Cardiorespiratory Responses to Graded Exercise at Increased Ambient Air Pressure

Abstract

Abstract The separate and combined effects of increased inspired oxygen and nitrogen pressures on cardiorespiratory and metabolic responses to graded exercise (50, 100, and 150 W) were assessed by comparing data from identical work experiments performed under three different ambient conditions, viz . with the subjects breathing ( A ) air at 1.0 ATA, (5) oxygen at 1.0 ATA, and (C) air at 4.5 ATA (same inspired Po 3 as in B ). In general, the physiological responses to the various work loads were qualitatively similar in the three conditions, but for a given load quantitative differences were observed. By comparing Condition C with A it was found that a rise in both the O 2 and N 2 pressures resulted in the following changes at the highest work load: significant increments in Vos, Vco 2 , end‐tidal and mixed expired Pco 2 , and oxygen pulse (Vo 2 per heart beat), significant reductions in heart rate, VD, VD/VT, and ventilatory equivalents for oxygen (v̇ I /v̇ CO2 ) and carbon dioxide (v̇ I /v̇ CO2 ), and no consistent changes in Vi and respiratory exchange ratio. When related to v̇ O2 , i.e . to the metabolic rather than the ergometric load, Vi was lower in C than in A . By comparing Condition B with A, and C with B, evidence was obtained that the above changes in Vi, Pco 2 , ventilatory equivalents, oxygen pulse, and heart rate were caused in part by the rise in O 2 pressure, and in part by factors related to the rise in N 2 pressure, whereas the changes in VD and VD/VT were due mainly to the raised O 2 pressure, and the changes in Vo 2 and Vco 2 to the raised N s pressvire.