Thesis Defence: Examining the Effects of Shear Rate on Flow Mediated Dilation in Children and Adults

Nadhiyya Shabir, supervised by Dr. Ali McManus, will defend their thesis titled “Examining the Effects of Shear Rate on Flow Mediated Dilation in Children and Adults” in partial fulfillment of the requirements for the degree of Master of Science in Health and Exercise Sciences.

An abstract for Nadhiyya Shabir’s thesis is included below.

Defences are open to all members of the campus community as well as the general public. Please email ali.mcmanus@ubc.ca to receive the Zoom link for this defence.

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ABSTRACT

Variations in shear stimulus has been shown to impact endothelial function, specifically flow mediated dilation (FMD). Studies have shown that increases in shear rate improves FMD and overall vascular health while decreases in shear rate leads to reductions in FMD and increases risk of cardiovascular diseases. Although this pattern is noticed in adult studies, there are limited studies that investigate this relationship in children. Therefore, the aim of this study was to examine the relationship between shear rate and flow FMD in children and adults. Nine adults men and seven boys completed two experimental conditions passive heat and low-pressure cuff intended to up-regulate and down-regulate shear rate respectively. Superficial femoral artery diameter, flow, shear rate and FMD were measured pre and post each condition. Mean shear rate increased significantly post passive heat in children (103.1 s-1 to 230.4 s-1) and adults (29.9 s-1 to 140.3 s-1) with a greater increase in adults than children. Despite the increases in mean shear rate and antegrade shear rate, FMD did not significantly improve post passive heat in either the boys or men. Mean shear rate decreased significantly following the low pressure cuff condition in children (142.4 s-1 to 101.1 s-1 ) and adults (33.7 s-1 to 23.8 s-1 ). The significant increases in retrograde shear rate post low pressure cuff was accompanied by a significant decline in FMD in children (4.3% to 2.58%) and adults (4.13% to 2.86%). We conclude that passive heat can increase shear rates and flow in both children and adults but may not be enough to stimulate an increase in FMD. Low pressure cuffing can reduce the shear stimulus the relationship between shear rate and FMD in children and adults. These findings show for the first time that down-regulation of shear rate reduces FMD in children and adults and has implications for our understanding of development vasomotor physiology.