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

Introduction: 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. Methods: 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. Results: 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 = j0.83, P<0.001) and the magnitude of dilation in women (younger: r = j0.82; older: r = j0.73, P<0.001) and younger men (r = j0.66, 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. Conclusions: 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.