Submitted on May 17, 2007
Accepted on August 14, 2007
Do vasoregulatory mechanisms in exercising human muscle compensate for changes in arterial perfusion pressure?
Kathryn L Walker1, Natasha R Saunders1, Dennis Jensen2, Jennifer L Kuk1, Suzi-Lai Wong2, Kyra E Pyke2, Erin M Dwyer2, and Michael E. Tschakovsky1*
1 School of Kinesiology and Health Studies, Queen's University, Kingston, Canada
2 Kingston, Canada; School of Kinesiology and Health Studies, Queen's University, Kingston, Canada
* To whom correspondence should be addressed. E-mail: mt29{at}post.queensu.ca.
We tested the hypothesis that vasoregulatory mechanisms completely counteract the effects of sudden changes in arterial perfusion pressure on exercising muscle blood flow. 12 healthy young subjects (7 female, 5 male) lay supine and performed 30% MVC rhythmic isometric handgrip contractions (2 s contraction/ 2 s relaxation). Forearm blood flow (FBF; Echo and Doppler ultrasound), mean arterial blood pressure (MAP; arterial tonometry) and heart rate (HR; ECG) were measured. Moving the arm between above heart (AH) and below heart (BH) level during contraction in steady state exercise achieved sudden ~30 mmHg changes in forearm arterial perfusion pressure (FAPP). We analysed cardiac cycles during relaxation (FBFrelax). AH to BH transition: FBFrelax 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 (FVCrelax) increased by ~19%). FVCrelax was restored by the second relaxation. Continued slow decreases in FVCrelax stabilized by 2 min without restoring FBFrelax. BH to AH transition: FBFrelax decreased immediately, in excess of the decrease in FAPP (~37% vs. ~29%). FVCrelax decreased by ~14% suggesting pressure related passive recoil of resistance vessels. The pattern of FVCrelax was similar to that in the AH to BH transition, and FBFrelax 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.
