Baroreflex responsiveness is maintained during isometric exercise in humans

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Abstract
The simultaneous rise in heart rate and arterial pressure during isometric handgrip exercise suggests that arterial baroreflex control may be altered. We applied incremental intensities of neck suction and pressure to nine healthy young men to alter carotid sinus transmural pressure. Carotid stimuli were delivered during 1) supine control, 2) “anticipation” of beginning exercise, and 3) handgrip (20% of maximum voluntary contraction). Anticipation was a quiet period, immediately preceding the beginning of handgrip, when no muscular work was being performed. Compared with control, the R-R interval prolongation and mean arterial pressure decline provoked by carotid stimuli were decreased during the anticipation period. These data suggest that influences from higher central neural locations may alter baroreflex function. Furthermore, we derived stimulus-response curves relating carotid sinus transmural pressure to changes in R-R interval and mean arterial pressure. These curves were shifted during handgrip; however, calculated regression slopes were not changed from control. The data indicate that isometric handgrip exercise has a specific influence on human carotid baroreflex control of arterial pressure and heart period: baroreflex function curves are shifted rightward during handgrip, whereas baroreflex sensitivity is unchanged. Furthermore, central neural influences may be partially involved in these alterations.