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This presentation focuses on the effects of static lung loading (SLL) on diver performance. It is noted that SLL may arise from depth differences between the diver's chest and his breathing gear. Studies are reviewed in which subjects undergoing wet, simulated dives in a pressure chamber were exposed to SLL ranging from 14.7 to -14.7 mmHg (+20 to -20 cmH2O) while breathing air at depths down to 58 m (190 ft). The subjects, assuming a prone or an upright position, performed leg exercise on an underwater bicycle ergometer. Various measurements of respiratory function were made. By applying a scoring scale for dyspnea it was found that in addition to being more pronounced as exercise and depth (gas density) increased, the dyspnea was most pronounced with negative SLL. Positive SLL alleviated the dyspnea. The dyspnea also tended to be more pronounced in the prone than in the upright posture. It was speculated that this may have been partly due to more of a compression effect on the extra thoracic airways by water pressure in the former than in the latter posture. There were no marked differences in gas exchange and end-tidal gas concentrations with different static lung loads, and it was hypothesized that differences in respiratory muscular strain may have accounted for the differences in dyspnea with different SLLs. That the dyspnea was inspiratory in nature would agree with the observation that positive SLL aiding inspiration would be perceived as beneficial. A breathing apparatus design that counteracts undesirable SLL is reviewed.
Thirteen healthy males were repeatedly studied during the exposure to a moderate hyperbaric environment of 4--6, 7 and 9 ATA, in a hyperbaric chamber and partly during immersion in sea water (3.5--4 ATA). The maximal duration of the exposure was 35 min and that of decompression 90 min. As compared to the dynamics of the change found in controls, under hyperbaric conditions a significant prolongation of the visual reaction time (especially during sea dives), and an impairment of the mental performance in an arithemetical calculation test were found. There occurs an increase of the excretion in urine of cortisol, epinephrine and vanillylmandelic acid, especially after immersion in sea.
INTRODUCTION: Diving mammals can cope with oxidants which are produced in excess during the reoxygenation of hypoxic tissues. This study addresses the question of whether antioxidants can adapt and whether it allows humans to tolerate the hypoxic stress induced by a single breath-holding in the course of a dynamic diving exercise and protect them from oxidative insult. METHODS: There were 20 male subjects who performed submaximal apnea dynamic diving (ADD). Nine control subjects stayed out of the water and breathed normally. Venous blood samples were collected 1 h before and immediatly after ADD. RESULTS: ADD induced a significant increase in plasma glutathione peroxidase (GPx-3) activity (from 397.5 +/- 44.4 to 410 +/- 43 U x L(-1)), blood reduced glutathione (GSH) (from 1060 +/- 302 to 1292 +/- 213 micromol x L(-1)), and in plasma creatine kinase activity (from 215 +/- 137 to 235 +/- 152 U x L(-1)). The activity of the erythrocyte superoxide dismutase and glutathione peroxidase, as well as the blood oxidized glutathione and the plasma thiobarbituric acid reactive substances concentrations, were maintained at their basal level. The level of training, characterized by the duration and distance of the dive, had no effect on the markers used. CONCLUSION: GPx-3 and GSH could constitute the most readily mobilizable antioxidants that would then contribute to the buffering against a sudden increase in the generation of radical oxygen species. These biomarkers could be used as tools for establishing oxidative stress during hypoxia. The response of GPx-3 to hypoxia could be of physiological relevance.
The effect of repeated exposure to ambient pressures of 5 bar (500 kPa), in atmospheres comprising normal partial pressures of oxygen [0.2 bar (20 kPa)] and nitrogen [0.8 bar (80 kPa)] and 4 bar (400 kPa) helium, on cardiac function and morphology was assessed in conscious rats. Ten test rats underwent chamber dives daily for 40 consecutive days, and ten control rats were exposed in the same chamber for an equal period of time, but in air at 1 bar (100 kPa). Cardiac output (Qc) and myocardial blood flow (Qmyocardial) were determined by the microsphere method. After 40 days, the body mass was 7% greater in the control than in the test rats (P < 0.05), although they were given exactly the same amount of standard food. The test rats had a significantly higher (7% absolute, 12% ventricular mass to body mass, P < 0.05) heart mass (left ventricular myocardium, including the ventricular septum) than the control rats. The percentage tissue dry mass of the right and left ventricles was equal in the two groups. Microscopic examination revealed a number of small focal necroses in the left ventricle of the test rats but none in the control rats. The left ventricular pressure (LVP) and the maximum velocity of LVP increase (contractility) and decrease were significantly increased (25%-96%, P < 0.001) in the pre-exposed compared to the control rats at 1 bar (100 kPa). The systolic arterial pressure, heart rate and respiratory frequency were similar in the two groups at 1 bar (100 kPa).(ABSTRACT TRUNCATED AT 250 WORDS)
Decompression sickness (DCS) is a potentially crippling disease caused by intracorporeal bubble formation during or after decompression from a compressed gas underwater dive. Bubbles most commonly evolve from dissolved inert gas accumulated during the exposure to increased ambient pressure. Most diving is performed breathing air, and the inert gas of interest is nitrogen. Divers use algorithms based on nitrogen kinetic models to plan the duration and degree of exposure to increased ambient pressure and to control their ascent rate. However, even correct execution of dives planned using such algorithms often results in bubble formation and may result in DCS. This reflects the importance of idiosyncratic host factors that are difficult to model, and deficiencies in current nitrogen kinetic models. Models describing the exchange of nitrogen between tissues and blood may be based on distributed capillary units or lumped compartments, either of which may be perfusion- or diffusion-limited. However, such simplistic models are usually poor predictors of experimental nitrogen kinetics at the organ or tissue level, probably because they fail to account for factors such as heterogeneity in both tissue composition and blood perfusion and non-capillary exchange mechanisms. The modelling of safe decompression procedures is further complicated by incomplete understanding of the processes that determine bubble formation. Moreover, any formation of bubbles during decompression alters subsequent nitrogen kinetics. Although these factors mandate complex resolutions to account for the interaction between dissolved nitrogen kinetics and bubble formation and growth, most decompression schedules are based on relatively simple perfusion-limited lumped compartment models of blood: tissue nitrogen exchange. Not surprisingly, all models inevitably require empirical adjustment based on outcomes in the field. Improvements in the predictive power of decompression calculations are being achieved using probabilistic bubble models, but divers will always be subject to the possibility of developing DCS despite adherence to prescribed limits.
In Amazon River dolphins, bottle-nosed dolphins and white whales, comparative studies have been made on cardiac electrical activity using electrocardiographic and telemetric techniques. In all the species investigated, certain dependence of cardiac cycle duration on the phase of respiratory pause was observed. A pronounced bradycardia was noted in diving animals which reflects the level of their adaptation to hypoxia and hypoxemia. Autocorrelation functions of the dynamic sequences of cardiac intervals were calculated. The presence of "slow" waves in cardiac cycle was shown which were considerably increased during diving.
Compressed air, and more recently hyperbaric oxygen, have been used and misused in medical treatment for more than 300 years. Advances in physiology have led to rational protocols for hyperbaric oxygen use. Hyperbaric oxygen will enhance wound healing by fibroblast and capillary proliferation, suppress infection, reduce edema, reverse CNS damage from carbon monoxide and cyanide poisoning, and reduce clostridial alpha toxins. Monoplace and multiplace chambers are used for treatment during which EKG and oxygen tissue monitoring, as well as hemodynamic and respiratory support, can be continued, iatrogenic air embolism and diving decompression sickness demand immediate treatment. Investigative uses of adjunct therapy for several other clinical problems include treatment of MS, acute spinal cord injuries, and acute MI. Specific indications agreed on by the Undersea and Hyperbaric Medicine Society are recognized by most third-party payers including Medicare, Champus, and HMSA. Hyperbaric medicine remains a fertile area for basic physiologic investigation and outcomes research.
Physico-chemical principles set constraints on the response of biological systems to high-pressure gases and to pressure per se. They also indicate the mechanisms that may be involved. Classical thermodynamics, intermolecular forces and the theory of solutions and many other areas of physical chemistry have contributed to our understanding of the problems faced by divers breathing gases at high pressure, in particular the high pressure neurological syndrome, inert gas narcosis and decompression sickness. The value and the limitations of physico-chemical arguments when applied to the problems of underwater physiology are analysed.
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BACKGROUND: Water evaporation diminishes in high pressure environment, however it is unknown whether insensible water dissipation from the human skin falls as a function of the increased environmental pressure. We designed the present study to measure cutaneous insensible water loss at various pressures during exposure to a simulated saturation dive. METHODS: Four healthy male volunteers were exposed to eight different pressures between 1 and 18.4 atmospheres absolute (atm abs). Resting insensible water loss from the skin was measured as change in the body weight and corrected for the weight of the respiratory CO2 - O2 gas exchange and the respiratory water dissipation. RESULTS: We made an equation for the relationship between cutaneous insensible water loss and environmental pressure as: w = 14.5 X p(-0.48), where, w is cutaneous insensible water loss in g x m(-2) x h(-1), and P is the environmental pressure in atm abs. The average cutaneous insensible water loss (15.3 g x m(-2) x h(-1)) at normal atmosphere decreased (p < 0.01) to 4.2 g x m(-2) x h(-1) (reduced by 73%) during a saturation dive to 18.4 atm abs. CONCLUSION: The amount of insensible water loss estimated from the equation was comparable to that of reported observations.
During the EXEMSI experiment, an international crew of 4 subjects (1 woman and 3 men) was confined for 60 days in a normobaric diving chamber (with 1060 mbar atmospheric pressure) to simulate life in a space station and to assess the effects of confinement on psychological and physiological factors. Blood pressure and blood volume regulating hormones (atrial natriuretic peptide, renin, aldosterone) and urine data (24-h urine outputs, ionogram) were measured before (BDC: baseline data collection), during (D: day) and after (R: recovery) confinement. We also measured energy expenditure and total body water, 14 days before, and after 27 days of confinement, by the double-labeled water method. We found a marked increase in 24-h urine output during most of the confinement in the men and the woman. Body weight (-1.8 +/- 0.9 kg) and energy expenditure (-1064 +/- 143 kcal/d, p<0.01) decreased in the 3 men. The total body water (TBW) decreased by 1.5 +/- 1.2 l in the men. Stress was not indicated by plasma and urine catecholamines but plasma growth hormone was elevated on D2 (p<0.01 vs. BDC) in the men. This study shows that confinement conditions can modify body fluid (increases in 24-h urine outputs and TBW changes) and energetic metabolisms.
From 1989-91, the Divers Alert Network monitored recreational divers for Doppler-detected venous gas emboli (VGE) and depth-time profiles following multi-day, repetitive, multi-level exposures. A Spencer score >0 occurred in 61 of 67 subjects (91%) and 205 of 281 dives (73%). No subject developed decompression sickness (DCS) on monitored days although 102 dives (36.3%) scored at Spencer Grades 2 or 3 (High Bubble Grade, HBG). We recorded the depth-time profiles with Suunto dive computers and estimated exposure severity with a probabilistic decompression algorithm. The HBG incidence increased 53% over the range of exposure severity (p < 0.001) in the divers, was approximately 20% higher for repetitive dives than for first dives, and decreased approximately 25% over the 6-8 days of multi-day diving (p < 0.001) suggesting a phenomenon similar to DCS adaptation. The observed HBG incidence was approximately 20% higher for males than females. Older male divers had a 25% increase in observed incidence of HBG while older female divers showed a 55% increase when compared to their younger counterparts.
The purpose of this study was to compare age-specific hospitalization, disability, and mortality rates for diving-related and stress-induced disorders between U.S. Navy enlisted divers (n = 11,584) and a matched sample of nondiver enlistees (n = 11,517). Divers had significantly higher hospitalization rates than controls for the category of environmentally induced disorders and deflected nasal septum as well as for joint disorders at ages 23-28. Controls had significantly higher hospitalization rates for stress-related disorders (e.g., alcohol and drug abuse and transient situational disturbances) and circulatory diseases (e.g., cardiovascular disease). Higher rates of medical and physical evaluation board actions for stress-related disorders were observed among controls than among divers. For both groups, medical board, physical evaluation board, and mortality rates increased with age as did hospitalizations for musculoskeletal diseases, stress-related disorders, and circulatory diseases. Subsequent research will examine the long-term health effects associated with divers job-related accidents as well as hospitalizations for environmentally induced disorders and musculoskeletal conditions.
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For the operation of manned spacecraft, the removal of CO2 from the cabin atmosphere, produced by its inhabitants, is essential. This is accomplished by chemical absorption in a gas processing unit, a process which requires energy and consumables. Therefore, in terms of resource management, the CO2-level should be kept as high as possible. Otherwise, considering crew health and performance and also the interference with life science experiments, the CO2 load should be as on Earth, close to zero. In order to obtain more information about the permissible CO2 level for future space missions and also to clarify Space Station design criteria, NASA-ESA-DARA have initiated a ground-based simulation study with two different CO2 levels: 0.7% (first campaign) and 1.2% CO2 (second campaign). For this study the deep diving facility of DLR was used to provide atmospheric control and long-term habitation for the test subjects in studying the effect of increased CO2 on physiological and psychological functions. A number of experiments were implemented, which tested selected effects of raised CO2 on humans. Four male subjects stayed in the chamber for 26 d in each campaign, in order to perform the different tests in repeated trials, with the aim of evaluating possible long-term effects. CO2 was controlled by absorption with soda lime, flushing with fresh air and the addition of CO2, if necessary. Essentially, the CO2 produced by the subjects was used to maintain the level at 0.7 and 1.2%, respectively. Basic control of CO2 was carried out in the soda lime container of the Life Support System. In order to maintain the required level, the amount of gas flowing through the soda lime could be adjusted by a remote controlled bypass. With this set-up it was possible to keep CO2 at an average level between 0.67 and 0.73% in the first campaign and between 1.17 and 1.23% in the second campaign. The results of the experiments support the current CO2 limits for space operations, insofar as values around 1% do not impose any severe restrictions to human habitation for at least several weeks, whereas life sciences experiments especially sensitive to CO2 influences have to be carefully evaluated for possible interferences.
The immune system of astronauts is disturbed during and after spaceflight. This situation may result from stressors encountered during the flight (microgravity, radiation, psychological stress, or confinement) or from physiological changes (demineralization or fluid shift). Therefore, ground-based investigations should be designed to determine the effects of these factors on the immune system. Very little is known about the influence of confinement or isolation on immune reactions. However, interesting data exist from experiments with animals and humans under different conditions (submarines, antarctic expeditions, single-person cave isolation, and underwater diving). The question remains as to whether these results can be extrapolated to spaceflight. Therefore, investigations of humans under isolation conditions analogous to space missions have been performed by Russian and, more recently, European investigators. Such investigations are important for understanding the physiological and psychological disturbances that occur during long periods of confinement, especially when future lunar and martian missions are considered.