Abstract
It has been assumed that ventricular excitation rhythm follows atrial excitation rhythm during dynamic exercise in humans. To examine whether this assumption is true, we measured electrocardiogram (ECG) and analyzed the beat-to-beat changes in PP, PR and RR intervals before, during, and after dynamic exercise in 11 sedentary and 9 trained subjects. Stair-stepping exercise was performed for 10 min in the upright posture. In sedentary subjects, the mean value of RR intervals before exercise was the same as that of PP interval (650±65ms) and the mean PR interval was 163±19ms. RR interval decreased during exercise to 378±21ms similar to PP interval, and PR interval also decreased to 145±11ms. Although the standard deviation (SD) of RR intervals before exercise coincided with SD of PP intervals, it became smaller during exercise than SD of PP intervals. On the contrary, SD of PR intervals was increased during exercise from 8.6±2.3ms to 9.0±3.4ms. The similar results were observed in the trained subjects. These findings indicated that beat-to-beat ventricular excitation rhythm does not simply follow atrial excitation rhythm during dynamic exercise, although the average value of RR intervals over a certain period is always the same as that of PP intervals. We conclude that ventricular excitation rhythm seems to be more stable during exercise than atrial excitation rhythm, because PR interval changed during exercise so as to cancel an alteration in the preceding PP interval in humans. [Jpn J Physiol 54 Suppl:S95 (2004)]
