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Biomedical subjects

M Choy

Publications and source records attributed to M Choy.

14 recordsLinked to original sources
PubMed1992

Fate of the atrioventricular endocardial cushions in the developing chick heart.

To determine the fate of the atrioventricular endocardial cushions in cardiac development, we used staining methods for extracellular fibronectin, which is abundant in the endocardial cushions, and actin, which is abundant in the myocytes. White Leghorn chick embryo hearts were harvested at Hamburger and Hamilton stages 26 to 36, and serial sections of the atrioventricular valve region were stained. Before atrioventricular valve formation, fibronectin and actin staining reveal separation between the fibronectin-rich endocardial cushions and the actin-rich myocardial layer. The developing mitral valve leaflets at all of the observed stages contain a fibronectin-rich matrix but no actin-rich myocytes. In contrast, the tricuspid band includes both fibronectin matrix and actin-rich cells. We conclude that the mitral valve leaflets in the chick form predominantly from the endocardial cushion tissue, and the tricuspid band receives contributions from both the endocardial cushions and surrounding myocardium.

Actins↗
PubMed1992

Properties of human thymic B cells.

B cells, distinct from those seen in myasthenia gravis, are present in normal human thymic medulla, concentrated around the Hassall's corpuscles. We have shown that they constitute 33 +/- 4.8% of the total cells in the thymic medulla. In tissue sections they were often seen to have rosettes of thymocytes around them, a relationship which was maintained when the cells were isolated from the thymus. Thymic B cells expressed cytoplasmic immunoglobulins IgD, IgM and IgG but only rarely IgA. Unlike murine thymic B cells, human thymic B cells were CD5-. Freshly isolated thymic B cells were activated cells, but they rapidly became quiescent and died in culture over a 10-day period unless stimulated with mitogens. Thymic B cells responded to polyclonal B-cell activators SAC and TPA and when stimulated, maintained their relationship with thymocytes. Electron microscopic studies showed that two morphologically different thymocyte populations associated with the B cells. The plasma membranes of larger thymocytes were juxtaposed to the B-cell membrane, but smaller thymocytes with darker cytoplasm were associated with the B cells via cytoplasmic strands. Studies in mice have suggested that B cells are involved in thymic negative selection. The close association between activated B cells and thymocytes observed in this study supports this hypothesis.

B-Lymphocytes↗
PubMed1991

Transforming growth factor-beta 1 localized within the heart of the chick embryo.

Transforming growth factor-beta 1 is a pleiotropic peptide mediator of growth, differentiation, and extracellular matrix synthesis. In the embryonic chick heart prior to the formation of the endocardial cushions, evidence from in vitro experiments suggests that transforming growth factor-beta 1 may be an inducer of the differentiation of atrioventricular endothelial cells into endocardial cushion mesenchyme. Further in vitro evidence suggests that the factor stimulates mesenchymal cell proliferation, and, thus, growth of the cushions. Using an antibody made against a peptide duplicating the aminoterminal 30 amino acid sequence of transforming growth factor-beta 1, we stained sections of stage 11, 18, 23, 26, and 36 chick hearts by an in situ immunofluorescence technique. Transforming growth factor-beta 1 staining localized to the endocardial surface and epicardial surface of the stage 11 heart, but it decreased from these locations in later stages. The cardiac jelly (stage 11), endocardial cushions (stage 18, 23, and 26), and, subsequently, the heart valve leaflets (stage 36) stained intensely for the growth factor.

Animals↗
PubMed1991

Effects of ischemia on epicardial segment shortening.

To evaluate the effects of nontransmural ischemia on epicardial contractile function, we implanted sonomicrometers in 15 open-chest, anesthetized (halothane) dogs. One cylindrical crystal (radiating ultrasound 360 degrees) was used as a transmitter for three conventional flat plate crystals arrayed to measure epicardial segment shortening along three different axes that were deviated 0 degree (parallel), 45 degrees (oblique), and 90 degrees (perpendicular) from surface fiber orientation in the anteroapical or posterior-basal left ventricle. During baseline conditions, epicardial shortening was maximal parallel with fiber orientation. Shortening decreased in a non-linear manner as deviation from fiber orientation increased, but there were significant differences between the two left ventricular regions suggesting that more substantial lateral strain occurs in the anterior-apical than the posterior-basal area. During coronary inflow restriction, changes in epicardial segment shortening also varied greatly depending on location and alignment. At levels of wall thickening impairment associated with normal subepicardial perfusion, changes in epicardial function were restricted to the segments aligned perpendicular to fiber orientation whereas the parallel and oblique segments displayed moderate dysfunction or none at all. Thus, transmural tethering modifies epicardial segmental motion during coronary inflow restriction, but the severity of the influence depends on the alignment and location of the epicardial measurements.

Animals↗
PubMed1991

Sonographic spectrum of fetal cardiac hypoplasia.

Four cases of hypoplastic left ventricle and three cases of hypoplastic right ventricle detected sonographically prenatally are presented. A four-chamber view of the heart was abnormal in all seven cases. The sonographic appearance of the hypoplastic ventricle was variable, being smaller than normal in six of seven cases and not being identified at all in one case. Other ultrasound findings included an atrial septal defect (n = 7); increased size of the contralateral ventricle (n = 6); nonvisualization or poor visualization of the outflow tract of the affected ventricle (n = 6), and intact ventricular septum (n = 5). In one of four cases of hypoplastic left ventricle the pregnancy was terminated; the other three infants died within 5 days after birth. One of the three fetuses with hypoplastic right ventricle was aborted. Of the remaining two infants included one had tricuspid atresia with a ventricular septal defect and one had pulmonary atresia with an intact ventricular septum. Both infants are alive, have had palliative surgery, and will be considered for a more definitive surgical repair. An abnormal four-chamber view of the heart should alert those performing routine obstetrical ultrasound to a possible hypoplastic ventricle, so that the pregnant woman can be referred to a center capable of performing more sophisticated fetal echocardiography.

Abortion, Induced↗
PubMed1991

Implementing a computerized operating room management system.

The Queen's Medical Center implemented a computerized operating room management system in 1987 that includes surgery scheduling, intraoperative recording, and resource tracking. In addition to the important functional components, the system provides management with a better tool for decision-making. The purpose of this article is to describe this implementation. Background is provided to identify the manual system's deficiencies followed by the anticipated benefits of the computer system. The paper concentrates on Queen's implementation experiences in coding the surgical procedure information, confronting staff anxiety, managing the changing roles of the staff and providing adequate resources. Minimum requirements for a successful implementation include designating an effective project leader, assigning system responsibilities to the user, relieving all operational responsibilities from key members of the project team and providing adequate resources to support the system.

Appointments and Schedules↗
PubMed1991

Ebstein's anomaly appearing in the neonate. A new surgical approach.

Ebstein's anomaly appearing during the neonatal period carries a high mortality rate. These infants exhibit cyanosis, acidosis, and congestive heart failure. The pathophysiologic characteristics consist of severe tricuspid regurgitation and functional pulmonary atresia. As a result of the inability of the right ventricle to generate forward flow through the pulmonary arteries, these infants remain dependent on ductal patency. Since May 1988, five newborn infants with severe Ebstein's anomaly have been admitted for treatment at our institution. At initial examination, they weighed 3.6 +/- 1.8 kg and had a mean oxygen tension of 29.6 +/- 2.3 mm Hg and a mean pH of 7.20 +/- 0.05. Chest roentgenography demonstrated a mean cardiothoracic ratio of 0.81 +/- 0.02. As determined by echocardiography, the right atria were massively enlarged, severe tricuspid regurgitation was present in all patients, and the pulmonary valves were not opening. All infants were dependent on prostaglandin E1 and attempts to wean them from this drug were unsuccessful. Palliative treatment consisted of tricuspid closure with autologous pericardium and an aortopulmonary shunt of 4 mm polytetrafluoroethylene tubing. There were no operative or late deaths. At discharge, mean oxygen tension was 42.2 +/- 0.85 mm Hg and mean systemic oxygen saturation was 83.2% +/- 1.94%. Infants have grown satisfactorily during the follow-up period. Three infants have since returned for further surgical intervention. One infant, at 11 months of age, underwent a Glenn anastomosis for progressive oxygen desaturation. Two infants have returned, at ages 23 and 22 months, for Fontan procedures, which represent their definitive operative management. We believe this new procedure offers excellent palliative treatment for Ebstein's anomaly in critically ill neonates. Feasibility of later definitive correction is demonstrated by the good results obtained with the Fontan procedure in two infants.

Ebstein Anomaly↗
PubMed1990

Regulation of proliferation of embryonic heart mesenchyme: role of transforming growth factor-beta 1 and the interstitial matrix.

Proliferation of atrioventricular cushion mesenchyme of the embryonic avian heart maintained in three-dimensional aggregate culture is stimulated by interaction with the interstitial matrix. Chicken serum or transforming growth factor-beta 1, which stimulates proliferation, induces matrix deposition in regions of the aggregate showing high labeling indices with tritiated thymidine. Dispersed heart mesenchyme interstitial matrix introduced into serum-free culture is incorporated into the aggregate and stimulates cellular proliferation similar to serum or transforming growth factor-beta 1. Proliferation is reversibly inhibited by the peptide Gly-Arg-Gly-Asp-Ser-Pro. It is suggested that transforming growth factor-beta 1 stimulates the production of interstitial matrix and that a sufficient stimulus for proliferation in this system is the presence of the matrix, which acts as the adhesive support for cellular anchorage.

Animals↗
PubMed1989

Hereditary long Q-T syndrome presenting as epilepsy: electroencephalography laboratory diagnosis.

Patients with hereditary Q-T interval prolongation can present with seizures, syncope, and sudden death. In 2 siblings with autosomal dominant familial long Q-T syndrome, electroencephalographic examinations performed 6 and 2 years before diagnosis included electrocardiographic tracings documenting the cardiac abnormality. A timely diagnosis of this condition may have prevented the death of 1 of these patients. Measurement of the corrected Q-T interval on electrocardiographic tracings obtained in the electroencephalography laboratory should be considered in selected patients.

Adolescent↗
PubMed1987

Paradoxical hypertension after repair of coarctation of the aorta in children: balloon angioplasty versus surgical repair.

The incidence and possible causes of paradoxical hypertension were evaluated in eight children who underwent balloon dilatation and seven children who underwent surgical repair of coarctation of the aorta. Both procedures resulted in a significant reduction in the coarctation gradient. Both systolic and diastolic blood pressures increased in the surgical group after repair, whereas systolic pressures decreased and diastolic pressures remained unchanged after balloon angioplasty. In the surgical group, but not in the balloon angioplasty group, plasma catecholamines and plasma renin activity rose during the first 2 days after relief of the coarctation. The data presented in this report support the hypothesis that the sympathetic nervous system and the renin angiotensin system are important mediators of the paradoxical hypertension that occurs after surgical repair of coarctation. Furthermore, balloon angioplasty of coarctation of the aorta does not stimulate either system and thus paradoxical hypertension is not a complication of this procedure.

Angioplasty, Balloon↗
PubMed1978

Body temperature and 5-hydroxytryptamine during early postnatal maturation in mice.

A relationship between the maturational increases in body temperature and brain indoleamines has been explored through altering brain 5-hydroxytryptamine (5-HT) content. Effects on body temperature at approximately constant ambient temperature (about 24 degrees C) have been studied following pharmacological manipulations in mice up to 16 days postpartum. Administration of 5-hydroxytryptophan (5-HTP) to increase 5-HT levels was associated with decreased body temperature throughout the maturational period. Depletion of 5-HT with p-chlorophenylalanine (p-CPA) was associated with increased body temperature at all ages studied, although 5-HT depletion was less effective in young animals than in older animals. The drug NSD-1034 acts at a different enzymatic step, and is effective in both central and peripheral tissues to reduce 5-HT and norepinephrine (NE) levels. NSD-1034 decreased body temperature up to 10 days of age; however, the effect was reversed at about 14 days, and the drug increased body temperature significantly in 16-day-old animals. These results suggest a role for 5-HT in the mechanisms of heat production in early postnatal life.

Animals↗