Course Of Defect Research Articles

Congenital heart anomaly «single ventricle»: structural and functional diagnosis in everyday practice

Diagnosis and description of rare congenital heart anomalies are great challenges for the ultrasonographer. The biggest difficulties arise in hospitals, which do not have specialization in pediatrics or cardiac surgery. A rare form of congenital heart defects is a group of anomalies, unitedly defined as «single ventricle». Severe hemodynamic disturbances and unfavorable course of the disease reduce the possibility to detect this defect in adolescence or adulthood. Single ventricle, as the anomaly main feature, can occur in different forms of pathology. The most commonly single ventricle syndrome includes left heart hypoplasia, tricuspid atresia, and double inlet single ventricle syndromes. The most favorable course have cases when a single ventricle anatomically is left ventricle along with separate and properly formed atrioventricular valves, in the absence of main arteries significant stenosis and their normal location. This variant of a double inlet single ventricle is known as the «Holmes heart». Echocardiographic diagnosis allows to detail the anatomical and functional defects that are present in each case. Detailed identification of diagnostic features allows to specify the diagnosis and avoid inconsistencies in the obtained data interpretation. We present a clinical case of one of the most rare forms of these disease. The described case feature, in addition to its rarity, is long compensated course of defect. The lack of obvious signs of heart failure in this case may be due to a number of factors, such as a balance between the pulmonary and systemic circulation, absence of progressive changes in the pulmonary circulation blood vessels, atrioventricular valves functional adequacy, the absence of stenosis and valves changes of the main arteries, anatomically left ventricle with sufficient contractility.

Inhibition of void dissolution by vacancies

Dissolution of voids is a classical problem in the theory of sintering. The foundations of the theory were established by Frenkel, Pines and Geguzin (see Refs. 1 and 2 for a review). However, an important aspect of the problem appears to have been overlooked by previous workers. In a recent paper, the present authors identified a mechanism which inhibits processes associated with vacancy generation during grain growth, especially in fine grain sized materials [3]. The essence of the mechanism is the rise of the free energy of the system due to vacancy production in the course of defect ‘dissolution’ (decrease of the total area of grain boundaries) which under certain conditions may inhibit the rate of the primary process. A similar effect may also be operative in the case of void dissolution which is accompanied by a massive release of vacancies into the surrounding bulk of the material. In this paper we consider the conditions for intermittent temporary arrest of the void dissolution process leading to an effective decrease of the rate of dissolution.

Incidence and natural course of trabecular ventricular septal defect: Two-dimensional echocardiography and color Doppler flow imaging study

This study was designed to determine the prevalence of trabecular ventricular septal defect (t-VSD) in neonates and to evaluate the effects of its location, morphologic features, and size on its natural course during infancy. One thousand twenty-eight term newborn infants were examined by color Doppler flow imaging with orthogonal ultrasonographic views. Ten girls and 11 boys (2.0%) were found to have t-VSD. The natural course of the defect was examined in 42 consecutive cases, consisting of this group of 21 neonates and another group of 21 neonates with t-VSD. The morphologic features of the defect within the trabecular septum were classified as one or two defects (36 cases) and as a mesh-like defect (six cases). Reduction in size began from the right ventricular side or from within the trabecular septum. Spontaneous closure occurred most commonly during the first 6 months of life and was observed in 32 cases (76%) by 12 months of age: the frequency of closure was not related to the morphologic features and the initial size of the defect, but apical defects tended to have higher persistent patency than did defects in other locations (p less than 0.05). We conclude that the frequency of t-VSD in neonates and the frequency of spontaneous closure during early infancy are higher than previously believed. This information is important for predicting the natural course of t-VSD and deciding on its proper management.

An analysis of tensile decohesion along an interface

A COHESIVE zone type interface model, taking full account of finite geometry changes, is used to study the decohesion of a viscoplastic block from a rigid substrate. Dimensional considerations introduce a characteristic length into the formulation. The specific boundary value problem analysed is one of plane strain tension with a superposed hydrostatic stress. For a perfect interface, if the maximum traction that the viscoplastic block can support is greater than the interfacial strength, decohesion takes place in a primarily tensile mode. If this maximum traction is lower than the interfacial strength, a shear dominated decohesion initiates at the block edge. Imperfections in the form of a non-bonded portion of the interface are considered. The effects of imposed stress triaxiality, size scale, loading rate and interfacial properties on the course of defect dominated decohesion are illustrated. The characterization of decohesion initiation and propagation in terms of rice's ( J. appl. Mech. 35, 379, 1968) J-integral is investigated for a variety of interface descriptions and values of the superposed hydrostatic stress.