Airway Model Research Articles

Deep anatomy learning for lung airway and artery-vein modeling with contrast-enhanced CT synthesis.

Endobronchial intervention requires detailed modeling of pulmonary anatomical substructure, such as lung airway and artery-vein maps, which are commonly extracted from non-contrast computed tomography (NCCT) independently using automatic segmentation approaches. We aim to make the first attempt to jointly train a CNN-based model for airway and artery-vein segmentation along with synthetic contrast-enhanced CT (CECT) generation. A multi-task framework is proposed to simultaneously generate three segmentation maps and synthesize CECTs. We first design a collaborative learning model with tissue knowledge interaction for lung airway and artery-vein segmentation. Meanwhile, a conditional adversarial training strategy is applied to generate CECTs from NCCTs guided by artery maps. Additionally, CECT identity and reconstruction help to regularize the model for plausible NCCT to CECT translation. Extensive experiments were conducted to evaluate the performance of the proposed framework based on three datasets (90 NCCTs for the airway task, 55 NCCTs for the artery-vein task and 100 CECTs for the artery task). The results demonstrate the effective improvement of our proposed method compared to other methods and configurations that can achieve more accurate segmentation maps (Dice score coefficients for these three tasks are: 93.6%, 80.7% and 82.4%, respectively) and realistic CECTs simultaneously. The ablation study further verifies the effectiveness of the components of the designed model. This study demonstrates the model potential in multi-task learning that integrates anatomically relevant segmentation and performs NCCT to CECT translation. Such an interaction approach promotes mutually for both promising segmentation results and plausible synthesis.

Comparison of silicone double-lumen tube and polyvinyl chloride single-lumen tube in fiberoptic tracheal intubation on a difficult airway model: a randomized controlled non-inferiority trial

The management of patients with history or suspicion of difficult intubation can be challenging, especially in surgical procedures requiring one-lung ventilation. The ease of insertion of silicone double lumen tube (DLT) have previously been shown to be comparable to polyvinyl single lumen tube (SLT) in fiberoptic bronchoscope (FOB) tracheal intubation. Hence, in difficult airway situation, we hypothesized that the performance of insertion of silicone DLT would also be non-inferior to polyvinyl SLT in FOB intubation. We used a neck collar to mimic patients with difficult airway. 80 patients who required one-lung ventilation were enrolled in a prospective, randomized, non-inferiority trial. Patients were randomly allocated to the DLT or SLT groups (SLT with bronchial blocker). Neck collar was supplied to all patients before FOB intubation. The time of insertion for FOB, railroading, tracheal intubation, and total procedure were measured. The difficulty of railroading was evaluated in 4 grades. In the DLT group, the railroading was significantly shorter and easier comparing to the SLT group. The total procedure was also simpler and faster in the DLT group. While simulated difficult airways may not fully replicate actual difficult airways, we suggest that fiberoptic intubation with silicone DLT could be a feasible first-line option for patients with expected difficult airways requiring lung separation, unless the size of the DLT relative to the patient’s airway is problematic.Trial registration: NCT03392766.

Use of a 3D Printed, Color-Coded Airway Model for Bronchoscopy Training and Anatomy Learning

Aim: Tracheobronchial anatomy for bronchoscopy education is challenging. 3D printing (3DP) is a promising technology to design bronchoscopy simulators. Materials & m ethods: We created a 3DP tracheobronchial model and color-coded the airways to train first-year pulmonary fellows. A pre- and post-test, practical test and post-test questionnaires were used to evaluate the curriculum implementation. Results: For six fellows the pre- and post-test mean score improved from 11.5/22 (SD = ±1.71) to 16.2/22 (SD = ±2.79). Practical testing mean was 34.5/54 (SD = ±5.82). Questionnaires rated the 3DP model favorably. Conclusion: Our pilot curriculum using a color-coded 3DP model demonstrated improvement in airway identification with favorable ratings by fellows. We posit conceptual frameworks in play and how we address them in future models.

Interactive mold design for paediatric lower airway manikin manufacturing: a feasibility study

According to previous research, shore 40 A casting silicone is currently one of the more suitable materials for simulating the physical behavior of the airways in medicine simulation. This is essential to attain high-fidelity manikins that can perfectly mimic the simulated anatomic region, not just geometrically, but also in terms of haptic feedback. Due to the geometrical complexity of the tracheo-bronchial tree, mold design is a difficult and time-consuming process. An interactive modeling procedure for modeling mold parts for tracheo-bronchial tree casting is proposed in this paper, with the purpose of reducing modeling time without compromising quality. Following the definition of a standard modeling procedure, this was implemented in the Matlab language by using an IGES and STL editing toolbox. By using the interactive procedure it is possible to reduce the time required for virtual modeling from several hours to less than 1 min. Given this preliminary result, the proposed procedure will be further tested and developed in the near future, with the possibility of automating other lower airway modeling steps, such as vent generation and mounting holes/pins.

Utilizing a Functional Lumen Imaging Probe for Evaluation of the Pediatric Airway, A Pilot Study.

Accurate and reproducible measurements of the pediatric airway are critical for diagnostic evaluation and management of subglottic and tracheal stenosis. The endoluminal functional lumen imaging probe (EndoFLIP) is a catheter-based imaging probe which utilizes impedance planimetry to calculate luminal parameters, including cross-sectional area and compliance. Herein, we demonstrate the feasibility of this system for multidimensional evaluation of the pediatric airway. 3D-printed pediatric laryngotracheal models were created based on computed tomography scans, then artificially deformed to simulate both circumferential and posterior subglottic stenosis. Two observers made six measurements of the minimum cross-sectional area (MCSA) and length of stenosis of each model with EndoFLIP. Agreement between observer measurements and model dimensions was evaluated using Lin's concordance correlation coefficient; inter-observer reliability was assessed using intraclass correlation. Four models were created: two without pathology (MCSA: 132.4, 44.3 mm2 ) and two with subglottic stenosis (MCSA: 28.7, 59.7 mm2 , stenotic length 27.8, 24.4 mm). Observer measurements of MCSA and length of stenosis demonstrated high concordance with the models (r = 0.99, 0.95, p < 0.001) with a mean error of 4.5% and 18.2% respectively. There was a low coefficient of variation (0.6%-2.8%) for measurements, indicating high precision. Interrater reliability was high for both MCSA and stenotic length (ICC: 0.99, 0.98). The EndoFLIP system allows for accurate and reproducible measurements of cross-sectional area and stenotic length in pediatric airway models. This method may provide further advantages in the evaluation of airway distensibility, as well as measurements of asymmetric airway pathology. NA Laryngoscope, 134:108-112, 2024.

25 Using Advanced in Vitro Approaches to Elucidate the Differential Toxicity of Nitrogen Dioxide and Particulate Matter in Ambient Air Pollution

Abstract Ambient nitrogen dioxide (NO2) and particulate matter (PM) concentrations are often found to be proportional, such that inhalation of one pollutant is expected to be accompanied by the inhalation of the other. Epidemiological evidence consistently demonstrates the health burdens associated with the inhalation of NO2 and PM, though has difficulty deciphering the inhalation hazard of either pollutant individually. Airway models can be exposed to NO2 and PM separately or as a co-exposure in vitro, allowing mechanisms of toxicity to be elucidated. Herein, NCI-H441 cells were exposed to either 780 ng/cm2 Printex 90 carbon black (CB) (a surrogate model of PM) using a VitroCell Cloud12, 5 ppm NO2 (within a modified Coy hypoxic cabinet) or a combination of NO2+CB over 24 hours. Cytotoxicity was not altered by NO2 or CB (trypan blue exclusion assay), however CB, and to a lesser extent CB+NO2 exposure resulted in a non-significant increase in membrane permeability (p&amp;gt;0.05). qPCR revealed no alterations in expression of superoxide dismutase 1 (SOD1) for any exposure condition. Both CB and NO2 exposures resulted in significantly increased IL6 and IL8 release (ELISA) (p&amp;lt;0.05), although co-exposure of the two pollutants did not augment the detected IL6 or IL8 levels. These data indicate NO2 and CB produce an inflammatory response in this model, though little evidence suggests that NO2 and CB act in an additive or synergistic manner via this pathway. Additional work remains ongoing to establish the mechanisms of toxicity utilising an anatomically relevant triple cell co-culture of the alveolar epithelial barrier.

106 Establishing a Physiologically Relevant in Vitro Airway Model to Assess the Impacts of Environmental Exposures, Like Smoking, on Covid-19 Susceptibility.

Abstract Air-liquid interface (ALI) cultures are commonly used for 3D modelling of the human airways and to examine the effects of direct exposure to airborne toxicants. We explored the suitability of human epithelial cell lines (RPMI 2560, HBEC-3KT, CALU-3 and A549) and primary cells (nasal, bronchiolar and small airways) grown at ALI as a physiologically relevant model to examine whether environmental exposures can increase the susceptibility of the human airways to SARS-COV-2 infection. Cultures were kept at ALI for up to 28 days to allow differentiation. Trans-epithelial electrical resistance (TEER) was measured weekly. Cells were harvested at 0, 7, 14, 21 and 28 days, and transcriptional markers of basal, ciliated and mucus-producing cells together with SARS-COV-2 viral entry genes (ACE2, TMPRSS2 and Furin) and other genes of interest, were assessed by reverse-transcription quantitative PCR. Each cell line yielded differentiated models, with upregulation of markers of ciliated and mucus producing cells from day 7. In contrast to primary cells, immortalised cell lines did not produce cilia but, mucus was produced. TEER values increased with time, as expected, but values and therefore formation of tight junctions differed between models. Similarly, expression of viral entry genes increased as cells differentiated with marked differences across the different models. This study will be used to select the most appropriate ALI model for investigating the effect of environmental exposures such as smoking and vaping on susceptibility to SARS-COV-2 infection.

Evaluation of training effectiveness in simulation-based cricothyroidotomy programme for evidence-informed hospital management: An executive summary

This is an executive summary of an evaluation of simulation-based training effectiveness using modified Kirkpatrick model. With implementation of a new emergency surgical airway model, this study addressed overall organisational impacts and prioritisation strategies in resources allocation from the lens of an Industrial/Organisational (I/O) Psychologist in-training.

Non-spherical drug particle deposition in human airway using computational fluid dynamics and discrete element method

Currently, the air pollution and the respiratory disease problems that affect human health are increasing rapidly. Hence, there is attention for trend prediction of the located deposition of inhaled particles. In this study, Weibel’s based human airway model (G0-G5) was employed. The computational fluid dynamics and discrete element method (CFD-DEM) simulation was successfully validated by comparison to the previous research studies. The CFD-DEM achieves a better balance between numerical accuracy and computational requirement when comparing with the other methods. Then, the model was used to analyze the non-spherical drug transport with different drug particle sizes, shapes, density, and concentrations. The results found that all the studied factors affected the drug deposition and particle out-mass percentage except the drug concentration. The drug deposition was increased with the increasing of particle size and particle density due to the influence of particle inertia. The Tomahawk-shaped drug deposited easier than the cylindrical drug shape because of the different drag behavior. For the effect of airway geometries, G0 was the maximum deposited zone and G3 was the minimum deposited zone. The boundary layer was found around bifurcation due to the shear force at the wall. Finally, the knowledge can give an essential recommendation for curing patients with pharmaceutical aerosol. The design suggestion of a proper drug delivery device can be summarized.

External airway splint placement for severe pediatric tracheobronchomalacia

ObjectiveTo present external airway splinting with bioabsorbable airway supportive devices (ASD) for severe, life-threatening cases of pediatric tracheomalacia (TM) or tracheobronchomalacia (TBM). MethodsA retrospective cohort was performed for 5 pediatric patients with severe TM or TBM who underwent ASD placement. Devices were designed and 3D-printed from a bioabsorbable material, polycaprolactone (PCL). Pre-operative planning included 3-dimensional airway modeling of tracheal collapse and tracheal suture placement using nonlinear finite element (FE) methods. Pre-operative modeling revealed that triads along the ASD open edges and center were the most effective suture locations for optimizing airway patency. Pediatric cardiothoracic surgery and otolaryngology applied the ASDs by suspending the trachea to the ASD with synchronous bronchoscopy. Respiratory needs were trended for all cases. Data from pediatric patients with tracheostomy and diagnosis of TM or TBM, but without ASD, were included for discussion. ResultsFive patients (2 Females, 3 Males, ages 2–9 months at time of ASD) were included. Three patients were unable to wean from respiratory support after vascular ring division; all three weaned to room air post-ASD. Two patients received tracheostomies prior to ASD placement, but continued to experience apparent life-threatening events (ALTE) and required ventilation with supraphysiologic ventilator settings. One patient weaned respiratory support successfully after ASD placement. The last patient died post-ASD due to significant respiratory co-morbidity. ConclusionASD can significantly benefit patients with severe, unrelenting tracheomalacia or tracheobronchomalacia. Proper multidisciplinary case deliberation and selection are key to success with ASD. Pre-operative airway modeling allows proper suture placement to optimally address the underlying airway collapse.

Effect of Age and Head Position on Total and Regional Aerosol Deposition in Three-Dimensional Models of Human Intranasal Airways Using a Mucosal Atomization Device.

Background: This study examined the effect of age and head position on total and regional deposition of aerosol delivered by a mucosal atomization device (MAD™) in three-dimensional (3D) models of the intranasal airways of an 18-, 5-, and 2-year-old human. Models consisted of four pieces: anterior nose and nasal cavity that was divided horizontally into upper, middle, and lower thirds. Methods: Models were tested six times at supine, supine with head backward at 45° (supine45), and sitting with head backward at 45° (sitting45). The MAD delivered saline/fluorescein aerosol into model nostrils, during static airflow. Model pieces were tested for fluorescence using a fluorometer, and deposition calculated as percent fluorescence per piece relative to its reference. Total deposition (four pieces combined) and regional deposition (four pieces separately) were calculated. Results: Age and head position had little effect on total deposition. In contrast, deposition in the upper and middle third supine45 and in the lower third sitting45 was significantly different in the 2-year-old model, compared with the two older models. In addition, some head positions significantly increased deposition in the upper, middle, and lower thirds within each model, compared with other positions. Upper deposition was significantly greater at supine45, compared with sitting45 (18-year-old) and supine45, compared with supine and sitting45 (5-year-old). Middle deposition was significantly greater at supine and supine45, compared with sitting45 (2-year-old). Lower deposition was significantly greater at sitting45, compared with supine45 (18-year-old); supine and sitting45, compared with supine45 (5-year-old); and sitting45, compared with supine45 and supine (2-year-old). Conclusions: Age and head position significantly affected regional deposition of aerosol delivered by the MAD in these 3D models. Such models might be used to study other methods for targeting intranasal regions with aerosolized medications in children and adults.

Development of a micronucleus test using the EpiAirway™ organotypic human airway model

BackgroundThe use of organotypic human tissue models in genotoxicity has increased as an alternative to animal testing. Genotoxicity is generally examined using a battery of in vitro assays such as Ames and micronucleus (MN) tests that cover gene mutations and structural and numerical chromosome aberrations. At the 7th International Workshop on Genotoxicity Testing, working group members agreed that the skin models have reached an advanced stage of maturity, while further efforts in liver and airway models are needed [Pfuhler et al., Mutat. Res. 850–851 (2020) 503135]. Organotypic human airway model is composed of fully differentiated and functional respiratory epithelium. However, because cell proliferation in organotypic airway models is thought to be less active, assessing their MN-inducing potential is an issue, even in the cytokinesis-blocking approach using cytochalasin B (CB) [Wang et al., Environ. Mol. Mutagen. 62 (2021) 306–318]. Here, we developed a MN test using EpiAirway™ in which epidermal growth factor (EGF) was included as a stimulant of cell division.ResultsBy incubating EpiAirway™ tissue with medium containing various concentrations of CB, we found that the percentage of binucleated cells (%BNCs) almost plateaued at 3 μg/mL CB for 72 h incubation. Additionally, we confirmed that EGF stimulation with CB incubation produced an additional increase in %BNCs with a peak at 5 ng/mL EGF. Transepithelial electrical resistance measurement and tissue histology revealed that CB incubation caused the reduced barrier integrity and cyst formation in EpiAirway™. Adenylate kinase assay confirmed that the cytotoxicity increased with each day of culture in the CB incubation period with EGF stimulation. These results indicated that chemical treatment should be conducted prior to CB incubation. Under these experimental conditions, it was confirmed that the frequency of micronucleated cells was dose-dependently increased by apical applications of two clastogens, mitomycin C and methyl methanesulfonate, and an aneugen, colchicine, at the subcytotoxic concentrations assessed in %BNCs.ConclusionsWell-studied genotoxicants demonstrated capability in an organotypic human airway model as a MN test system. For further utilization, investigations of aerosol exposure, repeating exposure protocol, and metabolic activation are required.

Establishment and digital simulation of upper airway in patients with adenoid hypertrophy

Objective: To analyze the flow field characteristics of the upper airway in patients with different adenoid hypertrophy using computational fluid dynamics (CFD). Methods: From November 2020 to November 2021, the cone-beam CT (CBCT) data of 4 patients [2 males and 2 females,age range 5-7 years, mean (6.0±1.2) years] with adenoid hypertrophy who were hospitalized in the Department of Orthodontics and the Department of Otolaryngology at Hebei Eye Hospital were selected. The degree of adenoid hypertrophy in the 4 patients was divided into normal S1 (A/N<0.6), mild hypertrophy S2 (0.6≤A/N<0.7), moderate hypertrophy S3 (0.7≤A/N<0.9) and severe hypertrophy S4 (A/N≥0.9) according to the ratio of adenoid thickness to the width of nasopharyngeal cavity (A/N). The CFD model of the upper airway was established using ANSYS 2019 R1 software, and the internal flow field of the CFD model was numerically simulated. Eight sections were selected as observation and measurement planes for flow field information. Relevant flow field information includes airflow distribution, velocity variation, and pressure variation. Results: In the S1 model, the maximum pressure difference occurred in the 4th and 5th observation planes (ΔP=27.98). The lowest pressures and the maximum flow rates of S2 and S3 were located in the 6th observation plane. The airflow in S1 and S2 models completely passed through the nasal cavity. In the S3 model, the mouth-to-nasal airflow ratio was close to 2∶1. In S4 model, the airflow completely passed through the mouth; in the S1 and S2 models, hard palates were subjected to a downward positive pressure with a pressure difference of 38.34 and 23.31 Pa, respectively. The hard palates in S3 and S4 models were subjected to a downward negative pressure with a pressure difference of -2.95 and -21.81 Pa, respectively. Conclusions: The CFD model can objectively and quantitatively describe the upper airway airflow field information in patients with adenoid hypertrophy. With the increasing degree of adenoid hypertrophy, the nasal ventilation volume gradually decreased, whereas the oral space ventilation volume gradually increased, and the pressure difference between the upper and lower surfaces of the palate gradually decreased until the pressure became negative.

Effect of transient breathing cycle on the deposition of micro and nanoparticles on respiratory walls

Background and objectiveFrom various perspectives (e.g. inhalation exposure and drug delivery), it is important to provide insights into the behavior of inhaled particles in the human respiratory system. Although most of the experimental and numerical studies have relied on an assumption of steady inhalation, the transient breathing profile is a key factor in particle deposition in the respiratory tract. In this study, particle transportation and deposition were predicted in a realistic human airway model during a breathing cycle and the effects of steady-state and transient flows on the deposition fraction were observed using computational fluid dynamics. MethodsTwo transient breathing cycles with different respiratory durations were considered to evaluate the effects of respiration duration on particle transport and deposition characteristics. Two types of steady breathing conditions with corresponding steady-state respiratory volumes were reproduced. The Lagrangian discrete phase model approach was used to investigate particle transportation and deposition under transient breathing conditions. Additionally, the Eulerian approach was used to analyze the transport of nanoparticles in the gas phase. A total of >50,000 monodispersed particles with aerodynamic diameters ranging between 2 nm and 10 μm were selected for comprehensive deposition predictions for particle sizes ranging from the nano- to microscale. ResultsThe predicted results were compared with the experimental data. The particle deposition fraction in the nasal cavity and tracheal regions showed differences between the steady and transient simulations. In addition, particle analysis under steady inhalation conditions cannot accurately predict particle transportation and deposition in the lower airway. Furthermore, the breathing cycle had a significant effect on the deposition fraction of the particles and the behavior of the inhaled particles. ConclusionsTransient simulation mimicking the breathing cycle was observed to be an important factor in accurately predicting the transportation and deposition of particles in the respiratory tract.

Assessing the Impact of Transcutaneous Maxillary Distraction Osteogenesis on Pharyngeal Airway Volume in Children with Cleft Lip and Palate: A 3D Evaluation Study.

Cleft lip and cleft palate (CLCP) patients often have a retrusive maxilla and a severe skeletal Class III malocclusion, which can result in velopharyngeal insufficiency (VPI). The aim of this study was to evaluate the changes in the volume of the 3D airway in CLCP children after maxilla distraction using the transcutaneous maxillary distraction osteogenesis (TMDO) method. 15 children with bilateral or unilateral CLCP were included in the study. 3D CBCT images were taken before and after distraction and were segmented and reconstructed to create a 3D airway model. The airway was divided into three regions: the upper, oropharyngeal, and hypopharyngeal airway. Pearson correlation tests were used to assess correlations between volume changes and corresponding skeletal and dental landmark movements (Point N, ANS, A, B, Pog, U1, and L1). The results showed that the ANS point advanced 9.85 ± 3.60 mm, and the A point advanced 14.22 ± 4.57 mm. The total airway volume change increased by 2535.06 ± 2791.80 mm3. However, there was no significant correlation between the A/ANS/U1 and the three different airway regions. Only B/Pog/L1 showed a positive correlation with these airway regions, with a high correlation between B/Pog/L1 and the hypopharyngeal airway region. TMDO can result in greater anterior advancement of the maxilla and an increase in airway volume, but the changes in bony landmarks did not show a strong positive correlation with the increase in airway volume as expected. Further investigation is needed to analyze the influence of surrounding soft tissue on the changes in airway volume.

A computational analysis on the impact of multilevel laryngotracheal stenosis on airflow and drug particle dynamics in the upper airway.

Laryngotracheal stenosis (LTS) is a type of airway narrowing that is frequently caused by intubation-related trauma. LTS can occur at one or multiple locations in the larynx and/or trachea. This study characterizes airflow dynamics and drug delivery in patients with multilevel stenosis. Two subjects with multilevel stenosis (S1 = glottis + trachea, S2 = glottis + subglottis) and one normal subject were retrospectively selected. Computed tomography scans were used to create subject-specific upper airway models. Computational fluid dynamics modeling was used to simulate airflow at inhalation pressures of 10, 25, and 40 Pa, and orally inhaled drug transport with particle velocities of 1, 5, and 10 m/s, and particle size range of 100 nm-40 µm. Subjects had increased airflow velocity and resistance at stenosis with decreased cross-sectional area (CSA): S1 had the smallest CSA at trachea (0.23 cm2) and resistance = 0.3 Pa·s/mL; S2 had the smallest CSA at glottis (0.44 cm2), and resistance = 0.16 Pa·s/mL. S1 maximal stenotic deposition was 4.15% at trachea; S2 maximal deposition was 2.28% at glottis. Particles of 11-20 µm had the greatest deposition, 13.25% (S1-trachea) and 7.81% (S2-subglottis). Results showed differences in airway resistance and drug delivery between subjects with LTS. Less than 4.2% of orally inhaled particles deposited at stenosis. Particle sizes with most stenotic deposition were 11-20 µm and may not represent typical particle sizes emitted by current-use inhalers.

Tracing the origin of large respiratory droplets by their deposition characteristics inside the respiratory tract during speech.

Origin of differently sized respiratory droplets is fundamental for clarifying their viral loads and the sequential transmission mechanism of SARS-CoV-2 in indoor environments. Transient talking activities characterized by low (0.2 L/s), medium (0.9 L/s), and high (1.6 L/s) airflow rates of monosyllabic and successive syllabic vocalizations were investigated by computational fluid dynamics (CFD) simulations based on a real human airway model. SST k-ω model was chosen to predict the airflow field, and the discrete phase model (DPM) was used to calculate the trajectories of droplets within the respiratory tract. The results showed that flow field in the respiratory tract during speech is characterized by a significant laryngeal jet, and bronchi, larynx, and pharynx-larynx junction were main deposition sites for droplets released from the lower respiratory tract or around the vocal cords, and among which, over 90% of droplets over 5 µm released from vocal cords deposited at the larynx and pharynx-larynx junction. Generally, droplets' deposition fraction increased with their size, and the maximum size of droplets that were able to escape into external environment decreased with the airflow rate. This threshold size for droplets released from the vocal folds was 10-20 µm, while that for droplets released from the bronchi was 5-20 µm under various airflow rates. Besides, successive syllables pronounced at low airflow rates promoted the escape of small droplets, but do not significantly affect the droplet threshold diameter. This study indicates that droplets larger than 20 µm may entirely originate from the oral cavity, where viral loads are lower; it provides a reference for evaluating the relative importance of large-droplet spray and airborne transmission route of COVID-19 and other respiratory infections.

Numerical study on cooling characteristics in the distal airway model of the non-heart-beating donor lung cooled by hypothermic ventilation

Hypothermic ventilation can protect non-heart-beating donor lung against warm ischemia noninvasively in vivo, and has been expected to solve the problem of severe shortage of donor lung. However, a lack of knowledge of the heat and mass transfer mechanisms during whole process limits the application of this technique in clinical practice. In this case, we investigated the cooling characteristics of this process in a 3D distal airway represent generations 12–19 (G12-19) model, and computational fluid dynamics (CFD) method was used for calculation. The influence of ventilation conditions including Reynolds number (Re), inlet temperature (Tin) and the strengthening effect of droplet spraying were considered. Numerical results indicate that smaller Re instead favor internal cooling in the distal airway. For example, the variation of Re from 10 to 40 will make the outlet temperature of G19 increased from 22.2 °C to 35.9 °C after thermal equilibration (Tin = 10 °C). Adding droplets spraying could improve the cooling efficiency in the distal airway compared with cold air only. Without complete evaporation of the droplets inside the airway (i.e. Re = 10, Tin = 10 °C), the outlet temperature was effectively reduced by 44.0% for G12-15 airway and 51.9% for G16-19 acinus compared to ventilation alone. These findings reveal the reasons for the poor cooling effect of distal airway and can be used to optimize the hypothermic ventilation technique in future.

A Novel Trans-Tracheostomal Retrograde Inhalation Technique Increases Subglottic Drug Deposition Compared to Traditional Trans-Oral Inhalation.

Subglottic stenosis represents a challenging clinical condition in otolaryngology. Although patients often experience improvement following endoscopic surgery, recurrence rates remain high. Pursuing measures to maintain surgical results and prevent recurrence is thus necessary. Steroids therapy is considered effective in preventing restenosis. Currently, however, the ability of trans-oral steroid inhalation to reach and affect the stenotic subglottic area in a tracheotomized patient is largely negligible. In the present study, we describe a novel trans-tracheostomal retrograde inhalation technique to increase corticosteroid deposition in the subglottic area. We detail our preliminary clinical outcomes in four patients treated with trans-tracheostomal corticosteroid inhalation via a metered dose inhaler (MDI) following surgery. Concurrently, we leverage computational fluid-particle dynamics (CFPD) simulations in an extra-thoracic 3D airway model to gain insight on possible advantages of such a technique over traditional trans-oral inhalation in augmenting aerosol deposition in the stenotic subglottic region. Our numerical simulations show that for an arbitrary inhaled dose (aerosols spanning 1-12 µm), the deposition (mass) fraction in the subglottis is over 30 times higher in the retrograde trans-tracheostomal technique compared to the trans-oral inhalation technique (3.63% vs. 0.11%). Importantly, while a major portion of inhaled aerosols (66.43%) in the trans-oral inhalation maneuver are transported distally past the trachea, the vast majority of aerosols (85.10%) exit through the mouth during trans-tracheostomal inhalation, thereby avoiding undesired deposition in the broader lungs. Overall, the proposed trans-tracheostomal retrograde inhalation technique increases aerosol deposition rates in the subglottis with minor lower-airway deposition compared to the trans-oral inhalation technique. This novel technique could play an important role in preventing restenosis of the subglottis.

The effect of the mucus layer and the inhaled air conditions on the droplets fate in the human nasal cavity: A numerical study

In this work, the behavior of inhaled water droplets with initial sizes of 1–30 μm was studied under a sinusoidal cyclic breathing pattern. The maximum flow rate was 15 L/min, and the effect of inhaled air humidity and a humid mucus layer was considered. The geometry of the nasal airway model was created using magnetic resonance imaging (MRI) scans of a healthy male’s nose. The airflow and droplet motion governing equations were solved using an Eulerian-Lagrangian computational fluid dynamics (CFD) approach. A convection-diffusion-controlled model was used to analyze the size change of droplets. The main focus of this study was on the behavior and fate of the droplets, including their changes in size, as well as their evaporation, deposition, and penetration patterns. However, other parameters, including airflow velocity, temperature, and vapor concentration, were also evaluated. Based on the results, the mucus layer can significantly reduce the droplets evaporation to the extent that evaporation of initially 12 μm droplets reduces by about 90% due to the presence of the mucus layer. However, the inhaled air humidity and the mucus layer have little effect on the deposition fraction. The deposition rate mainly linearly depends on the initial droplet size. In the presence of the mucus layer, droplets with an initial size of 10 μm are mostly susceptible to penetration; around 80% can exit the nasal cavity. The critical range of droplets initial size is 5–10 μm. As the relative humidity of the inhaled air changes, the evaporation and penetration behavior of droplets with the critical range of size alters dramatically. Besides, in all cases, the deposition fraction of droplets smaller than 5 μm is almost zero.