Gas phase formation and Doppler monitoring during decompression with elevated oxygen

Subjects in 150 man-dives were precordially monitored with a 5-MHz Doppler ultrasound bubble detector. These measurements were made during a series of dives conducted to test decompression tables that utilize changes of breathing mixtures and a time-average PIO2 of 1.9 b during the entire decompression period. Precordially detected bubbles at depth were predictive for limb pain in divers approximately 50% of the time; however, 70% of the divers encountered bends problems in the absence of precordially detectable bubbles. Thus, while the presence of venous return bubbles can be associated with a risk factor for bends, the Doppler method appears to lack the specificity needed for personal dive monitoring. During the oxygen-breathing portions of the decompression individual bubbles could not be detected precordially. The amplitude of the Doppler-detected pulmonary artery flow sound increased, however, and possibly indicated the presence of numerous microbubbles.