Computational Fluid Dynamics Modeling of Respiratory Airflow in Tracheobronchial Airways of Infant, Child, and Adult

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.

Effect of laryngeal jet on dry powder inhaler aerosol deposition: a numerical simulation

Although pulmonary drug delivery has been deeply investigated, the effect of the laryngeal jet on particle deposition during drug delivery with dry powder inhalers (DPI) has not been evaluated profoundly. In this study, the flow structure and particle deposition pattern of a DPI in two airway models, one with mouth-throat region including the larynx and the other one without it, are numerically investigated. The results revealed that the laryngeal jet has a considerable effect on particle deposition. The presence of laryngeal jet leads to 4-fold and 2-fold higher deposition efficiencies for inlet flow rates of 30 and 90 L/min, respectively.

Breathing on chip: Dynamic flow and stretch accelerate mucociliary maturation of airway epithelium in vitro

Human lung function is intricately linked to blood flow and breathing cycles, but it remains unknown how these dynamic cues shape human airway epithelial biology. Here we report a state-of-the-art protocol for studying the effects of dynamic medium and airflow as well as stretch on human primary airway epithelial cell differentiation and maturation, including mucociliary clearance, using an organ-on-chip device. Perfused epithelial cell cultures displayed accelerated maturation and polarization of mucociliary clearance, and changes in specific cell-types when compared to traditional (static) culture methods. Additional application of airflow and stretch to the airway chip resulted in an increase in polarization of mucociliary clearance towards the applied flow, reduced baseline secretion of interleukin-8 and other inflammatory proteins, and reduced gene expression of matrix metalloproteinase (MMP) 9, fibronectin, and other extracellular matrix factors. These results indicate that breathing-like mechanical stimuli are important modulators of airway epithelial cell differentiation and maturation and that their fine-tuned application could generate models of specific epithelial pathologies, including mucociliary (dys)function.

Computational fluid-particle dynamics modeling of ultrafine to coarse particles deposition in the human respiratory system, down to the terminal bronchiole

BACKGROUND AND OBJECTIVES

Suspended respirable airborne particles are associated with human health risks and especially particles within the range of ultrafine (< 0.1 μm) or fine (< 2.5 μm) have a high possibility of penetrating the lung region, which is concerned to be closely related to the bronchial or alveoli tissue dosimetry. Nature complex structure of the respiratory system requires much effort to explore and comprehend the flow and the inhaled particle dynamics for precise health risk assessment. Therefore, this study applied the computational fluid-particle dynamics (CFPD) method to elucidate the deposition characteristics of ultrafine-to-coarse particles in the human respiratory tract from nostrils to the 16^th generation of terminal bronchi.

METHODS

The realistic bronchi up to the 8^th generation are precisely and perfectly generated from computed tomography (CT) images, and an artificial model compensates for the 9^th-16^th bronchioles. Herein, the steady airflow is simulated at constant breathing flow rates of 7.5, 15, and 30 L/min, reproducing human resting-intense activity. Then, trajectories of the particle size ranging from 0.002 - 10 μm are tracked using a discrete phase model.

RESULTS

Here, we report reliable results of airflow patterns and particle deposition efficiency in the human respiratory system validated against experimental data. The individual-related focal point of ultrafine and fine particles deposition rates was actualized at the 8^th generation; whilst the hot-spot of the deposited coarse particles was found in the 6^th generation. Lobar deposition characterizes the dominance of coarse particles deposited in the right lower lobe, whereas the left upper-lower and right lower lobes simultaneously occupy high deposition rates for ultrafine particles. Finally, the results indicate a higher deposition in the right lung compared to its counterpart.

CONCLUSIONS

From the results, the developed realistic human respiratory system down to the terminal bronchiole in this study, in coupling with the CFPD method, delivers the accurate prediction of a wide range of particles in terms of particle dosimetry and visualization of site-specific in the consecutive respiratory system. In addition, the series of CFPD analyses and their results are to offer in-depth information on particle behavior in human bronchioles, which may benefit health risk assessment or drug delivery studies.

Physics-informed neural entangled-ladder network for inhalation impedance of the respiratory system

BACKGROUND AND OBJECTIVES

The use of machine learning methods for modelling bio-systems is becoming prominent which can further improve bio-medical technologies. Physics-informed neural networks (PINNs) can embed the knowledge of physical laws that govern a system during the model training process. PINNs utilise differential equations in the model which traditionally used numerical methods that are computationally complex.

METHODS

We integrate PINNs with an entangled ladder network for modelling respiratory systems by considering a lungs conduction zone to evaluate the respiratory impedance for different initial conditions. We evaluate the respiratory impedance for the inhalation phase of breathing for a symmetric model of the human lungs using entanglement and continued fractions.

RESULTS

We obtain the impedance of the conduction zone of the lungs pulmonary airways using PINNs for nine different combinations of velocity and pressure of inhalation. We compare the results from PINNs with the finite element method using the mean absolute error and root mean square error. The results show that the impedance obtained with PINNs contrasts with the conventional forced oscillation test used for deducing the respiratory impedance. The results show similarity with the impedance plots for different respiratory diseases.

CONCLUSION

We find a decrease in impedance when the velocity of breathing is lowered gradually by 20%. Hence, the methodology can be used to design smart ventilators to the improve flow of breathing.

Fluid dynamics of the upper airway in pediatric patients with severe laryngomalacia

Laryngomalacia is the top cause of pediatric laryngeal wheeze. We used computational fluid dynamics to study the inspiratory airflow dynamics in severe pediatric laryngomalacia. Computed tomography was performed on the upper airways of two infants, one with severe laryngomalacia and one with normal airway, and 3D models were reconstructed. ANSYS CFD-POST software was used to simulate airflow in these models to compare the volumetric flow rate, flow velocity, pressure, wall shear, and vortex. The volume flow rate in the laryngomalacia model was significantly reduced compared with the control model. Under inspiratory pressures, the peak flow velocity, pressure, and shear force in the control model appeared at the soft palate stenosis, while that in the laryngomalacia model appeared at the supraglottis stenosis. In both models, the maximum flow velocity and shear force increased with decreasing inspiratory pressure, while the minimum pressure decreased with decreasing inspiratory pressure. In the control model, the airflow vortex appeared anteriorly below the posterior section of the soft palate. In the laryngomalacia model, the vortex appeared anteriorly below the posterior section of the soft palate and anteriorly below the vocal folds. Our methodology provides a new mechanistic understanding of pediatric laryngomalacia.

Numerical modeling and development of a dual lung simulator using partitioned fluid-structure interaction approach for ventilator testing

New designs of mechanical ventilators require extensive testing before utilizing the ventilator on a patient. Test lungs are commonly used to understand the behavior of new designs of ventilators and the lung mechanics. The current study aims to develop a numerical model of dual test lungs utilizing the partitioned fluid-structure interaction (FSI) approach and test it against the available experimental data of volume-controlled ventilation. Two breathing rates of 12 and 18 bpm were studied at two different tidal volumes of 500 and 600 ml for spontaneous breathing. It is found that with an increase in the compliance (tidal volume/pressure rise) of the lung, the peak pressure rise inside the test lung decreases irrespective of the breathing rate. The maximum average pressure of 44.73, 27.45, and 14 cm H₂ O is observed for static lung compliances of 10, 21 , and 39 ml/cm H₂ O, respectively at a tidal volume of 600 ml. Similarly, the maximum von-misses stress was higher (498 kPa) for the lung with lower compliance (10 ml/cm H₂ O) as compared to the lung with higher compliance (39 ml/cm H₂ O) at the end of inspiration. This study forms a basis for using computational methods to model simple lung simulators that can effectively investigate the lung mechanics for both spontaneous and ventilated breathing. Thus, it can be utilized as a reference to test novel designs of mechanical ventilators.

Infection Control Improvement of a Negative-Pressurized Pediatric Intensive Care Unit

The COVID-19 pandemic caused by the novel SARS-CoV-2 virus raises alarming concern around the healthcare facilities due to the significant increase in patient inflow. Negative-pressurized isolation rooms have been utilized in various health care facilities to isolate the patients from active community contact. Several studies have highlighted isolation rooms improvement. However, limited knowledge is available regarding the isolation room facilities for pediatric intensive care units (PICU) to accommodate more than one pediatric patient. In this aspect, this study investigates a negative-pressurized isolation facility in PICU with minimal design modifications with the possibility that it can accommodate more than one pediatric patient. The field measurement tests were conducted to ensure the design compliance of Taiwan CDC. Then, computational fluid dynamics (CFD) was further utilized to numerically evaluate the HVAC system role and the ventilation performance towards infection control. A protected air-jet curtain system with a new ventilation layout was proposed through this study to enhance the protection for both pediatric patients and medical staff. The concentration decay was monitored and recorded within 900 s to evaluate the performance. The concentration can be reduced to 504 ppm for case 1, 620 ppm for case 2, 501 ppm for case 3, and 486 ppm for case 4. In addition, the injected bioaerosol particles could be well diluted dealing with two patients presents a good performance. The results revealed that this proposed configuration could feasibly accommodate two patients with a significant contamination control to protect the medical staff and patients.

Analysis of flow field and turbulence predictions in a lung model applying RANS and implications for particle deposition

Airflow and aerosol deposition in the human airways are important aspects for applications such as pulmonary drug delivery and human exposure to aerosol pollutants. Numerical simulations are widely used nowadays to shed light in airflow features and particle deposition patterns inside the airways. For that purpose, the Euler/Lagrange approach is adopted for predicting flow field and particle deposition through point-particle tracking. Steady-state RANS (Reynolds-averaged Navier-Stokes) computations of flow evolution in an extended lung model applying different turbulence models were conducted and compared to measurements as well as high resolution LES (large-eddy simulations) for several flow rates. In addition, various inlet boundary conditions were considered and their influence on the predicted flow field was analysed. The results showed that the mean velocity field was simulated reasonably well, however, turbulence intensity was completely under-predicted by two-equation turbulence models. Only a Reynolds-stress model (RSM) was able predicting a turbulence level comparable to the measurements and the high resolution LES. Remarkable reductions in wall deposition were observed when wall effects were accounted for in the drag and lift force expressions. Naturally, turbulence is an essential contribution to particle deposition and it is well known that two-equation turbulence models considerably over-predict deposition due to the spurious drift effect. A full correction of this error is only possible in connection with a Reynolds-stress turbulence model whereby the predicted deposition in dependence of particle diameter yielded better agreement to the LES predictions. Specifically, with the RSM larger deposition is predicted for smaller particles and lower deposition fraction for larger particles compared to LES. The local deposition fraction along the lung model was numerically predicted with the same trend as found from the measurements, however the values in the middle region of the lung model were found to be somewhat larger.

VIVID: In Vivo End-to-End Molecular Communication Model for COVID-19

As an alternative to ongoing efforts for vaccine development, scientists are exploring novel approaches to provide innovative therapeutics, such as nanoparticle- and stem cell-based treatments. Thus, understanding the transmission and propagation dynamics of coronavirus inside the respiratory system has attracted researchers' attention. In this work, we model the transmission and propagation of coronavirus inside the respiratory tract, starting from the nasal area to alveoli using molecular communication theory. We performed experiments using COMSOL, a finite-element multiphysics simulation software, and Python-based simulations to analyze the end-to-end communication model in terms of path loss, delay, and gain. The analytical results show the correlation between the channel characteristics and pathophysiological properties of coronavirus. For the initial 50% of the maximum production rate of virus particles, the path loss increases more than 16 times than the remaining 50%. The delayed response of the immune system and increase in the absorption of virus particles inside the respiratory tract delay the arrival of virus particles at the alveoli. Furthermore, the results reveal that the virus load is more in case of asthmatic patients as compared to the normal subjects.

The lower respiratory airway wall in children in health and disease

Alone or in association with other lung or thorax component disorders, the airway wall (AWW) remains one of the most frequently involved elements in paediatric lung diseases. A myriad of AWW disorders will present with similar symptomatology. It is thus important for the clinician to reappraise the normal development and structure of the AWW to better understand the underlying disease patterns. We herein provide an overview of the structure of the AWW and a description of its development from the fetal period to adulthood. We also detail the most common AWW changes observed in several acute and chronic respiratory disorders as well as after cigarette smoke or chronic pollution exposure. We then describe the relationship between the AWW structure and lung function. In addition, we present the different ways of investigating the AWW structure, from biopsies and histological analyses to the most recent noninvasive airway (AW) imaging techniques. Understanding the pathophysiological processes involved in an individual patient will lead to the judicious choice of nonspecific or specific personalised treatments, in order to prevent irreversible AW damage.

Polydisperse Aerosol Transport and Deposition in Upper Airways of Age-Specific Lung

A comprehensive understanding of airflow characteristics and particle transport in the human lung can be useful in modelling to inform clinical diagnosis, treatment, and management, including prescription medication and risk assessment for rehabilitation. One of the difficulties in clinical treatment of lung disorders lies in the patients’ variable physical lung characteristics caused by age, amongst other factors, such as different lung sizes. A precise understanding of the comparison between different age groups with various flow rates is missing in the literature, and this study aims to analyse the airflow and aerosol transport within the age-specific lung. ANSYS Fluent solver and the large-eddy simulation (LES) model were employed for the numerical simulation. The numerical model was validated with the available literature and the computational results showed airway size-reduction significantly affected airflow and particle transport in the upper airways. This study reports higher deposition at the mouth-throat region for larger diameter particles. The overall deposition efficiency (DE) increased with airway size reduction and flow rate. Lung aging effected the pressure distribution and a higher pressure drop was reported for the aged lung as compared to the younger lung. These findings could inform medical management through individualised simulation of drug-aerosol delivery processes for the patient-specific lung.

Open oral cavity has little effects on upper airway aerodynamics in children with obstructive sleep apnea syndrome: A computational fluid dynamics study based on patient-specific models

Obstructive sleep apnea syndrome (OSAS) is a common disorder with recurrent pharyngeal airway collapse and sleep disruption. Recently, great progress has been made in investigating the physical mechanism of OSAS development and treatment using computational fluid dynamics (CFD). However, previous studies always neglected the oral cavity artificially in the patient's upper airway CFD model, but did not give any specific explanation. The oral cavity effect on the OSAS upper airway flow is still a matter of unclear. This paper reconstructed the patient-specific upper airway models based on the cone beam computed tomography images of ten children subjects (seven boys and three girls) and used CFD to simulate both the steady and unsteady expiration and inspiration states in the upper airway model with or without the oral cavity. A series of pressure measurement experiments based on the in vitro 1:1 scaled airway model were performed to validate the reliability of the present CFD methods. Finally, the CFD results indicate that the open oral cavity is almost a region of flow stasis with constant pressure, and both the upper airway aerodynamics with and without the oral cavity have the similar trends, with the maximum average relative difference less than 6%. The present study shows that the open oral cavity causes very little impacts on the upper airway flow of the children patients with OSAS using the nasal respiration only, and confirms the reasonability of ignoring the oral cavity for CFD simulation.

Toxicity of Ortho-phthalaldehyde Aerosols in a Human In Vitro Airway Tissue Model

Ortho-phthalaldehyde (OPA) is a chemical disinfectant used for the high-level sterilization of heat-sensitive medical instruments. Although OPA is considered a safer alternative to glutaraldehyde, no exposure limits have been established for respiratory exposures to ensure the safety of OPA sterilization and the safe use of OPA-treated medical instruments. In order to address data gaps in the toxicological profile of OPA, we treated human in vitro air-liquid-interface (ALI) airway cultures at the air interface with various concentrations of OPA aerosols for 10 consecutive days. Temporal tissue responses were evaluated at multiple time points during the treatment phase as well as 10 days following the last exposure. The disturbance of glutathione (GSH) homeostasis occurred as early as 20 min following the first exposure, while oxidative stress persisted throughout the treatment phase, as indicated by the sustained induction of heme oxygenase-1 (HMOX-1) expression. Repeated exposures to OPA aerosols resulted in both functional and structural changes, including the inhibition of ciliary beating frequency, aberrant mucin production, decreases in airway secretory cells, and tissue morphological changes. While OPA-induced oxidative stress recovered to control levels after a 10 day recovery period, functional and structural alterations caused by the high concentration of OPA aerosols failed to fully recover over the observation period. These findings indicate that aerosolized OPA induces both transient and relatively persistent functional and structural abnormalities in ALI cultures under the conditions of the current study.

Structural and functional development in airways throughout childhood: Children are not small adults

Children are not small adults and this fact is particularly true when we consider the respiratory tract. The anatomic peculiarities of the upper airway make infants preferential nasal breathers between 2 and 6 months of life. The pediatric larynx has a more complex shape than previously believed, with the narrowest point located anatomically at the subglottic level and functionally at the cricoid cartilage. Alveolarization of the distal airways starts conventionally at 36-37 weeks of gestation, but occurs mainly after birth, continuing until adolescence. The pediatric chest wall has unique features that are particularly pronounced in infants. Neonates, infants, and toddlers have a higher metabolic rate, and consequently, their oxygen consumption at rest is more than double that of adults. The main anatomical and functional differences between pediatric and adult airways contribute to the understanding of various respiratory symptoms and disease conditions in childhood. Knowing the peculiarities of pediatric airways is helpful in the prevention, management, and treatment of acute and chronic diseases of the respiratory tract. Developmental modifications in the structure of the respiratory tract, in addition to immunological and neurological maturation, should be taken into consideration during childhood.