Abstract
The purpose of this study was to elucidate the changes in systolic and diastolic time intervals which accrue along with increase of HR during a prolonged exercise.
Fifteen male collegiate distance runners performed bicycle ergometer exercise of 70% maximal oxygen intake for 60 minutes. Electrocardiogram, phonocardiogram, pulse wave using ear densitogram and its derivative were recorded throughout the exercise, and then HR, STI, DT (diastolic time) and QS2/DT were caluculated from the tracings.
The results obtained are as follows:
1. At the initial phase of the exercise, DT decreased markedly to result in rapid increase of QS2/DT. When HR was between 130-150 beats/min, however, the rate of decrease of QS2 was greater than that of DT, so QS2/DT showed a tendency to decrease. When HR was more than 150, QS2 reached a plateau but DT still continued to decrease, and QS2/DT turned to increase again.
2. LVET decreased slowly throughout the exercise, whereas PEP decreased rapidly within initial two minutes and kept a steady state thereafter. The change in QS2 after two minutes of exercise seemed to depend on LVET.
3. LVETi and QS2i showed a similar change as that in QS2/DT but the change in QS2i was less obvious than that in LVETi.
4. PEN and PEP/LVET decreased rapidly in the initial two minutes, thereafter they continued to increase more slowly with increase of HR until the end of exercise.
Conclusively, HR continued to increase monotonously during prolonged exercise of a constant intensity, while systolic and diastolic time intervals varied the directions and patterns of their changes during the exercise.
