Some aspects of upper respiratory tract reflexes.

Respiratory and cardiovascular reflexes have been elicited from receptors in the nose and larynx in the anaesthetized dog. Cigarette smoke in the nose causes reflex apnoea, bradycardia and vasoconstriction, probably due to systemic absorption through the nose. Stimulation of laryngeal nerve also results in reflex apnoea, bradycardia, and limb vasoconstriction. When asphyxia supervenes due to apnoea, stimulation of the carotid body chemoreceptors occurs which normally cause, as primary effects, hyperpnoea and bradycardia. However, it has been shown that stimulation of the laryngeal receptors inhibits the carotid body respiratory reflex and facilitates the carotid body cardio-inhibitory reflex, the latter leading to temporary cardiac arrest. The clinical implications of this finding are discussed.