1,720,986 research outputs found
Computational fluid dynamics models and congenital heart diseases
Full text linkMathematical modelling is a powerful tool to investigate hemodynamics of the circulatory system. With improving imaging techniques and detailed clinical investigations, it is now possible to construct patient-specific models of reconstructive surgeries for the treatment of congenital heart diseases. These models can help clinicians to better understand the hemodynamic behaviour of different surgical options for a treated patient. This review outlines recent advances in mathematical modelling in congenital heart diseases, the discoveries and limitations these models present, and future directions that are on the horizon
Patient-specific modeling of cavopulmonary connections.
No full textSurgery for the treatment of congenital heart diseases has been improving very rapidly in recent years. The developed surgical repairs often impose major reconstructive procedures, creating a totally new circulation. The so-called ‘Fontan circulation’ refers to a cardiovascular configuration resulting from a group of operations used to by-pass the non-functional right heart (Fontan and Baudet, 1971). In such a univentricular circulation, the blood returning from the body reaches the lungs via direct blood vessel connections without a pumping chamber. Different surgical procedures have been developed to create the Fontan circulation. One of these procedures is the Total CavoPulmonary Connection (TCPC) (de Leval et al., 1988). In the TCPC the superior and the inferior venae cavae (SVC and IVC, respectively) are directly connected to the right pulmonary artery, the latter by means of an intra-atrial or an extra cardiac tunnel. This final configuration is often obtained through an intermediate stage, the Bidirectional CavoPulmonary Anastomosis (BCPA), where only the SVC is connected to the right pulmonary artery. With particular reference to patient-specific modeling of cavopulmonary connections, the prescription of realistic outlet boundary conditions is required as they control blood flow split into
each pulmonary artery. Helping pediatric cardiac surgeons in designing the most effective TCPC by means of a patient-specific ‘virtual surgery’ simulation is quite a tough challenge for bioengineers. Local abnormal flows, as may occur in patients with surgical corrections of congenital heart diseases, might selectively cause mid/long-term adaptation processes in the different pulmonary branches, thus varying local and global pulmonary resistances. In the present study, left and right pulmonary resistances were estimated in a BCPA clinical case on the basis of measured pressures and flow data and patient-specific fluid dynamic simulations. The aim of the study is to assess possible unbalanced lung resistances and verify whether pulmonary resistances change after the TCPC surgical creation
A multiscale model for the study of cardiac biomechanics in single-ventricle surgeries: A clinical case
Full text linkComplex congenital heart disease characterized by the underdevelopment of one ventricular chamber (single ventricle (SV) circulation) is normally treated with a three-stage surgical repair. This study aims at developing a multiscale computational framework able to couple a patient-specific three-dimensional finite-element model of the SV to a patient-specific lumped parameter (LP) model of thewhole circulation, in a closed-loop fashion. A sequential approach was carried out: (i) cardiocirculatory parameters were estimated by using a fully LP model; (ii) ventricular material parameters and unloaded geometry were identified by means of the stand-alone, three-dimensional model of the SV; and (iii) the three-dimensional model of SV was coupled to the LP model of the circulation, thus closing the loop and creating a multiscale model. Once the patient-specific multiscale model was set using pre-operative clinical data, the virtual surgery was performed, and the post-operative conditions were simulated. This approach allows the analysis of local information on ventricular function aswell as global parameters of the cardiovascular system. This methodology is generally applicable to patients suffering from SV disease for surgical planning at different stages of treatment. As an example, a clinical case from stage 1 to stage 2 is considered here
Hemodynamic effects of different pulmonary artery banding, ascending aorta and aortic coarctation diameters in the hybrid Norwood circulation: a computational study.
No full text
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Multiscale models of the hybrid palliation for hypoplastic left heart syndrome.
No full textA less-invasive procedure that combines interventional stent placement in the ductus arteriosus and surgical banding of the branch pulmonary arteries has been recently introduced in the treatment of the hypoplastic left heart syndrome (HLHS). The hemodynamic behaviour of this hybrid approach has not been examined before in a mathematical model. In this study, a mathematical model of the hybrid procedure for HLHS is described, applying a multiscale approach that couples 3D models of the area of the surgical operation and lumped parameter models of the remaining circulation. The effects of various degrees of pulmonary banding and different stent sizes inserted in the ductus arteriosus on pulmonary-systemic flow ratio, cardiac output and oxygen delivery were assessed. Computational results suggest that balanced systemic and pulmonary blood flow and optimal systemic oxygen delivery are sensitive to the degree of pulmonary arterial banding and not to the size of the ductal stent
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Computational fluid dynamic study of flow optimization in realistic models of the total cavopulmonary connections.
No full textObjectives and background. In the Fontan circulation,
pulmonary and systemic vascular resistances are
in series. The influence of various inferior vena cava to
pulmonary artery connections in this unique circulatory
arrangement was evaluated using computation
fluid dynamics methods.
Methods. Realistic three-dimensional models of total
cavopulmonary connections were created from angiographic
measurements to include the hepatic vein, superior
vena cava, and branches of the pulmonary arteries.
Steady-state finite volume analyses were
performed using identical in vivo boundary conditions.
Computational solutions calculated the percent
hydraulic power dissipation and left-to-right pulmonary
arterial flow distribution.
Results. Simulations of the lateral tunnel, intraatrial
tube, extracardiac conduit with left and right
pulmonary artery anastomosis demonstrated extracardiac
conduit with left pulmonary artery anastomosis
having the lowest energy loss. Varying the extracardiac
conduit from 10 to 30 mm resulted in the least
energy dissipation at 20 mm. Serial dilation of the
lateral tunnel pathway showed a small incremental
worsening of energy loss.
Conclusions. Maximizing energy conservation in a
low-energy flow domain, such as the Fontan circulation,
can be significant to its fluid dynamic performance.
Although computational modeling cannot predict
postoperative failure or functional outcome, this
study confirms the importance of local geometry of the
surgically created pathway in the total cavopulmonary
connection
- …
