Increased forearm blood flow in longstanding Type 1 diabetic patients without microvascular complications

According to the 'haemodynamic hypothesis', chronic hyperglycaemia induces an increase in tissue perfusion that predisposes to microangiopathy. We hypothesized that patients with longstanding diabetes mellitus (DM), who have not developed microvascular complications, would have normal tissue perfusion.

In six Type 1 diabetic patients (age 43.4 +/- 1.1 years; DM duration 25.3 +/- 2.6 years.; HbA(1c) 8.5 +/- 0.7%), who had no evidence of microvascular complications, and six age- and gender-matched healthy volunteers (Control) we measured haemodynamic parameters including forearm blood flow (FBF; plethysmography) and sympathetic tone, an important regulator of blood flow, by the combination of plasma sampling (catecholamine levels), microneurography and power spectral analysis of blood pressure and heart rate.

FBF was increased in the diabetic compared with control subjects (4.8 +/- 1.2 vs. 2.2 +/- 0.3 ml/dl per min, P < 0.05) and forearm vascular resistance (FVR) was decreased (25 +/- 6 and 43 +/- 3 arbitrary units, P < 0.05). Heart rate was higher in diabetic subjects (77 +/- 10 vs. 57 +/- 2 beats/min, P < 0.05). All parameters of sympathetic tone were similar in diabetic and control subjects.

In patients with Type 1 diabetes, without signs of microvascular complications and with diabetes duration of > 20 years, skeletal muscle blood flow was increased while sympathetic tone was normal. These results suggest that increased blood flow does not inevitably lead to microvascular complications and challenge the hypothesis that it has a causative role in the pathophysiology of complications.