Abstract
The chick embryo has long been a favorite model system for morphologic and physiologic studies of the developing heart, largely because of its easy visualization and amenability to experimental manipulations. However, this advantage is diminished after 5 days of incubation, when rapidly growing chorioallantoic membranes reduce visibility of the embryo. Using highโfrequency ultrasound, we show that chick embryonic cardiovascular structures can be readily visualized throughout the period of Stages 9โ39. At most stages of development, a simple ex ovo culture technique provided the best imaging opportunities. We have measured cardiac and vascular structures, blood flow velocities, and calculated ventricular volumes as early as Stage 11 with values comparable to those previously obtained using video microscopy. The endocardial and myocardial layers of the preโseptated heart are readily seen as well as the acellular layer of the cardiac jelly. Ventricular inflow in the preโseptated heart is biphasic, just as in the mature heart, and is converted to a monophasic (outflow) wave by ventricular contraction. Although blood has softโtissue density at the ultrasound resolutions and developmental stages examined, its movement allowed easy discrimination of perfused vascular structures throughout the embryo. The utility of such imaging was demonstrated by documenting changes in blood flow patterns after experimental conotruncal banding. Developmental Dynamics 236:3503โ3513, 2007. ยฉ 2007 WileyโLiss, Inc.