Influence of Neuropathy on the Microvascular Response to Local Heating in the Human Diabetic Foot

Abstract

1. The diabetic neuropathic foot exhibits excess arteriovenous anastomotic shunt flow due to a reduced sympathetic vasoconstrictor tone. Local axon reflexes (mediating postural vasoconstriction, for example) are preserved even in severe diabetic neuropathy. This excess shunt flow and its local neurogenic control may be important in the development of complications of the neuropathic limb. 2. The response of arteriovenous anastomoses to local heating was assessed in 13 diabetic patients with neuropathy (12 insulin-dependent), 10 diabetic control patients (seven insulin-dependent) and 10 normal control subjects. The aim was to study the local reflex control of arteriovenous flow when central sympathetic tone had been largely removed. 3. The change in skin blood flow on local heating to 44 degrees C was measured by using a laser Doppler flowmeter in standard environmental conditions with the foot at heart level. Two sites were assessed: (i) the plantar surface of the great toe (a site in which skin blood flow is dominated by arteriovenous shunt flow) and (ii) the dorsum of the foot (a site without anastomotic flow). 4. It was found that when heat was applied to the plantar surface of the great toe in the diabetic patients with neuropathy a paradoxical decrease in flow through arteriovenous anastomoses occurred, flow declining to 65% (P less than 0.05) of its resting value. This could be compared with an increase in flow over the same time period of 262% and 228% (P less than 0.01) in diabetic control patients and normal subjects, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Streptozotocin-induced diabetes differentially affects sympathetic innervation and control of plantar metatarsal and mesenteric arteries in the rat

“…These studies have demonstrated that both type 1 (insulin dependent) and type 2 (noninsulin dependent) diabetic patients with signs of sensory and/or autonomic neuropathy (e.g., orthostatic hypertension) have increased skin blood flow under basal conditions (2,33) and attenuated reductions in skin blood flow (i.e., vasoconstriction) in response to sympathetic arousal [e.g., produced by mental arithmetic (2) or postural stimuli (29)]. Importantly, deficits in sympathetic vasoconstriction of arterial vessels supplying plantar skin can be demonstrated in both type 1 and type 2 diabetic patients at an early phase of diabetic neuropathy (31,35), perhaps suggesting that sympathetic neurons supplying these vessels are particularly vulnerable to the effects of diabetes.…”

Cutaneous Structural and Biochemical Correlates of Foot Complications in High-Risk Diabetes

“…Diabetes can be complicated by a range of neurologic, biochemical, inflammatory, and vascular skin deficits that may increase the risk of foot complications (6,9,10,14). Our goal was to determine whether high-risk patients exhibited specific skin structural and functional deficits that could serve as potential biomarkers and may ultimately predispose to foot complications.…”

Diabetes mellitus and the nervous system

“…The best known is the reduction of peripheral vasoconstriction in response to sympathetic stimuli either on coughing or standing up—the latter in part responsible for orthostatic hypotension. Paradoxical responses also occur—notably, the vasoconstrictor response which takes place on heating rather than the expected vasodilatation,49 and the vascular effects of insulin which lead to a reduction rather than an increase of peripheral vascular resistance and may be the mechanism by which insulin exacerbates orthostatic hypotension 50…”