INFLUENCE OF LUNG-VOLUME ON RESPIRATORY RESPONSES TO SPONTANEOUS BLADDER CONTRACTIONS

Spontaneous bladder contractions (SBCs) in decerebrate, vagotomized, p aralyzed, ventilated cats have been shown to decrease phrenic and hypo glossal inspiratory nerve activities, as well as the activities of oth er respiratory motor nerves. To determine whether vagal afferents from the lung influence the respiratory inhibition associated with SBCs, w e recorded phrenic and hypoglossal nerve activities in decerebrate, pa ralyzed, vagally intact cats. The animals were ventilated by a servo-r espirator, which inflated the lungs in accordance with integrated phre nic nerve activity. Maintained increases in end-expiratory lung volume were produced by the application of 2-10 cm H2O positive end-expirato ry pressure (PEEP). SBCs were accompanied by decreases in both phrenic and hypoglossal peak integrated nerve activities, as well as by marke d decreases in respiratory frequency. The reduction of respiratory fre quency was greater with higher levels of PEEP, a few animals becoming apneic during SBCs. After bilateral vagotomy, SBCs continued to decrea se phrenic and hypoglossal peak integrated nerve activities as previou sly reported, but the reduction of. respiratory frequency was much les s striking than when the vagi were intact. These results indicate that activity of vagal afferents from the lung augments the respiratory in fluence of SBCs. Furthermore, SBCs in vagally intact animals can induc e periodic breathing. (C) 1997 Elsevier Science B.V.