3 years ago

Voluntary apnea during dynamic exercise activates the muscle metaboreflex in humans.

Mayumi Matsumoto, Masashi Ichinose, Takeshi Nishiyasu, Narumi Yoshitake, Naoto Fujii
Voluntary apnea during dynamic exercise evokes marked bradycardia, peripheral vasoconstriction and pressor responses. However, the mechanism(s) underlying the cardiovascular responses seen during apnea in exercising humans is unknown. We therefore tested the hypothesis that the muscle metaboreflex contributes to the apnea-induced pressor response during dynamic exercise. Thirteen healthy subjects participated in apnea and control trials. In both trials, subjects performed a two-legged dynamic knee extension exercise at a workload that elicited heart rates around 100 beats/min. In the apnea trial, after reaching a steady state, subjects began voluntary apnea. Immediately after cessation of the apnea, arterial occlusion was initiated at both thighs and the subjects stopped exercising. The occlusion was sustained for 3-min in the post exercise period. In the control trial, the occlusion was started without the subjects performing the apnea. The apnea induced marked bradycardia, pressor responses and decreases in arterial O2 saturation, cardiac output and total vascular conductance (TVC). In addition, arterial blood pressure was significantly higher and TVC was significantly lower in the apnea trials than the control trials throughout the occlusion period. In separate sessions, we measured apnea-induced changes in exercising leg blood flow (LBF) in the same subjects. LBF was significantly reduced by apnea and reached the resting level at the peak of the apnea response. We conclude that the muscle metaboreflex is activated by the decrease in oxygen delivery to the working muscle during apnea in exercising humans and contributes to the large pressor response.

Publisher URL: http://doi.org/10.1152/ajpheart.00367.2017

DOI: 10.1152/ajpheart.00367.2017

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