Modification of laryngospasm in response to changes in PaCO2 and PaO2 in the cat

In order to study the effects of PaCO2 and PaO2 on the laryngeal closure reflex, changes in laryngeal resistance of the isolated cat larynx were measured before and during the stimulation of the superior laryngeal nerve (SLN) at various levels of PaCO2 and PaO2. The results showed that laryngeal resistance before SLN stimulation [LR (baseline)] increased slightly during hypocapnia. SLN stimulation produced laryngospasm which was defined as a sharp rise in the laryngeal resistance. Hypercapnia alone and hypoxia alone increased ventilation but decreased the degree and duration of laryngospasm due to SLN stimulation. On the other hand, hypocapnia augmented and prolonged the duration of this laryngospasm. These results suggest that PaCO2 and PaO2 regulate the laryngeal closure reflex in a way such that the degree of laryngospasm changes in inverse proportion to the activity of the respiratory center.