Continuous measurement of hematocrit using an intravascular catheter equipped with a fiberoptic transmission cell

Purpose. The purpose of this study was to measure intravascular hematocrit values continuously by using a fiberoptic probe based on near-infrared photometry. Methods. We produced a catheter 1.5 mm in diameter that used a pair of plastic fibers. One of the fibers, the measuring fiber, was used to measure the optical density of blood, and the other, the reference fiber, was used to decrease the signal-to-noise ratio. We employed an 805-nm laser diode as the light source. Two photodiodes were used to measure the intensity of the light transmitted through the two fibers, and the output signals were amplified and sent to a personal computer through an analog-to-digital converter. Results. The hematocrit values obtained by this fiberoptic continuous measurement agreed well with those obtained by microcentrifugation within physiological ranges. Conclusions. This method is effective for monitoring the rapid changes in hematocrit.