Ankle-Brachial Pressure Index

When stenotic lesions are present in any of the major arteries of the lower limb (except the deep femoral and internal iliac arteries), the systolic pressure measured at the ankle will be reduced relative to the systolic pressure measured in the brachial artery. The ratio of ankle systolic pressure to brachial artery systolic pressure is termed the ankle-brachial pressure index and is normally about 1.1. (The ratio is greater than 1.0 because the shape of the arterial pressure pulse changes from the ascending aorta to the periphery with the systolic pressure increasing and the diastolic pressure falling at peripheral sites.) With moderate stenosis, this index at rest may be around 0.8; with severe stenosis, the ratio may be less than 0.5.

During exercise, the increased flow across the stenotic lesion increases the pressure drop across the lesion resulting in a fall in distal pressures. Therefore, the ankle-brachial pressure index decreases during exercise when there is a proximal stenotic lesion.

Revised 11/08/07