Estimation of contact time and diffusing capacity for oxygen in the chorioallantoic vascular plexus

The contact time of erythrocyte in the chorioallantioc capillaries of chicken embryos was estimated by referring to the oxygenation rate measured with a microphotometer. The chorioallantioc membrane was excised from an incubated egg and the SO2 of blood in it's capillary was changed by varying the gas composition around the membrane from the venous blood PO2 level to the air space gas. The oxygenation time (te) required to attain the level of arterialized blood SO2 was measured as the contact time (tc) in the capillaries, which resulted in 0.87, 0.74, 0.57, 0.49 and 0.36 sec for 10, 12, 14, 16 and 18 days of incubation, respectively. The obtained te value coincided with the contact time calculated from the CO diffusing capacity referring to the reaction rate of CO with oxygenated erythrocyte. Using the te value, the diffusing capacity for O2 in the chorioallantoic capillary was calculated; 1.1, 2.2, 4.4, 6.0 and 6.6 x 10(-3) ml-min-1 - mm Hg-1 for the same incubation days as above. The capillary blood volume (Vc) was also estimated, which increased from about 16 to 35 mul during development from 10 to 18 days. The values of DO2 and Vc converted per kg weight of embryo at the days near hatching were similar to those per kg body weight estimated in human lung.