Contribution of the carotid body chemoreceptors to eupneic ventilation in the intact, unanesthetized dog

We used extracorporeal perfusion of the reversibly isolated carotid sinus region to determine the effects of specific carotid body (CB) chemoreceptor inhibition on eupneic ventilation (Vi) in the resting, awake, intact dog. Four female spayed dogs were studied during wakefulness when CB was perfused with 1) normoxic, normocapnic blood; and 2) hyperoxic (>500 mmHg), hypocapnic ( approximately 20 mmHg) blood to maximally inhibit the CB tonic activity. We found that CB perfusion per se (normoxic-normocapnic) had no effect on Vi. CB inhibition caused marked reductions in Vi (-60%, range 49-80%) and inspiratory flow rate (-58%, range 44-87%) 24-41 s following the onset of CB perfusion. Thereafter, a partial compensatory response was observed, and a steady state in Vi was reached after 50-76 s following the onset of CB perfusion. This steady-state tidal volume-mediated hypoventilation ( approximately 31%) coincided with a significant reduction in mean diaphragm electromyogram (-24%) and increase in mean arterial pressure (+12 mmHg), which persisted for 7-25 min until CB perfusion was stopped, despite a substantial increase in CO(2) retention (+9 Torr, arterial Pco(2)) and systemic respiratory acidosis. We interpret these data to mean that CB chemoreceptors contribute more than one-half to the total eupneic drive to breathe in the normoxic, intact, awake animal. We speculate that this CB contribution consists of both the normal tonic sensory input from the CB chemoreceptors to medullary respiratory controllers, as well as a strong modulatory effect on central chemoreceptor responsiveness to CO(2).