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1 Noll Laboratory, The Pennsylvania State University, University Park, Pennsylvania, United States; Kinesiology, The Pennsylvania State University, University Park, Pennsylvania, United States
2 Noll Laboratory, The Pennsylvania State University, University Park, Pennsylvania, United States; Physiology, The Pennsylvania State University, University Park, Pennsylvania, United States
3 Noll Laboratory, The Pennsylvania State University, University Park, Pennsylvania, United States; Kinesiology, The Pennsylvania State University, University Park, Pennsylvania, United States; Physiology, The Pennsylvania State University, University Park, Pennsylvania, United States
* To whom correspondence should be addressed. E-mail: dnp3{at}psu.edu.
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 (20-30 yrs) and 14 older (60-79 yrs) healthy women at rest, during and following 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 (brachial ~1300-1400 s-1; popliteal ~400-500 s-1). FMD (% change above diameter measured during occlusion) was ~50-60% lower (p < 0.05) in the brachial (young = 15.8 ± 0.8%; older = 8.1 ± 1.5%) and popliteal (young = 4.6 ± 0.7%; older = 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 the brachial and popliteal arteries in older women. These results suggest 1) brachial and popliteal FMD (following 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.
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