A blood-gas nomogram of the chick fetus: blood flow distribution between the chorioallantois and fetus

This paper presents equations for quantifying the relationships between the O2 and CO2 concentrations and tensions in the blood of the 18-day chick fetus. A blood-gas nomogram showing these relationships is presented. Starting with the reported chorioallantoic artery and vein gas tensions and using the blood-gas equations, the range of embryonic arterial and venous gas tensions as well as the distribution of the cardiac output and the degree of mixing between the chorioallantoic and embryonic circulations are explored. It is concluded that at least 65% of the blood in the chorioallantoic artery consists of blood of embryonic mixed venous composition. A model of the blood flow distribution is proposed in which chorioallantoic and embryonic flows are equal, with 70% of the blood returning from the tissues of the embryo going to the chorioallantois and vice versa.