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At least 793 records · Page 44Linked to original sources
PubMed1979

Adrenal function and the incidence of bends after decompression in mice: effect of adrenalectomy, corticosteroids, decompression intensity, and time of day.

The adrenocortical endocrine subsystem has been demonstrated to enhance mammalian tolerance to harsh environmental conditions, including hypoxia and temperature extremes. In a series of factorial experiments, mice were exposed to one of three elevated hydrostatic pressures for 30 min and then decompressed (0.75 atm/s). It was demonstrated that 1) tolerance to decompression does not differ significantly (P greater than 0.3) in surgically intact, sham adrenalectomized, or in adrenalectomized animals; 2) intraperitoneal administration of pharmacologic doses (0.4, 1.0, and 2.0 mg/mouse) or corticosterone or deoxycorticosterone acetate does not significantly enhance (P greater than 0.1) survivorship when compared to vehicle-injected controls; and 3) the incidence of decompression sickness (DS) does not fluctuate with time of day (P greater than 0.4). In a fourth study, the plasma concentration of corticosterone was quantitated in 1) colony control mice, 2) mice exposed to the 1-ATA chamber environment (chamber control), or 3) mice compressed to 3, 5, 7, 9, or 11 ATA and then decompressed. In general, plasma corticosterone in symptom-free mice was elevated approximately threefold (P less than 0.05) by exposure to the 1-ATA chamber environment and by decompression from 3 to 11 ATA. At 11 ATA, plasma corticosterone levels in decompressed mice exhibiting decompression sickness symptoms were significantly elevated (P less than 0.05) compared to the levels observed in decompressed symptom-free mice. These studies indicate that adrenocortical function does not enhance tolerance to decompression in mice.

Adrenal Cortex Hormones↗
PubMed2003

Evaluation of decompression safety in an occupational diving group using self reported diving exposure and health status.

BACKGROUND: Many occupational diving groups have substantially different diving patterns to those for which decompression schedules are validated. AIMS: To evaluate tuna farm occupational diving practice against existing decompression models and describe a method for collecting and modelling self reported field decompression data. METHODS: Machine readable objective depth/time profiles were obtained from depth/time recorders worn by tuna farm occupational divers. Divers' health status was measured at the end of each working day using a self administered health survey that produces an interval diver health score (DHS) with possible values ranging from 0 to 30. Depth/time profiles were analysed according to existing decompression models. The contribution of diving exposure and between diver variability to DHS was evaluated using linear regression. RESULTS: The mean risk of decompression sickness was calculated as 0.005 (SD 0.003, n = 383). The mean DHS following diving was 3 (SD 2, n = 383) and following non-diving activities was 1 (SD 1, n = 41). After accounting for between diver variability in intercept, DHS was found to increase one unit for every 1% increase in the risk of decompression sickness. CONCLUSIONS: A method has been established for the collection and analysis of self reported objective decompression data from occupational diving groups that can potentially be used as the basis for development of purpose designed occupational diving decompression schedules.

Decompression↗
PubMed1992

Failure of the straight-line DCS boundary when extrapolated to the hypobaric realm.

The lowest pressure (P2) to which a diver can ascend without developing decompression sickness (DCS) after becoming equilibrated at some higher pressure (P1) is described by a straight line with a negative y-intercept. We tested whether extrapolation of such a line also predicts safe decompression to altitude. We substituted tissue nitrogen pressure (P1N2) calculated for a compartment with a 360-min half-time for P1 values; this allows data from hypobaric exposures to be plotted on a P2 vs. P1N2 graph, even if the subject breathes oxygen before ascent. In literature sources, we found 40 reports of human exposures in hypobaric chambers that fell in the region of a P2 vs. P1N2 plot where the extrapolation from hyperbaric data predicted that the decompression should be free of DCS. Of 4,576 exposures, 785 persons suffered decompression sickness (17%), indicating that extrapolation of the diver line to altitude is not valid. Over the pressure range spanned by human hypobaric exposures and hyperbaric air exposures, the best separation between no DCS and DCS on a P2 vs. P1N2 plot seems to be a curve which approximates a straight line in the hyperbaric region but bends toward the origin in the hypobaric region.

Altitude↗
PubMed1982

Delayed treatment of dysbarism: a retrospective review of 50 cases.

Fifty cases of decompression sickness are reviewed in which recompression treatment was delayed for 12 hours or longer after the onset of dysbaric symptoms. Twenty-four patients (48%) had pain only. The other 26 patients (52%) had more serious decompression sickness; two patients may have had air embolisms. Ninety percent of the patients recovered either completely (66%) or substantially (24%) with recompression and associated treatment, although standard recompression protocols had to be lengthened in many of the cases.

Adult↗
PubMed1984

A model of spinal cord dysbarism to study delayed treatment: II. Effects of treatment.

Using the spinal cord decompression sickness model described in Part I, we explored the effects of delay to treatment on the recovery of spinal evoked potentials (SEP). The primary treatments of oxygen at 60 fsw (2.8 bar) and air at 165 fsw (6.0 bar) were studied. In this exploratory study the results were surprisingly poor in all treatments applied. There is evidence that in this model a delay of 15-18 min between diagnosis and start of therapy would generally allow some recovery of SEP, which would rarely be complete. Supporting experiments involving cord ischemia are described. The results from this study enabled us to design a set of practicable experimental criteria for the purpose of discovering the optimal combinations of oxygen and pressure for the treatment of spinal cord decompression sickness.

Animals↗
PubMed2002

Using animal data to improve prediction of human decompression risk following air-saturation dives.

To plan for any future rescue of personnel in a disabled and pressurized submarine, the US Navy needs a method for predicting risk of decompression sickness under possible scenarios for crew recovery. Such scenarios include direct ascent from compressed air exposures with risks too high for ethical human experiments. Animal data, however, with their extensive range of exposure pressures and incidence of decompression sickness, could improve prediction of high-risk human exposures. Hill equation dose-response models were fit, by using maximum likelihood, to 898 air-saturation, direct-ascent dives from humans, pigs, and rats, both individually and combined. Combining the species allowed estimation of one, more precise Hill equation exponent (steepness parameter), thus increasing the precision associated with human risk predictions. These predictions agreed more closely with the observed data at 2 ATA, compared with a current, more general, US Navy model, although the confidence limits of both models overlapped those of the data. However, the greatest benefit of adding animal data was observed after removal of the highest risk human exposures, requiring the models to extrapolate.

Algorithms↗
PubMed1992

Women in the fast jet cockpit--aeromedical considerations.

Historically, women have demonstrated the capacity to be successful aviators. A review of the scientific literature between 1966 and 1991 pertinent to the role of women in military aviation revealed only minor differences of questionable operational significance between men and women. Women may be more susceptible to motion sickness, radiation, and decompression sickness than men, but may be more resistant to cold water immersion and altitude sickness. Although men are on the average, larger, stronger, and more aerobically fit than women, there are large variations within each sex and a large overlap between the sexes. Gender differences in work performance, G tolerance, heat stress, and injury rate disappear when allowance is made for size, strength, and fitness. Aeromedical selection criteria can, thus, address individual characteristics without reference to gender. The possibility of fetal damage in the early stages of pregnancy (before diagnosis) appears to be perhaps the biggest single medical concern in allowing women access to all aviation and space careers.

Aerospace Medicine↗
PubMed2005

Exercise during a 3-min decompression stop reduces postdive venous gas bubbles.

PURPOSE: Decompression sickness is initiated by the formation of gas bubbles in tissue and blood if the divers return to surface pressure too fast. The effect of exercise before, during, and after dive on bubble formation is still controversial. We have reported recently that strenuous aerobic exercise 24 h before simulated dive ameliorates venous bubble formation. The objective of this field study was to evaluate whether mild, continuous exercise during decompression has a similar impact. METHODS: Ten healthy, military male divers performed an open-sea field dive to 30 m of sea water breathing air, remaining at pressure for 30 min. During the bottom and decompression the subjects performed fin underwater swimming at about 30% of maximal oxygen uptake. Each diver underwent two randomly assigned dives, one with and one without exercise during the 3-min decompression period. Monitoring of venous gas emboli was performed in the right heart with ultrasonic scanner every 20 min for 60 min after reaching surface pressure in supine rest and during forced two-cough procedure. RESULTS: The study demonstrates that a mild, continuous exercise during decompression significantly reduced the average number of bubbles in the pulmonary artery from 0.9 +/- 0.8 to 0.3 +/- 0.5 bubbles per square centimeter in supine rest, as well as during two-cough procedure, which decreased from 4.6 +/- 4.5 to 0.9 +/- 0.9 bubbles per square centimeter. No symptoms of decompression sickness were observed in any subject. CONCLUSION: These results, obtained in the field conditions, indicate that a mild, underwater swimming during a 3-min decompression period reduces postdive gas bubbles formation.

Croatia↗
PubMed1975

Supportive evidence for altered platelet function in the dived rat.

A study was conducted on the changes in platelet function and platelet count in the Sprague-Dawley rat induced by a bends-producing N2-O2 compression-decompression cycle. In those instances where mild to moderate cases of decompression sickness were produced, a decrease in platelet reactivity to ADP-induced aggregation occurred immediately postdive along with an increase in inhibition of aggregation by prostaglandin E1. Both effects returned to control levels 24 hours postdive. In moderately affected animals, platelet counts were lower than normal 24 hours postdive but were similar to control values 72 hours postdive. These results tend to support current hypotheses regarding the etiological relationship between disseminated intravascular coagulation and decompression sickness as a function of bubble nucleation.

Adenosine Diphosphate↗
PubMed2001

The "bends" and neurogenic bladder dysfunction.

Decompression sickness (the "bends") is a well-known risk of scuba diving. The pathophysiology and treatment is well documented. In the urologic data, no reference to the development of a neurogenic bladder as a result of an episode of the bends was found. We present the evaluation and management of a previously asymptomatic man who developed detrusor hyperreflexia after an episode of decompression sickness. Urologists in coastal communities should be aware of the potential risk of the development of neurogenic bladder.

Decompression Sickness↗
PubMed1991

The physiology of spacecraft and space suit atmosphere selection.

The majority of the environmental factors which comprise the spacecraft and space suit environments can be controlled at "Earth normal" values, at optimum values, or at other values decided upon by spacecraft designers. Factors which are considered in arriving at control values and control ranges of these parameters include physiological, engineering, operational cost, and safety considerations. Several of the physiological considerations, including hypoxia and hyperoxia, hypercapnia, temperature regulation, and decompression sickness are identified and their impact on spacecraft and space suit atmosphere selection are considered. The past experience in controlling these parameters in U.S. and Soviet spacecraft and space suits and the associated physiological responses are reviewed. Current areas of physiological investigation relating to environmental factors in spacecraft are discussed, particularly decompression sickness which can occur as a result of change in pressure from Earth to spacecraft or spacecraft to space suit. Physiological considerations for long-term lunar or Martian missions will have different impacts on atmosphere selection and may result in the selection of atmospheres different than those currently in use.

Atmospheric Pressure↗
PubMed2005

Exercise ending 30 min pre-dive has no effect on bubble formation in the rat.

INTRODUCTION: We have previously shown that exercise performed 20 h before a dive significantly reduces bubble formation in both rats and humans. Furthermore, exercise performed closer to the dive did not prevent bubble formation. HYPOTHESIS: The present study was designed to determine whether exercise 30 min prior to a dive promotes bubble formation. The occurrence of many bubbles is linked to a higher risk of developing decompression sickness. METHODS: A total of 58 Sprague-Dawley rats were randomly divided into a sedentary control group (n = 29) and an exercise group (n = 29). Rats in the exercise group ran on a treadmill for a total of 90 min at variable intensity up to 85-90% of VO2max. Then, 30 min after exercise, one rat from each group rested in a pressure chamber at 700 kPa (7 atm) breathing air, performing a simulated dive. Bottom time was 45 min; decompression rate was 50 kPa x min(-1) (0.5 atm x min(-1)). Immediately after surfacing (100 kPa, 1 atm), the rats were anesthetized and bubbles were measured discontinuously for the next 60 min. RESULTS: There were no significant differences in survival (p = 0.55), median bubble grade (p = 0.67), survival time (p = 0.53), or the number of rats getting a bubble score > or = 2 (p = 0.79) between the groups. CONCLUSION: The same type and intensity of exercise that reduces bubble formation when performed 20 h prior to a dive neither promotes nor reduces bubble formation if performed 30 min before a dive. The present data indicate that exercise completed 30 min before a dive does not increase the risk of developing decompression sickness in the rat.

Animals↗
PubMed1989

[Incidents in sports diving].

Barotrauma of the ear is the most frequent incident in sport-diving. In some cases, inner ear disorders appear. Barotrauma with rupture of the lung can provoke gas embolism into the central nervous system and unconsciousness. Gas embolism into the spinal cord and decompression sickness of the spinal cord provoke practically the same neurological disturbances. The lower half of the body is mostly affected. Drowning in sport-diving is mostly the result of loss of consciousness resulting from hypoxia or hyperoxia, nitrogen-narcosis or gas embolism into the brain. Inner ear disorders, gas embolism in the brain or the spinal cord, decompression sickness of the spinal cord or the muscles and joints require treatment in the pressure chamber with hyperbaric oxygen. This treatment remains effective even if started some days after the dive.

Barotrauma↗
PubMed1977

Intracardial gas bubbles of altitude after negative pressure breathing.

The influence of negative pressure breathing on the appearance of intracardial gas bubbles at a subsequent decompression to altitude was investigated in five subjects using the precordial Doppler ultrasound technique. Every subject was tested for a suitable exposition that, after 30 min oxygen breathing at surface, caused both intracardial bubbles and decompression sickness. An identical exposition followed a week later, except that oxygen breathing at the surface now included negative pressure breathing. In all cases, negative pressure breathing caused a delay of the onset of both intracardial bubbles and bends and, in some cases, neither bubbles nor bends appeared at all. The total amount of bubbles was always less after negative pressure breathing. Thus, negative pressure breathing in connection with decompression may reduce the amount of intracardial bubbles and the risk of decompression sickness. This may be of importance in diving procedures and in the construction of diving devices.

Altitude↗
PubMed1999

Mathematical model of gas bubble evolution in a straight tube.

Deep sea divers suffer from decompression sickness (DCS) when their rate of ascent to the surface is too rapid. When the ambient pressure drops, inert gas bubbles may form in blood vessels and tissues. The evolution of a gas bubble in a rigid tube filled with slowly moving fluid, intended to simulate a bubble in a blood vessel, is studied by solving a coupled system of fluid-flow and gas transport equations. The governing equations for the fluid motion are solved using two techniques: an analytical method appropriate for small nondeformable spherical bubbles, and the boundary element method for deformable bubbles of arbitrary size, given an applied steady flow rate. A steady convection-diffusion equation is then solved numerically to determine the concentration of gas. The bubble volume, or equivalently the gas mass inside the bubble for a constant bubble pressure, is adjusted over time according to the mass flux at the bubble surface. Using a quasi-steady approximation, the evolution of a gas bubble in a tube is obtained. Results show that convection increases the gas pressure gradient at the bubble surface, hence increasing the rate of bubble evolution. Comparing with the result for a single gas bubble in an infinite tissue, the rate of evolution in a tube is approximately twice as fast. Surface tension is also shown to have a significant effect. These findings may have important implications for our understanding of the mechanisms of inert gas bubbles in the circulation underlying decompression sickness.

Atmospheric Pressure↗
PubMed1979

Use of oxygen for optimizing decompression.

For over 70 years, decompression has been facilitated by the use of elevated oxygen partial pressures. Oxygen has been administered even though little is known about the proper dosage or the way in which this benefit is derived. The historical literature indicates that there is an envelope or narrow range of oxygen partial pressures that can be used. If the oxygen is too low, the incidence of decompression sickness increases; if the oxygen is too high, oxygen poisoning becomes a problem. The present study was designed to explore this oxygen envelope and to define the relationships between oxygen partial pressure, exposure time, and pressure, and to delineate their effects on pressure-reduction limits. To define the ED50 (the effective dose that produced signs of decompression sickness in 50% of the animals), we exposed 820 female albino rats to 42 experimental conditions. Results suggest that the optimum oxygen level and the size of the oxygen envelope both depend on the ambient hydrostatic pressure and the exposure time. For short "shallow" exposures, the optimum oxygen level is high and the oxygen envelope is large; for long "deep" exposures, the optimum oxygen level is reduced and the envelope is restricted.

Animals↗
PubMed1989

Hyperbaric oxygen therapy in clinical application. A report of a 12-year experience.

Hyperbaric oxygen (HBO) has become a useful treatment in clinical diseases. All the treatment profiles (Death/Time) were performed under the safe limit of unit pulmonary toxicity dose (UPTD). Between June 1976 and December 1987, we had treated 1288 cases with HBO. The effective rates (cure or improvement) were 97.5% for decompression sickness, 96.3% for chronic osteomylitis, 90% for chronic skin ulcer, 89.4% for crush injury, 81.3% for gas intoxication, 76.1% for burn injury, 73.3% for cerebrovascular accident, 57.1% for gas gangrene, 50% for retinal artery insufficiency, and 45.5% for head or spinal cord injury. Only 3 patients suffered from oxygen toxicity and relieved immediately. To the serious decompression sickness, the comparative study between the conventional treatment table and our modified table revealed increased cure rate(25.8% versus 50.0%, P less than 0.05), and decreased recurrence rate (16.1% versus 4.1%, P less than 0.05). In burn patients with 35-70% area involved and 15-45 years of age, the comparative analysis showed a reduced mortality rate of 6.8% for the HBO treated group as opposed to 14.8% for the non-HBO treated group, P less than 0.05.

Adolescent↗
PubMedDate not supplied

Decompression tables and dive-outcome data: graphical analysis.

We compare outcomes of experimental air dives with prescriptions for ascent given by various air decompression tables. Among experimental dives compiled in the U.S. Navy Decompression Database, many profiles that resulted in decompression sickness (DCS) have longer total decompression times (TDTs, defined as times spent at decompression stops plus time to travel from depth to the surface) than profiles prescribed by the U.S. Navy table; thus, the divers developed DCS despite spending more time at stops than the table requires. The same is true to a lesser extent for the table used by the Canadian forces. A few DCS cases occurred in profiles having longer TDTs than those of the VVal-18 table and a table prepared at the University of Pennsylvania. The TDTs for 2.2% risk according to the probabilistic NMRI'98 Model are often far longer than TDTs of experimental dives that resulted in DCS. This analysis dramatizes the large differences among alternative decompression instructions and illustrates how the U.S. Navy table provides too little time at stops when bottom times are long.

Decompression↗