Ramp and step increases in shear stress result in a similar magnitude of brachial artery flow-mediated dilation
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There is evidence that the endothelium is responsive to both the rate and magnitude of increases in shear stress. However, whether flow-mediated dilation stimulated by sustained increases in shear stress (SS-FMD) is rate sensitive in humans is unknown. The purpose of this investigation was to test whether ramp (gradual) and step (instantaneous) increases in shear stress elicit disparate SS-FMD.
Young, healthy men (n = 18, age = 22 ± 2 years, body mass index = 25 ± 3 kg m−2) performed two 11-min bouts of rhythmic handgrip exercise; one with a 5.5-min ramp-increase in shear stress and one with an immediate step increase in shear stress. Ramp increases in shear stress were achieved through incremental increases in handgrip exercise intensity [increases of 4% maximum voluntary contraction (MVC) every 30 s for 5.5 min, ending at 44% MVC] and step increases in shear stress were achieved through a combination of arterial compression and commencing handgrip exercise at 44% MVC.
Shear rate was greater in the step versus ramp protocol in minutes 1–6, but not different thereafter. Similarly, SS-FMD was greater in the step versus ramp protocol during minutes 2–6, but similar in minutes 7–11 (minute 11: ramp 8.7 ± 4.6%; step 9.4 ± 3.6%; P = 0.343). SS-FMD continued to increase over time with maintenance of a steady shear stress stimulus (step minutes 2–11: 0.51 ± 0.36% min−1; ramp minutes 7–11: 0.64 ± 0.57% min−1; P = 0.259).
These findings indicate that in the brachial artery of humans, the magnitude of SS-FMD is determined by the magnitude and duration, but not the rate, of increases in shear stress.
KeywordsSS-FMD Endothelial function Handgrip exercise Rate of increase Rate sensitivity Conduit artery
Mean arterial pressure
Maximum voluntary isometric contraction
Sustained stimulus flow-mediated dilation
JCT was supported by an Alexander Graham Bell Doctoral Canada Graduate Scholarship (Natural Sciences and Engineering Research Council of Canada; NSERC), JSW was supported by an NSERC undergraduate student research award, and this study was funded by an NSERC Discovery Grant (KEP).
KEP and JSW conceived and designed the research. JSW and JCT performed the data collection and analysis. JCT drafted the manuscript. KEP and JSW revised the manuscript for important intellectual content. All authors read and approved the final version of the manuscript for submission.
Compliance with ethical standards
Conflict of interest
The authors declare no conflict of interest.
- Barton M, Turner AT, Newens KJ, Williams CM, Thompson AK (2011) Minimum recovery time between reactive hyperemia stimulus in the repeated measurement of brachial flow-mediated dilatation. Ultrasound Med Biol 37(6):879–883. https://doi.org/10.1016/j.ultrasmedbio.2011.03.007 CrossRefPubMedGoogle Scholar
- Bellien J, Iacob M, Gutierrez L, Isabelle M, Lahary A, Thuillez C, Joannides R (2006) Crucial role of NO and endothelium-derived hyperpolarizing factor in human sustained conduit artery flow-mediated dilatation. Hypertension 48(6):1088–1094. https://doi.org/10.1161/01.HYP.0000246672.72188.bd CrossRefPubMedGoogle Scholar
- Frangos JA, Huang TY, Clark CB (1996) Steady shear and step changes in shear stimulate endothelium via independent mechanisms–superposition of transient and sustained nitric oxide production. Biochem Biophys Res Commun 224(3):660–665. https://doi.org/10.1006/bbrc.1996.1081 CrossRefPubMedGoogle Scholar
- Jazuli F, Pyke KE (2011) The impact of baseline artery diameter on flow-mediated vasodilation: a comparison of brachial and radial artery responses to matched levels of shear stress. Am J Physiol Heart Circ Physiol 301(4):H1667–H1677. https://doi.org/10.1152/ajpheart.00487.2011 CrossRefPubMedGoogle Scholar
- Joannides R, Costentin A, Iacob M, Compagnon P, Lahary A, Thuillez C (2002) Influence of vascular dimension on gender difference in flow-dependent dilatation of peripheral conduit arteries. Am J Physiol Heart Circ Physiol 282(4):H1262–H1269. https://doi.org/10.1152/ajpheart.00209.2001 CrossRefPubMedGoogle Scholar
- Mullen MJ, Kharbanda RK, Cross J, Donald AE, Taylor M, Vallance P, Deanfield JE, MacAllister RJ (2001) Heterogenous nature of flow-mediated dilatation in human conduit arteries in vivo: relevance to endothelial dysfunction in hypercholesterolemia. Circ Res 88(2):145–151. https://doi.org/10.1161/01.RES.88.2.145 CrossRefPubMedGoogle Scholar
- Szijgyarto IC, Poitras VJ, Gurd BJ, Pyke KE (2014) Acute psychological and physical stress transiently enhances brachial artery flow-mediated dilation stimulated by exercise-induced increases in shear stress. Appl Physiol Nutr Metab 39(8):927–936. https://doi.org/10.1139/apnm-2013-0384 CrossRefPubMedGoogle Scholar
- Woodman RJ, Playford DA, Watts GF, Cheetham C, Reed C, Taylor RR, Puddey IB, Beilin LJ, Burke V, Mori TA, Green D (2001) Improved analysis of brachial artery ultrasound using a novel edge-detection software system. J Appl Physiol (1985) 91 (2):929–937. https://doi.org/10.1152/jappl.2001.91.2.929
- Wray DW, Witman MA, Ives SJ, McDaniel J, Fjeldstad AS, Trinity JD, Conklin JD, Supiano MA, Richardson RS (2011) Progressive handgrip exercise: evidence of nitric oxide-dependent vasodilation and blood flow regulation in humans. Am J Physiol Heart Circ Physiol 300(3):H1101–H1107. https://doi.org/10.1152/ajpheart.01115.2010 CrossRefPubMedPubMedCentralGoogle Scholar