Influence of breathing pattern on oxygen exchange during hypoxia and exercise

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 (Sc'O2). This permits calculation of the corresponding end-capillary PO2 (Pc'O2). We have used this technique to study the effect of spontaneous and imposed breathing patterns on mean Pc'O2, amplitude of Pc'O2 (delta Pc'O2) and minute ventilation (VE). The studies were conducted during mild hypoxia, at rest and exercise. The amplitude of delta Pc'O2 is inversely related to breathing frequency. When frequency is constant, patterns with with prolonged expiration or end-expiratory pauses produce large delta Pc'O2 and greater VE. This effect is reversed with prolonged inspiration or end-inspiratory pauses. Spontaneous breathing patterns produced smaller delta Pc'O2, 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 Pc'O2 and VE.