart rate during sleep (baroreflex sensitivity; BRS) has been shown to be depressed in obstructive sleep apnoea (OSA), and improved after treatment with continuous positive airway pressure (CPAP). Whether CPAP also acutely affects BRS during sleep in uncomplicated severe OSA is still debatable. Blood pressure was monitored during nocturnal polysomnography in 18 patients at baseline and during first-time CPAP application. Spontaneous BRS was analysed by the sequence method, and estimated as the mean sequence slope. CPAP did not acutely affect mean blood pressure or heart rate but decreased cardiovascular variability during sleep. Mean BRS increased slightly during CPAP application (from 6.5+/-2.4 to 7.5+/-2.9 ms x mmHg(-1)), mostly in response to decreasing blood pressure. The change in BRS did not correlate with changes in arterial oxygen saturation or apnoea/hypopnoea index. The small change in baroreflex control of heart rate during sleep at first application of continuous positive airway pressure in severe obstructive sleep apnoea was unrelated to the acute resolution of nocturnal hypoxaemia, and might reflect autonomic adjustments to positive intrathoracic pressure, and/or improved sleep architecture. The small increase in baroreflex control of heart rate during sleep may be of clinical relevance as it was accompanied by reduced cardiovascular variability, which is acknowledged as an independent cardiovascular risk factor.
Abstract: Spectral analysis of cardiovascular signals has been extensively used to investigate circulatory homeostatic mechanisms. However, the nature of very low-frequency (VLF) fluctuations remains unclear. Because we previously observed enhanced VLF fluctuations in blood pressure (BP) in the sympathectomized rat (a model characterized by markedly increased plasma epinephrine levels), the aims of our study were to assess whether the genesis of VLF fluctuations in BP depends on circulating catecholamines and to determine which adrenergic receptor(s) and which membrane ion channel(s) are involved. We used continuous intra-arterial BP recordings from unanesthetized unrestrained rats to compute the power of VLF fluctuations in BP in the intact condition, during acute ganglionic blockade with hexamethonium, and after restoration of BP levels by infusion (in addition to hexamethonium) of adrenergic agonists (epinephrine, norepinephrine, and clonidine) or nonadrenergic vasoconstrictors (vasopressin). Effects of infusion of specific adrenergic receptor blockers (propranolol, prazosin, and yohimbine) with hexamethonium and catecholamines and infusion of various membrane ion channel blockers on VLF fluctuations in BP were also evaluated. Our results are as follows. 1) Ganglionic blockade drastically reduced BP levels and VLF fluctuations. 2) All vasoconstrictors restored BP levels, but only adrenergic vasoconstrictors generated striking VLF fluctuations in BP. 3) Catecholamine-induced fluctuations were abolished by alpha2-, but not alpha1- or beta-, adrenergic receptor blockade and by Ba2+-sensitive K+ channel or L-type Ca2+ channel, but not by other ion channel, blockers. We conclude that, in the conscious, unrestrained ganglion-blocked rat, catecholamine infusion generates VLF fluctuations in BP through stimulation of alpha2-receptors and activation of Ba2+-sensitive K+ channels. These fluctuations may have (patho)physiological relevance under conditions of disrupted circulatory homeostasis.
Abstract: We investigated how complexity-based estimators of heart rate variability can detect changes in cardiovascular autonomic drive with respect to traditional measures of variability. This was done by analyzing healthy subjects and paraplegic patients with different autonomic impairment due to low (vascular impairment only) or high (cardiac and vascular impairment) spinal cord injury, during progressive autonomic activations. While traditional techniques only quantified the effects of the autonomic activation, not distinguishing the effects of the lesion level, some recently proposed complexity estimators could also reveal the pathologic alterations in the autonomic control of heart rate. These estimators included the detrended fluctuation analysis coefficient (sensitive to both low and high autonomic lesions), sample entropy (sensitive to low-level lesions) and the largest Lyapunov exponent (sensitive to high-level lesions). Thus complexity-based methods provide information on the autonomic function from the heart rate dynamics that cannot be obtained by traditional techniques. This finding supports the combined use of both complexity-based and traditional methods to investigate the autonomic cardiovascular control from a more comprehensive perspective.
Abstract: Estimation of self-similarity is a promising tool for quantifying alterations in cardiovascular dynamics. To evaluate the as yet unexplored influence of sympathetic vascular regulation on the scaling exponent, namely on the parameter characterizing self-similarity, we studied patients with a spinal cord injury as a model of progressively impaired vascular control. We considered 24 able-bodied subjects (AB) and 23 paraplegics with increasing lesion levels: between T(12) and L(4) (n=7); T(5) and T(11) (n=9); and C(6) and T(4) (n=7). We recorded the heart rate in three conditions characterized by increasing sympathetic activation: supine (SUP), sitting (SIT) and exercise (EXE). We calculated the scaling exponent by detrended fluctuation analysis (H(DFA)). Sympathetic activation had different effects on H(DFA), depending on the lesion level. H(DFA) tended to decrease in AB from SUP (0.85+0.02; mean+SEM) and SIT (0.84+0.02) to EXE (0.79+0.02). It remained constant in the T(12)-L(4) group (0.92+0.04, 0.94+0.05 and 0.94+0.04, respectively), while it increased significantly in the T(5)-T(11) group (0.88+0.07, 0.94+0.05, 1.00+0.08) and increased even more in the C(6)-T(4) group (0.83+0.07, 0.91+0.05, 1.06+0.06). Results suggest that heart-rate self-similarity depends on vascular sympathetic control, because it is altered by spinal-cord lesions, even when cardiac neural control is intact.
Abstract: The intention of this study was to test the hypothesis that, in heart failure patients, dietary supplementation of polyunsaturated fatty acids (PUFA) enhances arterial baroreceptor control of the cardiovascular system.
Abstract: Angiotensin-converting enzyme (ACE) inhibitors, which are frequently administered in patients with heart disease, have a known inhibitory effect on erythropoiesis. The aim of this study was to detect whether early ACE inhibitor administration slows recovery from anemia following recent cardiac surgery.
Abstract: This study compared spontaneous baroreflex sensitivity (BRS) estimates obtained from an identical set of data by 11 European centers using different methods and procedures. Noninvasive blood pressure (BP) and ECG recordings were obtained in 21 subjects, including 2 subjects with established baroreflex failure. Twenty-one estimates of BRS were obtained by methods including the two main techniques of BRS estimates, i.e., the spectral analysis (11 procedures) and the sequence method (7 procedures) but also one trigonometric regressive spectral analysis method (TRS), one exogenous model with autoregressive input method (X-AR), and one Z method. With subjects in a supine position, BRS estimates obtained with calculations of alpha-coefficient or gain of the transfer function in both the low-frequency band or high-frequency band, TRS, and sequence methods gave strongly related results. Conversely, weighted gain, X-AR, and Z exhibited lower agreement with all the other techniques. In addition, the use of mean BP instead of systolic BP in the sequence method decreased the relationships with the other estimates. Some procedures were unable to provide results when BRS estimates were expected to be very low in data sets (in patients with established baroreflex failure). The failure to provide BRS values was due to setting of algorithmic parameters too strictly. The discrepancies between procedures show that the choice of parameters and data handling should be considered before BRS estimation. These data are available on the web site (http://www.cbi.polimi.it/glossary/eurobavar.html) to allow the comparison of new techniques with this set of results.
Abstract: In this study we propose a procedure to automatically check the hypothesis of steady state from the dynamics of the cardiovascular signals, based on the 'run test'. The total number of runs rtot is computed from the series of systolic and diastolic blood pressures and R-R intervals. If rtot is lower than a given threshold, the steady-state hypothesis is rejected. Because of long-term correlations affecting the cardiovascular series, the thresholds at the 5% significance level were estimated calculating the rtot distributions from a public database of cardiovascular signals collected in steady-state conditions. The procedure was applied to quantify the steadiness of baseline recordings, and to identify sub-periods of steady state during a sequence of physical activities. Results showed the capability of the procedure to automatically detect steady-state conditions, and to identify when the steadiness is lost because of disturbing factors or transients occurring during the recording.
Abstract: Continuous blood pressure monitoring is an essential prerequisite for any study on blood pressure variability. Invasive procedures are no longer acceptable for research projects in a clinical setting, and recently developed devices able to record blood pressure on a beat-by-beat basis in a non-invasive fashion may represent valuable alternative tools. This article will briefly review the available information on the most recent advances in this field. It will focus on further developments of the original technology for finger blood pressure monitoring introduced by Penáz, as well as on newer devices that have been proposed over the last few years for non-invasive cardiovascular monitoring both in research and in clinical studies.
Abstract: Target organ damage in hypertensive patients is related to their increased average blood pressure and greater 24-hour blood pressure variability. Whether the rate of blood pressure changes is also greater in hypertension, producing a greater stress on arterial walls, is not known, however. Our study aimed at addressing this issue by computer analysis of 24-hour ambulatory intra-arterial blood pressure recordings in 34 subjects (29 males), 13 normotensive subjects and 21 uncomplicated hypertensive subjects (mean age+/-SD, 40.4+/-11.8 years). The number, slope (mm Hg/s), and length (beats) of systolic blood pressure ramps of 3 or more consecutive beats characterized by a progressive increase (+) or reduction (-) in systolic blood pressure of at least 1 mm Hg per beat were computed for each hour and for the whole 24-hour period. Twenty-four-hour average systolic blood pressure was 112.9+/-2.1 and 159.4+/-5.7 mm Hg in normotensive and hypertensive subjects, respectively. Over the 24 hours, the number and length of systolic blood pressure ramps were similar in both groups, whereas the slope was markedly different (24-hour mean+/-SE slope, 4.80+/-0.30 in normotensives and 6.50+/-0.40 mm Hg/s in hypertensives, P<0.05). Ramp slope was not influenced by age or reflex pulse interval changes, but it was greater for higher ramp initial systolic blood pressure values. Thus, in daily life, hypertensive subjects are characterized by steeper blood pressure changes than normotensives, and this, regardless of the mechanisms, may have clinical implications, because it may be associated with greater traumatic effect on the vessel walls of hypertensive patients.
Abstract: Indices of heart rate variability (HRV) based on fractal signal models have recently been shown to possess value as predictors of mortality in specific patient populations. To develop more powerful clinical indices of HRV based on a fractal signal model, the study investigated two HRV indices based on a monofractal signal model called fractional Brownian motion and an index based on a multifractal signal model called multifractional Brownian motion. The performance of the indices was compared with an HRV index in common clinical use. To compare the indices, 18 normal subjects were subjected to postural changes, and the indices were compared on their ability to respond to the resulting autonomic events in HRV recordings. The magnitude of the response to postural change (normalised by the measurement variability) was assessed by analysis of variance and multiple comparison testing. Four HRV indices were investigated for this study: the standard deviation of all normal R-R intervals; an HRV index commonly used in the clinic; detrended fluctuation analysis, an HRV index found to be the most powerful predictor of mortality in a study of patients with depressed left ventricular function; an HRV index developed using the maximum likelihood estimation (MLE) technique for a monofractal signal model; and an HRV index developed for the analysis of multifractional Brownian motion signals. The HRV index based on the MLE technique was found to respond most strongly to the induced postural changes (95% CI). The magnitude of its response (normalised by the measurement variability) was at least 25% greater than any of the other indices tested.
Abstract: We sought to evaluate whether changes in resting baroreflex control of heart rate are a distinctive feature of healthy subjects with a history of syncope prone to a positive tilt-test response.
Abstract: Our study aimed at elucidating the effects of acute central hypervolemia induced by water immersion (WI) on renal hemodynamics, hormonal responses and on cardiovascular control in hypertensive patients, as well as at evaluating the possible role of the opioidergic system (OS) in determining these effects. Thirteen essential hypertensives were studied for 2 h before and for 2 h during WI. This was done twice, without and with i.v. injection of the OS antagonist naloxone. Before and during WI alone, glomerular filtration rate (GFR), effective renal plasma flow (ERPF), renal vascular resistance (RVR), mean arterial pressure (MAP), pulse interval (PI), spontaneous baroreflex sensitivity (BRS), Low frequency to High frequency (LF/HF) ratio in PI spectra, hematocrit, urinary sodium excretion, plasma renin activity (PRA) and aldosterone (PA) were assessed. Based on their response to WI, hypertensives were subdivided into two groups: ERPF+ (n = 7) in whom WI increased ERPF, and ERPF- (n = 6) in whom WI reduced ERPF. ERPF+ displayed a higher BRS than ERPF- at baseline and during WI. A suppression of PRA and PA and an increase in MAP and urinary sodium excretion were found in both groups. In ERPF+ naloxone caused RVR and MAP to increase during WI and this response was associated with a blockade of the increase in ERPF in this group, while BRS and natriuresis were unchanged. In ERPF- naloxone did not affect WI-induced MAP, ERPF, RVR and BRS changes, while it blunted sodium excretion. Our data provide the first evidence of a differentiate renal hemodynamic response to WI in hypertension; they also suggest that while OS may significantly potentiate the renal vasodilatory response to WI in ERPF+, it does not affect the natriuretic response nor the changes in systemic cardiovascular regulation induced by central hypervolemia.
Abstract: The role of the arterial baroreflex in the cardiovascular changes associated with the obstructive sleep apnea syndrome (OSAS), and the effect of nasal continuous positive airway pressure (CPAP) treatment on baroreflex function during sleep are unknown. Baroreflex control of heart rate was studied in 29 normotensive patients with OSAS under no treatment, in 11 age-matched control subjects, and in 10 patients at CPAP withdrawal after 5.5 +/- 3.7 (range 3-14) months of treatment. Baroreflex control of heart rate was assessed by "sequence method" analysis of continuous blood pressure recordings (Finapres) obtained during nocturnal polysomnography. In untreated OSAS, baroreflex sensitivity (BRS) was low during wakefulness and non-rapid eye movement (REM) stage 2 sleep compared with control subjects, and correlated inversely with mean lowest Sa(O(2)) and the blood pressure increase after apneas. After CPAP treatment, the apnea-hypopnea index was lower, and mean lowest Sa(O(2)) higher than before treatment. After CPAP, patients were more bradycardic, blood pressure and its standard deviation decreased as Sa(O(2)) improved in non-REM stage 2 sleep, and BRS increased (nocturnal wakefulness: +59%; non-REM stage 2 sleep: +68% over pretreatment values). Our data suggest that baroreflex dysfunction in OSAS may be at least partly accounted for by nocturnal intermittent hypoxemia, and can be reversed by long-term CPAP treatment.
Abstract: In healthy subjects, progressive beat-to-beat increases or decreases in systolic blood pressure (SBP) ramps are not always accompanied by baroreflex-driven lengthening or shortening in pulse interval (PI) ramps, respectively. This phenomenon has been quantified by a new index, the baroreflex effectiveness index (BEI), defined as the ratio between the number of SBP ramps followed by the respective reflex PI ramps and the total number of SBP ramps observed in a given time window. Specificity of BEI was shown in eight cats by a -89% reduction of BEI after sinoaortic denervation. In 14 healthy humans, the 24-h average BEI value was 0.21, with a marked day-night modulation ( approximately 0.25 day, approximately 0.15 night) in counterphase with modulation of baroreflex sensitivity (BRS). Our analysis indicates that 1) in normal subjects, arterial baroreflex can induce beat-by-beat PI changes in response to only 21% of all SBP ramps, possibly because of central inhibitory influences or of interferences at sinus node level by nonbaroreflex mechanisms and 2) BEI provides information on the baroreflex function that is complementary to BRS.
Abstract: Newer techniques to evaluate baroreflex sensitivity (BRS) are based on the analysis of blood pressure (BP) and heart rate (HR) time series in the time or frequency domain. These novel approaches are steadily gaining popularity, since they do not require injection of vasoactive substances, nor do they rely on a complex experimental set-up.
Abstract: This review deals with a number of issues related to blood pressure variability. These include: historical aspects, with reference to the first pioneering observations; methodological aspects, focusing on the different methods for quantifying blood pressure variability; description of the characteristics of blood pressure variability over the 24 hours; mechanisms involved in determining the different magnitude of this phenomenon in different subjects, such as behavioral factors, central and reflex neural influences, humoral and mechanical factors; blood pressure variability as a probe to assess spontaneous baroreflex sensitivity; effects of aging and hypertension on blood pressure variability, with a discussion of the clinical relevance of this phenomenon in the prognostic evaluation of patients; effects of drugs on blood pressure variability. Finally methodological aspects related to the use of noninvasive ambulatory blood pressure monitoring in the assessment of blood pressure variability are discussed.
Abstract: The aim of our study was to assess the effects of lacidipine, a long-acting calcium antagonist, on 24-hour average blood pressure, blood pressure variability, and baroreflex sensitivity. In 10 mildly to moderately hypertensive patients with type II diabetes mellitus (aged 18 to 65 years), 24-hour ambulatory blood pressure was continuously monitored noninvasively (Portapres device) after a 3-week pretreatment with placebo and a subsequent 4-week once daily lacidipine (4 mg) or placebo treatment (double-blind crossover design). Systolic blood pressure, diastolic blood pressure, and heart rate means were computed each hour for 24 hours (day and night) at the end of each treatment period. Similar assessments were also made for blood pressure and heart rate variability (standard deviation and variation coefficient) and for 24-hour baroreflex sensitivity, which was quantified (1) in the time domain by the slope of the spontaneous sequences characterized by progressive increases or reductions of systolic blood pressure and RR interval and (2) in the frequency domain by the squared ratio of RR interval and systolic blood pressure spectral power approximately 0.1 and 0.3 Hz over the 24 hours. Compared with placebo, lacidipine reduced the 24-hour, daytime, and nighttime systolic and diastolic blood pressure (P<0.05) with no significant change in heart rate. It also reduced 24-hour, daytime, and nighttime standard deviation (-19.6%, -14.4%, and -24.0%, respectively; P<0.05) and their variation coefficient. The 24-hour average slope of all sequences (7.7+/-1.7 ms/mm Hg) seen during placebo was significantly increased by lacidipine (8.7+/-1.8 ms/mm Hg, P<0.01), with a significant increase being obtained also for the 24-hour average alpha coefficient at 0.1 Hz (from 5.7+/-1.5 to 6.4+/-1.3 ms/mm Hg, P<0.01). Thus, in diabetic hypertensive patients, lacidipine reduced not only 24-hour blood pressure means but also blood pressure variability. This reduction was accompanied by an improvement of baroreflex sensitivity. Computer analysis of beat-to-beat 24-hour noninvasive blood pressure monitoring may offer valuable information about the effects of antihypertensive drugs on hemodynamic and autonomic parameters in daily life.
Abstract: The present study compares the spectral characteristics of 24-h blood pressure variability estimated invasively at the brachial artery level with those estimated by measurement of blood pressure at the finger artery using the non-invasive Portapres device. Broad-band spectra (from 3x10(-5) to 0.5 Hz) were derived from both finger and intra-brachial pressures recorded simultaneously for 24 h in eight normotensive and twelve hypertensive ambulant subjects. At frequencies lower than 0.07 Hz, higher spectral estimates were obtained by Portapres than by intra-brachial measurements. The maximum overestimation occurred in systolic pressure at around 10(-2) Hz, where the amplitude of the oscillations was two times greater when measured by Portapres. A less pronounced overestimation was found for diastolic pressures. The maximum overestimation was greater during daytime than during night-time. At around 0.1 Hz, invasive and non-invasive spectra were similar. At the respiratory frequencies (0.15-0.50 Hz), the power spectra were overestimated by Portapres during daytime, and underestimated at night. These results provide reference information for the correct interpretation of Portapres data in the estimation of 24-h blood pressure spectral power.
Abstract: In animals and humans, baroreceptor modulation of the sinus node in daily life can be studied by identification of the number of sequences in which systolic blood pressure (SBP) and pulse interval (PI) linearly decrease or increase for several beats. It is also studied by power spectral analysis of SBP and PI in regions where their powers are coherent, although, in contrast to the sequence method, whether this frequency-domain method specifically reflects the baroreceptor-heart rate reflex has not been adequately tested. We recorded intra-arterial BP for approximately 3.5 h in eight conscious cats, first intact and then 7-10 days after sinoaortic denervation (SAD). Sensitivity of baroreceptor-heart rate reflex was assessed in 120-s segments by the square root of the ratio of PI and SBP spectral powers (alpha) in the regions around 0.1 (MF) and 0.3 (HF) Hz, and coherence between PI and SBP spectral powers in MF and HF regions was computed. SAD increased overall SBP variability and reduced PI variability throughout the frequency range examined. SAD markedly reduced (P < 0.01) both alpha-MF (-65.6%) and alpha-HF (-79. 9%) and consistently reduced the number of coherent segments [i.e., where coherence (K2) > 0.5] and average coherence values in the MF region. In the HF region, however, SAD did not alter the number of coherent segments, and although average coherence value throughout the HF band was reduced, in restricted portions of the band (different between animals), a high coherence value survived denervation. No significant changes were seen in any measured variables in five sham-operated cats. Thus the frequency-domain method specifically reflects baroreflex modulation of heart rate in the MF region only. In the HF region, in contrast, baroreflex and nonbaroreflex influences on the sinus node both contribute to a variable degree to determination of heart rate responses to BP oscillations. If used to study baroreflex function in daily life, this method should use the coefficient derived from MF data.
Abstract: Portapres is a noninvasive, beat-to-beat finger blood pressure (BP) monitor that has been shown to accurately estimate 24-hour intra-arterial BP at normal and high BPs. However, no information is available on the ability of this device to accurately track ambulatory BP variability. In 20 ambulatory normotensive and hypertensive subjects, we measured 24-hour BP by Portapres and through a brachial artery catheter. BP and pulse interval variabilities were quantified by (1) the SDs of the mean values (overall variability) and (2) spectral power, computed either by fast Fourier transform and autoregressive modeling of segments of 120-second duration for spectral components from 0.025 to 0.50 Hz or in a very low frequency range (between 0.00003 and 0.01 Hz) by broadband spectral analysis. The 24-hour SD of systolic BP obtained from Portapres (24+/-2 mm Hg) was greater than that obtained intra-arterially (17+/-1 mm Hg, P<0.01), but the overestimation was less evident for diastolic (3+/-1 mm Hg, P<0.01) and mean (3+/-1 mm Hg, P<0.01) BP. The BP spectral power <0.15 Hz was also overestimated by Portapres more for systolic than for diastolic and mean BPs; similar findings were obtained by the fast Fourier transform, the autoregressive approach, and focusing on the broadband spectral analysis. BP spectral power >0.15 Hz obtained by the Portapres was similar during the day but lower during the night when compared with those obtained by intra-arterial recordings (P<0.01). No differences were observed between Portapres and intra-arterial recordings for any estimation of pulse interval variabilities. The overestimation of BP variability by Portapres remained constant over virtually the entire 24-hour recording period. Thus, although clinical studies are still needed to demonstrate the clinical relevance of finger BP variability, our study shows that Portapres can be used with little error to estimate 24-hour BP variabilities if diastolic and mean BPs are used. For systolic BP, the greater error can be minimized by using correction factors.
Abstract: In 10 healthy smokers, finger blood pressure was recorded continuously for 1 h in a supine control condition and for 1 h while smoking four cigarettes, one every 15 min. Smoking increased average systolic blood pressure (+19%, P < 0.01) and its variability and reduced pulse interval (reciprocal of heart rate, -22%, P < 0.01) and its variability. Baroreflex sensitivity, as assessed by the slope of spontaneous hypertension/bradycardia or hypotension/tachycardia sequences and by the alpha-coefficient (squared ratio between pulse interval and systolic blood pressure spectral powers at 0.1 Hz) was significantly decreased (P < 0.01) during smoking, whereas there were no effects of smoking on the reflex changes in pulse interval induced by carotid baroreceptor stimulation through a neck suction device. Sham smoking by a drinking straw had no effects on any of the above parameters. Thus, when assessed in the absence of laboratory maneuvers in daily life conditions, baroreflex sensitivity is markedly impaired by smoking. This impairment may contribute to the smoking-induced increase in blood pressure and heart rate as well as to the concomitant alterations in their variability.
Abstract: This paper presents a new procedure specifically aimed at providing a dynamical detection of the oscillations occurring in long-term heart-rate (HR) tracings. The procedure is based on a time-variant state-space modelling of the fourth-order cumulants of the HR signal. The state-space estimator was selected because of its demonstrated capability to distinguish between deterministic and stochastic components of the signal, while the fourth-order cumulants of the signal were used as input of the model to further reduce adverse effects of coloured, white and l/f Gaussian noise possibly present in the input data. The procedure was tested by the analysis of simulated signals and its performance was compared with the results obtained by state-space modelling applied directly on the test signals (instead of on the fourth-order cumulants of the signals) and by the more traditional auto-regressive modelling. The comparison has shown a clear superiority of the proposed procedure over the other techniques in discriminating deterministic oscillations from coloured noise. Finally, the applicability of the procedure to biological data was verified by analysing five experimental HR tracings recorded in normal subjects during laboratory and daily life conditions.
Abstract: The sequence technique and the spectral estimation of the alpha coefficient are currently employed for the assessment of "spontaneous" baroreflex sensitivity (BRS). The comparison of performance and effectiveness of these techniques is obtained by the analysis of systolic blood pressure (SBP) and pulse interval (PI) tracings recorded in conscious cats before and after baroreceptor denervation. Results indicate that (1) the average BRS estimates obtained by the sequence technique and by the alpha coefficient at the respiratory frequency are similar, (2) the alpha coefficients computed at the respiratory frequency tend to be higher than alpha coefficients estimated at 0.1 Hz, and (3) in spite of what is traditionally claimed, the PI-SBP coherence does not seem to represent a reliable parameter to enhance the specificity of the spectral estimate, because coherence values often remain above the 0.5 threshold also after baroreceptor denervation.
Abstract: Systolic blood pressure (SBP) variability is increased and R-R interval variability is reduced in the elderly. Little is known, however, about how SBP and R-R interval variabilities change in the very elderly. More important, however, it is not known which frequency components of SBP and R-R interval variability are affected significantly. We addressed this issue in subjects older than 70 years by broadband spectral analysis, which allows all variability components from the lowest to the highest frequency to be considered. In 20 very elderly normotensive subjects (mean +/- SD age, 78.1 +/- 6.8 years) and 28 normotensive adult subjects (36.1 +/- 7.1 years), noninvasive finger blood pressure and R-R intervals were recorded continuously for 30 minutes in the supine position and 15 minutes in the upright position. SBP and R-R interval power spectral densities were computed over the entire frequency region between 0.005 Hz (0.007 Hz in the upright position) and 0.5 Hz. Overall SBP variability (SD) was greater and overall R-R interval variability was less in very old subjects than in adult subjects. All spectral R-R interval powers were reduced significantly in very elderly individuals. The spectral SBP powers were greater in the very elderly group than in the adult group only in the very-low-frequency range (<0.04 Hz). This was true in the supine and the standing positions. With subjects in the standing position, the shape of the broadband spectra differed in the very old and adult subjects because in the former group the increase in SBP and R-R interval power around 0.1 Hz that was seen in the latter was blunted. Therefore, in very elderly subjects a reduction in overall R-R interval variability is accounted for by a reduction in all of its frequency components. The accompanying increase in overall BP variability, however, results from a nonhomogeneous behavior of its frequency components, which consists of an increase in the very low frequency and a concomitant reduction in the higher frequency powers. The mechanisms responsible for these changes may be complex, but at least they may in part reflect the baroreflex impairment and autonomic dysfunction that characterize aging.
Abstract: We investigated whether respiration influences pulmonary arterial input impedance during transition from inspiration to expiration in five anesthetized, spontaneously breathing dogs. Impedance (Z) was separately assessed for heart beats occurring in inspiration, in expiration, and during the transition from inspiration to expiration (transitional beat). Transitional beats were scored by the ratio between the fraction of beat falling in expiration and the total beat duration [expiratory fraction (Efr)] to quantify their position within the transition. In transitional beats, input resistance linearly increased with Efr; Z modulus at the heart-rate frequency (fHR) decreased up to -50% for Efr = 50%. Z phase at fHR was greater than in inspiration for Efr <40% and lower for Efr >50%. Unlike blood flow velocity, mean value and first harmonic of pulmonary arterial pressure were correlated to Efr and paralleled the changes of input resistance and Z at fHR. This indicates that respiration influences Z through modifications in arterial pressure. The evidence of important respiratory influences on Z function may help the pathophysiological interpretation of dysfunctions of the right heart pumping action, such as the so-called cor pulmonale.
Abstract: Diabetic autonomic dysfunction is associated with a high risk of mortality which makes its early identification clinically important. The aim of our study was to compare the detection of autonomic dysfunction provided by classical laboratory autonomic function tests with that obtained through computer assessment of the spontaneous sensitivity of the baroreceptor-heart rate reflex (BRS) by time domain and frequency domain techniques. In 20 normotensive diabetic patients (mean age +/- SD 41.9 +/- 8.1 years) with no evidence of autonomic dysfunction on laboratory autonomic testing (D0) blood pressure (BP) and ECG were continuously monitored over 15 min in the supine position. BRS was assessed as the slope of the regression line between spontaneous increases or reductions in systolic BP and linearly related lengthening or shortening in RR interval over sequences of at least 4 consecutive beats (sequence method), or as the squared ratio between RR interval and systolic BP spectral powers around 0.1 Hz. We compared the results with those of 32 age-matched normotensive diabetic patients with abnormal autonomic function tests (D1) and with those of 24 healthy age-matched control subjects with normal autonomic function tests (C). Compared to C, BRS was markedly less in D1 when assessed by both the slope of the two types of sequences (data pooled) and by the spectral method (-71.3% and -60.2% respectively, both p < 0.01). However, BRS was consistently although somewhat less markedly reduced in D0, the reduction being clearly evident for all the estimates (-57.0% and -43.5%, both p < 0.01). The effects were more evident than those obtained by the simple quantification of the RR interval variability. These data suggest that time and frequency domain estimates of spontaneous BRS allow earlier detection of diabetic autonomic dysfunction than classical laboratory autonomic tests. The estimates can be obtained by short non-invasive recording of the BP and RR interval signals in the supine patient, i.e. under conditions suitable for routine outpatient evaluation.
Abstract: To assess spontaneous baroreceptor-heart rate reflex sensitivity during sleep in patients with obstructive sleep apnea syndrome, a condition associated with increased cardiovascular morbidity and mortality and characterized by marked sympathetic activation, which is believed to originate from hypoxic chemoreceptor stimulation, although little is known of other possible mechanisms such as baroreflex impairment.
Abstract: The aim of this study was to determine whether spontaneous respiration influences pulmonary artery input impedance, a question that has received little attention in the literature. Impedance values were assessed during three different phases of the respiratory cycle, namely inspiration, expiration and postexpiration (i.e. the null respiratory flow period between expiration and the next inspiration) in five anaesthetized spontaneously breathing dogs. Firstly, impedance values during postexpiration were taken as the reference baseline, and compared with values obtained during inspiration and expiration. Then, differences between values in inspiration and in expiration were tested, taking impedance during inspiration as the baseline. Differences with respect to postexpiration were found for three parameters of input impedance: input resistance, characteristic impedance, and the frequency at the first zero-crossing of the impedance phase from negative to positive values (f(cross)). Input resistance was significantly lower in inspiration (85% of the baseline), characteristic impedance was significantly greater in inspiration and in expiration (112 and 119% respectively), and f(cross) was significantly lower in expiration (89%). By contrast, only input resistance differed significantly when inspiration was compared to expiration. Therefore, spontaneous respiration was shown to influence input impedance significantly. The observed changes in characteristic impedance and f(cross) might be explained by a stiffening of the pulmonary artery wall, due to neural and/or mechanical factors, during inspiration and expiration.
Abstract: This paper focuses on a number of methods for the analysis of the relationship between the arterial baroreflex and different components of blood pressure and heart rate variability. Broad-band spectral analysis techniques have allowed us to obtain experimental evidence that the arterial baroreflex exerts its influence not only on fast but also on slow components of blood pressure and heart rate, i.e., on components with periods longer than 60 sec. Focusing on faster changes in blood pressure and heart rate, both time domain and frequency domain techniques have been developed to track the sensitivity of baroreflex heart rate modulation over time, either in laboratory or in daily life conditions. These approaches have considerably broadened our understanding of the role of baroreflex modulation of the heart and peripheral circulation in a number of pathological and physiological conditions.
Abstract: Sino-aortic denervation (SAD) is employed in cats to evaluate the baroreflex influence on blood pressure (BP) and pulse interval (PI) spectral components from 0.00008 to 0.9 Hz as assessed by FFT wide-band spectra and their 1/f modelling; and the linear coupling between BP and PI and between systolic and diastolic BP as assessed by coherence analysis. Specific procedures have been developed to obtain an effective smoothing of spectra and coherence functions. SAD induced an increase in BP powers from 0.03 to 0.0006 Hz and a power reduction of most of the remaining BP components; a reduction of PI powers at all frequencies; marked deviations of BP spectra from the 1/f trend; a reduction of the coherence between BP and PI from 0.12 to 0.5 Hz and a coherence enhancement at lower frequencies. These findings indicate that the arterial baroreflex modulates both fast and slow spectral components of BP and PI; homogeneously enhances PI fluctuations at all frequencies; produces differentiated effects on BP fluctuations along the frequency axis; and at low frequencies exerts the buffering action on BP through strategies which reduce the BP-PI linear link.
Abstract: The effects of aging on the dynamic modulation of baroreflex sensitivity over 24 h was assessed in eight elderly (mean age +/- SD, 63.9 +/- 3.2 yr) and in eight young (23.9 +/- 6.1 yr) mild or moderate essential hypertensive patients, who were subject to a 24-h intra-arterial (Oxford technique) blood pressure recording in ambulatory conditions. The sensitivity of baroreflex control of the heart rate was dynamically assessed by quantifying 1) the slope of the regression line between pulse interval (the reciprocal of heart rate) and systolic blood pressure changes over spontaneously occurring hypertension-bradycardia or hypotension-tachycardia sequences (time domain analysis) and 2) the ratio between spectral-powers of pulse interval and systolic blood pressure around 0.1 Hz (alpha-coefficient: frequency domain analysis). The 24-h average sequence slope was lower in old than in young individuals (4.4 +/- 0.5 vs. 9.9 +/- 1.3 and 4.8 +/- 0.7 vs. 8.4 +/- 1.4 ms/mmHg for hypertension-bradycardia and hypotension-tachycardia sequences, respectively; P < 0.05 for both). Similar results were obtained by using the alpha-coefficient approach. The marked nighttime increase in baroreflex sensitivity observed in young individuals was much less evident in the elderly. Thus 24-h baroreflex sensitivity is markedly impaired by aging. The impairment becomes manifest also as an inability to increase baroreflex sensitivity at night.
Abstract: We examined the extent to which sympathetic influences are reflected by spectral powers of blood pressure and pulse interval in specific frequency bands in spontaneously behaving Wistar-Kyoto rats subjected to continuous intraarterial blood pressure recording. The rats were pretreated with 6-hydroxydopamine (150 mg/kg twice in 1 week, n = 19) to produce chemical sympathectomy or received vehicle (n = 15). In the sympathectomized group, additional monitoring sessions were performed with rats under alpha-adrenergic receptor blockade with phenoxybenzamine (n = 8), beta-receptor blockade with propranolol (n = 7), or cholinergic receptor blockade with atropine (n = 8). Blood pressure signals were analyzed by a computer to calculate spectral powers (fast Fourier transform) in the low-frequency (0.025 to 0.1 Hz), mid-frequency (0.1 to 0.6 Hz), and high-frequency (0.8 to 3.0 Hz) bands. In sympathectomized rats, low-frequency power of blood pressure was 70% greater than in intact rats, whereas mid-frequency power was 60% smaller (P < .05 for both) and high-frequency power was unchanged. High-frequency power of pulse interval was also unchanged in sympathectomized rats, whereas low- and mid-frequency powers were reduced by approximately 50% (P < .05). No further alterations in spectral powers were observed by adding alpha- or beta-adrenergic blockade to sympathectomy, whereas adding cholinergic blockade caused a striking reduction in all pulse interval powers. Thus, mid-frequency blood pressure power depends on sympathetic but also to a substantial extent on nonsympathetic influences. Sympathetic influences do not contribute to low-frequency blood pressure power, having instead a restraining effect. The low- and mid-frequency pulse interval powers depend on both sympathetic and vagal influences. Thus, no blood pressure or pulse interval power in the mid- and low-frequency ranges can be regarded as a specific marker of sympathetic activity.
Abstract: To determine whether spectral powers of blood pressure and pulse interval can specifically reflect sympathetic and parasympathetic effects in unanesthetized, free-moving spontaneously hypertensive rats (SHR).
Abstract: We dynamically evaluated the effects of beta-blockade on the sensitivity of arterial baroreflex control of heart rate in 10 mild or moderate essential hypertensive patients in whom blood pressure was recorded intra-arterially for 24 hours in ambulatory conditions. Twenty-four-hour baroreflex sensitivity was assessed by both (1) a time-domain approach based on the calculation of the slope of the regression line between linearly related progressive increases in systolic blood pressure and pulse interval (+PI/+SBP sequences) and decreases in systolic blood pressure and pulse interval (-PI/-SBP sequences) and (2) a frequency-domain approach, ie, the ratio between the spectral powers of pulse interval and systolic blood pressure around 0.1 Hz (alpha coefficient). Data were obtained before and after 1 month of administration of either acebutolol (n = 5) or labetalol (n = 5). Before treatment, the 24-hour average slopes of the +PI/+SBP and -PI/-SBP sequences were 4.36 +/- 0.32 and 4.05 +/- 0.27 ms/mm Hg, respectively, while the alpha coefficient was 7.78 +/- 0.7 ms/mm Hg. After beta-blockade, these values were increased by 25.3 +/- 6.8%, 25.0 +/- 8.0%, and 32.1 +/- 9.3%, respectively (P < .01 for all values). Thus, beta-blockers potentiate baroreflex sensitivity in daily life. Time-domain and frequency-domain methods yielded superimposable results in dynamically evaluating 24-hour baroreflex sensitivity and its changes after beta-blockade.
Abstract: The aim of our study was to assess whether the Finapres device is able to accurately monitor not only average blood pressure values but also blood pressure variability. To examine this issue, we analyzed 30-minute recordings of finger and intra-arterial pressure simultaneously obtained at rest in 14 patients. We compared systolic blood pressure, diastolic blood pressure, mean arterial pressure, pulse interval (the reciprocal of heart rate), overall variability (standard deviation), and specific time-domain and frequency-domain components. Systolic blood pressure, diastolic blood pressure, mean arterial pressure, and pulse interval spectral powers were computed by fast Fourier transform over three frequency bands: low frequency (0.025 to 0.07 Hz), midfrequency (0.07 to 0.14 Hz), and high frequency (0.14 to 0.35 Hz). The coherence, ie, the degree of association between blood pressure and pulse interval powers obtained by the two techniques, was also assessed. Standard deviations of diastolic blood pressure, mean arterial pressure, and pulse interval were similar when assessed from the two recordings, whereas standard deviation of systolic blood pressure was overestimated by analysis of finger pressure recordings. All powers of diastolic blood pressure and mean arterial pressure and high-frequency powers of systolic blood pressure estimated from analysis of finger blood pressure tracings were superimposable to those obtained by analyzing invasive recordings. Low-frequency and midfrequency powers of intra-arterial systolic blood pressure were significantly overestimated by the analysis of finger blood pressure tracings (+13.7 +/- 4.4 mm Hg2, P < .01, and +2.3 +/- 0.9 mm Hg2, P < .05).(ABSTRACT TRUNCATED AT 250 WORDS)
Abstract: Spectral analysis of blood pressure and heart rate signals allows overall blood pressure and heart rate variabilities to be split into their different frequency components. When used to analyze 24 h discontinuous blood pressure recordings, the low sampling frequency that characterizes these devices allows only the slow fluctuations in day and night blood pressure to be adequately described by the spectral approach. Conversely, spectral analysis of continuous blood pressure recordings provides information both on fast and slow changes in blood pressure and heart rate. Because blood pressure and heart rate powers are characterized by a 1/f distribution over the 24 h, slow fluctuations in blood pressure and heart rate contribute most importantly to 24 h variance, while faster components provide only a minor contribution. However, spectral analysis of the latter has raised considerable interest due to the possible association of these components with cardiovascular regulatory mechanisms. It is now possible to perform 24 h dynamic spectral analysis of blood pressure and heart rate on continuous blood pressure recordings obtained noninvasively by a finger pressure device.
Abstract: Sinoaortic denervation (SAD) is accompanied by an increase in blood pressure (BP) and a reduction in pulse-interval (PI) variance. Little is known, however, about the effect of SAD on the complex BP and PI variability pattern, which is identified by spectral analysis. In nine unanesthetized cats in which intra-arterial BP was monitored before and 7-10 days after SAD, spectral powers (estimated by fast Fourier transform) were calculated for the low frequency (LF, 0.025-0.07 Hz), midfrequency (MF, 0.07-0.14 Hz), and high frequency (HF, 0.14-0.60 Hz) band. The very low frequency (VLF) BP and PI components (VLF less than 0.025 Hz) were also estimated. SAD increased systolic BP variance and decreased PI variance. The reduction of PI variance was paralleled by significant and marked reductions in all PI powers including the VLF components. In contrast, the increase in systolic BP variance was accompanied by a marked increase in LF power, a decrease in MF power, and no change in HF power. The VLF BP components increased after SAD for frequencies between 0.025 and 0.0012 Hz, whereas a sudden marked reduction was observed below 0.0012 Hz. Similar results were obtained for diastolic BP powers. Thus the reduction in PI variance induced by SAD is paralleled by a reduction in all PI fluctuations identified by spectral analysis. This is not the case for the SAD-related increase in BP variance, which is accompanied by an increase, no change, or even a reduction in the different BP spectral components.(ABSTRACT TRUNCATED AT 250 WORDS)
Abstract: Blood pressure and pulse interval are characterized not only by erratic variations but also by rhythmic fluctuations at low-, mid-, and high-frequency (0.025-0.07, 0.07-0.14, and 0.14-0.35 Hz, respectively). However, information on these phenomena has largely been derived from analysis of short-term recordings taken in standardized laboratory conditions. In seven normotensive and 10 untreated mild essential hypertensive subjects, power spectrum analysis was performed on the intra-arterial blood pressure and pulse interval signal collected over a 24-hour period using the fast Fourier transform algorithm and splitting the recording into contiguous segments of 256 beats. About 70% of the segments were suitable for the analysis; the segments excluded for a nonstationary signal amounted to only 30%. All powers were characterized by a high segment-to-segment variability, but in each subject the mid- and high-frequency powers of diastolic blood pressure and the mid-frequency power of systolic blood pressure were markedly reduced during the night as compared with the daytime period, whereas the opposite occurred for the low- and high-frequency powers of the pulse interval. Over the 24-hour period, mid- and high-frequency powers of blood pressure were positively correlated to each other, but both accounted for less than 25% of the 24-hour blood pressure variance. No difference between mean normalized power values of normotensive and hypertensive subjects was observed.(ABSTRACT TRUNCATED AT 250 WORDS)
Abstract: A procedure for the 24 h tracking of the 0.25, 0.1, and 0.05 Hz oscillations in blood pressure (BP) and pulse interval (PI) in ambulant subjects has been developed. It includes: 1) sampling of a 24 h intra-arterial BP recording, extraction of the systolic (S) and diastolic (D) BP and PI from each heart beat followed by storage into separate series; 2) high-pass filtering and a splitting of each series into consecutive records of 256 values; 3) estimation of power spectral density (PSD) via FFT in each stationary record, and finally, computation of the power of each target oscillation. Using this procedure we analyzed data from ten hospitalized free-moving subjects in whom BP was recorded by the Oxford technique. The results revealed different patterns of the 0.25, 0.1, and 0.05 oscillations over the day-night cycle, showing a differentiated involvement during the 24 h of the mechanisms responsible for such rhythmic phenomena. Moreover, in order to reinforce the meaning of the obtained results and to exclude the possible negative effects due to the drawbacks typical of the FFT algorithm, we also performed a second spectral estimate based on the AR modeling. The obtained results validates the FFT approach.
Abstract: This chapter contains descriptions of (1) signal processing techniques for the analysis of data derived from devices providing a discontinuous measure of blood pressure, (2) techniques for the analysis of continuous arterial blood pressure recordings, (3) the main methods for the analysis of blood pressure variability, and (4) techniques for the estimation of the baroreflex function from the analysis of spontaneous fluctuations of blood pressure and heart rate.
Abstract: The reverse arrangement test is used for evaluating whether a sequence of ordered data is derived from independent observations of the same random variable by detecting whether a significant trend underlies the observations. It is a nonparametric test, making no assumptions about the distribution of the input data and about a model for the possible trend.
Abstract: The Wigner–Ville distribution is a time–frequency distribution developed for the analysis of timevarying spectra. Indeed, the interpretation of classic Fourier analysis (FFT), which decomposes the power of a signal into frequency components by quantifying the power spectrum, may became problematic when the frequency content changes over time. In fact, the power spectrum cannot indicate when specific spectral components occur or how they change in intensity and frequency. Thus, when the signal is characterized by a time-varying spectrum, it is preferable to decompose the signal power by a joint function of time and frequency. The Wigner–Ville distribution W(t, f ) quantifies the fraction of the power in a certain frequency
band during a certain time range, representing the “instantaneous†spectrum of a nonstationary signal s(t).
Abstract: Z-analysis is a method for determining the association between two probabilistic events, A and B, on the basis of the calculation of a statistical link coefficient, Z(A,B). The Z(A,B) coefficient may range between −1, when A and B are mutually exclusive events, and +1, when A is included within B; it is equal to 0 when A and B are independent. Intermediate values between −1 and 0 quantify the partial exclusion of B by A, while values between 0 and +1 quantify the partial dependence of B on A.
Abstract: The Lomb periodogram is a generalization of the periodogram (see Spectral Analysis) for unequally spaced series. Many biomedical time series are sampled irregularly because of missing data due to instrumental failures or because the nature of the measured variable makes the sampling interval intrinsically uneven. Since traditional spectral estimators need even sampling rates, unevenly spaced series should be interpolated and resampled before spectral analysis.
By contrast, the method proposed by Lomb does not require interpolation and resampling.
Abstract: Zero-padding is a procedure that consists of extending the length of a time series by adding zeros. For instance, if {x0, x1, . . . , xM−1} is a sequence of M data, the zero-padded sequence of length N = M + 5 is {x0, x1, . . . , xM−1, 0, 0, 0, 0, 0}. Adding zeros to a time series before computing the Discrete Fourier Transform (DFT) results in the evaluation of a Fourier transform with additional interpolated values.
Abstract: The Barahona–Poon test is used to detect nonlinear dynamics in time series (see Nonlinear Time Series Analysis). Nonlinear dynamical systems may generate deterministic signals, which can be easily mistaken for random noise. Distinguishing nonlinear deterministic dynamics, or “chaosâ€, from random
noise helps understand the physical process generating the data, and may improve short-term prediction (see Forecasting). In practice, however, identifying nonlinear dynamics is difficult because methods to detect chaos are often degraded by measurement noise, and need long data sets. The test proposed by C. S. Poon and M. Barahona is particularly suitable to detect chaos in short and noisy time series
Abstract: The Levinson–Durbin algorithm is a method for finding the solution b to a system
of p linear equations A × b = c, where A is a p × p symmetric Toeplitz matrix (a Toeplitz matrix is composed of elements that are constant along the diagonals) and c is a known p-dimensional column vector. Systems with A both symmetric and Toeplitz can be found in several applications, like spectral estimation, filter design (see Kalman Filter), or linear prediction.
Abstract: Broadband smoothing is a procedure to reduce the estimation variance of fast Fourier transform (FFT) power spectra (see Spectral Analysis), which results in estimation variance and frequency resolution not constant over the frequency axis, as in conventionally smoothed spectra.
Abstract: The Choi–Williams distribution is a transform that represents the spectral content of nonstationary signal with a bidimensional time–frequency map. How well a time-frequency distribution represents a nonstationary signal depends on how fast the changes in the frequency content of the signal are. When they are relatively slow, the standard method of representation is the spectrogram, that is, the calculation of the Fourier (see Fast Fourier Transform (FFT)) spectrum over a short-time running window. When the spectral characteristics change more rapidly, a higher resolution in time and frequency is needed, and methods like the Wigner–Ville Distribution are
preferred.
Abstract: Spontaneous progressive changes in systolic blood pressure (SBP) are not invariably followed by baroreflex-driven changes in pulse interval (PI). In order to quantify this phenomenon we propose a new index, termed Baroreflex Effectiveness Index (BEI), defined as the ratio between the number of times that SBP progressive changes are followed by progressive changes in PI in the same direction and the total number of SBP changes occurring in a given time window.
In this study we applied this new index on data collected in two pilot groups of young and elderly subjects during spontaneous behaviour.
Abstract: Nitric oxidc is continuously released in the circulation where it can quickly modify the hemodynamic conditions and therefore affect blood pressure variability. Nevertheless the effect of nitric oxide on blood pressure variability has not been completely elucidated; moreover it remains unknown whether nitric oxide acts independently, in concert or in opposition with the autonomic nervous system. In order to answer these questions we studied the effects of nitric oxide synthesis inhibition in intact, sympathectomized (Sympx) and sino-aortic denervated (SAD) conscious WKY rats. Mean arterial pressure (MAP) and pulse interval (PI) were continuously recorded for 60 minutes both in absence and in presence of an 1-arginine analogue, 1-NMMA (iv bolus 100 mg.kg-1, followed by a 1.5 mg.kg-1 .min-1 infusion for 60 minutes). Data were analyzed by means of FFT power spectral analysis in the HF (3.0 to 0.8 Hz), MF (0.6 to 0.1 Hz), and LF (0.1 to 0.025 Hz) frequency bands. Sympathectomy moderately reduced MAP whereas SAD did not change it significantly. 1-NMMA increased MAP (intact: from 97.2±3.6 to 135.4±4.2 mmHg, p<0.01; Sympx: from 73.6±3.9 to 124.3±5.9 mmHg, p<0.01; SAD: from 101.0±14.5 to 141.1±19.4 mmHg, p<0.01). Spectral analysis of both MAP and PI showed a different effect of 1-NMMA in the three groups of rats: 1-NMMA reduced significantly MF power of MAP in intact rats (from 1.67±0.60 to 0.75± 0.24 mmHg2 p<0.001) and in SAD rats (from 2.90±0.80 to 1.86±0.90, p <0.05) but not in sympathectomized rats (from 0.67±0.37 to 0.60±0.32 mmHg2, p=ns). Concerning PI, 1-NMMA increased significantly LF power in sympathectomized rats and HF power in both intact and sympathectomized rats (all p<0.01) but it did not modify spectral powers in SAD rats. In conclusion our data suggest that 1) nitric oxide contributes to generate overall blood pressure variability in the mid frequency range and 2) this effect is related to an interaction between nitric oxide and sympathetic neural influences.
Abstract: Background. Blood pressure fluctuations over the 24 hours include both fast and slow changes. While most studies have focused on the former components, recent evidence suggests that also slower blood pressure variations may have physiological and clinical relevance. A method recently proposed to quantify these slower blood pressure components is broad band spectral analysis.
Methods and Results: Broad band spectral analysis consists in the estimation of a single spectrum obtained by considering all data included in a long term recording and in the quantification of the power of all frequency components, from the slowest to the fastest ones. Application of this method to recordings obtained in animais before and after surgical baroreceptor denervation has shown that not only fast but also slow blood pressure and heart rate fluctuations are under baroreflex control. Clinical applications of broad band spectral analysis have included 1] the quantification of the age-induced changes in the different components of blood pressure and heart variability, 2] the assessment of the effects of treatment on blood pressure and heart rate fluctuations in hypertensive patients, and 3] the assessment of the prognostic value of slow heart rate fluctuations in post-myocardial infarction patients.
Conclusions: Broad band spectral analysis represents a unique tool for the quantification of all components of blood pressure and heart rate variability and for the assessment of their possible changes in diseased conditions or under the effects of treatment.
Abstract: The sensitivity of the baroreceptor-heart rate reflex has been suggested to have a prognostic value in a number of diseases. In particular, mortality after myocardial infarction, in heart failure patients and in diabetic patients seems to be inversely related to the sensitivity of cardiac baroreflex modulation. These data were obtained, however, by means of traditional laboratory tests, which are affected by important limitations. A deeper insight into the features of daily life baroreflex cardiovascular control can now be obtained by techniques which allow spontaneous baroreflex sensitivity to be assessed in daily life conditions, without need of any intervention on the patient. The various methods currently available to assess spontaneous baroreflex sensitivity are hereby discussed, focusing on the similarities and differences between them and with the traditional laboratory approaches. In particular, the characteristic features and the possible clinical usefulness of the sequence method will be discussed more in details.
Abstract: The first observations of a 1/f trend in the spectrum of heart rate (HR) and blood pressure (BP) signals date back to 1982 and 1990, respectively. Ever since, a number of studies have suggested that the analysis of this spectral trend may be a valuable tool for investigating the physiological mechanisms involved in cardiovascular regulation and for assessing their derangement in pathological conditions. The spectral analysis of BP and HR tracings recorded in cats before and after the surgical opening of the baroreflex loop, offered us the opportunity to address some yet unclear aspects related to the 1/f trend occurring in BP and HR spectra, namely: 1) the role played by the baroreflex in the genesis of the 1/f trend; 2) the ability of a single 1/f curve to correctly model the spectra; 3) the methodology required for the estimation of the regression line corresponding to the 1/f curve when spectra are plotted in a log-Iog scale. The results we obtained indicate that 1) baroreflex denervation disrupts the 1/f trend of BP spectra but does not modify the same trend in the HR spectra; 2) in pathological conditions a single 1/f line may be inadequate to describe the BP spectra; and 3) the slope of the regression line representing the 1/f trend strongly dependent on the frequency region over which the line is estimated, thus prompting for the establishment of standards in the modeling procedure.
Abstract: In the present paper the use of wide-band spectral analysis to simultaneously investigate fast and slow components of blood pressure (BP) and heart rate (HR) variability is addressed from both a methodological and a practical point of view. After a short review of the technical problems involved in this kind of analysis, the results obtained by the wide-band spectral approach in evaluating the effects of sino-aortic baroreceptor denervation (cats) and aging (humans) on the different components of BP and HR variability are presented. An important finding from use of wide-band spectral analysis is that the power of the BP spectral components tends to be inversely related to the frequency (1/f trend), namely, the slower the BP fluctuation the higher its contribution to the overall BP variance. The occurrence of slow BP fluctuations of pronounced magnitude, however, may appear in apparent contrast with the anti-oscillatory action of the arterial baroreflex. A possible explanation for this paradoxical phenomenon is that also the sensitivity of the baroreflex is modulated in a 1/f fashion. Experimental data supporting this hypothesis are shown.
Abstract: The relationship between sympathetic activity and specific spectral components of blood pressure (BP) variability has been investigated in conscious Wistar Kyoto (WKY) rats and in spontaneously hypertensive rats (SHR), the latter being characterized by sympathetic overactivity.
The study was based on the evaluation of BP spectral powers in SHR and WKY rats with intact sympathetic nervous system and after abolition of efferent sympathetic activity obtained by chemical sympathectomy. In each spontaneously behaving rat, systolic blood pressure, diastolic blood pressure and pulse interval (the reciprocal of heart rate) were monitored beat-to-beat for 90 min. The spectral powers of these parameters were calculated by FFT technique and integrated over three frequency bands (HF 0.8-3 Hz, MF 0.1-0.6 Hz and LF 0.025-0.1 Hz). The obtained data showed a non-univocal relationship between sympathetic activity and the MF and LF components of BP variability. Furthermore, to estimate the residual components of BP variability in sympathectomized SHR and WKY rats also beyond the LF band, a wideband analysis from 0.0007 to 3 Hz was computed. Our results indicated that the abolition of sympathetic efferent activity did not cancel the differences of BP spectral profiles between SHR and WKY rats, thus suggesting that these differences are due, at least in part, to structural and/or humoral factors.
Abstract: Computer analysis of blood pressure and heart rate fluctuations and the quantification of their interaction in the time (sequence method) or in the frequency domain (spectral analysis) offer a dynamic evaluation of the sensitivity of baroreflex control of the heart (BRS) in daily life conditions. Use of these techniques in the analysis of 24 hour intra-arterial blood pressure and heart rate recordings has shown that in real life BRS is continuously modulated over time and is characterized by a pronounced increase at night as compared to the daytime. In a number of pathophysiological states (hypertension, aging and autonomic failure), average 24 hour BRS is markedly lower than in normal subjects and its day-night modulation is blunted to a variable extent. These time domain and frequency domain techniques provide generally superimposable results and represent unique tools not only to quantify differences in BRS between different steady-state conditions, but also to track fast changes in BRS induced by behavioural stimuli on a minute-to- minute basis. They offer a deeper insight into daily life cardiovascular regulation in normal and diseased conditions with no need of external interventions.
Abstract: This work presents an algorithm based on blood pressure signal analysis for the dynamic estimation of the respiratory rate and for tracking the effects of respiration on blood pressure and heart rate. This method was used to assess the respiratory influences on long term blood pressure tracings recorded in free-moving animals, where a direct recording of the respiratory activity was not available.
Abstract: As already reported, the FINAPRES device is able to monitor blood pressure (BP) variations in a beat-to-beat fashion both in resting conditions and during different laboratory manoevres, providing BP values close to those simultaneously recorded by an intra-arterial line. Whether this applies not only to the assessment of BP mean values but also to the evaluation of specific components of BP variability, as determined by spectral analysis, is not known however. We have addressed this issue by assessing the spectral characteristics of BP and heart rate (pulse interval, PI) of continuous finger and intra-arterial BP recordings simultaneously obtained in 14 untreated essential hypertensive patients. Spectral powers were computed by Fast Fourier Transform (FFT) over three frequency bands defined as Low Frequency (LF, 0.025-0.07 Hz), Mid Frequency (MF, 0.07-0.14 Hz) and High Frequency (HF, 0.14-0.35 Hz) band. All powers of mean arterial pressure (MAP) and diastolic (D) BP estimated from analysis of finger BP tracings were superimposable to those obtained by analysing intra-arterial recordings. This was the case also for HF powers of systolic (S) BP, while LF and MF powers of intra-arterial SBP were over-estimated by the analysis of finger BP tracings (+ 13.7± 4.4 mmHg2; p<0.01 and +2.3±0.9 mmHg2; p<0.05). Thus beat-to-beat finger BP recording seems to represent an acceptable substitute of invasive recording also in the analysis of BP and PI spectral components. Some caution is needed, however, in interpreting LF and MF powers of SBP which are overestimated by the analysis of finger BP tracings.
Abstract: Seismocardiography is the body-surface recording of vibrations produced by the beating heart. A high frequency (HF) accelerometric component of the seismocardiogram (SCG) is related to the heart sounds generated by the closure of atrio-ventricular and semilunar valves. This paper evaluates the feasibility of recording the SCG component associated to cardiac sounds by means of a wearable device originally designed for monitoring ECG, respiratory movements, body accelerations and posture in freely moving subjects. The method is based on the averaging of the HF component of the acceleration vector measured by the wearable system, and on the subsequent extraction of features from its envelope. The method is applied on data recorded in healthy volunteers in different postures and during sleep. Results indicate that it is possible to reliably identify the time of occurrence of the first and second heart sound within the cardiac cycle. They also show significant differences in the HF component of SCG between supine and standing postures. Analyzing the HF SCG in a volunteer sleeping at high altitude (4554 m asl) substantial differences were also found among three body positions (lying supine or on the left or right side). These differences are likely to reflect changes in cardiac mechanics induced by different postures of the body.
Abstract: Seismocardiogram (SCG) is the recording of the minute body accelerations induced by the heart activity, and reflects mechanical aspects of heart contraction and blood ejection. So far, most of the available systems for the SCG assessment are designed to be used in a laboratory or in controlled behavioral and environmental conditions. In this paper we propose a modified version of a textile-based wearable device for the unobtrusive recording of ECG, respiration and accelerometric data (the MagIC system), to assess the 3d sternal SCG in daily life. SCG is characterized by an extremely low magnitude of the accelerations (in the order of g × 10(-3)), and is masked by major body accelerations induced by locomotion. Thus in daily life recordings, SCG can be measured whenever the subject is still. We observed that about 30 seconds of motionless behavior are sufficient for a stable estimate of the average SCG waveform, independently from the subject's posture. Since it is likely that during spontaneous behavior the subject may stay still for at least 30 seconds several times in a day, it is expected that the SCG could be repeatedly estimated and tracked over time through a prolonged data recording. These observations represent the first testing of the system in the assessment of SCG out of a laboratory environment, and open the possibility to perform SCG studies in a wide range of everyday conditions without interfering with the subject's activity tasks.
Abstract: We present an algorithm for assessing the ECG signal quality in real time. The algorithm is designed for small systems with low computational power.
The method estimates the ECG cepstrum on a running window of 10 s and calculates the power of the highest peak in the “quefrency†band of the mean cardiac interval (between 0.25 and 2.0 s). If the ECG is corrupted by noise, the power of this cepstral peak is just a fraction of the total power. The ECG quality index (QI) is defined as ratio between the power of the cepstral peak and the total cepstral power. Examples with ECG of different signal quality from different leads illustrate the method. Moreover, two overnight ECG recordings were analyzed by setting the threshold for ECG acceptability at QI>0.40. ECG signals were classified acceptable for 99.8% and 60% respectively of the recordings time. These percentages were similar to those scored visually by an expert operator (100% and 67% respectively).
Abstract: Ambulatory blood pressure monitoring (ABPM) devices provide 24-hour profiles of mean arterial pressure (MAP) and heart rate (HR) by inflating an arm-cuff every 15 minutes during daytime and every 20 minutes during night-time. Aim of this work is to evaluate whether the intrinsic structure of ABPM dynamics can be described during day and night subperiods by calculating the fractal dimension (FD) of MAP and HR.
For this aim, first we evaluated the performances a recently proposed FD estimator on short segments of fractional Brownian motions. Then we applied the new FD estimator on 24-hour ABPM recordings of two healthy volunteers. The FD estimator showed good performances on synthesized data, with lower bias compared to Higuchi’s method. FD estimates of real data tended to be higher during the day. In particular, FD of daytime MAP (1.84 ±0.06 M±SD) was substantially higher than 1.5, suggesting that anticorrelation mechanisms may influence the diurnal long-term regulation of blood pressure.
Abstract: Neurodegenerative diseases (NDD) require a constant care and attention in pharmacological therapy and rehabilitation, exercises administration, functional assessments and management of daily life. In this paper, we discuss a possible role of pervasive solutions with respect to NDD, on the basis of the overall progress of ICT and on the experience achieved in our department in three fields: Assistive Technology, NDD quantitative assessment, and design and development of wearable devices.
Abstract: The sequence technique is commonly employed to estimate the baroreflex sensitivity from the analysis of systolic blood pressure (SBP) and RR Interval (RRI) recordings. Traditionally, the RRI+/SBP- and RRI-/SBP+ sequences are excluded from this analysis.
Abstract: The Push-Pull Effect (PPE) is a physiological phenomenon defined as a reduction of +Gz tolerance induced by a previous exposure to a -Gz acceleration, that may lead to loss of consciousness. Aim of this study was to evaluate, for the first time, the cardiac rhythm changes associated with PPE during real flights. Data were collected in 3 pilots during flights on the Aermacchi MB- 339-CD aircraft. In each flight, lasting about 60 minutes, ECG, respiration and 3D accelerations were recorded by a new smart garment (the MagIC System). The flight protocol included a maneuver eliciting a reference +5Gz acceleration for 15 seconds (Ref+5G), followed, after a while, by a push-pull maneuver with a profile characterized by a 5-s acceleration at -1Gz (PP-1G) and, with a 1G/s onset, by 15 seconds at +5Gz (PP+5G), so to induce the push-pull gravitational stress. From each ECG recording, a beat-by-beat RR Interval (RRI) series was derived. RRI mean, standard deviation (SDNN) and the RRI Root Mean Square of Successive Difference (RMSSD) were estimated in each pilot during the Ref+5G and the PP+5G maneuvers. As compared with Ref+5G, all pilots displayed significant reductions in RRI mean, SDNN and RMSSD during PP+5G. These findings are compatible with a PP-induced enhancement in the sympathetic drive to the heart -as shown by the reduction in RRI mean and SDNN- and a concomitant deactivation of the parasympathetic control as shown by the reduction in RMSSD.
Abstract: Women, which have lower risks of cardiovascular events, are characterized by higher heart rate entropy. Aim of this study is to evaluate whether also the fractal structure of heart rate and blood pressure, as quantified by DFA, differs between men and women. In 33 male and 23 female volunteers, we recorded R-R intervals (RRI) and systolic (S) and diastolic (D) blood pressure (BP) for 10' in 3 conditions: supine rest, sitting at rest and sitting during exercise. We calculated a spectrum of scale exponent α(t) as function of the time scale t, by DFA. We also calculated traditional spectral indexes for assessing cardiac and vascular autonomic tone. We found gender related differences in α(t) only during supine rest. Women had significantly lower α(t) of RRI at scales <;6 s, and higher α(t) of BP at the longer scales, the difference being significant for DBP at t>;60s. Results may in part be explained by gender differences in cardiac autonomic tone at rest.
Abstract: Extreme environments such as high altitude represent a challenging testbed for both people and instruments. During a recent expedition to the slopes of Mt. Everest, (Highcare Expedition), we monitored ECG, respiration, oxygen saturation and posture in five climbers during sleep. Data were collected by using a recently developed textile-based wearable system (the MagIC system). The polysomnographic acquisitions were performed at sea level in indoor environment, and at 6000 and 6800 m asl in tents. The collected data allowed us to investigate performances and usability of MagIC system as a polysomnographic device at very-high altitude. In this paper we report on the results of this evaluation.
Abstract: In the developed countries, healthcare systems are evolving under the pressure of the population ageing, the necessity of reducing the increasing healthcare costs and the availability of new technologies. Telemedicine and eHealth solutions are gaining importance in this reference frame. Recently we participated in the final validation phase of a wide European Project, Heartfaid, aimed at building an eHealth platform for the remote monitoring and management of patients suffering from chronic heart failure. In this context, we designed and developed a simple multimodal subsystem for the home acquisition and transmission of data collected from the patients, composed of a vest embedding textile electrodes, a touchscreen computer and a UMTS dongle. In this paper we report the results of this experience where we explored the usability of such a simplified interface for home monitoring of cardiac patients
Abstract: Calculation of approximate entropy (ApEn) requires to select the correct threshold ldquorrdquo. Previous studies recommended r to be between 0.1 and 0.25 times the signal standard deviation, and now r=0.2 is used in almost all HRV studies. Recently it has been claimed that for fast signal dynamics, r=0.2 may lead to erroneous conclusions, while r maximizing ApEn, rMAX, correctly assesses entropy. We verified 1) if rMAX differs from r=0.2 also for HR; and 2) if all r values in the 0.1-0.25 range provide similar ApEn measures. For this aim, we recorded R-R intervals in 10 young subjects for 10psila, in supine and sitting positions, and calculated ApEn(r) for r between 0.02 and 1.20, identifying rMAX and ApEn(rMAX). rMAX felt into the recommended range, but it significantly differed from 0.2. At the extremes of the range, the effects of posture change on ApEn were even opposite: ApEn(0.25) decreased while ApEn(0.1) increased. Therefore the choice of r is critical even in HRV studies
Abstract: The aim of our study was to prove the existence of a spectral peak at the pedaling frequency in the heart rate spectra, during exercise test on the cycloergometer, and to describe its characteristics. This was done by studying four young healthy volunteers (2M/2F, 18-22 yrs) while pedaling on a cycloergometer with incremental workloads, by mean of a 3-lead ECG and a 7 TV-camera optoelectronic device for recording pedal movements and respiratory movements of the thorax. A clear spectral peak in the HRV spectrum at the pedaling frequency appeared for certain workloads in all subjects. The power of this peak represented a significant fraction of the power of the respiratory peak. Since the overall displacement of the chest was the same regardless of the work load, we can exclude that the spectral peak at the pedaling frequency is due to a motion artifact, and we can rather hypothesize that it is related to the muscle pump mechanism.
Abstract: On the basis of indirect evidences it has been hypothesized that during space missions the almost complete absence of gravity might impair the baroreflex control of circulation. In the first part of this paper we report results obtained from a series of experiments carried out to directly verify this hypothesis during the 16-day STS 107 Shuttle flight. Spontaneous baroreflex sensitivity was assessed in four astronauts before flight (baseline) and at days 0-1, 6-7 and 12-13 during flight, both at rest and while performing moderate exercise. Our results indicate that at rest the baroreflex sensitivity significantly increased in the early flight phase, as compared to pre-flight values and tended to return to baseline in the mid-late phase of flight. During exercise, baroreflex sensitivity was lower than at rest, without any difference among pre-flight and in-flight values. These findings seem to exclude the hypothesis of an impairment of the baroreflex control of heart rate during exposure to microgravity, at least over a time window of 16 days. In the second part of the paper we propose a novel textile-based methodology for heart rate and other vital signs monitoring during gravity stress. The positive results obtained from its use during parachute jumps support the use of smart garments for the unobtrusive assessment of physiological parameters in extreme environments.
Abstract: The fractal structure of heart rate is usually quantified by estimating a short-term (alpha(1)) and a long-term (alpha(2)) scaling exponent by Detrended Fluctuations Analysis (DFA). Evidence, however, has been provided that heart rate is a multifractal signal, better characterized by a large number of scaling exponents. Aim of this study is to verify whether two scaling exponents only from DFA provide a sufficiently accurate description of the possibly multifractal nature of cardiovascular signals. We measured ECG and finger arterial pressure in 33 volunteers for 10 minutes during each of 3 conditions: supine rest (SUP); sitting at rest (SIT); light physical exercise (EXE). DFA was applied on the beat-by-beat series of R-R interval (RRI) and mean arterial pressure (MAP). We then computed the local scaling exponent alpha(n), defined as the slope of the detrended fluctuation function F(n) around the beat scale n, in a log-log plot. If alpha(1) and alpha(2) correctly model the multiscale structure of blood pressure and heart rate, we should find that alpha(n) is constant over a short-term and a longterm range of beat scales. Results show that only the long-term alpha2 exponent provides a relatively good approximation of the multiscale structure of RRI and MAP. Moreover, posture and physical activity have important effects on local scaling exponents, and on the range of beat scales n where alpha(n) can be approximated by a constant alpha2 coefficient.
Abstract: We recently developed a textile-based system for the unobtrusive assessment of vital signs. The system, named MagIC, was originally designed to collect data in elderly people and cardiac patients while living in a confined environment. Extending the area of application of MagIC from clinics to daily life meant to pay particular attention to the garment design and to the amount of intelligence embedded into the system. In this paper we addressed both these issues by illustrating 1) a new methodology we are developing to help the design of smart garments for daily life applications and 2) an example of embedded intelligence developed for an application of MagIC in ergonomics.
Abstract: Seismocardiogram (SCG) is the recording of body vibrations induced by the heart beat. SCG contains information on cardiac mechanics, in particular heart sounds and cardiac output. In this paper we present a new wearable device for SCG recordings during long term monitorings, and the results of a validation test in 4 subjects. The system is based on the integration of the MagIC smart shirt (i.e., a textile-based wearable system for the assessment of ECG and respiratory movements), and an external triaxial MEMS accelerometer positioned on the left clavicle. SCG was estimated as the average of accelerations occurred in each heart beat. The SCG components due to the valve closure and to recoil forces following the heart contraction (ballistocardiogram) were extracted by high-pass (>18 Hz) and band-pass (0.6-20 Hz) filters respectively. Then the difference between the I and J waves of the ballistocardiogram (|I-J| index, possibly related to the cardiac output) was identified by an ad-hoc procedure and compared with the model flow indirect estimation of cardiac output. Validation on 4 volunteers showed that: 1) our wearable system provides statistically consistent estimates of both heart-sound related vibrations and recoil movements; 2) reliable estimates of the |I-J| index can be obtained by considering about 1 minute of SCG recording in stationary conditions; and 3) changes of the |I-J| index during exercise correlate well with changes of cardiac output estimated by the model flow.
Abstract: Self similarity is a promising tool for quantifying alterations in cardiovascular dynamics, although the effect of the autonomic control on the scaling structure of cardiovascular signals is still unknown. To address this issue, we studied spinal-cord injured subjects as a model of progressively impaired vascular control. We considered 24 able-bodied subjects (AB) and 23 paraplegics with lesion at different levels: between T12 and L4 (N=7); T5 and T11 (N=9); and C6 and T4 (N=7). We recorded blood pressure and heart rate in three conditions characterized by increasing sympathetic activation: supine (SUP); sitting (SIT); and exercise (EXE). We calculated the scaling exponent of mean arterial pressure, H MAP, and of R-R interval, H RRI, by detrended fluctuation analysis. The sympathetic activation had different effects on the scaling exponent, depending on the lesion level. HRRI did not change significantly from SUP to SIT and to EXE in the AB and T12 -L4 group, while it increased in the T5-T11 and C6-T4 groups. Also for H MAP sympathetic activation produced changes which depend on the level of the spinal lesion. In particular, our results suggest that heart-rate self similarity depends on the vascular sympathetic control, because it is altered by the spinal-cord lesion even when the cardiac neural control is intact.
Abstract: A new textile-based wearable system, named MagIC (Maglietta Interattiva Computerizzata) has been recently developed for getting unobtrusive recordings of cardiorespiratory and motion signals during spontaneous behavior. The system is composed of a vest, including textile sensors for ECG and breathing frequency detection, and a portable electronic board for motion assessment, signal preprocessing and wireless data transmission to a remote computer. In this study the MagIC System has been used to monitor vital signs 1) in cardiac inpatients in bed and during physical exercise and 2) in healthy subjects during exercise and under gravitational stress. All recordings showed a correct identification of arrhythmic events and a correct estimation of RR Interval. The positive results obtained in this study support the routine use of the system in a clinical setting, experimental environments, daily life conditions and sport.
Abstract: Little is known on the effects of autonomic alterations on the characteristics of self-similarity of cardiovascular time series. To clarify this issue, changes in scaling exponents for blood pressure and heart rate following sympathetic and parasympathetic blockades were studied. We recorded RR interval (RRI) and mean arterial pressure (MAP) beat by beat in 8 volunteers before and after administration of: propranolol, a non specific beta1 and beta2 cardiac and vascular antagonist; clonidine, an alpha2 agonist; and atropine, blocker of cardiac vagal activity. Self-similarity coefficients for RRI, HRRI , and MAP, HMAP, were estimated by detrended fluctuations analysis. Under baseline condition, HMAP was significantly greater than HRR. Sympathetic blockades reduced HRRI only, while vagal blockade increased both HRRI and HMAP. Results revealed differences in the scaling structures of MAP and RRI, and in the way their self-similarity is influenced by the autonomic regulation
Abstract: We presents a new textile-based wearable system, named MagIC (Maglietta Interattiva Computerizzata), for the unobtrusive recording of cardiorespiratory and motion signals during spontaneous behavior in daily life and in a clinical environment. MagIC is composed of a vest, including textile sensors for ECG and breathing frequency detection, and a portable electronic board for motion assessment, signal preprocessing and wireless data transmission to a remote computer. MagIC has been tested in freely moving subjects at work, at home, while driving and cycling. Applicability of the system in a clinical setting is now under evaluation. Recordings performed on cardiac inpatients in bed and during physical exercise showed 1) good signals quality; 2) a correct identification of arrhythmic events; and 3) a correct estimation of the tacogram. These results encourage the further tuning of the MagIC system for a routine use in the clinical practice
Abstract: The paper presents a new textile-based wearable system for the unobtrusive recording of cardiorespiratory and motion signals during spontaneous behavior along with the first results concerning the application of this device in daily life and in a clinical environment. The system, called MagIC (Maglietta Interattiva Computerizzata), is composed of a vest, including textile sensors for detecting ECG and respiratory activity, and a portable electronic board for motion detection, signal preprocessing and wireless data transmission to a remote monitoring station. The MagIC system has been tested in freely moving subjects at work, at home, while driving and cycling and in microgravity condition during a parabolic flight. Applicability of the system in cardiac in-patients is now under evaluation. Preliminary data derived from recordings performed on patients in bed and during physical exercise showed 1) good signal quality over most of the monitoring periods, 2) a correct identification of arrhythmic events, and 3) a correct estimation of the average beat-by-beat heart rate. These positive results supports further developments of the MagIC system, aimed at tuning this approach for a routine use in clinical practice and in daily life.
Abstract: The occurrence of the R peak (tR), and the area of the QRS complex (AQRS) are among the features estimated from each ECG wave. To estimate these parameters ECG is traditionally sampled at a high sampling rate (250-500 Hz). However, since tR and AQRS are identified by the selective analysis of the QRS complex and since the QRS maximal frequency component is about 25 Hz, we propose a new procedure to identify tR and AQRS from ECG sampled at the relatively low rate dictated by the frequency content of the QRS complex. The procedure identifies each QRS complex from the sampled ECG, and estimates tR and AQRS after interpolation of the QRS complex. The interpolation is obtained as the inverse discrete Fourier transform (IDFT) of the zero-padded DFT of the QRS. The technique was tested on a public database of ECG. Results showed that by this technique tR and AQRS can be accurately derived from ECG sampled at frequency as low as 70 Hz.
Abstract: The specific role of autonomic vascular control in determining non-linear behaviour of RR intervals is not clear. In 10 T12-L4 paraplegic subjects (light vascular autonomic impairment), 12 T5-T11 paraplegic subjects (moderate vascular autonomic impairment), and 24 controls RR time series were recorded (10 min): 1) in resting supine position; 2) sitting on the wheelchair and 3) during a light (5 W) arm exercise. Fractal dimension (FD), approximate entropy (ApEn) and the α scaling exponent (α-DFA, detrended fluctuation analysis) were calculated. The lesional level significantly affected ApEn (p = 0.004), FD (p = 0.007) and α-DFA (p = 0.002). Autonomic activation did not influence FD and α-DFA, but significantly affected ApEn (p = 0.035). It seems that FD and α-DFA are influenced by the changes in non-linear RR dynamics due to vascular autonomic impairment but not to autonomic activation, whereas ApEn may be equally responsive to either condition
Abstract: This study proposes a new simplified approach for estimating the latency in the baroreflex control of heart rate by the analysis of systolic blood pressure (SBP) and RR interval (RRI) spontaneous variability. Application of this technique on SBP and RRI 24-h recordings, allowed us to identify a large fluctuation of the baroreflex latency over time with a circadian pattern characterised by a reduction of the latency at night. Since our approach provides a quantification of the latency in terms of heart beats, there was the possibility that the results would be influenced by the RRI. The observed absence of any significant correlation between latency and RRI excluded this adverse possibility. These results encourage the use of the proposed procedure for obtaining a simple and noninvasive measure of the baroreflex latency in daily life condition.
Abstract: A new algorithm is proposed for the online Fourier analysis of unevenly sampled data. The method is based on the theoretical evaluation of the Fourier Transform of a function linearly interpolating the data, and does not require actual interpolation and re-sampling. The method is particularly suitable for the running evaluation of power spectra. In fact, when a new sample is available, the spectrum can be updated simply by performing calculations on the last sample, without the need to calculate the Fourier Transform again over the whole data record. Applications with simulated and real data show the capability of the algorithm to efficiently estimate the Fourier transform of unevenly sampled cardiovascular data, beat after beat.
Abstract: A new procedure has been developed to (1) investigate the coupling between arterial blood pressure and heart rate variability in daily life and (2) identify the baroreflex contribution to such a coupling. The algorithm is based on the estimation of cross-mutual information (CMI) between systolic blood pressure (SBP) and RR-interval (RRI) beat-to-beat values. CMI has been selected because of its capability to quantify both linear and nonlinear components of the coupling between variables. This procedure has been used to analyze data recorded in spontaneously behaving cats before and seven days after surgical opening of the baroreflex loop as obtained by a sino-aortic denervation. Use of CMI indicates that over a time scale on the order of minutes the arterial baroreflex is the major determinant of the SBI-RRI link, accounting for about 2/3 of the total (linear and nonlinear) coupling measured between these variables
Abstract: The effects of sinoaortic denervation on systolic blood pressure (SBP), diastolic blood pressure (DBP), pulse interval (PI), renal sympathetic nerve activity (RSNA) and respiratory activity (RA) were investigated in conscious Wistar rats by wide-band spectral and coherence analysis. Signals were recorded for 90 minutes, six hours after sinoaortic denervation (SAD) in eight such rats, and in eight sham-operated rats. After SAD, the animals showed higher blood pressure (BP) mean and variability, higher heart rate and RSNA, and lower PI variability and respiratory frequency. The rhythmic component centred at 0.4 Hz, seen in RSNA in sham rats was blunted after SAD. The results suggest that PI variability and the RSNA component at 0.4 Hz depend on baroreceptors and may contribute to regulating BP within a physiological range of variability
Abstract: A new index, the cross-power index (CPI), is proposed to quantify the severity of obstructive sleep apnea syndrome (OSAS) in terms of its cardiovascular effects. On the basis of the influences that recurring drops in oxygen saturation have on systolic blood pressure variability of OSAS patients, CPI is defined as the integral of the cross-spectrum modulus between systolic blood pressure and oxygen saturation. In a test group of 22 subjects, CPI correctly identified all 15 OSAS patients included in the pool. Moreover, evaluation of CPI in six OSAS patients sleeping with and without a CPAP (continuous positive airway pressure) device demonstrated that CPAP treatment substantially reduced the components of blood pressure variability that were correlated with oxygen saturation. These first applications of CPI support the use of this index to identify OSAS patients, to evaluate the efficacy of CPAP in their treatment and to quantify the cardiovascular effect of OSAS
Abstract: The Lomb periodogram is a method for the spectral analysis of randomly sampled data. For this property and for the ability to estimate spectral peaks beyond the mean Nyquist frequency, the Lomb approach was proposed for the spectral analysis of heart rate (HR). The features of the Lomb periodogram, however hold for a random sampling while the sampling frequencies of the HR series are equal to the same HR values and thus include systematic oscillations and 1/f noise typical of HR variability. The aim of this study is to investigate whether the rhythmic oscillations and the 1/f noise may influence the performances of the Lomb method. This is done by applying the Lomb procedure to simulated HR series and to real HR data. Results indicate that the valuable features of the Lomb periodogram are in part nullified by the specific characteristics of the HR signal
Abstract: The aim of this study was to evaluate whether use of heart period (HP) or heart rate (HR) may influence the spectral estimate of changes in heart rhythm variability (HRV) induced by physical exercise. For this purpose, power spectra were derived from both HP and HR signals monitored in 8 subjects before, during and after cycling. Powers around 0.1 (LF) and 0.3 (HF) Hz were computed, along with their ratio (LF/HF). Results indicate that HP and HR spectra provide different descriptions of HRV changes in response to exercise. LF and HF powers differed markedly whenever significant changes in the mean heart rhythm occurred in some cases leading to opposite conclusions. A logarithmic transformation of HP and HR signals was proposed to obtain a univocal estimation of NRV spectra
Abstract: The aim of this work was to study the influences of the autonomic nervous system on blood pressure and heart rate spontaneous variability by separate blockades of sympathetic and parasympathetic efferent activity. In normotensive rats the effects of sympathetic and parasympathetic blockade were evaluated making use of a specific wide-band spectral and coherence analysis of systolic blood pressure, SBP, and pulse interval, PI. After sympathectomy, PI spectral components were significantly reduced between 0.012 and 0.22 Hz while SBP components were reduced between 0.08 and 1.53 Hz but increased between 0.0024 and 0.039 Hz; sympathectomy also increased the coherence modulus below 0.02 Hz. Parasympathetic blockade decreased all the PI spectral components, the SBP respiratory fluctuations and uncoupled SBP and PI at the respiratory frequency
Abstract: Blood pressure variability was found to follow a 1/f behaviour. The aim of the authors' study was to verify whether this phenomenon was associated with a concomitant 1/f modulation of the baroreflex sensitivity. In 8 ambulant subjects, systolic blood pressure and pulse interval were continuously monitored for 24 hours and jointly analysed by a sequential procedure to obtain a dynamic estimation of baroreflex sensitivity over day and night. A single spectrum was estimated via FFT from each 24-h sensitivity profile and the presence of the 1/f pattern was evaluated by fitting such a spectrum by a 1/f curve. The authors' results indicate that the baroreflex sensitivity is characterised by marked and systematic short and long-term changes actually following a 1/f behaviour
Abstract: In eight conscious cats, the spectral characteristics of systolic blood pressure and heart rate have been estimated before and after surgical opening of the arterial baroreflex obtained by denervation of carotid and aortic baroreceptors. Each spectrum was fitted by the 1/fα model and the residuals were analyzed to determine which regions of the spectra are reliably described by the model in intact conditions and after baroreflex denervation. The study indicated that the baroreflex plays a primary role in producing the 1/ fα shape of systolic pressure components at frequencies <0.02 Hz and of heart rate components in a band from 0.2 to 0.05 Hz
Abstract: The effects of the surgical opening of the baroreflex loop on the spectral components of systolic blood pressure (SBP) and pulse interval (PI) variability in 8 unrestrained cats are analyzed. In each cat, the spectral characteristics were estimated from intraarterial blood pressure tracings recorded before and after surgical sino-aortic baroreceptor denervation (SAD). The analysis focused on two different spectral regions. The first region included spectral components having periods ranging from 1.6 to 40 seconds, while the second region (partially overlapping the first one) included components with periods from 10 seconds up to 1.5 hours. The opening of the baroreflex loop caused nonhomogeneous effects on the various components of SBP and PI variability. These findings evidence a differentiated involvement of the baroreceptors in controlling SBP and PI variations characterized by different time constants
