Erythrocyte velocity and total blood flow in the extraembryonic circulation of early chick embryos determined by digital video technique

RBC velocity was determined in the major blood vessels of the extraembryonic circulation of early chick embryos between Day 4 and Day 6 of development using fluorescent-labeled erythrocytes. Measurements were performed by applying a digital frame-by-frame video technique. The expenditure of operator interaction was minimized by computer support. Velocity measurements of more than 15,000 labeled blood cells were evaluated for mean RBC velocity and volume flow of 354 venous blood vessel segments. Linear regression for the power function of the calculated volume flow vs the vessel diameter yielded an exponent of 2.77 at Day 4, increasing to 2.96 by Day 6. Applying Murray's model of energetic cost, these data indicate that in the course of development the newly formed extraembryonic vascular system is optimized in terms of minimizing cardiac work. The total extraembryonic blood flow as calculated from the sum of the volume flows of the main veins was 656 ± 218 and 1169 ± 409 nl/sec at Day 4 and Day 6, respectively. Using previously determined values of blood oxygen concentration, embryonic oxygen uptakes of 9.6 nl/sec (Day 4) and 40.2 nl/sec (Day 6) were calculated.