Local regulation of subcutaneous forefoot blood flow during orthostatic changes in normal subjects, in sympathetically denervated patients and in patients with occlusive arterial disease.

Local blood flow regulation was studied on the forefoot by the 133-Xenon wash-out method. In 21 normal limbs blood flow decreased 36% when the foot was lowered 40 cm below heart (local vasoconstrictor response). During elevation blood flow was constant to 20 cm, and flow decreased only 10% at further elevation to 40 cm, corresponding to a drop in vascular resistance of 15% (autoregulation of blood flow). In six sympathetically denervated limbs blood flow decreased only 6%, significantly less than in the normal limbs. Autoregulation of blood flow was preserved in these limbs. In 22 limbs with intermittent claudication blood flow decreased only 19%, significantly less than in the normal limbs. However, taking into account the additional increase in arterial pressure that occurs, when a limb with arterial occlusion is lowered there was no significant difference (p = 0.26) in the increase in vascular resistance between the two groups. During elevation vascular resistance decreased significantly in the claudicants indicating preservation of autoregulation. In limbs with rest pain blood flow increased 28% during lowering, and when the additional increase in arterial blood pressure was accounted for, a significant increase in vascular resistance of 21% was noted. During elevation blood flow decreased significantly, and the estimated vascular resistance in this group did not decrease significantly. The study suggests that the increase in blood flow and the relief of ischaemic rest pain induced by lowering are due to an additional increase in arterial pressure rather than due to dilatation of arterioles.