Vasodilatory capacity of the skin in venous disease and its relationship to transcutaneous oxygen tension

Abstract

Abstract Low transcutaneous oxygen tension (Ptc,O2) values in the supramalleolar skin of patients with venous disease are often reported. This measurement involves heating the skin to 43°C to cause maximum vasodilatation and is valid only if liposclerotic and normal skin can vasodilate to the same degree. Forty-four limbs were studied, 15 with lipodermatosclerosis (LDS), 14 with uncomplicated varicose veins, and 15 controls. A Ptc,O2 electrode was modified to incorporate a laser Doppler probe. Laser Doppler flux was measured in the supramalleolar skin before and after local heating to 43°C and the relative increase in flux was measured. The Ptc,O2 was then measured at the same site and on the chest. Vasodilatory capacity was expressed as the ratio of peak:basal laser Doppler flow, and the Ptc,O2 was expressed as a leg:chest ratio. Median laser Doppler flow was higher in limbs with LDS (median 67 mV) than in normal limbs (median 40 mV) (P<0·03). Ptc,O2 was higher in control limbs (median ratio 0·94) than in limbs with LDS (median 0·53) (P < 0·006). The microcirculation in LDS had less capacity to vasodilate after heating (median factor of increase 5·4) than normal skin (median factor of increase 12·3) (P<0·001). A simple regression analysis was performed on all pairs of data, and revealed a correlation between Ptc,O2 and vasodilatory capacity (r = 0·524, P<0·001). The results indicate that low Ptc,O2 levels in venous disease reflect an inability of the microcirculation to increase its flow in response to local heating; inferences about the oxygen content of liposclerotic skin at normal temperatures cannot be drawn using this technique.