Separation of the inspiratory and expiratory reflex effects of alternate-breath oscillation of PACO2 during hypoxia.

Four healthy young men and women, selected for the responsiveness and steadiness of their breathing, were studied in rest and mild exercise (58 runs) while receiving alternate inspirates of low and high PCO2 (0 and 8.6 kPa). PACO2 oscillated between ca. 6 and 7.5 kPa (45-55 torr); PACO2 was held steady at more than one level between 6 and 9.6 kPa (45-72 torr). Using cross-correlation analysis, the phase relations were determined between the alternating PACO2 and the following reflex outputs: mean inspiratory and expiratory flows (VI and VE) and the reciprocal of the duration of expiration (1/TE), the two expiratory variables being lumped together for purposes of expression, but not of calculation. T1, being relatively unaffected alternating PACO2, was not re-studied (see companion paper). The common patterns of significant reflex alternation were: VI alone, usually in phase (with PACO2), 24%; VE alone, usually in phase, 17%; both inspiratory and expiratory variables, in phase with CO2 and each other, 15%; both inspiratory and expiratory variables, the expiratory being out of phase with both CO2 and with the inspiratory, 23%. Some runs showed a mixture of phase relations. In 71%, end-expiratory lung volume (VL,E' formerly called FRC) alternated significantly. It is concluded that expiratory events can be influenced by peripheral chemoreceptors independently of inspiration.