Comparison was made between intentional and postural tremor amplitudes with a 2-to 50-Hz bandwidth in four men rapidly compressed from surface to 13.1, 25.2, and 37.3 ATA in 4 h while breathing helium-oxygen mixtures (Predictive Studies IV, University of Pennsylvania). Excursions with compression rates of 20 and 40 ft/min were then made to 49.4 ATA on exposure days 2 and 3, returning to saturation at 37.3 ATA for 6 additional days. During compression from 25.2 to 37.3 ATA, there were increases in tremor amplitudes for both intentional and postural tremor in the 3-to 7-Hz and 8- to 12-Hz ranges. Both types of tremor showed increases in amplitudes at 49.4 ATA on exposure days 2 and 3. Amplitude changes in postural tremor, which occurred only on the fastest compression to 49.4 ATA, were less evident than those in intentional tremor during the remaining dive profile, and adaptation to pressure exposure could be defined by day 8. Intentional tremors did not show adaptation at pressure.
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