The effects of continuous positive pressure breathing (CPPB) on the respiratory and cardiovascular systems were studied on six healthy male volunteers during rest and during moderate exercise. Exercise was performed in the upright position on a cycle ergometer at an intensity of 50% of maximal aerobic capacity for 20 minutes. Breathing pressures of 0, 8, and 16 cmH(,2)O with respect to ambient pressure were tested. Results indicated that inter-individual variability existed in. response to CPPB. During rest, CPPB tended to induce hyper-. ventilation. Correspondingly, the ventilatory equivalents for O(,2) and CO(,2) (V(,E)/V(,O(,2))(' )and V(,E)/V(,CO(,2))) and the end-tidal PO(,2) (P(,ET)O(,2)) increased, while the end-tidal P(,CO(,2)) (P(,ET)CO(,2)) decreased. The physiological deadspace/tidal volume ratio (V(,D)/V(,T)) increased in response to elevated breathing pressures during most tests, but not in all. Diffusing capacity for carbon monoxide had a tendency to increase during pressure breathing, but the change was variable and not significant. Cardiac output (Q)(' )tended to decrease in response to CPPB during rest due to a drop in stroke volume without a compensatory increase in heart rate. Some subjects maintained normal(' )Q during CPPB. No change or slight increases in mean arterial pressure indicated increased peripheral resistance in response to CPPB. During exercise, CPPB did not produce hyperventilation. Significant differences were found in V(,E)/V(,O(,2)),(' )V(,E)/V(,CO(,2)), P(,ET)O(,2), and P(,ET)CO(,2) between rest and exercise during CPPB, but not without CPPB. The V(,D)/V(,T) was not affected by CPPB during exercise. Diffusing capacity increased significantly during exercise under all conditions with a tendency towards greater increases during CPPB in some subjects. Q(' )continued to be reduced in some subjects during CPPB while exercising. Arterial pressures were normal during exercise and CPPB in those subjects showing a drop in(' )Q. The changes in the respiratory and cardiovascular systems seen during rest in response to CPPB are absent during exercise, with the exception of a lowered(' )Q. The performance of moderate exercise for short durations by healthy individuals does not appear to be influenced by CPPB.
