Numerical simulations for detailed airflow dynamics in a human nasal cavity

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.

A Novel Bionebulizer Approach to Study the Effects of Natural Mineral Water on a 3D In Vitro Nasal Model from Allergic Rhinitis Patients

Sulfurous thermal waters (STWs) are used as a complementary treatment for allergic rhinitis. However, there is scant data on the effects of STW on nasal epithelial cells, and in vitro models are warranted. The main aim of this study was to evaluate the dose and time effects of exposure to 3D nasal inserts (MucilAirTM-HF allergic rhinitis model) with STW or isotonic sodium chloride solution (ISCS) aerosols. Transepithelial electrical resistance (TEER) and histology were assessed before and after nebulizations. Chemokine/cytokine levels in the basal supernatants were assessed by enzyme-linked immunosorbent assay. The results showed that more than four daily nebulizations of four or more minutes compromised the normal epithelial integrity. In contrast, 1 or 2 min of STW or ISCS nebulizations had no toxic effect up to 3 days. No statistically significant changes in release of inflammatory chemokines MCP-1/CCL2 > IL-8/CXCL8 > MIP-1α/CCL3, no meaningful release of "alarmins" (IL-1α, IL-33), nor of anti-inflammatory IL-10 cytokine were observed. We have characterized safe time and dose conditions for aerosol nebulizations using a novel in vitro 3D nasal epithelium model of allergic rhinitis patients. This may be a suitable in vitro setup to mimic in vivo treatments of chronic rhinitis with STW upon triggering an inflammatory stimulus in the future.

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.

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.

Modelling the effects of post-FESS middle turbinate synechiae on sinonasal physiology: A computational fluid dynamics study

OBJECTIVE(S)

Chronic rhinosinusitis (CRS) is common and often requires surgical intervention. Surgical failure may lead to persistent symptoms and recalcitrant disease, often secondary to synechiae between the middle turbinate (MT) and lateral nasal wall. Synechiae prevention techniques have been extensively investigated, however evidence for the effect of synechiae on sinonasal physiology is lacking. We aimed to model the effects of MT synechiae on a post-functional endoscopic sinus surgery (FESS) sinonasal cavity using computational fluid dynamics (CFD).

METHODS

DICOM data from a CT-sinus of a healthy 25-year-old female was segmented to create a three-dimensional model. Virtual surgery was performed to simulate a "full-house" FESS procedure. Multiple models were created, each with a single unilateral virtual MT synechia of varying extent. CFD analysis was performed on each model and compared with a post-FESS control model without synechiae. Airflow velocity, humidity and mucosal surface and air temperature values were calculated.

RESULTS

All synechiae models demonstrated aberrant downstream sinonasal airflow. There was reduced ventilation of the ipsilateral frontal, ethmoid and sphenoid sinuses, with a concentrated central "jet" in the middle meatus region. Effects were proportionate to the size of synechiae. The impact on bulk inspired airflow was negligible.

CONCLUSION

Post-FESS synechiae between the MT and lateral nasal wall significantly disrupt local downstream sinus ventilation and nasal airflow. These findings may explain the persistent symptoms seen in post-FESS CRS patients with MT synechiae, reinforcing the importance of prevention and adhesiolysis. Larger cohort studies with multiple models of actual post-FESS patients with synechiae are required to validate these findings.

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.

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.

Icex: Advances in the automatic extraction and volume calculation of cranial cavities

The use of non-destructive approaches for digital acquisition (e.g. computerised tomography-CT) allows detailed qualitative and quantitative study of internal structures of skeletal material. Here, we present a new R-based software tool, Icex, applicable to the study of the sizes and shapes of skeletal cavities and fossae in 3D digital images. Traditional methods of volume extraction involve the manual labelling (i.e. segmentation) of the areas of interest on each section of the image stack. This is time-consuming, error-prone and challenging to apply to complex cavities. Icex facilitates rapid quantification of such structures. We describe and detail its application to the isolation and calculation of volumes of various cranial cavities. The R tool is used here to automatically extract the orbital volumes, the paranasal sinuses, the nasal cavity and the upper oral volumes, based on the coordinates of 18 cranial anatomical points used to define their limits, from 3D cranial surface meshes obtained by segmenting CT scans. Icex includes an algorithm (Icv) for the calculation of volumes by defining a 3D convex hull of the extracted cavity. We demonstrate the use of Icex on an ontogenetic sample (0-19 years) of modern humans and on the fossil hominin crania Kabwe (Broken Hill) 1, Gibraltar (Forbes' Quarry) and Guattari 1. We also test the tool on three species of non-human primates. In the modern human subsample, Icex allowed us to perform a preliminary analysis on the absolute and relative expansion of cranial sinuses and pneumatisations during growth. The performance of Icex, applied to diverse crania, shows the potential for an extensive evaluation of the developmental and/or evolutionary significance of hollow cranial structures. Furthermore, being open source, Icex is a fully customisable tool, easily applicable to other taxa and skeletal regions.

The influence of mouth opening on pharyngeal pressure loss and its underlying mechanism: A computational fluid dynamic analysis

Objective: During inspiration, mechanical energy generated from respiratory muscle produces a negative pressure gradient to fulfill enough pulmonary ventilation. The pressure loss, a surrogate for energy loss, is considered as the portion of negative pressure without converting into the kinetic energy of airflow. Mouth opening (MO) during sleep is a common symptom in patients with obstructive sleep apnoea-hypopnea syndrome (OSAHS). This study aimed to evaluate the effects of mouth opening on pharyngeal pressure loss using computational fluid dynamics (CFD) simulation. Methods: A total of four subjects who were morphologically distinct in the pharyngeal characteristics based on Friedman tongue position (FTP) grades were selected. Upper airway computed tomography (CT) scan was performed under two conditions: Mouth closing (MC) and mouth opening, in order to reconstruct the upper airway models. computational fluid dynamics was used to simulate the flow on the two different occasions: Mouth closing and mouth opening. Results: The pharyngeal jet was the typical aerodynamic feature and its formation and development were different from mouth closing to mouth opening in subjects with different Friedman tongue position grades. For FTP I with mouth closing, a pharyngeal jet gradually formed with proximity to the velopharyngeal minimum area plane (plane_Amin). Downstream the plane_Amin, the jet impingement on the pharyngeal wall resulted in the frictional loss associated with wall shear stress (WSS). A rapid luminal expansion led to flow separation and large recirculation region, corresponding to the interior flow loss. They all contributed to the pharyngeal total pressure loss. While for FTP I with mouth opening, the improved velopharyngeal constriction led to smoother flow and a lower total pressure loss. For FTP IV, the narrower the plane_Amin after mouth opening, the stronger the jet formation and its impingement on the pharyngeal wall, predicting a higher frictional loss resulted from higher WSS. Besides, a longer length of the mouth opening-associated constant constrictive segment was another important morphological factor promoting frictional loss. Conclusion: For certain OSAHS patients with higher Friedman tongue position grade, mouth opening-related stronger jet formation, more jet breakdown and stronger jet flow separation might contribute to the increased pharyngeal pressure loss. It might require compensation from more inspiratory negative static pressure that would potentially increase the severity of OSAHS.

Numerical modelling of micron particle inhalation in a realistic nasal airway with pediatric adenoid hypertrophy: A virtual comparison between pre- and postoperative models

Adenoid hypertrophy (AH) is an obstructive condition due to enlarged adenoids, causing mouth breathing, nasal blockage, snoring and/or restless sleep. While reliable diagnostic techniques, such as lateral soft tissue x-ray imaging or flexible nasopharyngoscopy, have been widely adopted in general practice, the actual impact of airway obstruction on nasal airflow and inhalation exposure to drug aerosols remains largely unknown. In this study, the effects of adenoid hypertrophy on airflow and micron particle inhalation exposure characteristics were analysed by virtually comparing pre- and postoperative models based on a realistic 3-year-old nasal airway with AH. More specifically, detailed comparison focused on anatomical shape variations, overall airflow and olfactory ventilation, associated particle deposition in overall and local regions were conducted. Our results indicate that the enlarged adenoid tissue can significantly alter the airflow fields. By virtually removing the enlarged tissue and restoring the airway, peak velocity and wall shear stress were restored, and olfactory ventilation was considerably improved (with a 16∼63% improvement in terms of local ventilation speed). Furthermore, particle deposition results revealed that nasal airway with AH exhibits higher particle filtration tendency with densely packed deposition hot spots being observed along the floor region and enlarged adenoid tissue area. While for the postoperative model, the deposition curve was shifted to the right. The local deposition efficiency results demonstrated that more particles with larger inertia can be delivered to the targeted affected area following Adenoidectomy (Adenoid Removal). Research findings are expected to provide scientific evidence for adenoidectomy planning and aerosol therapy following Adenoidectomy, which can substantially improve present clinical treatment outcomes.

Improvements in airflow characteristics and effect on the NOSE score after septoturbinoplasty: A computational fluid dynamics analysis

Septoturbinoplasty is a surgical procedure that can improve nasal congestion symptoms in patients with nasal septal deviation and inferior turbinate hypertrophy. However, it is unclear which physical domains of nasal airflow after septoturbinoplasty are related to symptomatic improvement. This work employs computational fluid dynamics modeling to identify the physical variables and domains associated with symptomatic improvement. Sixteen numerical models were generated using eight patients' pre- and postoperative computed tomography scans. Changes in unilateral nasal resistance, surface heat flux, relative humidity, and air temperature and their correlations with improvement in the Nasal Obstruction Symptom Evaluation (NOSE) score were analyzed. The NOSE score significantly improved after septoturbinoplasty, from 14.4 ± 3.6 to 4.0 ± 4.2 (p < 0.001). The surgery not only increased the airflow partition on the more obstructed side (MOS) from 31.6 ± 9.6 to 41.9 ± 4.7% (p = 0.043), but also reduced the unilateral nasal resistance in the MOS from 0.200 ± 0.095 to 0.066 ± 0.055 Pa/(mL·s) (p = 0.004). Improvement in the NOSE score correlated significantly with the reduction in unilateral nasal resistance in the preoperative MOS (r = 0.81). Also, improvement in the NOSE score correlated better with the increase in surface heat flux in the preoperative MOS region from the nasal valve to the choanae (r = 0.87) than in the vestibule area (r = 0.63). Therefore, unilateral nasal resistance and mucous cooling in the preoperative MOS can explain the perceived improvement in symptoms after septoturbinoplasty. Moreover, the physical domain between the nasal valve and the choanae might be more relevant to patient-reported patency than the vestibule area.

The Need for Innovation in Rhinoplasty

Rhinoplasty is a challenging surgery and results are not always perfect. There are many obstacles to achieving optimal results. Among these are inadequate instrumentation, the unpredictability of healing, imprecise planning, and many more. Furthermore, selecting patients who can most benefit from surgery is equally important. In this article, some of the more pressing areas of rhinoplasty that need innovation are discussed. From proper patient selection, to advances in education, to the standardization of training programs, to the development of sophisticated implants, the future of rhinoplasty surgery lies in continued creativity and innovation.

Comparison of rhinomanometric and computational fluid dynamic assessment of nasal resistance with respect to measurement accuracy

PURPOSE

Computational fluid dynamics (CFD)-based calculation of intranasal airflow became an important method in rhinologic research. Current evidence shows weak to moderate correlation as well as a systematic underprediction of nasal resistance by numerical simulations. In this study, we investigate whether these differences can be explained by measurement uncertainties caused by rhinomanometric devices and procedures. Furthermore, preliminary findings regarding the impact of tissue movements are reported.

METHODS

A retrospective sample of 17 patients, who reported impaired nasal breathing and for which rhinomanometric (RMM) measurements using two different devices as well as computed tomography scans were available, was investigated in this study. Three patients also exhibited a marked collapse of the nasal valve. Agreement between both rhinomanometric measurements as well as between rhinomanometry and CFD-based calculations was assessed using linear correlation and Bland-Altman analyses. These analyses were performed for the volume flow rates measured at trans-nasal pressure differences of 75 and 150 Pa during inspiration and expiration.

RESULTS

The correlation between volume flow rates measured using both RMM devices was good (R² > 0.72 for all breathing states), and no relevant differences in measured flow rates was observed (21.6 ml/s and 14.8 ml/s for 75 and 150 Pa, respectively). In contrast, correlation between RMM and CFD was poor (R² < 0.5) and CFD systematically overpredicted RMM-based flow rate measurements (231.8 ml/s and 328.3 ml/s). No differences between patients with and without nasal valve collapse nor between inspiration and expiration were observed.

CONCLUSION

Biases introduced during RMM measurements, by either the chosen device, the operator or other aspects as for example the nasal cycle, are not strong enough to explain the gross differences commonly reported between RMM- and CFD-based measurement of nasal resistance. Additionally, tissue movement during breathing is most likely also no sufficient explanation for these differences.

Detailed Assessment of Nasal Inter-Chamber Anatomical Variations and Its Effect on Flow Apportionment and Inhalation Exposure Patterns

Although many parametric studies have been conducted in developing standardized nasal geometry and analysing associated airflow dynamics, most of them are based on symmetrical nasal chambers assumption, while the inter-chamber variations due to the morphological asymmetry of the two nasal chambers are much less investigated. To address this issue, this paper presents an inter-chamber anatomical variability study by developing a shape comparison method to quantify inter-chamber anatomical differences. Then the anatomical deviation is correlated with the flow apportionment and the associated nanoparticle deposition patterns using CFD method. Results show that noticeable inter-chamber difference is observed especially in the inferior and middle passages where most inhaled flow is distributed to. Additionally, the shape of vestibule notch and septum deviation contributes to the discrepancy flow behaviour between two chambers. Consequently, these differences lead to variations in regional nanoparticle deposition, especially for 1 nm particles in the olfactory region, where the inter-chamber differences can reach up to 400%. Our results suggest that the inter-chamber anatomical variation should be considered when developing standardized nasal models.

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.

Designing nanoformulation for the nose-to-brain delivery in Parkinson's disease: Advancements and barrier

Parkinson's disease (PD), a neurodegenerative disorder characterized by the degeneration of dopaminergic neurons, which results in the loss of motor activity. In the management of PD, the primary aim is to increase the dopamine content in the brain either by delivering the precursors of dopamine or by inhibiting the molecules responsible for dopamine degradation. Due to the low bioavailability, a higher dosage of drugs needs to be administered repeatedly for achieving the desired therapeutic effect. This repeated high dose not only increases the severe side effects but also produces tolerance in the body. Often, direct administration of drugs fails to ameliorate the symptoms as the unmodified drugs cannot cross the blood-brain barrier (BBB). Nanotherapeutic is at the forefront of the alternative treatment against the central nervous system (CNS) disorders due to the ability to circumvents the BBB. Here, all the available treatments for PD have been discussed with their limitation. The current trends of nanotherapeutics for PD have been explored. Suitability and formulation prospects for nasal delivery have been analyzed in detail to explore new research scope. The most effective approach is the nose-to-brain delivery for targeting drugs directly to the brain. This delivery bypasses the BBB and concentrates more drugs at the target site. Thus, developments of nose-to-brain delivery of nanoformulations explicit the new scope to manage PD better. This article is categorized under: Therapeutic Approaches and Drug Discovery > Emerging Technologies Nanotechnology Approaches to Biology > Nanoscale Systems in Biology.

Detailed comparison of anatomy and airflow dynamics in human and cynomolgus monkey nasal cavity

Nonhuman primates are occasionally used as laboratory models for sophisticated medical research as they bear the closest resemblance to humans in morphometry and physiological functions. A range of nonhuman primate species have been employed in the inhalation toxicity, nasal drug delivery and respiratory viral infection studies, and they provided valuable insight to disease pathogenesis while other laboratory animals such as rodents cannot recapitulate due to the lesser degree of similarity in metabolism, anatomy and cellular response to that of humans. It is anticipated that nonhuman primate models of respiratory diseases will continue to be instrumental for translating biomedical research for improvement of human health, and the confidence in laboratory data extrapolation between species will play a pivotal role. From the morphometry and flow dynamics point of view, this study performed a detailed comparative analysis between human and a cynomolgus monkey nasal airway, with intention to provide high-fidelity qualitative and quantitative linkage between the two species for more effective laboratory data extrapolation. The study revealed that cynomolgus monkey could be a good human surrogate in nasal inhalation studies; however, care should be given for interspecies data extrapolation as subtle differences in anatomy and airflow dynamics were present between the two species.

In-silico investigation of airflow and micro-particle deposition in human nasal airway pre- and post-virtual transnasal sphenoidotomy surgery

Sphenoid sinus, located posterior to the nasal cavity, is difficult to reach for a surgery. Several operation procedures are available for sphenoidotomy, including endoscopic surgeries. Although the endoscopic sinus surgery is minimally invasive with low post-operative side effects, further optimization is required. Transnasal sphenoidotomy is a low invasive alternative to transethmoidal sphenoidotomy, but it still needs to be studied to understand its effects on the airflow pattern and the particle deposition. In this work, we simulated airflow and the micro-particle deposition in the nasal airway of a middle-aged man to investigate the change in particle deposition in the sphenoid sinus after virtual transnasal sphenoidotomy surgery. The results demonstrated that after transnasal sphenoidotomy, particle deposition in the targeted sphenoid sinus was an order of magnitude lower than that observed after virtual transethmoidal sphenoidotomy surgery. In addition, the diameter of the particles for the peak deposition fraction in the targeted sinus was shifted to smaller diameters after the transnasal sphenoidotomy surgery compared with that in the post-transethmoidal condition. These results suggest that the endoscopic transnasal sphenoidotomy can be a better procedure for sphenoid surgeries as it decreases the chance of bacterial contaminations and consequently lowers the surgical side effects and recovery time.

Particle inhalability of a standing mannequin with large airways in a ventilated room

This study presents a series of numerical simulations for airflow field and particle dispersion and deposition around a mannequin inside a ventilated room. A 3-D airway system of a volunteer subject with a large respiratory system was reconstructed from the nostril inlet to the end of the tracheobronchial tree 4th generation and was integrated into a standing mannequin at the center of a room. The room ventilation system supplied air through a diffuser and expelled air via a damper in three modes. The airflow field was first evaluated by solving the governing equations and the k-ω SST transitional turbulence model using the Ansys-Fluent software. Then spherical particles with various diameters were released into the room, and their trajectories were evaluated using the Lagrangian approach. Aspiration fraction and particle deposition for inhalation flow rates of 15 and 30 L/min were analyzed using a modified discrete random walk (DRW) stochastic model using a user-defined function (UDF) coupled to the Ansys-Fluent discrete phase model. For the first ventilation mode, a recirculation flow region formed behind the mannequin that led the airflow streamlines to the breathing zone. A recirculation flow formed in front of the face for the second ventilation mode that led the airflow streamlines out of the mannequin breathing zone. For the third mode, however, there was no strong recirculation flow zone around the mannequin. Simulation results showed that the aspiration fraction in the first ventilation mode was higher than the other modes. In addition, the regional deposition rates and deposition patterns of particles inside the respiratory system were presented for each region. Accordingly, most large particles were trapped in the nasal passage; however, some large particles penetrated deeper into the airway due to the large airway size. For the higher breathing rate, the percentage of large escaped particles from the lobe branches dropped by a factor of 7 compared to the lower breathing rate.

Which Nasal Airway Dimensions Correlate with Nasal Airflow and with Nasal Breathing Sensation?

Background: Rhinoplasty modifies the nasal pyramid, thereby also modifying the nasal airway. Objectives: To correlate the sensation of nasal breathing, as measured by patient-reported outcome measures, and nasal airflow, as assessed by peak nasal inspiratory flow (PNIF), with nasal airway dimensions, as measured on computed tomography (CT) images. Methods: Fifty Caucasian patients were studied through visual analogue scale (VAS), nasal obstruction symptom evaluation (NOSE) and PNIF. Measurements of the nasal airway were made on CT images: minimal distance between septum and inferior and middle turbinates, nasal valve angle, and nasal valve area. Results: There was a significant association between PNIF and nasal valve area, between VAS and the narrower nasal valve angle and between NOSE and minimal distance between septum and middle turbinate of the narrower side. Conclusions: This study suggests that the dimensions of the nasal valve and of the middle nasal airway have a substantial impact on nasal breathing capacity. It also highlights the importance of unilateral nasal airway obstruction to nasal breathing.

Nasal airflow of patient with septal deviation and allergy rhinitis

A numerical simulation of a patient’s nasal airflow was developed via computational fluid dynamics. Accordingly, computerized tomography scans of a patient with septal deviation and allergic rhinitis were obtained. The three-dimensional (3D) nasal model was designed using InVesalius 3.0, which was then imported to (computer aided 3D interactive application) CATIA V5 for modification, and finally to analysis system (ANSYS) flow oriented logistics upgrade for enterprise networks (FLUENT) to obtain the numerical solution. The velocity contours of the cross-sectional area were analyzed on four main surfaces: the vestibule, nasal valve, middle turbinate, and nasopharynx. The pressure and velocity characteristics were assessed at both laminar and turbulent mass flow rates for both the standardized and the patient’s model nasal cavity. The developed model of the patient is approximately half the size of the standardized model; hence, its velocity was approximately two times more than that of the standardized model.

Numerical simulation of unsteady airflow in a nasal cavity for various sizes of maxillary sinus opening in a virtual endoscopic surgery

Functional endoscopic sinus surgery (FESS) is performed to treat sinusitis when treatment with medication fails. In the present study, three different virtual maxillary sinus endoscopic surgeries were performed on a realistic 3-D computational model of the nasal cavity of an adult male under the supervision of a specialist. They included only uncinectomy, uncinectomy + 8mm Middle Meatal Antrostomy (MMA) and uncinectomy + 18 mm MMA. Simulations were performed for two human activity respiratory rates, including rest and moderate activities, and effects of different surgeries and respiratory rates on maxillary sinus were investigated. It was found that after endoscopic sinus surgery, the volume of air entering the maxillary sinus increased significantly, and as the size of the MMA increased, or the breathing condition changed from rest to moderate activity, this volume of air increased. For the rest condition, on average for both nasal passages, for uncinectomy +8 mm MMA, around 15 % of the inhaled flow and 7 % of the exhaled flow enter the maxillary sinuses. For uncinectomy +18 mm MMA, these values are 24 % and 14 %, respectively. As human activity increases, a lower portion of inhaled and exhaled air enters the maxillary sinuses. For the moderate activity condition, on average for both nasal passages, for uncinectomy +8 mm MMA, around 11 % of the inhaled flow and 6 % of the exhaled flow rate enters the maxillary sinus. For uncinectomy +18 mm MMA, these values are 16 % and 8%, respectively. Comparing the steady and unsteady simulation results showed that the quasi-steady flow assumption could predict the flow in the maxillary sinus and the volume of air entering the sinuses, almost at any moment of respiration, with acceptable accuracy.

The Virtual Nose: Assessment of Static Nasal Airway Obstruction Using Computational Simulations and 3D-Printed Models

Background: The use of virtual noses to predict the outcome of surgery is of increasing interests, particularly, as detailed and objective pre- and postoperative assessments of nasal airway obstruction (NAO) are difficult to perform. The objective of this article is to validate predictions using virtual noses against their experimentally measured counterpart in rigid 3D-printed models. Methods: Virtual nose models, with and without NAO, were reconstructed from patients' cone beam computed tomography scans, and used to evaluate airflow characteristics through computational fluid dynamics simulations. Prototypes of the reconstructed models were 3D printed and instrumented experimentally for pressure measurements. Results: Correlation between the numerical predictions and experimental measurements was shown. Analysis of the flow field indicated that the NAO in the nasal valve increases significantly the wall pressure, shear stress, and incremental nasal resistance behind the obstruction. Conclusions: Airflow predictions in static virtual noses correlate well with detailed experimental measurements on 3D-printed replicas of patient airways.

An Overview of Computational Fluid Dynamics Preoperative Analysis of the Nasal Airway

Evaluation of the nasal airway is crucial for every patient with symptoms of nasal obstruction as well as for every patient with other nasal symptoms. This assessment of the nasal airway comprises clinical examination together with imaging studies, with the correlation between findings of this evaluation and symptoms reported by the patient being based on the experience of the surgeon. Measuring nasal airway resistance or nasal airflow can provide additional data regarding the nasal airway, but the benefit of these objective measurements is limited due to their lack of correlation with patient-reported evaluation of nasal breathing. Computational fluid dynamics (CFD) has emerged as a valuable tool to assess the nasal airway, as it provides objective measurements that correlate with patient-reported evaluation of nasal breathing. CFD is able to evaluate nasal airflow and measure variables such as heat transfer or nasal wall shear stress, which seem to reflect the activity of the nasal trigeminal sensitive endings that provide sensation of nasal breathing. Furthermore, CFD has the unique capacity of making airway analysis of virtual surgery, predicting airflow changes after trial virtual modifications of the nasal airway. Thereby, CFD can assist the surgeon in deciding surgery and selecting the surgical techniques that better address the features of each specific nose. CFD has thus become a trend in nasal airflow assessment, providing reliable results that have been validated for analyzing airflow in the human nasal cavity. All these features make CFD analysis a mainstay in the armamentarium of the nasal surgeon. CFD analysis may become the gold standard for preoperative assessment of the nasal airway.

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.

Intranasal Nanoemulsions for Direct Nose-to-Brain Delivery of Actives for CNS Disorders

The treatment of various central nervous system (CNS) diseases has been challenging, despite the rapid development of several novel treatment approaches. The blood–brain barrier (BBB) is one of the major issues in the treatment of CNS diseases, having major role in the protection of the brain but simultaneously constituting the main limiting hurdle for drugs targeting the brain. Nasal drug delivery has gained significant interest for brain targeting over the past decades, wherein the drug is directly delivered to the brain by the trigeminal and olfactory pathway. Various novel and promising formulation approaches have been explored for drug targeting to the brain by nasal administration. Nanoemulsions have the potential to avoid problems, including low solubility, poor bioavailability, slow onset of action, and enzymatic degradation. The present review highlights research scenarios of nanoemulsions for nose-to-brain delivery for the management of CNS ailments classified on the basis of brain disorders and further identifies the areas that remain unexplored. The significance of the total dose delivered to the target region, biodistribution studies, and long-term toxicity studies have been identified as the key areas of future research.

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.

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.

Numerical study on the heat-recovery capacity of the human nasal cavity during expiration

The characteristics of the thermal field in the human nasal cavity during the expiration period were investigated using computational fluid dynamics. Heat and water-vapor recovery features were quantitatively investigated under realistic distributions of the epithelial surface and air temperature. A constant expiratory flow rate of 250 mL/s was assumed. The epithelial surface temperature was approximately 34.3-34.4 °C in the nasopharynx and 33.5-33.6 °C in the vestibule region, and these values are in good agreement with the measurement data in the literature. We observed that heat-recovery from the exhaled air mostly occurred in the posterior turbinate region, and the amount of heat recovered is estimated to be approximately 1/3 of the heat supply during inspiration. Because of this heat transfer from the exhaled air to the epithelial surface, the temperature of the epithelial surface increased in this region, and the exhaled air temperature dropped through the turbinate airway. Water-vapor recovery primarily occurs in the posterior segments of the turbinates; however, the amount of water-vapor transfer was approximately 1/5 of that in inspiration. Accordingly, the relative humidity of the exhaled air remained constant throughout the airway.

Three-dimensional analysis of sexual dimorphism in the soft tissue morphology of the upper airways in a human population

OBJECTIVES

Several studies have analyzed the sexual dimorphism of the skeletal cranial airways. This study aimed to quantify the three-dimensional (3D) morphology of the soft tissues of the upper airways in a human population. We addressed hypotheses about morphological features related to respiratory and energetic aspects of nasal sexual dimorphism.

METHODS

We reconstructed 3D models of 41 male and female soft tissue nasal airways from computed tomography data. We measured 280 landmarks and semilandmarks for 3D-geometric morphometric analyses to test for differences in size and 3D morphology of different functional compartments of the soft tissue airways.

RESULTS

We found statistical evidence for sexual dimorphism: Males were larger than females. 3D features indicated taller and wider inflow tracts, taller outflow tracts and slightly taller internal airways in males. These characteristics are compatible with greater airflow in males.

DISCUSSION

The differences in 3D nasal airway morphology are compatible with the respiratory-energetics hypothesis according to which males differ from females because of greater energetic demands. Accordingly, structures related to inflow and outflow of air show stronger signals than structures relevant for air-conditioning.

Side asymmetry in nasal resistance correlate with nasal obstruction severity in patients with septal deformities: Computational fluid dynamics study

OBJECTIVES

The objective of this study was to investigate the relationship between side asymmetry in nasal resistance (NR) and severity of the nasal airway obstruction (NAO) in patients with different types of nasal septal deformity (NSD).

DESIGN

Computational fluid dynamics (CFD) study.

SETTING

The study was conducted in a tertiary medical centre.

PARTICIPANTS

The study included 232 patients, who were referred to the CT examination of the paranasal sinuses. Exclusion criteria were sinonasal and respiratory diseases that may interfere with the nasal obstruction. The presence and the type of NSD were recorded according to the Mladina's classification.

MAIN OUTCOME MEASURES

The presence and severity of NAO in each patient were assessed by NOSE questionnaire. Eight computational models of the nasal cavity were created from CT scans. Models represented seven Mladina's NSD types and a straight septum of a symptomless patient. CFD calculated airflow partitioning and NR for each nasal passage. Side differences in NR were calculated by the equation ∆NR = NR_left  - NR_right . The relationship between NOSE scores, airflow partitioning and side differences in NR was explored using Spearman's correlation analysis.

RESULTS

Mladina's types of NSD showed differences in airflow partitioning and the degree of side asymmetry in NR. A significant positive correlation was detected between side differences in NR and NOSE scores (R = .762, P = .028). A significant negative correlation was found between the per cent of unilateral airflow and NR (R = -.524, P = .037).

CONCLUSIONS

Our results demonstrated that side asymmetry in NR could explain differences in NAO severity related to the NSD type.

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.

In silico approaches to respiratory nasal flows: A review

The engineering discipline of in silico fluid dynamics delivers quantitative information on airflow behaviour in the nasal regions with unprecedented detail, often beyond the reach of traditional experiments. The ability to provide visualisation and analysis of flow properties such as velocity and pressure fields, as well as wall shear stress, dynamically during the respiratory cycle may give significant insight to clinicians. Yet, there remains ongoing challenges to advance the state-of-the-art further, including for example the lack of comprehensive CFD modelling on varied cohorts of patients. The present article embodies a review of previous and current in silico approaches to simulating nasal airflows. The review discusses specific modelling techniques required to accommodate physiologically- and clinically-relevant findings. It also provides a critical summary of the reported results in the literature followed by an outlook on the challenges and topics anticipated to drive research into the future.

An automated segmentation framework for nasal computational fluid dynamics analysis in computed tomography

The use of computational fluid dynamics (CFD) to model and predict surgical outcomes in the nasal cavity is becoming increasingly popular. Despite a number of well-known nasal segmentation methods being available, there is currently a lack of an automated, CFD targeted segmentation framework to reliably compute accurate patient-specific nasal models. This paper demonstrates the potential of a robust nasal cavity segmentation framework to automatically segment and produce nasal models for CFD. The framework was evaluated on a clinical dataset of 30 head Computer Tomography (CT) scans, and the outputs of the segmented nasal models were further compared with ground truth models in CFD simulations on pressure drop and particle deposition efficiency. The developed framework achieved a segmentation accuracy of 90.9 DSC, and an average distance error of 0.3 mm. Preliminary CFD simulations revealed similar outcomes between using ground truth and segmented models. Additional analysis still needs to be conducted to verify the accuracy of using segmented models for CFD purposes.

CFD analysis of the flow structure in a monkey upper airway validated by PIV experiments

Inhalation exposure to airborne contaminants has adverse effects on humans; however, related research is typically conducted using in vivo/in vitro tests on animals. Extrapolating the test results is complicated by anatomical and physiological differences between animals and humans and a lack of understanding of the transport mechanism inside their respective respiratory tracts. This study determined the detailed air-flow structure in the upper airway of a monkey. A steady computational fluid dynamics simulation, which was validated by previous particle image velocimetry measurements, was adopted for flow rates of 4 L/min and 10 L/min to analyze the flow structure from the nasal/oral cavities to the trachea region in a monkey airway model. The low Reynolds number type k-ε model provided a reasonably accurate prediction of the airflow in a monkey upper airway. Furthermore, it was confirmed that large velocity gradients were generated in the nasal vestibule and larynx regions, as well as increased turbulent air kinetic energy and wall sheer stress.

In silico investigation of sneezing in a full real human upper airway using computational fluid dynamics method

BACKGROUND AND OBJECTIVE

Sneezing is one of the most critical conditions that can occur in the human upper airway. As some reports confirm the injury to the human upper respiratory airway while sneezing. Therefore, the accurate study of the distribution of pressure and velocity in this case is of great importance.

METHODS

In the present study, using a real human upper airway model, the pressure and velocity of the airflow generated in the tract during the sneezing have been investigated. Also, considering the results from a spirometer device as a boundary condition in the simulation process, the calculations have become reliable.

RESULTS

According to the results, during sneezing, taking into account that the average outlet flow rate from the mouth is 4.79 L/s, the velocity of outlet airflow from the mouth and nose reaches 5.3 and 8.4 m/s, respectively. These values were 11.5 and 19, respectively, when the desired maximum flow rate was 10.58 L/s. It can be concluded that the increasing of trachea flow rate, leads to higher percentage of the outlet flow rate from the nose . The highest average pressure and velocity have been occurred in the trachea. Among other salient results of this report, increased average static pressure of larynx to approximately 10 kPa can be pointed which indicates that this area is critical so that the thyroid cartilage defect is likely to occur. It is also noteworthy that the increase of speed at nasopharynx is up to 125 m/s so that the cross-section changing in this area leads the fluid acts as a jet flow. Due to the specific geometry of the nasal cavity, some streams similar to poor shocks are formed, these shocks get stronger by increasing of the flow rate. The thyroid cartilage and nasal cavity are exposed to maximum static pressure extremums, respectively.

CONCLUSIONS

We introduced a model simulating a normal sneezing for two cases using a healthy 30-year-old male person. We believe that the model should be applied for different persons and an atlas of data could be obtained from different cases. This may help the medical system to have more data about the sneezing process.

Evaluation of the Golden Ratio in Nasal Conchae for Surgical Anatomy

PURPOSE

The golden ratio is reached by the fractal model of the number sequence which is known as the "Fibonacci series" and has a convergent ratio of approximately 1.618 between 2 consecutive Fibonacci numbers. Golden ratio relationships have been shown in several plants in the nature and several organs and structures in the human body. The conchae, which form an important part of the nasal valve, have a special geometric significant in terms of providing turbulence to the laminar airflow that passes to the nasal cavity.

METHODS

This study made golden ratio calculations on 34 adults aged 20 to 45 years over computed tomography (CT) images. Totally, 34 volunteers (male, n = 18 and female, n = 16) with no nasal pathologies participated in the study. Using Adobe Photoshop, golden ratio calculations were made by applying the Fibonacci spiral on the images that best showed the conchae and meatuses on the CT images.

RESULTS

The intersection points of the spiral that was projected on the inferior and middle nasal concha were determined as S0, S1, S2, S3, and S4. The distances of S0-S1, S1-S2, S2-S3, and S3-S4 were measured. The concha measurements of the women showed significantly similar values to the golden ratio constant of ∼1.618 in the RS3/S4 and LS3/S4 measurements.

CONCLUSION

We found that the S3/S4 region that captured the golden ratio in our study corresponds to the base part of the inferior nasal concha, and its place of spiraling in the nasal cavity is observed to have an important role in creating vortices.

Correlation of regional deposition dosage for inhaled nanoparticles in human and rat olfactory

Background

Nose-to-brain transport of airborne ultrafine particles (UFPs) via the olfactory pathway has been verified as a possible route for particle translocation into the brain. The exact relationship between increased airborne toxicant exposure and neurological deterioration in the human central nervous system, is still unclear. However, the nasal olfactory is undoubtedly a critical junction where the time course and toxicant dose dependency might be inferred.

Method

Computational fluid-particle dynamics modeling of inhaled nanoparticles (1 to 100 nm) under low to moderate breathing conditions (5 to 14 L/min – human; and 0.14 to 0.40 L/min – rat) were performed in physiologically realistic human and rat nasal airways. The simulation emphasized olfactory deposition, and variations in airflow and particle flux caused by the inter-species airway geometry differences. Empirical equations were developed to predict regional deposition rates of inhaled nanoparticles on human and rat olfactory mucosa in sedentary breathing. Considering, breathing and geometric differences, quantified correlations between human and the rat olfactory deposition dose against a variety of metrics were proposed.

Results

Regional deposition of nanoparticles in human and the rat olfactory was extremely low, with the highest deposition (< 3.5 and 8.1%) occurring for high diffusivity particles of 1.5 nm and 5 nm, respectively. Due to significant filtering of extremely small particles (< 2 nm) by abrupt sharp turns at front of the rat nose, only small fractions of the inhaled nanoparticles (in this range) reached rat olfactory than that in human (1.25 to 45%); however, for larger sizes (> 3 nm), significantly higher percentage of the inhaled nanoparticles reached rat nasal olfactory than that in human (2 to 32 folds). Taking into account the physical and geometric features between human and rat, the total deposition rate (#/min) and deposition rate per unit surface area (#/min/mm²) were comparable for particles> 3 nm. However, when body mass was considered, the normalized deposition rate (#/min/kg) in the rat olfactory region exceeded that in the human. Nanoparticles < 1.5 nm were filtered out by rat anterior nasal cavity, and therefore deposition in human olfactory region exceeded that in the rat model.

Conclusion

Regional deposition dose of inhaled nanoparticles in a human and rat olfactory region was governed by particle size and the breathing rate. Interspecies correlation was determined by combining the effect of deposition dosage, physical\geometric features, and genetic differences. Developed empirical equations provided a tool to quantify inhaled nanoparticle dose in human and rat nasal olfactory regions, which lay the ground work for comprehensive interspecies correlation between the two species. Furthermore, this study contributes to the fields in toxicology, i.e., neurotoxicity evaluation and risk assessment of UFPs, in long-term and low-dose inhalation exposure scenarios.

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.

Examining mesh independence for flow dynamics in the human nasal cavity

Increased computational resources provide new opportunities to explore sophisticated respiratory modelling. A survey of recent publications showed a steady increase in the number of mesh elements used in computational models over time. Complex geometries such as the nasal cavity exhibit sharp gradients and irregular curvatures, leading to abnormal flow development across their surfaces. As such, a robust method for examining the near-wall mesh resolution is required. The non-dimensional wall unit y⁺ (often used in turbulent flows) was used as a parameter to evaluate the near-wall mesh in laminar flows. Mesh independence analysis from line profiles showed that the line location had a significant influence on the result. Furthermore, using a single line profile as a measure for mesh convergence was unsuitable for representing the entire flow field. To improve this, a two-dimensional (2D) cross-sectional plane subtraction method where scalar values (such as the velocity magnitude) on a cross-sectional plane were interpolated onto a regularly spaced grid was proposed. The new interpolated grid values from any two meshed models could then be compared for changes caused by the different meshed models. The application of this method to three-dimensional (3D) volume subtraction was also demonstrated. The results showed that if the near-wall mesh was sufficiently refined, then narrow passages were less reliant on the overall mesh size. However, in wider passages, velocity magnitudes were sensitive to mesh size, requiring a more refined mesh.

NASAL INTERNAL AND EXTERNAL AERODYNAMICS FOR HEALTHY AND BLOCKED CAVITIES

Human nasal airflow in a healthy and partially blocked cavities is investigated using computational and experimental means. While previous studies focused on the flow inside the nasal cavity, this study also looks at the external air stream coming out of the nostrils. The aim is to investigate the airflow subject to partial blocking in the nasal cavity and assess the potential of using a flow visualization method to identify abnormal nasal geometry. Two methods of study are used: Computational Fluid Dynamics (CFD) and experiment based on Particle Image Velocimetry (PIV). Nasal cavity geometry is reconstructed from CT scans. The flow visualization Schileren method is also demonstrated. The computational results agree well with the previous results in terms of Nasal Resistance (NR) and character of the internal flow. Good agreement is also found in the external aerodynamics during expiration between the computational and experimental results. Several generic partial blockages are investigated to show changes in NR, turbulence energy and the air stream leaving the nostrils during expiration. Anterior blockages are found to have more profound effects on all these three aspects, but all show effects on the external air stream. A possible universal angle for the external air stream emitted by a healthy nasal cavity is discussed.