Fluid-Structure Interaction Simulation of Multiple Overlapping Uncovered Stent Intervention in Aortic Dissection / 医用生物力学

Objective To propose a one-way fluid-structure interaction (FSI) method based on an idealized aortic dissection model, so as to analyze the hemodynamics and wall stress in the false lumen (FL) under the influence of multiple overlapping uncovered stents (MOUS). Methods Upon establishment of the numerical model, the models were divided into two categories according to whether the model involved FL perfused branch artery. The characteristics of hemodynamics and wall stress state in the post-operative scenarios were simulated under different surgical strategies. The wall stress state of the FL before and after thrombosis formation was also compared and analyzed. ResultsThe release process of the stents had little influence on wall stress of the FL. The high velocity and high wall shear stress (WSS) area in the FL could not be reduced by using the MOUS alone. If only the proximal entry tear was blocked with a covered stent-graft, the distal end would maintain a region of high flow rate and high WSS. The combination of covered stent-graft and MOUS would result in a region of low flow rate and low WSS, as well as reduced wall pressure and wall stress in the FL. Compared with the model with FL perfused branch arteries, the model without it was more likely to form a region of low flow rate and low WSS after surgery. However, blood pressure in the FL was relatively higher. The formation of thrombus in the FL could greatly reduce wall stress in the area covered by the thrombus. Conclusions The method proposed in this study can simultaneously investigate hemodynamics and wall stress characteristics of the FL, and provide support for studying mechanical mechanism of FL thrombolysis induced by MOUS and the post-operative aortic expansion.

RE: Relation of Late Gadolinium Enhancement to Increased Ventricular Wall Stress in Dilated Cardiomyopathy

No abstract available.

Estimación del estrés parietal sistólico del ventrículo izquierdo por imagen de resonancia magnética: Una nueva aproximación al estudio de la poscarga / Estimation of the systolic parietal stress of the left ventricle by magnetic resonance imaging. A new approach to the study of the overload

Objetivo: Determinar el estrés meridional parietal sistólico del ventrículo izquierdo por imagen de resonancia magnética en sujetos sanos. Material y métodos: Se estudiaron 21 sujetos sanos: 11 pertenecían al sexo masculino y 10 al femenino: su edad varió entre 26 y 31 años (29.33). Se les realizó el estudio de resonancia magnética de corazón utilizando el eje corto a nivel de los músculos papilares, de donde se obtuvieron las áreas epicárdicas y endocárdicas de la cavidad ventricular izquierda tanto en diastole como en sístole mediante el trazado con un lápiz electrónico, posteriormente se calculó el radio de cada área trazada, con el valor del radio, se calculó el espesor diastólico y sistólico; para posteriormente obtener la relación grosor/radio. Ya obtenida la relación grosor/radio tanto en diastole como sístole se calculó el grado de cambio entre ambos valores y el porcentaje de dicho cambio. Finalmente se calculó el estrés meridional parietal sistólico desarrollado por el ventrículo izquierdo mediante la siguiente fórmula: S=PVI x A4/A3-A4 x 1.35. PVI: presión sistólica del ventrículo izquierdo (promedio de 5 tomas simultáneas de presión arterial sistólica, obtenidas mediante esfingomanómetro). A4: área endocárdica en sístole; A3: área epicárdica en sístole. El valor obtenido en esta ecuación se multiplicó por 1.35 para convertir mmHg en gm/cm². Resultados: La presión arterial sistólica media fue de 103.24 ± 10.27 mmHg; A3 (media 27.58 ± 2.29); A4 (media 6.84 ± 0.71); siendo el estrés meridional sistólico del ventrículo izquierdo de 46.12 ± 4.9 gm/cm², no existiendo diferencias significativas en cuanto al sexo. Conclusiones: Con este nuevo método es posible determinar con mayor exactitud de manera no invasiva, a través de la mejor definición de sus bordes epicárdicos y endocárdicos, las áreas y los radios de la cavidad ventricular izquierda tanto en sístole como en diastole, determinar el grosor de la pared y su relación con el radio, esto para una mejor valoración de la función ventricular, en especial en los sujetos con sobrecargas de presión o de volumen que deprimen la función ventricular.

Objective: To determine the systolic parietal stress of the left ventricle by image of magnetic resonance in healthy subjects. Material and methods: 21 healthy subjects studied: 11 male and 10 female: the ages among 26 and 31 years (29.33). A magnetic resonance of heart was made using the short axis at the level of the papillary muscles, from where the epicardio and endocardio areas of the left ventricular cavity were obtained in diastolic as in systolic by means of the layout with an electronic pencil, later the radius of each drawn up area was calculated, with the value of the radius, the diastolic and systolic thickness was calculated; to obtain the relation between thickness/radio. Once the relation was obtained between thickness/radio in diastole as systole the degree of change between both values and the percentage of this change was calculated. Finally, the systolic parietal stress developed by the left ventricle was calculate with the following formula: S=PVI x A4/A3-A4 x 1.35.PVI: systolic pressure of the left ventricle (the average of 5 synchronized systolic arterial pressures, obtained by an esphingomanometer). A4: endocardio area in systole; A3: epicardial area in systole. The value obtained in this equation was multiplied per 1.35 to turn mmHg gm/cm². Results: The average of the arterial systolic pressure was of 103.24 ± 10.27 mmHg; A3 (average 27.58 ± 2.29); A4 (average 6.84 ± 0.71); being the systolic stress of the left ventricle of 46.12 ± 4.9 gm/cm², not existing significant differences between sexes. Conclusions: With this new method it is possible to determine with greater exactitude in a noninvasive way, through the best definition of its epicardio and endocardic edges, the areas and the radio of the left ventricular cavity in systole as in diastole, to determine the thickness of the wall and its relation with the radius, for one better valuation of the ventricular function, specially in those subjects with overloads of volume or pressure that depress the ventricular function.

B-Type Natriuretic Peptide Predicts Clinical Presentations and Ventricular Overloading in Patients with Heart Failure

Brain natriuretic peptide (BNP), a neurohormone secreted from the ventricular myocardium in response to hemodynamic load/wall stress, in congestive heart failure (CHF). This study was performed to evaluate the correlation between BNP level and clinical presentations and hemodynamic parameters obtained by echo-Doppler (echo-Doppler) analysis, and its relation with disease severity and ventricular load/wall stress. CHF patients (n=246) were subgrouped by clinical presentations and echo-Doppler findings into 4 groups: diastolic HF only, chronic HF, acute HF, and chronic HF with acute exacerbation. A BNP level of 81.2 pg/ml showed a sensitivity/ specificity of 53.3%/98.4% for detecting CHF (AUC, 0.882; p< 0.0001), and was found to be closely related with the NYHA classification (p< 0.0001). Log BNP was related with LVEF (r2=0.3015, p< 0.0001) and the Meridional wall stress index (r2=0.4052, p< 0.0001). The difference between the BNP levels of the subgroups and BNP control was significant (p< 0.0001), exept between the HF group and the controls; control (n=114, 20.9 +/- 31.4pg/ml), only diastolic HF (n=84, 89.8 +/- 117.6pg/ml), chronic HF (n=60, 208.2 +/- 210.2pg/ml), acute HF (n=28, 477.9 +/- 498.4 pg/ml), chronic HF with acute exacerbation (n= 74, 754.1 +/- 419.2pg/ml). The BNP level was significantly higher in the only diastolic HF group than in the asymptomatic control group with diastolic dysfunction (89.8 +/- 12.8 vs. 22.8 +/- 5.1pg/ml, p< 0.0001). BNP may be a good indicator for the differential diagnosis of a broad spectrum of heart failures. And, elevated BNP might help to diagnose diastolic HF in patients with diastolic dysfunction.

Prognostic Indices after Mitral Valve Replacement in Patients with Chronic Mitral Regurgitation

Chronic mitral regurgitation may be well tolerated for decades because of favorable conditions like increased preload and decreased afterload. However, in some patients with underlying overt myocardial dysfunction, opertive correction of mitral regurgitation may result in persistent left ventricular dysfunction. Myocardial dysfunction in mitral regurgitation initially occurs subclinically and may becoma irreversible before symptoms of congestive heart failure develop. In order to identify latent myocardial dysfunction, we evaluated prognostic values of several indices from patient's characteristics, echocardiogram, cardiac catheterization data and contrast left ventriculogram in 49 patients with chronic mitral regurgitation who received mitral valve replacement. The patients were defined as Groups I who had improved symptoms with decreased left ventricular end-diastolic dimension after operation and Group II who had persistent symptoms and progressed left ventricular end-diastolic dimension, or not decreased until left ventricular end-diastolic dimension 60mm after operation. The results were as follows: 1) There was no significant difference in age, sex, duration of symptoms, preoperative NYHA functional status, and aortic cross clamping time during operation between Group I and Group II. 2) There was no significant difference in echocardiographic left ventricular end-diastolic dimension between group I and group II. There were significantly more dilated left ventricular end-diastolic dimension of Group II than that of Group I and significantly more depressed fractional shortening of Group II than that of Group I. There was significantly more increased end-diastolic wall stress of Group II than of Group I. 3) There was no significant difference in cardiac index, mean pulmonary artery pressure, mean pulmonary capillary wedge pressure and left ventricular end-diastoic pressure between Group I and Group II. 4) There were significantly more increased end-diastolic volume index and end-diastolic volum index of Group II than those of Group I, but no significant difference in ejection fraction between Group I and Group II. There was significantly more decreased ratio of end-diastolic circumferential midwall stress to end-diastolic volume index of Group II than that of Group I. 5) In Group I, end-systolic dimension, end-systolic dimension and end-systolic wall stress were decreased significantly after operation. In Group II, end-systolic dimension was decreased significantly after operation. 6) Values for combination of end-systolic left ventricular dimension greater than 28mm/m2 and end-systolic wall stress greater than 190mmHg predicted a Group II outcome with a sensitivity of 88.2%, a specificity of 93.8%, positive predictive value of 88.2% and negative predictive value of 93.8%. Values of combination of end-systolic left ventricular dimension greater than 28mm/m2 and fractional shortening less than 32% predicted a Group II outcome with a sensitivity of 88.2% a specificity of 90.6%, positive predictive value of 83.3% and negative predictive value of 93.5%, a specificity of 90.6%, positive predictive valve of 83.3% and negative predictive value of 93.5%. According to the above results, noninvasive hemodynamic variables such as end-systolic left ventricular dimension, fractional shortening and end-systolic wall stress would be useful guideline for follow-up and determining the optimal time for surgical intervention in patients with chronic mitral regurgitation.