Development of a new instrument to measure oxygen saturation and total hemoglobin volume in local skin by near-infrared spectroscopy and its clinical application

The oxygen saturation (StO₂) and total hemoglobin volume in cutaneous blood are closely related to cutaneous metabolism and are important factors in determining the skin color. Most conventional apparatuses for the measurement of cutaneous metabolism have been designed to evaluate qualitative changes in the oxyhemoglobin volume, deoxyhemoglobin volume, and their sum (total Hb volume) relative to their baseline values. In this study, we developed an instrument for non-invasive evaluation of individual and regional differences in StO₂ and Hb volume, a system unaffected by melanin (Kao PSA system model III), and examined the validity of its application. First, changes in StO₂ and total Hb volume in the antebrachial region during venous occlusion and devascularization by compression of the brachial region were evaluated. Changes in total Hb volume following venous occlusion were found to reflect the cutaneous blood flow. Also, StO₂ was considered to reflect the state of oxygen consumption by the skin, because it was markedly reduced during devascularization. Next, the subjects were exposed to graded hypobaric conditions, and the relationships among StO₂, arterial blood oxygen saturation (SaO₂), and venous blood oxygen saturation (SvO₂) were studied. StO₂ showed significant positive correlations with SaO₂ (r=0.811, P<0.001) and SvO₂ (r=0.966, P<0.001), and its correlation with SvO₂ was particularly strong. Therefore, StO₂ was found to be closely dependent on SvO₂. Lastly, StO₂, total Hb volume, and other parameters were measured in healthy women (aged 20–69 years), and their regional differences and age- associated changes were evaluated. These regional differences (angle of mouth > cheek > forehead) and age-associated decreases in StO₂ are considered to be caused by the age-associated decreases in the cutaneous blood flow. Received: 21 May 1999 / Revised: 19 November 1999 / Accepted: 24 November 1999