Alteration from apneusis to more regular rhythmic respiration in decerebrate cats

In spontaneously breathing or paralyzed, ventilated, decerebrate cats. bilateral pneumotaxic center lesions and bilateral vagotomy resulted in apneusis characterized by a marked prolongation of inspiratory duration (TI) and, concomitantly, an elevation of tidal volume (VT) and reduction of respiratory frequency (f). Subsequent placement of medial or lateral lesions in the caudal pons or medulla reduced TI and VT, increased f, and restored a more regular rhythmic respiratory pattern. Placement of these pontile or medullary lesions in animals with pneumotaxic center lesions prevented the development of a typical apneustic pattern upon vagotomy. Large rostral pontile lesions did not change apneusis in spontaneous breathing animals whereas, in paralyzed, ventilated cats, these lesions resulted in some decrease of TI. It is concluded that apneusis generation is not equatable simply with a summation of caudal pontile respiratory unit activities. Rather, activity inherent to intrapontile and/or pontomedullary feedback circuits is considered as a necessary requisite for apneusis development. Interaction of these circuits with an inspiratory off-switch mechanism is considered probable.