I I Development and Evaluation of a Noninvasive Hemoglobinometer

Measurement of hemoglobin concentration is among the most common clinical procedures. It is necessary in screening for anemia and is a means of providing a general assessment of physical well-being. Current methods for measuring hemoglobin concentration are invasive, requiring blood access. This paper describes a novel technique for measuring hemoglobin concentration noninvasively. The method takes advantage of the unique optical properties of hemoglobin to make the measurement. A vascularized tissue bed is transilluminated with a narrow linewidth optical source at an isobestic wavelength of oxyand deoxy-hemoglobin. The transmitted light intensity is measured as the tissue is compressed, which causes an increase in the transmitted optical signal by forcing blood out of the optical path. The Lambert-Beer Law, modified to include optical scattering by tissue, provides the basic principle upon which the technique is based. The theory is discussed and an experimental prototype device is described. Preliminary analysis of experimental results shows a correlation between measurements obtained using the noninvasive tissue compression/transillumination method and hemoglobin concentrations measured by a clinical (invasive) hemoglobinometer. However, noise in the data are cause for concern, and may limit the clinical utility of the technique. Possible explanations for the variability in experimental results are given, along with suggestions for possible improvements to the device and technique.