title: Evidence for Shear Stress-Mediated Dilation of the Internal Carotid Artery in Humans.
abstract: Increases in arterial carbon dioxide tension (hypercapnia) elicit potent vasodilation of cerebral arterioles. Recent studies have also reported vasodilation of the internal carotid artery during hypercapnia, but the mechanism(s) mediating this extracranial vasoreactivity are unknown. Hypercapnia increases carotid shear stress, a known stimulus to vasodilation in other conduit arteries. To explore the hypothesis that shear stress contributes to hypercapnic internal carotid dilation in humans, temporal changes in internal and common carotid shear rate and diameter, along with changes in middle cerebral artery velocity, were simultaneously assessed in 18 subjects at rest and during hypercapnia (6% carbon dioxide). Middle cerebral artery velocity increased significantly (69±10-103±17 cm/s; P<0.01) along with shear in both the internal (316±52-518±105 1/s; P<0.01) and common (188±40-275±61 1/s; P<0.01) carotids. Diameter also increased (P<0.01) in both carotid arteries (internal: +6.3±2.9%; common: +5.8±3.0%). Following hypercapnia onset, there was a significant delay between the onset of internal carotid shear (22±12 seconds) and diameter change (85±51 seconds). This time course is associated with shear-mediated dilation of larger conduit arteries in humans. There was a strong association between change in shear and diameter of the internal carotid (r=0.68; P<0.01). These data indicate, for the first time in humans, that shear stress is an important stimulus for hypercapnic vasodilation of the internal carotid artery. The combination of a hypercapnic stimulus and continuous noninvasive, high-resolution assessment of internal carotid shear and dilation may provide novel insights into the function and health of the clinically important extracranial arteries in humans.
authors: From the School of Sport Science, Exercise and Health, University of Western Australia, Perth, Australia (H.H.C., C.L.A., I.H.A.H., A.H., E.R., K.J.S., R.L.H., D.J.G.); Department of Nutrition, Exercise and Sports, University of Copenhagen, Denmark (H.H.C.); Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, Canada (K.J.S., P.N.A., R.L.H.); and Research Institute for Sport and Exercise Science, Liverpool John Moores University, United Kingdom (H.H.C., C.L.A., D.J.G.). hoc@nexs.ku.dk.
authors: Howard H
authors: HH
authors: Carter
authors: From the School of Sport Science, Exercise and Health, University of Western Australia, Perth, Australia (H.H.C., C.L.A., I.H.A.H., A.H., E.R., K.J.S., R.L.H., D.J.G.); Department of Nutrition, Exercise and Sports, University of Copenhagen, Denmark (H.H.C.); Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, Canada (K.J.S., P.N.A., R.L.H.); and Research Institute for Sport and Exercise Science, Liverpool John Moores University, United Kingdom (H.H.C., C.L.A., D.J.G.).
authors: Ceri L
authors: CL
authors: Atkinson
authors: From the School of Sport Science, Exercise and Health, University of Western Australia, Perth, Australia (H.H.C., C.L.A., I.H.A.H., A.H., E.R., K.J.S., R.L.H., D.J.G.); Department of Nutrition, Exercise and Sports, University of Copenhagen, Denmark (H.H.C.); Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, Canada (K.J.S., P.N.A., R.L.H.); and Research Institute for Sport and Exercise Science, Liverpool John Moores University, United Kingdom (H.H.C., C.L.A., D.J.G.).
authors: Ilkka H A
authors: IH
authors: Heinonen
authors: From the School of Sport Science, Exercise and Health, University of Western Australia, Perth, Australia (H.H.C., C.L.A., I.H.A.H., A.H., E.R., K.J.S., R.L.H., D.J.G.); Department of Nutrition, Exercise and Sports, University of Copenhagen, Denmark (H.H.C.); Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, Canada (K.J.S., P.N.A., R.L.H.); and Research Institute for Sport and Exercise Science, Liverpool John Moores University, United Kingdom (H.H.C., C.L.A., D.J.G.).
authors: Andrew
authors: A
authors: Haynes
authors: From the School of Sport Science, Exercise and Health, University of Western Australia, Perth, Australia (H.H.C., C.L.A., I.H.A.H., A.H., E.R., K.J.S., R.L.H., D.J.G.); Department of Nutrition, Exercise and Sports, University of Copenhagen, Denmark (H.H.C.); Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, Canada (K.J.S., P.N.A., R.L.H.); and Research Institute for Sport and Exercise Science, Liverpool John Moores University, United Kingdom (H.H.C., C.L.A., D.J.G.).
authors: Elisa
authors: E
authors: Robey
authors: From the School of Sport Science, Exercise and Health, University of Western Australia, Perth, Australia (H.H.C., C.L.A., I.H.A.H., A.H., E.R., K.J.S., R.L.H., D.J.G.); Department of Nutrition, Exercise and Sports, University of Copenhagen, Denmark (H.H.C.); Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, Canada (K.J.S., P.N.A., R.L.H.); and Research Institute for Sport and Exercise Science, Liverpool John Moores University, United Kingdom (H.H.C., C.L.A., D.J.G.).
authors: Kurt J
authors: KJ
authors: Smith
authors: From the School of Sport Science, Exercise and Health, University of Western Australia, Perth, Australia (H.H.C., C.L.A., I.H.A.H., A.H., E.R., K.J.S., R.L.H., D.J.G.); Department of Nutrition, Exercise and Sports, University of Copenhagen, Denmark (H.H.C.); Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, Canada (K.J.S., P.N.A., R.L.H.); and Research Institute for Sport and Exercise Science, Liverpool John Moores University, United Kingdom (H.H.C., C.L.A., D.J.G.).
authors: Philip N
authors: PN
authors: Ainslie
authors: From the School of Sport Science, Exercise and Health, University of Western Australia, Perth, Australia (H.H.C., C.L.A., I.H.A.H., A.H., E.R., K.J.S., R.L.H., D.J.G.); Department of Nutrition, Exercise and Sports, University of Copenhagen, Denmark (H.H.C.); Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, Canada (K.J.S., P.N.A., R.L.H.); and Research Institute for Sport and Exercise Science, Liverpool John Moores University, United Kingdom (H.H.C., C.L.A., D.J.G.).
authors: Ryan L
authors: RL
authors: Hoiland
authors: From the School of Sport Science, Exercise and Health, University of Western Australia, Perth, Australia (H.H.C., C.L.A., I.H.A.H., A.H., E.R., K.J.S., R.L.H., D.J.G.); Department of Nutrition, Exercise and Sports, University of Copenhagen, Denmark (H.H.C.); Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, Canada (K.J.S., P.N.A., R.L.H.); and Research Institute for Sport and Exercise Science, Liverpool John Moores University, United Kingdom (H.H.C., C.L.A., D.J.G.).
authors: Daniel J
authors: DJ
authors: Green
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D001783:Blood Flow Velocity; D002245:Carbon Dioxide / Q000008:administration & dosage*; D002343:Carotid Artery, Internal / Q000000981:diagnostic imaging / Q000502:physiology*; D005260:Female; D006801:Humans; D006935:Hypercapnia / Q000000981:diagnostic imaging*; D008297:Male; D012016:Reference Values; D012039:Regional Blood Flow; D018570:Risk Assessment; D012494:Sampling Studies; D012737:Sex Factors; D013314:Stress, Mechanical; D018608:Ultrasonography, Doppler / Q000379:methods; D014655:Vascular Resistance; D059289:Vascular Stiffness; D014664:Vasodilation / Q000502:physiology*; D055815:Young Adult
chemical_list: D002245:Carbon Dioxide
keywords: carbon dioxide; carotid arteries; cerebral arteries; shear stress; vasodilation