Are the dynamic response characteristics of brachial artery flow-mediated dilation sensitive to the magnitude of increase in shear stimulus?

• Published in: Journal of applied physiology (1985) Vol. 105; no. 1; pp. 282 - 292
• Main Authors: Pyke, K. E, Hartnett, J. A, Tschakovsky, M. E
• Format: Journal Article
• Language: English
• Published: Bethesda, MD Am Physiological Soc 01.07.2008; American Physiological Society
• Subjects: Adult; Biological and medical sciences; Blood pressure; Blood Pressure - physiology; Brachial Artery - anatomy & histology; Brachial Artery - diagnostic imaging; Brachial Artery - physiology; Electrocardiography; Endothelium, Vascular - physiology; Forearm - physiology; Fundamental and applied biological sciences. Psychology; Heart Rate - physiology; Hot Temperature; Humans; Laser-Doppler Flowmetry; Male; Pressure; Shear stress; Studies; Ultrasonic imaging; Ultrasonography; Vasodilation - physiology; Veins & arteries; Vertebrata; Stimulus; Mammalia; Brachial artery; hyperemia; Ultrasound; Doppler ultrasound; Endothelium
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/japplphysiol.01190.2007

Queen's University, Kingston, Ontario, Canada Submitted 8 November 2007 ; accepted in final form 6 May 2008 The purpose of this study was to determine the dynamic characteristics of brachial artery dilation in response to step increases in shear stress [flow-mediated dilation (FMD)]. Brachial artery diameter (BAD) and mean blood velocity (MBV) (Doppler ultrasound) were obtained in 15 healthy subjects. Step increases in MBV at two shear stimulus magnitudes were investigated: large (L; maximal MBV attainable), and small (S; MBV at 50% of the large step). Increase in shear rate (estimate of shear stress: MBV/BAD) was 76.8 ± 15.6 s –1 for L and 41.4 ± 8.7 s –1 for S. The peak %FMD was 14.5 ± 3.8% for L and 5.7 ± 2.1% for S ( P < 0.001). Both the L (all subjects) and the S step trials (12 of 15 subjects) elicited a biphasic diameter response with a fast initial phase (phase I) followed by a slower final phase. Relative contribution of phase I to total FMD when two phases occurred was not sensitive to shear rate magnitude ( r 2 = 0.003, slope P = 0.775). Parameters quantifying the dynamics of the FMD response [time delay (TD), time constant ( )] were also not sensitive to shear rate magnitude for both phases (phase I: TD r 2 = 0.03, slope P = 0.376, r 2 = 0.04, slope P = 0.261; final phase: TD r 2 = 0.07, slope P = 0.169, r 2 = 0.07, slope P = 0.996). These data support the existence of two distinct mechanisms, or sets of mechanisms, in the human conduit artery FMD response that are proportionally sensitive to shear stimulus magnitude and whose dynamic response is not sensitive to shear stimulus magnitude. Doppler ultrasound; hyperemia; endothelium Address for reprint requests and other correspondence: M. E. Tschakovsky, Associate Professor, Human Vascular Control Laboratory, School of Kinesiology and Health Studies, Queen's Univ., Kingston, ON K7L 3N6, Canada (e-mail: mt29{at}queensu.ca )