Impact of retrograde shear rate on brachial and superficial femoral artery flow-mediated dilation in older subjects

Abstract

An inverse, dose-dependent relationship between retrograde shear rate and brachial artery endothelial function exists in young subjects. This relationship has not been investigated in older adults, who have been related to lower endothelial function, higher resting retrograde shear rate and higher risk of cardiovascular disease.

Aim: To investigate the impact of a step-wise increase in retrograde shear stress on flow-mediated dilation in older males in the upper and lower limbs.

Methods: Fifteen older (68 ± 9 years) men reported to the laboratory 3 times. We examined brachial artery flow-mediated dilation before and after 30-min exposure to cuff inflation around the forearm at 0, 30 and 60 mmHg, to manipulate retrograde shear rate. Subsequently, the 30-min intervention was repeated in the superficial femoral artery. Order of testing (vessel and intervention) was randomised.

Results: Increases in cuff pressure resulted in dose-dependent increases in retrograde shear in both the brachial and superficial femoral artery in older subjects. In both the brachial and the superficial femoral artery, no change in endothelial function in response to increased retrograde shear was observed in older males ('time' P = 0.274, 'cuff*time P = 0.791', 'cuff*artery*time P = 0.774').

Conclusion: In contrast with young subjects, we found that acute elevation in retrograde shear rate does not impair endothelial function in older humans. This may suggest that subjects with a priori endothelial dysfunction are less responsive or requires a larger shear rate stimulus to alter endothelial function.

Keywords: Atherosclerosis; Echo-doppler; Endothelial function; Retrograde shear stress; Shear stress pattern.