Summary.Peripheral blood flow is known to be qualitatively increased in diabetic patients with neuropathy. We have measured the actual blood flow in the feet of diabetic patients with neuropathy using non-invasive mercury strain gauge plethysmography and Doppler sonogram techniques and shown that it is increased on average five times above normal at an ambient temperature of 20 ~ -22 ~ Moreover, reduction of this high flow by sympathetic arousal stimuli proved possible in those with severe painful neuropathy contrasting strongly with failure to reverse it in those with severe non-painful sensory neuropathy. Reduction of blood flow was associated with reduction in neuropathic pain. We studied 22 diabetic patients with severe sensory neuropathy and eight with painful neuropathy. High resting foot blood flows were demonstrated in both groups with neuropathy. The big toe flow in those with severe sensory neuropathy was 29.3 + 9.2 ml. rain-1. 100m1-1 (mean+-SD) and in the painful neuropathy group, 25.9+_7.5, compared with 5.2+2.4ml.min -1. 100m1-1 in the non-diabetic control subjects (p<0.001). High foot skin temperatures were also recorded in the groups with neuropathy, reflecting the high blood flow. The subjects with painful neuropathy retained the ability to constrict peripheral blood vessels in response to arousal stimuli, and reduce peripheral flow on average by 32% compared with the patients with sensory neuropathy who responded on average by only 10%. The demonstration of a peripheral sympathetic defect, responsible for the high blood flow and the potential reversal of such flow in painful neuropathy may be important in our further understanding of the aetiology of such pain and its treatment.Key words: Diabetes mellitus, peripheral blood flow, sensory neuropathy, painful neuropathy, peripheral sympathetic neuropathy.During the nineteenth century, the feet of diabetic patients with peripheral neuropathy were observed to be hot and erythematous [1] and the blood flow in such feet was considered to be increased. This increase is now thought to be due to the dilation of denervated arteriovenous shunts [2-9] normally controlled by sympathetic nerves.Measurement of actual blood flow in diabetic neuropathic feet has only been undertaken in one previous study [10]. Blood flow was not found to be increased in neuropathic subjects probably because the studies were conducted by waterbath plethysmography at 32~ causing vasodilatation and increased flow in the control subjects.The aim of this study was to measure the magnitude of resting foot blood flow in a group of diabetic patients with severe sensory neuropathy and to discover whether the hot, burning foot, so characteristic of distal painful neuropathy, also has a high resting flow resulting from a peripheral sympathetic defect. In addition, the sympathetic responses of both types of neuropathy were tested to discover whether either retained the ability to reduce peripheral flow by vasoconstriction, and whether any benefits might result from this.
Subjects and metho...