Abstract: OBJECTIVE: Mechanical support of a failing heart is typically performed with rotary blood pumps running at constant speed, which results in a limited control on cardiac workload and nonpulsatile hemodynamics. A potential solution to overcome these limitations is to modulate the pump speed to create pulses. This study aims at developing a pulsatile control algorithm for rotary pumps, while investigating its effect on left ventricle unloading and the hemodynamics. METHODS: The CentriMag (Levitronix GmbH, Zürich, Switzerland) rotary blood pump was implanted in 5 sheep and cannulated from the ventricular apex to the descending aorta. A modified controller was connected to the pump yielding direct speed control via analog voltage. Pump speed modulation patterns, including sine, saw tooth, triangle, and square waveforms with 2 different phase shifts, were synchronized with heartbeat. Various hemodynamic parameters, such as left ventricular pressure and volume, coronary flow, and arterial pressure, were analyzed to examine the influence of pump support. RESULTS: The pump speed modulation significantly affected left ventricular pressure and volume and arterial pressure, whereas coronary flow was not influenced by pump support mode. Stroke work in the pulsatile modes varied from 69% to 91% of baseline value and from 74% to 96% of constant speed value. Consequently, cardiac workload can be adjusted to provide relaxation, which may lead to myocardial recovery. CONCLUSIONS: A synchronized pulsing rotary blood pump offers a simple and powerful control modality for heart unloading. This technique provides pulsatile hemodynamics, which is more physiologic than continuous blood flow and may be useful for perfusion of the other organs.
Abstract: Surgical treatment of mitral leaflet prolapse using artificial neochordae shows excellent outcomes. Upcoming devices attempt the same treatment in a minimally invasive way but target the left ventricular apex as an anchoring point, rather than the tip of the corresponding papillary muscle. In this study, cine cardiac magnetic resonance imaging was used to compare these 2 different anchoring positions and their dynamic relationship with the mitral leaflets.
Abstract: In this study, the effect of time derivatives of flow rate and rotational speed was investigated on the mathematical modeling of a rotary blood pump (RBP). The basic model estimates the pressure head of the pump as a dependent variable using measured flow and speed as predictive variables. Performance of the model was evaluated by adding time derivative terms for flow and speed. First, to create a realistic working condition, the Levitronix CentriMag RBP was implanted in a sheep. All parameters from the model were physically measured and digitally acquired over a wide range of conditions, including pulsatile speed. Second, a statistical analysis of the different variables (flow, speed, and their time derivatives) based on multiple regression analysis was performed to determine the significant variables for pressure head estimation. Finally, different mathematical models were used to show the effect of time derivative terms on the performance of the models. In order to evaluate how well the estimated pressure head using different models fits the measured pressure head, root mean square error and correlation coefficient were used. The results indicate that inclusion of time derivatives of flow and speed can improve model accuracy, but only minimally.
Abstract: Right axillary artery (RAA) cannulation is increasingly used in cardiac surgery. Little is known about resulting flow patterns in the aorta. Therefore, flow was visualized and analyzed. A mock circulatory circuit was assembled based on a compliant transparent anatomical silicon aortic model. A RAA cannula was connected to a continuous flow rotary blood pump (RBP), pulsatile heart action was provided by a pneumatic ventricular assist device (PVAD). Peripheral vascular resistance, regional flow and vascular compliance were adjusted to obtain physiological flow and pressure waveforms. Colorants were injected automatically for flow visualization. Five flow distributions with a total flow of 4Â l/min were tested (%PVAD:%RBP): 100:0, 75:25, 50:50, 25:75, 0:100. Colorant distribution was assessed using quantitative 2D image processing. Continuous flow from the RAA divided in a retrograde and an antegrade portion. Retro- to antegrade flow ratio increased with increasing RAA-flow. At full RBP support flow was stagnant in the ascending aorta. There were distinct flow patterns between the right- and left-sided supra-aortic branches. At full RBP support retrograde flow was demonstrated in the right carotid and right vertebral arteries. Further studies are needed to confirm and evaluate the described flow patterns.
Abstract: The PediaFlow pediatric ventricular assist device is a miniature magnetically levitated mixed flow pump under development for circulatory support of newborns and infants (3-15 kg) with a targeted flow range of 0.3-1.5 L/min. The first generation design of the PediaFlow (PF1) was manufactured with a weight of approximately 100 g, priming volume less than 2 mL, length of 51 mm, outer diameter of 28 mm, and with 5-mm blood ports. PF1 was evaluated in an in vitro flow loop for 6 h and implanted in ovines for three chronic experiments of 6, 17, and 10 days. In the in vitro test, normalized index of hemolysis was 0.0087 ± 0.0024 g/100L. Hemodynamic performance and blood biocompatibility of PF1 were characterized in vivo by measurements of plasma free hemoglobin, plasma fibrinogen, total plasma protein, and with novel flow cytometric assays to quantify circulating activated ovine platelets. The mean plasma free hemoglobin values for the three chronic studies were 4.6 ± 2.7, 13.3 ± 7.9, and 8.8 ± 3.3 mg/dL, respectively. Platelet activation was low for portions of several studies but consistently rose along with observed animal and pump complications. The PF1 prototype generated promising results in terms of low hemolysis and platelet activation in the absence of complications. Hemodynamic results validated the magnetic bearing design and provided the platform for design iterations to meet the objective of providing circulatory support for young children with exceptional biocompatibility.
Abstract: OBJECTIVE: This study evaluates the feasibility of off-pump native aortic valve removal in preparation for transapical aortic valve replacement. Off-pump aortic valve replacement is performed by balloon predilatation of the native valve followed by insertion of a stented prosthesis. In patients with calcified annuli and cusps, particulate embolization, suboptimal prosthesis sizing, and perivalvular leaks may occur. Therefore, native valve removal may improve outcomes after transapical aortic valve replacement.
METHODS: The aortic cusps were sequentially removed from 10 pigs in an off-pump procedure. A temporary valve was inserted percutaneously into the ascending aorta to prevent aortic regurgitation. The electrocardiogram, coronary blood flow, and arterial, left atrial, and ventricular pressures were continuously monitored.
RESULTS: Removal of the aortic cusps caused a drop in diastolic arterial pressure and its equalization with left ventricular diastolic pressure. Systolic pressure decreased by 13.5%. Left atrial pressure increased by 86.0%. Coronary blood flow decreased by 39.9% and its pattern changed from mostly diastolic to mostly systolic. Electrocardiographic signs of ischemia appeared almost immediately. Percutaneous insertion of a temporary valve in the ascending aorta increased diastolic pressure and caused a tendency toward echocardiographic normalization.
CONCLUSIONS: Aortic valve removal in a healthy beating heart causes acute massive aortic regurgitation, hemodynamic instability, and the rapid onset of myocardial ischemia. Reduction of left ventricular volume overload, by placement of a temporary valve in the ascending aorta, mitigates myocardial distress, helps stabilize hemodynamic parameters, and may be a useful tool to allow surgical manipulations of the aortic valve and annulus during transapical aortic valve replacement procedures.
Abstract: Fluid dynamic analysis of turbodynamic blood pumps (TBPs) is often conducted under steady flow conditions. However, the preponderance of clinical applications for ventricular assistance involves unsteady, pulsatile flow-due to the residual contractility of the native heart. This study was undertaken to demonstrate the importance of pulsatility and the associated time derivative of the flow rate (dQ/dt) on hemodynamics within a clinical-scale TBP. This was accomplished by performing flow visualization studies on a transparent model of a centrifugal TBP interposed within a cardiovascular simulator with controllable heart rate and stroke volume. Particle image velocimetry triggered to both the rotation angle of the impeller and phase of the cardiac cycle was used to quantify the velocity field in the outlet volute and in between the impeller blades for 16 phases of the cardiac cycle. Comparison of the unsteady flow fields to corresponding steady conditions at the same (instantaneous) flow rates revealed marked differences. In particular, deceleration of flow was found to promote separation within the outlet diffuser, while acceleration served to stabilize the velocity field. The notable differences between the acceleration and deceleration phases illustrated the prominence of inertial fluid forces. These studies emphasize the importance of dQ/dt as an independent variable for thorough preclinical validation of TBPs intended for use as a ventricular assist device.
Abstract: The characteristic depressed hemodynamic state and gradually declining circulatory function in Fontan patients necessitates alternative postoperative management strategies incorporating a system level approach. In this study, the single-ventricle Fontan circulation is modeled by constructing a practical in vitro bench-top pulsatile pediatric flow loop which demonstrates the ability to simulate a wide range of clinical scenarios. The aim of this study is to illustrate the utility of a novel single-ventricle flow loop to study mechanical cardiac assist to Fontan circulation to aid postoperative management and clinical decision-making of single ventricle patients. Two different pediatric ventricular assist devices, Medos and Pediaflow Gen-0, are anastomosed in two nontraditional configurations: systemic venous booster (SVB) and pulmonary arterial booster (PAB). Optimum ventricle assist device strategy is analyzed under normal and pathological (pulmonary hypertension) conditions. Our findings indicate that the Medos ventricular assist device in SVB configuration provided the highest increase in pulmonary (46%) and systemic (90%) venous flow under normal conditions, whereas for the hypertensive condition, highest pulmonary (28%) and systemic (55%) venous flow augmentation were observed for the Pediaflow ventricular assist device inserted as a PAB. We conclude that mechanical cardiac assist in the Fontan circulation effectively results in flow augmentation and introduces various control modalities that can facilitate patient management. Assisted circulation therapies targeting single-ventricle circuits should consider disease state specific physiology and hemodynamics on the optimal configuration decisions.
Abstract: Recently developed technologies allow aortic valve implantation off-pump in a beating heart. In this procedure, the native, stenotic aortic valve is not removed, but simply crushed by a pressure balloon mounted on a percutaneous catheter. Removal of the native aortic cusps before valve replacement may reduce the incidence of annular or cuspal calcium embolization and late perivalvular leaks and increase implantable valve size. However, a temporary valve system in the ascending aorta may be necessary to maintain hemodynamic stability by reducing acute aortic regurgitation and left ventricular volume overload. This study evaluates the hemodynamic effects of a wire-mounted, monoleaflet, temporary valve apparatus in a mechanical cardiovascular simulator. Aortic flow, systemic pressure and left ventricular pressure were continuously monitored. An intraluminal camera obtained real-time proximal and distal images of the valve in operation. Insertion of the parachute valve in the simulator increased diastolic pressure from 7 to 38 mm Hg. Cardiac output increased from 2.08 to 4.66 L/min and regurgitant volume decreased from 65 to 23 mL. In conclusion, placement of a temporary valve in the ascending aorta may help maintain hemodynamic stability and improve off-pump aortic valve replacement.
Abstract: The time-varying elastance theory of Suga et al. is widely used to simulate left ventricular function in mathematical models and in contemporary in vitro models. We investigated the validity of this theory in the presence of a left ventricular assist device. Left ventricular pressure and volume data are presented that demonstrate the heart-device interaction for a positive-displacement pump (Novacor) and a rotary blood pump (Medos). The Novacor was implanted in a calf and used in fixed-rate mode (85 BPM), whereas the Medos was used at several flow levels (0-3 l/min) in seven healthy sheep. The Novacor data display high beat-to-beat variations in the amplitude of the elastance curve, and the normalized curves deviate strongly from the typical bovine curve. The Medos data show how the maximum elastance depends on the pump flow level. We conclude that the original time-varying elastance theory insufficiently models the complex hemodynamic behavior of a left ventricle that is mechanically assisted, and that there is need for an updated ventricular model to simulate the heart-device interaction.
Abstract: The very limited options available to treat ventricular failure in children with congenital and acquired heart diseases have motivated the development of a pediatric ventricular assist device at the University of Pittsburgh (UoP) and University of Pittsburgh Medical Center (UPMC). Our effort involves a consortium consisting of UoP, Children's Hospital of Pittsburgh (CHP), Carnegie Mellon University, World Heart Corporation, and LaunchPoint Technologies, Inc. The overall aim of our program is to develop a highly reliable, biocompatible ventricular assist device (VAD) for chronic support (6 months) of the unique and high-risk population of children between 3 and 15 kg (patients from birth to 2 years of age). The innovative pediatric ventricular assist device we are developing is based on a miniature mixed flow turbodynamic pump featuring magnetic levitation, to assure minimal blood trauma and risk of thrombosis. This review article discusses the limitations of current pediatric cardiac assist treatment options and the work to date by our consortium toward the development of a pediatric VAD.
Abstract: The very limited options available to treat ventricular failure in patients with congenital and acquired heart diseases have motivated the development of a pediatric ventricular assist device (VAD). Our effort involves a consortium consisting of the University of Pittsburgh, Carnegie Mellon University, Children's Hospital of Pittsburgh, World Heart Corporation, and LaunchPoint Technologies, LLC. The overall aim of our program is to develop a highly reliable, biocompatible VAD for chronic support (6 months) of the unique and high-risk population of children between 3 kg and 15 kg (patients from birth to 2 years of age). The innovative pediatric VAD we are developing (PediaFlow) is based on a miniature mixed-flow turbodynamic pump featuring magnetic levitation, with the design goal being to assure minimal blood trauma and risk of thrombosis. This article discusses the limitations of current pediatric cardiac assist treatment options and the work to date by our consortium toward the development of a pediatric VAD.
Abstract: Various automatic algorithms are now being developed to calculate left ventricular (LV) and right ventricular (RV) ejection fraction from tomographic radionuclide ventriculography. We tested the performance of 4 of these algorithms in estimating LV and RV volume and ejection fraction using a dynamic 4-chamber cardiac phantom.
METHODS: We developed a realistic physical, dynamic 4-chamber cardiac phantom and acquired 25 tomographic radionuclide ventriculography images within a wide range of end-diastolic volumes, end-systolic volumes, and stroke volumes. We assessed the ability of 4 algorithms (QBS, QUBE, 4D-MSPECT, and BP-SPECT) to calculate LV and RV volume and ejection fraction.
RESULTS: For the left ventricle, the correlations between reference and estimated volumes (0.93, 0.93, 0.96, and 0.93 for QBS, QUBE, 4D-MSPECT, and BP-SPECT, respectively; all with P < 0.001) and ejection fractions (0.90, 0.93, 0.88, and 0.92, respectively; all with P < 0.001) were good, although all algorithms underestimated the volumes (mean difference [+/-2 SDs] from Bland-Altman analysis: -39.83 +/- 43.12 mL, -33.39 +/- 38.12 mL, -33.29 +/- 40.70 mL, and -16.61 +/- 39.64 mL, respectively). The underestimation by QBS, QUBE, and 4D-MSPECT was greater for higher volumes. QBS, QUBE, and BP-SPECT could also be tested for the right ventricle. Correlations were good for the volumes (0.93, 0.95, and 0.97 for QBS, QUBE, and BP-SPECT, respectively; all with P < 0.001). In terms of absolute volume estimation, the mean differences (+/-2 SDs) from Bland-Altman analysis were -41.28 +/- 43.66 mL, 11.13 +/- 49.26 mL, and -13.11 +/- 28.20 mL, respectively. Calculation of RV ejection fraction correlated well with true values (0.84, 0.92, and 0.94, respectively; all with P < 0.001), although an overestimation was seen for higher ejection fractions.
CONCLUSION: Calculation of LV and RV ejection fraction based on tomographic radionuclide ventriculography was accurate for all tested algorithms. All algorithms underestimated LV volume; estimation of RV volume seemed more difficult, with different results for each algorithm. The more irregular shape and inclusion of a relatively hypokinetic RV outflow tract in the right ventricle seemed to cause the greater difficulty with delineation of the right ventricle, compared with the left ventricle.
Abstract: Pulsatile operation of rotary blood pumps (RBPs) has received interest due to potential concern with nonphysiological hemodynamics. This study aimed to gain insight to the effects of various RBP modes on the heart-device interaction. A Deltastream diagonal pump (Medos Medizintechnik GmbH) was inserted in a cardiovascular simulator with apical-to-ascending aorta cannulation. The pump was run in continuous mode with incrementally increasing rotating speed (0-5000 rpm). This was repeated for three heart rates (50-100-150 bpm) and three levels of left ventricular (LV) contractility. Subsequently, the Deltastream was run in pulsatile mode to elucidate the effect of (de)synchronization between heart and pump. LV volume and pressure, arterial pressure, flows, and energetic parameters were used to evaluate the interaction. Pump failure (0 rpm) resulted in aortic pressure drops (17-46 mm Hg) from baseline. In continuous mode, pump flow compensated by diminished aortic flow, thus yielding constant total flow. High continuous rotating speed resulted in acute hypertension (mean aortic pressure up to 178 mm Hg). In pulsatile mode, unmatched heart and pulsatile pump rates yielded unphysiologic pressure and flow patterns and LV unloading was found to be highly dependent on synchronization phase. Optimal unloading was achieved when the minimum rotating speed occurred at end-systole. We conclude that, in continuous mode, a perfusion benefit can only be achieved if the continuous pump flow exceeds the preimplant (baseline) cardiac output. Pulsatile mode of support results in complex pressure and volume variations and requires accurate triggering to achieve optimal unloading.
Abstract: BACKGROUND: Automatic and semi-automatic algorithms to calculate ejection fraction (EF) from planar radionuclide ventriculography (PRV) have been used for many years in nuclear medicine. Validation of these algorithms is scarce and often performed on outdated versions of the software. Nevertheless, clinical trials where PRV is being used as the 'gold standard' for EF are numerous. Because of the importance attributed to the EF calculated by these programs, the accuracy of the resulting EF was assessed with a dynamic left ventricular physical phantom.
METHODS: A dynamic left ventricular phantom was used to simulate 21 combinations of various ejection fractions (7-66%) and end diastolic volumes (27-290 ml). For each combination, a planar radionuclide ventriculograph was acquired, converted to an interfile format and transferred into processing stations with 10 different contemporaneously available commercial algorithms. The gold standard was the 'real' EF of the phantom, derived from the exact volume of the ventricle in end diastolic and end systolic position. Correlation and Bland-Altman analysis was performed between the real EF and the calculated EF.
RESULTS: The correlation for all data was excellent (r=0.98), the mean difference was very acceptable (0.98%). Nevertheless, Bland-Altman analysis showed a significant trend in the difference between real and calculated EF, with a growing underestimation for higher ranges of EF, due to an overestimation of background in larger volumes compared to smaller ones.
CONCLUSION: The determination of EF from PRV, calculated with commercially available algorithms, correlates closely to the real EF of a dynamic left ventricular phantom. This phantom can be used in the development and validation of algorithms for PRV studies, in software audits and in quality assurance procedures.
Abstract: BACKGROUND: Ventricular assist devices are gaining ground in the therapeutic treatment of chronic heart failure. These devices are sometimes used as a bridge to recovery by unloading the left ventricle (LV) and restoring its function. It is therefore important to preserve the heart muscle and apply less invasive implantation methods.
METHODS: In this study ventricular unloading was achieved in 7 healthy sheep with a rotary blood pump at different pump flow levels. Ventricular cannulation via the left atrium (LA) and through the mitral valve was compared to atrial cannulation. The unloading of the heart was assessed with LV pressure-volume loops, derived energetic parameters, and an estimate of LV wall stress.
RESULTS: No significant difference between the cannulations was found for any flow or pressure. LA cannulation, however, resulted in significantly lower stroke volumes and stroke work for all pump flow levels. Irrespective of cannulation site, LV volumes and energetic parameters showed a significant decrease with increasing pump flow.
CONCLUSION: LV assist with a rotary blood pump can provide sufficient unloading with atrial cannulation.
Abstract: BACKGROUND: Calculation differences between various gated blood pool (GBP) single photon emission computed tomography (SPECT) (GBPS) algorithms may arise as a result of different modeling assumptions. Little information has been available thus far regarding differences for right ventricular (RV) function calculations, for which GBPS may be uniquely well suited.
METHODS AND RESULTS: Measurements of QBS (Cedars-Sinai Medical Center, Los Angeles, Calif) and BP-SPECT (Columbia University, New York, NY) algorithms were evaluated. QBS and BP-SPECT left ventricular (LV) ejection fraction (EF) correlated strongly with conventional planar-GBP LVEF for 422 patients (r = 0.81 vs r = 0.83). QBS correlated significantly more strongly with BP-SPECT for LVEF than for RVEF (r = 0.80 vs r = 0.41). Both algorithms demonstrated significant gender differences for 31 normal subjects. BP-SPECT normal LVEF (67% +/- 9%) was significantly closer to values in the magnetic resonance imaging (MRI) literature (68% +/- 5%) than QBS (58% +/- 9%), but both algorithms underestimated normal RVEF (52% +/- 7% and 50% +/- 9%) compared with the MRI literature (64% +/- 9%). For 21 patients, QBS correlated similarly to MRI as BP-SPECT for LVEF (r = 0.80 vs r = 0.85) but RVEF correlation was significantly weaker (r = 0.47 vs r = 0.81). For 16 dynamic phantom simulations, QBS LVEF correlated similarly to BP-SPECT (r = 0.81 vs r = 0.91) but QBS RVEF correlation was significantly weaker (r = 0.62 vs r = 0.82). Volumes were lower by QBS than BP-SPECT for all data types.
CONCLUSIONS: Both algorithms produced LV parameters that correlated strongly with all forms of image data, but all QBS RV relationships were significantly different from BP-SPECT RV relationships. Differences between the two algorithms were attributed to differences in their underlying ventricular modeling assumptions.
Abstract: The PUCA II pump is a minimally invasive intra-arterial left ventricular assist device that can be used as an alternative for the intra-aortic balloon pump (IABP). In this study, we assessed the cardiac unloading and organ perfusion capacities of both PUCA II and IABP in an in vitro set up, consisting of a heart simulator and a silicone arterial tree, mimicking anatomical geometry and flow distribution. The IABP was positioned in the descending aorta, while the PUCA II was tested both in 'trans-aortic' and 'abdominal' positions. All devices were driven by the same Arrow AutoCat IABP driver at different pump rates. Apart from flow, arterial pressure and pulse pressure, we also calculated haemodynamic indices for myocardial oxygen supply and demand. The 'abdominal' PUCA II assist and the IABP both provide mild unloading of the heart, and a limited improvement of arterial pressure and flow. The 'trans-aortic' PUCA II assist greatly enhances flow and pressure, but does not unload the heart properly in the tested configuration.
Abstract: Although there is increasing interest in the automatic processing of tomographic radionuclide ventriculography (TRV) studies, validation is mainly limited to a comparison of TRV results with data from planar radionuclide ventriculography (PRV) or gated perfusion single photon emission computed tomography (SPECT). The aim of this study was to use a dynamic physical cardiac phantom to validate the ejection fraction (EF) and volumes from PRV and TRV studies. A new dynamic left ventricular phantom was constructed and used to obtain 21 acquisitions in the planar and tomographic mode. The directly measured volumes and EFs of the phantom during the acquisitions were considered as the gold standard for comparison with TRV and PRV. EFs were calculated from PRV by backgroundâcorrected endâdiastolic and endâsystolic frames. Volumes and EFs were calculated from TRV by region growing with different lower thresholds to search for the optimal threshold. EF from PRV correlated significantly with the real EF (r = 0.94, P = 0.00). The optimal threshold value for volume calculation from TRV in 336 cases was 50% (r = 0.98, P = 0.00) yielding the best slope after linear regression. When considering these calculated endâdiastolic and endâsystolic volumes, EF correlated well (r = 0.99, P = 0.00) with the real EF, and this correlation was significantly (P = 0.04) higher than that of the EF from PRV. Our experiments prove that EF measured by TRV yields more accurate results compared with PRV in dynamic cardiac phantom studies.
Abstract: We have developed a biventricular dynamic physical cardiac phantom to test gated blood-pool (GBP) SPECT image-processing algorithms. Such phantoms provide absolute values against which to assess accuracy of both right and left computed ventricular volume and ejection fraction (EF) measurements.
METHODS: Two silicon-rubber chambers driven by 2 piston pumps simulated crescent-shaped right ventricles wrapped partway around ellopsoid left ventricles. Twenty experiments were performed at Ghent University, for which right and left ventricular true volume and EF ranges were 65-275 mL and 55-165 mL and 7%-49% and 12%-69%, respectively. Resulting 64 x 64 simulated GBP SPECT images acquired at 16 frames per R-R interval were sent to Columbia University, where 2 observers analyzed images independently of each other, without knowledge of true values. Algorithms automatically segmented right ventricular activity volumetrically from left ventricular activity. Automated valve planes, midventricular planes, and segmentation regions were presented to observers, who accepted these choices or modified them as necessary. One observer repeated measurements >1 mo later without reference to previous determinations.
RESULTS: Linear correlation coefficients (r) of the mean of the 3 GBP SPECT observations versus true values for right and left ventricles were 0.80 and 0.94 for EF and 0.94 and 0.95 for volumes, respectively. Correlations for right and left ventricles were 0.97 and 0.97 for EF and 0.96 and 0.89 for volumes, respectively, for interobserver agreement and 0.97 and 0.98 for EF and 0.96 and 0.90 for volumes, respectively, for intraobserver agreement. No trends were detected, though volumes and right ventricular EFs were significantly higher than true values.
CONCLUSION: Overall, GBP SPECT measurements correlated strongly with true values. The phantom evaluated shows considerable promise for helping to guide algorithm developments for improved GBP SPECT accuracy.
Abstract: Due to the increased appeal of rotary blood pumps for long-term cardiac assist, we conducted a study of their capacity to unload the left ventricle (LV). We used a validated mathematical model of the cardiovascular system and implemented the pump characteristics of an investigational microdiagonal pump (Medos). The influence of the pump on systemic hemodynamics, LV energetic parameters, and wall stress was evaluated in continuous and synchronous pulsatile modes of operation. For the continuous mode simulations, the influence of heart rate, LV contractility, and pump speed was assessed in a parametric study. For the pulsatile mode, different onsets of a synchronous time-varying pump speed pattern were tested. Our data indicate that the effectiveness of unloading in continuous mode depends on the contractility of the native ventricle. Hypocontractile ventricles are most easily unloaded, while ventricles with moderate contractility require high continuous pump speeds to achieve notable unloading. In pulsatile mode, the pump timing is an important determinant of pump/cardiovascular system interaction, with a counterpulsation setting yielding the best unloading.
Abstract: The aim of this study was to test the truCATHTM/ truCOMMSTM continuous cardiac output catheter/monitor in a computer-controlled pulsatile mock loop system. The pulmonary artery catheter is equipped with two thermistors and a heating coil which maintains a 2°C temperature difference between the thermistors. The required electrical power is assumed to be an indicator of cardiac output. The catheter was tested under a variety of loading conditions including changes in heart rate (60, 75, 90, 120 beats/mm), filling pressures (0â15 mmHg), ventricular driving pressures (22â135 mmHg), and pulmonary resistance (0.08â1.47 mmHg·s/mL) in random combinations, generating flows of 1.5â10 L/min. Fluid temperature was varied between 32 and 42°C. Our data demonstrate a good linear relation between the electrical power output of the TruCATHTM/TruCOMMSTM catheter and the actual flow as measured volumetrically. The system appeared to be sensitive to fluid temperature changes, but dimensionless analysis with Womersley and Reynolds numbers revealed that it is a direct consequence of the temperature-dependent water viscosity. We conclude that the TruCATHTM/TruCOMMSTM is a potentially useful clinical tool but the absolute correspondence between the catheter output and the patient's actual cardiac output remains to be assessed.
Abstract: The "pulsatile catheter" (PUCA) pump is a minimally invasive intra-arterial left ventricular assist device intended for acute support of critically ill heart failure patients. To assess the hydrodynamic performance of the PUCA II, driven by an Arrow AutoCat IABP driver, we used a (static) mock circulatory system in which the PUCA II was tested at different loading conditions. The PUCA II was subsequently introduced in a (dynamic) cardiovascular simulator (CVS) to mimic actual in vivo operating conditions, with different heart rates and 2 levels of left ventricular (LV) contractility. Mock circulation data shows that PUCA II pump performance is sensitive to afterload, pump rate and preload. CVS data demonstrate that PUCA II provides effective LV unloading and augments diastolic aortic pressure. The contribution of PUCA II to total flow is inversely related to LV contractility and is higher at high heart rates. We conclude that, with the current IABP driver, the PUCA II is most effective in 1:1 mode in left ventricles with low contractility.
Abstract: The aim of this study was to perform combined hydrodynamic and Doppler echocardiographic tests of the Omnicarbon 21 mm cardiac valve in aortic position in our Pulse Duplicator System for simultaneous assessment of valve performance and valve leakage data. During forward flow conditions, measured mean pressure gradients are between 4.5 and 20.2 mmHg (11.9 +/- 4.4 mmHg) for cardiac outputs between 3.6 and 5.3 /min (4.5 +/- 0.4 /min). Doppler-derived mean pressure gradients are between 2.0 and 170 mmHg (9.3 +/- 3.9 mmHg) for the same flow conditions. Effective Orifice area is 1.31 +/- 0.08 cm2 and the performance index is 0.74 +/- 0.04, using the actual geometric orifice area, and 0.38 +/- 0.02, using the tissue annulus diameter, for a cardiac output of 4.5 +/- 0.4 l/min. Regurgitation volumes are below 3 ml. There is a trend to an effect of valve orientation on hemodynamics.
Abstract: In this study, we used a mathematical model to study the influence of backflow through a failing rotary blood pump. We performed simulations based on animal experiments that were published earlier by Nishida et al., who used the Medos Microdiagonal pump to assess the acute effect of sudden pump failure. The mathematical model consists of validated cardiac and arterial modules and a pump module. We could evaluate the influence of pump failure with mechanoenergetic parameters and wall stress obtained from model output. Simulations were performed at baseline and after 15 min of backflow in a control group and a heart failure group. Simulation results agreed well with the experiment. Stroke volume, aortic flow, and stress time integral increased significantly because of pump failure. However, total systemic flow and arterial pressure were not altered by backflow, and a life-threatening situation did not appear.
Abstract: Previous in vitro testing (mainly in aortic position) and clinical experience (often based on Doppler echocardiographic observations) demonstrated an excellent hemodynamic behavior of the On-X valve. However, integrative studies including simultaneous hemodynamic pressure and flow measurements and Doppler echocardiography are lacking. Using our computer-controlled mock loop system, two samples of the Mitral 27/29 and one sample of the Conform-X Mitral 25/33 are tested in mitral position. Data include transvalvular pressure gradient and flow as well as transthoracic Doppler echocardiography. The valves are tested under three pressure conditions (ventricular systolic pressure of 100, 130, and 160 mm Hg) at three different heart rates (60, 100, and 140 beats/min). In addition, ventricular pressure conditions simulating fibrillation are imposed. Both valve types show similar hydrodynamic characteristics and have an effective orifice area of 2.1 cm2 and a performance index of 0.56 for a cardiac output of 3.5 L/min. Regurgitant volumes remain below 6 ml.
Abstract: Evidence has been gathered that biomechanical factors have a significant impact on cell differentiation and behavior in in vitro cell cultures. The aim of this bioreactor is to create a physiological environment in which tissue engineered (TE) aortic valves seeded with human cells can be cultivated during a period of several days. The bioreactor consists of 2 major parts: the left ventricle (LV) and the afterload consisting of a compliance, representing the elastic function of the large arteries, and in series a resistance, mimicking the arterioles and capillaries. The TE aortic valve is placed between the LV and the compliance. With controllable resistance, compliance, stroke volume and frequency, and hydrodynamic conditions can be changed over a wide physiological range. This study resulted in a prototype of a compact pulsatile flow system for the creation of TE aortic valves. In addition a biocompatibility study of the used materials is performed.
Abstract: A new mock circulatory system (MCS) was designed to evaluate and characterise the hydraulic performance of ventricular assist devices (VADs). The MCS consists of a preload section and a multipurpose afterload section, with an adjustable compliance chamber (C) and peripheral resistor (Rp) as principal components. The MCS was connected to a pulse duplicator system for validation, simulating a wide range of afterload conditions. Both pressure and flow were measured, and the values of the different components calculated. The data perfectly fits a 4-element electrical analogon (EA). The MCS was further used to assess the hydrodynamic characteristics of the Medos VAD as an example of a displacement pump. Data was measured for various MCS settings and at different pump rates, yielding device specific pump function graphs for water and pig blood. Our data demonstrate (i) flow sensitivity to preload and afterload and (ii) the effect of test fluid on hemodynamic performance.
