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.


OBJECTIVE
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.
Air Force Research Laboratory, Biodynamics and Protection Division, Brooks Air Force Base, TX 78235-5104, USA. ulf.balldin@brooks.af.mil
Ulf I
UI
Balldin
Andrew A
AA
Pilmanis
James T
JT
Webb
D000293:Adolescent; D000328:Adult; D000337:Aerospace Medicine; D001132:Arm / Q000502:physiology; D003665:Decompression Sickness / Q000209:etiology*; D005080:Exercise Test; D018478:Extravehicular Activity / Q000009:adverse effects; D006801:Humans; D015994:Incidence; D007866:Leg / Q000502:physiology; D008297:Male; D008875:Middle Aged; D009068:Movement / Q000502:physiology; D010102:Oxygen Inhalation Therapy; D011446:Prospective Studies; D016683:Supine Position; D013997:Time Factors; D016474:Weight-Bearing; D018474:Weightlessness Simulation / Q000009:adverse effects* / Q000379:methods
NASA Discipline Environmental Health; Non-NASA Center