Numerical modeling of particle deposition in a realistic respiratory airway using CFD-DPM and genetic algorithm.

In this study, a realistic model of the respiratory tract obtained from CT medical images was used to solve the flow field and particle motion using the Eulerian-Lagrangian approach to obtain the maximum particle deposition in the bronchial tree for the main purpose of optimizing the performance of drug delivery devices. The effects of different parameters, including particle diameter, particle shape factor, and air velocity, on the airflow field and particle deposition pattern in different zones of the lung were investigated. In addition, a genetic algorithm was employed to obtain the maximum particle deposition in the bronchial tree and the effect of the aforementioned parameters on particle deposition. Reverse flow, vortex formation, and laryngeal jet all affect the airflow structure and particle deposition pattern. The mouth-throat region had the highest deposition fraction at various flow rates. A change in the deposition pattern with an increased deposition fraction in the throat was observed owing to the increased diameter and shape factor of the particles, resulting from the higher inertia and drag force, respectively. The particle deposition analysis showed that three parameters, shape factor, diameter, and velocity, are directly related to particle deposition, and the diameter is the most effective parameter for particle deposition, with an effect of 60% compared to the shape factor and velocity. Finally, the prediction of the genetic algorithm reported a maximum particle deposition in the bronchial tree of 17%, whereas, based on the numerical results, the maximum particle deposition was reported to be 16%. Therefore, there is a 1% difference between the prediction of the genetic algorithm and the numerical results, which indicates the high accuracy of the prediction of the genetic algorithm.

Aneurysm geometric features effect on the hemodynamic characteristics of blood flow in coronary artery: CFD simulation on CT angiography-based model.

The main purpose of the present numerical study is to evaluate the influences of aneurysm geometric features on the hemodynamic conditions within the left coronary arteries (LCA). Simulations have been conducted in two major parts: Section (I) encompassing three different cases (case 1, case 2, and case 3), in which three various sizes of the bifurcation region ([Formula: see text], [Formula: see text], and [Formula: see text]) were considered for each case, and Section (II) also consists of three distinct cases (case 4, case 5, and case 6) which two different positions (P1 and P2; proximal and distal to the main bifurcation, respectively) were taken into account for a fusiform aneurysm located on their left circumflex branch. Prediction and assessment of the correlation between morphological characteristics of an aneurysm with atherosclerosis and thrombosis were performed using quantitative and qualitative results including streamline and velocity contours, wall shear stress, oscillatory shear index, and relative residence time. Depending on the various cases, the time-averaged wall shear stress (TAWSS) of the bifurcation region for models of [Formula: see text] was nearly 18-24% fewer than [Formula: see text], and around 74-81% fewer than intact models. Moreover, the smaller size of the LCA dilation results in less flow recirculation and, accordingly, the lower risk of blood clotting. Additionally, the TAWSS of the aneurysm in the P1 model of case 4 was found 16.4% lower than in P2; however, the values for P1 models of case 5 and case 6 were higher than in P2 by close to 16.3% and 12.5%, respectively. Furthermore, it was concluded that the intricate geometry of LCAs, especially pre-aneurysm curvatures, have remarkable effects on the hemodynamics within the aneurysms. Even though a limited number of cases were used in this study, due to the scarcity of similar works, the outcomes of this computational evaluation can positively contribute to clinical decision-making in the assessment of coronary aneurysms.

Flow Structure and Particle Deposition Analyses for Optimization of a Pressurized Metered Dose Inhaler (pMDI) in a Model of Tracheobronchial Airway.

Inhalation therapy plays an important role in management or treatment of respiratory diseases such asthma and chronic obstructive pulmonary diseases (COPDs). For decades, pressurized metered dose inhalers (pMDIs) have been the most popular and prescribed drug delivery devices for inhalation therapy. The main objectives of the present computational work are to study flow structure inside a pMDI, as well as transport and deposition of micron-sized particles in a model of human tracheobronchial airways and their dependence on inhalation air flow rate and characteristic pMDI parameters. The upper airway geometry, which includes the extrathoracic region, trachea, and bronchial airways up to the fourth generation in some branches, was constructed based on computed tomography (CT) images of an adult healthy female. Computational fluid dynamics (CFD) simulation was employed using the k-ω model with low-Reynolds number (LRN) corrections to accomplish the objectives. The deposition results of the present study were verified with the in vitro deposition data of our previous investigation on pulmonary drug delivery using a hollow replica of the same airway geometry as used for CFD modeling. It was found that the flow structure inside the pMDI and extrathoracic region strongly depends on inhalation flow rate and geometry of the inhaler. In addition, regional aerosol deposition patterns were investigated at four inhalation flow rates between 30 and 120 L/min and for 60 L/min yielding highest deposition fractions of 24.4% and 3.1% for the extrathoracic region (EX) and the trachea, respectively. It was also revealed that particle deposition was larger in the right branches of the bronchial airways (right lung) than the left branches (left lung) for all of the considered cases. Also, optimization of spray characteristics showed that the optimum values for initial spray velocity, spray cone angle and spray duration were 100 m/s, 10° and 0.1 sec, respectively. Moreover, spray cone angle, more than any other of the investigated pMDI parameters can change the deposition pattern of inhaled particles in the airway model. In conclusion, the present investigation provides a validated CFD model for particle deposition and new insights into the relevance of flow structure for deposition of pMDI-emitted pharmaceutical aerosols in the upper respiratory tract.

Dry powder inhaler aerosol deposition in a model of tracheobronchial airways: Validating CFD predictions with in vitro data.

Effective drug delivery into the lungs plays an important role in management of pulmonary diseases that affect millions all around the world. The main objective of this investigation is to study airflow structure, as well as transport and deposition of micron-size particles at different inhalation flow rates in a realistic model of human tracheobronchial airways. The airway model was developed based on computed tomography (CT) images of a healthy 48-years-old female, which includes extrathoracic, trachea, and bronchial airways up to fourth generations. Computational fluid dynamics (CFD) simulations were performed to predict transport and deposition of inhaled particles and the results were compared to our previous in vitro experiments. Airflow structure was studied through velocity contours and streamlines in the extrathoracic region, where the onset of turbulence, reverse flow and subsequently vortex formation, and laryngeal jet are found to be critical phenomenons in the formation of airflow and deposition patterns. The deposition data was presented by deposition efficiency (DE) and deposition fraction (DF) against impaction parameter and Stokes number. At all of the inhalation flow rates, highest values of deposition fractions were devoted to the mouth-throat (MT), tracheobronchial tree (TB), and trachea (Tra), respectively (At 60 L/min: MT = 6.7%, TB = 5.3%, Tra = 1.9%). The numerical deposition data showed a good agreement with the experimental deposition data in most of the airway regions (e.g. less than 10% difference between the deposition fractions in the tracheobronchial region). Enhancing inhalation flow rate in all of the airway regions led to an uptrend in deposition rate due to the increase of particles inertia and turbulence level. In addition, the increase of particle deposition with enhancing inhalation flow rate in all of the sections including extrathoracic, trachea, and tracheobronchial tree suggesting that inertial impaction is the dominant deposition mechanism due to the increase of inertial force. In conclusion, the validated CFD model provided an opportunity to cover the limitations of our previous experimental investigation on aerosol deposition of commercial inhalers and became an efficient method for further studies.

Investigation of left heart flow using a numerical correlation to model heart wall motion.

A three-dimensional computational fluid dynamics (CFD) method has been developed to model the flow in the left heart including atrium and ventricle. Since time resolution of the medical scans does not fit the requirements of the CFD calculations, the main challenge in a numerical simulation of heart chambers is wall motion modeling. This study employs a novel three-dimensional approximation scheme to correlate the wall boundary and grid movement in systole and diastole. It uses a geometry extracted from medical images in the literature and deformed based on the reported flow rates. The opening and closing of the mitral (MV) and the aortic valve (AV) considered as simultaneous events. Unstructured tetragonal grids were used for the meshing of the domain. The calculation was performed by a Navier-Stokes solver using the arbitrary Lagrange-Euler (ALE) formulation. Results show that the proposed correlation for the wall motion could predict the main features of heart flows.