Detection of microvascular impairment in type I diabetics by laser Doppler flowmetry

The use of a laser Doppler flowmeter to detect microcirculatory impairment and abnormalities in sympathetic neural control of blood flow in the hands and feet was evaluated. Measurements were carried out in 15 insulin dependent diabetic patients with retinopathy, 14 uncomplicated diabetics and 15 normal subjects. Three tests were assessed (1) the hyperaemic response of the skin microcirculation to local heating at 44 degrees C; (2) the reactive hyperaemic response of the skin microcirculation to 2 min arterial occlusion; and (3) the peripheral vasoconstrictor reflexes to cold challenge and inspiratory gasp. Tests (1) and (2) were applied to the dorsum of the hand and foot and test (3) to the pulp of the fingertip and toe. All tests were carried out with the subjects peripherally vasodilated by indirect heating. At the hand no differences were found between the groups for any of the measures. The hyperaemic response to local heating at the dorsum of the foot showed that the maximum flow in complicated diabetics was significantly lower than that in uncomplicated patients (P less than 0.01) and in normal subjects (P less than 0.002). A new measure, the time for flow to increase to 3 times basal flow, was longer in the complicated group compared with the uncomplicated (P less than 0.02) and the normal groups (P less than 0.001). This test also showed that the response in the uncomplicated group was slower than in the normal group (P less than 0.01). The post-occlusive hyperaemic response did not differ between groups. Measurement of vasoconstrictor reflexes showed that the complicated group had a poorer response to cold challenge at the big toe than the uncomplicated group (P less than 0.02) and the complicated group generally tended to have poorer responses than the other two groups. In conclusion, we have found that the hyperaemic response to local heating can detect microvascular impairment in diabetes before other complications become apparent and that the vasoconstriction test may be able to identify individuals with peripheral sympathetic neuropathy.