Baroreflex control of heart rate during cardiac sympathectomy by epidural anesthesia in lightly anesthetized humans.
To evaluate the effects of acute sympathetic denervation on the baroreflex control of heart rate, baroreflex sensitivities were compared in lightly anesthetized humans who had either cervical (N = 20) or lumbar epidural anesthesia (N = 18), or neither (N = 18). Levels of anesthesia during cervical block using 10 ml of 2% mepivacaine without epinephrine were C3-T7 and T7-S1 during lumbar epidural block. Baroreflex sensitivity was assessed with a pressor test using phenylephrine infusion to increase systolic blood pressure by 60 mm Hg within 2 min. There were no statistically significant differences in the baroreflex sensitivities in the absence of epidural block and during lumbar epidural block, the slopes of the regression line (in msec of RR interval change per mm Hg increase in systolic blood pressure, i.e., msec/mm Hg) relating systolic pressure and the succeeding pulse interval being 3.8 +/- 1.4 (mean +/- SD) and 3.7 +/- 1.7, respectively. The mean slope during cervical block, 1.1 +/- 1.2 msec/mm Hg, was significantly different from the slopes observed in the absence of epidural block and during lumbar epidural block (P less than 0.01). The results suggest that cardiac sympathectomy induced by epidural anesthesia can suppress partially baroreceptor function by interrupting sympathetic efferent fibers innervating the heart during high levels of epidural anesthesia, but that lumbar sympathectomy during epidural anesthesia is unlikely to affect baroreceptor activity.
D000328:Adult; D000767:Anesthesia, Epidural; D000768:Anesthesia, General; D001794:Blood Pressure / Q000187:drug effects; D006321:Heart / Q000294:innervation*; D006339:Heart Rate / Q000187:drug effects*; D006801:Humans; D008161:Lumbosacral Region; D008875:Middle Aged; D009333:Neck; D010656:Phenylephrine / Q000494:pharmacology; D011311:Pressoreceptors / Q000187:drug effects*; D012018:Reflex / Q000187:drug effects; D013564:Sympathetic Nervous System / Q000187:drug effects
D010656:Phenylephrine