Relation of femoral diameter, shear rate, and dilatory response to knee extensor exercise.

Abstract

Younger women typically exhibit marked dilation of the common femoral artery (CFA) during knee extensor exercise; this is in apparent contrast to subject groups with larger (men) and/or older (older women) vessels, which on average display much smaller exercise-induced increases in CFA diameter. To gain additional insight into this variation, the present study closely examined within- and between-group relationships among CFA diameter, shear rate, and the magnitude of exercise-induced CFA dilation. Healthy women (15 younger and 18 older) and men (15 younger and 13 older) performed graded single-leg knee extensor exercise while CFA diameter and blood velocity were measured using Doppler ultrasound. Resting CFA diameter was smaller (P < 0.05) in women (younger: 0.71 ± 0.02 cm; older: 0.72 ± 0.02 cm) compared with men (younger: 0.84 ± 0.01 cm; older: 0.97 ± 0.03 cm). Resting CFA diameter was inversely associated with peak shear rate (combined groups: r = -0.83, P < 0.001) and the magnitude of dilation in women (younger: r = -0.82; older: r = -0.73, P < 0.001) and younger men (r = -0.66, P < 0.01) but not in older men (r = -0.17, P = 0.56). The dilatory response of the CFA to graded increases in shear rate showed a continuum across groups best described by a quadratic function (r2 = 0.89). Using piecewise regression modeling, a threshold diameter of 0.79 cm was identified below which diameter is inversely related to the magnitude of CFA dilation but above which little to no dilation was present. The CFA dilates to knee extensor exercise in women and men, the magnitude of which varies because of differences in shear rate across CFA diameters.