A study was conducted to elucidate the changes in circulatory responses to sudden strenuous exercise (SSE) using beat-by-beat analysis of heart rate (HR), stroke volume (SV) and blood pressure (BP) . The effects of warming-up on these responses were also studied.
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 of 80% VO₂max for 5 min followed by SSE. The interval between SSE and warming-up varied from 5 to 30 min. A control experiment was also performed without warming-up.
The main results obtained were as follows :
1) BP decreased in the initial stage of SSE, followed by a steep increase. This temporary drop in BP was prevented by warming-up. This might contribute to the prevention of myocardial ischemia which is occasionally observed in the initial stage of SSE without warming-up.
2) Time constants of HR and SV during SSE were shortened by warming-up with long intervals, while the time constant of BP was shortened when the interval was short.
3) The recovery response of each parameter was accelerated by warming-up, but the effect of warming-up had almost disappeared after a 30 min interval.
These results suggest the following conclusions :
Warming-up accelerates the up-stroke and recovery of circulatory responses to SSE, but these effects of warming-up are strongly influenced by interval time. In particular, the effect of recovery acceleration is almost abolished by a 30 min interval.

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.

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. A control experiment was also conducted without warming-up.
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, Weissler's equation) were shortened. PEP/LVET did not change in the initial stage of the recovery period, while electrical systolic time (QT) and QS₂ shortend 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.

This study was undertaken to clarify the relationship between respiratory period and respiratory arrhythmia. Five healthy male university students voluntarily changed the respiratory period over a range of 3-30 seconds while maintaining tidal volume constant (; 21) . Maximum and minimum cardiac cycles (RRmax and RRmin) and amplitude of cardiac cycle variability (ΔRR), the difference between RRmax and RRmin, were measured from electrocardiogram and respiratory curve.
1. Amplitude of cardiac cycle variability was small for shorter respiratory periods and increased with respiratory period, attaining maximum at respiratory periods of 8-14 seconds followed by decrease at longer respiratory periods.
2. The time from the onset of inspiration to the minimum cardiac cycle was the same for respiratory periods of 8-14 seconds (about 3.6 seconds) .
3. Phase difference between cardiac cycle variability and respiration was determined at each respiratory period. When the minimum or maximum cardiac cycle coincided with the onset of inspiration, this situation being defined as 0°, RRmin was delayed by 180°, 90°, and 0° at respiratory periods of 2.3, 14.4, and 26.5 seconds, respectively and by 360°, 270°, and 180° at respiratory periods of 2.7, 15.0, and 27.3 seconds, respectively.
Based on these results, respiratory arrhythmia is concluded to be quite stable at respiratory periods of 8-14 seconds. At short respiratory periods, tachycardia was found to occur during inspiration and bradycardia during expiration. During long respiratory periods, bradycardia was noted during inspiration and tachycardia during expiration.

To investigate the responses of heart rate and plasma catecholamines to exercise at various intensities, seven healthy adult males performed 6-min bouts of cycling exercise at 30, 50, 70 and 90% of maximal oxygen consumption (VO₂max) . Heart rate (HR), plasma noradrenaline (NA), plasma adrenaline (A), blood lactate (La) and coefficient of variation of R-R intervals (CVRR) were determined i n each case.
The following results were obtained:
1) CVRR showed a sharp decline to the extent of 50%VO₂max, then fell more slightly for heavier exercise.
2) NA and A significantly increased from resting value at 50%VO₂max, and followed by further increase with exercise intensity. NA/A increasd in proportion to exercise intensity.
3) The results of multiple regression analysis of HR (dependent variable) and NA, A and CVRR (independent variables) indicated the greatest standardized partial regression coefficient for CVRR in the case of low intensity exercise, and for NA with high intensity exercise.
4) La increased abruptly at 70%VO₂max, whereas NA and A rose drastically at 90%VO₂max.
The conclusion based on these results is as follows: HR is mainly influenced by change in parasympathetic tone to the extent of 50%VO₂max, whereas sympathetic and adrenomedullary activity are the main factors controlling HR in heavier exercise. Within the submaximal level of exercise, sympathetic activity increases more markedly than that of adrenomedullary activity. Abrupt increase in La may be independent of catecholamines.