Shear-mediated dilation of the internal carotid artery occurs independent of hypercapnia

TY - JOUR

T1 - Shear-mediated dilation of the internal carotid artery occurs independent of hypercapnia

AU - Hoiland, Ryan L

AU - Smith, Kurt J

AU - Carter, Howard Henry

AU - Lewis, Nia C S

AU - Tymko, Michael M

AU - Wildfong, Kevin W

AU - Bain, Anthony R

AU - Green, Daniel J

AU - Ainslie, Philip N

N1 - CURIS 2017 NEXS 353

PY - 2017

Y1 - 2017

N2 - Evidence for shear stress as a regulator of carotid artery dilation in response to increased arterial CO2 was recently demonstrated in humans during sustained elevations in CO2(hypercapnia); however, the relative contributions of CO2and shear stress to this response remains unclear. We examined the hypothesis that, after a 30-s transient increase in arterial CO2tension 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, 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-min steady-state and transient 30-s hypercapnic tests (both +9 mmHg CO2). Internal carotid artery dilation was lower in the transient compared with 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 transient (time: 16.8 ± 13.2 vs. 59.4 ± 60.3 s, P < 0.01) and steady-state (time: 18.2 ±14.2 vs. 110.3 ± 79.6 s, P < 0.01) tests. Internal carotid artery dilation was positively correlated with shear rate area under the curve in the transient (r2 ± 0.44, P < 0.01) but not steady-state (r2 ± 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. NEW & NOTEWORTHY Shear stress dilates the internal carotid artery in humans. This vasodilatory response occurs independent of other physiological factors, as demonstrated by our transient CO2 test, and is strongly correlated to shear area under the curve. Assessing carotid shear-mediated dilation may provide a future avenue for assessing cerebrovascular health and the risk of cerebrovascular events.

AB - Evidence for shear stress as a regulator of carotid artery dilation in response to increased arterial CO2 was recently demonstrated in humans during sustained elevations in CO2(hypercapnia); however, the relative contributions of CO2and shear stress to this response remains unclear. We examined the hypothesis that, after a 30-s transient increase in arterial CO2tension 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, 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-min steady-state and transient 30-s hypercapnic tests (both +9 mmHg CO2). Internal carotid artery dilation was lower in the transient compared with 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 transient (time: 16.8 ± 13.2 vs. 59.4 ± 60.3 s, P < 0.01) and steady-state (time: 18.2 ±14.2 vs. 110.3 ± 79.6 s, P < 0.01) tests. Internal carotid artery dilation was positively correlated with shear rate area under the curve in the transient (r2 ± 0.44, P < 0.01) but not steady-state (r2 ± 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. NEW & NOTEWORTHY Shear stress dilates the internal carotid artery in humans. This vasodilatory response occurs independent of other physiological factors, as demonstrated by our transient CO2 test, and is strongly correlated to shear area under the curve. Assessing carotid shear-mediated dilation may provide a future avenue for assessing cerebrovascular health and the risk of cerebrovascular events.

KW - Blood Flow Velocity

KW - Carbon Dioxide

KW - Carotid Artery, Internal

KW - Female

KW - Humans

KW - Hypercapnia

KW - Male

KW - Mechanotransduction, Cellular

KW - Shear Strength

KW - Stress, Mechanical

KW - Vasodilation

KW - Young Adult

KW - Clinical Trial

KW - Journal Article

U2 - 10.1152/ajpheart.00119.2017

DO - 10.1152/ajpheart.00119.2017

M3 - Journal article

C2 - 28389602

SN - 0363-6135

VL - 313

SP - H24-H31

JO - American Journal of Physiology - Heart and Circulatory Physiology

JF - American Journal of Physiology - Heart and Circulatory Physiology

IS - 1

ER -