Passive flexion and femoral vein flow: a study using a motorized foot mover.

The effect of rhythmic passive flexion of the foot on femoral vein blood volume flow rate has been investigated in 11 patients undergoing surgery for varicose veins. With rates of flexion varying from 24 to 50 per minute and with amplitudes varying from 20 degrees to 50 degrees it has been shown that the peak femoral vein flow can be increased to twice its normal value and that its pulsatility can be increased elevenfold. These increases are proportional to both the rate and the amplitude of the flexion, the maximum occurring, theoretically, when the foot is flexed +/-28 degrees about a line perpendicular to the leg.The investigation has further shown that the effects of sustained passive flexion are maintained, without appreciable dimunition, for 30 minutes and that the maximum increases are produced in those patients who have the lowest resting flows. It is suggested that per-operative passive flexion of the feet may be a good prophylactic against postoperative deep vein thrombosis.