September 17, 2022Experimental Physiology
Brachial artery responses to acute hypercapnia: The roles of shear stress and adrenergic tone
Key result
Prazosin increases hypercapnic brachial artery flow and shear rate but fails to cause shear-mediated vasodilation.
- P<0.001
- n=26
Why the study?
The contributions of shear stress and alpha1-adrenergic tone to brachial artery vasodilatation during acute hypercapnia were not established.
Does alpha-1-adrenergic blockade or shear stress alteration affect brachial artery vasodilation during hypercapnia in healthy adults?
Population
14 healthy adults (study 1) and 12 healthy adults (study 2)
Comparison
Arterial compression vs control arm (study 1); prazosin vs placebo with and without compression (study 2)
Design
Physiological study (study 1) and randomized, double-blind, placebo-controlled trial (study 2)
Authors
Discussion
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Implication
Alpha-1 blockade augments hypercapnic brachial flow and shear without vasodilation in healthy adults; extends evidence that shear alone is insufficient for conduit artery dilation.
Study Design
Type
RCT (n=26)
Blinding
Double-blind
Randomization
Randomized
Structured PICO
Does alpha-1-adrenergic blockade or shear stress alteration affect brachial artery vasodilation during hypercapnia in healthy adults?
P
Population
Healthy young adults (Study 1: n=14, 7 male/7 female, mean age 27 ± 4 years; Study 2: n=12, 9 male/3 female, mean age 26 ± 4 years)
I
Intervention
Study 1: Hypercapnia (partial pressure of end-tidal carbon dioxide +10.2 ± 0.3 mmHg above baseline for 12 min) with manual compression of one brachial artery to reduce shear stress. Study 2: Hypercapnia with alpha-1-adrenergic receptor blockade (prazosin 0.05 mg/kg)
C
Comparator
Study 1: Contralateral control arm without compression. Study 2: Matching placebo
O
Outcome
Brachial artery diameter, blood flow, conductance, and shear ratesurrogate
Main Result
p-value: p=<0.001
Even in the absence of alpha-1-adrenergic restraint, downstream microvascular vasodilation during hypercapnia is insufficient to cause shear-mediated vasodilation in the brachial artery in healthy young adults.
Cite This Study
Carr et al. (2022) conducted an RCT in Healthy young adults (n=26). Prazosin (α₁-adrenergic receptor blockade) during hypercapnia vs. Placebo was evaluated on Brachial artery flow, conductance and shear rate (p=<0.001). Alpha-1-adrenergic receptor blockade with prazosin increased brachial artery flow, conductance, and shear rate during hypercapnia (P<0.001), but did not cause shear-mediated vasodilatation.