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Shear-Mediated Dilation of the Internal Carotid Artery Occurs Independent of Hypercapnia.

Hoiland, RL and Smith, KJ and Carter, HH and Lewis, NCS and Tymko, MM and Wildfong, KW and Bain, AR and Green, DJ and Ainslie, PN (2017) Shear-Mediated Dilation of the Internal Carotid Artery Occurs Independent of Hypercapnia. American Journal of Physiology Heart and Circulatory Physiology. ISSN 1522-1539

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Abstract

Evidence for shear stress as a regulator of carotid artery dilation in response to increased arterial carbon dioxide was recently demonstrated in humans during sustained elevations in CO2 (hypercapnia); however, the relative contributions of CO2 and shear stress to this response remains unclear. We examined the hypothesis that, following a 30-second transient increase in arterial CO2 tension and consequent increase in internal carotid artery shear stress, internal carotid artery diameter would increase, indicating shear-mediated dilation, in the absence of concurrent hypercapnia. In 27 healthy participants the partial pressures of end-tidal O2 and CO2, ventilation (pneumotachography), blood pressure (finger-photoplethysmography), heart-rate (electrocardiogram), internal carotid artery flow, diameter and shear stress (high resolution duplex ultrasound) and middle cerebral artery blood velocity (transcranial Doppler) were measured during 4-minute steady state and transient 30-second hypercapnic tests (both +9mmHg CO2). Internal carotid artery dilation was lower in the transient, compared to the steady state hypercapnia (3.3±1.9% vs. 5.3±2.9%, respectively; P<0.03). Increases in internal carotid artery shear stress preceded increases in diameter in both the transient (time: 16.8±13.2s vs. 59.4±60.3s; P<0.01) and steady state (time: 18.2±14.2s vs. 110.3±79.6s; P<0.01) tests. Internal carotid artery dilation was positively correlated with shear rate area under the curve in the transient (r(2)=0.44; P<0.01), but not steady state (r(2)=0.02; P=0.53) trial. Collectively, these results suggest that hypercapnia induces shear-mediated dilation of the internal carotid artery in humans. This study further promotes the application and development of hypercapnia as a clinical strategy for the assessment of cerebrovascular vasodilatory function and health in humans.

Item Type: Article
Uncontrolled Keywords: 0606 Physiology, 1116 Medical Physiology
Subjects: R Medicine > RC Internal medicine > RC1200 Sports Medicine
Divisions: Sport & Exercise Sciences
Publisher: Amercian Physiological Society
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Date Deposited: 25 May 2017 11:09
Last Modified: 25 May 2017 11:09
DOI or Identification number: 10.1152/ajpheart.00119.2017
URI: http://researchonline.ljmu.ac.uk/id/eprint/6418

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