Computational investigation of dust mite allergens in a realistic human nasal cavity

Endoscopic and Radiologic Central Compartment Disease as Predictors of Perennial Inhalant Allergen Sensitization in Chronic Rhinosinusitis

BACKGROUND

Central compartment atopic disease (CCAD) is a recently described variant of chronic rhinosinusitis (CRS) strongly associated with atopy. The association between central compartment disease (CCD) and inhalant allergy is not well established in South-East Asia, where perennial allergic rhinitis is common.

OBJECTIVES

The primary objective was to evaluate endoscopic and radiologic CCD as predictors of perennial allergen sensitization in primary CRS. The secondary objective was to compare clinical characteristics of CCAD with other CRS subtypes (CRSwNP and CRSsNP).

METHODS

A retrospective study of consecutive patients with primary CRS who underwent endoscopic sinus surgery at our institution was performed. Allergen sensitization was confirmed by skin or serum testing. Endoscopy records and computed tomography scans of paranasal sinuses were reviewed for CCD. The diagnostic accuracy of endoscopic and radiologic CCD in predicting atopy was calculated.

RESULTS

There were 104 patients (43 CCAD, 30 CRSwNP and 31 CRSsNP). Endoscopic CCD was significantly associated with aeroallergen sensitization (odds ratio (OR) 3.99, 95% confidence interval (CI) 1.65-9.67, P = 0.002). Endoscopic CCD predicted atopy with 57% sensitivity, 72% specificity, 69% positive predictive value and positive likelihood ratio of 2.05. Radiologic CCD was not associated with aeroallergen sensitization (OR 0.728, 95%CI 0.292-1.82, P = 0.496). There were more CCAD patients who reported hyposmia (86% vs 42%, P < 0.001) and had anosmia on olfactory testing than CRSsNP (65% vs 14%, P = 0.015). The prevalence of atopy was significantly higher in CCAD than CRSwNP and CRSsNP (70% vs 37% and 42%, P = 0.015 and P = 0.05, respectively). Median serum total immunoglobulin E was higher in CCAD (283 IU/ml) and CRSwNP (127 IU/ml) than CRSsNP (27 IU/ml, P = 0.006 and P = 0.042, respectively).

CONCLUSIONS

Endoscopic CCD was a better predictor of inhalant allergy than radiologic CCD in primary CRS, in a locale of perennial allergic rhinitis.

Numerical and experimental analysis of pollen inhalation exposure in nasal airways following various middle turbinectomy

BACKGROUND

Middle turbinectomy (MT) has always been controversial. MT significantly alters the anatomy and redistributes the inhaled air. The current study is designed to quantify the effect of MT with varying resection volumes on airflow and associated pollen inhalation exposure characteristics in the nasal airways.

METHODS

Six realistic models following bilateral comprehensive Functional Endoscopic Sinus Surgery (FESS) deriving from CT images were constructed and their corresponding post-MT models with four types of MT procedures were virtually conducted. Inhalation exposure to pollen particles was simulated by the Computational Fluid-Particle Dynamics (CFPD) approach and validated through in vitro experiments.

RESULTS

Following the excision of the middle turbinate, a significant escalation in airflow was observed within the upper-middle region of the nasal cavities. Pollen deposition was observed to be more prominent in the nasal septum, laryngopharynx, and maxillary sinus, varying with the types of MT procedures. Notably, particles with diameters smaller than 50 μm exhibited two distinct "high peaks" and three "small peaks" within the nasal airways.

CONCLUSION

MT resulted in increased airflow volume within the upper-middle region of the nasal cavities. Following MT, notable shifts in pollen particle deposition hot spots were observed, transitioning from the nasal vestibule, nasal septum, and middle meatus to the nasal septum and laryngopharynx. These findings are anticipated to contribute valuable perspectives on pollen inhalation exposure risk assessments following diverse MT surgical interventions.

Effect of different degrees of adenoid hypertrophy on pediatric upper airway aerodynamics: a computational fluid dynamics study

To improve the diagnostic accuracy of adenoid hypertrophy (AH) in children and prevent further complications in time, it is important to study and quantify the effects of different degrees of AH on pediatric upper airway (UA) aerodynamics. In this study, based on computed tomography (CT) scans of a child with AH, UA models with different degrees of obstruction (adenoidal-nasopharyngeal (AN) ratio of 0.9, 0.8, 0.7, and 0.6) and no obstruction (AN ratio of 0.5) were constructed through virtual surgery to quantitatively analyze the aerodynamic characteristics of UA with different degrees of obstruction in terms of the peak velocity, pressure drop (△P), and maximum wall shear stress (WSS). We found that two obvious whirlpools are formed in the anterior upper part of the pediatric nasal cavity and in the oropharynx, which is caused by the sudden increase in the nasal cross-section area, resulting in local flow separation and counterflow. In addition, when the AN ratio was ≥ 0.7, the airflow velocity peaked at the protruding area in the nasopharynx, with an increase 1.1-2.7 times greater than that in the nasal valve area; the △P in the nasopharynx was significantly increased, with an increase 1.1-6.8 times greater than that in the nasal cavity; and the maximum WSS of the posterior wall of the nasopharynx was 1.1-4.4 times larger than that of the nasal cavity. The results showed that the size of the adenoid plays an important role in the patency of the pediatric UA.

A Prospective Analysis of Systemic and Local Aeroallergen Sensitivity in Central Compartment Atopic Disease

OBJECTIVE

To compare systemic allergen sensitivity and local allergen sensitivity in the sinonasal tissue of patients with a recently identified subtype of chronic rhinosinusitis strongly associated with allergy: central compartment atopic disease (CCAD).

STUDY DESIGN

Prospective cohort study.

SETTING

Academic tertiary care rhinology clinic.

METHODS

Fifteen participants with endoscopic and radiographic evidence of CCAD underwent systemic allergy testing with skin testing and measurement of serum specific immunoglobulin E (sIgE) to 15 regionally common aeroallergens. Local allergen sensitivity was determined by measuring sIgE to these same 15 allergens in their sinonasal tissue. sIgE testing was performed by ImmunoCAP assay.

RESULTS

Of the 15 participants, 14 were sensitive to at least 1 allergen locally in the central compartment and systemically on skin or serum testing. Among all participants, 4 were sensitive to allergens on central compartment sIgE testing that they were not sensitive to on skin and serum sIgE testing (range, 1-8 discordant allergens). Comparisons between local and systemic aeroallergen sensitivity results showed statistically significant correlations (P < .05) ranging from weak to strong.

CONCLUSION

Systemic allergy testing is recommended in the initial workup for CCAD. Local allergen sensitivities may be present in a subset of patients with CCAD. Further study of the clinical significance of these sensitivities should be undertaken in CCAD, with evaluation of the role of medical therapies and allergen immunotherapy in the treatment of CCAD.

Nasal Irrigation Delivery in Three Post-FESS Models From a Squeeze-bottle Using CFD

Purpose

Nasal saline irrigation is highly recommended in patients following functional endoscopic sinus surgery (FESS) to aid the postoperative recovery. Post-FESS patients have significantly altered anatomy leading to markedly different flow dynamics from those found in pre-op or non-diseased airways, resulting in unknown flow dynamics.

Methods

This work investigated how the liquid stream disperses through altered nasal cavities following surgery using Computational Fluid Dynamics (CFD). A realistic squeeze profile was determined from physical experiments with a 27-year-old male using a squeeze bottle with load sensors. The administration technique involved a head tilt of 45-degrees forward to represent a head position over a sink. After the irrigation event that lasted 4.5 s, the simulation continued for an additional 1.5 s, with the head orientation returning to an upright position.

Results

The results demonstrated that a large maxillary sinus ostium on the right side allows saline penetration into this sinus. The increased volume of saline entering the maxillary sinus limits the saline volume available to the rest of the sinonasal cavity and reduces the surface coverage of the other paranasal sinuses. The average wall shear stress was higher on the right side than on the other side for two patients. The results also revealed that head position alters the sinuses’ saline residual, especially the frontal sinuses.

Conclusion

While greater access to sinuses is achieved through FESS surgery, patients without a nasal septum limits posterior sinus penetration due to the liquid crossing over to the contralateral cavity and exiting the nasal cavity early.

Numerical Simulation of Aspergillus Niger Spore Deposition in Nasal Cavities of a Population in Northwest China

Background: As common pathogens in the human respiratory tract, fungal-spore-related health risks have been challenging to evaluate properly. This paper presents numerical simulations of particle deposition of Aspergillus niger spores in human nasal cavities. Methods: 30 healthy adults (including 60 nasal chambers) who lived in northwest China were recruited to conduct a nasal cavity numerical simulation using computational fluid dynamics–discrete phase model (CFD-DPM). The deposition rate in each anatomic area and its influencing variables, such as body position and respiratory flow rate, were analyzed. Results: (1) Under a resting condition, only about 5.57% ± 1.51% Aspergillus niger spores were deposited in the nasal cavity, while most of them escaped from the nasopharynx, and 0.31% ± 0.20% spores entered the maxillary sinus; (2) under an exercising condition, spores deposited in the nasal cavity were about 2.09 times as many as that in the resting state; (3) in a lying position, the A. niger spores deposited evenly on the lateral wall of the nasal cavity and the sinus when compared with a standing position. However, the deposition rate in each anatomic area did not change significantly.

Wet surface wall model for latent heat exchange during evaporation

Air conditioning is a dual heat and mass transfer process, and the human nasal cavity achieves this through the mucosal wall surface, which is supplied with an energy source through the sub-epithelial network of capillaries. Computational studies of air conditioning in the nasal cavity have included temperature and humidity, but most studies solved these flow parameters separately, and in some cases, a constant mucosal surface temperature was used. Recent developments demonstrated that both heat and mass transfer need to be modeled. This work expands on existing modeling efforts in accounting for the nasal cavity's dual heat and mass transfer process by introducing a new subwall model, given in the Supplementary Materials. The model was applied to a pipe geometry, and a human nasal cavity was recreated from CT-scans, and six inhalation conditions were studied. The results showed that when the energy transfer from the latent heat of evaporation is included, there is a cooling effect on the mucosal surface temperature.

On the design of particle filters inspired by animal noses

Passive filtering is a common strategy to reduce airborne disease transmission and particulate contaminants across scales spanning orders of magnitude. The engineering of high-performance filters with relatively low flow resistance but high virus- or particle-blocking efficiency is a non-trivial problem of paramount relevance, as evidenced in the variety of industrial filtration systems and face masks. Next-generation industrial filters and masks should retain sufficiently small droplets and aerosols while having low resistance. We introduce a novel 3D-printable particle filter inspired by animals' complex nasal anatomy. Unlike standard random-media-based filters, the proposed concept relies on equally spaced channels with tortuous airflow paths. These two strategies induce distinct effects: a reduced resistance and a high likelihood of particle trapping by altering their trajectories with tortuous paths and induced local flow instability. The structures are tested for pressure drop and particle filtering efficiency over different airflow rates. We have also cross-validated the observed efficiency through numerical simulations. We found that the designed filters exhibit a lower pressure drop, compared to commercial masks and filters, while capturing particles bigger than approximately 10 μm. Our findings could facilitate a novel and scalable filter concept inspired by animal noses.

Biomedical and biophysical limits to mathematical modeling of pulmonary system mechanics: a scoping review on aerosol and drug delivery

Undoubtedly, the construction of the biomechanical geometry systems with the help of computer tomography (CT) and magnetic resonance imaging (MRI) has made a significant advancement in studying in vitro numerical models as accurately as possible. However, some simplifying assumptions in the computational studies of the respiratory system have caused errors and deviations from the in vivo actual state. The most important of these hypotheses is how to generate volume from the point cloud exported from CT or MRI images, not paying attention to the wall thickness and its effect in computational fluid dynamic method, statistical logic of aerosol trap in software; and most importantly, the viscoelastic effect of respiratory tract wall in living tissue pointed in the fluid-structure interaction method. So that applying the viscoelastic dynamic mesh effect in the form of the moving deforming mesh can be very effective in achieving more appropriate response quality. Also, changing the volume fraction of the pulmonary extracellular matrix constituents leads to changes in elastic modulus (storage modulus) and the viscous modulus (loss modulus) of lung tissue. Therefore, in the biomedical computational methods where the model wall is considered flexible, the viscoelastic properties of the texture must be considered correctly.

From SARS-CoV-2 infection to COVID-19 morbidity: an in silico projection of virion flow rates to the lower airway via nasopharyngeal fluid boluses

Background: While the nasopharynx is initially the dominant upper airway infection site for SARS-CoV-2, the physiologic mechanism launching the infection at the lower airway is still not well-understood. Based on the rapidity of infection progression to the lungs, it has been hypothesized that the nasopharynx may be acting as the primary seeding zone for subsequent contamination of the lower airway via aspiration of virus-laden boluses of nasopharyngeal fluids. Methodology: To examine the plausibility of the aspiration-driven mechanism, we have computationally tracked the inhalation process in three anatomic airway reconstructions and have quantified the nasopharyngeal liquid volume transmitted to the lower airspace during each aspiration. Results: Extending the numerical trends on aspiration volume to earlier records on aspiration frequencies indicates a total aspirated nasopharyngeal liquid volume of 0.3 – 0.76 ml/day. Subsequently, for mean sputum viral load, our modeling projects that the number of virions reaching the lower airway will range over 2.1×106 – 5.3×106 /day; for peak viral load, the corresponding number hovers between 7.1×108 – 1.8×109. Conclusions: The virion transmission findings fill in a key piece of the mechanistic puzzle on the systemic progression of SARS-CoV-2, and subjectively point to health conditions like dysphagia, with proclivity to increased aspiration, as some of the potential underlying risk factors for aggressive lung infections.

Inhalation and deposition of spherical and pollen particles after middle turbinate resection in a human nasal cavity

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/m³ 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.

Effects of head tilt on squeeze-bottle nasal irrigation - A computational fluid dynamics study

Nasal irrigation is a widely recognized treatment for several sinonasal diseases. However, there is a lack of clear evidence-based guidelines for optimal irrigation delivery to improve lavage and topical drug delivery. This study uses computational fluid dynamics (CFD) to assess the effects of different head tilt positions on sinonasal coverage, residence time and shear stresses in squeeze-bottle nasal irrigation. A sinonasal cavity computational model was constructed from a high-resolution CT scan of a healthy, 25-year-old Asian female. The Volume of Fluid method was used to track the interface between the two immiscible fluids (air and water). The direction of gravity was varied to simulate different head tilt-positions (0° Straight, 45° Forward, 45° Left, 45° Right and 45° Backward) during nasal irrigation with 150 mL liquid via a squeeze bottle through the left nostril for 2 s with a 0.1 s acceleration/deceleration time. The results showed that the 45° backward head tilt position was the most effective in delivering irrigation to the ethmoid, frontal and sphenoid sinuses. Altering head tilt had minimal impact on irrigation delivery to the maxillary sinuses. Maximum wall shear stresses seen in localized areas of the sinus mucosa varied significantly with different head tilt angles. However, the difference in mean wall shear stress on the sinus surfaces was marginal with changing head tilt position. The findings suggest that an optimized head tilt position can be identified to improve liquid irrigation to targeted sinuses, as per treatment requirements (lavage and topical drug delivery).

Computational characterization of inhaled droplet transport to the nasopharynx

How human respiratory physiology and the transport phenomena associated with inhaled airflow in the upper airway proceed to impact transmission of SARS-CoV-2, leading to the initial infection, stays an open question. An answer can help determine the susceptibility of an individual on exposure to a COVID-2019 carrier and can also provide a preliminary projection of the still-unknown infectious dose for the disease. Computational fluid mechanics enabled tracking of respiratory transport in medical imaging-based anatomic domains shows that the regional deposition of virus-laden inhaled droplets at the initial nasopharyngeal infection site peaks for the droplet size range of approximately 2.5-19 [Formula: see text]. Through integrating the numerical findings on inhaled transmission with sputum assessment data from hospitalized COVID-19 patients and earlier measurements of ejecta size distribution generated during regular speech, this study further reveals that the number of virions that may go on to establish the SARS-CoV-2 infection in a subject could merely be in the order of hundreds.

Computational modelling of nasal respiratory flow

CFD has emerged as a promising diagnostic tool for clinical trials, with tremendous potential. However, for real clinical applications to be useful, overall statistical findings from large population samples (e.g., multiple cases and models) are needed. Fully resolved solutions are not a priority, but rather rapid solutions with fast turn-around times are desired. This leads to the issue of what are the minimum modelling criteria for achieving adequate accuracy in respiratory flows for large-scale clinical applications, with a view to rapid turnaround times. This study simulated a highly-resolved solution using the large eddy simulation (LES) method as a reference case for comparison with lower resolution models that included larger time steps and no turbulence modelling. Differences in solutions were quantified by pressure loss, flow resistance, unsteadiness, turbulence intensity, and hysteresis effects from multiple cycles. The results demonstrated that sufficient accuracy could be achieved with lower resolution models if the mean flow was considered. Furthermore, to achieve an established transient result unaffected by the initial start-up quiescent effects, the results need to be taken from at least the second respiration cycle. It was also found that the exhalation phase exhibited strong turbulence. The results are expected to provide guidance for future modelling efforts for clinical and engineering applications requiring large numbers of cases using simplified modelling approaches.

The influenza virus, SARS-CoV-2, and the airways: Clarification for the otorhinolaryngologist

The influenza virus and SARS-CoV-2 cause trivial upper and severe lower respiratory infections (Influenza virus 290,000 to 650,000 deaths/year). These viruses come into contact with the airways either by direct projection, by secondary inhalation of airborne droplets, or by handling (fomites). The objective of this article is to clarify the mechanisms of production and penetration of droplets of secretions emitted during all expiratory phenomena likely to transport these viruses and come into contact with the respiratory mucosa. The droplets>5μm follow the laws of ballistics, those<5μm follow Brownian motion and remain suspended in the air. The aerosols of droplets are very heterogeneous whether the subject is healthy or sick. During an infectious period, not all droplets contain viral RNA. If these RNAs are detectable around patients, on surfaces, and in the ambient air at variable distances according to the studies (from 0.5m to beyond the patient's room), this is without prejudice to the infectious nature (viability) of the virus and the minimum infectious dose. There is a time lag between the patient's infectious period and that of RNA detection for both viruses. Subsequently, the inhaled particles must meet the laws of fluid dynamics (filtration) to settle in the respiratory tree. All of this partly explains the contagiousness and the clinical expression of these two viruses from the olfactory cleft to the alveoli.

Characterization of nasal irrigation flow from a squeeze bottle using computational fluid dynamics

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.