Effects of Pa co, and Pao, on threshold for the inspiratory-augmenting reflex in cats

and pao,, respectively) on the threshold for the inspira-tory-augmenting reflex produced by hyperinflations of the lungs were investigated in 12 anesthetized paralyzed cats. Inflation threshold for elicitation of the inspiratory-augmenting reflex [VT(IT)] increased with increasing levels of Pace, and decreased with decreasing levels of PaoZ. These effects of Pace, and Pao, on VT(IT) were observed even after bilateral sinus nerve resec-tion. These results suggest that CO2 and 02 may act directly on central mechanisms which are responsible for elicitation of the inspiratory-augmenting reflex. augmented breaths; hypoxia; hypercapnia LARGE INFLATIONS of the lungs can cause a vagally mediated inspiratory-augmenting reflex (8,ll). Although the afferent pathway of this reflex has not been fully determined, lung irritant receptors or rapidly adaptin