Orthostatic changes in first-toe blood pressure in normal subjects and in patients with occlusive arterial disease.

Orthostatic changes in first-toe systolic blood pressure, measured with cuff and strain-gauge technique, were compared with changes expected according to hydrostatic calculations. Twenty-five limbs with occlusive arterial disease were studied. When the first toe was lowered 40 cm below the heart, the toe blood pressure--corrected for changes in systemic blood pressure--rose on median 3.9 (-8.7 to 11.4) mmHg more than expected. The difference was statistically significant. Elevation of the first toe 40 cm above the heart did not lead to significant deviation from the expected blood pressure. Twelve normal limbs showed no significant deviations in blood pressure during the orthostatic changes. It is proposed that the additional increase in the indirectly measured systolic pressure also represents an additional increase in the mean arterial blood pressure. The mechanism of this additional increase seems to be reflex vasoconstriction in the distal tissues, reducing the pressure gradient across the proximal collateral vessels. The additional increment may contribute to the abnormalities of local blood flow regulation observed in ischaemic limbs.