Embryonic stroke volume and cardiac output in the chick

Cine recordings of the hearts of chick embryos of 3 days and 2 hr to 4 days and 21 hr incubation were projected and measured. The measurements were converted to volumes. Stroke volume was determined from the difference in end diastolic and end systolic volume and multiplied by heart rate to yield cardiac output. Mean stroke volume was 0.0058 (±0.00036 SEM) mm³ per mg body wt; mean cardiac output was 0.956 (± 0.061 SEM) mm³/min per mg body wt. Stroke volume and cardiac output rose above their control values after intravascular injection of Ringer's solution, and even more so after the injection of dextran solution. The increases in stroke volume were due to increases in end diastolic volume, in the case of dextran injected embryos they occurred in spite of a simultaneous increase in end systolic volume. It is concluded that the rise in cardiac output with growth of the embryo is in large part due to an increase in stroke volume, and that the increase in stroke volume depends in part on the known increase in embryonic blood volume. The experiments further suggest that a rapid hydrostatic and osmotic equilibrium exists between embryonic blood plasma and an extra vascular compartment.