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To analyze the effect of different endoscopic endonasal approaches (EEAs) on nasal airflow and heating and humidification in patients with pituitary adenoma (PA) by computational fluid dynamics (CFD). A three-dimensional pre-surgical model (Pre) of the nasal cavity and 6 that were post-EEA surgery were created from computed tomography scans as follows: small posterior septectomy (0.5 cm, sPS), middle posterior septectomy (1.5 cm, mPS), large posterior septectomy (2.5 cm, lPS), and sPS with middle turbinate resection (sPS-MTR), mPS-MTR, and lPS-MTR. Simulations were performed by CFD to compare the changes in different models. The temperature in the nasal vestibule rose more rapidly than in other parts of the nasal cavities in all models. There were no apparent differences in temperature and humidity among the models in sections anterior to the middle turbinate head (C6 section). MTR significantly influenced airflow distribution between the bilateral nasal cavities and the different parts of the nasal cavity, while changes in temperature and humidity in each section were mainly affected by MTR. The temperature and humidity of the choana and nasopharynx of each postoperative model were significantly different from those of the preoperative model and the change in values significantly correlated with the surface-to-volume ratio (SVR) of the airway. Changes due to the different nasal structures caused different effects on nasal function following the use of EEA surgery for the treatment of PA. CFD provided a new approach to assess nasal function, promising to provide patients with individualized preoperative functional assessment and surgical planning. [ABSTRACT FROM AUTHOR]

Background: Nasal saline irrigation has become standard of care in various sinonasal conditions, including allergic and nonallergic rhinitis, chronic rhinosinusitis, and in the postoperative patient. Evidence regarding the mechanisms and dynamics of liquid flow through the sinonasal cavity remains limited due to inadequate experimental models (cadaveric, 3‐dimensional [3D] printed, imaging of labeled dyes and radioisotopes). We aimed to develop a computational fluid dynamics (CFD) model of nasal irrigation to demonstrate sinonasal surface coverage, residence times across the mucosal surfaces, and shearing force of irrigation. Methods: A nasal cavity geometry derived from high‐resolution paranasal sinus computed tomography (CT) scans of a healthy, unoperated, 25‐year‐old patient was created. CFD analysis was performed to assess the distribution of nasal irrigation from a tapered nozzle bottle at a forward head‐tilt position of 45 degrees with a 2‐second burst at 35 mL/second. Results: The model demonstrates nasal irrigation from ipsilateral to contralateral with precise measures of velocity, pressure, wall shear stress, and mapping of surface coverage and residence times at specific locations and times. The nasal cavity experiences almost complete coverage of irrigation, while overflow from the nasal cavity facilitates moderate coverage of the ipsilateral maxillary (40%) and anterior ethmoid sinuses (30%). Negligible coverage of the sphenoid and frontal sinuses was noted. Conclusion: Detailed physical mechanisms of liquid irrigation injected from a commonly used squeeze bottle were shown. Ipsilateral maxillary and ethmoid sinus penetration are primarily due to overflow rather than direct jet entry, confirming the recommendation of larger volumes of irrigation to "flood" the sinus ostia. [ABSTRACT FROM AUTHOR]

Understanding the inhalation, transport and deposition of smoke particles during fire missions are important to evaluating the health risks for firefighters. In this study, measurements from Underwriters Laboratories' large-scale fire experiments on smoke particle size distribution and concentration in three residential fire scenes were incorporated into models to investigate the fate of inhaled toxic ultrafine particulates in a realistic firefighter nasal cavity model. Deposition equations were developed, and the actual particle dosimetry (in mass, number and surface area) was evaluated. A strong monotonic growth of nasal airway dosages of simulated smoke particles was identified for airflow rates and fire duration across all simulated residential fire scene conditions. Even though the "number" dosage of arsenic in the limited ventilation living room fire was similar to the "number" dosage of chromium in the living room, particle mass and surface area dosages simulated in the limited living room were 90–200 fold higher than that in the ventilated living room. These were also confirmed when comparing the dosimetry in the living room and the kitchen. This phenomenon implied that particles with larger size were the dominant factors in mass and surface area dosages. Firefighters should not remove the self-contained breathing apparatus (SCBA) during fire suppression and overhaul operations, especially in smoldering fires with limited ventilation. [ABSTRACT FROM AUTHOR]

Abstract Intranasal drug delivery has attracted significant attention because of the opportunity to deliver systemic drugs directly to the blood stream. However, the mucociliary clearance poses a challenge in gaining high efficacy of intranasal drug delivery because cilia continuously carry the mucus blanket towards the laryngeal region. To better understand mucus flow behaviour on the human nasal cavity wall, we present computational model development, and evaluation of mucus motion on a realistic nasal cavity model reconstructed from CT-scans. The model development involved two approaches based on the actual nasal cavity geometry namely: (i) unwrapped-surface model in 2D domain and (ii) 3D-shell model. Conservation equations of fluid motion were applied to the domains, where a mucus production source term was used to initiate the mucus motion. The analysis included mucus flow patterns, virtual saccharin tests and quantitative velocity magnitude analysis, which demonstrated that the 3D-shell model results provided better agreement with experimental data. The unwrapped-surface model also suffered from mesh-deformations during the unwrapping stage and this led to higher mucus velocity compared to experimental data. Therefore, the 3D-shell model was recommended for future mucus flow simulations. As a first step towards mucus motion modelling this study provides important information that accurately simulates a mucus velocity field on a human nasal cavity wall, for assessment of toxicology and efficacy of intranasal drug delivery. [ABSTRACT FROM AUTHOR]

Inhalation exposure to smoke particles emitted from fire grounds could induce respiratory and cardiovascular diseases to firefighters and emergency responders. Understanding the detailed smoke-particle deposition distribution and dosages in nasal airway is of significant value to inhalation risk assessment. In this study, a realistic firefighter nasal airway model, accounting for facial features and external environment was employed to study the inhalation and deposition of smoke particles emitted from a composite deck fire. Particle size distribution and concentration used in the simulation were from the Underwriters Laboratories’ large-scale fire experimental data. Deposition patterns and a method for calculating particles dosimetry (in number, mass and surface area) were analyzed. The dosages in the firefighter nasal cavity, middle turbinate, middle meatus, onto the face and penetrated under various inspiration rates were discussed. The aspiration ratio was also considered in the exposure inhalation risk assessments. Three deposition hot spots were identified in the nasal cavity: nasal vestibule, nasopharynx and middle meatus. The breathing flow rate did not affect the aspiration ratio significantly, while the particle density was an obvious impact factor to aspiration ratio of larger size of micron particles (> 5 µm). Greater than 97% of number dosages were from nanoparticles in all simulated areas, yet the nanoparticle mass dosages and surface dosages only took up around 50%. In addition, majority (about 98%) of particles in composite deck fire scenario penetrated into lower airways or even into the lungs. Meanwhile, the dosages in all metrics onto the face were less than those in nasal cavity, but higher than those in the middle meatus and turbinate. Smaller sized particles (such as nanoparticles) were more likely to deposit onto the face than being inhaled into nasal cavity at high flow rate due to the intensive diffusion. Mass carrier (larger sized) particles tended to run into middle turbinate than to middle meatus. [ABSTRACT FROM AUTHOR]

Rats have been widely used as surrogates for evaluating the health effects of inhaled airborne particulate matter. To provide a thorough understanding of particle transport and deposition mechanisms in the rat nasal airway, this article presents a computational fluid dynamics (CFD) study of particle exposure in a realistic rat nasal passage under a resting flow condition. Particles covering a diameter range from 1 nm to 4 µm were passively released in front of the rat’s breathing zone, and the Lagrangian particle tracking approach was used to calculate individual particle trajectories. Detailed particle deposition analysis shows the deposition of inertial particles >2 µm is high in the rat nasal vestibule and more than 70% of all inhaled inertial particles were trapped in this region. While for diffusive nanoparticles, the vestibule filtration effect is reduced, only less than 60% of inhaled nanoparticles were blocked by the anterior nasal structures. The particle exposure in the olfactory region only shows notable deposition for diffusive nanoparticles, which peaks at 9.4% for 5 nm particles. Despite the olfactory deposition remains at a low level, the ratio between the olfactory and the main passage is kept around 30-40% for 10-800 nm particles, which indicates a particle-size-independent distribution pattern in the main nasal passage and olfactory. This study provides a deep understanding of particles deposition features in a rat nasal passage, and the research findings can aid toxicologist in inter-species exposure-response extrapolation study. [ABSTRACT FROM AUTHOR]

An urgent demand of assessing passengers' exposure risks in airliner cabins was raised as commercial airliners are one of the major media that carrying and transmitting infectious disease worldwide. In this study, simulations were conducted using a Boeing 737 cabin model to study the transport characteristics of airborne droplets and the associated infection risks of passengers. The numerical results of the airflow field were firstly compared against the experimental data in the literature to validate the reliability of the simulations. Airborne droplets were assumed to be released by passengers through coughing and their transport characteristics were modelled using the Lagrangian approach. Numerical results found that the particle travel distance was very sensitive to the release locations, and the impact was more significant along the longitudinal and horizontal directions. Particles released by passengers sitting next to the windows could travel much further than the others. A quantifiable approach was then applied to assess the individual infection risks of passengers. The key particle transport information such as the particle residence time yielded from the Lagrangian tracking process was extracted and integrated into the Wells-Riley equation to estimate the risks of infection. Compared to the Eulerian-based approach, the Lagrangian-based approach presented in this study is more robust as it addresses both the particle concentration and particle residence time in the breathing zone of every individual passenger. [ABSTRACT FROM AUTHOR]

Micron-sized particle deposition in anatomically realistic models of a rat and human nasal cavity was numerically investigated. A steady laminar inhalation flow rate was applied and particles were released from the outside air. Particles showing equivalent total particle deposition fractions were classified into low, medium and high inertial particle. Typical particle sizes are 2.5, 9 and 20 μm for the human model and 1, 2 and 3 μm for the rat model, respectively. Using a surface-mapping technique the 3D nasal cavity surface was “unwrapped” into a 2D domain and the particle deposition locations were plotted for complete visual coverage of the domain surface. The total surface area comparison showed that the surface area of the human nasal model was about ten times the size of the rat model. In contrast, the regional surface area percentage analysis revealed the olfactory region of the rat model was significantly larger than all other regions making up ∼55.6% of the total surface area, while that of the human nasal model only occupying 10.5%. Flow pattern comparisons showed rapid airflow acceleration was found at the nasopharynx region and the nostril region for the human and rat model, respectively. For the human model, the main passage is the major deposition region for micro-particles. While for the rat model, it is the vestibule. Through comparing the regional deposition flux between human and rat models, this study can contribute towards better extrapolation approach of inhalation exposure data between inter-subject species. [ABSTRACT FROM PUBLISHER]

Highlights: [•] A new visualization technique that transforms 3D nasal cavity into a 2D domain. [•] Pressure distribution and wall shear stresses mapped onto a 2D domain. [•] Regions hidden by the curved airway geometry are revealed through the 2D domain. [•] Applications of technique include inter-individual geometry and particle inhalation. [ABSTRACT FROM AUTHOR]

Social distance will remain the key measure to contain COVID-19 before the global widespread vaccination coverage expected in 2024. Containing the virus outbreak in the office is prioritised to relieve socio-economic burdens caused by COVID-19 and potential pandemics in the future. However, "what is the transmissible distance of SARS-CoV-2" and "what are the appropriate ventilation rates in the office" have been under debate. Without quantitative evaluation of the infection risk, some studies challenged the current social distance policies of 1–2 m adopted by most countries and suggested that longer social distance rule is required as the maximum transmission distance of cough ejected droplets could reach 3–10 m. With the emergence of virus variants such as the Delta variant, the applicability of previous social distance rules are also in doubt. To address the above problem, this study conducted transient Computational Fluid Dynamics (CFD) simulations to evaluate the infection risks under calm and wind scenarios. The calculated Social Distance Index (SDI) indicates that lower humidity leads to a higher infection risk due to weaker evaporation. The infection risk in office was found more sensitive to social distance than ventilation rate. In standard ventilation conditions, social distance of 1.7 m–1.8 m is sufficient distances to reach low probability of infection (PI) target in a calm scenario when coughing is the dominant transmission route. However in the wind scenario (0.25 m/s indoor wind), distance of 2.8 m is required to contain the wild virus type and 3 m is insufficient to contain the spread of the Delta variant. The numerical methods developed in this study provide a framework to evaluate the COVID-19 infection risk in indoor environment. The predicted PI will be beneficial for governments and regulators to make appropriate social-distance and ventilation rules in the office. • In standard ventilation conditions, 1.7 m-1.8 m is sufficient to reach low infection. • A social distance of 2.8 m is required to contain the wild virus type. • A social distance of 3 m is not insufficient for the Delta variant. • The infection is higher in a dryer environment due to a stronger evaporation effect. [ABSTRACT FROM AUTHOR]

• Virtual middle turbinate resection surgery performed on nasal cavity. • Aerodynamic behaviour of pollen was compared with spherical particles. • Two constant flow rates of 5 L/min, and 15 L/min were performed. • An inhalation efficiency curve is proposed which introduced an inhalation parameter, d ae 2 Q − 0.825. • Middle turbinate excision led to increased allergen deposition on the septum. • Middle turbinate plays a protective role in preventing allergen impaction on the septum. Middle turbinate resection significantly alters the anatomy and redistributes the inhaled air. The superior half of the main nasal cavity is opened up, increasing accessibility to the region. This is expected to increase inhalation dosimetry to the region during exposure to airborne particles. This study investigated the influence of middle turbinate resection on the deposition of inhaled pollutants that cover spherical and non-spherical particles (e.g. pollen). A computational model of the nasal cavity from CT scans, and its corresponding post-operative model with virtual surgery performed was created. Two constant flow rates of 5 L/min, and 15 L/min were simulated under a laminar flow field. Inhaled particles including pollen (non-spherical), and a spherical particle with reference density of 1000 kg/m 3 were introduced in the surrounding atmosphere. The effect of surgery was most prominent in the less patent cavity side, since the change in anatomy was proportionally greater relative to the original airway space. The left cavity produced an increase in particle deposition at a flow rate of 15 L/min. The main particle deposition mechanisms were inertial impaction, and to a lesser degree gravitational sedimentation. The results are expected to provide insight into inhalation efficiency of different aerosol types, and the likelihood of deposition in different nasal cavity surfaces. [ABSTRACT FROM AUTHOR]

Inhaled viral droplets may immediately be expelled and cause an escalating re-transmission. Differences in the deposition location of inhaled viral droplets may have a direct impact on the probability of virus expelling. This study develops a numerical model to estimate the region-specific deposition fractions for inhalable droplets (1–50 μ m) in respiratory airways. The results identified a higher deposition fraction in the upper airways than the lower airways. Particularly for droplets larger than 10 μ m, the relatively high deposition fraction in the oral/laryngeal combined region warns of its easy transmission through casual talking/coughing. Moreover, considering droplet sizes' effect on virus loading capacity, we built a correlation model to quantify the potential of virus expelling hazards, which suggests an amplified cascade effect on virus transmission on top of the existing transmission mechanism. It therefore highlights the importance of considering the instant expelling possibilities from inhaled droplets, and also implies potentials in restricting a rapid secondary transmission by measures that can lower down droplet deposition in the upper airways. • The rapid re-transmission of COVID-19 via close contact people is probable. • 1–50 μ m particles account for most of particles from a cough. • The high deposition rate in the oral/laryngeal region for droplets larger than 10 μ m warns of the easy expelling for re-transmission. • The re-transmission potential is estimated as 14.9% in the oral–nasal inhalation scenario. [ABSTRACT FROM AUTHOR]

Laminar fluid-particle flows in bend geometries are present in many industrial, pharmaceutical, and biomedical applications. Particle deposition has been studied extensively; however, little attention has been paid to the effect of particle sedimentation on particle position and deposition in different pipe geometry combinations. This study presented a comprehensive analysis of sedimentation effects on particle flow behaviour in 90° circular pipe bends of micron particles in laminar pipe flows. Pipe geometry combinations consisted of eight pipe diameters, nine bend radii, and 30 particle diameters in a range of 1 to 100 μm. The results demonstrated the locations of particles that sedimented to the bottom half of the straight pipe section, and the particle positions upstream from the pipe bend entrance, which was no longer in a fully developed profile. These new locations represent the effects of gravity, pulling the particles down. While obtaining these positions can be found through CFD analysis, we proposed an analytical solution to predict the particle trajectory from different release locations that would help to identify the initial particle distribution at locations upstream to the bend, to obviate the need for long upstream straight pipe sections in the CFD analysis. [Display omitted] • The effect of particle sedimentation on pipe geometry combinations was studied. • The study emphasized the sedimentation for micron particles in laminar pipe flows. • Combinations: 8 pipe diameters, 9 bend radii, and 30 particle diameters in microns. • Sedimentation caused particle deposition on the inner wall side of the pipe bend. • To obviate the need for long upstream straight pipe sections in the CFD analysis. [ABSTRACT FROM AUTHOR]

A major issue among computational respiratory studies is the wide variety of nasal morphologies being studied, caused by both inter-population and inter-subject variations. Six nasal cavity geometries exhibiting diverse geometry variations were subjected to steady inhalation flow rate of 15 L/min. to determine if any consistent flow behaviour could be found. Despite vastly different geometries we were able to identify consistent flow patterns including relatively high velocity in the nasal valve region, followed by flow continuing predominantly in the inferior half of the airway. We also found conformity among models where the inhaled air reached a near-conditioned state by the middle of the nasal cavity. Air from the front of the face reached the olfactory regions while air from the lateral sides of the face moved through the inferior half of the nasal cavity. The ability to predict gross flow features provides a baseline flow field to compare against. This contributes towards establishing well defined flow predictions and be used as a comparison for future larger studies. [ABSTRACT FROM AUTHOR]

Chronic rhinosinusitis (CRS) is a common sinonasal condition that debilitates quality of life. Nasal sprays are inefficient for targeting the sinuses because of the highly inertial atomised droplets. This study evaluated sinus drug delivery via a nebuliser in a human nasal cavity using Computational Fluid Dynamics (CFD) simulations of different breathing conditions. The nebuliser was quantified through high-speed imaging of the spray plume and average velocity, while laser diffraction was used for droplet size distributions. A CT scan was acquired of a 75-year-old male with a confirmed diagnosis of CRS, and airway segmentation was performed to extract the nasal cavity and sinuses. Virtual surgery was then performed on the computational model. Two nozzle designs for the nebuliser under normal breathing, slow exhalation, and breath hold were investigated. The results demonstrated that drug delivery with a fully blocked nostril with a breath hold notably improved deposition targeting the maxillary sinuses and ethmoid sinuses, while using a nozzle that allowed co-flow of air was recommended for targeting the frontal and sphenoid sinuses. • A breath-hold following inhalation with nebulised droplets <15 μm improved ethmoid sinus deposition. • An occluded nostril with 15 μm droplets improved maxillary sinus deposition. • A fully blocked nostril with a breath hold improved deposition in the maxillary sinuses and ethmoid sinuses. • A partially blocked nostril improved deposition in the frontal and sphenoid sinuses. [ABSTRACT FROM AUTHOR]

• This study examined the impact of nasal adhesions on airflow and mucosal cooling. • A 'no-adhesion' model was compared against five replica models with adhesions. • Adhesions caused changes in airflow and mucosal cooling downstream. • Anterior adhesions created greater disruption to local airflow and mucosal cooling • Posterior adhesions had a small effect on overall airflow and mucosal cooling. Nasal adhesions are a known postoperative complication following surgical procedures for nasal airway obstruction (NAO); and are a common cause of surgical failure, with patients often reporting significant NAO, despite relatively minor adhesion size. Division of such nasal adhesions often provides much greater relief than anticipated, based on the minimal reduction in cross-sectional area associated with the adhesion. The available literature regarding nasal adhesions provides little evidence examining their quantitative and qualitative effects on nasal airflow using objective measures. This study examined the impact of nasal adhesions at various anatomical sites on nasal airflow and mucosal cooling using computational fluid dynamics (CFD). A high-resolution CT scan of the paranasal sinuses of a 25-year-old, healthy female patient was segmented to create a three-dimensional nasal airway model. Virtual nasal adhesions of 2.5 mm diameter were added to various locations within the nasal cavity, representing common sites seen following NAO surgery. A series of models with single adhesions were created. CFD analysis was performed on each model and compared with a baseline no-adhesion model, comparing airflow and heat and mass transfer. The nasal adhesions resulted in no significant change in bulk airflow patterns through the nasal cavity. However, significant changes were observed in local airflow and mucosal cooling around and immediately downstream to the nasal adhesions. These were most evident with anterior nasal adhesions at the internal valve and anterior inferior turbinate. Postoperative nasal adhesions create local airflow disruption, resulting in reduced local mucosal cooling on critical surfaces, explaining the exaggerated perception of nasal obstruction. In particular, anteriorly located adhesions created greater disruption to local airflow and mucosal cooling, explaining their associated greater subjective sensation of obstruction. [ABSTRACT FROM AUTHOR]