Department of Dermatology, University Hospital, Tübingen, Germany

Correspondence: Dr med. M. Hahn, Universitäts-Hautklinik, Liebermeisterstr. 25, 72076 Tübingen, Germany

Received 29 April 1997; Revised 18 August 1997; Accepted 28 January 1998.

Abstract

There is increasing evidence that endothelial damage occurs at a very early stage during the course of systemic scleroderma. Endothelial damage is accompanied by impaired microvascular function, which has clearly failed in patients with systemic scleroderma, as evidenced by necrosis of the fingertips in severe cases. We investigated two important determinants of microvascular function, namely capillary blood pressure and capillary red blood cell velocity, simultaneously in the same capillary. In patients with systemic scleroderma and in healthy volunteers matched for age and sex, capillary blood pressure was measured by direct cannulation and capillary red blood cell velocity by video microscopy. Capillary blood pressure and capillary red blood cell velocity were significantly lower in patients (14.27 4.34 mmHg, 230 310 m per s) than in healthy controls (19.06 3.69 mmHg, p < 0.008, and 910 240 m per s, p < 0.003) at an ambient temperature of 22°C, whereas no significant difference in skin temperature was observed (23.7 0.9°C vs 24.7 1.9°C) and no occlusion of finger arteries was detected. Capillary blood pressure in enlarged capillaries did not differ from that in normal-shaped capillaries in the patients (correlation of diameter and capillary blood pressure, R² = 0.04), which was also the case with capillary red blood cell velocity (R² = 0.13). Capillary pulse pressure amplitude and capillary red blood cell velocity showed a strong correlation (R² = 0.81), suggesting that the pressure gradient across the capillary loop, which is the driving force for capillary red blood cell velocity, was mainly dependent on precapillary resistance. These observations reflect the inadequate microvascular function in systemic scleroderma, which may be due mainly to a pathophysiologic functional increase in precapillary resistance, even at comfortable ambient temperatures.