Changes in maximal performance of inspiratory and skeletal muscles during and after the 7.1-MPa Hydra 10 record human dive

During the 7.1-MPa hydrogen-helium-oxygen record human dive, we tested the hypothesis that the increased ambient pressure would alter the maximal musc le performance, specifically that breathing dense gas would lead to fatigue of the respiratory muscle. A group of hand muscles (adductor pollicis, AP) and the inspiratory muscles (IM) were studied in three professional divers . Maximal voluntary contractions (MVC) of AP and maximal inspiratory pressu re (P-imax) generated by IM were measured prior to the dive, during compres sion and decompression, and then 1 and 2 months after the dive. The decreas e in MVC (-22%) was significant at 3.1 MPa, i.e. at the beginning of the in troduction of hydrogen into the breathing mixture, whereas P-imax fell prog ressively during the dive and decompression (maximal Delta P-imax = -55%), a significant reduction still being measured 1 month after the dive. The al tered IM function was attributed to the consequences of long-term ventilato ry loading, a condition associated with breathing a dense gas. The transien t decrease in MVC of the skeletal muscle would indicate a possible effect o f the hyperbaric environment, possibly the high partial pressure of hydroge n, on neuromuscular drive.