Hematocrit measurement by differential optical geometry in a short-term

Abstract

An optical fiber carries a light beam through a cardiovascular catheter and projects the beam into the patient's bloodstream. Two other fibers, spaced in a very carefully controlled configuration from the first, receive light scattered by corpuscles (and blood-vessel walls) and transmit this reflected light back through the catheter to respective detectors outside the patient's body. If preferred, two input fibers and a single output fiber--or other techniques for providing differential geometry--may be used instead. Electronic instrumentation finds the ratio of the two light fluxes, thus cancelling out unknown variables such as input light intensity and optical--connector attenuation. The known differential geometry between the two light paths permits calibration of the ratio measurement in terms of corpuscular concentration--i.e., hematocrit. Light at only one wavelength suffices for the measurement. Advanced forms of the invention correct for proximity of blood-vessel walls. This system is particularly compatible with optical-fiber measurements of oxygen saturation, as either or both of the light paths already provided may be used for the oxygen reflectometry.