Respiratory responses to exercise in Divers at 0.4 MPa ambient air pressure

Abstract

Object: This study was carried out to evaluate changes in the breathing pattern of divers during exercise at an elevated ambient air pressure equivalent to a depth of 30 m of seawater. Methods: A total of 22 healthy male subjects performed graded bicycle exercise in a dry hyperbaric chamber up to a maximum of 3.5 W kg⁻¹ body weight at normal (0.1 MPa) and at elevated ambient air pressure (0.4 MPa). The exercise ventilation (VE), tidal volume (VT), breathing frequency (BF), oxygen uptake (VO₂), carbon dioxide elimination (VCO₂), and heart rate (HR) were measured. Perceived dyspnea was assessed by Borg scale ratings. Results: Comparison of respiratory indices between conditions (0.1 versus 0.4 MPa) revealed a significant reduction in VE, VT, BF, and HR during exercise at 0.4 MPa. VO₂ and VCO₂ did not differ significantly between conditions. Likewise, no significant difference between conditions emerged in perceived dyspnea. Conclusion: Ventilation is significantly impaired during heavy bicycle exercise at 0.4 MPa. This is obviously not apparent with regard to subjective perception of dyspnea.