Development of a system to measure circulating blood volume using infra-red laser.

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Optical fiber probe implantable into vascular bed was developed for in situ determination of hematocrit continuously. This system consists of a flexible catheter-type optical fiber, a laser source, and a laser photo-detector. The catheter was constructed from double-lumen plastic tube(outer diameter, 1.5 mm ; inner diameter, 0.7 mm) in which transmitter and receiver plastic optical fibers were installed. At the top portion, a slit of 1 mm was made, and the hematocrit value of blood flowing through the slit was monitored continuously. As the light source, light with 805-nm wave length (an isosbestic wave length for oxy- and deoxy-hemoglobin) was obtained with diode (KLS-810-3W, Kette). Light intensity from the receiver fiber was monitored with a silicone photo diode (S2386-18K, Hamamatsu). The light intensity was amplified with a photosensor amplifier (C2719, Hamamatsu), and recorded with micro-computer (PC-386, EPSON) after A/D conversion.This system was evaluated in vitro, using suspension solution of washed erythrocyte with varied hemotocrit, which showed high coincidence with the theoretical value by Loewinger's formula. Animal experiments were performed on anesthetized rabbits. The fiber probe was inserted into the right atrium of rabbit. The hematocrit value was monitored continuously in vivo, and the value was compared the hematocrit value obtained with centrifugation method on sampled blood. Highly significant correlation was observed between the values obtained with conventional method and the present method, although about 1% of deviation was observed after infusion of saline. This finding suggests that the existence of uneven distribution of infused saline in blood vessel system.During the course of this experiment, we succeeded to develop a method to visualize oxygen distribution in tissue. By combining these two methods, it will be possible to analyze oxygen delivery in more detail.