Age and flow-mediated dilation: a comparison of dilatory responsiveness in the brachial and popliteal arteries

Previous investigations of age-associated changes in flow-mediated vasodilation (FMD) in women have been limited to the upper extremity and have not accounted for possible age differences in the stimulus for dilation. The purpose of the present study was to compare age differences in brachial and popliteal FMD and its stimulus (changes in shear rate following occlusion). Ultrasound-derived diameters and Doppler flow velocities of the brachial and popliteal arteries were measured in 14 young (20- to 30-yr-old) and 14 older (60- to 79-yr-old) healthy women at rest and during and after 5 min of distal cuff occlusion. Resting diameters were similar (both P > 0.39) in both age groups. Peak shear rate did not differ with age in either artery: approximately 1,300-1,400 and approximately 400-500 s(-1) in brachial and popliteal arteries, respectively. FMD (percent change above diameter measured during occlusion) was approximately 50-60% lower (P < 0.05) in the brachial (15.8 + 0.8% vs. 8.1 + 1.5%) and popliteal (4.6 +/- 0.7% vs. 1.8 +/- 0.4%) arteries of the older women. The normalized response of the brachial and popliteal arteries (%FMD per unit change in shear rate) was also reduced with age (55% and 53%, respectively) but did not exhibit limb specificity. Additionally, endothelium-independent dilation, as assessed by administration of nitroglycerin, was similarly blunted (by 45-65%) in brachial and popliteal arteries of older women. These results suggest that 1) brachial and popliteal artery FMD (after 5 min of distal occlusion) are similarly reduced with age, 2) when normalized to the change in shear stimulus, both arteries are equally responsive to 5 min of distal cuff occlusion in women, and 3) the age-associated decline in FMD may be attributable in part to diminished smooth muscle responsiveness.