An analysis of respiratory frequency alterations in vagotomized, decerebrate cats

Changes in inspiratory (TI), expiratory (TE) and total respiratory cycle (TTOT) durations with hypercapnia- of hypoxia-induced tidal volume (VT) elevations were evaluated in midcollicular decerebrate cats. As VT increased, TI, TE, and TTOT decreased for most animals having intact vagi. Following vagotomy, TI, TE, and TTOT increased with hypercapnia for cats which had TI, TE and TTOT values shorter than 1.6, 3.7 and 5.2 sec respectively while breathing 100% O2; values longer than these forecast hypercapnia-induced decreases in each parameter. Similar systematic changes were not evident for hypoxia-induced responses. Varying the midbrain transection level or pentobarbital administration altered TI, TE and TTOT values while breathing 100% O2; however, the predictability of hypercapnia-induced responses, based on data analysis from midcollicular decerebrate cats, was maintained. It is concluded that the vagally-independent brainstem frequency controller is sensitive to hypercapnia and hypoxia. The predictability of hypercapnia-induced TI, TE and TTOT changes in vagotomized animals is considered in the context of previous models for respiratory rhythm generation.