An evaluation of precordial ultrasonic monitoring to avoid bends at altitude.

Several investigators have reported that intravascular bubbles can be detected in decompressed subjects before they develop bends. The altitude exposures were generally of short duration with a limited number of subjects. This important preliminary finding needed to be verified in a larger sampling of long duration altitude exposures. In this experiment, 32 subjects in 82 flights were taken to 27,500 ft simulated altitude for 8 h or until the subject developed mild but steady joint pain (bends). Many subjects took more than one flight. At altitude, the subjects were monitored for circulating bubbles by a team of well-trained, experienced technicians. It was determined that bubbles, clearly audible even to untrained observers, occurred in 77% of the flights in which the subjects developed bends. On the other hand, no bubbles were found in 61% of the flights in which the subjects remained bends free even though the subjects were monitored by more than one experienced technician. Therefore, at 27,500 ft ultrasonic monitoring will miss about 25% of the subjects who developed bends (false negatives) and will incorrectly identify a little less than half of the subjects who do not develop bends as potential benders (false positives).

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.