Indirect measurement of systolic blood pressure in the lower limb using a mercury in rubber strain gauge

The systolic blood pressure in the thigh, calf, and first toe was measured in 30 normal subjects between the ages of 13 and 55, using a mercury in rubber strain gauge on the toe as the indicator of systolic pressure. The thigh and calf systolic pressures were on average 2·8 mm Hg (SD± 12·8) and 5·2 mm Hg (SD± 12·2), respectively, above that of the brachial artery measured by auscultation. The mean toe systolic pressure was 5·1 mm Hg (SD ± 14·7) below that of the arm when allowances were made for the hydrostatic pressure effect caused by the difference in height between the arm and toe. After correction for changes in arm systolic pressure which occurred between the measurements, the elevation in thigh and calf systolic pressure over the arm was greatest in the older subjects. However, the drop in toe systolic pressure below that of the arm was most marked in the younger subjects. Pressure gradients have been calculated between the thigh and calf and between the calf and toe. The thigh systolic pressure is on average 2·4 mm Hg below that of the calf. The mean calf systolic pressure is 10·4 mm Hg above that of the toe. We conclude that the mercury in rubber strain gauge on the toe is an accurate measurement of systolic blood pressure in the lower limb, is extremely simple to perform, and will be of value in detecting systolic pressure gradients. The pressure measurements may be used to predict run-off problems before surgery for peripheral arterial disease and for selecting more accurately those patients with critical ischaemia.