SYMPATHETIC NERVE ACTIVITY CONTROL OF BLOOD PRESSURE DURING RECOVERY FROM DYNAMIC EXERCISE

Abstract

Mean arterial pressure (MAP) decreases rapidly during inactive recovery from dynamic exercise. We hypothesized that this decrease is accompanied by a parallel decrease in sympathetic nerve activity (SNA), which is mediated, in part, by withdrawal of the muscle metaboreflex. METHODS 9 subjects were studied (5 males; 4 females). SNA (microneurography, n=9), MAP (femoral catheter, n=8), oxygen uptake (VO2) and heart rate (ECG) were measured during baseline, 5 minutes of arm ergometry at 50% of their arm maximal workload, and 5 minutes of inactive recovery. In addition, 5 subjects repeated the procedure with arm cuff occlusion of 90 mmHg applied at exercise termination to trap metabolites and maintain activation of the muscle metaboreceptors. Data are reported during the first 30 seconds of recovery (R1) and during minute 2 (R2). Mean ± SE are presented. RESULTS SNA increased to 240±38% of baseline during exercise (p < 0.01), and decreased to 184±35% during the first 30 sec of recovery (R1) and to 160±38% after 2 min of recovery (R2). R1 and R2 were significantly less than exercise (p = 0.003). Recovery with cuffs resulted in a maintenance of SNA during R1 (p = 0.09) and R2 (p = 0.006) compared to no occlusion. Similarly, MAP decreased 14±2 at R1 and 17±2 at R2 (p < 0.001), and decreased only 5±1 and 6±1 with cuffs. CONCLUSION These data support our hypothesis that rapid decreases in MAP during recovery from exercise are associated with parallel decreases in SNA. Moreover, this response appears to be importantly mediated by withdrawal of the muscle metaboreflex. Supported by NASA grant NAG9–1262.