1. In order to determine whether rheological changes occur in neuropathic diabetic patients in the absence of smoking, proteinuria, retinopathy or other factors thought to influence haemorheology, three groups of subjects were studied; 24 non-diabetic control subjects (C), 24 non-neuropathic (D) and 24 neuropathic (N) diabetic patients. The groups were matched for age, sex, type and duration of diabetes. No patient or control was a current smoker. No patient had clinically detectable retinopathy or microalbuminuria. Neuropathy was defined as a peroneal conduction velocity < 40 ms−1. All subjects were tested resting semi-recumbent after a light breakfast.

2. There were no significant differences in rheological or microvascular parameters between uncomplicated diabetic patients and non-diabetic control subjects, although peroneal nerve motor conduction velocity was significantly reduced in otherwise uncomplicated diabetic patients [C 51.7 ± 6.0 ms−1 (mean ± SD) versus D 45.1 ± 5.2 ms−1 (P<0.05 C versus D)].

3. Transcutaneous oxygen and laser Doppler flux measured at 44°C were higher in control subjects than in neuropathic diabetic patients [C 76 ± 16 mmHg versus D 71 ± 10 mmHg versus N 63 ± 9 mmHg, and C 72 ± 40 flow units versus D 64 ± 41 flow units versus N 50 ± 26 flow units respectively (both P not significant C versus D, P<0.05 N versus C).

4. Erythrocyte aggregation, plasma viscosity and plasma fibrinogen were all significantly higher in the neuropathic diabetic patients compared with non-diabetic control subjects (all P<0.05 N versus C). Erythrocyte filtration was not significantly different between groups but was lower in diabetic patients. Whole-blood viscosity (corrected to 45% haematocrit) was significantly higher at both high (100 s−1) and low (1 s−1) shear rates in neuropathic diabetic patients than in non-diabetic control subjects (both P not significant C versus D, P<0.05 N versus C). There were no significant differences in whole-blood viscosity at a shear rate of 0.01 s−1.

5. In summary, there were no significant differences in rheological or microvascular parameters between matched groups of uncomplicated diabetic patients and control subjects, but erythrocyte aggregation, fibrinogen and plasma and corrected whole-blood viscosity were all significantly different in neuropathic diabetic patients compared with control subjects, as were assessments of microvascular flow. These results suggest that haemorheological changes are associated with disturbances of microvascular flow and diabetic peripheral neuropathy in the absence of other diabetic complications.

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