RESUMEN
In this study, the motion and deformation of a red blood cell in a Poiseuille flow through microvessels under the effect of a uniform transverse magnetic field is comprehensively investigated to get a better insight into blood hemorheology. The rheology of the RBC and the surrounding blood flow are examined numerically in two dimensions using a Finite Element Method. It is essential to know that the flow patterns of blood change in the presence of an RBC. The simulation results demonstrate that the magnetic field has significant influence on the flow stream and the behavior of the RBC, including the motion and the cells deformation.
Asunto(s)
Deformación Eritrocítica , Modelos Cardiovasculares , Deformación Eritrocítica/fisiología , Eritrocitos/fisiología , Hemorreología/fisiología , Campos Magnéticos , ReologíaRESUMEN
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.
Asunto(s)
Inhaladores de Dosis Medida , Nebulizadores y Vaporizadores , Administración por Inhalación , Adulto , Aerosoles , Diseño de Equipo , Femenino , Humanos , Pulmón , Tamaño de la PartículaRESUMEN
The external fields, such as the magnetic force, have made advances in many industrial and biotechnology applications during the past century, although the changes in the structure of materials under the impact of the electromagnetic fields have not entirely been clear yet. The molecular simulation technique by providing extensive data from the configuration and orientations of the atoms is becoming the effective useful tool for scientists in a wide range of research areas. This paper presents an extended velocity Verlet algorithm inside the Nanoscale Molecular Dynamics (NAMD) package that enhances the NAMD features with the capability to compute the magnetic field force. We described how this novel feature has been implemented inside the package. Moreover, the results are reported for the rotation of a charged particle, and the thermo-physical properties of water in the presence of a magnetic field confirming how this developed NAMD source code provides accurate measurements compared with other available data.
Asunto(s)
Algoritmos , Campos Magnéticos , Simulación de Dinámica Molecular , Programas InformáticosRESUMEN
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.
Asunto(s)
Inhaladores de Polvo Seco , Hidrodinámica , Administración por Inhalación , Aerosoles , Simulación por Computador , Femenino , Humanos , Persona de Mediana Edad , Tamaño de la PartículaRESUMEN
Pulmonary drug delivery has gained great interest as an important subject of research over the past decades given the lung diseases which are affecting millions of people suffer from these diseases. Drug delivery into the respiratory system is influenced by many anatomical and physiological factors such as lung morphometry, breathing patterns, fluid dynamics, particle properties, etc. The respiratory airway structure is one of these parameters which greatly influences the deposition pattern of inhaled drug particles. There have been a wide variety of major morphometric studies, conducted using cadavers to increase an understanding of the respiratory airway anatomy and provide important information for developing realistic airway models. Casting as one of the first methods, was utilized for morphometric studies providing a hollow model for in vitro investigations. The above-mentioned morphometric data were utilized to describe the first idealized airway model as a simple symmetric description of the branching airways, later followed by more realistic asymmetric models. However, even these asymmetric airway models were not good enough to reflect the anatomical complexities of the human respiratory airway and contained several major limitations which made them inefficient. Further attempts alongside with the progress of technology led to introduction of the stochastic and image-based models which provided more realistic and efficient tools for numerical and experimental investigations. The main objective of this study is to provide a comprehensive review about the development of different perspectives of the respiratory airway modeling over the past decades. The following sections will present useful information about anatomy of the human respiratory tract, and different viewpoints of the respiratory airway modeling, including their historical routes, strengths, and deficiencies.
Asunto(s)
Pulmón/anatomía & histología , Pulmón/fisiología , Modelos Biológicos , Mecánica Respiratoria/fisiología , Sistema Respiratorio/anatomía & histología , Administración por Inhalación , Aerosoles/administración & dosificación , Sistemas de Liberación de Medicamentos/métodos , Humanos , Pulmón/efectos de los fármacos , Mecánica Respiratoria/efectos de los fármacos , Fenómenos Fisiológicos Respiratorios/efectos de los fármacos , Sistema Respiratorio/efectos de los fármacosRESUMEN
PURPOSE: In the present work, a comparison between MDI and DPI for evaluating performance of the devices were carried out by experimentally investigating the deposition parameters through a realistic airway replica. METHODS: Computed tomography (CT) images of the respiratory airway of a healthy subject were used to develop the realistic model. The airway replica was included extrathoracic, trachea, and tracheobronchial tree up to fourth generations which was fabricated by rapid prototyping. Afterward, in vitro experiments were performed to validate the airway model by comparing the total deposition (G0 to G3) of present replica with available data in the literature. Drug deposition (Salbutamol) in the model was measured by determining concentration of the segments sample by High Performance Liquid Chromatography (HPLC) assay. RESULTS: Deposition parameters were used for investigating the deposition patterns of the inhaled particles. Results showed that inertial impaction is the dominant mechanism in the most regions of the replica. It was found that the MDI delivered more drug to the tracheobronchial tree compared to the DPI for three different flow rate. CONCLUSION: The developed realistic respiratory airways model provided an opportunity to more accurately evaluate the performance of drug delivery devices and studying mechanisms of the drug deposition.