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Do vasoregulatory mechanisms in exercising human muscle compensate for changes in arterial perfusion pressure?

Human Vascular Control Laboratory, School of Kinesiology and Health Studies and Department of Physiology, Queen's University, Kingston, Ontario, Canada

Submitted 17 May 2007 ; accepted in final form 14 August 2007

We tested the hypothesis that vasoregulatory mechanisms completely counteract the effects of sudden changes in arterial perfusion pressure on exercising muscle blood flow. Twelve healthy young subjects (7 female, 5 male) lay supine and performed rhythmic isometric handgrip contractions (2 s contraction/ 2 s relaxation 30% maximal voluntary contraction). Forearm blood flow (FBF; echo and Doppler ultrasound), mean arterial blood pressure (arterial tonometry), and heart rate (ECG) were measured. Moving the arm between above the heart (AH) and below the heart (BH) level during contraction in steady-state exercise achieved sudden 30 mmHg changes in forearm arterial perfusion pressure (FAPP). We analyzed cardiac cycles during relaxation (FBF_relax). In an AH-to-BH transition, FBF_relax increased immediately, in excess of the increase in FAPP (69% vs. 41%). This was accounted for by pressure-related distension of forearm resistance vasculature [forearm vascular conductance (FVC_relax) increased by 19%]. FVC_relax was restored by the second relaxation. Continued slow decreases in FVC_relax stabilized by 2 min without restoring FBF_relax. In a BH-to-AH transition, FBF_relax decreased immediately, in excess of the decrease in FAPP (37% vs. 29%). FVC_relax decreased by 14%, suggesting pressure-related passive recoil of resistance vessels. The pattern of FVC_relax was similar to that in the AH-to-BH transition, and FBF_relax was not restored. These data support rapid myogenic regulation of vascular conductance in exercising human muscle but incomplete flow restoration via slower-acting mechanisms. Local arterial perfusion pressure is an important determinant of steady-state blood flow in the exercising human forearm.

vasodilation; vasoconstriction; muscle blood flow; myogenic; metabolism