Interrelationships Between Ventilatory And Circulatory Responses At The Onset Of Dynamic Exercise

Introduction
It is well-known that ventilation increases abruptly from the resting level within the first 20s at the start of dynamic
exercise (Phase I), while heart rate also increases suddenly at that time [1]. Nevertheless, little is known
about the interrelationship between ventilatory and circulatory responses during this initial stage of exercise. The
purpose of this study is, therefore, to elucidate the relationships between ventilatory and circulatory responses at the
onset of dynamic exercise in various kinds of groups.

Methods
Sedentary males; 13 elderly, 41 adults and 10 children, trained adults; 11 sprinters, and sedentary females; 7 adults,
participated in this study. Minute ventilation (VI), heart rate (HR) and mean blood pressure (MBP) were measured
continuously while subjects performed bilateral leg extension-flexion movements for 20s for about six times with light
weights around both ankles [2]. In order to normalize the data among the different subjects, relative changes were
calculated from resting values (0%) and steady state values (100%) which were the mean values of the last 30s during
the same exercise for 3min. We regarded the value of the relative change at 15s after the start of exercise as gain, and
the time for reaching half of the gain as the response time.

Results
VI and HR increased rapidly at the onset of exercise while BP transiently decreased and returned to the resting level
during the first 20s of exercise. The mean values of the gain of VI were about 56% while those of HR were 89%. The
gain of VI and HR showed high and significant correlations (Fig 1) but the gain of MBP wasn’t significantly correlated
with that of VI or HR. There were no significant correlations of the response times among the three parameters.

Discussion / Conclusions
Our results indicated that subjects who have a high ventilatory response should also have a high heart rate response, and
the results suggested that ventilation and heart rate should show similar responses at the start of exercise within the first
20s. This would be attributed to respiratory and circulatory centers having the same neural inputs (central command and
peripheral reflex) and this is a very important system in maintaining oxygen supply during exercise. It is concluded that
the cardio-respiratory system should respond simultaneously and similarly at the onset of dynamic exercise.

References
[1]. Mateika, J H. and Duffin, J. (1995). Eur J Appl Physiol, 71, 1-27.
[2]. Ishida, K. et al. (2000). J Appl Physiol 89, 1771-1777.

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