Central and peripheral chemoreflex loop gain in normal and carotid body-resected subjects

Abstract

In 7 normal (N) volunteers and 4 who had bilateral carotid body resection (CBR), 5-min hypercapnic steps (to PETCO2 [end tidal CO2 tension] = 48 torr) were generated with PETO2 [end tidal O2 tension] maintained constant under euoxic and hypoxic (PETO2 = 53 torr) conditions. The ventilatory response was studied by fitting a 2-compartment model that included peripheral and central gains, time delays and time constants to the data. Hypoxia increased the speed and magnitude of the ventilatory on-transient to hypercapnia in N subjects, consistent with CO2-O2 interaction at the peripheral chemoreceptors. Ventilatory responses were slower in the carotid body-resected subjects in euoxia and hypoxia. Hypoxia increased the speed of the off-transient in normal and carotid body-resected subjects. Hypoxia markedly increased peripheral gain in N subjects; this gain was not significantly different from zero in the carotid body-resected group. The gain of the slow (central) component in carotid body-resected subjects was approximately half that of the normal controls. The peripheral chemoreceptors may influence the functioning of the central respiratory control mechanisms.