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1 Department of Physiology, Faculty of Medicine, Free University of Brussels, Brussels, Belgium
2 Department of Cardiology, Erasme Hospital, Free University of Brussels, Brussels, Belgium
* To whom correspondence should be addressed. E-mail: houssiere_anne{at}yahoo.fr.
To investigate the effects of muscle metaboreceptor activation during hypoxic static exercise, we recorded muscle sympathetic nerve activity (MSNA), heart rate, blood pressure, ventilation and blood lactate in 13 healthy subjects (22+/-2 yrs) during 3 minutes of three randomised interventions: isocapnic hypoxia (10 % O2) (chemoreflex activation), isometric handgrip exercise in normoxia (metaboreflex activation), and isometric handgrip exercise during isocapnic hypoxia (concomitant metaboreflex and chemoreflex activation). Each intervention was followed by a forearm circulatory arrest to allow persistent metaboreflex activation in the absence of exercise and chemoreflex activation. Handgrip increased blood ressure, MSNA, heart rate, ventilation and lactate (all p<0.001). Hypoxia without handgrip increased MSNA, heart rate and ventilation (all p<0.001), but did not change blood pressure and lactate. Handgrip enhanced blood pressure, heart rate, MSNA and ventilation responses to hypoxia (all p<0.05). During circulatory arrest after handgrip in hypoxia, heart rate returned promptly to baseline values while ventilation decreased but remained elevated (p<0.05). In contrast, MSNA, blood pressure and lactate returned to baseline values during circulatory arrest after hypoxia without exercise, but remained markedly increased after handgrip in hypoxia (p<0.05). We conclude that metaboreceptors and chemoreceptors exert differential effects on the cardiorespiratory and sympathetic responses during exercise in hypoxia.
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