Breath-by-breath effects of imposed alternate-breath oscillations of alveolar CO 2

Abstract

Earlier work on respiratory effects of alternate breaths of CO 2-free and CO 2-rich gas in hypoxia or high oxygen has been extended by recording breath-by-breath V t, V e and breath duration T. During test periods P a co 2, alternated between slightly above resting and about 10 torr higher P o 2 was the same in both gas mixtures: thus P o 2 was steady at 55–65 or about 550 torr. In controls a co 2, was 5 torr above resting, identical gas mixtures being supplied from both sources. With p a co 2 , steady, alternation of ve occurred once in 10 tests. Significant alternation of V̇ e accompanied alternation of a co 2, in 8 out of 10 tests during hypoxia but in none of 6 tests in high oxygen. Significant alternation of V̇ t and t often occurred under all three conditions; twice alternation ofVE was associated with no alternation of V̇ t or t. V̇ t and t were positively correlated, thereby stabilising V̇ e, but less so when ve showed alternation. It is concluded that (1) alternation of chemical drive was effective only when arterial chemoreceptors were sensitised to CO 2 by hypoxia; (2) though effective breathby-breath, these gas oscillations do not affect mean ve, thus alternating rising and falling stimuli cancel each other exactly when they occur at the same phase of the respiratory cycle: human respiration responds to change of chemical drive strictly on the basis of sign. In this respect men appear to behave differently from anaesthetised dogs.