Blood flow patterns have been outlined in the chick embryo heart. The initial flow pattern adapts to the heart form but soon vascular forces affect cardiogenesis. Spiralling of the blood streams in the sinus venosus appears to lead to an expansion of this chamber. The atrial septum forms between parallel streams and evidence is presented that blood flow contributes to septation. Interatrial flow develops with a fusion of the inflow streams bringing the entire systemic venous return into the right atrium when the left atrium receives a small pulmonary return; the difference in pressures is believed to lead to perforation of the septal wall.The ventricular septum also forms between parallel bloodstreams. Inhibition of the left ventricular outflow, brought about by the application of trypan blue to the embryos, was associated with the production of ventricular septal defects. Higher pressures in the left ventricles, brought about by increased vascular resistance to these chambers, led to the defects as evidenced by left to right flow through the defects. An interpretation of the origin of this common congenital anomaly is thus offered.Hemodynamic factors in cardiogenesis have long been under consideration (cf. Goerttler, '58; Jaffee, '62) and are becoming a more frequent subject of experimental analyses (Goerttler, '58; Jaffee, '62; Rychter, '62). Yet descriptions of blood flow through critical stages in cardiac development, based upon direct observations, are not available. Bremer ('32) described blood flow in the chick embryo heart to 48 hours of incubation in his pioneering study.The present report is based upon observations of blood flow in chick embryo hearts from 43 hours to the sixth day of incubation, a period in which most major cardiac structures are formed. Many of these observations were recorded with motion pictures (Jaffee, '63b). Experimental analysis of hemodynamic factors in cardiac development are in progress and a preliminary report is included. MATERIALS AND METHODSWhite Leghorn eggs were incubated in a forced draft incubator at 38.5"C; embryos were removed with vitelline circulations intact and placed in large flat bottomed depression slides, following Patten and Kramer ('33). Blood flow patterns were observed in over 150 embryos rang-ANAT. REC., 151: 69-76. ing from 43 hours to six days incubation. Motion pictures were taken as previously described (Jaffee, '63a).Small areas of the egg shells were cut out with hack saw blades for the experimental procedures and closed with pieces of cover slips and sealed with paraffin. Electrocautery was carried out successfully in 12 embryos in a region lateral to the embryo at 36 hours. Branches of the vitelline veins were tied off at 72 hours in 24 embryos, utilizing 7-0 silk suture.Trypan blue, dissolved to 0.1% in Locke's solution, was dropped over embryos through the windows in amounts from 0.1 to 0.35 ml. The dye was also applied to the branchial region by means of previously saturated (with trypan blue) blocks of agar. Both procedures follow...

Bloodstream flow patterns have been outlined in the arterial outflow tract (ventricular outflow tract and bulbus arteriosus) of the chick embryo heart during the period in which septation takes place. Hemodynamic factors underlying flow changes during this period are discussed.The mapping of flow patterns did not support the concept of a conoventricular flange reported previously. Septation was found to take place between two separate and discrete bloodstreams. The cellular nature of the aorticopulmonary septum has been described. The spiral ridges that farm this septum expand by cellular growth, explaining the ability of this septum to develop against the direction of blood flow. The aorticopulmonary septum divides about two-thirds of the arterial outflow tract; the h a l partitioning of the most proximal portion of the outflow tract was found to take place by means of the apposition of endocardia1 cushion tissue masses.Failure of aorticopulmonary septum development (truncus arteriosus communis persistens) was found to follow fusion of the bloodstreams in experimental studies. In experimental aortic stenosis the appearance of a small left stream was found to be followed by the development of a stenotic aorta. Thus in the first instance the septum apparently cannot develop unless the streams remain separate and in the second case the size of the primordial bloodstreams appears to determine the diameter of the vessel.

Moderate hypoxia (5% 0,) and moderate hypoxia + hypercapnea (5% 0 2 + 2 % C02) administered to Hamilton-Hamburger stage17 (60-h) chick embryos produced significant frequencies of brain, eye, and limb malformations, as observed grossly, and cardiovascular malformations, as found in serial sections. Hypoxia f hypercapnea was more lethal (survival rate, 49%) than hypoxia alone (mean survival rate, 6 5 % ) but the frequencies of malformations produced by both procedures were in the same range. When moderate hypoxia + hypercapnea was utilized hemorrhages, heart and blood vessel distention, bradycardia, and the disappearance of blood-flow patterns occurred. Such changes were previously found to be produced by moderate hypoxia alone. Since cardiovascular malformations were produced under conditions known to affect hemodynamics, it is postulated that these events are related.

Patterns of blood flow have been observed at several critical stages in the development of the frog heart. Shortly after the onset of circulation (Shumway stage 20) two inflowing streams were noted to cross in the sinus venoms and then continue through the atrium, parallel to each other. With the development of the hepatic return (stage 24) the right stream becomes much larger and its course diverted into the area that will become the definitive right atrium. The smaller left stream is then noted to flow around the right stream with the development of a spiralling of the streams. The left stream now leads into the area which will become the left atrium. This is the hemodynamic situation as the interatrial septum forms; the septum forms between the streams. ExperimentaI and histological evidence indicate that the interatrial septum is formed by a molding action of the bloodstreams on the tissues of the atrial wall.Experimental modifications of the vascular morphology of the anuran embryo have been found to influence the form of the developing heart (Jaffee, '62a). In order to evaluate hemodynamic factors involved in cardiogenesis more precisely a mapping of the bloodstreams within the developing heart itself is in progress. The observations to be described have been made of the venous inflow into the developing anuran heart with special reference to the formation of the interatrial septum. Histological aspects of septa1 development are included. METHODS AND MATERIALSEmbryos of the Leopard frog (Rana pipiens) were obtained by induced breeding, For observing the heart, specimens were anesthetized with tricaine methanesulfonate, placed in depression slides filled with amphibian Ringer solution and the ventral body wall opened exposing the heart. Observations of the sinus venosus and atrium were facilitated by displacing the ventricle cephalad with a glass needle held by a micromanipulator, and by displacing the intestine caudad.Observations were made on the stage of a compound microscope with transmitted light for the most part. Embryos of Shumway stages 20 to 22 could not be transilluminated and observations of blood flow in the atria of these specimens was made by placing a quartz rod dorsal to the heart using the technique developed by Knisely ('36). Motion pictures of blood flow were taken with a Bolex Rex 16mm camera at 16 frames per sec.Techniques for producing cardiac anomalies in this form as well as the histological methods utilized have been described (Jaffee, '62a). RESULTSTwo streams of blood cells flowing parallel to each other were observed in the atria at stages 20 to 22. This was of special interest since Bremer ('32) has described a crossing of the streams in the atria of the embryonic chick. The pattern of blood flow through the atrium noted at stages 20 to 22 was again seen at stage 23 when transillumination of the embryo was possible. Crossing of the bloodstreams was noted in the sinus venosus at this time.The sinus venosus at stage 23 is a symmetrical structure with a broad base which re...

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