Evaluation of static work load in a helium-oxygen saturation dive at 31 ATA

The purpose of the present study is to evaluate the static work load as a model work in Submersible Decompression Chamber (SDC) during a deep sea saturation dive with helium-oxygen gas mixture. Heart rate (HR) and electromyogram (EMG) power spectrum changes were studied during a 7-minute static work, half-rising posture or flexed knee posture in four healthy male subjects. During the static work, EMG of the rectus femoris was recorded with surface electrodes, and changes in the EMG power spectrum were presented in the ratio of a high-frequency to low-frequency band (H/L ratio) after the Fourier transform analysis. The HR decreased at 31 ATA and increased remarkably after the decompression to 1 ATA. HR at post-decompression was higher than pre-compression. The lowering phenomena of EMG presented by H/L ratios during the static work were similarly observed in all three conditions. But the changes of the high and low frequency components were different in the post-decompression condition from the pre-compression and 31 ATA conditions. HR as a parameter of static work load might underestimate the work load at the hyperbaric environment due to hyperbaric bradycardia and overestimate it after decompression by "decompression tachycardia." The EMG lowering phenomenon observed after decompression might not be caused by the same mechanism as seen in the pre-compression and hyperbaric environments. Extreme care must be taken to evaluate the static work load not only at hyperbaric helium-oxygen environments but after decompression from a deep saturation dive.