Hemodynamics of the stage 12 to stage 29 chick embryo

Doppler echocardiography of normal and abnormal embryonic mouse heart

To evaluate normal embryonic mouse heart development using Doppler echocardiography and to quantify changes in normal embryonic mouse cardiac function with increasing gestational age from the time of cardiac septation, a new method was applied using Doppler echocardiography. Trisomic embryos were screened to evaluate a model of abnormal cardiac anatomy. The development of the embryonic heart in mice has been well studied anatomically, but there are limited physiologic studies. A new method has been developed to assess the mouse fetal heart in a similar fashion to the current use of echocardiography in the chick embryo and the human fetus. This method was applied to normal mouse embryos known to survive and to abnormal trisomy embryos that die during gestation and have cardiac failure. To analyze early normal embryonic heart hemodynamics, Doppler echocardiograms were performed on n = 129 C57B1/6J mouse embryos from d 10 through 19 of gestation and 20 embryos with trisomy 16 (gestational d 11-14). The maximal blood velocities recorded at the inflow and outflow of the embryonic heart were analyzed for heart rate, peak early and peak late inflow and outflow velocities, and measurements were made of systolic ejection, filling, and other time intervals normalized for heart rate. A high velocity holosystolic or diastolic velocity with altered time intervals was identified as atrioventricular or semilunar valvular regurgitation, respectively. Inflow and outflow velocities increased with increasing gestational age. The time period of isovolemic contraction time was present before and undetectable after gestational d 17, whereas the total filling time increased. Ejection time and isovolemic relaxation time had no significant change. No valvular regurgitation was detected in normal embryos. These echocardiographic patterns are similar to those observed for human embryos. Abnormal Doppler findings were present (inflow or outflow valvular regurgitation) in 55% of trisomy 16 embryos. Echocardiographic data can now be obtained beginning at d 11 in the mouse embryo for analyses relating to abnormal heart development. A noninvasive technique may be invaluable to monitor the physiologic condition of embryos within a litter and to detect and monitor those embryos where heart defects may be expected. Qualitative markers of embryonic congestive heart failure such as valvular regurgitation may be present and detectable with structural valvular abnormalities or failing cardiac physiology. The mouse embryo is an appropriate animal model to analyze normal and abnormal mammalian heart development and function.

Cardiac neural crest is essential for the persistence rather than the formation of an arch artery

Double-label immunohistochemistry was used to compare early aortic arch artery development in cardiac neural crest-ablated and sham-operated quail embryos ranging from stage 13 to stage 18. The monoclonal antibody QH-1 labeled endothelial cells and their precursors, and HNK-1 labeled migrating neural crest cells. In the sham-operated embryos, the third aortic arch artery developed from a lumenizing strand of endothelial precursors that became separated from the pharyngeal endoderm by migrating cardiac neural crest cells as they ensheathed the artery. The arch artery of the neural crest-ablated embryos lumenized but failed to become separated from the pharyngeal endoderm, indicating that neural crest is unnecessary for the early formation of the aortic arch artery. However, once blood flow was initiated through the third arch artery of crest-ablated embryos at stage 16, the artery became misshapen and sinusoidal. By embryonic day 3, abnormal connections to the dorsal aorta occurred and bilateral symmetry was lost, suggesting that the loss of neural crest-derived ectomesenchyme destabilizes the nascent artery. Although here we show no loss of the third arch artery, past studies have reported hypoplasia or missing carotids in older neural crest-ablated embryos (Bockman et al. [1987] Am. J. Anat. 180:332-341; Bockman et al. [1989] Anat. Rec. 225:209-217; Nishibatake et al. [1987] Circulation 75:255-264; Tomita et al. [1991] Circulation 84:1289-1295). We suggest that the cardiac neural crest is essential for the persistence of an arch artery, but not its formation. Furthermore, since changes in the development of the arch artery are seen prior to the formation of the tunica media, it is suggested that a critical period is reached in the development of the arch artery, after lumenization, but prior to the formation of the tunica media, which necessitates the presence of the cardiac neural crest.

Erythrocyte velocity and total blood flow in the extraembryonic circulation of early chick embryos determined by digital video technique

RBC velocity was determined in the major blood vessels of the extraembryonic circulation of early chick embryos between Day 4 and Day 6 of development using fluorescent-labeled erythrocytes. Measurements were performed by applying a digital frame-by-frame video technique. The expenditure of operator interaction was minimized by computer support. Velocity measurements of more than 15,000 labeled blood cells were evaluated for mean RBC velocity and volume flow of 354 venous blood vessel segments. Linear regression for the power function of the calculated volume flow vs the vessel diameter yielded an exponent of 2.77 at Day 4, increasing to 2.96 by Day 6. Applying Murray's model of energetic cost, these data indicate that in the course of development the newly formed extraembryonic vascular system is optimized in terms of minimizing cardiac work. The total extraembryonic blood flow as calculated from the sum of the volume flows of the main veins was 656 +/- 218 and 1169 +/- 409 nl/sec at Day 4 and Day 6, respectively. Using previously determined values of blood oxygen concentration, embryonic oxygen uptakes of 9.6 nl/sec (Day 4) and 40.2 nl/sec (Day 6) were calculated.