Effect of coronary occlusion on arterial baroreflex control of heart rate.

To determine whether the baroreflex control of heart rate is altered during acute myocardial ischaemia, the baroreflex slope was measured at the control state, during coronary occlusion, and at the recovery phase in nine conscious dogs. The baroreflex slope was obtained by relating the R-R interval to the preceding systolic pressure during phenylephrine-induced transient hypertension. The baroreflex slope was reduced during coronary occlusion (18.8 +/- 3.8 ms.kPa-1, mean +/- SE) compared with that at the control state (41.4 +/- 6.0 ms.kPa-1). This reduction in the baroreflex slope during coronary occlusion was also present after propranolol, which suggests that this reduction of the slope during myocardial ischaemia is not due to a simultaneous increase in beta-adrenergic activity. These results suggest that the reflex originating from the cardiac receptors may modulate heart rate response to arterial baroreceptor stimulation.