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1 Kinesiology, The University of Western Ontario, London, Canada
2 Département de Médecine Nucléaire & Ultrasons, Université de Tours, Tours, France
3 Unite Med & Physiol Spatiale, University Hospital Trousseau, TOURS, France
4 Cardiorespiratory + Vascular Dynamics Laboratory, University of Waterloo, Faculty of Applied Health Sciences, Waterloo, Canada
* To whom correspondence should be addressed. E-mail: kshoemak{at}uwo.ca.
The mechanism of the pressor response to small muscle mass (e.g. forearm) exercise and during metaboreflex activation may include elevations in cardiac output (Q) or total peripheral resistance (TPR). Increases in Q must be supported by reductions in visceral venous volume to sustain venous return as heart rate (HR) increases. Therefore, this study tested the hypothesis that increases in Q, supported by reductions in splanchnic volume (portal vein constriction), explain the pressor response during handgrip exercise and metaboreflex activation. Seventeen healthy women performed two minutes of static ischemic handgrip exercise and two minutes of post exercise circulatory occlusion (PECO) while HR, stroke volume and superficial femoral artery flow (Doppler), blood pressure (Finometer), portal vein diameter (ultrasound imaging), and muscle sympathetic nerve activity (MSNA; microneurography) were measured followed by the calculation of Q, TPR and leg vascular resistance (LVR). Compared with baseline, MAP (P<0.001) and Q (P<0.001) both increased in each min of exercise accompanied by a ~5% reduction in portal vein diameter (P<0.05). MAP remained elevated during PECO whereas Q decreased below exercise levels. MSNA was elevated above baseline during the second minute of exercise and through the PECO period (P<0.05). Neither TPR nor LVR were changed from baseline during exercise and PECO. The data indicate that the majority of the blood pressure response to isometric handgrip exercise in females was due to mobilization of central blood volume and elevated stroke volume and Q rather than elevations in total or limb vascular resistance.
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