A study was conducted to examine the recovery of vagal activity after strenuous exercise based on changes in the magnitude of respiratory cardiac cycle variability, changes in the phase of this variability and the mechanism of the change. Six healthy male university students were studied for 5 h after exhaustive treadmill running. For cardiac cycle (RR) and blood pressure, the magnitude of respiratory variability and phase difference between respira-tory variability and respiration were measured. Respiratory period and tidal volume were maintained at 6 s and 21, respectively.
1. The amplitude of respiratory RR variability decreased markedly after exercise and returned almost to normal after 2 h of recrvery. The phase of RR delayed with exercise, proceeded rapidly 2 h after exercise and progressively after that.
2. The amplitude and phase of respiratory systolic blood pressure variability were almost stable before and after exercise.
Based on these results, we conclude that vagal activity inhibited by strenuous exercise recovers about 2 h after the end of exercise. The delay in the phase of respiratory cardiac cycle variability with exercise may reflect inhibition of vagal activity.

The relationship between arterial blood pressure and accelerated plethysmogram (APG) obtained by differentiating two times digital plethysmogram was studied in five healthy male university students. Finger arterial blood pressure was found to change by inflating the cuff of a sphygmomanometer placed on the upper arm followed by gradual deflation. APG and blood pressure were analyzed in the beat by beat mode. Room temperature was maintained at 23-24°C.
The following results were obtained :
1) Component“a”of APG became higher, and“b”and“e”components became increased with systolic blood pressure (SBP) .
2) Component“a”of APG decreased, as did also“b”and“e”components with increase in diastolic blood pressure (DBP) and arteriolar elasticity.
3) The two mechanisms for increase in SBP were increase in blood volume, and increase in peripheral resistance. The wave pattern of APG (A-G) changed from G to A by the former, and A to G by the latter.
These findings clearly show the relationship between APG and arterial blood pressure depend on the particular mechanism involved. The simultaneous mesurement of APG and blood pressure may serve as a useful means for measuring peripheral hemodynamics.

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.

This study was undertaken to clarify the influence of respiratory blood pressure variability upon the relationship between respiratory period and respiratory cardiac cycle variability. In 4 healthy male university students respiratory period was varied over the range of 6-20 sec while tidal volume was maintained constant (21) and in 5 other male students tidal volume was varied over the range of 1.0-2.5l while respiratory period was maintained constant (6 sec) . For cardiac cycle (RR) and systolic and diastolic blood pressure (SBP and DBP), amplitude of respiratory variability and phase difference between respiratory variability and respiration were measured.
1. Patterns of change of amplitude of RR and of SBP were similar when respiratory period was changed.
2. When respiratory period was short (6sec), RR was nearly in phase with SBP. However, as respiratory period increased, the phases of RR and SBP had a tendency to proceed, with the tendency being more pronounced in the latter. Thus, when respiratory period was prolonged (20 sec), SBP led RR.
3. Phase relationship between respiratory SBP variability and respiration did not change when tidal volume was changed.
4. Respiratory DBP variability became more marked as respiratory period increased, and showed more marked phase shift than did respiratory SBP variability. Therefore, of those parameters DBP occurred earlier.
Based on these results, it is concluded that respiratory RR variability is closely related to respiratory SBP variability when respiratory period is changed, but that the phase difference between RR and SBP reflects the effect of pulmonary stretch reflex which is dependent on respiratory period.

This study was designed to evaluate the effect of exercise duration on the relation between sympathetic and adrenomedullary activities. Six trained subjects completed the following two exercise protocols ; six 2-min exercise sessions at 100% maximal O₂uptake (VO₂max) interspersed with 10-min recovery periods, and three 10-min exercise sessions at 80%VO₂max interspersed with 10-min recovery periods. Plasma noradrenaline (NA), plasma adrenaline (A), NA/A ratio (NA/A), heart rate (HR), coefficient of variation of R-R intervals (CVRR) and blood lactate (La) were measured. With repetition of exercise sessions in both protocols, HR, NA and A gradually increased. CVRR rapidly decreased at the first exercise session and remained unchanged thereafter. NA/A increased by the first exercise session, but decreased by the following exercise sessions. NA in the second exercise session at 100%VO₂max was significantly lower than that in the first. We conclude that, at the beginning of exercise, the increase of sympathetic activity is more dominant than that of adrenomedullary activity, whereas, with prolongation of exercise duration, the increase of adrenomedullary activity becomes more dominant than that of sympathetic activity,

Using near-infrared spectroscopy, we monitored changes of oxygenated hemoglobin and myoglobin contents [oxy (Hb+Mb) ], deoxygenated hemoglobin and myoglobin contents [deoxy (Hb+Mb) ], and total hemoglobin and myoglobin contents [total (Hb+Mb) ] of the thigh muscle at rest and during incremental bicycle exercise and recovery in 10 healthy male volnuteers. Gas exchange parameters were also measured in breath-by-breath mode.
The following results were obtained :
1) During low-intensity exercise (216 kpm/min), oxy (Hb+Mb) increased, while deoxy (Hb+Mb) and total (Hb+Mb) decreased. These changes are thought to reflect an increase in arterial blood flow to the exercising muscle and an increase in venous return.
2) During high-intensity exercise (above 972 kpm/min), oxy (Hb+Mb) decreased, while deoxy (Hb+Mb) increased. These findings probably reflect increased O₂extraction.
3) Upon cessation of exercise, oxy (Hb+Mb) and total (Hb+Mb) increased, and deoxy (Hb+Mb) decreased abruptly. These changes probably reflect post-exercise hyperemia with decreased O₂extraction.
4) Oxy (Hb+Mb) level at ventilatory threshold (VT) was the same as or higher than that of resting condition, indicating that VT occurs when the level of O₂in the vessels of the thigh muscle is relatively high.
5) Spontaneous fluctuation of oxy (Hb+Mb) with frequency of 7-10 cycles/min was observed. This fluctuation was more marked during exercise than during rest or recovery.
These findings suggest that the influence of increased blood flow and venous return on oxy (Hb+Mb), deoxy (Hb+Mb) and total (Hb+Mb) are greater than that of O₂extraction during low intensity exercise, whereas the influence of O₂extraction increases with exercise intensity.
Near-infrared spectroscopy provides valuable information with regard to O₂transport and O₂extraction in the exercising muscle.

Amplitude and phase response of ventilation (V_E), carbon dioxide output (VCO₂) and oxygen uptake (VO₂) during sinusoidally varying work load for periods (T) of 1-16 min were studied in six healthy men. The relationships between these parameters and aerobic capacity (VO₂max, ATVO₂) were also examined. The results and conclusions obtained were as follows:
(1) The relationship between the period (T) of exercise and amplitude response of VO₂, VCO₂ and V_E was well described by first-order exponential models. However, the relationship between the period of exercise and the phase shift (phase responses of VO₂, VCO₂, and V_E) was better described by complex models comprising a first-order exponential function and a linear equation. This can be explained by Karpman's threshold theory.
(2) High negative correlations were observed between the steady-state amplitude (A) of phase response or the time constants (r) of amplitude response and VO₂max, and ATVO₂. Significantly high negative correlations for all gas exchange parameters may be more rapid in individuals with greater aerobic capacity.
(3) A close relationship between the response of VCO₂ and V_E was demonstrated by a higher correlation coefficient than that between VO₂ and VCO₂ or between VO₂ and V_E. This can be partly, but not completely, explained by the cardiodynamic theory.

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.

To study the effects of prolonged kendo practice in a hot environment on cardiovascular function, certain hemodynamic parameters were measured in 5 male college kendo fencers before and after 1 hour of kendo practice performed at a dry bulb temperature of 30.4t and wet bulb temperature of 26.2°C After kendo practice, body weight was significantly decreased and both hematocrit and blood viscosity were significantly increased. The left ventricular end-diastolic dimension and the left atrial dimension, measured by echocardiography, were significantly reduced after kendo practice, and stroke volume, ejection fraction, and fractional shortening were also significantly decreased after practice. The same fencers were subjected to lower body negative pressure testing designed to reduce the left ventricular end-diastolic dimension to the same degree as kendo practice, and comparable decreases in stroke volume, ejection fraction, and fractional shortening were observed. The ratio of end-systolic wall stress to end-systolic volume index was significantly increased during both kendo practice and lower body negative pressure testing. We conclude that prolonged kendo practice in a hot environment impairs cardiac pump function by reducing preload in parallel with the decrease in venous return, that myocardial contractility may not deteriorate despite marked hemoconcentration, and that fluid intake during practice may prevent deterioration of cardiovascular function.

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.