Skin SO2 Measurement Using Visible Lightguide Spectrophotometry in a Black Population: A Feasibility Study

The aim of the study was to investigate the influence of melanin content on the visible wavelength range spectrophotometricmeasurement of SO2 in the skin of normal healthy black and white volunteers. The reactive hyperaemia induced by a 5-minute period of tourniquet occlusion of the brachial artery, as manifested in the change in skin SO2, was compared with the reactive hyperaemia index (RHI) and arterial stiffness index (AI) as measured using the Endo-PAT2000® peripheral arterial tonometry device. Further measurements were carried out on a diabetic patient with critical ischaemia. The measurements in the normal volunteers and the patient showed that there that there was no correlation between SO2 and melanin index (r2 = 0.02). There was a poor correlation between the degree of reactive hyperaemia as assessed using tissue SO2 measurement and the parameters derived using the Endo-PAT2000® device. Measurements on the critically ischaemic lower limb of the diabetic patient revealed a mean medial/lateral SO2 of 26.3% and a degree of tissue hypoxia (the percentage of recordings with an SO2 of 15% or less) of 16.2%. This pilot study demonstrated that themeasurement of tissue SO2 in the skin of black subjects is feasible, not only under conditions of normal perfusion, but also in critical limb ischaemia.