The vasculature of one lung of unanesthetized spontaneously breathing decerebrate cats was isolated and congested with blood. Such pulmonary vascular congestion (PVC) consistently resulted in a shallow tachypnea associated with expiratory activation of the diaphragm and thyroarytenoid muscles, signifying augmented expiratory braking. With progressive increases in pulmonary vascular pressure, tachypnea and expiratory braking increased progressively and ultimately obscured phasic activity in the diaphragm and thyroarytenoid. Thus the apnea caused by PVC constitutes not an arrest of neural respiratory activity but rather a continuous activation of thoracic inspiratory and laryngeal adductor muscles. When capsaicin, a neurotoxin that activates nonmyelinated afferents, was injected into the pulmonary artery of the isolated lung, it produced changes in timing and distribution of respiratory motor output that resembled those with PVC but were more abrupt in onset. Capsaicin, applied perineurally to the cervical vagi, preferentially blocked the conduction of nonmyelinated afferent fibers. This procedure, which produced little degradation in Hering-Breuer reflexes, eliminated tachypnea and expiratory braking caused by PVC or capsaicin injection. The results indicate that activation of pulmonary vagal afferent fibers of C or A-delta category in unanesthetized cats reflexly modifies the respiratory motor output in a way that resembles the human response to PVC or pulmonary embolism. This is a brain stem reflex.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.