Human tolerance to 100% oxygen at 9.5 psia during five daily simulated 8-hour EVA exposures.

Extravehicular activity (EVA) currently involves decompression to 4.3 psia. This degree of decompression carries a significant potential for decompression sickness (DCS) which could be alleviated if a pressure of 9.5 psia could be maintained in the pressure suit. Previous studies have not evaluated the potential for oxygen toxicity at 9.5 psia. Twenty-one subjects were exposed to 100% oxygen at 9.5 psia for 5 consecutive days, 8 h.d-1 while performing moderate exercise to simulate a typical work-week in the proposed pressure suit environment. No DCS or venous gas bubbles were detected. Pulmonary function tests, physical exams, blood analyses, arterial oxygen saturation monitoring, and X-rays showed no evidence of oxygen toxicity under these conditions. These results suggest that a 100% oxygen, 9.5 psia pressure suit environment could avoid both DCS and oxygen toxicity during EVAs of comparable duration and physical activity.

Blood factors and venous gas emboli: surface to 429 mmHg (8.3 psi).

Analyses of 43 parameters were performed on blood obtained from 30 volunteer subjects before and after a 6-h chamber decompression from the surface to 429 mmHg. Eight subjects (5 male, 3 female) were bubble-prone (bubble grades 3 and 4), and 22 (15 male, 7 female) were resistant (bubble grade 0) to forming bubbles as detected with precordial Doppler. Significant (P less than 0.05) differences include the following: higher levels of cholesterol in the bubble-prone males and combined subjects (males and females) than in their resistant counterparts; higher magnesium in the bubble-prone males; shorter preexposure prothrombin time in bubble-prone males and combined subjects; increased partial thromboplastin time in bubble-prone females vs. the resistant females, who showed a decrease during exposure; higher preexposure hemoglobin, hematocrit, and red blood cell count in the bubble-prone females; and significant reduction in hemoglobin, red blood cell count, and serum osmolality in the bubble-prone females during the exposure relative to changes in the resistant females. In this study, high cholesterol and hemoconcentration seem to be characteristics of bubble-prone subjects.