The short-latency respiratory response to sudden withdrawal of hypercapnia and hypoxia in man.

Five healthy young male subjects were maintained in a state of mild asphyxia (PA,CO2 ∼ 45 torr, 6·0 kPa, PA,O2 ∼ 50 torr, 6·6 kPa), i.e. with moderately strong drives from both arterial and intracranial chemoreceptors. VT, TT and TI were recorded and V and TE derived breath by breath. The arterial chemoreceptor component was briefly and abruptly reduced, perhaps silenced, by two separate procedures, each repeated twenty-four times on each subject: B, removal of hypercapnia (two breaths hypoxia with PI,CO2 = 0 through a separate inspiratory line) and C, removal of asphyxia (two breaths O2). In control tests, A, the maintenance mixture was replaced by an identical mixture, using an identical manipulation. For each subject means of B and C were compared with means of A and with each other. Quick reflex changes (first three breaths) in V, VT and TE in tests B were not appreciably different from those in tests C in any subject; changes in TI were minimal in all. Thus removal of only the hypercapnic component of the arterial chemoreflex drive appears to be as efficient as the removal of both components simultaneously.