Abstract
Insulin deficient, type I diabetic patients have reduced skin blood flow reserve. It is not known whether these skin perfusion abnormalities also exist in non-insulin dependent (type II) diabetic patients. An additional open question is whether the reduced skin blood flow is due to increased resistance of the cutaneous microvasculature or to decreased peripheral perfusion pressure due to increased atherosclerosis in the diabetic population. We measured skin blood flow by laser Doppler flowmetry in patients with type II non-insulin treated diabetes. Limb systolic blood pressure was measured distally using a sensitive sonar Doppler device at the finger and toe. The ratio of pressure to flow was computed as an index of peripheral blood flow resistance. To assess the effect of cutaneous blood flow resistance, we elicited maximal vasodilation by increasing local skin temperature directly at the site of the laser Doppler probe. We compared blood flow and pressure in diabetic patients with the values in non-diabetic control patients. As a further control population, we also assessed these same parameters in non-diabetic patients with peripheral vascular disease, which may be expected to decrease large arterial blood flow pressure without directly affecting the microvasculature. There were 68 type II diabetic patients, 18 non-diabetic control subjects, and 25 non-diabetic patients with intermittent claudication. We measured skin blood flow at the dorsal surfaces of the finger and toe, sites with primarily nutritive capillary perfusion, and at the plantar surfaces of the finger and toe, where arteriovenous shunt perfusion predominates. Heat stimulated flow was markedly lower for the diabetic patients at the finger dorsal surface (16.5 ± 1.4 ml/min/ 100 g vs 29.8 ± 4.4 ml/min/100 g in the non-diabetic group (p <0.05). The resistance index was 13.2 ± 1.9 in the diabetic patients and 6.8 ± 1.7 in the controls (p <0.05). At the toe dorsum, basal temperature flow was significantly lower in the diabetic group (0.6 ± 0. 1 ml/ min/100 g) than in the non diabetic group (1.1 ± 0.2 ml/ min/100 gm) with resistance index almost twice as high (379 ± 32) in the diabetic group versus non-diabetic controls (208 ± 36) [p <0.01 for both comparisons]. With the local application of heat, there was a much larger increase in flow in the non-diabetic subjects than in the diabetic group. The resistance index dropped much more with heat stimulation for the non-diabetic patients (10.8 ± 3.3) than for the diabetic patients (50.6 ± 10.4) [p <0.01] There was a lesser rise in flow at the toe pulp surface with heat in the diabetic patients (31.3 ± 3.0 ml/ min/199 gm) than in the control subjects (45.4 ± 5.9 ml/ min/100 gm; p <0.05) with a higher resistance index (13 ± 4) than in the non-diabetic subjects (4 ± 1) [p <0.05]. The claudication patients had substantially greater flow at the toe dorsal surface at basal temperature (2.2 ± 0.4 ml/min/100 gm) with significantly lower resistance index (126 ± 24) than the non-diabetic controls (p <0.05). At 44°C, toe dorsum flow was significantly higher (17.8 ± 3.7 ml/min/100 gm) than in the diabetic patients with lower resistance index (17.0 ± 6.6) [p <0.05]. Toe pulp flow at basal temperature was significantly higher (10.1 ± 2.0 ml/min/100 gm) than in either the diabetic (3.8 ± 0.6) or non-diabetic control groups (3.5 ±1.4) [p <0.05]. Skin blood flow is impaired in diabetes. The reduction is due to increased resistance in the capillary bed rather than to reduced perfusion pressure. The increased resistance was found only in the diabetic patients, not in the non-diabetic patients with peripheral vascular disease. To the contrary, there appeared to be a compensatory decrease in skin flow resistance in the patients with peripheral vascular disease. Thus, there is a small vessel disease which impairs cutaneous perfusion in diabetes, but there is no such effect on skin blood flow in non-diabetic patients with large vessel disease.