Consideration of Resting Retrograde Shear on Endothelial Function as Assessed by Flow-Mediated Dilation in Healthy Adults.

Shear patterns influence endothelial function. Indeed, previous cell and animal studies have demonstrated that experimentally induced elevations in retrograde shear impair endothelial function. Similarly, experimental augmentation of retrograde shear in humans has been shown to reduce endothelial function in healthy adults. To date, no studies have investigated whether resting retrograde shear influences measures of endothelial function. Thus, we hypothesized that having higher retrograde shear rate (SR) and oscillatory shear index (OSI) at rest is associated with lower flow-mediated dilation (FMD) measures in healthy adults. Brachial artery FMD, retrograde-SR, and OSI were measured using duplex Doppler ultrasound in 88 healthy adults (18-45 years, 46 females). FMD was negatively correlated with resting retrograde-SR (r= -0.307, p= 0.004) and this relationship was similar in males (r= -0.310, p= 0.045) and females (r= -0.326, p= 0.027). Likewise, FMD was negatively correlated with OSI in the full cohort (r= -0.403, p< 0.001) as well as in males and females separately (males: r= -0.352, p= 0.022, females: r= -0.446, p= 0.002). Furthermore, subgroup analyses based on magnitude of retrograde-SR (in tertiles) demonstrated that participants with the highest retrograde SR and OSI at rest had the lowest FMD values [e.g., (no retrograde-SR FMD: 8.6±4.2%); (Tertile 1 retrograde-SR: 3.9±2.1 -1/s, FMD: 6.9±2.8%); (Tertile 2 retrograde-SR: 13.5±4.0 -1/s, FMD: 5.7±3.1%); and (Tertile 3 retrograde-SR: 42.8±21.1 -1/s, FMD: 4.6±2.1%, p< 0.001)]. Collectively, these findings suggest that having higher baseline resting retrograde-SR and OSI prior to FMD measures are associated with lower FMD values in healthy adults.