Abstract: An optical method for obtaining hematocrit values of blood uses the light transmittance properties of blood as a means of acquiring information about the blood sample. An algorithm is used to calculate the hematocrit value based on the absorbance spectra obtained at wavelengths of approximately 500 nm and 800 nm. These absorbance wavelengths are selected for their insensitivity to the oxygen saturation level of hemoglobin. Additionally, the algorithm has demonstrated insensitivity to plasma and other blood constituent scattering effects.

Abstract: A calibration boot for use with an optical catheter includes a plurality of materials, each having a different reflectivity characteristic with respect to known wavelengths of light. The boot is positioned over the distal end of the optical catheter and light is emitted from the distal end of the optical catheter into one of the materials at a time. At each emission, the reflected or backscattered light is measured by a detector and a plurality of signals are obtained. The plurality of readings are used to calibrate the overall optical catheter and system. The use of a plurality of calibration signals improves the overall system accuracy, particularly where two or more variables are present in the measured parameter. In the preferred system, the parameter being sensed in the oxygenatin of blood invasively.

Abstract: An apparatus and method are described for defining a small interrogation volume in a liquid sample suspected of containing an analyte. The apparatus and method utilize a dual optical fiber probe constructed with the ends of the optical fibers at the liquid-fiber interface spatially oriented such that the intersection of their longitudinal axes forms an included angle ranging from about 40.degree. to 140.degree.. By appropriate choice of the numerical aperture and core diameter of the optical fibers and the separation distance between the longitudinal axes of the optical fibers at the liquid-fiber interface, a finite interrogation volume of predetermined size and independent of the total liquid sample volume can be defined. The apparatus and method substantially reduce background interference with corresponding increase in assay sensitivity.

Abstract: An apparatus and method are described for defining a small interrogation volume in a liquid sample suspected of containing an analyte. The apparatus and method utilize a dual optical fiber probe constructed with the ends of the optical fibers at the liquid/fiber interface spatially oriented such that the intersection of their longitudinal axes forms an included angle ranging from about 40.degree. to 140.degree.. By appropriate choice of the numerical aperture and core diameter of the optical fibers and the separation distance between the longitudinal axes of the optical fibers at the liquid/fiber interface, a finite interrogation volume of predetermined size and independent of the total liquid sample volume can be defined. The apparatus and method substantially reduce background interference with corresponding increase in assay sensitivity.