Power spectral analysis of intentional and postural tremor during a simulated heliox dive to 31ATA.

Intentional and postural tremor were measured from four Japanese divers during a simulated heliox dive to 31ATA, including phases of predive, compression, depth, decompression, and postdive. The FFT power spectra of tremors were obtained in the frequency range of 0-31.5Hz with an incremental step of 0.5Hz. Attention was focused upon total power density because there were no remarkable changes in tremor frequency associated with ambient pressure. For postural tremor, two (subjects A and B) out of four divers showed significant increases in power density between 7 and 14Hz with increasing pressure. As for the other two divers, the power density remained fairly constant throughout the experiment. Increases in intentional tremor amplitude occurred only in subject B during dive. Adaptation to hyperbaric environment was not demonstrated during dive in subjects who showed increases in tremor amplitude. Under moderate helium pressure (31ATA), a variable individual composition is one of the important factors of tremors, although multifactorical causes have been implicated.