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 performed to investigate the validity of the derivative of the ear densitogram for measurement of left ventricular ejection time (LVET) .<BR>Nine male college students performed bicycle exercise at an initial work load of 0 watt (W), subsequently increasing by 60W every 3 min up to 240W. The LVET derived from the derivative of the ear densitogram (LVETe) was compared with that derived from the carotid pulse wave (LVETc) obtained at the same time.<BR>The results were as follows:<BR>1. There was a high correlation coefficient, r=0.987 (P<0.01), between LVETe and LVETc.<BR>2. At rest, LVETe showed a tendency to coincide with LVETc. In contrast, LVETe became longer than LVETc during exercise, and the higher HR became, the larger the difference between the two.<BR>3. In the individual regression equations between LVETe and LVETc, the slopes and the intercepts were nearly identical.<BR>4. The following equation was proposed for the correction of LVETe during exercise. LVET=-0.147⋅HR+ LVETe+ 8.3<BR>From these findings, it was concluded that the validity of the derivative of the ear densitogram for estimation of LVET is sufficiently high. LVETe at rest is valid for the estimation of LVET without correction. During exercise, however, LVETe shows a tendency to be longer than LVETc, and thus it is desirable to correct LVETe using the above equation.
RESUMEN
The purpose of this study was to investigate the effects of contraction force and the pooled blood volume in the calf on the pumping action of calf muscle contraction. Calf blood volume was controlled by lower body negative pressure (LBNP) and isometric contraction of calf extensor muscle was performed using a handmade dynamometer in recumbent position. The relative volume changes (ΔV/V%) of calf were determined using rubber straingage, when isometric contractions (5, 10, 20, 40 and 60 kg) of the calf muscle were repeated under LBNP of 0, -20, -40, and -60 mmHg.<BR>During resting condition, Δ V/V was increased by 1.04% under -20 mmHg LBNP, 1.88% under -40 mmHg, and 2.54% under -60 mmHg. These increases of ΔV/V were due to the increased blood pooling in the calf. It was shown that the increased blood volume was almost expelled by several bouts of muscle contractions of proper force. The optimum force of contractions for expelling pooled blood was 20 kg under -20mmHg LBNP, and 40 kg under -40 and -60 mmHg LBNP. And it was apparent that the effectiveness of muscle pump was accumulated with repeating contractions, arriving to a plateau after several bouts.<BR>It was shown that the effect of muscle pump in the given contraction force was more effective under the condition with more amount of blood contained in the calf, but the muscle pumping action by light contraction forces couldn't overcome the effect of severe LBNP.
RESUMEN
The purpose of this study was to investigate the effects of contraction force and the pooled blood volume in the calf on the pumping action of calf muscle contraction. Calf blood volume was controlled by lower body negative pressure (LBNP) and isometric contraction of calf extensor muscle was performed using a handmade dynamometer in recumbent position. The relative volume changes (ΔV/V%) of calf were determined using rubber straingage, when isometric contractions (5, 10, 20, 40 and 60 kg) of the calf muscle were repeated under LBNP of 0, -20, -40, and -60 mmHg.<BR>During resting condition, Δ V/V was increased by 1.04% under -20 mmHg LBNP, 1.88% under -40 mmHg, and 2.54% under -60 mmHg. These increases of ΔV/V were due to the increased blood pooling in the calf. It was shown that the increased blood volume was almost expelled by several bouts of muscle contractions of proper force. The optimum force of contractions for expelling pooled blood was 20 kg under -20mmHg LBNP, and 40 kg under -40 and -60 mmHg LBNP. And it was apparent that the effectiveness of muscle pump was accumulated with repeating contractions, arriving to a plateau after several bouts.<BR>It was shown that the effect of muscle pump in the given contraction force was more effective under the condition with more amount of blood contained in the calf, but the muscle pumping action by light contraction forces couldn't overcome the effect of severe LBNP.
RESUMEN
In order to evaluate the effect of muscle pump on blood circulation at the start and end of exercise, cardiac responses to pedaling exercise at 75 watt in the supine position were investigated under lower body negative pressure (LBNP) of -60mmHg. Six healthy male college students volunteered for subjects. Cardiac output (Q), stroke volume (SV), thoracic impedance (ZO) and heart rate (HR) were determined by using ensemble-averaged impedance cardiogram and ECG.<BR>The results obtained were as follows.<BR>1) By the initiation of exercise under LBNP, SV and Q promptly and more markedly increased and ZO decreased than the control experiment which were done under normal pressure. These changes were suggested to be caused by mobilization of previously pooled blood in the legs by muscle pump. Effects of muscle pump arrived to a plateau within about 30 sec after the start of exercise. And these effects were immediately disappeard by the cessation of exercise.<BR>2) By the release of LBNP during resting condition, the same changes were observed in SV, Q and ZO as in the start of exercise under LBNP. However HR decreased in the case while it increased in the case of exercise in LBNP. This difference in HR might be the result of the chronotropic effects by the exercise.<BR>3) In the very early phase of exercise in the control exercise, SV decreased and ZO increased. These changes were probably caused by superiority of chronotropic action by the exercise to increase in venous return in this position.<BR>These results led us to a conclusion that the effect of muscle pump appeares immediately by the start of the exercise and it arrives at plateau within about 30 sec. This effect is immediately disappeared by the cessation of exercise.
RESUMEN
The purpose of this investigation is to evaluate the effects of muscle pump by pedaling exercise on blood circulation and define its properties. Lower body pressurization device equipped with bicycle ergometer was used to provide negative pressure on the lower body of subjects in recumbent position. Seven healthy male collage students volunteered for subjects.<BR>Whole experiment for each subjects was divided into control stage (0 mmHg), -20, -40, and -60 mmHg LBNP (lower body negative pressure) stage. Preceeded by resting period, 25, 75, and 125 W exercise in experiment 1, 50 and 100 W exercise in experiment 2 were loaded using bicycle ergometer with revolution of 60 rpm during each stage. Following parameters were determined: HR, SV, Q, and blood pressure.<BR>The results obtained were as follows;<BR>(1) In resting condition, LBNP caused significant decrease in SV and Q in spite of marked compensatory increase in HR.<BR>(2) These effects of LBNP were cancelled in -20 mmHg or mostly cancelled in -40 and -60 mmHg by pedaling exercise of 50 W or more.<BR>(3) Effect of muscle pump by pedaling exercise is apparent in light exercise such as 25 or 50 W arriving to a plateau with more intensive load.<BR>(4) Muscle pump action by the same exercise condition is more effective under more severe LBNP.<BR>(5) Light exercise in LBNP caused decrease in HR, probably because of pressure reflex initiated by restoration of blood pressure.<BR>These results leed us to a conclusion that light pedaling exercise produces a powerful pumping action nearly enough to compensate the circulatory disturbance by strong LBNP.
RESUMEN
The purpose of this study is to evaluate the effects of muscle pump of pedaling exercise on blood circulation. Lower body pressurization device was used to provide negative pressure and positive pressure on the lower body of subjects in recumbent position. This device is also equipped with bicycle ergometer in it. Five healthy male college students volunteered for subjects.<BR>Whole experiment for each subject was divided into pre-control stage (0 mmHg), LBPP (lower body positive pressure) stage (+40mmHg), LBNP (lower body negative pressure) stage (-40 mmHg) and post-control stage (0 mrHg) . 50 (watt) exercise and 100 (watt) exercise preceded by resting period were loaded during each stage and following parameters were determined: ECG, phonocardiogram, carotic pulse wave, VO<SUB>2</SUB>, cardiac output, and blood pressure. Pre-ejection period index (PEPi), Left ventricular ejection time index (LVETi), PEP/LVET and stroke volume (SV) were calculated from the recorded data.<BR>Results suggested following conclusions:<BR>1) In rest condition, LBNP caused marked increase in HR, PEPi, and PEP/LVET and remarkable decrease in Q, SV, and LVETi. These findings indicate that LBNP affects venous return and exaggerates venous pooling in lower body.<BR>2) It was shown that muscle pump of pedaling exercise counteracts the effects of LBNP and the findings mentioned above were largely abolished by pedaling exercise of 100 (watt) .<BR>3) LBPP caused no apparent change in the studied parameters except blood pressure. Blood pressure increased by LBPP probably because of rising in total peripheral resistance.