Response of R wave amplitude to postural changes and to exercise. A study of healthy subjects and patients surviving acute myocardial infarction.

The effects of postural changes and bicycle ergometer exercise tests on R wave amplitude were studied in 10 sedentary and 21 physically active healthy men as well as in 158 male survivors of myocardial infarction. In the latter group recordings were made 6-8 weeks, 5 months and 12 months after the infarction, and also the effect of physical activity during the first post-infarction year on the R wave height responses was studied. At rest in the supine position the R wave amplitudes in the three groups studied were almost similar, but in the sitting position at rest and at the beginning of the exercise the R wave amplitudes were significantly higher in physically active healthy men than in sedentary healthy men or infarction patients. Physical training during the first post-infarction year induced only negligible changes in the R wave amplitude response to postural changes and exercise. The mechanisms which may underlie these different responses of R wave amplitude to postural changes and to exercise are discussed.