Human arterial responses to isometric exercise: the role of the muscle metaboreflex
Résumé
The effects of exercise on the distensibility of large and medium sized arteries are poorly understood, but can be attributed to a combination of local vasodilator effects of exercise opposed by sympathetic vasoconstrictor tone. We sought to examine this relationship at the conduit artery level, with particular reference to the role of the sympathoexcitatory muscle metaboreflex. The effect of maintained muscle metaboreflex activation on a previously passive or exercised limb femoral artery was investigated. 10 healthy volunteers performed 2 minutes of isometric ankle plantar-flexion at 40% MVC, in conjunction with 2 minutes of either non-ischemic isometric handgrip (HG, control condition) or ischemic handgrip (IHG) at 40% MVC. IHG was followed by 2 minutes of post exercise circulatory occlusion (PECO) to maintain muscle metaboreflex activation. Femoral-tibial pulse wave velocity (FTPWV) was measured in the exercised or contra-lateral limb at baseline and immediately following calf exercise. Blood pressure (BP) and heart rate (HR) were measured continuously throughout. In the HG condition, BP and HR returned promptly to baseline post exercise whilst exercised leg FTPWV was decreased (less stiff) by 0.6m/s (P<0.05) and non-exercised leg PWV was not changed from baseline. PECO caused a sustained increase in BP but not HR in the IHG condition. Contra-lateral leg PWV increased (stiffened) during PECO by 0.9m/s (P<0.05), whereas exercised limb FTPWV was not changed from baseline. Muscle metaboreflex activation causes a systemic stiffening of the arterial tree, which can overcome local exercise induced decreases in arterial PWV.
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