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Biomedical subjects

Andrew A Pilmanis

Publications and source records attributed to Andrew A Pilmanis.

At least 19 recordsLinked to original sources
PubMed2005

Altitude decompression sickness between 6858 and 9144 m following a 1-h prebreathe.

INTRODUCTION: The zero prebreathe altitude threshold for developing 5% decompression sickness (DCS) symptoms in men has been reported to be 6248 m (20,500 ft). However, such an altitude threshold when 1 h of oxygen prebreathe is used has not been well documented and was the primary purpose of this study. METHODS: The 51 male human subjects were exposed to 9144 m (30,000 ft), 8382 m (27,500 ft), 7620 m (25,000 ft), and/or 6858 m (22,500 ft) for 8 h. They were monitored for symptoms of DCS and venous gas emboli (VGE). RESULTS: DCS symptom incidence after 4 h of exposure decreased with exposure altitude from 87% at 9144 m to 26% at 6858 m. VGE were lower during the 4-h 6858-m exposures (32%) than at the higher altitudes (76-85%). The symptom incidences during the first 4 h of exposure were lower at 6858 m and 7620 m following a 1-h prebreathe as compared with analogous zero-prebreathe exposures. There were no differences between incidences of VGE or DCS at any of the four altitudes after 8 vs. 4 h of exposure. CONCLUSION: The altitude threshold for 5% DCS symptoms is below 6858 m after 1 h of prebreathe. However, during 6858-m and 7620-m exposures, a 1-h prebreathe is highly beneficial in reducing DCS incidence and delaying the onset of DCS, keeping the incidence to less than 6% during the first 90 min of exposure. Use of 4-h vs. 8-h exposures does not appear to underestimate DCS risk at or above 7620 m.

Adult↗
PubMed2005

Depressurization in military aircraft: rates, rapidity, and health effects for 1055 incidents.

INTRODUCTION: Aircraft cabin depressurization is a rare event but one which demands attention because of the grave potential for aircrew incapacity in flight. The purpose of the current study was to determine rates of depressurization incidents for U.S. military aircraft, to examine their causes, and to evaluate the medical importance of these incidents. METHODS: The U.S. Navy and U.S. Air Force safety center databases were searched for decompression incidents during FY1981-FY2003. A total of 1055 incidents were analyzed as to the cause, speed of onset, and adverse health effects (hypoxia, barotrauma, DCS, or any combination of these). The causes of each incident were identified and classified by aircraft type. RESULTS: The number of incidents per airframe varied from 1 (in many airframes) to 276 in the T-38. The number of total hours flown ranged from 16,332 in the T-6 to 8,101,607 in the C-130. The number of sorties flown ranged from 8800 in the B-2 to 3,543,061 in the C-130. Of 35 common airframes, 30 showed rates between 0 and 20 incidents per million flying hours. Depressurization was "slow" in 83% of incidents. Of the 1055 incidents, only 350 (33.2%) involved adverse health effects. Hypoxia occurred in 221 incidents, DCS in 83, and barotrauma in 71. Only 4 (0.4%) resulted in a fatality. Of the 199 incidents involving hypoxia, 12 (6%) occurred below 4267 m (14,000 ft). CONCLUSION: Most reported military aircraft depressurization incidents are slow and do not affect aircrew health. Rates have decreased dramatically since the 1980s. Still, this study lends support to continuing hypobaric chamber training for military pilots.

Aerospace Medicine↗
PubMed2005

Altitude decompression sickness susceptibility: influence of anthropometric and physiologic variables.

INTRODUCTION: There is considerable variability in individual susceptibility to altitude decompression sickness (DCS). The Air Force Research Laboratory Altitude DCS Research Database consists of extensive information on 2980 altitude exposures conducted with consistent procedures and endpoint criteria. We used this database to quantify the variation in susceptibility and determine if anthropometric and/or physiologic variables could be used to predict DCS risk. METHODS: There were 240 subjects who participated in at least 4 of 70 exposure profiles in which between 5 and 95% of all subjects tested developed DCS symptoms. A subject/study ratio (SSR) was calculated by dividing the DCS experienced by a subject during all their exposures by the DCS incidence for all subjects who participated in the identical exposures. The SSR was used to identify the relative susceptibility of subjects for use in analyzing possible relationships between DCS susceptibility and the variables of height, weight, body mass index, age, percent body fat, and aerobic capacity. RESULTS: The DCS incidence was 46.5% during 1879 subject-exposures by subjects exposed at least 4 times. A significant relationship existed between higher DCS susceptibility and the combination of lower aerobic capacity and greater weight (p < 0.05). DISCUSSION: Despite a correlation, less than 13% of the variation in DCS susceptibility was accounted for by the best combination of variables, weight and VO2max. CONCLUSION: Differences in DCS susceptibility cover a wide range and appear to be related to some anthropometric and physiologic variables. However, there was insufficient correlation to allow prediction of an individual's susceptibility.

Adaptation, Physiological↗
PubMed2005

Partial pressure of nitrogen in breathing mixtures and risk of altitude decompression sickness.

BACKGROUND: Many aircraft oxygen systems do not deliver 100% O2. Inert gases can be present at various levels. The purpose of this study was to determine the effect of these inert gas levels on decompression sickness (DCS). METHODS: Subjects were exposed for 4 h to 5486 m (18,000 ft) with zero prebreathe, using either mild (Test A) or strenuous exercise (Test B), and breathing 60%N2/40%O2. Test C used a breathing mixture of 40%N2/60%O2 at 6858 m (22,500 ft) with zero prebreathe and mild exercise. Test D investigated a breathing mixture of 2.8%N2/4.2%argon/93%O2 with 4 h exposures to 7620 m (25,000 ft), mild exercise, and 90 min of preoxygenation. The controls were from previous studies using similar conditions and 100% O2. RESULTS: The DCS risk for Tests A and B and the Control for B was 7%; the Control for Test A was 0% (n.s.). Breathing the 40%N2/60%O2 mixture (Test C) resulted in 43% DCS compared with 53% DCS with 100% O2 (n.s.). When the 2.8%N2/4.2%argon/93%O2 mixture was used, the results showed 25% DCS compared with 31% DCS with 100% O2 (n.s.). CONCLUSIONS: The increased nitrogen and argon levels in the breathing gas while at altitudes of 5486 m to 7620 m did not increase DCS risk. These results support the concept of using the partial pressure gradient of inert gases instead of the percentage of N2 or argon in a breathing gas mixture to determine the risk of DCS during altitude exposure.

Aerospace Medicine↗
PubMed2005

Decompression sickness during simulated extravehicular activity: ambulation vs. non-ambulation.

BACKGROUND: Extravehicular activity (EVA) is required from the International Space Station on a regular basis. Because of the weightless environment during EVA, physical activity is performed using mostly upper-body movements since the lower body is anchored for stability. The adynamic model (restricted lower-body activity; non-ambulation) was designed to simulate this environment during earthbound studies of decompression sickness (DCS) risk. DCS symptoms during ambulatory (walking) and non-ambulatory high altitude exposure activity were compared. The objective was to determine if symptom incidences during ambulatory and non-ambulatory exposures are comparable and provide analogous estimates of risk under otherwise identical conditions. METHODS: A retrospective analysis was accomplished on DCS symptoms from 2010 ambulatory and 330 non-ambulatory exposures. RESULTS: There was no significant difference between the overall incidence of DCS or joint-pain DCS in the ambulatory (49% and 40%) vs. the non-ambulatory exposures (53% and 36%; p > 0.1). DCS involving joint pain only in the lower body was higher during ambulatory exposures (28%) than non-ambulatory exposures (18%; p < 0.01). Non-ambulatory exposures terminated more frequently with non-joint-pain DCS (17%) or upper-body-only joint pain (18%) as compared with ambulatory exposures, 9% and 11% (p < 0.01), respectively. DISCUSSION: These findings show that lower-body, weight-bearing activity shifts the incidence of joint-pain DCS from the upper body to the lower body without altering the total incidence of DCS or joint-pain DCS. CONCLUSIONS: Use of data from previous and future subject exposures involving ambulatory activity while decompressed appears to be a valid analogue of non-ambulatory activity in determining DCS risk during simulated EVA studies.

Decompression Sickness↗
PubMed2005

Headache and altitude decompression sickness: joint pain or neurological pain?

INTRODUCTION: Exposure to reduced ambient pressure may result in decompression sickness (DCS). Headache is among the DCS symptoms encountered and is usually regarded as neurological DCS, which is traditionally classified as serious DCS. Since cranial sutures may be considered joints, it is possible that some headaches are actually joint pain and when associated with decompression sickness need not be neurological DCS. METHODS: Records were individually recovered from the Davis Hyperbaric Laboratory at Brooks City-Base, TX. Information was extracted using a detailed survey instrument. Possible joint pain headache cases were identified using three criteria: headache localized at a suture, normal neurologic exam, and resolution within 30 min of hyperbaric oxygen treatment. RESULTS: A total of 729 records documenting treatment for DCS were scrutinized. Of these, 70 cases of altitude DCS with headache were examined. Analysis, using the three criteria, showed 23% (16 cases) of altitude headache DCS symptoms could potentially be re-classified as joint pain. CONCLUSION: Generally, headache DCS is considered neurological DCS. However, since cranial sutures are joints, both histologically and functionally, and since DCS most commonly affects joints, headache DCS may, at times, be joint pain DCS. Indeed, retrospective data analysis suggests that this possibility exists. Such a reclassification from neurological to joint pain DCS would lessen the aeromedical impact of a DCS headache.

Adult↗
PubMed2004

Altitude decompression sickness symptom resolution during descent to ground level.

INTRODUCTION: Altitude decompression sickness (DCS) is a health risk associated with the conduct of high altitude airdrop operations, high altitude reconnaissance, future fighter operations, hypobaric chamber training, unpressurized flight, and extravehicular activity (EVA) in space. The treatment for DCS includes the provision of 100% oxygen (O2) at ground level (GLO) and/or hyperbaric oxygen therapy (HBO). In this paper we examine the effect of repressurization to ground level from hypobaric conditions on DCS symptoms. Timely recompression (descent at first recognition of any DCS symptom) may be a safe, effective treatment for the large majority of DCS symptoms. METHODS: Data from altitude chamber exposures recorded in the Air Force Research Laboratory (AFRL) Altitude DCS Database were reviewed to determine the level of recompression required for complete resolution of 1,699 observed symptoms. RESULTS: Of the 1,699 DCS symptoms reviewed, 66 (3.9%) resolved at altitude, 117 (6.9%) resolved at ground level, and 1,433 (84.3%) resolved during descent. Increasing the pressure by 138 mmHg from the altitude of exposure where symptoms occurred resolved roughly 50% of symptoms. Little resolution of symptoms was noted with recompressions of < 50 mmHg. The greatest rate of symptom resolution occurred with recompressions of 50-250 mmHg. CONCLUSION: These findings support the concept that descent and postflight, ground-level oxygen may be sufficient to relieve the majority of altitude DCS symptoms. HBO may be reserved for serious, recurring, delayed, or refractory symptoms. The findings also suggest a need for further study of DCS symptom resolution.

Aerospace Medicine↗
PubMed2004

Decompression sickness risk model: development and validation by 150 prospective hypobaric exposures.

INTRODUCTION: High altitude exposure has an inherent risk of altitude decompression sickness (DCS). A predictive DCS model was needed to reduce operational risk. To be operationally acceptable, such a theoretical model would need to be validated in the laboratory using human subjects. METHODS: The Air Force Research Laboratory (AFRL) has conducted numerous studies on human subjects exposed to simulated altitudes in hypobaric chambers. The database from those studies was used to develop a statistical altitude DCS model. In addition, a bubble growth model was developed using a finite difference method to solve for bubble radius as a function of time. The bubble growth model, integrated with the statistical model, constitutes the AFRL DCS Risk Assessment Model. Validation of the model was accomplished by comparing computer predictions of DCS risk with results from subsequent prospective human subject exposures. There were five exposure profiles, not previously found in the database, covering a wide parameter of ranges of altitude (18,000-35,000 ft), exposure time (180-360 min), prebreathe time (0-90 min), and activity level (rest-strenuous) that were used. The subjects were monitored for DCS symptoms and venous gas emboli. RESULTS: There were 30 subjects who were exposed to each of the 5 altitude profiles. The DCS incidence onset curves predicted by the model were not significantly different from the experimental values for all scenarios tested and were generally within +/- 5% of the actual values. CONCLUSION: A predictive altitude DCS model was successfully developed and validated.

Altitude Sickness↗
PubMed2004

Altitude decompression sickness at 7620 m following prebreathe enhanced with exercise periods.

INTRODUCTION: Over 80% altitude decompression sickness (DCS) was reported during a 4-h exposure with mild exercise to 7620 m (25,000 ft) without prebreathe. Prebreathe for more than 1 h would be necessary to reduce the DCS risk below 40%. Use of a single period of exercise to enhance prebreathe effectiveness has been successfully tested and used during some U-2 operations. The current tests used multiple exercise sessions to enhance prebreathe (MEEP) as a means of improving denitrogenation efficiency. METHODS: Two MEEP profiles, 30 or 60 min, preceded 4-h exposures to 7620 m with mild, upper-body exercise while breathing 100% oxygen. Resting prebreathe controls were from published studies at the same laboratory. Both MEEP profiles involved 10 min of strenuous dual-cycle ergometry (75% of maximal oxygen uptake) at the beginning of prebreathe. After a 15-min rest period during the 60-min prebreathe, an additional 5 min of strenuous ergometry was performed. Mild exercise was performed during 15 of the last 20 min of both prebreathe profiles. RESULTS: The 60-min MEEP resulted in 25% DCS and the 30-min MEEP 40% DCS (N.S.). The 25% incidence of DCS following the 60-min MEEP profile was significantly less than the 63% DCS following an equal-time, resting prebreathe control. Following the 30-min MEEP, DCS incidence was not greater than the incidence following a 60-min, resting prebreathe control. There was a lower incidence of venous gas emboli during the MEEP exposures than during resting control exposures. CONCLUSION: Denitrogenation with multiple periods of exercise provides a shorter alternative to resting prebreathe for reducing DCS risk during exposure to 7620 m.

Adolescent↗
PubMed2004

Central nervous system decompression sickness and venous gas emboli in hypobaric conditions.

INTRODUCTION: Altitude decompression sickness (DCS) that involves the central nervous system (CNS) is a rare but potentially serious condition. Identification of early symptoms and signs of this condition might improve treatment. METHODS: We studied data from 26 protocols carried out in our laboratory over the period 1983-2003; all were designed to provoke DCS in a substantial proportion of subjects. The data set included 2843 cases. We classified subject-exposures that resulted in DCS as: 1) neurological DCS of peripheral and/or central origin (NEURO); 2) a subset of those that involved only the CNS (CNS); and 3) all other cases, i.e., DCS cases that did not have a neurological component (OTHER). For each case, echo imaging data were used to document whether venous gas emboli (VGE) were present, and their level was classified as: 1) any level, i.e., Grade 1 or higher (VGE-1); and 2) high level, Grade 4 (VGE-4). RESULTS: There were 1108 cases of altitude DCS in the database; 218 were classified as NEURO and 49 of those as CNS. VGE-1 were recorded in 83.8% of OTHER compared with 58.7% of NEURO and 55.1% of CNS (both p < 0.001 compared with OTHER). The corresponding values for VGE-4 were 48.8%, 37.0%, and 34.7% (p < 0.001, compared to OTHER). Hyperbaric oxygen (HBO) was used to treat about half of the CNS cases, while all other cases were treated with 2 h breathing 100% oxygen at ground level. DISCUSSION: Since only about half of the rare cases of hypobaric CNS DCS cases were accompanied by any level of VGE, echo imaging for bubbles may have limited application for use as a predictor of such cases.

Altitude↗
PubMed2003

Gender not a factor for altitude decompression sickness risk.

INTRODUCTION: Early, retrospective reports of the incidence of altitude decompression sickness (DCS) during altitude chamber training exposures indicated that women were more susceptible than men. We hypothesized that a controlled, prospective study would show no significant difference. METHODS: We conducted 25 altitude chamber decompression exposure profiles. A total of 291 human subjects, 197 men and 94 women, underwent 961 exposures to simulated altitude for up to 8 h, using zero to 4 h of preoxygenation. Throughout the exposures, subjects breathed 100% oxygen, rested or performed mild or strenuous exercise, and were monitored for precordial venous gas emboli (VGE) and DCS symptoms. RESULTS: No significant differences in DCS incidence were observed between men (49.5%) and women (45.3%). However, VGE occurred at significantly higher rates among men than women under the same exposure conditions, 69.3% and 55.0% respectively. Women using hormonal contraception showed significantly greater susceptibility to DCS than those not using hormonal contraception during the latter two weeks of the menstrual cycle. Significantly higher DCS incidence was observed in the heaviest men, in women with the highest body fat, and in subjects with the highest body mass indices and lowest levels of fitness. CONCLUSION: No differences in altitude DCS incidence were observed between the sexes under our test conditions, although men developed VGE more often than women. Age and height showed no significant influence on DCS incidence, but persons of either sex with higher body mass index and lower physical fitness developed DCS more frequently.

Aerospace Medicine↗
PubMed2003

Case history of serious altitude decompression sickness following rapid rate of ascent.

Neurologic and respiratory decompression sickness (DCS) symptoms occurring in the same individual represent complications rarely observed in altitude research. A case is presented of multi-symptom serious DCS resulting from exposure to 12,192 m (40,000 ft). Following 90 min of preoxygenation, the patient was decompressed in a hypobaric chamber from ground level to 12,192 m in 30 s. After 69 min at altitude he developed substernal chest pressure and the flight was immediately terminated. During the chamber descent the patient appeared disoriented. By 5486 m (18,000 ft) his chest pressure had resolved. The post-flight medical exam revealed multiple neurological abnormalities. He underwent a Table VI hyperbaric oxygen treatment with complete resolution of all abnormal neurological findings.

Aerospace Medicine↗
PubMed2003

The risk of altitude decompression sickness at 12,000 m and the effect of ascent rate.

INTRODUCTION: Loss of aircraft cabin pressurization can result in very rapid decompression rates. The literature contains reports of increased or unchanged levels of altitude decompression sickness (DCS) resulting from increasing the rate of decompression. We conducted two prospective exposure profiles to quantify the DCS risk at 12,192 m (40,000 ft), and to determine if there was a greater DCS hazard associated with a much higher rate of decompression than typically used during past DCS studies. METHODS: The 63 human subjects participated in 80 altitude chamber decompression exposures to a simulated altitude of 12,192 m (2.72 psia; 18.75 kPa) for 90 min, following preoxygenation with 100% oxygen for 90 min. Half of the subject-exposures involved an 8-min decompression (1,524 mpm; 5,000 fpm) and the other half experienced a 30-s decompression (mean of 24,384 mpm; 80,000 fpm). Throughout each ascent and exposure, subjects were seated at rest and breathed 100% oxygen. At altitude, they were monitored for precordial venous gas emboli (VGE) and DCS symptoms. RESULTS: The higher decompression rate yielded 55.0% DCS and 72.5% VGE and the lower rate produced 47.5% DCS and 65.0% VGE. Chi square and log rank tests based on the Kaplan-Meier analyses indicated no difference in the incidence or onset rate of DCS or VGE observed during the two profiles. CONCLUSION: Decompression rate to altitude up to 24,384 mpm was found not to have an effect on DCS risk at altitude. However, research is needed to define the DCS risk with decompression rates greater than 24,384 mpm. It was also found that the onset time to DCS symptoms decreases as altitude increases.

Adult↗
PubMed2003

Staged decompression to 3.5 psi using argon-oxygen and 100% oxygen breathing mixtures.

INTRODUCTION: The current extravehicular activity (EVA) space suit at 4.3 psia causes hand and arm fatigue and is too heavy for Martian EVA. A 3.5 psia EVA pressure suit requires increased preoxygenation time but would reduce structural complexity, leak rate, and weight while increasing mobility, comfort, and maintainability. On Mars, nitrogen and argon are available to provide the inert gas necessary for a fire-resistant habitat atmosphere, eliminating need for transport. This study investigated breathing argon/oxygen and 100% oxygen gas mixtures during staged decompression prior to exposure to 3.5 psia. METHOD: During this study, 40 subjects each completed 3 hypobaric exposures to 3.5 psia for 3 h in a reclined position: (A) a 4-h 25-min 14.7-psia (ground level) denitrogenation (100% oxygen breathing) prior to exposure to 3.5 psia; (B) the same as A, utilizing a 7.3-psia stage denitrogenation; and (C) the same as B, with 62% argon-38% oxygen (ARGOX) during the stage. Venous gas emboli (VGE) were monitored with echocardiography. RESULTS: Decompression sickness (DCS) incidence at 3.5 psia with ARGOX at 7.3 psia (C) was significantly higher than with oxygen breathing with or without staged decompression: there was 78% DCS for C compared with 33% and 55% DCS, respectively, for A and B. The corresponding VGE incidences were 73% (C) compared with 33% (A) and 45% (B). CONCLUSION: Preoxygenation at a 7.3-psia stage resulted in a higher DCS risk at 3.5 psia than ground level preoxygenation. It is suggested that an 8.0-psia stage pressure could eliminate this difference. Unfavorable results after preoxygenation with ARGOX indicate argon on-gassing was significant.

Adolescent↗
PubMed2002

Non-invasive measurement of pulmonary artery pressure in humans with simulated altitude-induced venous gas emboli.

BACKGROUND: Decompression to simulated altitude causes super-saturation of nitrogen desolved in body tissues and can result in venous gas emboli (VGE), which are usually "cleared" in the lung. Large intravenous boli of air administered to animals increase pulmonary artery pressure (PAP), and may induce cross-over of gas to the left side of the heart (creating dangerous arterial gas emboli). This study was conducted to determine whether high VGE grades induced at simulated altitude elevate PAP in humans. METHODS: Eight human subjects with subclinical tricuspid regurgitation were exposed to simulated altitude of > or = 24,000 ft (7315 m) for up to 4 h. Systolic PAP was derived from Doppler ultrasound echo imaging measurements of peak flow velocity of the regurgitant jet. VGE was rated using the Spencer scale. A technique of "bubble titration" was employed with changes in exercise and altitude to maintain sufficient bubbles without decompression sickness. RESULTS: All subjects developed grade III-IV VGE, but 3 developed decompression sickness, resulting in earlier termination. Pre-exposure systolic PAP averaged 24.4 +/- 1.3 (SE) mm Hg. After 1, 2, 3 and 4 h, systolic PAP was 23.7 +/- 1.2 (n = 8), 23.4 +/- 1.1 (n = 8), 23.3 +/- 1.0 (n = 6), and 25.9 +/- 0.6 (n = 5) mm Hg, respectively. Systolic PAP remained unchanged, in spite of bubble grades III-IV for up to 4 h. CONCLUSION: As systolic PAP did not increase with hypobaric exposures that created substantial VGE, the bubble loading was not sufficient to overwhelm the lung clearing capacity. The risk of high PAP resulting in VGE cross-over is low during typical operational altitude exposures.

Aerospace Medicine↗
PubMed2002

The effect of repeated altitude exposures on the incidence of decompression sickness.

INTRODUCTION: Repeated altitude exposures in a single day occur during special operations parachute training, hypobaric chamber training, unpressurized flight, and extravehicular space activity. Inconsistent and contradictory information exists regarding the risk of decompression sickness (DCS) during such hypobaric exposures. HYPOTHESIS: We hypothesized that four short exposures to altitude with and without ground intervals would result in a lower incidence of DCS than a single exposure of equal duration. METHODS: The 32 subjects were exposed to 3 different hypobaric exposures--condition A: 2 h continuous exposure (control); condition B: four 30-min exposures with descent/ascent but no ground interval between the exposures; condition C: four 30-min exposures with descent/ascent and 60 min of ground interval breathing air between exposures. All exposures were to 25,000 ft with 100% oxygen breathing. Subjects were observed for symptoms of DCS, and precordial monitoring of venous gas emboli (VGE) was accomplished with a SONOS 1000 echo-imaging system. RESULTS: DCS occurred in 19 subjects during A (mean onset 70+/-29 min), 7 subjects in B (60+/-34 min), and 2 subjects in C (40+/-18 min). There was a significant difference in DCS incidence between B and A (p = 0.0015) and C and A (p = 0.0002), but no significant difference between B and C. There were 28 cases of VGE in A (mean onset 30+/-23 min), 21 in B (41+/-35 min), and 21 in C (41+/-32 min) with a significant onset curve difference between B and A and between C and A, but not between B and C. Exposure A resulted in four cases of serious respiratory/neurological symptoms, while B had one and C had none. All symptoms resolved during recompression to ground level. CONCLUSION: Data indicate that repeated simulated altitude exposures to 25,000 ft significantly reduce DCS and VGE incidence compared with a single continuous altitude exposure.

Adolescent↗
PubMed2002

The effect of simulated weightlessness on hypobaric decompression sickness.

BACKGROUND: A discrepancy exists between the incidence of ground-based decompression sickness (DCS) during simulated extravehicular activity (EVA) at hypobaric space suit pressure (20-40%) and crewmember reports during actual EVA (zero reports). This could be due to the effect of gravity during ground-based DCS studies. HYPOTHESIS: At EVA suit pressures of 29.6 kPa (4.3 psia), there is no difference in the incidence of hypobaric DCS between a control group and group exposed to simulated weightlessness (supine body position). METHODS: Male subjects were exposed to a hypobaric pressure of 29.6 kPa (4.3 psi) for up to 4 h. The control group (n = 26) pre-oxygenated for 60 min (first 10 min exercising) before hypobaric exposure and walking around in the altitude chamber. The test group (n = 39) remained supine for a 3 h prior to and during the 60-min pre-oxygenation (also including exercise) and at hypobaric pressure. DCS symptoms and venous gas emboli (VGE) at hypobaric pressure were registered. RESULTS: DCS occurred in 42% in the control and in 44% in simulated weightlessness group (n.s.). The mean time for DCS to develop was 112 min (SD +/- 61) and 123 min (+/- 67), respectively. VGE occurred in 81% of the control group subjects and in 51% of the simulated weightlessness subjects (p = 0.02), while severe VGE occurred in 58% and 33%, respectively (p = 0.08). VGE started after 113 min (+/- 43) in the control and after 76 min (+/- 64) in the simulated weightlessness group. CONCLUSIONS: No difference in incidence of DCS was shown between control and simulated weightlessness conditions. VGE occurred more frequently during the control condition with bubble-releasing arm and leg movements.

Adolescent↗