Rabbit Cardiovascular Responses during PEEP before and after Vagotomy 1

Abstract

Summary

Heart rate (HR), mean arterial pressure (MAP), and mean right atrial pressure (MRAP) were measured in 15 pentobarbital-anesthetized rabbits, with vascularly isolated carotid sinuses, during increases in positive end expiratory pressures (PEEP) of 2.5, 5.0, and 7.5 cm H₂O. Also, peak reflex bradycardia (ΔHR) and depression of arterial blood pressure (ΔMAP) to left aortic nerve stimulation (LANS) were recorded during the PEEP changes in aortic and subsequently vagal denervated animals. Responses were measured with the carotid sinus receptors detecting systemic pressure (closed loop (CL) condition) and with sinus region pressures held constant (open loop (OL) condition). Results demonstrated that both HR and MAP were altered by an increase in PEEP. Analysis of HR, and ΔHR to LANS responses during OL conditions, suggested the reflex involvement of cardiopulmonary afferent to cardiac efferent vagal fibers during PEEP changes. Vascular responses to increased PEEP occurred in the presence or absence of arterial baroreceptors and, while reduced, were not abolished following vagotomy.