Abstract: Breath-hold diving (BHD) is both a recreational activity, performed by thousands of enthusiasts in Europe, and a high-performance competitive sport. Several "disciplines" exist, of which the "no-limits" category is the most spectacular: using a specially designed heavy "sled", divers descend to extreme depths on a cable, and then re-ascend using an inflatable balloon, on a single breath. The current world record for un-assisted descent stands at more than 200 meters of depth. Equalising air pressure in the paranasal sinuses and middle ear cavities is a necessity during descent to avoid barotraumas. However, this requires active insufflations of precious air, which is thus unavailable in the pulmonary system. We describe a diver who, by training, is capable of allowing passive flooding of the sinuses and middle ear with (sea) water during descent, by suppressing protective (parasympathetic) reflexes during this process. Using this technique, he performed a series of extreme depth breath-hold dives in June 2005, descending to 209 meters of sea water on one breath of air.
Abstract: OBJECTIVE: To investigate whether prehydration 90 min prior to a dive could decrease bubble formation, and to evaluate the consequent adjustments in plasma volume (PV), water balance and plasma surface tension (ST). METHODS: Eight military divers participated in a crossover trial of pre-dive hydration using saline-glucose beverage (protocol 1) and a control dive with no prehydration (protocol 2). Drink volume was 1300 ml (Osmolality = 324 mOsml-1) and drinking time was 50-60 min. The diving protocol consisted of an open-sea field air dive at 30 msw depth for 30 min followed by a 9 min stop at 3 msw. Haemodynamic parameters, body weight measurements, urine volume and blood samples were taken before/after fluid intake and after the dive. Decompression bubbles were examined by a precordial pulsed Doppler. RESULTS: Bubble activity was significantly lower for protocol 1 than for protocol 2. PV increased after fluid ingestion by 3,5 % and returned toward baseline after diving for protocol 1, whereas it decreased by 2,2 % after diving for protocol 2. Differences in post-dive PV between the 2 conditions were highly significant. Body weight loss before/after diving and post-dive urine volume after diving were significant in both protocols but the relative decline in weight remained lower for protocol 1 than for protocol 2, with reduction of negative water balance due to higher fluid retention. There were no differences in ST after fluid intake and after diving for the 2 protocols. CONCLUSION: Pre-dive oral hydration decreases circulatory bubbles, thus offering a relatively easy means of reducing DCS risk. The prehydration condition allowed to attenuate dehydration and prevent hypovolemia induced by the diving session. Hydration and diving did not change plasma surface tension in this study.
Abstract: In our previous research, a deep 5-min stop at 15 msw (50 fsw), in addition to the typical 3-5 min shallow stop, significantly reduced precordial Doppler detectable bubbles (PDDB) and "fast" tissue compartment gas tensions during decompression from a 25 msw (82 fsw) dive; the optimal ascent rate was 10 msw (30 fsw/min). Since publication of these results, several recreational diving agencies have recommended empirical stop times shorter than the 5 min stops that we used, stops of as little as 1 min (deep) and 2 min (shallow). In our present study, we clarified the optimal time for stops by measuring PDDB with several combinations of deep and shallow stop times following single and repetitive open-water dives to 25 msw (82 fsw) for 25 mins and 20 minutes respectively; ascent rate was 10 msw/min (33 fsw). Among 15 profiles, stop time ranged from 1 to 10 min for both the deep stops (15 msw/50 fsw) and the shallow stops (6 msw/20 fsw). Dives with 2 1/2 min deep stops yielded the lowest PDDB scores--shorter or longer deep stops were less effective in reducing PDDB. The results confirm that a deep stop of 1 min is too short--it produced the highest PDDB scores of all the dives. We also evaluated shallow stop times of 5, 4, 3, 2 and 1 min while keeping a fixed time of 2.5 min for the deep stop; increased times up to 10 min at the shallow stop did not further reduce PDDB. While our findings cannot be extrapolated beyond these dive profiles without further study, we recommend a deep stop of at least 2 1/2 mins at 15 msw (50 fsw) in addition to the customary 6 msw (20 fsw) for 3-5 mins for 25 meter dives of 20 to 25 minutes to reduce PDDB.
Abstract: Renal (peritubular) tissue hypoxia is a well-known physiological trigger for erythropoietin (EPO) production. We investigated the effect of rebound relative hypoxia after hyperoxia obtained under normo- and hyperbaric oxygen breathing conditions. A group of 16 healthy volunteers were investigated before and after a period of breathing 100% normobaric oxygen for 2 h and a period of breathing 100% oxygen at 2.5 ATA for 90 min (hyperbaric oxygen). Serum EPO concentration was measured using a radioimmunoassay at various time points during 24-36 h. A 60% increase (P < 0.001) in serum EPO was observed 36 h after normobaric oxygen. In contrast, a 53% decrease in serum EPO was observed at 24 h after hyperbaric oxygen. Those changes were not related to the circadian rhythm of serum EPO of the subjects. These results indicate that a sudden and sustained decrease in tissue oxygen tension, even above hypoxia thresholds (e.g., after a period of normobaric oxygen breathing), may act as a trigger for EPO serum level. This EPO trigger, the "normobaric oxygen paradox," does not appear to be present after hyperbaric oxygen breathing.
Abstract: Using a standardized contrast-enhanced transesophageal echocardiographic technique, a group of divers was reexamined for the presence and size of patent foramen ovale (PFO) 7 years after their initial examinations. Unexpected but significant increases in the prevalence and size of PFO were found, suggesting a possible increasing risk for decompression sickness in these divers over time.
Abstract: Objective: The purpose of this study was to define the optimal irradiation conditions of a KTP laser during root planing treatment. Methods: The surfaces of 60 single-root human teeth were scaled with conventional instruments before lasing. The pulpal temperature increase was measured by means of one thermocouple placed in the pulp chamber and a second one placed on the root surface at 1 mm from the irradiation site. The influence of variables of coloration by Acid Red 52 (photosensitizer), scanning speed, dentin thickness, and probe position was analyzed for a constant exposure time of 15 sec and 500 mw (spot size diameter, 0.5 mm). The pulpal temperature was below 3 degrees C for the adjustments. Results: The irradiation on one point of root surface had the following results: The application of photosensitizer on the root surface before lasing produced a 50% higher temperature rise within the pulp than in the case without the application of the photosensitizer. The temperature rise in the pulp chamber was below 3 degrees C with the following settings of 500 mw: PW = 10 msec and PRR < 35; or PW= 20 msec and PRR < 20 Hz. On the other hand, for the same irradiation conditions, the temperature rise on the surface of the root was always below 7 degrees C. However, the temperature increase became higher than 7 degrees C (on the surface of the root) in the case of P > 500 mw, PW > 50 msec and PRR > 10 Hz of root surface or a scanning speed of irradiation of 1 mm/sec for a linear irradiation of 4 mm. Conclusion: The KTP laser may be used safely without thermal damage to pulp and periodontal tissue with respect to the biologically acceptable previously described parameters.
Abstract: The prevalence of a Patent Foramen Ovale is described in merely 30% of the asymptomatic population. This patency has been shown to be an increasing risk factor for paradoxical cerebral embolization. Some desaturation or decompression situations in human activities such as scuba diving or altitude flight are prone to provoke embolisations. The association with the presence of a patent Foramen Ovale and the onset of cerebral decompression sickness seems to be presenting an odds ratio value of about 5.1.1 The presence of asymptomatic brain lesion-like "spots" has been investigated in a randomized population of diving individuals (n=42 randomized out of 200). The inclusion criteria were drastic and included: age (less than 41 years of age); diving experience (more than 200 logged dives); no decompression sickness episodes; no contraindications for the MRI examination; and no known central nervous system conditions. Data of the magnetic resonance investigation of the brain has been performed in 42 (diving) volunteers fully informed on the experimental procedures. The statistical comparison (Anova test after Kolmogorov-Smirnov compatibility testing and Neuman–Keuls discriminant post-test) of the fractal dimension obtained by means of the box counting method with the slope analysis (Harfa fractal analysis program). The comparison was performed with known pathological images such as multiple sclerosis (a pathology not emerging from vascular problems), ischemic thrombotic lesions (vascular problem), diver's asymptomatic brain spots, and the arteriography of the internal carotid in non-pathological humans (clearly vascular). The statistical difference (p<0.001) between the vascular related images, as well as the absence of statistical difference (p>0.05) with the non-vascular spots images advocates with a non-vascular origin of the diver's asymptomatic spots and thus the link between the patency of the cardiac Foramen Ovale and the brain "spots" seems not to be as clear as it was believed
Abstract: In spite of many modifications to decompression algorithms, the incidence of decompression sickness (DCS) in scuba divers has changed very little. The success of stage, compared to linear ascents, is well described yet theoretical changes in decompression ratios have diminished the importance of fast tissue gas tensions as critical for bubble generation. The most serious signs and symptoms of DCS involve the spinal cord, with a tissue half time of only 12.5 minutes. It is proposed that present decompression schedules do not permit sufficient gas elimination from such fast tissues, resulting in bubble formation. Further, it is hypothesized that introduction of a deep stop will significantly reduce fast tissue bubble formation and neurological DCS risk. A total of 181 dives were made to 82 fsw (25 m) by 22 volunteers. Two dives of 25 min and 20 min were made, with a 3 hr 30 min surface interval and according to 8 different ascent protocols. Ascent rates of 10, 33 or 60 fsw/min (3, 10, 18 m/min) were combined with no stops or a shallow stop at 20 fsw (6 m) or a deep stop at 50 fsw (15 m) and a shallow at 20 fsw (6 m). The highest bubbles scores (8.78/9.97), using the Spencer Scale (SS) and Extended Spencer Scale (ESS) respectively, were with the slowest ascent rate. This also showed the highest 5 min and 10 min tissue loads of 48% and 75%. The lowest bubble scores (1.79/2.50) were with an ascent rate of 33 fsw (10 m/min) and stops for 5 min at 50 fsw (15 m) and 20 fsw (6 m). This also showed the lowest 5 and 10 min tissue loads at 25% and 52% respectively. Thus, introduction of a deep stop significantly reduced Doppler detected bubbles together with tissue gas tensions in the 5 and 10 min tissues, which has implications for reducing the incidence of neurological DCS in divers.
Abstract: To investigate whether the intensity and duration of a sustained contraction influences reflex regulation, we compared sustained fatiguing contractions at 25 % and 50 % of maximal voluntary contraction (MVC) force in the human abductor pollicis brevis (APB) muscle. Because the activation of motoneurones during fatigue may be reflexively controlled by the metabolic status of the muscle, we also compared reflex activities during sustained and intermittent (6 s contraction, 4 s rest) contractions at 25 % MVC for an identical duration. The short-latency Hoffmann(H) reflex and the long-latency reflex (LLR) were recorded during voluntary contractions, before, during and after the fatigue tests, with each response normalised to the compound muscle action potential (M-wave). The results showed that fatigue during sustained contractions was inversely related to the intensity, and hence the duration, of the effort. The MVC force and associated surface electromyogram (EMG) declined by 26.2 % and 35.2 %, respectively, after the sustained contraction at 50 % MVC, and by 34.2 % and 44.2 % after the sustained contraction at 25 % MVC. Although the average EMG increased progressively with time during the two sustained fatiguing contractions, the amplitudes of the H and LLR reflexes decreased significantly. Combined with previous data (Duchateau & Hainaut, 1993), the results show that the effect on the H reflex is independent of the intensity of the sustained contraction, whereas the decline in the LLR is closely related to the duration of the contraction. Because there were no changes in the intermittent test at 25 % MVC, the results indicate that the net excitatory spinal and supraspinal reflex-mediated input to the motoneurone pool is reduced. This decline in excitation to the motoneurones, however, can be temporarily compensated by an enhancement of the central drive.
Abstract: Scuba divers with patent foramen ovale (PFO) may be at risk for paradoxical nitrogen gas emboli when performing maneuvers that cause a rebound blood loading to the right atrium. We measured the rise and fall in intrathoracic pressure (ITP) during various maneuvers in 15 divers. The tests were standard isometric exercises (control), forceful coughing, knee bend (with and without respiration blocked), and Valsalva maneuver (maximal, gradually increased to reach control ITP, and as performed by divers to equalize middle ear pressure). All the maneuvers, as well as the downward slope of ITP at the release phase, were related to the control value. ITP levels were significantly higher than the standard isometric effort during a breath-hold knee bend (172%, P < 0.001), cough (133%, P < 0.05), and maximal Valsalva (136%, P < 0.05) whereas "usual" Valsalva maneuvers produced ITPs significantly lower than the standard (28%, P < 0.001). The downward slope of the pressure release curve was not significantly different among the different maneuvers (P < 0.1447). We conclude that maneuvers other than the usual divers' Valsalva are more likely to cause post-release central blood shift, both by the levels of ITP reached and by the time during which these ITPs are sustained. Divers (especially with PFO) should be advised to refrain from strenuous leg, arm, or abdominal exercise after decompression dives.
Abstract: Patency of the foramen ovale (PFO) may be a cause of unexplained decompression sickness (DCS) in sports divers. To assess the relationship between PFO and DCS, a case-control study was undertaken in a population of Belgian sports divers. Thirty-seven divers who suffered from neurological DCS were compared with matched control divers who never had DCS. All divers were investigated with transesophageal contrast echocardiography for the presence of PFO. PFO size was semiquantified on the basis of the amount of contrast passage. Divers with DCS with lesions localized in the high cervical spinal cord, cerebellum, inner ear organs, or cerebrum had a significantly higher prevalence of PFO than divers with DCS localizations in the lower spinal cord. For unexplained DCS (DCS without commission of any diving procedural errors), this difference was significant for large PFOs only. We conclude that PFO plays a significant role in the occurrence of unexplained cerebral DCS, but not of spinal DCS. We further stress the importance of standardization and semiquantification of future PFO studies that use transesophageal contrast echocardiography.
Abstract: The effects of fatigue on the electromyographic (EMG) reflex activities were compared during sustained voluntary contractions and contractions evoked by electrical stimulation (30 Hz) in the human first dorsal interosseus (FDI). Short latency (SL), medium latency (ML) and long latency (LL) reflex responses to a ramp-and-hold stretch of the muscle were recorded and analysed in 27 healthy subjects of both sexes. The amplitude of the reflex components was normalized as function of the amplitude of the surface action potential (SAP) recorded in response to the supramaximal stimulation of the motor nerve. The results indicate that for a similar reduction of force, SL and ML are significantly reduced after fatigue induced by voluntary contractions but they are not when the fatigue test is performed by electrical stimulation at the motor point. In voluntary fatigue experiments, the LL component showed no significant decrease below control values, but an enhancement was observed during electrically evoked contraction. This enhancement remained above control values for at least 15 min during the recovery period, whereas SL and ML decreases returned to control within 5 min after the fatigue tests. The electrical stimulation applied to the skin overlying the FDI at an intensity lower than the motor threshold did not affect SL and ML, but enhanced LL for about 15 min. On the contrary, the anaesthesia of the skin overlying the FDI induced a decrease in LL without significant change of SL and ML. It is concluded that muscle reflex fatigue is present during sustained voluntary contractions and decreases SL and ML responses to quick stretches.(ABSTRACT TRUNCATED AT 250 WORDS)
