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 spectrophotometric measurement of SO(2) 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 SO(2), 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 SO(2) and melanin index (r(2) = 0.02). There was a poor correlation between the degree of reactive hyperaemia as assessed using tissue SO(2) 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 SO(2) of 26.3% and a degree of tissue hypoxia (the percentage of recordings with an SO(2) of 15% or less) of 16.2%. This pilot study demonstrated that the measurement of tissue SO(2) in the skin of black subjects is feasible, not only under conditions of normal perfusion, but also in critical limb ischaemia.