Scientific shallow saturation dive expedition using diving rebreathers and a specific dry habitat: medical management of the "Capsule" programme.

BACKGROUND: Scientific underwater exploration could benefit from professional diving facilities. This could allow marine research for durations far exceeding anything currently possible. The closed-circuit rebreather expansion provides new perspectives by unleashing divers and their diving bell. "Under the Pole Expeditions" developed an innovative compact underwater habitat for this purpose. MATERIALS AND METHODS: The habitat's depth was fixed at 20 m. Saturation lasted 3 days and was followed by a 245 min long decompression procedure with mandatory in-water phase. Isolation and environmental constraints will require specific medical and safety procedures. "In situ" medical concerns were considered, and a specific evacuation plan was established. This report describes the medical management of this atypical project and the systematic clinical follow-up mostly targeted on the cardiovascular system, fatigue and psychological tolerance. RESULTS: Seventeen individual saturation exposures were performed. All selected divers were professional. Neither severe illness nor decompression sickness was observed. These short-term saturation exposures appeared to be well tolerated. There was a relatively low bubble grade after decompression. Psychological tolerance appeared good. However, a transient moderate orthostatic hypotension suggested cardiovascular deconditioning after dive. CONCLUSIONS: This first experiment demonstrates the interest and feasibility of a shallow revisited saturation dive with rebreather use. This isolation requires medical accompaniment and rigorous preparation. Medical and physiological risks assessment is essential in this context and must be consolidated by new experiences.

A new form of admissible pressure for Haldanian decompression models.

In this article, we propose and study a new form of admissible pressure in the Haldanian framework. We then use it to study the surjectivity of the Gradient Factors on the space of the reachable decompression profiles, and investigate a particular case. This case leads to the proposition of a decompression strategy, whose crucial parameter is the ascent rate. An appropriate ascent rate is suggested as recommended by COMEX, through a physiologically relevantmethod. This new strategy enables the unification of the COMEX approach (not based on a tissuesaturation theory), with the Haldanian method.

Molecular hydrogen attenuates radiation-induced nucleobase damage to DNA in aerated aqueous solutions.

PURPOSE: The main aim of the present study is to gain mechanistic insights into the modulating effect of molecular hydrogen on the γ-radiation-induced alteration pathways of DNA nucleobases. MATERIALS AND METHODS: Aerated aqueous solutions of calf thymus DNA were exposed to a (60)Co source at doses ranging from 0 to 55 Gy under normoxic conditions, in the presence or not of 0.7 MPa hydrogen or helium. The measurement of several modified bases was performed using HPLC associated with electrospray ionization tandem pass spectrometry (HPLC-ESI-MS/MS). Bleaching of aqueous solutions of p-nitrosodimethylaniline (p-NDA) solutions was also used to allow the quantification of hydroxyl radical (•OH) formation. RESULTS: pNDA bleaching was significantly reduced in the presence of hyperbaric hydrogen. This is undoubtedly due to (•)OH scavenging by H2 since, under the same conditions, He had no effect. Similarly, base alterations were significantly reduced in the presence of hydrogen, as compared to controls under normal atmosphere or in the presence of helium. The relative proportions of modified nucleobases were not changed, showing that the only effect of H2 is to scavenge (•)OH without exhibiting reducing properties. CONCLUSIONS: Our findings demonstrate that H2 exerts a significant protection against radiation-induced DNA base damage in aqueous solutions, (•)OH scavenging being the only mechanism involved.

Doppler detection in Ama divers of Japan.

OBJECTIVE: Symptoms consistent with neurological decompression sickness (DCS) in commercial breath-hold (Ama) divers has been reported from a few districts of Japan. The aim of this study was to detect circulating intravascular bubbles after repetitive breath-hold diving in a local area where DCS has been reported in Ama divers. METHODS: The participants were 12 partially assisted (descent using weights) male Ama divers. The equipment (AQUALAB system) consisted of continuous-wave Doppler with a 5-MHz frequency, and the Doppler probe was placed in the precordial site with the ultrasonic wave directed into the pulmonary infundibulum. We carried out continuous monitoring for 10 minutes at the end of the series of repetitive dives, and the recordings were made on numerical tracks and graded in a blind manner by 2 experienced investigators, according to the Spencer Doppler code. RESULTS: Depths and number of dives were 8 to 20 m and 75 to 131 times. Mean diving duration and surface interval were 64 ± 12 seconds and 48 ± 8 seconds, respectively (mean ± SD). We detected the lowest grade of intravascular bubbles (Spencer's grade I) in an Ama diver whose mean surface interval was only 35.2 ± 6.2 seconds. His mean descending, bottom, and ascending times were 10.4 ± 1.6 seconds, 39.2 ± 8 seconds, and 18.2 ± 3.0 seconds, respectively, over the course of 99 dives. CONCLUSIONS: Intravascular bubbles may be formed after repetitive breath-hold dives with short surface intervals or after a long breath-holding session in Ama divers. Symptoms consistent with neurological accidents in repetitive breath-hold diving may be caused in part by the intravascular presence of bubbles, indicating the need for safety procedures.

A closed-circuit rebreather for the characterization of denitrogenation.

BACKGROUND: The denitrogenation methods currently used to characterize the washout kinetics of body nitrogen require costly devices that are not easily transportable for measurements in real conditions. An original and simple system to measure the denitrogenation kinetics of the human body at rest and at ambient pressure is presented here. METHODS: The nitrogen content accumulated in the loop of a closed-circuit rebreather supplied by pure oxygen was determined using galvanic oxygen sensors and a small size data logger for pressure, temperature, and relative humidity measurements. The method was applied to three subjects through a preliminary validation phase. The collected data, after processing, were compared: 1) to the results found in previous papers for similar experiments using other methods; and 2) to the results of a physiological gas exchanges model. RESULTS: Denitrogenation curves for 60-min and 120-min durations were obtained for the three subjects, with an interindividual variability being in agreement with their body fat percentage (560 +/- 140 ml for the subject with less body fat and 880 +/- 70 ml for the subject with more body fat) after 60 min. Both the experimental results found in the literature and the simulation results were compared to the present results. CONCLUSION: From a preliminary analysis, the proposed denitrogenation procedure proved to be adequate compared to other methods. An investigation of the method demonstrated that the system accuracy can be improved. A validation phase using more subjects may support the use of this new technology.

Decompression sickness in breath-hold divers: a review.

Although it has been generally assumed that the risk of decompression sickness is virtually zero during a single breath-hold dive in humans, repeated dives may result in a cumulative increase in the tissue and blood nitrogen tension. Many species of marine mammals perform extensive foraging bouts with deep and long dives interspersed by a short surface interval, and some human divers regularly perform repeated dives to 30-40 m or a single dive to more than 200 m, all of which may result in nitrogen concentrations that elicit symptoms of decompression sickness. Neurological problems have been reported in humans after single or repeated dives and recent necropsy reports in stranded marine mammals were suggestive of decompression sickness-like symptoms. Modelling attempts have suggested that marine mammals may live permanently with elevated nitrogen concentrations and may be at risk when altering their dive behaviour. In humans, non-pathogenic bubbles have been recorded and symptoms of decompression sickness have been reported after repeated dives to modest depths. The mechanisms implicated in these accidents indicate that repeated breath-hold dives with short surface intervals are factors that predispose to decompression sickness. During deep diving, the effect of pulmonary shunts and/or lung collapse may play a major role in reducing the incidence of decompression sickness in humans and marine mammals.

Gender differences in circulating bubble production after SCUBA diving.

OBJECTIVE: Differences in circulating bubble production have been described after exposures in altitude chambers between men and women. The present study was designed to examine gender differences in circulating bubble production after a dive. METHODS: Fifty-two men and 52 women performed the same dive profile (25 min to 35 m). Circulating bubbles were detected by continuous wave Doppler. Tests were conducted at sea in a boat, at 10-min intervals for 1 h after surfacing. Signals were graded according to the Spencer scale. The categorical data were then converted to a single number reflecting total bubble activity using the KISS index. RESULTS: Considering each measurement period, bubble grade was higher in men than women 30, 40 and 50 min postdive. On the contrary, bubble grade was comparable between men and women 10, 20 and 60 min after the dive. KISS index was significantly higher in men than women (6.77 [0.65-32.3] versus 0.91 [0-22.9], P<0.02). KISS index was significantly correlated with age, weight and body fat mass in the whole population and in the men and women separately. Postmenopausal women had a higher KISS index (42 [15-47]) when compared with premenopausal women and men older than 50 years. No difference in bubble production was found according to the use of oral contraceptive pills or the phase of the menstrual cycle. CONCLUSION: Overall, we observed fewer circulating bubbles in women than in men after an open sea SCUBA dive. This difference disappeared in the postmenopausal women.

Circulating venous bubbles in children after diving.

Doppler ultrasonic detection of circulating venous bubbles after a scuba dive is a useful index of decompression safety in adults, since a relationship between bubbles and the risk of decompression sickness has been documented. No study, however, has investigated circulating venous bubbles in young recreational divers after their usual dives. The aim of this study was to determine whether these bubbles would be detected in children who performed a single dive without any modification in their diving habits. Ten young recreational divers (13.1 +/- 2.3 years) performed their usual air dive. They were Doppler-monitored 20 min before the dive (12 +/- 3 m for 26 +/- 7 min) and for 60 min after surfacing, at 20-min intervals. No circulating venous bubbles were detected after the children surfaced. The results showed that during a usual shallow diving session, venous bubbles were not detected in children.

Activity-based rate-adaptive pacemakers under hyperbaric conditions.

OBJECTIVES: The aim of this study was to test a variety of currently available activity-based rate-adaptive pacemakers under hyperbaric conditions. BACKGROUND: Sports divers with pacemakers can dive under certain circumstances. The rate response of activity-sensing pacing under hyperbaric conditions has rarely been evaluated. MATERIALS AND METHODS: We manufactured a miniaturized hyperbaric chamber. A pacemaker inside was kept close to the corresponding telemetry wand placed on top of the chamber. An inflation device for coronary balloon angioplasty was used to create hydraulic pressure. Group I pacemakers were exposed to a 30 msw/98 fsw/4 ATA and after a 1-month waiting period to 60 msw/197 fsw-depth/7 ATA. Group II was exposed to only one dive to 60 msw. The electrogram and event marker telemetry were used to monitor the pacing stimuli and measurements were made for case distortion. RESULTS: The baseline pacing rate did not change in 27 tests. Return to baseline was shown during 18 tests after transient sensor-driven rate. There was a sensor rate response to manual brief shaking during and following testing. A case distortion was shown in 15 of 29 tests at 60 m. CONCLUSIONS: Modern accelerometers showed no sensitivity to pressure on the pacemaker can at 30 msw/98 fsw and 60 msw/197 fsw but in some devices responded to pressure changes. There was no pacing dysfunction or suppression of the sensor response despite the high incidence of case distortion at 60 msw/197 fsw. As a general rule, diving should not be allowed at depths greater than 20 msw/65 fsw.

Bubble incidence after staged decompression from 50 or 60 msw: effect of adding deep stops.

OBJECTIVES: The French Navy uses the Marine Nationale 90 (MN90) decompression tables for air dives as deep as 60 msw. The resulting incidence of decompression sickness (DCS) for deep dives (45-60 msw) is one case per 3000 dives. METHODS: Three protocols with experimental ascent profiles (EAPs) were tested in the wet compartment of a hyperbaric chamber. For each protocol, eight subjects dove to 50 or 60 msw and ascended according to the standard MN90 table or an EAP. Precordial bubbles were monitored with Doppler sensors at 30-min intervals after surfacing. Protocol I went to 60 msw and used deep stops beginning at 27 msw. Protocol II was a repetitive dive to 50 msw with a 3-h surface interval; the EAP made the first deep stop at 18 msw. Protocol III again went to 60 msw, but the EAP used a single, shorter deep stop at 25 msw. RESULTS: For Protocol I, all divers developed bubbles at Spencer grade 2-3 and still had bubbles 120 min after surfacing; there was no statistical difference between bubbling for the MN90 and EAP, but one diver presented a case of DCS after the EAP. For Protocol II, the EAP produced severe bubbling for the eight divers. Those findings led to stopping the EAPs with the longer deep stops used in Protocols I and II. Protocol III again showed no difference between the standard and modified profiles. DISCUSSION: The addition of deep stops requires careful consideration. Two of our EAPs made no difference and one produced increased bubbling.