Flow In Airways Research Articles

Heat and concentration analysis of two-layered muco-ciliary third grade fluid flow in human airways

Understanding the mechanisms involved in the movement and clearance of mucus within the human airways is important from a physiological perspective. A mathematical model of muco-ciliary two-layered fluid flow in a finite two-dimensional channel is proposed. Due to the presence of both the airway ciliary layer (ACL) and the periciliary liquid layer (PCL) in airways epithelial cells, the two-layered model is adopted. The third grade fluid models is used to characterize the viscoelastic nature of mucus secreted in the airways. The mathematical modeling of two-layer flow problem is simplified by using long wavelength and small Reynolds number approximation. A formulated set of partial differential equations (PDEs) is solved for series-form solutions of velocity, temperature, concentration, and pressure gradient by using the Adomian decomposition method (ADM). The analysis delineated that with an increase in pressure gradient at airways entrance ξ the velocity and temperature increases while concentration decreases. Deborah numbers impact ACL and PCL velocities differently, with De(A) influencing flow direction and De(P) causing fluid to flow faster in the forward direction. It also emphasizes the significance of the rate of thermal diffusion, viscous dissipation, and relaxation time. The results showed that the suggested two-layered muco-ciliary model provides a better description of mucus transport in the human airways. The pressure gradient at the airways entrance has a significant impact on mucus transport through the airways.

How microplastics are transported and deposited in realistic upper airways?

Microplastics are tiny plastic debris in the environment from industrial processes, various consumer items, and the breakdown of industrial waste. Recently, microplastics have been found for the first time in the airways, which increases the concern about long-term exposure and corresponding impacts on respiratory health. To date, a precise understanding of the microplastic transport to the airways is missing in the literature. Therefore, this first-ever study aims to analyze the microplastic transport and deposition within the upper lung airways. A computational fluid dynamics-discrete phase model approach is used to analyze the fluid flow and microplastic transport in airways. The sphericity concept and shape factor values are used to define the non-spherical microplastics. An accurate mesh test is performed for the computational mesh. The numerical results report that the highly asymmetric and complex morphology of the upper airway influences the flow fields and microplastic motion along with the flow rate and microplastic shape. The nasal cavity, mouth-throat, and trachea have high pressure, while a high flow velocity is observed at the area after passing the trachea. The flow rates, shape, and size of microplastics influence the overall deposition pattern. A higher flow rate leads to a lower deposition efficiency for all microplastic shapes. The nasal cavity has a high deposition rate compared to other regions. The microplastic deposition hot spot is calculated for shape and size-specific microplastic at various flow conditions. The findings of this study and more case-specific analysis will improve the knowledge of microplastic transport in airways and benefit future therapeutics development. The future study will be focused on the effect of various microplastic shapes on the human lung airways under the healthy and diseased airways conditions.

P226 Interpretation of spirometry parameters in adult patients with cystic fibrosis in North Macedonia

Assessment of lung function, the flow in large, medium and small airways through the analysis of functional diagnostics-spirometry and its parameters.

Numerical investigation of the effect of tracheostomy on flow and particle transport characteristics in human airways

Tracheostomy is a typical surgical procedure that has been widely practiced to address airway-related difficulties, such as airway obstruction or chronic conditions, that require long-term supportive ventilation. However, it may result in symptoms that detrimental to respiratory system. Computational fluid dynamics (CFD) is a noninvasive and efficient approach for observing the effects of tracheostomy. In this study, we introduced a CFD framework that can reveal the effects of tracheostomy tube insertion based on a comparison with the airflow of a normal airways. An automatic transformation method was developed using a patient's anatomical information to combine subject-specific airways with an artificial tracheostomy tube geometry and an idealized upper airway geometry for later comparison of characteristics of airflow and particle transport. The CFD scheme used for flow simulation in lungs was employed to achieve the behaviors of airflow. The tracheostomy tube generates a jet flow, resulting in twice greater wall shear stress (WSS) and 30 times greater viscous dissipation in the trachea compared to normal airway. The tracheostomized airway induces an intense turbulent jet, which enhances chaotic motion of the particles therein and allows particles to deposit more frequently on the surface. Subsequently, an increase in particle deposition is observed on the central airway's surface. The variation of pressure between inspiration and expiration phase was twice greater and the airflow resistance was also significantly higher compared to normal airway, implying the greater work of breathing. The novel framework could evaluate the efficiency and potential complications in performing tracheostomy beforehand by observing airflow behaviors.

A computed tomography imaging-based subject-specific whole-lung deposition model

The respiratory tract is an important route for beneficial drug aerosol or harmful particulate matter to enter the body. To assess the therapeutic response or disease risk, whole-lung deposition models have been developed, but were limited by compartment, symmetry or stochastic approaches. In this work, we proposed an imaging-based subject-specific whole-lung deposition model. The geometries of airways and lobes were segmented from computed tomography (CT) lung images at total lung capacity (TLC), and the regional air-volume changes were calculated by registering CT images at TLC and functional residual capacity (FRC). The geometries were used to create the structure of entire subject-specific conducting airways and acinar units. The air-volume changes were used to estimate the function of subject-specific ventilation distributions among acinar units and regulate flow rates in respiratory airway models. With the airway dimensions rescaled to a desired lung volume and the airflow field simulated by a computational fluid dynamics model, particle deposition fractions were calculated using deposition probability formulae adjusted with an enhancement factor to account for the effects of secondary flow and airway geometry in proximal airways. The proposed model was validated in silico against existing whole-lung deposition models, three-dimensional (3D) computational fluid and particle dynamics (CFPD) for an acinar unit, and 3D CFPD deep lung model comprising conducting and respiratory regions. The model was further validated in vivo against the lobar particle distribution and the coefficient of variation of particle distribution obtained from CT and single-photon emission computed tomography (SPECT) images, showing good agreement. Subject-specific airway structure increased the deposition fraction of 10.0-μm particles and 0.01-μm particles by approximately 10%. An enhancement factor increased the overall deposition fractions, especially for particle sizes between 0.1 and 1.0 μm.

CFD SIMULATIONS AND ANALYSES OF ASYMPTOMATIC AND SYMPTOMATIC NASAL AIRWAY OBSTRUCTIONS

The numerical simulations of the flow in nasal airways were performed for two different clinical cases. The results comprised the distributions of scalars at five different sections and included contours of pressure, velocity magnitude, turbulent kinetic energy and vorticity magnitude. Simulations showed the air branching occurring at the inferior meatus is unaffected by the variations in the volumetric flow rate or the changes in the flow regime through the olfactory cleft. However, the contractions and the following rapid change in the cross-section of the nasopharynx preclude the upward penetration of the vacuum field set by the lungs during the inhalation process. As a result, considerably low velocities and significant cross-sectional nonuniformities are observed, which lead to the appearances of the secondary flow structures and strong unsteadiness. Increased interactions between the airflow and the walls of the nasal cavity resulted in an increase in the vorticity on the right middle meatus and upper inferior meatus. The vorticity was also very high in the nostrils, where the flow was not fully developed.

The effect of the volumetric flow rate and endotracheal tube diameter on the pressure distribution in human airways

The comprehension of the fluid flow in the upper airways is of paramount importance when treating patients under clinical conditions that demand mechanical ventilation. Barotrauma and overdistension are related to undesirable pressures and might be responsible for morbidity and mortality. In the current work we use computational fluid dynamics to investigate the pressure field in the upper respiratory airways. We performed a set of simulations varying the volumetric flow rate of mechanical ventilators and we have shown that the pressure profile can be calculated by means of the volumetric flow rate in accordance with a mathematical expression given by Pav=aV˙2, where Pav is the average pressure at selected sections of the upper airways and V˙ is the volumetric flow rate. Numerical findings provide evidence that the constant a varies with the location of the plane in the upper airways. We also show that some particular diameters of endotracheal tubes (ETT) must be used with care for a given range of volumetric flow rates. Overall, we document an important relationship among pressure, volumetric flow rate and selected internal diameters from ETT.

Thermal analysis of airway mucus clearance by ciliary activity in the presence of inertial forces

In this study heat transfer effects on cilia induced mucus flow in human airways is presented. The elliptic wave pattern of cilia tips produces metachronal wave which enables the transportation of highly viscous mucus with nonzero inertial forces. Upper Convective Maxwell model is considered as mucus. The governing partial differential equations are transformed from the fixed frame to the wave frame by using Galilean transformation and viscous dissipation is also incorporated in the energy equation. The non-linear governing equations are evaluated by the perturbation technique by using software “MATHEMATICA” and pressure rise is computed by numerical integration. The impact of interested parameters on temperature profile, velocity, pressure rise and pressure gradient are plotted by the graphs. The comparison of velocities due to symplectic and antiplectic metachronal wave are also achieved graphically.

A quasi-3D model of the whole lung: airway extension to the tracheobronchial limit using the constrained constructive optimization and alveolar modeling, using a sac-trumpet model.

Existing computational models used for simulating the flow and species transport in the human airways are zero-dimensional (0D) compartmental, three-dimensional (3D) computational fluid dynamics (CFD), or the recently developed quasi-3D (Q3D) models. Unlike compartmental models, the full CFD and Q3D models are physiologically and anatomically consistent in the mouth and the upper airways, since the starting point of these models is the mouth–lung surface geometry, typically created from computed tomography (CT) scans. However, the current resolution of CT scans limits the airway detection between the 3rd–4th and 7th–9th generations. Consequently, CFD and the Q3D models developed using these scans are generally limited to these generations. In this study, we developed a method to extend the conducting airways from the end of the truncated Q3D lung to the tracheobronchial (TB) limit. We grew the lung generations within the closed lung lobes using the modified constrained constructive optimization, creating an aerodynamically optimized network aiming to produce equal pressure at the distal ends of the terminal segments. This resulted in a TB volume and lateral area of ∼165 cc and ∼2000 cm2, respectively. We created a “sac–trumpet” model at each of the TB outlets to represent the alveoli. The volumes of the airways and the individual alveolar generations match the anatomical values by design: with the functional residual capacity at 2611 cc. Lateral surface areas were scaled to match the physiological values. These generated Q3D whole lung models can be efficiently used for conducting multiple breathing cycles of drug transport and deposition simulations.

Lattice\u2013Boltzmann simulations for complex geometries on high-performance computers

Complex geometries pose multiple challenges to the field of computational fluid dynamics. Grid generation for intricate objects is often difficult and requires accurate and scalable geometrical methods to generate meshes for large-scale computations. Such simulations, furthermore, presume optimized scalability on high-performance computers to solve high-dimensional physical problems in an adequate time. Accurate boundary treatment for complex shapes is another issue and influences parallel load-balance. In addition, large serial geometries prevent efficient computations due to their increased memory footprint, which leads to reduced memory availability for computations. In this paper, a framework is presented that is able to address the aforementioned problems. Hierarchical Cartesian boundary-refined meshes for complex geometries are obtained by a massively parallel grid generator. In this process, the geometry is parallelized for efficient computation. Simulations on large-scale meshes are performed by a high-scaling lattice–Boltzmann method using the second-order accurate interpolated bounce-back boundary conditions for no-slip walls. The method employs Hilbert decompositioning for parallel distribution and is hybrid MPI/OpenMP parallelized. The parallel geometry allows to speed up the pre-processing of the solver and massively reduces the local memory footprint. The efficiency of the computational framework, the application of which to, e.g., subsonic aerodynamic problems is straightforward, is shown by simulating clearly different flow problems such as the flow in the human airways, in gas diffusion layers of fuel cells, and around an airplane landing gear configuration.

Three-dimensional modeling of human respiratory system for tasks of health risk assessment in the exposure to the chemicals inhalation

In the framework of multi-level model of accumulation of functional disorders in the human body under the influence of environmental factors there is delivered a sub-model of the “meso-level" of the respiratory system. The article is devoted to the three-dimensional modelling of the air flow in large airways of a human. The considered approaches can be applied for tasks of the health risk assessment in chemicals inhalation exposure.

High‐flow nasal therapy – modelling the mechanism

High‐flow nasal therapy – modelling the mechanism

STRIDOR IN A POST-ICH PATIENT: CONSERVATIVE MANAGEMENT IN A CURIOUS CASE OF AIRWAY COMPRESSION

SESSION TITLE: Cardiovascular Disease SESSION TYPE: Med Student/Res Case Report PRESENTED ON: 10/09/2018 07:30 AM - 08:30 AM INTRODUCTION: Stridor is usually caused by turbulent flow in the upper airways. We present a case of stridor due to a dissecting aortic aneurysm in a patient with an anomalous aortic arch. CASE PRESENTATION: A 65 year-old female smoker presented following a fall with hypertensive emergency and right cerebellar hematoma, believed to be due to uncontrolled hypertension. Initial evaluation showed somnolence and confusion without focal neurologic deficit. CT chest, abdomen and pelvis was performed to rule out a primary cancer with brain metastases as a cause of cerebellar hematoma. Chest CT incidentally showed a subacute type B aortic dissection extending down to the aortic bifurcation with involvement of both renal arteries.During hospitalization, the patient developed inspiratory stridor and expiratory wheezing worse with laying supine or on the right side. The stridor almost completely disappeared with sitting upright and improved by laying on the left side. Naso-laryngoscopy ruled out upper airway obstruction as a cause of stridor.Review of the chest CTA showed a right-sided aortic arch with aberrant left subclavian artery and Kommerell diverticulum. Tracheal narrowing was observed at two points. The proximal compression was caused by the anomalous aortic arch. The distal and severe narrowing involved the carina and both principal bronchi, right bronchus intermedius with complete right lower lobe atelectasis. The dynamic distal narrowing was due to interposition of central airways between widened thoracic aorta, the pulmonary artery and the heart. When supine, the heart would squeeze the interposed airways causing positon-dependent stridor.Due to recent ICH and contraindication for anticoagulation, the patient was not considered a surgical candidate. After hypertension was controlled, she was discharged with plan for surgical repair. DISCUSSION: Right-sided aortic arch is a rare congenital anomaly, reported in 0.1% of the population. It usually results from retained right fourth aortic arch and disappearance of the left fourth arch. The left subclavian artery has an aberrant origin arising from the remnant of the left aortic arch. This bulbous remnant at origin is called Kommerell diverticulum.Right-sided aortic arch is associated with congenital cyanotic heart disease, but majority of patients remain asymptomatic. Right-sided aortic arch with Kommerell diverticulum is a risk factor for aortic dissection. Atherosclerotic changes along with shear forces from the sharp aortic angle arch contribute to dissection. With the risk of dissection, surgical repair, including open, endovascular, or hybrid approaches, is the treatment for Kommerell diverticulum. CONCLUSIONS: Positional stridor can be an uncommon presentation of intrathoracic airway compression by dissecting aortic aneurysm. Right-sided aortic arch and Kommerell diverticulum are anomalies that contribute to the development of such compression. Reference #1: Herway, Seth T., Jonathan L. Benumof, Eugene Golts, and Gerard R. Manecke. 2015. "Major Positional Obstruction of the Trachea in a Patient with a Right-Sided Aortic Arch and Kommerell's Diverticulum." Journal of Cardiothoracic and Vascular Anesthesia 29(1):146-48. Retrieved (https://doi.org/10.1053/j.jvca.2013.08.003). Reference #2: Lin, Feng, Chang Chih Chen, Yu Jang Su, Yen Chun Lai, and Wen H. Chang. 2010. "Ruptured Aortic Aneurysm Presenting as a Stridor." International Journal of Gerontology 4(2):96-98. Reference #3: Kumar, Alok, Vikas Dutta, Sunder Negi, and GD Puri. 2016. "Vascular Airway Compression Management in a Case of Aortic Arch and Descending Thoracic Aortic Aneurysm." Annals of Cardiac Anaesthesia 19(3):568. Retrieved (http://www.annals.in/text.asp?2016/19/3/568/185568). DISCLOSURES: No relevant relationships by TsunKang Chiang, source=Web Response No relevant relationships by Ismail Dreshaj, source=Web Response No relevant relationships by Deb Leizman, source=Admin input No relevant relationships by Ramy Masroujeh, source=Web Response

Modeling Inspiratory Flow in a Porcine Lung Airway.

Inspiratory flow in a multigeneration pig lung airways was numerically studied at a steady inlet flow rate of 3.2 × 10-4 m3/s corresponding to a Reynolds number of 1150 in the trachea. The model was validated by comparing velocity distributions with previous measurements and simulations in simplified airway geometries. Simulation results provided detailed maps of the axial and secondary flow patterns at different cross sections of the airway tree. The vortex core regions in the airways were visualized using absolute helicity values and suggested the presence of secondary flow vortices where two counter-rotating vortices were observed at the main bifurcation and in many other bifurcations. Both laminar and turbulent flows were considered. Results showed that axial and secondary flows were comparable in the laminar and turbulent cases. Turbulent kinetic energy (TKE) vanished in the more distal airways, which indicates that the flow in these airways approaches laminar flow conditions. The simulation results suggested viscous pressure drop values comparable to earlier studies. The monopodial asymmetric nature of airway branching in pigs resulted in airflow patterns that are different from the less asymmetric human airways. The major daughters of the pig airways tended to have high airflow ratios, which may lead to different particle distribution and sound generation patterns. These differences need to be taken into consideration when interpreting the results of animal studies involving pigs before generalizing these results to humans.

Variations of flow in human airways as a consequence of lung diseases

The efficiency of drug delivery administered by inhalation depends, among other factors, such as size and shape of aerosol particles, significantly also on the flow in the airways. As many lung diseases change both the breathing pattern and the shape of airways, we focus in this study on the influence of several selected diseases on the distribution of flow between the lung lobes and on changes the diseases induce on the course of flowrate. First, we present results of a literature survey focused on the published records of pathological breathing patterns. In the second part, we describe the newly designed breathing simulator and the implementation of the patterns into it. The last part is focused on the experimental verification of fidelity of the simulated breathing patterns.

Mathematical Modelling to Simulate Biological Fluid Flow in a Collapsible Tube

The purpose of this paper is to advance a mathematical model for reviewing to simulate biological flows such as blood flow in arteries or veins, flow of urine in urethras and air flow in the bronchial airways. They can also be used to study and prediction of many diseases, as the lung disease (asthma and emphysema), or the cardiovascular diseases (heart stroke), Makinde (2005). In this work, laminar flow of an incompressible viscous fluid through a collapsible tube of circular cross section is considered. Collapsible tubes are easily deformed by negative transmural pressure owing to marked reduction of rigidity. Thus, they show a considerable nonlinearity and reveal various complicated phenomena Our objectives are to study the effect of temperature along the tube as the fluid Prandtl number and Reynolds number increases. We launch the mathematical formulation of the problem. The problem is solved by using power series and perturbation techniques with help of boundary conditions and results are displayed graphically for different flow characteristics, velocity profile.

Experimental methods for flow and aerosol measurements in human airways and their replicas

Recent developments in the prediction of local aerosol deposition in human lungs are driven by the fast development of computational simulations. Although such simulations provide results in unbeatable resolution, significant differences among distinct methods of calculation emphasize the need for highly precise experimental data in order to specify boundary conditions and for validation purposes. This paper reviews and critically evaluates available methods for the measurement of single and disperse two-phase flows for the study of respiratory airflow and deposition of inhaled particles, performed both in vivo and in replicas of airways. Limitations and possibilities associated with the experimental methods are discussed and aspects of the computational calculations that can be validated are indicated. The review classifies the methods into following categories: 1) point-wise and planar methods for velocimetry in the airways, 2) classic methods for the measurement of the regional distribution of inhaled particles, 3) standard medical imaging methods applicable to the measurement of the regional aerosol distribution and 4) emerging and nonconventional methods. All methods are described, applications in human airways studies are illustrated, and recommendations for the most useful applications of each method are given.

Numerical investigation of transient transport and deposition of microparticles under unsteady inspiratory flow in human upper airways

In the present study, unsteady airflow patterns and particle deposition in healthy human upper airways were simulated. A realistic 3-D computational model of the upper airways including the vestibule to the end of the trachea was developed using a series of CT scan images of a healthy human. Unsteady simulations of the inhaled and exhaled airflow fields in the upper airway passages were performed by solving the Navier-Stokes and continuity equations for low breathing rates corresponding to low and moderate activities. The Lagrangian trajectory analysis approach was utilized to investigate the transient particle transport and deposition under cyclic breathing condition. Particles were released uniformly at the nostrils’ entrance during the inhalation phase, and the total and regional depositions for various micro-particle sizes were evaluated. The transient particle deposition fractions for various regions of the human upper airways were compared with those obtained from the equivalent steady flow condition. The presented results revealed that the equivalent constant airflow simulation can approximately predict the total particle deposition during cyclic breathing in human upper airways. While the trends of steady and unsteady model predictions for local deposition were similar, there were noticeable differences in the predicted amount of deposition. In addition, it was shown that a steady simulation cannot properly predict some critical parameters, such as the penetration fraction. Finally, the presented results showed that using a detached nasal cavity (commonly used in earlier studies) for evaluation of total deposition fraction of particles in the nasal cavity was reasonably accurate for the steady flow simulations. However, in transient simulation for predicting the deposition fraction in a specific region, such as the nasal cavity, using the full airway system geometry becomes necessary.

Analysis of the impact of harmful factors in the workplace on functioning of the respiratory system of firefighters.

Firefighters are considered a healthy and fit group of individuals, well-prepared for taking action in disaster situations. While working, they suffer from exposure to certain toxic agents, especially combustion products generated when a fire takes place. Among them, the most frequent and the most toxic are: carbon monoxide, hydrogen cyanide, ammonia, and those resulting from PVC combustion - hydrochloride, phosgene and chloride. Additionally, fire-extinguisher powder can be inhaled and lead to certain lesion in the airways. The aim of study was to ascertain the influence of toxic agents present at the scene of fire on the lung tissue of firefighters, and also to study this on an animal model. The study group consisted of firefighters who had a minimum of 10 years service. After completing a questionnaire, their clinical status was ascertained based on a general examination, laboratory tests and lung function tests. Questionnaire analysis showed a high percentage of pathological symptoms in the studied group. The incidence of the symptoms correlated with the duration of occupational exposure to toxic agents. Among other results, obstruction of flow in medium airways in about 30% of the studied individuals represented the most important finding. Experimental tests were next performed on male Wistar rats, aged 3 months. They were insufflated with the solution of powdered fire-extinguisher, after which morphology specimens of lung tissue were studied. Evidence for disseminated fibrosis was obtained, which supported the previous clinical findings in the firefighters. The above shows correlation between occupational exposure and respiratory system involvement in firefighters. This justifies covering the group of firefighters with special medical care focused on prophilaxis, early detection and therapy of pulmonary diseases.

Helium–oxygen mixture for treatment in upper airway obstruction; a mini-review

Abstract In the 1930's Alan Barach introduced helium in combination with oxygen, heliox, to the medical world. He found that helium's physical properties help reduce the work of breathing, reduce airway resistance, and subsequently improve alveolar ventilation in obstructed airways. In the presence of airway narrowing, heliox has the benefits of increasing the tendency to laminar flow (which has lower resistance) and reducing resistance when turbulent flow occurs. Heliox, a helium–oxygen mixture, has since been used sporadically and only scattered reports are found on its use for treatment in patients with upper airway obstruction. The aim of the present review was to search and review the available evidence for its safe and effective clinical use. A total of 20 publications about the use of helium-containing gas mixture for the treatment of upper airway obstruction in adults were found in the search of public domain literature. Most case reports describe short-term beneficial effects, temporarily improving breathing and oxygenation. Authors of the case reports suggest helium–oxygen mixture as an optional bridge, while a more definite treatment takes action. There are, however, no prospective randomized controlled studies and thus there is lack of high-quality proof supporting its safe and efficacious use. In conclusion, the physiochemical properties promoting laminar flow in restricted airways and the sparse but still seemingly positive clinical experience favor the use of helium–oxygen mixture as a symptomatic rescue therapy. The risk for side effects, apart from the reduced oxygen concentration in the inspired gas, seems minor. There is, however, still a lack of evidence to support the general use of oxygen–helium mixture for upper airway compromise due to the sparse information available. Further studies, although not easily designed, are warranted.