Chest

Chest

Volume 101, Issue 5, Supplement, May 1992, Pages 299S-303S
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Autonomic Nervous System Adaptations to Short-term Exercise Training

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Signs of sympathetic hyperactivity and low parasympathetic activity have been found during the acute and recovery phases of myocardial infarction and have been associated with an increased risk of cardiac mortality. Beneficial effects of physical training have been recently reported in post-myocardial infarction patients. We tested the hypothesis that physical training would be effective in improving the autonomic balance by studying 22 patients with a first and recent myocardial infarction who were randomly assigned to enter or not enter a 4-week in-hospital physical training program. Spectral indices of heart rate variability were analyzed at rest and during 70° head-up tilt before and after the index training, not training period. As expected, physical training induced a significant increase in exercise duration (13.7 ± 0.8 vs 17.1 ± 0.1 min, p<0.001) and in the anaerobic threshold (9.5 ± 0.7 vs 12.0 ± 1.0 min, p<0.02) in trained patients, while no changes were observed in the untrained group. At entry, in both groups, spectral profile of heart rate variability was characterized by a predominant LF component and a smaller HF component with no further modification after head-up tilt. After 4 weeks, in resting conditions, no significant changes in spectral components were observed in both trained and untrained patients. After physical training, head-up tilt produced significant modifications in spectral profile with an increase in the LF component (84 ± 3 vs 69 ± 5 nu, p<0.01) and a decrease in the HF component (7 ± 1 vs 19 ± 4 nu, p<0.05) in trained patients, while no changes were observed in the untrained patients. Our data suggest that in postmyocardial infarction patients, 4 weeks of physical training may induce an improvement in the autonomic balance with a restoration toward normal in the reflex activity of the system.

Section snippets

Patients

The study population consisted of 22 male patients suffering from a first and recent myocardial infarction who were randomly assigned to enter or not enter a supervised physical training program.

Patients were excluded from randomization if they were older than 70 years, had arterial blood pressure of more than 160/90 mm Hg, had insulin-dependent diabetes, had atrial fibrillation or abnormal sinus node function, or had exercise-induced myocardial ischemia. All patients were in NYHA I class.

The

Exercise Stress Testing

At baseline, the 2 groups did not differ significantly in all ergometric parameters (Table 1).

In the untrained group, no difference has been observed between the first and second exercise stress test in the duration of exercise (14.6 ± 0.6 vs 14.7 ± 0.7 min) in heart rate at rest (75 ± 4.2 vs 74 ± 3.3 beats x min − 1) and at the same work load (155 ± 6.4 vs 148 ± 5.4 beats X min −1). The double product at the same work load (28,520 ± 1,534 vs 27,800 ± 1,412 mm Hg x beats x min − 1) and the

DISCUSSION

Our results support the concept of an impaired autonomic balance after myocardial infarction and do not show any spontaneous or time-related improvement between 4 and 8 weeks after the acute event. Four weeks of physical training did not induce any significant change of the autonomic balance in the resting state. When the system was placed under “stressful” condition, ie, when a reflex response was evoked by orthostatic stress, both the parasympathetic and the sympathetic limb showed a wider

Autonomic Nervous System and Myocardial Infarction

Signs of enhanced sympathetic activity and reduced parasympathetic cardiac outflow have been found in most patients with acute myocardial infarction17 and do persist in the postinfarction period.

Several mechanisms may be responsible for the disordered autonomic function after MI. The destruction, secondary to MI, of vagal and sympathetic endings, may alter neural feedback to the higher centers, resulting in an increase in sympathetic and/or reduced vagal discharge.20, 21, 22, 23 Alternatively,

Autonomic Nervous System and Exercise

The data quoted above focus on the role of impaired autonomic balance on mortality after myocardial infarction. Therefore, it follows that interventions effective in favoring its return toward normal values would be beneficial on cardiac mortality in post-MI patients by diminishing the vulnerability to life-threatening arrhythmias and sudden cardiac death.

In post-MI patients, physical training as part of a comprehensive rehabilitation program has been shown to improve16,17 long-term prognosis.

REFERENCES (41)

  • McReaveyD et al.

    Cardiac parasympathetic activity during the early hours of acute myocardial infarction.

    Br Heart J

    (1989)
  • ComePC et al.

    Nitroglycerin-induced severe hypotension and bradycardia in patients with acute myocardial infarction.

    Circulation

    (1976)
  • ImaizumiT et al.

    Impaired baroreflex control of vascular resistance and heart rate in acute myocardial infarction.

    Br Heart J

    (1984)
  • OsculatiG et al.

    Early alterations of the baroreceptor control of heart rate in patients with acute myocardial infarction.

    Circulation

    (1990)
  • LownB et al.

    Neural activity and ventricular fibrillation.

    N Engl J Med

    (1976)
  • CorrPB et al.

    Mechanisms controlling cardiac autonomic function and their relation to arrhythmogenesis.

  • SchwartzPJ et al.

    Autonomic mechanisms and sudden death: new insights from analysis of baroreceptor reflexes in conscious dogs with and without myocardial infarction.

    Circulation

    (1988)
  • La RovereMT et al.

    Baroreflex sensitivity, clinical correlates, and cardiovascular mortality among patients with a first myocardial infarction.

    Circulation

    (1988)
  • FarrellTG et al.

    Baroreflex sensitivity and electrophysiological correlates in patients after acute myocardial infarction.

    Circulation

    (1991)
  • OldridgeNB et al.

    Cardiac rehabilitation after myocardial infarction.

    JAMA

    (1988)

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    Copyright © 1992 The American College of Chest Physicians. Published by Elsevier Inc. All rights reserved.