An in vitro capillary system for studies on microcirculatory O2 transport

An in vitro artificial capillary system has been developed for use in examining the O2 transport properties of free hemoglobin and erythrocytes. The artificial capillary was constructed by casting a thin film of transparent silicone rubber around a strand of tungsten wire that was 24 micron in diameter. After the rubber had polymerized, the wire was removed. Typical dimensions of the silicone rubber film were 170 micron thick, 1 cm wide, 5 mm long in the direction of flow, and a 27-micron lumen diameter. The artificial capillary bed was mounted on a microscope and perfused by either hemoglobin solutions or cell suspensions. Fractional saturation was measured as a function of axial position by a dual-wave-length microspectrophotometer, and the flow rate was regulated precisely by a syringe pump. O2 release experiments were carried out by suffusing the gas space surrounding the artificial capillary film with 100% N2 and perfusing with an oxygenated sample. O2 uptake experiments were carried out by suffusing the gas space with O2-N2 mixtures and perfusing with deoxygenated samples. The axial velocities were varied from 3 to 15 mm/s. The residence time (the time a particular red cell or hemoglobin molecule has spent in the capillary) for 50% oxygenation of a 4 mM (heme) deoxyhemoglobin solution was approximately 0.05 s at 37 degrees C when the gas space surrounding the capillary contained air. The corresponding time for 50% oxygenation of an equivalent red cell suspension was approximately 0.25 s.(ABSTRACT TRUNCATED AT 250 WORDS)