Abdominal gas volume at altitude and at ground level.

Abstract

Abstract : The effect of decreasing pressure on abdominal gas volume in eighteen young military men was studied under simulated flight conditions and using a displacement volumeter. Studies showed that decompression causes the abdomen to expand but that relatively slight increase in intra-abdominal pressure occurs. Young military men at ground level ordinarily average 0.111 liter (BTPS) of abdominal gas--a statistically significant amount. This amount, in turn, is significantly less than the mean 0.218 liter (BTPS) occurring in subjects when a water-filled naso-gastric catheter connected to a pressure transducer was used. Expansion of the 0.104 liter of dry gases, with concomitant wetting, resulted in 0.500 liter (BTPS) of abdominal gas at an ambient pressure of 230 torr (29,600 ft. pressure:altitude). At this point, 50% of the subjects would be expected to report symptoms of abdominal fullness. At yet lower pressures, subjects reported pain in 6 among 36 man-flights, and at this time the average abdominal gas volume was computed to be 1.09 liters (BTPS). (Author)