Comparison of brachial dilatory responses to hypercapnia and reactive hyperemia

Justin R. Geijer, Neil E. Hultgren, Nicholas G. Evanoff, Aaron S. Kelly, Michael A. Chernin, Matthew G. Stoltman, Donald R. Dengel

Research output: Contribution to journalArticlepeer-review

3 Scopus citations


Flow-mediated dilation (FMD) relies on reactive hyperemia to stimulate the endothelium to release nitric oxide, causing smooth muscle relaxation. Hypercapnia also produces vasodilation, which is thought to be nitric oxide-independent. The purpose of this study was to compare and contrast the effects of hypercapnia and reactive hyperemia as stimuli for brachial artery dilation. On separate days, twenty-five participants underwent vasodilation studies via reactive hyperemia or hypercapnia (i.e. 10 mmHg increase in end-tidal carbon dioxide [PetCO2)]). During both studies changes in brachial artery diameter were recorded using continuous ultrasound imaging. Heart rate (HR) was measured throughout both tests. Resting HR (63 ± 11 versus 68 ± 14 beats min-1, p = 0.0027) and baseline brachial artery diameter measurements (4.57 ± 1.51 versus 5.28 ± 1.86 mm, p = 0.022) were significantly different between reactive hyperemia and hypercapnia, respectively. HR at peak dilation (65 ± 11 versus 76 ± 14 beats min-1, p < 0.0001), peak vessel dilation (8.68 ± 4.50 versus 5.28 ± 1.86%, p = 0.002), and time to peak dilation (90.8 ± 120.1 versus 658.3 ± 226.6 s, p < 0.0001) were also significantly different between reactive hyperemia and hypercapnia. The dynamics by which reactive hyperemia and hypercapnia stimulate vasodilation appear to differ. Hypercapnia produces a smaller and slower vasodilatory effect than reactive hyperemia. Further research is necessary to better understand the mechanisms of vasodilation under hypercapnic conditions.

Original languageEnglish (US)
Article number380
Pages (from-to)380-386
Number of pages7
JournalPhysiological Measurement
Issue number3
StatePublished - Feb 10 2016

Bibliographical note

Publisher Copyright:
© 2016 Institute of Physics and Engineering in Medicine.

Copyright 2018 Elsevier B.V., All rights reserved.


  • PCO
  • flow mediated dilation
  • hypercapnia
  • reactive hyperemia
  • ultrasound


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