A study was undertaken to determine whether the specific change in the ratio of systolic to diastolic time (QS₂/DT) observed during prolonged exercise¹⁷⁾ is dependent on HR or elapsed time, and also to elucidate the possible relationship between change in QS₂/DT and distance-running performance. Twelve male distance runners were divided into two groups, a high- (HP Group) and a low-performance (LP Group) group, according to their 10, 000-meter running performance. They performed 60-min exercise on a bicycle ergometer at a work load controlled so as to keep the HR at 150 bpm. HR, systolic time intervals (STIs) and DT were calculated from electrocardiogram, phonocardiogram and the derivative of ear densitogram.
In the time course of QS₂/DT, two crests were formed at 2 and 15 min after the start of exercise, and also two troughs were formed at 10 and 20 min. Some of these troughs and crests formed even when HR was kept constant. Patterns of change in QS₂, DT, QS₂/DT and other parameters were similar in the two groups. However, the absolute values of the parameters differed. QS₂, left ventricular ejection time (LVET) and QS₂/DT in the HP Group were lower than those in the LP Group, whereas DT in the HP Group was longer than that in the LP Group.
From these findings, it was concluded that the specific change seen in QS₂/DT during prolonged exercise is dependent not on the HR level but on elapsed time. The changes in STIs and DT during prolonged exercise are thus influenced by the distance-running performance of the subjects.