The effects of various time patterns of alveolar CO 2 and O 2 on breathing in man

We have studied the responses of human arterial chemoreceptors to various patterns of quick change of stimulation. (i) Transient abolition of hypercapnia lowers VE after 2 breaths (chemoreceptor latency) only if PAO2 is low, therefore hypoxia is necessary for an arterial chemoreceptor response to CO2. (ii) Alternate breaths of euoxia and hypoxia, and of eucapnia and hypercapnia, separately and combined, have no special effect on mean V. However, oscillating CO2 commonly causes breath-by-breath alternation of V, but only if hypoxia is present; oscillating only the low O2 seldom causes oscillation of V. Concluded (a) that chemoreceptor responses to delta-CO2 are quicker than to delta-O2; (b) that, above CO2 threshold, response to rising CO2 is equal and opposite to response to falling CO2. (iii) Three time patterns of PACO2 within single respiratory cycles have been compared in hypoxia. At a single mean arterial PCO2, a small sharp fall of PACO2 early in inspiration depresses mean V, while a smaller sharp fall of PACO2 late in inspiration increases mean V. Concluded that human respiratory system distinguishes between these rather similar patterns presumably through arterial chemoreceptor pathway since the phenomenon depends on the presence of hypoxia. The importance of exact timing is emphasised.