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).