Influence of breathing pattern on oxygen exchange during hypoxia and exercise

Abstract

During hypoxia, arterial oxygen saturation (SaO2) measured by ear oximeter shows cyclic fluctuations which are related to the pattern and rate of breathing. Continuous recordings of SaO2 may be corrected for distortion, due to circulatory transport, to yield approximate values for pulmonary end-capillary saturation (Sc2O2). This permits calculation of the corresponding end-capillary PO2 (Pc2O2). We have used this technique to study the effect of spontaneous and imposed breathing patterns on mean Pc2O2, amplitude of Pc2O2 (delta Pc2O2) and minute ventilation (VE). The studies were conducted during mild hypoxia, at rest and exercise. The amplitude of delta Pc2O2 is inversely related to breathing frequency. When frequency is constant, patterns with with prolonged expiration or end-expiratory pauses produce large delta Pc2O2 and greater VE. This effect is reversed with prolonged inspiration or end-inspiratory pauses. Spontaneous breathing patterns produced smaller delta Pc2O2, with lower VE than imposed patterns. These findings are compatible with animal studies which suggest the magnitude of PaO2 fluctuations produced by the breathing pattern may act as a feedback stimulus to ventilation. The breathing patterns, which are spontaneously chosen, produce the minimum delta Pc2O2 and VE.