CENTRAL AND PERIPHERAL CHEMOREFLEX LOOP GAIN IN NORMAL AND CAROTID BODY-RESECTED SUBJECTS

In seven normal (N) vonlunteers, and four who had had bilateral carotid body resection (CBR), 5-min hypercapnic steps (to PET(CO2) = 48 Torr) were generated with PET(O2) maintained constant under euoxic and hypoxic (PET(O2) = 53 Torr) conditions. The ventilatory response was studied by fitting a two-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. This suggests that the peripheral chemoreceptors may influence the functioning of the central respiratory control mechanisms.