Rayman, Gerrard Abdool; (1992) Cutaneous vascular haemodynamics in diabetes mellitus. Doctoral thesis (M.D.), University College London.

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Abstract

In this thesis the laser Doppler flowmeter and other microvascular methods were used to investigate the skin microcirculation in non-diabetic and diabetic subjects in order to gain a greater understanding of the normal microcirculation and to define abnormalities relevant to the diabetic state. The principle findings were- 1. The normal skin microvascular response to thermal and mechanical injury is a substantial increase in blood flow. In diabetic subjects with and without complications this hyperaemic response was reduced and degree of impairment was found to be greatest in those with the severest complications. 2. In diabetic patients, the diameter of foot skin capillaries was reduced and the basement membrane width was found to increase progressively with increasing severity of complications. These structural changes may partly explain the reduced hyperaemic responses and their relationship with severity of complications. These structural and functional abnormalities may be implicated in the pathogenesis and impaired healing of diabetic foot lesions. 3. In normal subjects, blood flow in the toe pulp fell by 80% when the foot was lowered 50 cm below the heart. Toe blood flow in neuropathic diabetic subjects was three fold higher than in normal subjects, and on lowering the foot this difference was even greater; dependent flow was seven fold higher and the fall in blood flow was only 50%. These findings are compatible with reduced central sympathetic tone and/or peripheral sympathetic nerve failure. 4. In young non-neuropathic diabetic subjects, the more severe stress of sitting still for 50 minutes with the foot 1 meter below heart level, also revealed an increase in toe pulp blood flow. This was associated with elevated capillary pressure, failure in the expected rise in plasma osmotic pressure, and increased foot swelling. These results provide evidence of capillary hypertension and impairment of oedema preventing mechanisms in the dependent foot of diabetic subjects. These abnormalities may be important in initiating structural and functional damage to the skin microcirculation.

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