Effects of combined β-adrenergic and cholinergic blockade on the initial ventilatory response to exercise in humans |
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Authors: | Koji Ishida Tatsuya Hayashi Toshio Moritani and Miharu Miyamura |
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Institution: | (1) Laboratory for Exercise Physiology, Research Center of Health, Physical Fitness and Sports, Nagoya University, Furocho, Chikusaku, Nagoya 464-01, Japan, JP;(2) Second Division Department of Medicine, Kyoto University School of Medicine, Kyoto, Japan, JP;(3) Graduate School of Human and Environmental Studies, Kyoto University, Kyoto, Japan, JP |
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Abstract: | To elucidate whether combined adrenergic and parasympathetic blockade would affect the ventilatory response to exercise,
especially at the initial stage (phase I), six healthy subjects performed a brief and light voluntary bilateral leg extension
exercise and passive movements under the conditions of control (before the blockade) and after intravenous administration
of combined β-adrenergic (propranolol, 0.2 mg · kg−1) and muscarinic (atropine, 0.04 mg · kg−1) receptor antagonists. The movements were continued only within two breaths after the onset of the motion. Ventilation increased
immediately and significantly (P<0.05) within the first breath at the onset of voluntary exercise in all conditions as compared with at rest. However, the
magnitude of increase in mean ventilation within two breaths at the start of exercise as against the resting value (delta
ventilation) was significantly less (P<0.05) after the combined blockades (2.5 l · min−1) than in the control condition (3.7 l · min−1). Passive movements showed a similar but smaller change as compared with voluntary exercise. The heart rate response to exercise
was attenuated by the combined blockade while cardiac output showed a slight change at the onset of exercise. It is concluded
that phase I should occur despite the inhibited activity of the β-adrenergic and the cholinergic systems; nevertheless, the
response was attenuated by the combined blockade. These results suggest a possible role of the β-adrenergic and/or cholinergic
systems in the rapid increase in ventilation that occurs at the start of exercise.
Accepted: 2 March 1997 |
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Keywords: | Exercise hyperpnoea Exercise onset Parasympathetic blockade Phase I Sympathetic blockade |
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