LATENCY OF PEAK TACHYCARDIA DURING GRADED HYPOTENSION

Abstract

1237 The aim of this study was to test the hypothesis that the latency of the reflex change in heart rate (HR) was related to the magnitude of the change in arterial blood pressure (ABP). Change in mean ABP (ΔMAP, monitored by intra-radial arterial catheter) was elicited by bolus injection of nitroprusside (NT) and phenylephrine (PE) in 6 normotensive healthy young subjects. The rate of ΔMAP appeared to be greater (P<0.01) during hypotension than during hypertension, whereas the ratio ofΔHR/ΔMAP was not statistically different between the drugs (see table).TableDuring PE induced hypertensive stimuli the bradycardiac latency was minimum. However, the tachycardiac latency, i.e., the time lag between the peak decrease in MAP and the peak tachycardia during NT induced hypotensive stimulation, was significantly (P<0.01) associated with ΔMAP, indicating the contribution of cardiac sympathetic activation. Furthermore, the delta tachycardia (the difference between tachycardia corresponding to the peak decrease in MAP and the peak tachycardia) was positively related(P<0.04) to the latency. We concluded that cardiac sympathetic mediated tachycardiac latency during graded hypotensive stimuli was does-response related.