Exo-Ocean Exploration with Deep-Sea Sensor and Platform Technologies

One of Saturn's largest moons, Enceladus, possesses a vast extraterrestrial ocean (i.e., exo-ocean) that is increasingly becoming the hotspot of future research initiatives dedicated to the exploration of putative life. Here, a new bio-exploration concept design for Enceladus' exo-ocean is proposed, focusing on the potential presence of organisms across a wide range of sizes (i.e., from uni- to multicellular and animal-like), according to state-of-the-art sensor and robotic platform technologies used in terrestrial deep-sea research. In particular, we focus on combined direct and indirect life-detection capabilities, based on optoacoustic imaging and passive acoustics, as well as molecular approaches. Such biologically oriented sampling can be accompanied by concomitant geochemical and oceanographic measurements to provide data relevant to exo-ocean exploration and understanding. Finally, we describe how this multidisciplinary monitoring approach is currently enabled in terrestrial oceans through cabled (fixed) observatories and their related mobile multiparametric platforms (i.e., Autonomous Underwater and Remotely Operated Vehicles, as well as crawlers, rovers, and biomimetic robots) and how their modified design can be used for exo-ocean exploration.

Hierarchical classification of G-protein-coupled receptors with data-driven selection of attributes and classifiers

We address the important bioinformatics problem of predicting protein function from a protein's primary sequence. We consider the functional classification of G-Protein-Coupled Receptors (GPCRs), whose functions are specified in a class hierarchy. We tackle this task using a novel top-down hierarchical classification system where, for each node in the class hierarchy, the predictor attributes to be used in that node and the classifier to be applied to the selected attributes are chosen in a data-driven manner. Compared with a previous hierarchical classification system selecting classifiers only, our new system significantly reduced processing time without significantly sacrificing predictive accuracy.

Blood pressure estimation in the human fetal descending aorta

OBJECTIVES

The objectives of this study were to estimate fetal blood pressure non-invasively from two-dimensional color Doppler-derived aortic blood flow and diameter waveforms, and to compare the results with invasively derived human fetal blood pressures available from the literature.

METHODS

Aortic pressures were calculated from digitally recorded color Doppler cineloops of the fetal descending aorta by applying the Womersley model in combination with the two-element Windkessel model, assuming constant pulse wave velocity during the second half of pregnancy. The results were compared with invasively derived human fetal blood pressures obtained from the literature.

RESULTS

In 21 normal pregnancies the estimated mean aortic pressure regression line increased linearly from 28 mmHg at 20 weeks of gestation to 45 mmHg at 40 weeks of gestation. The pulse pressure based on the regression line increased linearly from 21 mmHg at 20 weeks of gestation to 29 mmHg at 40 weeks of gestation. The aortic compliance exhibited a log linear relationship with the gestational age and a statistically significant eightfold increase was observed between 20 and 40 weeks. The aortic downstream peripheral resistance exhibited an exponentially decaying relationship across the same gestational age range. Non-invasively derived aortic systolic and diastolic aortic pressures were comparable with previously reported invasively derived systolic and diastolic umbilical arterial pressures; however, the mean pressures differed significantly from those reported in the umbilical artery in a separate study. The aortic systolic pressures calculated in this study were significantly higher than invasively derived left ventricular systolic pressures that have been previously reported in the literature.

CONCLUSIONS

This study demonstrates the feasibility of estimating arterial blood pressure in the human fetus. The method described is of potential use in assessing fetal blood pressure non-invasively, particularly for studying relative changes with time.

Cardiac morphology and blood pressure in the adult zebrafish

Zebrafish has become a popular model for the study of cardiovascular development. We performed morphologic analysis on 3 months postfertilization zebrafish hearts (n > or = 20) with scanning electron microscopy, hematoxylin and eosin staining and Masson's trichrome staining, and morphometric analysis on cell organelles with transmission electron photomicrographs. We measured atrial, ventricular, ventral, and dorsal aortic blood pressures (n > or = 5) with a servonull system. The atrioventricular orifice was positioned on the dorsomedial side of the anterior ventricle, surmounted by the single-chambered atrium. The atrioventricular valve was free of tension apparati but supported by papillary bands to prevent retrograde flow. The ventricle was spanned with fine trabeculae perpendicular to the compact layer and perforated with a subepicardial network of coronary arteries, which originated from the efferent branchial arteries by means of the main coronary vessel. Ventricular myocytes were larger than those in the atrium (P < 0.05) with abundant mitochondria close to the sarcolemmal. Sarcoplasmic reticulum was sparse in zebrafish ventricle. Bulbus arteriosus was located anterior to the ventricle, and functioned as an elastic reservoir to absorb the rapid rise of pressure during ventricular contraction. The dense matrix of collagen interspersed across the entire bulbus arteriosus exemplified the characteristics of vasculature smooth muscle. There were pressure gradients from atrium to ventricle, and from ventral to dorsal aorta, indicating that the valves and the branchial arteries, respectively, were points of resistance to blood flow. These data serve as a framework for structure-function investigations of the zebrafish cardiovascular system.

Fetal heart rate and umbilical artery velocity variability in fetuses with congenital cardiac defects: a preliminary study

OBJECTIVE

To examine whether variabilities in fetal heart rate and umbilical artery flow velocity are possible markers for hemodynamic dysfunction in fetuses with a congenital heart defect.

METHODS

Doppler studies of the umbilical artery velocity waveform were performed at 20-35 weeks of gestation in 13 patients with a congenital heart defect. We determined absolute and variability values for heart rate and flow velocities from umbilical artery velocity waveforms of at least 18 s duration. We compared these findings with normal controls matched for gestational age.

RESULTS

Fetuses with a congenital heart defect displayed decreased umbilical artery peak systolic and time-averaged velocities. However, variability in peak systolic and time-averaged velocities and fetal heart rate variability were increased compared with normal controls. Absolute fetal heart rates were similar between the two groups.

CONCLUSIONS

Marked cardiovascular changes occur in the fetus with a congenital heart defect compared with the normal healthy fetus. We propose that variability in fetal heart rate and umbilical artery blood flow velocity could be additional markers for impaired homeostasis in the presence of fetal congenital heart disease.

Power spectrum analysis of heart rate and blood flow velocity variability measured in the umbilical and uterine arteries in early pregnancy: a comparative study

OBJECTIVE

To compare power spectral derived variability parameters from the fetal side of the placental circulation with those from the maternal side of the placental circulation, during early pregnancy.

METHODS

Doppler velocity waveforms were obtained from both the umbilical and the uterine arteries in a study group of 40 pregnant women between 10 and 14 (n = 25) and 15 and 20 (n = 15) weeks of gestation. The coefficient of variation of both the beat-to-beat heart rate variability and the blood flow velocity variability was determined. The ratio of the integrated low-frequency components (< 0.2 Hz) and the integrated high-frequency components (> 0.2 Hz) from normalized power spectrum analysis (LH-ratio) was established, to reflect sympathovagal balance.

RESULTS

The coefficient of variation and LH-ratio of fetal heart rate variability constitute only a fraction of the same maternal heart rate variability parameters. Nevertheless a highly significant increase (P < 0.001) in LH-ratio was demonstrated with advancing gestational age. The coefficient of variation and LH-ratio of blood flow velocity variability were significantly lower in the fetal umbilical artery only in the 10-14-weeks' gestation group. Due to a decrease of the maternal uterine blood flow velocity variability parameters with advancing gestational age, statistically equal fetal and maternal values for coefficient of variation and LH-ratio were found in the 15-20 weeks' gestation group.

CONCLUSIONS

The increase in LH-ratio of fetal heart rate variability indicates functional development of the fetal autonomic nervous system at 15-20 weeks' gestation. The umbilical blood flow velocity variability may be secondary to maternal uterine arterial flow variability rather than due to primary changes in fetal cardiovascular function.

Cerebral infarction complicating Fontan surgery for cyanotic congenital heart disease

We report on four children who had cerebral vascular events in the first three months after the Fontan procedure for complex cyanotic congenital heart disease. Potential risk factors in these children included congestive heart failure, postoperative thrombocytosis, and cardiac arrhythmias. These cases suggest that children who undergo Fontan surgery may be at increased risk for cerebral infarction.

Structure and function of the developing zebrafish heart

The combination of optical clarity and large scale of mutants makes the zebrafish vital for developmental biologists. However, there is no comprehensive reference of morphology and function for this animal. Since study of gene expression must be integrated with structure and function, we undertook a longitudinal study to define the cardiac morphology and physiology of the developing zebrafish. Our studies included 48-hr, 5-day, 2-week, 4-week, and 3-month post-fertilization zebrafish. We measured ventricular and body wet weights, and performed morphologic analysis on the heart with H&E and MF-20 antibody sections. Ventricular and dorsal aortic pressures were measured with a servonull system. Ventricular and body weight increased geometrically with development, but at different rates. Ventricle-to-body ratio decreased from 0.11 at 48-hr to 0.02 in adult. The heart is partitioned into sinus venosus, atrium, ventricle, and bulbus arteriosus as identified by the constriction between the segments at 48-hr. Valves were formed at 5-day post-fertilization. Until maturity, the atrium showed extensive pectinate muscles, and the atrial wall increased to two to three cell layers. The ventricular wall and the compact layer increased to three to four cell layers, while the extent and complexity in trabeculation continued. Further thickening of the heart wall was mainly by increase in cell size. The bulbus arteriosus had similar characteristics to the myocardium in early stages, but lost the MF-20 positive staining, and transitioned to smooth muscle layer. All pressures increased geometrically with development, and were linearly related to stage-specific values for body weight (P < 0.05). These data define the parameters of normal cardiac morphology and ventricular function in the developing zebrafish.

Complete genome sequence of Neisseria meningitidis serogroup B strain MC58

The 2,272,351-base pair genome of Neisseria meningitidis strain MC58 (serogroup B), a causative agent of meningitis and septicemia, contains 2158 predicted coding regions, 1158 (53.7%) of which were assigned a biological role. Three major islands of horizontal DNA transfer were identified; two of these contain genes encoding proteins involved in pathogenicity, and the third island contains coding sequences only for hypothetical proteins. Insights into the commensal and virulence behavior of N. meningitidis can be gleaned from the genome, in which sequences for structural proteins of the pilus are clustered and several coding regions unique to serogroup B capsular polysaccharide synthesis can be identified. Finally, N. meningitidis contains more genes that undergo phase variation than any pathogen studied to date, a mechanism that controls their expression and contributes to the evasion of the host immune system.

Assessment of fetal heart rate variability and velocity variability by Doppler velocimetry of the descending aorta at 10-20 weeks of gestation

OBJECTIVES

Determination of gestational age-related modulations in fetal heart rate and descending aorta blood flow velocity in the early human fetus and comparison of aortic variability data with data obtained from the umbilical artery. It is hypothesized that these modulations present in the umbilical artery also occur in the descending aorta.

METHODS

Doppler studies of descending aorta velocity waveforms were performed at 10-20 weeks in 55 normal pregnant women. In 24 of the 55 women, Doppler recordings from both the descending aorta and the umbilical artery were collected. Absolute values and variability of fetal heart rate, peak systolic and time-averaged velocities were determined from flow velocity waveforms of at least 18 s in duration.

RESULTS

From 10 to 20 weeks of gestation, the descending aorta peak systolic and time-averaged velocities increased, whereas the fetal heart rate decreased. The descending aorta peak systolic variability also increased. However, the time-averaged velocity variability and fetal heart rate variability remained constant during the study period. In the subset of 24 women, the fetal heart rate variability and velocity variability data from the descending aorta and umbilical artery were not significantly different.

CONCLUSIONS

Reproducible fetal heart rate and velocity variability data can be derived from the descending aorta and umbilical artery. The increase in heart rate variability observed in the umbilical artery was not seen in recordings obtained from the descending aorta. Different fetal activity states may be the underlying mechanism for these heart rate variability discrepancies.

Do heart rate and velocity variability derived from umbilical artery velocity waveforms change prior to clinical pregnancy-induced hypertension?

OBJECTIVE

To investigate the hypothesis that alterations in heart rate variability, peak systolic velocity variability and time-averaged velocity variability in the human umbilical artery may predict early signs of dysfunctional fetal-placental coupling in pregnancies that later develop pregnancy-induced hypertension.

METHODS

Doppler flow velocity recordings from the umbilical artery were performed at 10-20 weeks of gestation in 12 nulliparous women who subsequently developed pregnancy-induced hypertension. From umbilical artery velocity waveforms of at least 12 s in duration we determined absolute values and beat-to-beat variability in fetal heart rate, peak systolic and time-averaged velocity and compared these findings with those in normal nulliparous pregnant women matched for gestational age.

RESULTS

Absolute values for fetal heart rate, peak systolic and time-averaged velocity as well as beat-to-beat variability in fetal heart rate did not differ significantly between women later developing pregnancy-induced hypertension and normal controls. However, variability in peak systolic velocity and time-averaged velocity were decreased in women who subsequently developed pregnancy-induced hypertension.

CONCLUSIONS

Whereas fetal heart rate variability was similar, umbilical artery flow velocity variability was reduced in women developing pregnancy-induced hypertension compared with controls. It is proposed from this study that variability of the umbilical artery flow velocity is associated with mechanical changes in the vascular bed of women who later develop pregnancy-induced hypertension.

Fetal heart rate and umbilical artery velocity variability in pregnancies complicated by insulin-dependent diabetes mellitus

OBJECTIVES

To examine the variability in fetal heart rate and absolute flow velocity, which are possible hemodynamic markers of cardiovascular homeostasis in pregnancies complicated by diabetes mellitus.

METHODS

Doppler studies of umbilical artery velocity waveforms were performed at 12-21 weeks of gestation in 16 women with well-controlled type I (insulin-dependent) diabetes mellitus. From umbilical artery velocity waveforms of at least 13 s in duration, we determined absolute values and beat-to-beat variability for fetal heart rate and umbilical artery flow velocities and compared these findings with normal controls matched for gestational age.

RESULTS

Fetuses of diabetic women displayed increased fetal heart rate variability and umbilical artery peak systolic velocity. Fetal heart rate, umbilical artery time-averaged velocity and variability in umbilical artery flow velocity were not essentially different between the two groups.

CONCLUSION

Fetal heart rate variability and umbilical artery peak systolic velocity may be markers for fetal cardiovascular homeostasis in pregnancies complicated by insulin-dependent diabetes mellitus.

Rate of coronary vascularization during embryonic chicken development is influenced by the rate of myocardial growth

OBJECTIVE

We tested the hypothesis that the degree of coronary microvessel formation in the embryonic heart is regulated by the magnitude of myocardial growth.

METHODS

The outflow tract of Hamburger-Hamilton stage 21 chicken hearts (prior to the onset of coronary vasculogenesis) was constricted in ovo with a loop of 10-0-nylon suture, and the hearts were studied at stages 29 and 36.

RESULTS

At stage 29 ventricular mass was 64% greater in the pressure-overloaded than in the hearts of sham-operated controls, but vascular volume density and numerical density, determined by electron microscopic morphometry, were identical. As demonstrated by histological morphometric evaluation, the compact region of the left ventricle at stage 29 was 43% thicker than the shams. However, by stage 36 heart mass, thickness of the compact region, and overall wall thickness (demonstrated by scanning electron microscopy) were significantly less than in the sham group of this stage, but vascular volume density was virtually identical in the two groups. Formation of the two main coronary arteries was clearly impeded in the banded hearts, i.e., the coronaries were stunted in their development or failed to completely form coronary ostia.

CONCLUSIONS

Vascular growth is proportional to myocardial growth in the embryonic, overloaded heart, but the persistence of the pressure overload results in a failure of or severe limitations in coronary artery development. These data support the hypothesis that vascular growth during this period of development is regulated, at least in part, by the rate and magnitude of myocardial growth.

Remodeling of chick embryonic ventricular myoarchitecture under experimentally changed loading conditions

Adult myocardium adapts to changing functional demands by hyper- or hypotrophy while the developing heart reacts by hyper- or hypoplasia. How embryonic myocardial architecture adjusts to experimentally altered loading is not known. We subjected the chick embryonic hearts to mechanically altered loading to study its influence upon ventricular myoarchitecture. Chick embryonic hearts were subjected to conotruncal banding (increased afterload model), or left atrial ligation or clipping, creating a combined model of increased preload in right ventricle and decreased preload in left ventricle. Modifications of myocardial architecture were studied by scanning electron microscopy and histology with morphometry. In the conotruncal banded group, there was a mild to moderate ventricular dilatation, thickening of the compact myocardium and trabeculae, and spiraling of trabecular course in the left ventricle. Right atrioventricular valve morphology was altered from normal muscular flap towards a bicuspid structure. Left atrial ligation or clipping resulted in hypoplasia of the left heart structures with compensatory overdevelopment on the right side. Hypoplastic left ventricle had decreased myocardial volume and showed accelerated trabecular compaction. Increased volume load in the right ventricle was compensated primarily by chamber dilatation with altered trabecular pattern, and by trabecular proliferation and thickening of the compact myocardium at the later stages. A ventricular septal defect was noted in all conotruncal banded, and 25% of left atrial ligated hearts. Increasing pressure load is a main stimulus for embryonic myocardial growth, while increased volume load is compensated primarily by dilatation. Adequate loading is important for normal cardiac morphogenesis and the development of typical myocardial patterns.

The Paediatric Cardiology Hall of Fame: Helen Brooke Taussig MD. May 24, 1898 to May 21, 1986

The life and accomplishments of Helen Taussig are reviewed at the centennial of her birth in 1898. Now, a little over 50 years since the first Blalock Taussig shunt in 1944, her legacy remains a model of brilliant scientific innovation and loving patient care.

Heart rate and flow velocity variability as determined from umbilical Doppler velocimetry at 10-20 weeks of gestation

1. The aim of this study was to define from umbilical artery flow velocity waveforms absolute peak systolic and time-averaged velocity, fetal heart rate, fetal heart rate variability and flow velocity variability, and the relation between fetal heart rate and velocity variables in early pregnancy.2.A total of 108 women presenting with a normal pregnancy from 10 to 20 weeks of gestation consented to participate in a cross-sectional study design. Doppler ultrasound recordings were made from the free-floating loop of the umbilical cord.3. Umbilical artery peak systolic and time-averaged velocity increased at 10-20 weeks, whereas fetal heart rate decreased at 10-15 weeks of gestation and plateaued thereafter. Umbilical artery peak systolic velocity variability and fetal heart rate variability increased at 10-20 and 15-20 weeks respectively.4. The inverse relationship between umbilical artery flow velocity and fetal heart rate at 10-15 weeks of gestation suggests that the Frank-Starling mechanism regulates cardiovascular control as early as the late first and early second trimesters of pregnancy. A different underlying mechanism is suggested for the observed variability profiles in heart rate and umbilical artery peak systolic velocity. It is speculated that heart rate variability is mediated by maturation of the parasympathetic nervous system, whereas peak systolic velocity variability reflects the activation of a haemodynamic feedback mechanism.

VEGF and bFGF stimulate myocardial vascularization in embryonic chick

We tested the hypothesis that early vascularization of the embryonic heart is enhanced after bolus injections of vascular, endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) into the vitelline vein before the onset of myocardial vasculogenesis (3.5 days, stage 21). Electron and light microscopy were utilized to obtain morphometric data. At stages 29 and 31, myocardial vessel volume or numerical density were higher in embryos injected with 50 ng bFGF than in the saline-injected controls. A VEGF injection increased vascular volume density at stage 29 and both volume and numerical, density at stage 31, bFGF, but not VEGF, was associated with an enhancement of the sinusoidal system (spongy layer of the ventricle) at stage 29. This effect disappeared by stage 31. In conclusion, 1) enhancement of bFGF or VEGF before myocardial vascularization increases vascular growth, but the initial effect of bFGF is greater; 2) the effects of these growth factors on vascular volume and numerical density are temporally dependent; and 3) bFGF, in addition to its effects on the coronary vasculature, influences ventricular modeling by apparently acting on myocytes as well as endothelial cells.

A quantitative study of the ventricular myoarchitecture in the stage 21-29 chick embryo following decreased loading

During the early developmental period, ventricular myoarchitecture undergoes a transition from a smooth-walled cardiac tube, to left and right ventricular chambers filled with a sponge-like network of trabecular struts. We measured the quantitative changes of ventricular myocardium properties in normal stage 21-29 chick embryos and after chronic verapamil suffusion, which is known to decrease work load and decelerate ventricular growth. The morphologic parameters (compact layer thickness, ventricular wall composition, porosity of different layers and trabecular orientation) were determined from scanning electron micrographs of transversely dissected perfusion-fixed hearts. A vascular bed of stage 21 chick embryos was suffused with 1 ng of verapamil at 1 microliter per hour up to stages 24, 27 and 29 via a miniosmotic pump. From stage 24, the thickness of the compact myocardium in the left ventricle was greater than that of the right. The increase in thickness was minimal between stages 24 and 27, while the predominantly radially arranged trabeculae comprised up to 75% to total myocardial mass. The ratio of intertrabecular spaces to trabeculae (local porosity) decreased form the ventricular center (70%) towards the compact myocardium (0%). In verapamil-treated embryos, the hearts were smaller and showed delayed development. The compact myocardium was thinner than normal, and the proportion of trabeculae was higher than in controls. The local porosity values were similar in control and experimental groups. Decreased load resulted in delayed growth and morphogenesis, expressed as persistence of trabeculae and a thinner compact myocardium. Embryonic heart pumping function is largely based on extensively developed trabeculation with regionally different properties.

An estimate of fetal autonomic state by spectral analysis of human umbilical artery flow velocity waveforms

OBJECTIVE

Determination of gestational age-related fluctuations in heart rate in the umbilical artery of the early human fetus.

METHODS

Doppler velocity recordings from human umbilical artery were obtained, in a cross-sectional study design in 137 singleton pregnancies at 10-20 weeks of gestation. After exclusion criteria were applied, data on 117 normal pregnancies were available and subdivided into group I: 10-12 weeks (n = 49); group II: 13-16 weeks (n = 43); and group III: 17-20 weeks (n = 25). Blood flow velocity waveforms were reconstructed from Doppler audio signals. Variability in heart rate was calculated using Fast Fourier Transforms (FFT). Individual heart rate variability power spectra were subdivided into frequency bands.

RESULTS

Fetal heart rate variability decreases at 10-20 weeks and demonstrates a shift to lower frequencies at 17-20 weeks.

CONCLUSIONS

Fetal heart rate variability is related to gestational age and shows a shift to lower frequencies which may reflect autonomic functional development.

Developmental changes in the myocardial architecture of the chick

BACKGROUND

Numerous studies describing myocardial architecture have been performed on the adult heart but considerably fewer have been made during embryonic or fetal development. To serve as a basis for interspecies comparison of ventricular morphology, and as a reference for studying the effects of experimental perturbations, we examined the development of chick throughout the entire incubation period.

METHODS

Chick hearts from stage 14 (day 2) to stage 46 (day 21) were perfusion-fixed, and sectioned in transverse, frontal and sagittal planes. The ventricular myocardial architecture was examined and photographed in the scanning electron microscope.

RESULTS

At embryonic stage 16 and earlier, the smooth-walled heart loop had an outer myocardial mantle, cardiac jelly, and endocardium. From stage 18, there was an outer compact and inner trabeculated myocardium. Trabeculated myocardium could be subdivided into the outer (basal) portion adjacent to the compact layer and the central (luminal) part. The outer basal layer could be distinguished from the inner luminal by shorter and finer trabeculae with small, round intertrabecular spaces. From stage 24, the patterns of trabeculae and intertrabecular spaces were ventricle-specific. Between stages 24 to 31, abundant trabeculations were present throughout both ventricular cavities. The trabeculae were initially radially arranged, but later adopted a spiral course, which persisted in a simplified form into adulthood.

CONCLUSIONS

The ventricular myocardium undergoes distinctive morphogenesis, characterized by changes in trabecular patterning and orientation. We speculate that the embryonic trabecular architecture reflects the directions of the main stresses. Unlike fetal and adult hearts, which rely mostly on the compact myocardial layer, the trabeculae play a crucial role in the contractile function of the embryonic heart.

Developmental changes in the myocardial architecture of the chick

BACKGROUND

Numerous studies describing myocardial architecture have been performed on the adult heart but considerably fewer have been made during embryonic or fetal development. To serve as a basis for interspecies comparison of ventricular morphology, and as a reference for studying the effects of experimental perturbations, we examined the development of chick throughout the entire incubation period.

METHODS

Chick hearts from stage 14 (day 2) to stage 46 (day 21) were perfusion-fixed, and sectioned in transverse, frontal and sagittal planes. The ventricular myocardial architecture was examined and photographed in the scanning electron microscope.

RESULTS

At embryonic stage 16 and earlier, the smooth-walled heart loop had an outer myocardial mantle, cardiac jelly, and endocardium. From stage 18, there was an outer compact and inner trabeculated myocardium. Trabeculated myocardium could be subdivided into the outer (basal) portion adjacent to the compact layer and the central (luminal) part. The outer basal layer could be distinguished from the inner luminal by shorter and finer trabeculae with small, round intertrabecular spaces. From stage 24, the patterns of trabeculae and intertrabecular spaces were ventricle-specific. Between stages 24 to 31, abundant trabeculations were present throughout both ventricular cavities. The trabeculae were initially radially arranged, but later adopted a spiral course, which persisted in a simplified form into adulthood.

CONCLUSIONS

The ventricular myocardium undergoes distinctive morphogenesis, characterized by changes in trabecular patterning and orientation. We speculate that the embryonic trabecular architecture reflects the directions of the main stresses. Unlike fetal and adult hearts, which rely mostly on the compact myocardial layer, the trabeculae play a crucial role in the contractile function of the embryonic heart.

Embryonic hypertension following exposure to teratogenic doses of 5-fluoro-2'-deoxyuridine

The teratogenicity of 5-fluoro-2'-deoxyuridine (FdU) is well established. Previously, we have demonstrated that teratogenic doses of FdU produce hematomas and suggested that those hematomas produced skeletal malformations in chicken embryos. In this study, the cardiovascular effects of teratogenic doses of FdU in chicken embryos were studied. A dose of either 0.026 micrograms FdU or 0.030 micrograms FdU was injected into the yolk sacs of fertile chicken eggs containing embryos at Hamburger and Hamilton stages 17-19 of development. The embryos were then returned to the incubator. Aortic systolic and diastolic blood pressure, blood velocity and heart rate were measured at stages 21, 24 or 27 using a servonull system and Doppler ultrasound. In addition, mean arterial blood pressure, blood flow, and stroke volume were calculated from these data. Similar data were also recorded from uninjected and saline injected control embryos. Systolic and mean arterial blood pressures were significantly increased in FdU-treated embryos at stage 27. The other parameters measured or calculated were not significantly different from control embryos. Our study suggests that elevated systolic blood pressure in chicken embryos treated with FdU may lead to hematoma formation and subsequent birth defects.

Pathogenetic mechanisms of congenital cardiovascular malformations revisited

Rapid advances in cardiovascular science have expanded our knowledge of the mechanisms of heart development. Epidemiologists have defined the prevalence of congenital cardiovascular malformations, developmental biologists have delineated cascades of cell lineage, and molecular geneticists have identified mutations and loci associated with familial heart and vascular defects. We are well on the way to a molecular understanding of congenital cardiovascular malformations. Thus, it seems appropriate to review the pathogenetic classification of congenital cardiovascular malformations in light of this new clinical and scientific evidence. This schema serves as a template for the scientist to organize clinical information relevant to the pathogenesis of cardiac defects and as a tool for the clinician in approaching the difficult task of counseling parents of children with congenital cardiovascular malformations.

Distribution of blood flow between embryo and vitelline bed in the stage 18, 21 and 24 chick embryo

OBJECTIVE

We defined the distribution of blood flow between the embryo and the extraembryonic vascular bed as an initial step in understanding the control of flow distribution in the early developing heart.

METHODS

Dorsal aortic blood flow of stage 18, 21, and 24 chick embryo (n > or = 7 at each stage) was measured with a 20 MHz pulsed-Doppler velocity meter. Analog waveforms were digitally sampled at 500 Hz. 1-5 x 10(3) yellow microspheres in saline suspension were injected into the vitelline vein. The embryo and the extraembryonic vascular bed were harvested and separated from each other. The dye on the microspheres from each portion was extracted and extrapolated from the standard curve of the absorbance of dye concentrations per number of microspheres quantified by spectrophotometry. Blood flow was calculated from the integral of blood velocity and aortic cross-sectional area multiplied by the fraction distribution of microspheres in the embryo and extraembryonic vascular bed. Data were presented as mean +/- standard error of the mean.

RESULTS

The proportion distribution of microspheres between embryo and extraembryonic vascular bed shifted from 18.7 +/- 2.5 vs. 81.3 +/- 2.5% at stage 18, 25.1 +/- 3.0 vs. 74.9 +/- 3.0% at stage 21, and 34.2 +/- 2.4 vs. 65.8 +/- 2.4% at stage 24. Indices of blood flow normalized to wet weight (mean +/- 95% confidence interval) were similar between the embryo and the extraembryonic vascular bed, but increased throughout the stages.

CONCLUSION

During embryogenesis, blood flow per unit mass is evenly distributed between the metabolically active embryo and the extraembryonic vascular bed.

Mechanics of cardiac looping

During the early stages of embryonic development, the heart is a smooth-walled, muscle-wrapped tube that bends and rotates in a vital, but poorly understood, morphogenetic process called looping. Since looping involves biomechanical forces, this paper examines two mechanically based hypotheses for the bending component of cardiac looping. The first hypothesis is that an initial tension in or near the dorsal mesocardium (DM), a longitudinal structure along the outside of the ventricle, drives the deformation. To relieve the bending stresses in the tube, the myocytes change shape passively, and then they deform actively to continue the process to completion of a full loop. In the second hypothesis, contraction of circumferentially arranged actin macrofilaments produces circumferential compression and longitudinal expansion (due to incompressibility) of the myocytes. The DM locally constrains the longitudinal deformation, forcing the tube to bend. The feasibility of these hypotheses was evaluated using theoretical models and published experimental results. The models, which consist of beams composed of two layers representing the DM and the ventricular myocardium, show that the hypotheses are consistent with most of the known data, but further studies are necessary. In this regard, the models provide a conceptual framework for designing experiments to investigate the mechanics of looping.

Effect of atrial natriuretic peptide on diastolic filling in the stage 21 chick embryo

Atrial natriuretic peptide (ANP) exerts hemodynamic effects by direct venodilation in the chick embryo. We hypothesized that ANP-induced venodilation affects ventricular diastolic filling resulting in reduced ventricular preload. Chick ANP (0.1 microgram in 10 microL of normal saline) was suffused onto the vitelline vascular bed in stage 21 (3 1/2 d) chick embryos. Equivalent aliquots of normal saline were suffused as sham controls, and normal embryos received no suffusion. We measured simultaneously dorsal aortic blood velocity and atrioventricular blood velocity with a 20-MHz pulsed-Doppler velocity meter. Analog wave forms were digitally sampled at 500 Hz, and the dorsal aortic cross-sectional area was used to calculate dorsal aortic blood flow. Passive ventricular filling volume equaled dorsal aortic stroke volume multiplied by the fraction of passive area; active filling volume equaled dorsal aortic stroke volume multiplied by the fraction of active area. Data were summarized as mean +/- SEM (n > or = 7 per group) and analyzed by analysis of variance. Cycle lengths were similar in ANP-suffused, sham control, and normal embryos. Dorsal aortic blood flow decreased from 0.49 +/- 0.04 mm3/S at baseline to 0.27 +/- 0.05 mm3/S at 4 min post-ANP suffusion (p < 0.05) and was unchanged in sham control and normal embryos (p > 0.05). Passive ventricular filling was reduced by ANP suffusion, whereas active filling was unaffected, resulting in a decreased passive/active filling ratio from 0.64 +/- 0.07 at baseline to 0.32 +/- 0.08 at 4 min in ANP-suffused embryos (p < 0.05). Passive/active ratio was unchanged in sham control and normal embryos. Thus, ANP-mediated vasodilation reduces cardiac output via decreased passive ventricular filling in the embryonic heart.

Epicardial strains in embryonic chick ventricle at stages 16 through 24

Embryonic cardiac development depends, in part, on the local biomechanical environment. Tracking the motions of microspheres attached to the embryonic chick ventricle, we computed two-dimensional epicardial strains at Hamburger-Hamilton stages 16, 18, 21, and 24 (2.5, 3.5, 4.0, and 4.5 days, respectively, of a 21-day incubation period). First, in a cross-sectional study, strains were measured in separate embryos at each stage (n > or = 19 per stage). Then, in a longitudinal study, strains were measured serially on the same heart, with the eggs resealed and reincubated between successive stages (n > or = 4 per stage). Although the heart undergoes major changes in mass, morphology, and loading during the studied stages, both studies showed that peak circumferential and longitudinal strains relative to end diastole were similar in magnitude (0.13 to 0.16) and did not change significantly across the stage range. The peak principal strains also showed no significant changes, with magnitudes of approximately 0.11 and 0.18. The shear strains were small, and their signs varied from one heart to another. These results suggest that wall strain is maintained within a relatively narrow range during primary cardiac morphogenesis.

A nonliner poroelastic model for the trabecular embryonic heart

A theoretical model is presented for the primitive right ventricle of the stage 21 chick embryo. At this stage of development, the wall of the heart is trabecular with direct intramyocardial blood flow. The model is a pressurized fluid-filled cylinder composed of a porous inner layer of isotropic myocardium and a relatively thin compact outer layer of transversely isotropic myocardium. The analysis is based on nonlinear poroelasticity theory, modified to include residual strain and muscle activation. Correlating theoretical and experimental pressure-volume loops and epicardial strains gives first-approximation constitutive relations for stage 21 embryonic myocardium. The results from the model suggest three primary conclusions: (1) Some muscle fibers likely are aligned in the compact layer, with a fiber angle approximately + 10 deg from the circumferential direction. (2) Blood is drawn into the wall of the ventricle during diastolic filling and isovolumic contraction and is squeezed out of the wall during systolic ejection, giving a primitive intramyocardial circulation before the coronary arteries form. As the heart rate increases, the transmural blood-flow velocity increases, but the volume of blood exchanged with the lumen per beat decreases. (3) Residual strain affects transmural stress distributions, producing nearly uniform stresses in the porous layer, where the peak end-systolic stress occurs. These results improve our understanding of the relation between form and function in the developing heart and provide directions for biological experiments to study cardiac morphogenesis.

Cardiovascular health and disease in children: current status. A Special Writing Group from the Task Force on Children and Youth, American Heart Association

More than 600,000 children in the United States have a congenital or acquired cardiac abnormality, and millions more are at risk of developing atherosclerotic disease in adulthood, a risk made particularly evident by the prevalence of cardiovascular risk factors in the young. There are barriers to optimum prevention and treatment of these conditions in children and youth. The AHA's Task Force on Children and Youth has described these barriers and outlined a series of recommendations and strategies to meet the challenges they impose. More research is needed, and research initiatives will be developed at scientific conferences designed to review critical areas of cardiac development and etiology of disease in children. Financial support for such research initiatives must be increased. Educational programs on cardiovascular risk factors will be extended to children and their families. When these programs are coordinated with efforts in the community and in schools, they will reduce the prevalence of cardiovascular risk factors. The task force recommends that various departments and committees of the AHA use their resources for the benefit of children: for example, by developing more research initiatives for funding by the AHA or NHLBI and increasing legislative and regulatory efforts in the areas such as mandatory school health programs and tobacco advertising. It is hoped that in the next decade, through research and educational efforts, many advances in the prevention and treatment of cardiovascular diseases in the young will be realized.

Tetralogy of Fallot. The first 300 years

The chronicle of tetralogy of Fallot is part of a dramatic evolution in cardiology, cardiac surgery, and understanding of the developing heart. Many new tools and concepts have evolved since Steno of Denmark first described the defect in 1673, and since Fallot of Marseilles coined the term tetralogy in 1888. Four major eras of progress can be recognized. The 1st, the era of pathologic anatomy, culminated in the publication of Maude Abbott's Atlas of Congenital Cardiac Disease in 1936. The next, the era of clinicophysiology and surgery, was highlighted by the 1st Blalock-Taussig anastomosis in 1944, by open-heart surgery 10 years later, and by a new team approach to cardiology. The 3rd, or infant era, began in the mid 1970s with successful intracardiac repair in infants, the rise of echocardiography, and the introduction of prostaglandin therapy. The current era of cardiac development (beginning in the 1990s) gives hope for early understanding of the molecular basis of tetralogy. Tribute is due to the surgical and medical pioneers, and to the pioneer patients and their families, for revolutionary changes in diagnosis and treatment. The challenge of the next 100 years lies in increased understanding of the molecular biology of the defect and in preserving the blend of humanism, scholarship, and skill that have graced the advances of the past 3 centuries.

Corrected QT interval prolongation in anthracycline-treated survivors of childhood cancer

PURPOSE

Comprehensive cardiac evaluations are currently recommended for all anthracycline-treated patients to detect subclinical cardiac failure. A screening test is needed that would easily and inexpensively identify patients who are at risk for late cardiac decompensation.

METHODS

We routinely reviewed the ECG and echocardiogram (ECHO) results of 52 of 56 anthracycline-treated long-term survivors of childhood cancer who had received > or = 100 mg/m2 of ANTH (ANTH = 1 mg/m2 of doxorubicin), and who were not in clinical heart failure. Exercise testing was performed in eight patients with a corrected QT interval (QTc) of > or = 0.43.

RESULTS

Zero of 15 patients (without chest radiation) who received less than 300 mg/m2 of ANTH versus six of 22 who received > or = 300 mg/m2 of ANTH had a QTc > or = 0.43 (P = .03). Three of 15 patients (with chest radiation) who received less than 300 mg/m2 of ANTH versus 12 of 22 who received > or = 300 mg/m2 of ANTH had a QTc > or = 0.43 (P = .03). For all patients (including those with chest radiotherapy), zero of 19 who received less than 300 mg/m2 of ANTH versus eight of 33 who received > or = 300 mg/m2 of ANTH had a QTc of > or = 0.45 (P = .025). Three of 19 who received less than 300 mg/m2 of ANTH versus 19 of 33 who received > or = 300 mg/m2 of ANTH had a QTc of > or = 0.43 (P = .003). One patient had decreased fractional shortening (FS) and QTc prolongation. Cardiac decompensation (with a FS of 24%) occurred with propranolol in a patient with previously normal FS but prolonged QTc. With exercise, the QTc became further prolonged in all four patients with a QTc of 0.44 to 0.46 and in two of four patients with a QTc of 0.43.

CONCLUSION

Prolongation of the QTc, a measure of myocardial repolarization, may reflect injury to myocardial cells. QTc prolongation may be predictive of an increased risk of late cardiac decompensation. If the utility of the QTc measure is confirmed, screening for evidence of myocardial damage can be easily and inexpensively performed by oncologists and primary caretakers.

Residual strain in the ventricle of the stage 16-24 chick embryo

Residual stress and strain, i.e., the stress and strain remaining in a solid when all external loads are removed, may be produced in biological tissues by differential growth. During cardiac development, residual stress and strain may play a role in cardiac morphogenesis by affecting ventricular wall stress. After a transmural radial cut, a passive ventricular cross section opens into a sector, and the size of the opening angle provides a measure of the circumferential residual strain. Residual strains were characterized in this manner for the apical region of the diastolic embryonic chick heart for Hamburger-Hamilton stages 16, 18, 21, and 24 (approximately 2.5, 3.5, 4.0, and 4.5 days, respectively, of a 21-day incubation period). The average opening angle at these stages was 107 +/- 10 degrees, 79 +/- 10 degrees, 73 +/- 11 degrees, and 74 +/- 7 degrees, respectively (n > or = 5 for each stage). These measured angles were correlated with changes in ventricular morphology. Scanning electron micrographs of the apex revealed that the wall of the ventricle is smooth at stage 16. Then at stage 18, myocardial trabeculae develop, forming ridges with primarily a circumferential orientation. By stage 21, the trabeculae develop into a mesh, giving the ventricular wall a spongelike appearance, and the preferred orientation is lost by stage 24. The large decrease in opening angle between stages 16 and 18 corresponded to the onset of trabeculation, which is the greatest change in form during the studied stages. We speculate that residual strain is an important biomechanical factor during cardiac morphogenesis.

Cardiac mechanics in the stage-16 chick embryo

A theoretical model is presented for the tubular heart of the stage-16 chick embryo (2.3 days of a 21-day incubation period). The model is a thick-walled, pseudoelastic cylindrical shell composed of three isotropic layers: the endocardium, the cardiac jelly, and the myocardium. The analysis is based on a shell theory that accounts for large deformation, material nonlinearity, residual strain, and muscle activation, with material properties inferred from available experimental data. We also measured epicardial strains from recorded motions of microspheres on the primitive right ventricles of stage-16 white Leghorn chick embryos. Relative to end diastole, peak axial and circumferential Lagrange strains occurred near end systole and had similar values. The magnitudes of these strains varied along the longitudinal axis of the heart (-0.16 +/- 0.08), being larger near the ends of the primitive right ventricle and smaller near midventricle. The in-plane shear strain was less than 0.05. Comparison of theoretical and experimental strains during the cardiac cycle shows generally good agreement. In addition, the model gives strong stress concentrations in the myocardial layer at end systole.

Analysis of dynamic atrial dimension and function during early cardiac development in the chick embryo

Although atrial morphologic changes are well documented, the description of early atrial function is limited. We used videomicroscopic methods to define the function of the contracting atrium in stage 16 to 24 white Leghorn chick embryos. We exposed the embryo in ovo (right side up) and imaged the ventricle, then repositioned the embryo (left side up) and imaged the atrium (n greater than or equal to 8 per stage). We traced the atrial endocardial border and then measured atrial perimeter (mm) and cross-sectional area (mm2). A 20-MHz pulsed Doppler velocity meter was used to measure atrioventricular blood velocity during atrial imaging in an additional six stage 21 embryos. Data were tested by analysis of variance and regression analysis. Mean heart rate change after repositioning was -4 +/- 1%. Atrial maximum and minimum area increased linearly versus embryo stage (y = 0.10x - 1.41, r = 0.89, p less than 0.05 and y = 0.05x - 0.67, r = 0.82, p less than 0.05, respectively). Shortening fraction (percentage of reduction) of atrial perimeter and area decreased from 32.3 +/- 2.0% to 27.5 +/- 1.8% (p less than 0.05) and 56.2 +/- 3.0% to 47.7 +/- 2.0% (p less than 0.05), respectively, from stage 16 to 24. During atrial contraction, the velocity of circumferential wall shortening increased linearly with stage (y = 0.22x - 2.08, r = 0.81, p less than 0.01); however, the velocity of lengthening was similar between stages (p = 0.45). Simultaneous atrial imaging and pulsed Doppler velocity measurement showed that passive atrioventricular flow occurred late in atrial lengthening and active atrioventricular flow occurred during atrial contraction.(ABSTRACT TRUNCATED AT 250 WORDS)

Pediatric cardiology research in 1990: a review of abstracts submitted to the Society for Pediatric Research, American Academy of Pediatrics, and American Heart Association Scientific Sessions

We assessed pediatric cardiology research by reviewing pediatric cardiology abstracts submitted in 1990 to the Society of Pediatric Research, American Academy of Pediatrics, and American Heart Association national meetings. Included were accepted and rejected studies. Abstracts were reviewed for disease being studied, methodology used to answer the research question, study design, and acceptance/rejection. Abstracts were analyzed from 123 institutions, 81 American and 42 foreign. Out of 423 abstracts, 307 (72.6%) were clinical and the remainder were basic science investigations. Slightly more than half of the clinical submissions were related to congenital heart disease. Coronary artery disease and inflammatory diseases accounted for 12% of clinical submissions. Echocardiography, clinical outcome measures, and electrophysiology were the most common research methodologies. Almost 80% of basic science research was performed in normal tissues; animal physiology, fetal physiology, and cellular/biochemical studies were the most common methodologies. With regard to study design, half of the clinical studies were retrospective and only 6% were either prospective epidemiologic or prospective controlled intervention trials. For basic sciences, 38% of abstracts were descriptions of phenomena and 62% were hypothesis testing, with developmental hypotheses being most common. Acceptance rates favored higher quality study design. However, areas of greatest interest to cardiologists, congenital heart disease, cardiomyopathy, and electrophysiology, had poorer quality study design than did other areas. We have shown broad interest in pediatric cardiology research. However, clinical studies frequently were retrospective or had uncontrolled study designs. Basic science research was performed at a small number of institutions and emphasized either description of phenomena or developmental biology of normal tissues.

Effect of chronic verapamil treatment on ventricular function and growth in chick embryos

Adjustment of myocardial mass to work load is a fundamental characteristic of the heart. We studied the effect of verapamil, a calcium channel blocker, on growth and function of chick embryonic ventricle. We treated stage 18 chick embryos with verapamil delivered to the extraembryonic vascular bed by a miniosmotic pump and compared them with saline-treated control and untreated embryos. At stages 24, 27, and 29, we measured ventricular pressure and dP/dt by a servo-null system, dorsal aortic stroke volume and dV/dt by pulsed-Doppler, and ventricular and embryo wet weights. Mean myocyte profile area was measured by digital planimetry technique, and cell growth response by DNA and protein assay. Verapamil treatment decreased ventricular pressure in experimental (P less than 0.05) compared with saline control and normal embryos; at stage 27, 1.59 +/- 0.21 vs. 2.17 +/- 0.05 and 2.35 +/- 0.08 (SE) mmHg, respectively. Mean dorsal aortic blood flow decreased in experimental (P less than 0.05) vs. control and normal embryos; at stage 27, 0.98 +/- 0.07 vs. 1.54 +/- 0.10 and 1.56 +/- 0.07 mm3/s, respectively. Stroke volume remained the same in all experimental, normal, and control embryos except at stage 29. Ventricular weight decreased in experimental (P less than 0.05) vs. control and normal embryos; at stage 27, 1.09 +/- 0.07 vs. 1.51 +/- 0.08 and 1.54 +/- 0.11 mg, respectively. Embryo weights, myocyte size, and cytoplasmic fractional volume were similar in all groups. Morphology of ventricles was normal. DNA was lower in experimental (P less than 0.05) compared with control and normal embryos.(ABSTRACT TRUNCATED AT 250 WORDS)

Diastolic filling characteristics in the stage 12 to 27 chick embryo ventricle

Cardiac output is affected by the diastolic filling characteristics of the ventricle. We hypothesized that the relative contributions of passive and active filling change as the ventricle develops from a smooth-walled tube to a trabeculated four-chamber heart. In stage 12 to 27 white Leghorn chick embryos, we simultaneously measured ventricular pressure with a servo-null micropressure system and dorsal aortic and atrioventricular velocities with a 20-MHz pulsed-Doppler velocity meter. The analog waveforms were sampled at 500 Hz and converted to digital format via an analog/digital board. We partitioned diastole into passive and active components. The passive phase began with the return of the pressure curve to baseline and extended to the onset of the a-wave. The active phase began with the upstroke of the atrial velocity curve and extended to the upstroke of the ventricular pressure curve at end-diastole. Data are presented as mean +/- SEM (n greater than or equal to 6 at each stage) and analyzed by analysis of variance and regression analysis. At similar cycle lengths ranging from 480 to 600 ms (p greater than 0.05), end-diastolic pressure increased from 0.24 +/- 0.02 mm Hg at stage 12 to 0.55 +/- 0.01 mm Hg at stage 27. Passive and active filling volumes were 92 (0.0038 +/- 0.0005 mm3) and 8% (0.0004 +/- 0.0002 mm3), respectively, at stage 12 and changed to 24 (0.23 +/- 0.08 mm3) and 76% (0.62 +/- 0.08 mm3), respectively, at stage 27. The ratio of passive to active filling volume decreased from 7.89 to 0.35.(ABSTRACT TRUNCATED AT 250 WORDS)

Ventricular pressure-area loop characteristics in the stage 16 to 24 chick embryo

The accurate description of embryonic cardiovascular function requires the adaption of standard measurement techniques to the small scale of the developing heart. In the mature heart, the analysis of ventricular pressure and volume accurately defines function. Because in vivo measures of volume are not feasible in the embryonic heart, we tested the hypothesis that ventricular pressure-area loops accurately define ventricular function in the stage 16 to stage 24 white Leghorn chick embryo. We simultaneously measured ventricular pressure with a servo-null pressure system and recorded video images at 60 Hz. The pressure waveform was superimposed onto the video image in real time. Video fields were planimetered for epicardial ventricular cross-sectional area and ventricular pressure. Pressure and area data were smoothed using a fast Fourier transform filter and plotted. Data are reported as mean +/- SEM, n greater than or equal to 4, and were tested by regression analysis and analysis of variance (p less than 0.05). Heart rate increased from 90 +/- 7 beats/min at stage 16 to 130 +/- 13 beats/min at stage 24. All pressure-area loops displayed diastolic filling, isometric contraction, ejection, and isometric relaxation, similar to pressure-volume loops of the mature heart. Isometric contraction time increased from 42 +/- 5 to 62 +/- 4 msec (p less than 0.05), while isometric relaxation time was 124 +/- 12 and 120 +/- 10 msec (p greater than 0.05) between stages 16 and 24, respectively. The maximum ratio of instantaneous ventricular pressure to area identified end systole better than peak ventricular pressure or minimum ventricular area. Thus, pressure-area relations define ventricular function in the embryonic chick heart.

Effect of changes in circulating blood volume on cardiac output and arterial and ventricular blood pressure in the stage 18, 24, and 29 chick embryo

We studied the hemodynamic effects of changing volume loading in the chick embryo, before autonomic innervation, to test the hypothesis that the Frank-Starling mechanism functions in the embryonic myocardium. Dorsal aortic blood velocity was measured by pulsed Doppler. Heart rate and aortic diameter were also measured to calculate cardiac output and stroke volume index. Vitelline arterial and ventricular pressures were measured with a servo-null micropressure system in stage 24 embryos. Infusing isotonic solution intravenously resulted in linear increases in stroke volume index for stages 18 (y = 388x + 6.89), 24 (y = 466x + 7.86), and 29 (y = 549x + 4.96). The slopes and intercepts were statistically the same for all three stages. Similar volume loading in stage 24 embryos initially increased mean arterial pressure linearly, but at higher loading conditions, the rate of rise lessens. Thus, volume loading resulted in a decrease in vascular resistance. Withdrawing blood from stage 24 embryos resulted in a decrease in ventricular peak systolic and end-diastolic pressures. With reinfusion of the blood, systolic and end-diastolic pressures initially rose above baseline levels and later returned to normal. We conclude that a length-tension relation is present in the preinnervated embryonic heart and that vascular resistance changes inversely with loading conditions. We speculate that these mechanisms are the primary hemodynamic control mechanism in the early chick embryo.

Maternal diabetes and cardiovascular malformations: predominance of double outlet right ventricle and truncus arteriosus

Most studies on the relationship of maternal diabetes to cardiovascular malformations (CVM) have been prospective investigations of pregnancy outcome and therefore could not identify associations with rare cardiac lesions. The results of a retrospective study shed new light on the risks of specific cardiac defects in diabetic pregnancies. The Baltimore-Washington Infant Study, a population-based case-control investigation of CVM, provides information on maternal diabetes reported in personal interviews. Among 2259 mothers of cases, 35 (1.5%) reported diabetes present before pregnancy (called "overt") and 95 (4.2%) reported diabetes only during pregnancy (called "gestational"). Among 2,801 mothers of controls, 14 (0.5%) had overt diabetes and 83 (3.0%) had gestational diabetes. Malformation-specific risks were expressed as odds ratios (OR) with 99.5% confidence intervals (CI). The strongest associations with overt maternal diabetes were found with double outlet right ventricle (OR 21.33; 99.5% CI 3.34, 136.26), and truncus arteriosus (OR 12.81; 99.5% CI 1.43, 114.64). No significant diagnosis-specific associations were found with gestational diabetes. Non-cardiac malformations were present in 23% of infants with CVM whose mothers had overt diabetes and in 26% of infants with CVM whose mother had gestational diabetes, in 32% of infants with CVM whose mothers did not have diabetes, and in 4% of controls. Double outlet right ventricle and truncus arteriosus are malformations dependent upon neural-crest-cell-derived ectomesenchymal tissues; these are precisely the conotruncal abnormalities that result from experimental ablation of the neural crest in chick embryos. The association with diabetes suggests a further etiologic link between these two lesions.

Correlation of ventricular area, perimeter, and conotruncal diameter with ventricular mass and function in the chick embryo from stages 12 to 24

Ventricular form and function are interrelated during cardiovascular development. The study of muscle mechanics requires the real-time measurement of length, area, or volume. Because volume measures are not currently possible in the embryonic heart, we tested the hypothesis that end-diastolic (ED) and end-systolic (ES) ventricular perimeter, area, and conotruncal diameter correlate with ventricular mass and function in the stage 12 to stage 24 white Leghorn chick embryo. Video images of the contracting heart were recorded at 60 Hz on 1/2" videotape and studied with a custom image-analysis workstation. ED and ES video fields were selected by maximum and minimum ventricular area and were planimetered for epicardial ventricular perimeter, area, and conotruncal diameter. Data are reported as (mean +/- SEM, n greater than or equal to 8) and were tested by analysis of variance and regression analysis. Heart rate calculated from cycle length increased from 78 +/- 6 beats/min at stage 12 to 162 +/- 5 beats/min at stage 24. ED and ES area increased geometrically versus stage (y = 0.53 - 0.08x + 0.004x2, r = 0.96, p less than 0.001; and y = 0.60 - 0.09x + 0.004x2, r = 0.98, p less than 0.001, respectively). ED and ES perimeter and conotruncal diameter increased linearly versus stage (r = 0.95, p less than 0.001; r = 0.96, p less than 0.001; and r = 0.93, p less than 0.001; r = 0.93, p less than 0.001, respectively). Shortening fraction for each measurement increased from stage 12 to 16 or 18 then decreased.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiac malformations in relatives of infants with hypoplastic left-heart syndrome

In a pilot study of relatives of infants with hypoplastic left-heart syndrome (HLHS), we obtained a medical history, cardiovascular examination, and echocardiogram in 48 first-degree relatives of 11 probands with isolated HLHS and 3 with HLHS and noncardiac malformations. Echocardiography confirmed heart defects in 5 of 41 relatives of patients with isolated HLHS. In four instances, the cardiac abnormality was unrecognized. Among 7 relatives of infants with HLHS and extracardiac anomalies, no heart defects were detected. Cardiac defects occurred in first-degree relatives of probands at a frequency higher than previously predicted by an additive multifactorial model of inheritance. These findings suggest that first-degree relatives of HLHS probands may have an increased risk for subclinical cardiac defects and that genetic factors likely contribute to the cause of left-heart blood-flow lesions.

Hemodynamics of the stage 12 to stage 29 chick embryo

The heart is the first functioning organ in the embryo and provides blood flow during cardiac morphogenesis from a muscle-wrapped tube a few cells thick to the four-chambered pump. We described the hemodynamics of the chick embryo from stage 12 (50 hours of a 21-day incubation) to stage 29 (6 days), during which the embryo weight increased 120-fold. We measured ventricular, embryo and extraembryonic vascular bed wet weights, dorsal aortic blood flow with a directional pulsed-Doppler velocity meter, and ventricular and vitelline arterial blood pressures with a servo-null micropressure system. The data are reported as mean +/- SEM. With rapid development and morphogenesis, dorsal aortic blood flow increased from 0.015 +/- 0.004 to 2.40 +/- 0.20 mm3/sec parallel to the geometric increase of wet embryo weight from 2.22 +/- 0.10 to 267.5 +/- 9.7 mg. Dorsal aortic blood flow normalized for embryo and extraembryonic weight remained relatively constant (Y = 2.13 + 0.02X, r = 0.23, SEE = 0.03). Stroke volume increased from 0.01 +/- 0.003 to 0.69 +/- 0.03 mm3, and heart rate doubled from 103 +/- 2 to 208 +/- 5 beats/min. Systolic, diastolic, and mean vitelline arterial pressure increased linearly from 0.32 +/- 0.01, 0.23 +/- 0.01, and 0.28 +/- 0.01 mm Hg at stage 12 to 2.00 +/- 0.06, 1.22 +/- 0.03, and 1.51 +/- 0.04 mm Hg, respectively, at stage 29. Ventricular peak systolic and end-diastolic pressure increased from 0.95 +/- 0.04 and 0.24 +/- 0.02 at stage 12 to 3.45 +/- 0.10 and 0.82 +/- 0.03 at stage 29, respectively. The hemodynamic waveforms were similar to those found in the four-chamber heart of the mature animal. These data are integral to understanding the interrelation of function and form during cardiac development.

Effect of heart rate increase on dorsal aortic flow before and after volume loading in the stage 24 chick embryo

In the stage 24 chick embryo, a paced increase in heart rate reduces stroke volume, presumably by rate-dependent decrease in passive filling. We hypothesized that rate-dependent stroke volume reduction could be abolished by volume loading. Dorsal aortic blood velocity was measured with a 20 mHz pulsed-Doppler meter from a 0.75-mm piezoelectric crystal (eight embryos), and atri-oventricular velocity was simultaneously measured from the ventricular apex (six embryos). Sinus venosus pacing (stimuli of 1 ms duration and less than 4 mA) was performed at intrinsic rate (P:I) and at 150% of intrinsic rate (P:150%I). Volume loading was performed during P:150%I by intravenous injection of 7.5 microL of chick Ringer's solution. Using atrioventricular velocity profile, stroke volume was divided into the proportion due to passive (E-phase) and active (A-phase) filling. Stroke volume was compared during P:I, P:150%I, immediately (P:150%I') and 30 s after (P:150%I") volume loading. Data (mean +/- SEM) were compared by ANOVA. During pacing, stroke volume (mm2/cycle) decreased but increased after volume loading (I, 0.43 +/- 0.03; P:I, 0.37 +/- 0.03; P:150%I, 0.19 +/- 0.03; P:150%I', 0.24 +/- 0.05; P:150%I", 0.28 +/- 0.04 (p less than 0.005). During P:150%I, E-phase filing disappeared and was not restored by volume loading, whereas, A-phase filling diminished but was restored by volume loading. In stage 24 chick embryos, rate-dependent stroke volume decrease is reversed by volume loading that restores stroke volume due to an increase in active filling but not passive filling. Thus, even at rapid heart rate, the embryonic ventricle responds to volume loading, indicating that the Frank-Starling relationship functions during tachycardia in the embryonic heart.