CARDIORESPIRATORY REFLEX CONTROL IN RATS WITH LEFT-VENTRICULAR DYSFUNCTION

Patients with heart failure exhibit a neurohumoral excitatory state an d abnormal baroreflex control of the cardiovascular system. We determi ned whether arterial baroreflexes are impaired during left ventricular dysfunction (LVD) caused by chronic myocardial infarction in the abse nce of congestive heart failure and whether abnormal central mechanism s contribute to this impairment. Baroreceptors were stimulated in anes thetized rats with and without LVD by increasing arterial pressure wit h phenylephrine. Lumbar sympathetic nerve and phrenic nerve activity a s well as heart rate were recorded. Rats were divided into different g roups based on infarct size. Rats with moderate LVD showed impaired ba roreflex control of sympathetic, ventilatory, and heart rate responses . Baroreflex gains were inversely related to the size of the infarct. The central gain for sympathetic nerve activity, obtained by using ele ctrical stimulation of the aortic depressor nerve, also was impaired. Baroreflex control of the cardiorespiratory system is thus impaired in rats with moderate LVD in the absence of congestive heart failure. Th e attenuated baroreflexes are likely due to abnormal afferent mechanis ms, although central mechanisms contribute to the impaired barosympath etic reflex.