Length-Normalized Pulse Photoplethysmography: A Noninvasive Method to Measure Blood Hemoglobin, Bronx, NY

AbstractTo determine whether blood hemoglobin concentration ([Hb]) could be measured noninvasively as the ratio of pulsatile changes in attenuation (absorbance plus scatter) of light (D) across a body part to changes in light path length (l), we measured transmission of near-infrared light (905±10 nm) through a finger, using a modified pulse oximeter, and simultaneously monitored fingertip diameter, using a sonomicrometer. In 25 subjects with [Hb] ranging from 3.1 to 18.2 gm/dl, and with normal oxygenation, average D/l ratio over 30–60 s correlated strongly with [Hb] measured by Coulter counter (r=0.84, p≪0.001), though with considerable scatter, with absolute value of differences averaging 17% of the mean. Using 12 gm/dl and 0.75 mm-1 as the lower limits of normal for [Hb] and D/l, respectively, two of nine normals had low (D/l) (78% specificity), and only one of 16 anemic subjects had borderline normal (D/l) (94%–100% sensitivity). The positive predictive value of a low (D/l) was 88% and the negative predictive value was 87.5%. With further development, this technique may reduce the need for phlebotomy, thereby reducing risks and costs and improving the experience of being a patient. © 2002 Biomedical Engineering Society. PAC2002: 8763Lk, 8714Ee