title: Exercise tolerance at 4 and 6 ATA.
abstract: Seven normal male subjects performed 5-min bicycle exercise ranging from 50-100% maximum oxygen uptake at 4 ATA and three were also studied at 6 ATA. At all pressures, the subjects breathed 0.2 ATA O2 plus nitrogen. All subjects were able to perform maximum work at all pressures. No pressure-dependent variations in heart rate, O2 uptake, or CO2 output were noted. At both 4 and 6 ATA, ventilation was decreased at exercise levels greater than 80% maximum O2 uptake. The magnitude of the decrease was not great, however, and signified only minor CO2 retention. In some instances exercise ventilation closely approached the 15-S maximum breathing capacity and these subjects noted severe dyspnea, possibly due to dynamic compression of large airways. In three subjects, respiratory frequency was measured as well as minute ventilation; this relationship did not change with depth. Subjects performing heavy exercise at 6 ATA noted disturbances of consciousness, presumably due to N2 narcosis.
mesh_terms: D000222:Adaptation, Physiological; D000328:Adult; D001273:Atmosphere Exposure Chambers; D001274:Atmospheric Pressure; D002245:Carbon Dioxide / Q000378:metabolism; D006339:Heart Rate; D006801:Humans; D008297:Male; D009326:Naval Medicine; D010101:Oxygen Consumption; D005082:Physical Exertion; D014692:Ventilation-Perfusion Ratio
chemical_list: D002245:Carbon Dioxide