Date of Award

1-1-1981

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Physiology and Pharmacology

Abstract

Mechanical ventilation with inspiratory positive pressure and positive, end-expiratory pressure (PEEP) has been used to improve arterial oxygenation and to re-expand and stabilize collapsed areas of the lung in patients with non-cardiogenic pulmonary edema and adult respiratory distress syndrome. However lung hyperinflation by PEEP results in decreased cardiac output and mean arterial pressure. The interaction of the mechanical and the neuroreflex effects which alter cardiovascular function during PEEP have not been examined in a study designed to evaluate the components (arterial baroreflex, cardiopulmonary mechanoreflex, and mechanical) and their integrated effects.This study examined the cardiovascular responses to 2.5 cm H(,2)O PEEP in sixteen sodium pentobarbital anesthetized rabbits. During the control of the carotid baroreflex (common carotid occlusion, OCC) the relative reflex components were assessed by comparison of responses to PEEP before and after selective denervation of: (1) the aortic baroreceptors (aortic nerve section), (2) both afferent and efferent vagal fibers (vagotomy) and (3) cardiac sympathetic efferents (beta-adrenergic blockade with propranolol). Changes in cardiac performance during PEEP were estimated from changes in left ventricular stroke work (LVSW). Alterations in LVSW are dependent in part upon reflex mediated changes in myocardial contractility (inotropic influences) and in part upon reflex mediated changes in vascular resistance.Prior to vagotomy LVSW was decreased 34% by PEEP during OCC. Following vagotomy this decrease was only 25% and was unchanged by beta-blockade. Cardiac reflex inotropic responses, as measured by the first derivative of left ventricular pressure with respect to time (LVdP/dT), decreased by 16% with PEEP during OCC in the neurally intact, aortic denervated and vagotomized states. This decrease was absent following beta-blockade. TPR was unchanged with PEEP during OCC prior to vagotomy, but was increased 10% following vagotomy. This increase was unchanged by beta-blockade, which implies non-vagally mediated reflex and/or mechanical influences.These results demonstrate that during PEEP the decrease in contractility is reflexly mediated by non-vagal cardiopulmonary afferents, while vasomotor tone is in part reflexly depressed by vagally subserved cardiopulmonary afferents and may also be reflexly depressed by non-vagal afferents.

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