Background: There is a growing interest in precisely estimating mean blood pressure (MBP) in large arteries. The form factor (FF) is the fraction of pulse pressure that must be added to diastolic pressure to estimate the actual MBP, i.e., the pressure integrated (averaged) over the whole cycle. It is admitted that FF of the radial artery is 0.33, while FF of the aorta and carotid and brachial arteries is in the 0.40–0.45 range. The FF of the femoral artery remains to be determined.

Methods: Sixty-five hemodynamically stable intensive care unit patients equipped with an indwelling femoral catheter were prospectively studied (mean age+/−SD = 64+/−14 years). FF of the femoral artery was calculated as the time-averaged MBP minus diastolic blood pressure difference divided by pulse pressure (FF = (MBP – DBP) / PP).

Results: Form factor of the femoral artery was 0.35+/−0.04 (n=65 range 0.22–0.47). FF was similar in female (n=23) and male (n=42) patients (0.36+/−0.05 vs 0.34+/−0.04, respectively) and in patients receiving vasopressors (n=43) or not (n=22) (0.34+/−0.05 vs 0.35+/−0.03, respectively). FF of the femoral artery was positively related to MBP (r²=0.11) and DBP (r²=0.07) (each P < 0.05) while it was not related to patient’s age, body height, body weight, heart rate, systolic pressure and PP.

Conclusions: The mean form factor of the femoral artery was 0.35, a value closer to the FF of radial artery than to the FF of central and brachial arteries. The implications for pressure wave transmission to the lower limbs remain to be studied.