title: Limb-specific differences in flow-mediated dilation: the role of shear rate.
abstract: We sought to examine flow-mediated vasodilation (FMD) in both the arm [brachial artery (BA)] and lower leg [popliteal artery (PA)] of 12 young, healthy subjects. Vessel diameter, blood velocity, and calculated shear rate were determined with ultrasound Doppler following a suprasystolic cuff occlusion (5 min) in both the BA and PA and an additional reduced occlusion period (30-120 s) in the BA to more closely equate the shear stimulus observed in the PA. The BA revealed a smaller diameter and larger postischemic cumulative blood velocity [area under curve (AUC)] than the PA, a combination that resulted in an elevated postcuff cumulative shear rate (AUC) in the BA (BA: 25,419 +/- 2,896 s(-1).s, PA 8,089 +/- 1,048 s(-1).s; P < 0.05). Thus, when expressed in traditional terms, there was a tendency for the BA to have a greater FMD than the PA (6.5 +/- 1.0 and 4.5 +/- 0.8%, respectively; P = 0.1). However, when shear rate was experimentally matched (PA: 4.5 +/- 0.8%; BA: -0.4 +/- 0.4%) or mathematically normalized (PA: 6.8 x 10(-4) +/- 1.6 x 10(-4)%Delta/s(-1).s; BA: 2.5 x 10(-4) +/- 0.4 x 10(-4)%Delta/s(-1).s), the PA revealed a greater FMD per unit of shear rate than the BA (P < 0.05). These data highlight the importance of assessing the shear stimulus to which each vessel is exposed and reveal limb-specific differences in flow-mediated dilation.
authors.affiliation: Department of Medicine, Physiology Division, 9500 Gilman Dr., University of California, San Diego, La Jolla, CA 92093-0623, USA.
authors.forename: Steven K
authors.initials: SK
authors.lastname: Nishiyama
authors.forename: D
authors.initials: D
authors.lastname: Walter Wray
authors.forename: Kimberly
authors.initials: K
authors.lastname: Berkstresser
authors.forename: Murali
authors.initials: M
authors.lastname: Ramaswamy
authors.forename: Russell S
authors.initials: RS
authors.lastname: Richardson
mesh_terms: D000328:Adult; D001783:Blood Flow Velocity / Q000502:physiology; D001916:Brachial Artery / Q000502:physiology*; D004730:Endothelium, Vascular / Q000502:physiology*; D006801:Humans; D008297:Male; D011150:Popliteal Artery / Q000502:physiology*; D012039:Regional Blood Flow / Q000502:physiology; D033081:Shear Strength; D014664:Vasodilation / Q000502:physiology*