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

The John Rankin Laboratory of Pulmonary Medicine, Department of Population Health Sciences, School of Medicine and Public Health, University of Wisconsin, Madison, Wisconsin

Submitted 11 December 2008 ; accepted in final form 23 February 2009

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 (I) 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 (20 mmHg) blood to maximally inhibit the CB tonic activity. We found that CB perfusion per se (normoxic-normocapnic) had no effect on I. CB inhibition caused marked reductions in I (–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 I was reached after 50–76 s following the onset of CB perfusion. This steady-state tidal volume-mediated hypoventilation (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 CO₂ retention (+9 Torr, arterial PCO₂) 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 CO₂.

control of breathing; eupnea; peripheral chemoreception