Preferential baroreflex control of left ventricular diastolic function at rest and during mild dynamic exercise.

Abstract

Carotid sinus hypotension elicits large baroreflex‐induced increases in peripheral resistance but has relatively little effect on left ventricular systolic function. However, baroreflex control over left ventricular relaxation is unknown and diastolic function can contribute importantly to overall cardiac performance, especially during periods of stress such as dynamic exercise. Therefore, we investigated the relative effects of bilateral carotid occlusion (BCO) on left ventricular systolic and diastolic function (±dP/dtmax/min) in conscious dogs at rest and during exercise (3.2 km/h). As expected, exercise caused a significant increase in heart rate (HR), +dP/dtmax, stroke volume (SV), and therefore cardiac output (CO) but also in total vascular conductance (TVC) and as a result arterial pressure (AP) remained unchanged. No significant change occurred in ‐dP/dtmin, thus ±dP/dtmax‐min ratio substantially increased. At rest and during mild dynamic exercise, BCO caused no significant change in CO and therefore the rise in AP was due to a significant decrease in TVC. BCO increased ‐dP/dtmin, with no change in +dP/dtmax, therefore ±dP/dtmax‐min ratio significantly decreased. We conclude that the increase in sympathetic activity to the heart elicited by carotid baroreceptor unloading preferentially improves left ventricular diastolic function. Supported by HL‐55473.