Abstract

Normal healthy subjects show a reflex rise in precapillary resistance in the skin of the foot when they rise from lying to standing. To investigate the integrity of this reflex in patients with diabetes mellitus blood flow in the plantar region of the big toe was measured, using a laser Doppler flowmeter. The responses of diabetic patients with and without peripheral sensory neuropathy and healthy control subjects matched for age and sex were studied, with the foot at heart level and the foot passively lowered to 50 cm below the heart. In normal subjects mean blood flow recorded during the third to fourth minute of dependency fell to 18.1 (SD 11.9)% of the preceding resting flow determined with the foot at heart level. In the diabetic patients without neuropathy blood flow fell to 28.9 (18.6)% of the preceding resting flow. In the diabetic patients with neuropathy blood flow fell to 53.5 (23.7)% of the preceding resting flow, which was significantly different from the value achieved by the diabetics without neuropathy (p less than 0.02) and the healthy controls (p less than 0.002). Six normal subjects were indirectly heated to release sympathetic tone and achieve the same mean skin temperature of the foot as the diabetic patients with neuropathy, and blood flow fell to 38.7 (24.3)% of the preceding resting flow, a value not significantly different from the response seen in the patients with neuropathy. These findings suggest that the postural control of blood flow in the foot is disturbed in patients with diabetic neuropathy, and this disturbance is compatible with a loss of sympathetic vascular tone. The resultant hyperperfusion on dependency may account for the oedema seen in some patients with neuropathy and may also act as a stimulus for the thickening of capillary basement membranes.