RESUMEN
A study was undertaken to elucidate the mechanism responsible for the specific changes in systolic time intervals (STIs), diastolic time (DT) and the ratio of total electromechanical systole to DT (QS<SUB>2</SUB>/DT), which were observed during prolonged exercise<SUP>17, 19)</SUP> Sixteen healthy male students performed short-term incremental maximal exercise and 40-min submaximal exercise with a work load requiring 65% of maximal oxygen consumption on a bicycle ergo-meter, Heart rate (HR), stroke volume (SV), blood pressure (BP), STIs and DT were calculated from electrocardiogram, phonocardiogram, derivative of ear densitogram, impedance cardiogram and finger arterial pressure wave.<BR>1) During the short-term exercise, STIs, DT and QS<SUB>2</SUB>/DT changed rectilinearly in accordance with increased HR, whereas they changed in a specific zigzag pattern during the prolonged exercise.<BR>2) During the prolonged exercise, SV and BP were lower than those during the short-term exercise, except for SV between 1 and 2 min after the start of the exercise. From 2 min onwards, left ventricular ejection time (LVET), QS<SUB>2</SUB> and QS<SUB>2</SUB>/DT became smaller than those during the short-term exercise.<BR>3) Differences between the measured values of LVET, pre-ejection period (PEP) and PEP/LVET and those predicted by multiple regression equations during the prolonged exercise were smaller than those during the short-term exercise.<BR>From these findings, it was concluded that the specific changes observed in STIs, DT and QS<SUB>2</SUB>/DT during prolonged exercise are produced by decrease of SV and BP in the early stage, and probably influenced by a decrease in myocardial contractility in the late stage.
RESUMEN
A study was undertaken to determine whether the specific change in the ratio of systolic to diastolic time (QS<SUB>2</SUB>/DT) observed during prolonged exercise<SUP>17)</SUP> is dependent on HR or elapsed time, and also to elucidate the possible relationship between change in QS<SUB>2</SUB>/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.<BR>In the time course of QS<SUB>2</SUB>/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 QS<SUB>2</SUB>, DT, QS<SUB>2</SUB>/DT and other parameters were similar in the two groups. However, the absolute values of the parameters differed. QS<SUB>2</SUB>, left ventricular ejection time (LVET) and QS<SUB>2</SUB>/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.<BR>From these findings, it was concluded that the specific change seen in QS<SUB>2</SUB>/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.
RESUMEN
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.<BR>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 QS<SUB>2</SUB>/DT were caluculated from the tracings.<BR>The results obtained are as follows:<BR>1. At the initial phase of the exercise, DT decreased markedly to result in rapid increase of QS<SUB>2</SUB>/DT. When HR was between 130-150 beats/min, however, the rate of decrease of QS<SUB>2</SUB> was greater than that of DT, so QS<SUB>2</SUB>/DT showed a tendency to decrease. When HR was more than 150, QS<SUB>2</SUB> reached a plateau but DT still continued to decrease, and QS<SUB>2</SUB>/DT turned to increase again.<BR>2. LVET decreased slowly throughout the exercise, whereas PEP decreased rapidly within initial two minutes and kept a steady state thereafter. The change in QS<SUB>2</SUB> after two minutes of exercise seemed to depend on LVET.<BR>3. LVETi and QS<SUB>2</SUB>i showed a similar change as that in QS<SUB>2</SUB>/DT but the change in QS<SUB>2</SUB>i was less obvious than that in LVETi.<BR>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.<BR>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.