title: Brachial artery vasodilatation during prolonged lower limb exercise: role of shear rate.
abstract: We recently observed a marked increase in brachial artery (BA) diameter during prolonged leg cycling exercise. The purpose of the present study was to test the hypothesis that this increase in BA diameter during lower limb exercise is shear stress mediated. Accordingly, we determined whether recapitulation of cycling-induced BA shear rate with forearm heating, a known stimulus evoking shear-induced conduit artery dilatation, would elicit comparable profiles and magnitudes of BA vasodilatation to those observed during cycling. In 12 healthy men, BA diameter and blood velocity were measured simultaneously using Doppler ultrasonography at baseline and every 5 min during 60 min of either steady-state semi-recumbent leg cycling (120 W) or forearm heating. At the onset of cycling, the BA diameter was reduced (-3.9 ± 1.2% at 5 min; P < 0.05), but it subsequently increased throughout the remainder of the exercise bout (+15.1 ± 1.6% at 60 min; P < 0.05). The increase in BA diameter during exercise was accompanied by an approximately 2.5-fold rise in BA mean shear rate (P < 0.05). Similar increases in BA mean shear with forearm heating elicited an equivalent magnitude of BA vasodilatation to that observed during cycling (P > 0.05). Herein, we found that in the absence of exercise the extent of the BA vasodilator response was reproduced when the BA was exposed to comparable magnitudes of shear rate via forearm heating. These results are consistent with the hypothesis that shear stress plays a key role in signalling brachial artery vasodilatation during dynamic leg exercise.
authors.affiliation: Department of Biomedical Sciences, E102 Veterinary Medicine, 1600 East Rollins Road, University of Missouri, Columbia, MO 65211, USA. padillaja@missouri.edu
authors.forename: Jaume
authors.initials: J
authors.lastname: Padilla
authors.forename: Grant H
authors.initials: GH
authors.lastname: Simmons
authors.forename: Lauro C
authors.initials: LC
authors.lastname: Vianna
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Davis
authors.forename: M Harold
authors.initials: MH
authors.lastname: Laughlin
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Fadel
mesh_terms: D000328:Adult; D001642:Bicycling / Q000502:physiology*; D001916:Brachial Artery / Q000502:physiology*; D015444:Exercise / Q000502:physiology; D005542:Forearm / Q000098:blood supply; D006358:Hot Temperature; D006801:Humans; D007866:Leg / Q000502:physiology*; D008297:Male; D012039:Regional Blood Flow / Q000502:physiology; D033081:Shear Strength; D018608:Ultrasonography, Doppler; D014664:Vasodilation / Q000502:physiology*