The role of afferent information from active muscle on hyperventilation during exercise

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We observed the ventilation during cuff occlusion limiting the flow from and into the active muscle after exercise cessation, as to test the hypothesis that afferent information from muscle metaboreceptors and mechanoreceptors increase ventilation in humans during exercise. The cuff occlusion after the cessation of exercise selectively stimulates metaboreceptors and metaboreceptors in muscles. The results obtained in the first year were that there was no significant difference in ventilation between cuff occlusion and control trials, while the end-tidal CO2 partial pressure, which indicates the arterial CO2 concentration, was lower during cuff occlusion than in control. This implies the possibility that stimulus to the carotid body CO2 sensor decreased by cuff occlusion compromise the increment of afferent information from muscle receptors.In the next series of experiments, we controlled inspired CO2 partial pressure to oscillate the end-tidal CO2 pressure during cuff occlusion. Six subjects performed 2-min isometric leg extension exercise at 30% of maximal *oluntary contraction. During 3-min cuff occlusion after the cessation of exercise in the experimental trial and corresponding period in the control trial, inspired CO2 was maintained at 0, 3.5 and 5%. The ventilation was plotted against the end-tidal CO2 partial pressure to observe the hyperventilation to a given arterial CO2 concentration by muscle afferent stimulus. The ventilation was higher at 38-42mmHg of end-tidal CO2 partial pressure in five of six subjects, and the increase in ventilation was small, suggesting that the stimulus to metaboreceptors plays a role increasing ventilation during exercise but the amount of this role is limited. We applied change of posture to investigate the mechanoreceptors, but obtained no clear result. The role of mechanoreceptors on ventilation still remains unclear.