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Ramp and step increases in shear stress result in a similar magnitude of brachial artery flow-mediated dilation

  • Joshua C. Tremblay
  • Jennifer S. Williams
  • Kyra E. PykeEmail author
Original Article
  • 37 Downloads

Abstract

Purpose

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.

Methods

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.

Results

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).

Conclusions

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.

Keywords

SS-FMD Endothelial function Handgrip exercise Rate of increase Rate sensitivity Conduit artery 

Abbreviations

FMD

Flow-mediated dilation

HR

Heart rate

MAP

Mean arterial pressure

MVC

Maximum voluntary isometric contraction

SS-FMD

Sustained stimulus flow-mediated dilation

Notes

Acknowledgements

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).

Author contributions

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.

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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2019

Authors and Affiliations

  1. 1.Cardiovascular Stress Response Laboratory, School of Kinesiology and Health StudiesQueen’s UniversityKingstonCanada

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