MICROCIRCULATORY COMPENSATION TO PROGRESSIVE ATHEROSCLEROTIC DISEASE

The precapillary resistance in the skin of the foot increases with sta nding. This mechanism, termed the venoarterial reflex (VAR) restricts arterial inflow, and avoids an excessive rise in capillary pressure. T his study tests the hypothesis that there is microcirculatory compensa tion to atherosclerotic disease of increasing severity. Foot skin perf usion (FSP) was measured in 100 limbs with a laser Doppler placed on t he plantar aspect of the great toe. Limbs were categorized as normal ( n = 31) with an ankle brackial index (ABI) greater than or equal to 0. 96, claudicants (n = 42) ABI 0.5-0.86, and critical ischemia (n = 27) with an ABI less than or equal to 0.49 or a pulse volume recording con sistent with severe peripheral vascular disease and symptoms of rest p ain or tissue loss. Segmental Doppler pressures and pulse volume recor dings were performed prior to laser Doppler measurements. Subjects wit h clinical signs or symptoms of chronic venous insufficiency were excl uded. The resting foot skin perfusion was measured in the horizontal a nd dependent position, with the patient supine and sitting. Comparison s within categories were done using Wilcoxon matched pairs signed rank test and between groups with Mann-Whitney U test for unpaired data. D ifferences were considered significant if they exceeded the 95% confid ence level (p value less than or equal to 0.05). Resting supine skin p erfusion was similar between nondiabetic normals and claudicants and d iabetic normals and claudicants. There was a significant decrease in t he foot skin perfusion (mean FSP +/- SEM) in the normal limb with a ch ange from the supine (7.8 +/- 2.2 ml/min/100 g) to the dependent (2.8 +/- 0.6 ml/min/100 g) position indicating an intact VAR. This was abse nt in 33% of the limbs with claudication. Limbs with critical ischemia demonstrated an increase in FSP with dependency (supine 4.0 +/- 1.0 m l/min/100 g) versus dependent (8.4 +/- 1.8 ml/min/100 g) and was prese nt in both diabetic and nondiabetic limbs. Microcirculatory compensati on occurs early in atherosclerotic limbs. Although supine FSP is simil ar in normals and claudicants, a greater percentage of claudicants dem onstrate a loss of the VAR. Critically ischemic limbs have increased F SP in the dependent position. These observations indicate that there a re microcirculatory alterations in limbs with claudication and assist in explaining why patients with ischemic rest pain obtain relief and d evelop edema with dependency.