Abstract

A study was conducted for further investigation of the mechanism of notch formation of heart rate (HR) in sudden strenuous exercise (SSE) and rapid increase in stroke volume (SV) right after SSE, which were the questions arised in the prior experiment. Six healthy male students volunteered for the study. A bicycle ergometer was prepared for SSE. The intensity and duration of SSE were 100 VO2max and 1 min, respectively. Warming-up consisting of 80 VO2max for 5 min preceeded SSE. The interval between SSE and warming-up varied from 5 to 30 min. The main results obtained were as follows: 1) Diastolic time (DT) temporarily elongated when a notch of HR was formed at the early stage of SSE. Warming-up prevented this formation. No notch was observed throughout total electromechanical systolic time (QS2), left ventricular ejection time (LVET) or preejection time (PEP). 2) DT was prolonged immediately after SSE, while LVET, PEPi (PEP index, Weisslers equation) were shortened. PEP/LVET did not change in the initial stage of the recovery period, while electrical systolic time (QT) and QS2 shortened and QT/QS2 increased temporarily. These results suggest the following conclusions: 1) Notch formation observed in heart rate is due to the temporary extension of DT at the early stage of SSE. 2) Decrease in afterload may be the main cause for the rapid increase in stroke volume after SSE, though other factors such as increase in preload, myocardial contractility and sympathetic tone should also be considered. Verf.-Referat