Abstract
Changes in inspiratory (T I), expiratory (T E) and total respiratory cycle (T TOT) durations with hypercapnia- or hypoxia-induced tidal volume (V T) elevations were evaluated in midcollicular decerebrate cats. As V T increased, T I, T E, and T TOT decreased for most animals having intact vagi. Following vagotomy, T I, T E, and T TOT increased with hypercapnia for cats which had T I, T E and T TOT values shorter than 1.6, 3.7 and 5.2 sec respectively while breathing 100% O 2; 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 T I, T E and T TOT values while breathing 100% O 2; however, the predictability of hypercapnia-induced responses, based on data analysis from midcollicular decerebrate cells, was maintained. It is concluded that the vagally-independent brainstem frequency controller is sensitive to hypercapnia and hypoxia. The predictability of hypercapnia-induced T I, T E and T TOT changes in vagotomized animals is considered in the context of previous models for respiratory rhythm generation.
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