The Effects Of Pulse Pressure On The Carotid Baroreflex During Mild Exercise

Abstract

Previously the carotid baroreflex (CBR)-mean arterial pressure (MAP) reflex function curve was not altered during low intensity dynamic exercise, suggesting a lack of a central command signal to reset the CBR. However, pulse pressure (PP) or systolic blood pressure (SBP) increases even during mild exercise. PURPOSE The purpose of this study was to investigate the effect of an increase in PP on the CBR function during mild exercise. METHODS The CBR-SBP response curve was determined in five subjects at rest and during 20 min bouts of exercise at a steady-state heart rate (HR) of 90 beats. min−1. Acute changes in carotid sinus transmural pressure were evoked using 5 s pulses of neck pressure and neck suction ranging from +40 to −80 Torr. Beat-to-beat changes in HR and arterial blood pressure were continuously recorded throughout. RESULTS While MAP was not changed (P > 0.05) PP increased significantly from 62.6 ± 2.7 at rest to 79.6 ± 6.8 mmHg during the exercise bout (p < 0.05). Correspondingly, modeling of the CBR-SBP response curve indicated the CBR was shifted upward and rightward without any change in maximal sensitivity (rest vs. EX90; −0.50 ± 0.13 vs. −0.51 ± 0.08 mmHg/ mmHg) from rest to mild exercise, as figure 1. CONCLUSION These results suggest that CBR-SBP response curve is reset to functionally operate around increased SBP or PP elicited by mild dynamic exercise despite no change in CBR-MAP function. Supported in part by NIH Grant #HL-045547