A study of factors governing fluid filtration in the diabetic foot.

The effect of lowering the foot on the factors governing fluid filtration in the foot were studied in 12 male insulin-dependent diabetic subjects and 10 controls. Toe skin blood flow, measured by laser Doppler flowmetry, was significantly higher during dependency in the diabetic group. In the control subjects, the colloid osmotic pressure of venous blood sampled from the foot rose to 47.7 mmHg (range 45.1-53.8) after 50 min of foot dependency. In the diabetic group, colloid osmotic pressure failed to rise to the same extent (median 36.7 mmHg; range 28.6-43.0; P < 0.001). Capillary pressure, measured directly by the Landis microinjection technique, was significantly higher in the diabetic group (85.3 +/- 1.7 (n = 6) vs. 92.2 +/- 4.6 cm H2O (n = 6); P < 0.007), as was foot swelling rate determined by mercury strain gauge plethysmography (0.069 +/- 0.022 vs. 0.099 +/- 0.025 ml min-1 100 ml-1; P < 0.02). These results suggest an impairment of the oedema-preventing mechanisms in diabetic subjects which may contribute to the risks of ulceration in the diabetic foot.