Vagal Control of Heart Rate during Hypoxia in the Cat 1

Abstract

Summary

In spinal cats whose ventilation is completely controlled the primary cardiac response to hypoxia includes vagal bradycardia. This bradycardia appears at distinct levels of PaO₂ which vary as a function of PaCO₂. The carotid chemoreceptors are chiefly responsible for eliciting reflex bradycardia while the aortic chemoreceptors make little or no contribution. This divergence of function is mirrored in the reflex control of respiration but not in the pressor response to hypoxia where both sets of receptors are important. A bradycardia which results directly from the action of hypoxia on the central nervous system can be distinguished from both peripheral reflex effects and the direct effects of hypoxia on the heart itself.