Differential long‐term cardiovascular compensations to sustained activation of carotid baroreceptor afferents

Abstract

Prolonged baroreflex activation (PBA) by electrical stimulation of the carotid sinuses produces sustained reductions in mean arterial pressure (MAP) and sympathetic activity. This technique bypasses mechanotransduction at the level of the baroreceptors producing controlled electrical activation of baroreceptor afferents. We used this technique to determine whether there are compensations that diminish the chronic blood pressure lowering effects of the baroreflex during activation with continuous trains of impulses. This was studied in 4 normotensive dogs using 24 hour recordings of MAP and heart rate (HR). Control values for MAP and HR were 93±4 mmHg and 54±2 bpm, respectively. Values for MAP after 1, 2 and 3 weeks of PBA were 64±1, 72±1, and 72±1 mmHg, respectively; the corresponding values for HR were 44±2, 44±1, and 44±1 bpm. Thus, during week 2, there was ~ a 30% reduction in the blood pressure lowering response to PBA, with no effect on PBA induced bradycardia. MAP did return to control levels after cessation of PBA, but only after a modest increase above control during the initial 7 days following discontinuation of PBA. These findings indicate that while PBA produces substantial sustained reductions in MAP, slowly developing central and/or peripheral mechanisms act differentially to partially restore MAP towards control levels without attenuating reflex‐induced decreases in HR. (HL‐51971).