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Computational Analysis of Airflow and Particle Deposition Fraction in The Biology, Engineering and Medicine Research Article ISSN: 2399-9632 Computational analysis of airflow and particle deposition fraction in the upper part of the human respiratory system Saghaian SE1*, Azimian AR2, Jalilvand R3, Dadkhah S4 and Saghaian SM5 1Department of Mechanical Engineering, University of Kentucky, Lexington, KY 40506, USA 2Department of Mechanical Engineering, Islamic Azad University Khomeini Shahr Branch, Isfahan, Iran 3Department of Mechanical Engineering, Isfahan University of Technology, Isfahan, Iran 4Department of Biology, University of Kentucky, Lexington, KY 40508, USA 5Department of Mechanical, Materials and Aerospace Engineering, Illinois Institute of Technology, Chicago, IL 60616, USA Abstract This research investigates the computational analysis of airflow during inspiration and the tracking of particles in the human respiratory system from the nasal cavity to the third generation of the lungs. Also, the effect of geometric features of nasal cavities on their airflow is evaluated in this study. The actual geometry of the respiratory tract was extracted from CT-Scan medical images of a healthy person using image processing software. The flow is evaluated in laminar and steady states. The airflow rate at nasal entrances was assumed to be 20 L/min, which is related to sitting and resting situations. The movement and deposition of particles with a diameter of 1-30 micrometers in different parts of the human respiratory system have also been evaluated. The fluid field and movements of solid particles were evaluated by Eulerian and Lagrangian methods, respectively. Based on the obtained results, the greater the diameter of the particles, the more particles will be deposited in the nasal cavity. Introduction The research of Zachow et al. [17] and Wen et al. [18] are examples of some recent numerical studies of the airflow. Moreover, Zamankhan The nose is the first passageway through which air can pass towards et al. [19], Xi and Longest [12], Wang et al. [14] and Se et al. [20] our lungs. The nasal cavity connects the ambient environment and the investigated the mechanics of airflow in human nasal airways in detail. pharyngeal portion of the upper airway, providing humans with warm The numerical analysis of the respiratory flow pattern in the upper and humidified air, protecting them from pathogens and particulate airway of a human being was presented by Wang et al. [21]. The airway matters from the inspired air, and enabling them with olfaction. All model in their work consisted of the nasal cavity, pharynx, larynx, and of these are associated with the airflow in the nasal cavity, which is trachea that was built based on the CT images of a healthy person. significantly determined by nasal morphology and flow rate. Developing an anatomically accurate human upper airway model based In the past several decades, experimental and numerical studies on multiple MRI axial scans. Mylavarapu et al. [22] conducted detailed of flow dynamics and particle deposition in the nasal cavity have been CFD simulations during expiration to investigate the fluid flow in the investigated by many researchers. As for experimental studies, Schreck airway regions where obstruction could occur. et al. [1] investigated the airflow through human nasal passages. Hahn Additionally, it is important to make sure that particle deposition et al. [2] evaluated the airflow in a nasal cavity replica model and found occurs at some targeted areas for therapeutic inhalation drug delivery that the airflow was laminar up to a breathing rate of 24 L/min. By and that drugs with sub-micrometer particles are used in order to producing models that replicate the nasal anatomy, Kim and Chung [3] efficiently deliver them to the lungs [23,24]. Thus, understanding the also showed the relation between geometric variations of the middle regional particle deposition in the human upper airway and the fraction turbinate and the airflow patterns in the nose. Hopkins et al. [4], Kelly of particles entering the lungs would be of major importance for using et al. [5], Taylor et al. [6] and Doorly et al. [7] have also performed a aerosol inhalation in controlled pulmonary drug delivery as well as series of experimental investigations of the airflow in the nasal cavity. establishing proper links between certain lung diseases and exposure to Recently, with the advantage of computational fluid dynamics hazardous airborne particulate matter. (CFD), numerous computational simulations of airflow and particle deposition patterns in the nasal cavity have been reported. These simulations are reconstructed by models from computed tomography *Correspondence to: Sayed E Saghaian, Smart Materials Laboratory, Department (CT) and Magnetic Resonance Imaging (MRI) scans. Computational of Mechanical Engineering, University of Kentucky, Lexington, KY40506-0503, simulations have become a new reliable trend for nasal airflow USA, E-mail: [email protected] exploration and demand fewer resources. The work of Liu et al. [8,9], Key words: human respiratory system, nasal cavity, lungs, computational analysis, Shanley et al. [10], Shi et al. [11], Xi and Longest [12], Kimbell [13], airflow, particle deposition Wang et al. [14], Moghadas et al. [15] and Abouali et al. [16] are a few Received: November 01, 2018; Accepted: November 09, 2018; Published: examples of researchers that have employed the CFD approach. November 14, 2018 Biol Eng Med, 2018 doi: 10.15761/BEM.1000155 Volume 3(6): 1-9 Saghaian SE (2018) Computational analysis of airflow and particle deposition fraction in the upper part of the human respiratory system Up to now, many experimental and numerical studies on particle transport and deposition through human nasal passages have been performed. Strong and Swift [25], Cheng et al. [26] and Swift et al. [27] measured the capture of ultrafine particles in the human nasal passage. Cheng et al. [28,29] and Cheng [30] have evaluated the deposition efficiency in the human nasal passage. Swift and Strong [31] presented an empirical relation for deposition efficiency in the human nasal passage for nano-sized particles by evaluating three persons. Measuring the particle deposition in different models that replicated the nasal airway, Kelly et al. [32] concluded that for nano-sized particles, the surface quality of the nasal pathway does not significantly affect the nasal deposition. However, micro-particle deposition efficiency is strongly related to the condition of the nasal pathway. Recently Xi et al. Figure 1. CT-scan images of an 18-year-old male from coronal, axial and sagittal directions [33] evaluated the transport and deposition of particles from the nasal radiologist separately and both confirmed the respiratory system of the cavity to the larynx based on a model extracted from MRI head images person to be healthy. of a 5-year old boy. As for numerical studies, computer simulations of particle deposition in the nasal cavity were reported by Zamankhan et A CT-scan is a noninvasive medical procedure that uses specialized al. [19], Shi et al. [11], Liu et al. [8] and Wang et al. [21]. X-ray equipment to produce cross-sectional images of the body. Although this device enables physicians to visualize the body from Borgstrom et al. [34] performed a literature survey on aerosol various angles, images are usually taken from three different angles deposition in humans and concluded that lung deposition is largely including coronel, sagittal and axial (as illustrated in Figure 1). Data determined by throat deposition as a major determinant for variability. extracted from the images were sent to a computer to reconstruct all of By using direct numerical simulation (DNS), Lin et al. [35] compared the individual “snapshots” into one or multiple cross-sectional images two different airway models, one of which was from the mouth up to of the internal organs and tissues. In a CT-scan, various densities of generation 6 and the other started from the trachea. They concluded tissue can be easily distinguished. Areas with high density, for example that the second model that lacked upper airway could not provide a bone tissues, were lighter than the darkly colored areas, such as air realistic airflow field in the lung. Thus, to reliably estimate the amount cavities where densities are lower. As one may notice from Figure 1, the of deposition of particles inhaled in the lungs, one should not ignore oral cavity and sinuses were also seen in black. In fact, distinguishing the upper airway. between the oral and nasal cavities, as well as determining the small Kesavanathan et al. [36] evaluated the deposition of micro-particles airways in the lungs, was among the factors that make the image in the respiratory tract in 40 people. They observed that the rate of processing phase more difficult. Comprehensive knowledge of the nasal deposition in these people is completely different, but in all cases, airway anatomy was crucial in this process. So, the images have been the number of particles that have been deposited is directly related viewed by a consultant physician in order to distinguish the areas more to the Impaction Parameter (IP). This parameter shows the number precisely. of particles that have been deposited. For spherical particles, IP is The challenges of the reconstruction process have been pointed defined as: out by many researchers [37,19]. Different methods were utilized to IP= Qd 2 generate an accurate 3-D model from the 2-D coronal cross-sections. (1) In the present study, the 3-D geometry of the human respiratory tract where d is the diameter of particles and Q is the airflow rate. was reconstructed as follows. First, CT-scan images with DICOM formatting were taken from the subject. Next, the CT-scan images were In this study, first, the air flow was numerically evaluated in a realistic processed by image processing software and the coordinates of the model of the human upper respiratory system during inspiration.
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