AJP - Heart and Circulatory Physiology, Vol 253, Issue 1 147-H153, Copyright © 1987 by American Physiological Society
Reflectance measurements of hematocrit and oxyhemoglobin saturation
J. M. Steinke and A. P. Shepherd
Fiberoptic oximeters measure oxyhemoglobin saturation from the optical
reflectance of whole blood, but the calibration of such oximeters is
hematocrit dependent. Therefore, using photon-diffusion theory and an
empirical approach, we have developed a new reflectance method that
determines hematocrit and correspondingly corrects the
oxyhemoglobin-saturation measurement. Our method employs four fiber-optic
light guides, a photodetector, and three inexpensive light-emitting diodes
(one with emissions at 660 nm and two at 813 nm). Hematocrit is determined
from the ratio of reflectances from the differently spaced emitting fibers
at 813 nm and is used to correct the 813-660 nm measurement of
oxyhemoglobin saturation. In red cell suspensions, the mean difference
between reflectance measurements of hematocrit and conventional
determinations was only 2.09% (r = 0.99), and when compared with
conventional gasometric measurements of oxyhemoglobin saturation, the
reflectance method yielded the same calibration curve for different
hematocrits and gave a mean difference of only 2.67%. Although the
technique is demonstrated with a cuvette appropriate for an extracorporeal
circulation in animal experiments, it could possibly be further developed
for fiber-optic catheter oximeters.
