91 DEVELOPMENTAL CHANGES IN VENTRICULAR FUNCTION IN THE CHICK EMBRYO

How ventricular function changes during embryonic development is unknown. We correlated measures of ventricular physiology with ventricular dry weight and myocyte myofibril and mitochondrial volume in stage 18 (3 day), 21 (3½ day), 24 (4 day), 27 (5 day) and 29 (6 day) chick embryos. In ovo measurements of ventricular pressure and dorsal aortic blood velocity were made with a servo null system and 20 MHz pulsed-Doppler respectively. dP/dt and dV/dt were electronically derived. Percent cell volume of mitochondria and myofibrils were determined from electron micrographs of the ventricular wall. From stage 18 to 29, ventricular weight increased from 28±2 μg (x±SEM) to 140±6 μg while embryo weight increased from 1.02±.05 mg to 15.36±.30 mg. Ventricular systolic and end-diastolic pressure, and dP/dt increased from 1.31±.05 mmHg, .23±.03 mmHg and 23±1 mmHg/s respectively to 3.45±.10 mmHg, .82±.03 mmHg.and 80±4 mmHg/s. Dorsal aortic dV/dt increased from 878±17 mm/s2 to 2076±65 mm/s2. Relative myofibril volume increased from 17% at stage 18 to 24% at stage 27 but decreased to 18% at stage 29, while mitochondria volume remained constant at 11%. With development, heart:embryo weight ratio and function measures indexed for myocardial weight or myofibril percent decreased as much as 50%. We speculate that the decrease in indexed function may be due to changes in energy utilization, available energy, or geometric shape of the developing heart.