STUDY OBJECTIVES: Exercise training has been shown to favorably affect the prognosis after acute myocardial infarction (AMI), but the mechanisms of such favorable effects remain speculative. The aim of this study was to determine whether exercise training improves baroreflex control of heart rate and muscle sympathetic nerve activity (MSNA) in patients with AMI. DESIGN: Prospective randomized clinical study. PARTICIPANTS: Thirty patients with an uncomplicated AMI were randomized into trained or untrained groups. Arterial BP, heart rate, and MSNA were measured at rest, and during baroreceptor stimulation (phenylephrine infusion) and baroreceptor deactivation (nitroprusside infusion). These measurements were performed at baseline and after 4 weeks of exercise training. MEASUREMENTS AND RESULTS: Peak oxygen uptake increased significantly (12.3 +/- 10.7% (mean +/- SD)) with exercise training. Resting MSNA reduced from 34 +/- 12 to 27 +/- 8 bursts/min in the trained group but not in the untrained group. Arterial baroreflex sensitivity (BRS) (from 8.9 +/- 3.0 to 10.3 +/- 3.0 ms/mmHg, p < 0.05) and MSNA response to baroreceptor stimulation (change of integrated MSNA from -47 +/- 23 to -70 +/- 21%, p < 0.01) improved significantly in the trained group, but not in the untrained group. Despite baroreceptor deactivation improving MSNA response in both groups, there was no significant difference between the two groups. CONCLUSIONS: Exercise training increased arterial BRS and decreased sympathetic nerve traffic after AMI, which indicate that the sympathoinhibitory effect of exercise training may, at least in part, contribute to the beneficial effect of exercise training in patients with AMI.

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