Geometry and airflow dynamics analysis in the nasal cavity during inhalation

Impact of Intra-Phenotypic Nasal Vestibular Variation on Local Airflow Dynamics

OBJECTIVES

Many individuals with healthy normal nasal anatomy and function exhibit a prominent notch indentation at the junction of the ala and sidewall, specifically around the anterior-superior region of the unilateral nasal vestibule up to the internal nasal valve. This study evaluates the influence of various sizes of notched indentations at the anterior nasal airway on local airflow pattern.

METHODS

A retrospective study involving 25 healthy individuals, each exhibiting at least one unilateral notched indentation (40 total airways). Each individual's notched indentation was quantified after subject-specific three-dimensional nasal airway reconstruction from radiographic images. Computational fluid dynamics modeling was used to simulate nasal inspiratory airflow in each nasal airway at 15 L/min. Localized airflow distributions passing through the inferior, middle, and superior regions were calculated at 15 cross sections.

RESULTS

Notched indentation size ranged 1.75-86.84 mm2 (average = 22.37 mm2). At the anterior airway, notched size significantly correlated with inferior airflow volume (R = 0.32, p = 0.04) but not in the middle (R = 0.21, p = 0.20) or superior (R = 0.06, p = 0.70) regions, whereas middle and superior regional resistance values were significantly correlated with notched size (middle: R = 0.54, p < 0.001; superior: R = 0.41, p = 0.009). Medially, resistance at the middle region significantly correlated with notched size (R = 0.56, p < 0.001). At the posterior airway, airflow distributions through the inferior, middle, and superior regions demonstrated weak correlation with notched size (inferior: R = 0.24, p = 0.14, middle: R = 0.24, p = 0.13; superior:R = 0.03, p = 0.83), whereas resistance was significantly correlated in the middle and inferior regions (middle: R = 0.56, p < 0.001;inferior: R = 0.43, p = 0.006).

CONCLUSIONS

Anterior nasal airway notched indentation size had significantly stronger influence on localized airflow volume through the anterior-inferior airway than other regions of the nasal passage.

LEVEL OF EVIDENCE

N/A Laryngoscope, 2024.

Assessing nasal airway resistance and symmetry: An approach to global perspective through computational fluid dynamics

This study aimed to explore the variability in nasal airflow patterns among different sexes and populations using computational fluid dynamics (CFD). We focused on evaluating the universality and applicability of dimensionless parameters R (bilateral nasal resistance) and ϕ (nasal flow asymmetry), initially established in a Caucasian Spanish cohort, across a broader spectrum of human populations to assess normal breathing function in healthy airways. In this retrospective study, CT scans from Cambodia (20 males, 20 females), Russia (20 males, 18 females), and Spain (19 males, 19 females) were analyzed. A standardized CFD workflow was implemented to calculate R-ϕ parameters from these scans. Statistical analyses were conducted to assess and compare these parameters across different sexes and populations, emphasizing their distribution and variances. Our results indicated no significant sex-based differences in the R parameter across the populations. However, moderate sexual dimorphism in the ϕ parameter was observed in the Cambodian group. Notably, no geographical differences were found in either R or ϕ parameters, suggesting consistent nasal airflow characteristics across the diverse human groups studied. The study also emphasized the importance of using dimensionless variables to effectively analyze the relationships between form and function in nasal airflow. The observed consistency of R-ϕ parameters across various populations highlights their potential as reliable indicators in both medical practice and further CFD research, particularly in diverse human populations. Our findings suggest the potential applicability of dimensionless CFD parameters in analyzing nasal airflow, highlighting their utility across diverse demographic and geographic contexts. This research advances our understanding of nasal airflow dynamics and underscores the need for additional studies to validate these parameters in broader population cohorts. The approach of employing dimensionless parameters paves the way for future research that eliminates confounding size effects, enabling more accurate comparisons across different populations and sexes. The implications of this study are significant for the advancement of personalized medicine and the development of diagnostic tools that accommodate individual variations in nasal airflow.

Beyond skeletal studies: A computational analysis of nasal airway function in climate adaptation

OBJECTIVES

Ecogeographic variation in human nasal anatomy has historically been analyzed on skeletal morphology and interpreted in the context of climatic adaptations to respiratory air-conditioning. Only a few studies have analyzed nasal soft tissue morphology, actively involved in air-conditioning physiology.

MATERIALS AND METHODS

We used in vivo computer tomographic scans of (N = 146) adult individuals from Cambodia, Chile, Russia, and Spain. We conducted (N = 438) airflow simulations during inspiration using computational fluid dynamics to analyze the air-conditioning capacities of the nasal soft tissue in the inflow, functional, and outflow tract, under three different environmental conditions: cold-dry; hot-dry; and hot-humid. We performed statistical comparisons between populations and sexes.

RESULTS

Subjects from hot-humid regions showed significantly lower air-conditioning capacities than subjects from colder regions in all the three conditions, specifically within the isthmus region in the inflow tract, and the anterior part of the internal functional tract. Posterior to the functional tract, no differences were detected. No differences between sexes were found in any of the tracts and under any of the conditions.

DISCUSSION

Our statistical analyses support models of climatic adaptations of anterior nasal soft tissue morphology that fit with, and complement, previous research on dry skulls. However, our results challenge a morpho-functional model that attributes air-conditioning capacities exclusively to the functional tract located within the nasal cavity. Instead, our findings support studies that have suggested that both, the external nose and the intra-facial soft tissue airways contribute to efficiently warming and humidifying air during inspiration. This supports functional interpretations in modern midfacial variation and evolution.

Long-term olfactory loss post-COVID-19: Pathobiology and potential therapeutic strategies

An acute loss of smell emerged as a striking symptom present in roughly half of the people infected with the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus in the early phases of the COVID-19 pandemic. In most COVID-19 patients, olfaction recovers over the course of a few weeks. However, a lasting partial or complete loss of smell, often associated with distorted olfactory perceptions termed parosmia, has emerged as a widespread problem impacting at least 5%-10% of those who experience anosmia due to COVID-19. Our inability to offer effective therapies to this hyposmic or anosmic population, comprising millions of patients, highlights an enormous unmet need for the medical system. Here, we summarize the current understanding of the pathobiology causing acute olfactory loss due to SARS-CoV-2 infection, focusing on how the virus interacts with the peripheral olfactory system, a major site of viral infection. We also explore the problem of long-COVID olfactory dysfunction, which may accompany other persistent systemic disorders collectively termed postacute sequelae of COVID-19. Specifically, we discuss an emerging model focused on unresolved immune cell activity driving ongoing dysfunction. Finally, we review current and future therapeutic approaches aimed at restoring olfactory function.

Computational Fluid Dynamics and Its Potential Applications for the ENT Clinician

This article is an examination of computational fluid dynamics in the field of otolaryngology, specifically rhinology. The historical development and subsequent application of computational fluid dynamics continues to enhance our understanding of various sinonasal conditions and surgical planning in the field today. This article aims to provide a description of computational fluid dynamics, the methods for its application, and the clinical relevance of its results. Consideration of recent research and data in computational fluid dynamics demonstrates its use in nonhistological disease pathology exploration, accompanied by a large potential for surgical guidance applications. Additionally, this article defines in lay terms the variables analyzed in the computational fluid dynamic process, including velocity, wall shear stress, area, resistance, and heat flux.

Nasal airway obstruction in patients with cleft lip nasal deformity: A systematic review

BACKGROUND

Cleft lip nasal deformity (CLND)-associated nasal airway obstruction (CL-NAO) may be inadequately characterized, with its functional implications subsequently underappreciated and neglected. The purpose of this systematic review is to (1) summarize the available assessment results in CL-NAO, (2) evaluate the reliability of current assessment tools, and (3) identify ongoing gaps and inconsistencies for future study.

METHODS

A systematic search of the MEDLINE, EMBASE, and Scopus databases was performed for articles studying CL-NAO. Articles focusing on noncleft populations or surgical techniques were excluded. Extracted data included information about study design, patient demographics, medical history, and assessment scores.

RESULTS

Twenty-six articles met criteria for inclusion. Assessments included patient-reported outcome measures (PROMs), anatomic characterizations of CLND, and nasal airflow and resistance studies. Objective assessments were generally more reliable than subjective assessments in CLND. Unilateral CLND was better represented in the literature than bilateral CLND. For unilateral CLND, the cleft side was more obstructed than the noncleft side, with stereotyped patterns of anterior nasal deformity but varied middle and posterior deformity patterns. Overall, there was considerable heterogeneity in study design regarding stratification of CLND cohorts by age, cleft phenotype and laterality, and surgical history.

CONCLUSIONS

A wide range of subjective and objective assessment tools were used to characterize CL-NAO, including PROMs, anatomic measurements, and airflow and resistance metrics. Overall, objective assessments of CL-NAO were more reliable than subjective surveys, which may have resulted from variable expectations regarding nasal patency in the CLND population combined with large heterogeneity in study design.

Parameter characteristics in intranasal drug delivery: A key to targeting medications to the olfactory airspace

BACKGROUND

The nose is a viable pathway for topical drug delivery to the olfactory cleft for treatment of obstructive smell loss and nose-to-brain drug delivery. This study investigates how variations in nasal vestibule morphology influence intranasal spray drug transport to the olfactory cleft and olfactory roof/bulb regions.

METHODS

The unilateral nasal vestibule morphology in three healthy subjects with healthy normal nasal anatomy was classified as Elongated (Subject DN001), Notched (Subject DN002), and Standard (Subject DN003). Computational fluid and particle dynamics modelling were used to simulate nasal airflow and drug particle transport to the olfactory cleft and olfactory roof/bulb regions in each subject-specific nasal cavity. To evaluate highest drug depositions in these regions, the particle transport simulations involved extensive parameter combination analyses: 6 inspiratory flow rates mimicking resting to sniffing (10-50 L/min); 5 spray release locations (Top, Bottom, Central, Lateral, and Medial); 5 head positions (Upright, Tilted Forward, Tilted Back, Supine, and Mygind); 3 particle velocities (1, 5, and 10 m/s); 350,000 μm-particles (1-100 μm) and 346,500 nanoparticles (10-990 nm).

FINDINGS

Particle size groups with highest depositions in olfactory cleft: DN001 left = 28.4% at 11-20 μm, right = 75.3% at 6-10 μm; DN002 left = 16.8% at 1-5 μm, right = 45.3% at 30-40 nm; DN003 left = 29.1% at 21-30 μm, right = 15.9% at 6-10 μm. Highest depositions in olfactory roof/bulb: DN001 left = 6.5% at 11-20 μm, right = 26.4% at 11-20 μm; DN002 left = 3.6% at 1-5 μm, right = 2.6% at 1-5 μm; DN003 left = 2.8% at 21-30 μm, right = 1.7% at 31-40 μm.

INTERPRETATION

DN001 (Elongated nasal vestibule) had the most deposition in the olfactory regions. Micron-particles size groups generally had better deposition in the olfactory regions.

Computational Rhinology: Unraveling Discrepancies between In Silico and In Vivo Nasal Airflow Assessments for Enhanced Clinical Decision Support

Computational rhinology is a specialized branch of biomechanics leveraging engineering techniques for mathematical modelling and simulation to complement the medical field of rhinology. Computational rhinology has already contributed significantly to advancing our understanding of the nasal function, including airflow patterns, mucosal cooling, particle deposition, and drug delivery, and is foreseen as a crucial element in, e.g., the development of virtual surgery as a clinical, patient-specific decision support tool. The current paper delves into the field of computational rhinology from a nasal airflow perspective, highlighting the use of computational fluid dynamics to enhance diagnostics and treatment of breathing disorders. This paper consists of three distinct parts-an introduction to and review of the field of computational rhinology, a review of the published literature on in vitro and in silico studies of nasal airflow, and the presentation and analysis of previously unpublished high-fidelity CFD simulation data of in silico rhinomanometry. While the two first parts of this paper summarize the current status and challenges in the application of computational tools in rhinology, the last part addresses the gross disagreement commonly observed when comparing in silico and in vivo rhinomanometry results. It is concluded that this discrepancy cannot readily be explained by CFD model deficiencies caused by poor choice of turbulence model, insufficient spatial or temporal resolution, or neglecting transient effects. Hence, alternative explanations such as nasal cavity compliance or drag effects due to nasal hair should be investigated.

Impact of nasal septal perforation on the airflow and air-conditioning characteristics of the nasal cavity

We investigated (1) how nasal septal perforations (NSPs) modify nasal airflow and air-conditioning characteristics and (2) how the modifications of nasal airflow are influenced by the size and location of the NSP. Computed tomography scans of 14 subjects with NSPs were used to generate nasal cavity models. Virtual repair of NSPs was conducted to examine the sole effect of NSPs on airflow. The computational fluid dynamics technique was used to assess geometric and airflow parameters around the NSPs and in the nasopharynx. The net crossover airflow rate, the increased wall shear stress (WSS) and the surface water-vapor flux on the posterior surface of the NSPs were not correlated with the size of the perforation. After the virtual closure of the NSPs, the levels in relative humidity (RH), air temperature (AT) and nasal resistance did not improve significantly both in the choanae and nasopharynx. A geometric parameter associated with turbinate volume, the surface area-to-volume ratio (SAVR), was shown to be an important factor in the determination of the RH and AT, even in the presence of NSPs. The levels of RH and AT in the choanae and nasopharynx were more influenced by SAVR than the size and location of the NSPs.

Insights into exercise-induced rhinitis based on nasal aerodynamics induced by airway morphology

BACKGROUND

Exercise-induced rhinitis (EIR) is a poorly understood phenomenon that may be related to increased inspiratory airflow. Characterization of the development of EIR is important to understand contributing factors.

OBJECTIVE

To characterize how different nasal morphologies respond to airflow-related variables during rapid/deep inspiratory conditions.

METHODS

Subject-specific nasal airways were reconstructed from radiographic images. Unilateral airways were classified as Standard, Notched, or Elongated accord to their distinct nasal vestibule morphology. Computational fluid dynamics simulations were performed at various airflow rates.

RESULTS

For all simulated flow rates, average resistance at the nasal vestibule, airflow velocity and wall sheer stress were highest in Notched. Average mucosal heat flux was highest in Standard. Notched phenotypes showed lower mean percent increases from 10 L/min to 50 L/min in all computed variables.

CONCLUSION

Resistance values and airflow velocities depicted a more constricted nasal vestibule in the Notched phenotypes, while perception of nasal mucosal cooling (heat flux) favored the Standard phenotypes. Different nasal phenotypes may predispose to EIR.

Comparison of microparticle transport and deposition in nasal cavity of three different age groups

Objective: The nasal cavity effectively captures the particles present in inhaled air, thereby preventing harmful and toxic pollutants from reaching the lungs. This filtering ability of the nasal cavity can be effectively utilized for targeted nasal drug delivery applications. This study aims to understand the particle deposition patterns in three age groups: neonate, infant, and adult.Materials and methods: The CT scans are built using MIMICS 21.0, followed by CATIA V6 to generate a patient-specific airway model. Fluid flow is simulated using ANSYS FLUENT 2021 R2. Spherical monodisperse microparticles ranging from 2 to 60 µm and a density of 1100 kg/m3 are simulated at steady-state and sedentary inspiration conditions.Results: The highest nasal valve depositions for the neonate are 25% for 20 µm, for infants, 10% for 50 µm, 15% for adults, and 15% for 15 µm. At mid nasal region, deposition of 15% for 20 µm is observed for infant and 8% for neonate and adult nasal cavities at a particle size of 10 and 20 µm, respectively. The highest particle deposition at the olfactory region is about 2.7% for the adult nasal cavity for 20 µm, and it is <1% for neonate and infant nasal cavities.Discussion and conclusions: The study of preferred nasal depositions during natural sedentary breathing conditions is utilized to determine the size that allows medication particles to be targeted to specific nose regions.

Characterizing Olfactory Dysfunction in Patients with Unilateral Cleft Lip Nasal Deformities

Background: Unilateral cleft lip nasal deformity (uCLND) is associated with olfactory dysfunction, but the underlying etiology remains poorly understood. Objective: To investigate the etiology of uCLND-associated olfactory dysfunction using clinical, computational, and histologic assessments. Methods: Inclusion criteria: uCLND patients >16 years undergoing septorhinoplasty. Exclusion criteria: prior septoplasty or rhinoplasty, pregnancy, sinusitis. Measured outcomes: patient-reported scores, rhinomanometry, smell identification and threshold tests, computational fluid dynamics (CFD) airflow simulations, and histologic analysis of olfactory epithelium. Results: Five uCLND subjects were included: 18-23 years, three male and two female, four left-sided cleft and one right-sided cleft. All subjects reported moderate to severe nasal obstruction. Smell identification and threshold tests showed varying degrees of hyposmia. Nasal resistance was higher on the cleft side versus noncleft side measured by rhinomanometry (median 3.85 Pa-s/mL, interquartile range [IQR] = 21.96, versus 0.90 Pa-s/mL, IQR = 5.17) and CFD (median 1.04 Pa-s/mL, IQR = 0.94 vs. 0.11 Pa-s/mL, IQR = 0.12). Unilateral olfaction varied widely and was dependent on unilateral percentage olfactory airflow. Biopsies revealed intact olfactory neuroepithelium. Conclusions: uCLND-associated olfactory dysfunction appears to be primarily conductive in etiology and highly susceptible to variations in nasal anatomy. Clinical Trial Registration number: NCT04150783.

Impact of the Location of Nasal Septal Deviation on the Nasal Airflow and Air Conditioning Characteristics

The location of nasal septal deviation (NSD) directly impacts nasal physiology. The objective is to examine, using computational fluid dynamics (CFD), the difference in the airflow and air conditioning characteristics according to the location of NSD. Twenty patients with septal deviation were divided into two: 10 caudal septal deviation (CSD) and 10 posterior septal deviation (PSD). Physiological variables were compared and numerical models for nasal cavity were created with CT scans. Cases with CSD had distinctive features including restricted airflow partition, larger nasal resistance, and decreased surface heat flux in the more obstructed side (MOS), and lower humidity and air temperature in the lesser obstructed side (LOS). Physiological differences were observed according to the location of septal deviation, CSD cases exhibit significantly more asymmetric airflow characteristics and air conditioning capacity between LOS and MOS.

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.

Numerical and Experimental Analysis of Drug Inhalation in Realistic Human Upper Airway Model

The demand for a more efficient and targeted method for intranasal drug delivery has led to sophisticated device design, delivery methods, and aerosol properties. Due to the complex nasal geometry and measurement limitations, numerical modeling is an appropriate approach to simulate the airflow, aerosol dispersion, and deposition for the initial assessment of novel methodologies for better drug delivery. In this study, a CT-based, 3D-printed model of a realistic nasal airway was reconstructed, and airflow pressure, velocity, turbulent kinetic energy (TKE), and aerosol deposition patterns were simultaneously investigated. Different inhalation flowrates (5, 10, 15, 30, and 45 L/min) and aerosol sizes (1, 1.5, 2.5, 3, 6, 15, and 30 µm) were simulated using laminar and SST viscous models, with the results compared and verified by experimental data. The results revealed that from the vestibule to the nasopharynx, the pressure drop was negligible for flow rates of 5, 10, and 15 L/min, while for flow rates of 30 and 40 L/min, a considerable pressure drop was observed by approximately 14 and 10%, respectively. However, from the nasopharynx and trachea, this reduction was approximately 70%. The aerosol deposition fraction alongside the nasal cavities and upper airway showed a significant difference in pattern, dependent on particle size. More than 90% of the initiated particles were deposited in the anterior region, while just under 20% of the injected ultrafine particles were deposited in this area. The turbulent and laminar models showed slightly different values for the deposition fraction and efficiency of drug delivery for ultrafine particles (about 5%); however, the deposition pattern for ultrafine particles was very different.

Gender Differences in Nasal Anatomy and Function Among Caucasians

Background: Anatomical variations influence nasal physiology, yet sex differences in physiology remains unclear. Objective: To investigate sex differences among Caucasians using computational fluid dynamics. Methods: Adult subjects were selected with normal nasal cone beam computed tomography (CBCT) images and Nasal Obstruction Symptom Evaluation scores ≤30. The CBCT images were used to create subject-specific airway models. Nasal surface area (SA) and volume were computed, and airflow and heat transfer were simulated. Results: The CBCT scans were taken from 23 females and 12 males. The SA and volume (males: mean = 25.0 cm3; females: mean = 19.5 cm3; p < 0.001; Cohen's d = 1.51) were significantly larger for males, but SA-to-volume ratio did not differ significantly. Although unilateral nasal resistance did not vary greatly, females had higher bilateral resistance (males: mean = 0.04 Pa.s/mL; females: mean = 0.05 Pa.s/mL; p = 0.044; Cohen's d = 0.37). Females had higher heat flux (males: mean = 158.5 W/m2; females: mean = 191.8 W/m2; p = 0.012; Cohen's d = 0.79), but males had larger SA where mucosal heat flux exceeds 50 W/m2. Conclusions: These findings suggest differences in normal nasal anatomy and physiology between Caucasian males and females, which may be useful when assessing sex-specific functional outcomes after nasal surgery.

Targeted drug delivery with polydisperse particle transport and deposition in patient-specific upper airway during inhalation and exhalation

Identifying the deposition pattern of inhaled pharmaceutical aerosols in the human respiratory system and understanding the effective parameters in this process is vital for more efficient drug delivery to this region. This study investigated aerosol deposition in a patient-specific upper respiratory airway and determined the deposition fraction (DF) and pressure drop across the airway. An experimental setup was developed to measure the pressure drop in the same realistic geometry printed from the patient-specific geometry. The unsteady simulations were performed with a flow rate of 15 L/min and different particle diameters ranging from 2 to 30 µm. The results revealed significant flow circulation after the nasal valve in the upper and oropharynx regions, and a maximum local velocity observed in the nasopharynx. Transient cumulative deposition fraction showed that after 2 s of the simulation, all particles deposit or escape the computational domain. About 30 % of the injected large particles (d_p ≥ 20 µm) deposited in the first 1 cm away from the nostril and more than 95 % deposited in the nasal airway before entering the oropharynx region. While almost 94 % deposition in trachea was composed of particles smaller than 5 µm. Approximately 20 % of inhaled fine particles (2-5 µm) deposited in the upper airway and the rest deposited in oropharynx, larynx and trachea.

Numerical and Machine Learning Analysis of the Parameters Affecting the Regionally Delivered Nasal Dose of Nano- and Micro-Sized Aerosolized Drugs

The nasal epithelium is an important target for drug delivery to the nose and secondary organs such as the brain via the olfactory bulb. For both topical and brain delivery, the targeting of specific nasal regions such as the olfactory epithelium (brain) is essential, yet challenging. In this study, a numerical model was developed to predict the regional dose as mass per surface area (for an inhaled mass of 2.5 mg), which is the biologically most relevant dose metric for drug delivery in the respiratory system. The role of aerosol diameter (particle diameter: 1 nm to 30 µm) and inhalation flow rate (4, 15 and 30 L/min) in optimal drug delivery to the vestibule, nasal valve, olfactory and nasopharynx is assessed. To obtain the highest doses in the olfactory region, we suggest aerosols with a diameter of 20 µm and a medium inlet air flow rate of 15 L/min. High deposition on the olfactory epithelium was also observed for nanoparticles below 1 nm, as was high residence time (slow flow rate of 4 L/min), but the very low mass of 1 nm nanoparticles is prohibitive for most therapeutic applications. Moreover, high flow rates (30 L/min) and larger micro-aerosols lead to highest doses in the vestibule and nasal valve regions. On the other hand, the highest drug doses in the nasopharynx are observed for nano-aerosol (1 nm) and fine microparticles (1-20 µm) with a relatively weak dependence on flow rate. Furthermore, using the 45 different inhalation scenarios generated by numerical models, different machine learning models with five-fold cross-validation are trained to predict the delivered dose and avoid partial differential equation solvers for future predictions. Random forest and gradient boosting models resulted in R² scores of 0.89 and 0.96, respectively. The aerosol diameter and region of interest are the most important features affecting delivered dose, with an approximate importance of 42% and 47%, respectively.

Analyses on the influence of normal nasal morphological variations on odorant transport to the olfactory cleft

OBJECTIVE

Olfaction requires a combination of sensorineural components and conductive components, but conductive mechanisms have not typically received much attention. This study investigates the role of normal nasal vestibule morphological variations in ten healthy subjects on odorant flux in the olfactory cleft.

MATERIALS AND METHODS

Computed tomography images were used to create subject-specific nasal models. Each subject's unilateral nasal cavity was classified according to its nasal vestibule shape as Standard or Notched. Inspiratory airflow simulations were performed at 15 L/min, simulating resting inspiration using computational fluid dynamics modeling. Odorant transport simulations for three odorants (limonene, 2,4-dinitrotoluene, and acetaldehyde) were then performed at concentrations of 200 ppm for limonene and acetaldehyde, and 0.2 ppm for dinitrotoluene. Olfactory cleft odorant flux was computed for each simulation.

RESULTS AND DISCUSSION AND CONCLUSION

Simulated results showed airflow in the olfactory cleft was greater in the Standard phenotype compared to the Notched phenotype. For Standard, median airflow was greatest in the anterior region (0.5006 L/min) and lowest in the posterior region (0.1009 L/min). Median airflow in Notched was greatest in the medial region (0.3267 L/min) and lowest in the posterior region (0.0756 L/min). Median olfactory odorant flux for acetaldehyde and limonene was greater in Standard (Acetaldehyde: Standard = 140.45 pg/cm2-s; Notched = 122.20 pg/cm2-s. Limonene: Standard = 0.67 pg/cm2-s; Notched = 0.65 pg/cm2-s). Median dinitrotoluene flux was greater in Notched (Standard = 2.86 × 10-4pg/cm2-s; Notched = 4.29 × 10-4 pg/cm2-s). The impact of nasal vestibule morphological variations on odorant flux at the olfactory cleft may have implications on individual differences in olfaction, which should be investigated further.

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.

The role of normal nasal morphological variations from race and gender differences on respiratory physiology

This study identifies anatomical and airflow-induced relationships based on nasal morphological variations due to inter- and intra-racial differences and gender. Subject-specific nasal airway reconstruction was created from computed tomography images in 16 subjects: 4 subjects from each ethnic group (Black, East Asian, Caucasian, and Latino) comprising of 2 males and 2 females. Volume, surface area and nasal index were calculated, as well as airflow rate and nasal resistance after computational fluid dynamics simulations in the nasal airway. Results showed that nasal airspace surface area (p = 0.0499) and volume (p = 0.0281) were significantly greater in males than in females. Nasal volume was greatest in East Asians (Median = 20.38cm³, Interquartile Range [IQR] = 4.58 cm³), Latinos had the greatest surface area (Median = 219.70cm², IQR = 29.56cm²). On average, East Asian and Black females had larger nasal index than their male counterparts. Caucasians had the highest median nasal resistance (0.050 Pa.s/mL, IQR = 0.025 Pa.s/mL). Results indicate that there exist anatomical variabilities based on race and gender. However, these variabilities may not significantly influence nasal function.

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.

Nasal airflow comparison in neonates, infant and adult nasal cavities using computational fluid dynamics

BACKGROUND AND OBJECTIVE

Neonates are preferential nasal breathers up to 3 months of age. The nasal anatomy in neonates and infants is at developing stages whereas the adult nasal cavities are fully grown which implies that the study of airflow dynamics in the neonates and infants are significant. In the present study, the nasal airways of the neonate, infant and adult are anatomically compared and their airflow patterns are investigated.

METHODS

Computational Fluid Dynamics (CFD) approach is used to simulate the airflow in a neonate, an infant and an adult in sedentary breathing conditions. The healthy CT scans are segmented using MIMICS 21.0 (Materialise, Ann arbor, MI). The patient-specific 3D airway models are analyzed for low Reynolds number flow using ANSYS FLUENT 2020 R2. The applicability of the Grid Convergence Index (GCI) for polyhedral mesh adopted in this work is also verified.

RESULTS

This study shows that the inferior meatus of neonates accounted for only 15% of the total airflow. This was in contrast to the infants and adults who experienced 49 and 31% of airflow at the inferior meatus region. Superior meatus experienced 25% of total flow which is more than normal for the neonate. The highest velocity of 1.8, 2.6 and 3.7 m/s was observed at the nasal valve region for neonates, infants and adults, respectively. The anterior portion of the nasal cavity experienced maximum wall shear stress with average values of 0.48, 0.25 and 0.58 Pa for the neonates, infants and adults.

CONCLUSIONS

The neonates have an underdeveloped nasal cavity which significantly affects their airway distribution. The absence of inferior meatus in the neonates has limited the flow through the inferior regions and resulted in uneven flow distribution.

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.

Effect of swirling flow and particle-release pattern on drug delivery to human tracheobronchial airways

The present study aims to investigate the effect of swirling flow on particle deposition in a realistic human airway. A computational fluid dynamic (CFD) model was utilized for the simulation of oral inhalation and particle transport patterns, considering the k-ω turbulence model. Lagrangian particle tracking was used to track the particles' trajectories. A normal breathing condition (30 L/min) was applied, and two-micron particles were injected into the mouth, considering swirling flow to the oral inhalation airflow. Different cases were considered for releasing the particles, which evaluated the impacts of various parameters on the deposition efficiency (DE), including the swirl intensity, injection location and pattern of the particle. The work's novelty is applying several injection locations and diameters simultaneously. The results show that the swirling flow enhances the particle deposition efficiency (20-40%) versus no-swirl flow, especially in the mouth. However, releasing particles inside the mouth, or injecting them randomly with a smaller injection diameter (d_inj) reduced DE in swirling flow condition, about 50 to 80%. Injecting particles inside the mouth can decrease DE by about 20%, and releasing particles with smaller d_inj leads to 50% less DE in swirling flow. In conclusion, it is indicated that the airflow condition is an important parameter for a reliable drug delivery, and it is more beneficial to keep the inflow uniform and avoid swirling flow.

The effect of decongestion on nasal airway patency and airflow

Nasal decongestant reduces blood flow to the nasal turbinates, reducing tissue volume and increasing nasal airway patency. This study maps the changes in nasal anatomy and measures how these changes affect nasal resistance, flow partitioning between superior and inferior cavity, flow patterns and wall shear stress. High-resolution MRI was applied to capture nasal anatomy in 10 healthy subjects before and after application of a topical decongestant. Computational fluid dynamics simulated nasal airflow at steady inspiratory flow rates of 15 L.min[Formula: see text] and 30 L.min[Formula: see text]. The results show decongestion mainly increases the cross-sectional area in the turbinate region and SAVR is reduced (median approximately 40[Formula: see text] reduction) in middle and lower parts of the cavity. Decongestion reduces nasal resistance by 50[Formula: see text] on average, while in the posterior cavity, nasal resistance decreases by a median factor of approximately 3 after decongestion. We also find decongestant regularises nasal airflow and alters the partitioning of flow, significantly decreasing flow through the superior portions of the nasal cavity. By comparing nasal anatomies and airflow in their normal state with that when pharmacologically decongested, this study provides data for a broad range of anatomy and airflow conditions, which may help characterize the extent of nasal variability.

The impact of nasal adhesions on airflow and mucosal cooling - A computational fluid dynamics analysis

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.

Analysis of nasal air conditioning in subjects with unilateral cleft lip nasal deformity

This study evaluated the impact of unilateral cleft lip nasal deformity (uCLND) on the ability of the nasal passages to warm and humidify inspired environmental air using computational fluid dynamics (CFD) modeling. Nasal air conditioning was simulated at resting inspiration in ten individuals with uCLND and seven individuals with normal anatomy. The overall heat and water transfer through nasal mucosa was significantly greater (p = 0.02 for both heat and moisture fluxes) on the non-cleft side than on the cleft side. Unilateral median and interquartile range (IQR) for heat flux (W/m²) was 190.3 (IQR 59.9) on the non-cleft side, 160.9 (IQR 105.0) on the cleft side, and 170.7 (IQR 87.8) for normal subjects. For moisture flux (mg/(s·m²), they were 357.4 (IQR 112.9), 298.7 (IQR 200.3) and 320.8 (IQR 173.0), respectively. Significant differences of SAHF50 between cleft side of uCLND and normal existed except for anterior region. Nevertheless, air conditioning ability in subjects with uCLND was generally comparable to that of normal subjects.

Dynamic characteristics of heat capacity of the human nasal cavity during a respiratory cycle

The dynamic characteristics of air-conditioning in the human nasal cavity during a respiratory cycle were investigated using unsteady numerical simulations to assess whether inhaled air is sufficiently conditioned by the nasal cavity. Variations in the epithelial surface temperature, surface heat, and water vapor fluxes were found to vary significantly during inspiration while providing substantial air conditioning to the inhaled air, but variations and magnitudes were significantly reduced during the expiration period. Air temperature (31.3-35.3 °C) and relative humidity (85.1-100 %) in the nasopharynx exhibited significant variations during inspiration. Flow rate-weighted average values of the air temperature and relative humidity during inspiration were estimated to be 32.0 °C and 89.1 %, respectively. Inhaled air did not attain alveolar conditions before reaching the nasopharynx, and was therefore thought to be insufficiently conditioned by the nasal cavity alone. A steady flow of approximately 250 mL/s appears to be useful for evaluating the accumulated thermal state of air in the nasopharynx during inspiration.

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.

Role of nasal vestibule morphological variations on olfactory airflow dynamics

BACKGROUND

The conductive mechanisms of olfaction are typically given little priority in the evaluation of olfactory function. The objective of this study is to investigate the role of nasal vestibule morphological variations on airflow volume at the olfactory recess in healthy subjects.

METHODS

Anatomically realistic three-dimensional nasal airway models were constructed from computed tomography scans in five subjects. Each individual's unilateral nasal cavity (10 total) was classified according to the shape of their nasal vestibule: Standard, Notched, or Elongated. Nasal airflow simulations were performed using computational fluid dynamics modeling at two inspiratory flow rates (15 L/min and 30 L/min) to reflect resting and moderate breathing rates. Olfactory airflow volume and cross-sectional flow resistance were computed.

FINDINGS

Average olfactory airflow volumes (and percent airflow in olfactory) were: 0.25 L/min to 0.64 L/min (3.0%-7.7%; 15 L/min simulations) and 0.53 L/min to 1.30 L/min (3.2%-7.8%; 30 L/min simulations) for Standard; 0.13 L/min - 0.47 L/min (2.0%-6.8%; 15 L/min simulations) and 0.06 L/min - 0.82 L/min (1.7%-6.1%; 30 L/min simulations) for Notched; and 0.07 L/min - 0.39 L/min (1.2%-5.4%; 15 L/min simulations) and 0.30 L/min - 0.99 L/min (2.1%-6.7%; 30 L/min simulations) for Elongated. On average, relative difference in olfactory resistance between left and right sides was 141.5% for patients with different unilateral phenotypes and 82.2% for patients with identical unilateral phenotype.

INTERPRETATION

Olfactory cleft airflow volume was highest in the Standard nasal vestibule phenotype, followed by Notched phenotype for 15 L/min simulations and Elongated phenotype for 30 L/min simulations. Further, intra-patient variation in olfactory cleft airflow resistance differs greatly for patients with different unilateral phenotypes compared to patients with identical unilateral phenotype.

Can computational fluid dynamic models help us in the treatment of chronic rhinosinusitis

PURPOSE OF REVIEW

The aim of this study was to review the recent literature (January 2017-July 2020) on computational fluid dynamics (CFD) studies relating to chronic rhinosinusitis (CRS), including airflow within the pre and postoperative sinonasal cavity, virtual surgery, topical drug and saline delivery (sprays, nebulizers and rinses) and olfaction.

RECENT FINDINGS

Novel CFD-specific parameters (heat flux and wall shear stress) are highly correlated with patient perception of nasal patency. Increased ostial size markedly improves sinus ventilation and drug delivery. New virtual surgery tools allow surgeons to optimize interventions. Sinus deposition of nasal sprays is more effective with smaller, low-inertia particles, outside of the range produced by many commercially available products. Saline irrigation effectiveness is improved using greater volume, with liquid entering sinuses via 'flooding' of ostia rather than direct jet entry.

SUMMARY

CFD has provided new insights into sinonasal airflow, air-conditioning function, the nasal cycle, novel measures of nasal patency and the impact of polyps and sinus surgery on olfaction. The deposition efficiency of topical medications on sinus mucosa can be markedly improved through parametric CFD experiments by optimising nasal spray particle size and velocity, nozzle angle and insertion location, while saline irrigation effectiveness can be optimized by modelling squeeze bottle volume and head position. More sophisticated CFD models (inhalation and exhalation, spray particle and saline irrigation) will increasingly provide translational benefits in the clinical management of CRS.

In vitro evaluation of regional nasal drug delivery using multiple anatomical nasal replicas of adult human subjects and two nasal sprays

Quantifying drug delivery to the site of action using locally-acting nasal suspension sprays is a challenging but important step toward understanding bioequivalence (BE) between test and reference products. The main objective of this study was to investigate the in vitro deposition pattern of two common but different locally-acting nasal suspension sprays using multiple nasal cavities. Twenty anatomically accurate nasal replicas were developed from high-resolution sinonasal computed tomography scans of adults with healthy nasal airways. The airways were segmented into two regions of anterior and posterior to the internal nasal valve. Both sides of the septum were considered separately; hence, 40 nasal cavities were studied. The positioning of the spray nozzle in all 40 cavities was characterized by the head angle, coronal angle, and the insertion depth. Despite using a controlled protocol to minimize the anterior losses, a wide range of variability in posterior drug delivery was observed. The observed intersubject variability using this in vitro method may have important implications for understanding BE of locally-acting nasal suspension sprays.

In situ-Like Aerosol Inhalation Exposure for Cytotoxicity Assessment Using Airway-on-Chips Platforms

Lung exposure to inhaled particulate matter (PM) is known to injure the airway epithelium via inflammation, a phenomenon linked to increased levels of global morbidity and mortality. To evaluate physiological outcomes following PM exposure and concurrently circumvent the use of animal experiments, in vitro approaches have typically relied on traditional assays with plates or well inserts. Yet, these manifest drawbacks including the inability to capture physiological inhalation conditions and aerosol deposition characteristics relative to in vivo human conditions. Here, we present a novel airway-on-chip exposure platform that emulates the epithelium of human bronchial airways with critical cellular barrier functions at an air-liquid interface (ALI). As a proof-of-concept for in vitro lung cytotoxicity testing, we recapitulate a well-characterized cell apoptosis pathway, induced through exposure to 2 μm airborne particles coated with αVR1 antibody that leads to significant loss in cell viability across the recapitulated airway epithelium. Notably, our in vitro inhalation assays enable simultaneous aerosol exposure across multiple airway chips integrated within a larger bronchial airway tree model, under physiological respiratory airflow conditions. Our findings underscore in situ-like aerosol deposition outcomes where patterns depend on respiratory flows across the airway tree geometry and gravitational orientation, as corroborated by concurrent numerical simulations. Our airway-on-chips not only highlight the prospect of realistic in vitro exposure assays in recapitulating characteristic local in vivo deposition outcomes, such platforms open opportunities toward advanced in vitro exposure assays for preclinical cytotoxicity and drug screening applications.

The effect of nasal shape on the thermal conditioning of inhaled air: Using clinical tomographic data to build a large-scale statistical shape model

In this paper, we investigate the heating function of the nasal cavity qualitatively, using a high-quality, large-scale statistical shape model. This model consists of a symmetrical and an asymmetrical part and provides a new and unique way of examining changes in nasal heating function resulting from natural variations in nasal shape (as obtained from 100 clinical CT scans). Data collected from patients suffering from different nasal or sinus-related complaints are included. Parameterized models allow us to investigate the effect of continuous deviations in shape from the mean nasal cavity. This approach also enables us to avoid many of the compounded effects on flow and heat exchange, which one would encounter when comparing different patient-specific models. The effects of global size, size-related features, and turbinate size are investigated using the symmetrical shape model. The asymmetrical model is used to investigate different types of septal deviation using Mladina's classification. The qualitative results are discussed and compared with findings from the existing literature.

From indoor exposure to inhaled particle deposition: A multiphase journey of inhaled particles

Indoor air quality and its effect on respiratory health are reliant on understanding the level of inhalation exposure, particle inhalability, and particle deposition in the respiratory airway. In the indoor environment, controlling airflow through different ventilation systems can reduce inhalation exposure. This produces a wide variety of complex flow phenomena, such as recirculation, coanda flow, separation, and reattachment. Airborne particles drifting through the air, that move within the breathing region become inhaled into nasal cavity the nostrils. Studies have developed the aspiration efficiency to assist in predicting the fraction of inhaled particles. Inside the nasal cavity, micron and submicron particle deposition occurs in very different ways (inertial impaction, sedimentation, diffusion) and different locations. In addition, fibrous particles such as asbestos are influenced by tumbling effects and its deposition mechanism can include interception. Indoor fluid-particle dynamics related to inhalation exposure and eventual deposition in the respiratory airway is presented. This study involves multi-disciplinary fields involving building science, fluid dynamics, computer science, and medical imaging disciplines. In the future, an integrated approach can lead to digital/in-silico representations of the human respiratory airway able to predict the inhaled particle exposure and its toxicology effect.

Functional relevance of computational fluid dynamics in the field of nasal obstruction: A literature review

BACKGROUND

Nasal airway obstruction (nasal obstruction) is a common symptom affecting the quality of life of patients. It can be estimated by patient perception or physical measurements. Computational fluid dynamics (CFD) can be used to analyse nasal ventilation modalities. There is a lack of comparative studies investigating the correlations between CFD variables and patient perception or physical measurements.

OBJECTIVE OF THE REVIEW

Our goal was to define correlations between CFD variables and patient perception and physical measurements. We also aimed to identify the most reliable CFD variable (heat flux, WSS, total pressure, temperature…) characterising nasal breathing perception.

TYPE OF REVIEW

Systematic literature review using PRISMA guidelines.

SEARCH STRATEGY

The selected studies were obtained from the US National Library of Medicine (PubMed) online database, MEDLINE (Ovid), Google Scholar and the Cochrane Library using a combination of MeSH terms (nose, paranasal sinus, fluid dynamics, rhinology) and non-MeSH terms (CFD, nasal airway, nasal airflow, numerical, nasal symptoms). Studies that did not incorporate objective or subjective clinical assessment were excluded.

EVALUATION METHOD

We compared all results obtained by authors regarding CFD variables and assessment of nasal airway obstruction (clinical or physical).

RESULTS

To compare nasal obstruction with CFD variables, most authors use CFD-calculated nasal resistances, airflow, heat flux, wall shear stress, total pressure, velocities and streamlines. We found that heat flux appears to be the CFD variable most closely correlated with patient perception. Total pressure, wall shear stress and velocities are also useful and show good correlations. Correlations between CFD-calculated nasal resistances and patient perception are stronger after correction of the nasal cycle.

CONCLUSIONS

The growing number of CFD studies on the nose has led to a better understanding of nasal obstruction. The clinical interpretation of previously unknown data, such as WSS and heat flux, is opening up new horizons in the understanding of this symptom. Heat fluxes are among the best CFD values correlated with patient perception. More studies need to be performed including temperature and humidity exchanges.

Detailed computational analysis of flow dynamics in an extended respiratory airway model

BACKGROUND

Understanding respiratory physiology can aid clinicians in diagnosing the cause of respiratory symptoms or shed light on drug delivery inhaler device optimisation. However, the sheer complexity of the human lung prohibits a full-scale study.

METHODS

In this study, a realistic respiratory airway model including large-to-small conducting airways was built. This airway model consists of subject-specific upper and lower airways, extending from nasal and oral openings to terminal bronchioles (up to the 15th generation). Based on the subject-specific airway model, topological information was extracted and a digital reference model that exhibits strong asymmetry and multi-fractal properties was provided. Inhalation flow rates 18 L/min and 50 L/min were adopted to understand inspiratory conditions subjecting to resting and light exercise inhalation modes. Regional airflow in terms of axial velocity and secondary flow vortices along the lung airway model was extracted.

FINDINGS

Obvious secondary flow currents were seen in the larynx-trachea segment and left main bronchus, while for the terminal conducting airway in the right lower lobe, the airflow tends to be much smoother with no secondary flow currents.

INTERPRETATION

This paper provides insights on respiratory physiology, especially in the lower lung airways, and will be potentially useful for diagnosis of lower airway diseases.

Matlab® toolbox for semi-automatic segmentation of the human nasal cavity based on active shape modeling

The nose is a complex and important organ with a multitude of functions. Computational fluid dynamics (CFD) has been shown to be a valuable tool to obtain a better understanding of the functioning of the nose. CFD simulations require a surface geometry, which is constructed from tomographic data. This can be a very time-consuming task when one chooses to exclude the sinuses from the simulation domain, which in general keeps the size of the CFD model more manageable. In this work, an approach for the semi-automatic construction of the human nasal cavity is presented. In the first part, limited manual interaction is needed to create a coarse surface model. In the next part, this result is further refined based on the combination of active shape modeling with elastic surface deformation. The different steps are bundled in a Matlab toolbox with a graphical interface which guides the user. This interface allows easy manipulation of the data during intermediate steps, and also allows manual adjustments of the reconstructed nasal surface at the end. Two results are shown, and the approach and its precision are discussed. These results demonstrated that the followed approach can be used for the semi-automatic segmentation of a human nasal cavity from tomographic data, substantially reducing the amount of operator time.

Targeting inhaled aerosol delivery to upper airways in children: Insight from computational fluid dynamics (CFD)

Despite the prevalence of inhalation therapy in the treatment of pediatric respiratory disorders, most prominently asthma, the fraction of inhaled drugs reaching the lungs for maximal efficacy remains adversely low. By and large drug delivery devices and their inhalation guidelines are typically derived from adult studies with child dosages adapted according to body weight. While it has long been recognized that physiological (e.g. airway sizes, breathing maneuvers) and physical transport (e.g. aerosol dynamics) characteristics are critical in governing deposition outcomes, such knowledge has yet to be extensively adapted to younger populations. Motivated by such shortcomings, the present work leverages in a first step in silico computational fluid dynamics (CFD) to explore opportunities for augmenting aerosol deposition in children based on respiratory physiological and physical transport determinants. Using an idealized, anatomically-faithful upper airway geometry, airflow and aerosol motion are simulated as a function of age, spanning a five year old to an adult. Breathing conditions mimic realistic age-specific inhalation maneuvers representative of Dry Powder Inhalers (DPI) and nebulizer inhalation. Our findings point to the existence of a single dimensionless curve governing deposition in the conductive airways via the dimensionless Stokes number (Stk). Most significantly, we uncover the existence of a distinct deposition peak irrespective of age. For the DPI simulations, this peak (∼ 80%) occurs at Stk ≈ 0.06 whereas for nebulizer simulations, the corresponding peak (∼ 45%) occurs in the range of Stk between 0.03-0.04. Such dimensionless findings hence translate to an optimal window of micron-sized aerosols that evolves with age and varies with inhalation device. The existence of such deposition optima advocates revisiting design guidelines for optimizing deposition outcomes in pediatric inhalation therapy.