Computational Modeling of Cardiovascular Flows using Smoothed Particle Hydrodynamics

This dissertation presents the first attempt to verify the capability of smoothed particle hydrodynamics (SPH), a meshfree particle method, to simulate pulsatile flow in the cardiovascular system. Smoothed particle hydrodynamics has been extensively used to simulate astrophysical phenomena, free surface flows and transient start-up of the internal flows under constant driving forces at low Reynolds numbers. However, most of the fluid flow phenomena are naturally unsteady with moderate Reynolds numbers. In this thesis, first, a series of benchmark cases are conducted to address internal oscillating flows at moderate Reynolds numbers. The performance of the two most commonly used formulations to model the diffusing viscous term and the XSPH variant, proposed to modify the movement of the particles, is investigated. The relation between particle resolution and sound speed to control compressibility effects in SPH simulations and the spatial convergence rate of the SPH discretization are examined. Furthermore, a modified formulation for wall shear stress calculations is suggested and an approach to implement inflow and outflow boundary conditions in SPH is introduced. It is also shown how SPH simulations with different particle resolutions exhibit behaviors equivalent to a finite volume scheme of different accuracy orders for moderate Reynolds numbers. The application of SPH to cardiovascular fluid dynamics is extended by simulating pulsatile flow inside a model of the heart’s left ventricle and through normal and dysfunctional prosthetic mechanical heart valves. The SPH simulations result in the realistic calculation of the shear stress loading on the blood components and illustrate the important role played by non-physiological flow patterns to shear-induced hemodynamic events

An in vitro model of aortic stenosis for the assessment of transcatheter aortic valve implantation

A significant number of elderly patients with severe symptomatic aortic stenosis are denied surgical aortic valve replacement (SAVR) because of high operative risk. Transcatheter aortic valve implantation (TAVI) has emerged as a valid alternative to SAVR in these patients. One of the main characteristics of TAVI, when compared to SAVR, is that the diseased native aortic valve remains in place. For hemodynamic testing of new percutaneous valves and clinical training, one should rely on animal models. However, the development of an appropriate animal model of severe aortic stenosis is not straightforward. This work aims at developing and testing an elastic model of the ascending aorta including a severe aortic stenosis. The physical model was built based on a previous silicone model and tested experimentally in this study. Experimental results showed that the error between the computer-aided design (CAD) file and the physical elastic model was <5%, the compliance of the ascending aorta was 1.15 ml/mm Hg, the effective orifice area (EOA) of the stenotic valve was 0.86 cm2, the peak jet velocity was 4.9 m/s and mean transvalvular pressure gradient was 50 mm Hg, consistent with as severe. An EDWARDS-SAPIEN 26 mm valve was then implanted in the model leading to a significant increase in EOA (2.22 cm2) and a significant decrease in both peak jet velocity (1.29 m/s) and mean transvalvular pressure gradient (3.1 mm Hg). This model can be useful for preliminary in vitro testing of percutaneous valves before more extensive animal and in vivo tests

Patterns of substance abuse among Iranian bipolar inpatients: a descriptive research on existing data

Introduction: Substance abuse/dependency is one of the most important comorbidity in bipolar patients. Therefore, recognizing the patterns of substance use is valuable in treatment and management of patients. This study was conducted to determine patterns of substance abuse among bipolar patients who were hospitalized in an educational hospital.Methods: This was a descriptive-analytical study on existing data of 322 patients with bipolar disorder admitted in the psychiatric ward of Imam-Hossein hospital. Types of used substances studied and some variables such as gender, types of bipolarity, duration of admission, age of onset of bipolar disorder, number of hospitalization and types of prescribed treatments were compared in users and nonusers groups.Results: In this study, 84 patients (26.1%) had substance abuse. 40.5% were using opioids, 6% mood-elevators, 7.1% alcohol, and 46.4% were using multiple substances.Conclusion: It can be concluded that substance abuse frequency among patients with bipolar disorder is high. Using more than one substance was the most frequent pattern of substance abuse in these patients as well. Thus, it is necessary to consider possible comorbidity of bipolar disorder in front of patients with substance related disorder.Declaration of Interest: None.Keywords: Bipolar disorder, Substance abuse

Psychometric Properties of the Preschool Age Psychiatric Assessment (PAPA) in Farsi: Based on DSM-5

ObjectivesThe first onset of many psychiatric disorders usually occurs inchildhood or adolescence. The structured interview of Preschool Age Psychiatric Assessment (PAPA) was developed in response to the need for a standardized and reliable method to assess psychiatric disorders in preschool-age children. This study aimed to translate DSM-5-based PAPA into Farsi and evaluate its face and content validity and reliability.Materials &amp; MethodsThe procedure was a forward translation of PAPA to Farsi, evaluation for face and content validity, finalization of items within the expert panel, backward translation to English, matching the original PAPA with randomly selected items from the backward translation version, and revision as needed, and finally evaluation for the validity of the changes for localization and cultural considerations. The interviews based on the final Farsi version were performed on thirty parents of children from two to five years old (chosen from Tabriz health centers) to determine the reliability and were repeated at an interval of two weeks. ResultsThe mean of CVI=0.91 and Modified Kappa=0.90 were obtained, and reliability with Cronbach’s alpha was 0.89.ConclusionThe Farsi version of the DSM-5-based PAPA diagnostic interview has good face and content validity and reliability

Meshfree simulations of ultrasound vector flow imaging using smoothed particle hydrodynamics

International audienc

An In Vitro Model of Aortic Stenosis for the Assessment of Transcatheter Aortic Valve Implantation

A significant number of elderly patients with severe symptomatic aortic stenosis are denied surgical aortic valve replacement (SAVR) because of high operative risk. Transcatheter aortic valve implantation (TAVI) has emerged as a valid alternative to SAVR in these patients. One of the main characteristics of TAVI, when compared to SAVR, is that the diseased native aortic valve remains in place. For hemodynamic testing of new percutaneous valves and clinical training, one should rely on animal models. However, the development of an appropriate animal model of severe aortic stenosis is not straightforward. This work aims at developing and testing an elastic model of the ascending aorta including a severe aortic stenosis. The physical model was built based on a previous silicone model and tested experimentally in this study. Experimental results showed that the error between the computer-aided design (CAD) file and the physical elastic model was &lt;5%, the compliance of the ascending aorta was 1.15 ml/mm Hg, the effective orifice area (EOA) of the stenotic valve was 0.86 cm 2 , the peak jet velocity was 4.9 m/s and mean transvalvular pressure gradient was 50 mm Hg, consistent with as severe. An EDWARDS-SAPIEN 26 mm valve was then implanted in the model leading to a significant increase in EOA (2.22 cm 2 ) and a significant decrease in both peak jet velocity (1.29 m/s) and mean transvalvular pressure gradient (3.1 mm Hg). This model can be useful for preliminary in vitro testing of percutaneous valves before more extensive animal and in vivo tests

Effect of aortic annulus size and prosthesis oversizing on the hemodynamics and leaflet bending stress of transcatheter Valves : an in vitro study

BACKGROUND: There are few data about the patient- and prosthesis-related factors influencing the hemodynamics of transcatheter heart valves (THVs). The objective of this in vitro study was to assess the effect of aortic annulus size and prosthesis oversizing on the valve hemodynamics and estimated leaflet bending stress of the Edwards SAPIEN balloon-expandable THV (Edwards Lifesciences, Irvine, CA). METHODS: The effective orifice area (EOA) of the 23-mm and 26-mm SAPIEN THVs were measured by Doppler echocardiography in a pulse duplicator under the following experimental conditions: (1) stroke volume of 20, 30, 50, 70, and 80 mL and (2) aortic annulus size of 19, 20, 21, and 22 mm for the 23-mm SAPIEN and 22, 23, and 24, and 25 mm for the 26-mm SAPIEN. The percentage of valve oversizing was calculated as follows: % OS = 100 × [(prosthesis nominal area - aortic annulus area)/aortic annulus area], where % OS is the percentage of oversizing. The leaflet bending stress was measured by high-speed camera imaging of the THV leaflet opening. RESULTS: The 2 independent determinants of valve EOA were the aortic annulus diameter (R(2) = 0.33; P < 0.001) and the stroke volume (R(2) = 0.63; P < 0.001). The prosthesis size and % OS were not independently related to EOA. However, a larger % OS was independently associated with higher peak systolic leaflet bending stress (¿R(2) = 0.11; P < 0.0001). CONCLUSIONS: The hemodynamic performance of THV is in large part determined by the aortic annulus diameter in which the valve is deployed. Oversizing (up to 20% in area) has no significant effect on valve EOA but is associated with higher leaflet bending stress, which might promote faster structural valve degeneration in the long termIntroduction : Il existe peu de donnees sur les facteurs li es au patient et à la prothèse influençant la performance hemodynamique des valves cardiaques par transcatheter (VCT). L ’objectif de cette etude in vitro etait d ’evaluer l ’effet de la taille de l’anneau aortique et du surdimensionnement de la prothèse sur l’hemodynamique valvulaire et l’estimation de la contrainte de flexion des feuillets de la VCT Edwards SAPIEN expansible par ballonnet (Edwards Lifesciences, Irvine, CA). Methodes : L’aire efficace de l’orifice (AEO) des VCT SAPIEN de 23 mm et de 26 mm a et e mesur ee par echocardiographie Doppler dans un duplicateur de pouls sous les conditions experimentales suivantes : 1) le volume transvalvulaire de 20, 30, 50, 70 et 80 ml; 2) la taille de l’anneau aortique de 19, 20, 21 et 22 mm pour la SAPIEN de 23 mm et de 22, 23, 24 et 25 mm pour la SAPIEN de 26 mm. Le pourcentage de surdimensionnement de la valve a et e calcul e comme suit : % de SD ¼ 100[(aire nominale de la prothèse e aire de l’anneau aortique)/aire de l’anneau aortique], où % de SD est le pourcentage du surdimensionnement. La contrainte de flexion des feuillets a et e mesuree par l ’imagerie par camera haute vitesse de l ’ouverture des feuillets de la VCT. Resultats : Les 2 determinants ind ependants de l ’AEO valvulaire etaient le diamètre de l ’anneau aortique (R2 ¼ 0,33; P < 0,001) et le volume transvalvulaire (R2 ¼ 0,63; P < 0,001). La taille de la prothèse et le % de SD n’etaient pas ind ependamment li es à l ’AEO. Cependant, un plus grand % de SD etait ind ependamment associ e à une plus grande contrainte de flexion des feuillets (DR2 ¼ 0,11; P < 0,0001). Conclusions : La performance hemodynamique de la VCT est en grande partie determin ee par le diamètre de l ’anneau aortique dans lequel la valve est deploy ee. Le surdimensionnement (jusqu ’à 20 % de l’aire) n’a pas d’effet significatif sur l’AEO valvulaire, mais est associe à une plus grande contrainte de flexion des feuillets, qui favoriserait une deg en erescence structurelle plus rapide de la valve à long terme