The Effect of Insulin Infusion on Capillary Blood Flow in the Diabetic Neuropathic Foot

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Abstract
The effect of a short-term improvement in glycaemic control induced by insulin infusion on foot skin capillary blood flow was previously unknown. In seven Type 2 (non-insulin-dependent) diabetic subjects with neuropathy capillary blood flow was measured in the great toe nailfold by television microscopy. An estimate of arteriovenous shunt flow was obtained simultaneously in the pulp of the great toe by laser Doppler flowmetry. After omission of oral hypoglycaemic therapy for 24 h mean blood glucose was 15.7 +/- 0.7 (SEM) mmol l-1. A priming infusion of 0.1 U kg-1 of insulin was given intravenously over 15 min, followed by a variable rate insulin infusion adjusted to steadily reduce blood glucose avoiding hypoglycaemia. At the end of the study blood glucose was reduced to 6.9 +/- 0.7 mmol l-1 (p less than 0.001). During the insulin infusion, capillary blood velocity increased by 28.8% (p less than 0.05), and the diameter of the capillary erythrocyte column increased from 7.6 +/- 0.2 to 9.2 +/- 0.3 micron (p less than 0.01). Thus during the insulin infusion, the calculated capillary flow increased to 226 +/- 36% above basal values (p less than 0.01). Laser Doppler flow did not change significantly, suggesting that during insulin infusion skin blood flow is redistributed with an increase in capillary flow relative to arteriovenous shunt flow.