Creation of a standardized geometry of the human nasal cavity

Anatomically-detailed segmented representative adult and pediatric nasal models for assessing regional drug delivery and bioequivalence with suspension nasal sprays

In vitro nasal models can potentially facilitate development and approval of nasal drug products. This study aims to evaluate the potential for using regional deposition measurements from in vitro nasal models to evaluate nasal spray performance across several products. To accomplish this, the posterior regions of six anatomically realistic nasal airway models of adult and pediatric subjects, representing Low (L), Mean (M) and High (H) posterior drug deposition (PD) for each of the two age groups, were segmented with high anatomical precision into five regions of interest. These models were previously developed with the goal of quantifying the range of intersubject variability of PD following administration of inhaled corticosteroids. The in vitro regional drug deposition values were measured for the reference listed drug (RLD) product for triamcinolone acetonide and two corresponding generic (test) nasal spray products, as well as an RLD product for fluticasone furoate nasal spray. In general, the pediatric models mostly demonstrated higher PD compared to the adult models. The majority (>85 %) of PD was confined to the front and the inferior meatus regions. Subsequent population bioequivalence (PBE) analyses of the regional nasal deposition suggested that the anatomical differences among subjects may impact the nasal spray performance across different nasal products.

Development of an Intranasal In Situ System for Ribavirin Delivery: In Vitro and In Vivo Evaluation

Recently, ribavirin has demonstrated effectiveness in treating glioblastoma through intranasal administration utilizing the nose-to-brain delivery route. Enhancing ribavirin's bioavailability can be achieved by utilizing intranasal stimuli-responsive systems that create a gel on the nasal mucosa. The research examined thermosensitive, pH-sensitive, and ion-selective polymers in various combinations and concentrations, chosen in line with the current Quality by Design (QbD) approach in pharmaceutical development. Following a thorough assessment of key parameters, the optimal composition of gellan gum at 0.5%, Poloxamer 124 at 2%, and purified water with ribavirin concentration at 100 mg/mL was formulated and subjected to in vivo testing. Through experiments on male rats, the nose-to-brain penetration mechanism of the active pharmaceutical ingredient (API) was elucidated, showcasing drug accumulation in the olfactory bulbs and brain.

Sound and Noise Sources in Sonotubometry: An Investigation of Eustachian Tube Assessment

This research aims to enhance the understanding of the acoustic processes occurring during sonotubometry, a method used to assess the Eustachian tube (ET) function. Recent advancements in digital signal processing enable a more comprehensive data analysis. In this project, a silicone model of the ET was developed to systematically study the existing noise and sound sources. These measurements were then compared with recordings from human subjects. Three distinct 'noise sources' were identified, which can influence the assessment of the ET opening using transmission measurements of the imposed signal: sound leakage from the speaker, a clicking noise at the initiation of ET opening, and rumbling/swallowing noise. Through spectral analysis, it was also possible to ascertain the spectral and temporal occurrence of these sound and noise types. The silicone model exhibited remarkable similarity to the healthy human ET, making it a robust experimental model for investigating the acoustics of sonotubometry. The findings underscore the significance of delving deeper into the analysed sound, as the noise occurring during sonotubometry can be easily misconstrued as an actual ET opening. Particularly, careful consideration is warranted when evaluating data involving clicking and swallowing noise.

Comparative Analysis of Micrometer-Sized Particle Deposition in the Olfactory Regions of Adult and Pediatric Nasal Cavities: A Computational Study

Direct nose-to-brain drug delivery, a promising approach for treating neurological disorders, faces challenges due to anatomical variations between adults and children. This study aims to investigate the spatial particle deposition of micron-sized particles in the nasal cavity among adult and pediatric subjects. This study focuses on the olfactory region considering the effect of intrasubject parameters and particle properties. Two child and two adult nose models were developed based on computed tomography (CT) images, in which the olfactory region of the four nasal cavity models comprises 7% to 10% of the total nasal cavity area. Computational Fluid Dynamics (CFD) coupled with a discrete phase model (DPM) was implemented to simulate the particle transport and deposition. To study the deposition of micrometer-sized drugs in the human nasal cavity during a seated posture, particles with diameters ranging from 1 to 100 μm were considered under a flow rate of 15 LPM. The nasal cavity area of adults is approximately 1.2 to 2 times larger than that of children. The results show that the regional deposition fraction of the olfactory region in all subjects was meager for 1-100 µm particles, with the highest deposition fraction of 5.7%. The deposition fraction of the whole nasal cavity increased with the increasing particle size. Crucially, we identified a correlation between regional deposition distribution and nasal cavity geometry, offering valuable insights for optimizing intranasal drug delivery.

Gold Nanoparticles: Tunable Characteristics and Potential for Nasal Drug Delivery

A general procedure to prepare gold nanourchins (GNUs) via a seed-mediated method was followed using dopamine hydrochloride as a reducing agent and silver nitrate salt (AgNO3) as a shape-directing agent. The novelty of this study comes from the successful incorporation of the prepared gold urchins as an aqueous suspension in a nasal pressurized metered dose inhaler (pMDI) formulation and the investigation of their potential for olfactory targeting for direct nose-to-brain drug delivery (NTBDD). The developed pMDI formulation was composed of 0.025% w/w GNUs, 2% w/w Milli-Q water, and 2% w/w EtOH, with the balance of the formulation being HFA134a propellant. Particle integrity and aerosolization performance were examined using an aerosol exposure system, whereas the nasal deposition profile was tested in a sectioned anatomical replica of human nasal airways. The compatibility of the gold dispersion with the nasal epithelial cell line RPMI 2650 was also investigated in this study. Colloidal gold was found to be stable following six-month storage at 4 °C and during the lyophilization process utilizing a pectin matrix for complete re-dispersibility in water. The GNUs were intact and discrete following atomization via a pMDI, and 13% of the delivered particles were detected beyond the nasal valve, the narrowest region in the nasal cavity, out of which 5.6% was recovered from the olfactory region. Moreover, the formulation was found to be compatible with the human nasal epithelium cell line RPMI 2650 and excellent cell viability was observed. The formulated GNU-HFA-based pMDI is a promising approach for intranasal drug delivery, including deposition in the olfactory region, which could be employed for NTBDD applications.

Comparison of Nasal Dimensions According to the Facial and Nasal Indices Using Cone-Beam Computed Tomography

The nasal cavity constitutes the foremost portion of the respiratory system, composed of the anterior nasal aperture, nostrils, and choanae. It has an intricate anatomical structure since it has various functions, such as heat exchange, humidification, and filtration. Accordingly, clinical symptoms related to the nose, such as nasal congestion, snoring, and nasal septal deviation, are closely linked to the complex anatomical structure of the nasal cavity. Thus, the nasal cavity stands as a paramount structure in both forensic and clinical contexts. The majority of relevant studies have performed comparisons between sexes, with studies making comparisons according to the FI and NI only and examining relative percentages. Furthermore, the nasal cavity was measured in 2D, and not 3D, in most cases. In this study, we conducted a 3D modeling and anthropometric assessment of the nasal cavity using a 3D analysis software. Furthermore, we aimed to investigate whether the size of the nasal cavity differs according to sex, facial index (FI), and nasal index (NI). We retrospectively reviewed the cone-beam computed tomography (CBCT) data of 100 participants (50 males, 50 females) aged 20-29 years who visited the dental hospital of Dankook University (IRB approval no. DKUDH IRB 2020-01-007). Our findings showed that nasal cavity sizes generally differed according to sex, FI, and NI. These findings provide implications for performing patient-tailored surgeries in clinical practice and conducting further research on the nasal cavity. Therefore, we believe that our study makes a significant contribution to the literature.

Characterizing regional drug delivery within the nasal airways

INTRODUCTION

The nose has been receiving increased attention as a route for drug delivery. As the site of deposition constitutes the first point of contact of the body with the drug, characterization of the regional deposition of intranasally delivered droplets or particles is paramount to formulation and device design of new products.

AREAS COVERED

This review article summarizes the recent literature on intranasal regional drug deposition evaluated in vivo, in vitro and in silico, with the aim of correlating parameters measured in vitro with formulation and device performance. We also highlight the relevance of regional deposition to two emerging applications: nose-to-brain drug delivery and intranasal vaccines.

EXPERT OPINION

As in vivo studies of deposition can be costly and time-consuming, researchers have often turned to predictive in vitro and in silico models. Variability in deposition is high due in part to individual differences in nasal geometry, and a complete predictive model of deposition based on spray characteristics remains elusive. Carefully selected or idealized geometries capturing population average deposition can be useful surrogates to in vivo measurements. Continued development of in vitro and in silico models may pave the way for development of less variable and more effective intranasal drug products.

A Cell-Based Nasal Model for Screening the Deposition, Biocompatibility, and Transport of Aerosolized PLGA Nanoparticles

The olfactory region of the nasal cavity directly links the brain to the external environment, presenting a potential direct route to the central nervous system (CNS). However, targeting drugs to the olfactory region is challenging and relies on a combination of drug formulation, delivery device, and administration technique to navigate human nasal anatomy. In addition, in vitro and in vivo models utilized to evaluate the performance of nasal formulations do not accurately reflect deposition and uptake in the human nasal cavity. The current study describes the development of a respirable poly(lactic-co-glycolic acid) nanoparticle (PLGA NP) formulation, delivered via a pressurized metered dose inhaler (pMDI), and a cell-containing three-dimensional (3D) human nasal cast model for deposition assessment of nasal formulations in the olfactory region. Fluorescent PLGA NPs (193 ± 3 nm by dynamic light scattering) were successfully formulated in an HFA134a-based pMDI and were collected intact following aerosolization. RPMI 2650 cells, widely employed as a nasal epithelial model, were grown at the air-liquid interface (ALI) for 14 days to develop a suitable barrier function prior to exposure to the aerosolized PLGA NPs in a glass deposition apparatus. Direct aerosol exposure was shown to have little effect on cell viability. Compared to an aqueous NP suspension, the transport rate of the aerosolized NPs across the RPMI 2650 barrier was higher at all time points indicating the potential advantages of delivery via aerosolization and the importance of employing ALI cellular models for testing respirable formulations. The PLGA NPs were then aerosolized into a 3D-printed human nasal cavity model with an insert of ALI RPMI 2650 cells positioned in the olfactory region. Cells remained highly viable, and there was significant deposition of the fluorescent NPs on the ALI cultures. This study is a proof of concept that pMDI delivery of NPs is a viable means of targeting the olfactory region for nose-to-brain drug delivery (NTBDD). The cell-based model allows not only maintenance under ALI culture conditions but also sampling from the basal chamber compartment; hence, this model could be adapted to assess drug deposition, uptake, and transport kinetics in parallel under real-life settings.

Fibres in the nasal cavity: A pilot study of the recovery, background, and transfer in smothering scenarios

In cases where the suspected cause of death is smothering, fibre traces recovered from the nasal cavity are hypothesised to refute or support this proposition. In order to carry out such evaluations, an efficient recovery method must first be established. This pilot study tested five different recovery methods on 3D printed models of nasal cavities. Among which, the use of the transparent AccuTrans® polyvinyl Siloxane casts demonstrated the best recovery efficiency with a median of 90% of deposited fibres recovered. The efficacy of this method was then verified on cadavers. Apart from a reliable recovery method, an understanding of the background population of fibres in nasal cavities, as well as the mechanisms of the transfer from the purported smothering textile to the nasal cavity is essential to evaluate the findings in these cases of suspected smothering. Samplings of the nasal cavities of 20 cadavers were thus carried out to gather data on the background population of fibres. Results showed that nasal cavities are not void of fibres, but the quantities are expected to be low, with a mean of 3.8 fibres per cavity recovered. Information on generic fibre class, colour, and length of these background fibres were also obtained with the use of low and high-power microscopy. The frequencies found in this population of fibres closely align with data from other population studies where black cotton was the most common. Finally, transfer experiments using the 3D printed models fitted with a respiratory pump to simulate breathing were carried out, along with testing on live volunteers in-vivo. The results demonstrated a verifiable transfer of fibres into the nasal cavity in smothering scenarios. Textiles of various shedding capacities were used in these tests and the findings suggest an influence of this variable on the quantities of fibres transferred.

What Are the Key Anatomical Features for the Success of Nose-to-Brain Delivery? A Study of Powder Deposition in 3D-Printed Nasal Casts

Nose-to-brain delivery is a promising way to improve the treatment of central nervous system disorders, as it allows the bypassing of the blood-brain barrier. However, it is still largely unknown how the anatomy of the nose can influence the treatment outcome. In this work, we used 3D printing to produce nasal replicas based on 11 different CT scans presenting various anatomical features. Then, for each anatomy and using the Design of Experiments methodology, we characterised the amount of a powder deposited in the olfactory region of the replica as a function of multiple parameters (choice of the nostril, device, orientation angle, and the presence or not of a concomitant inspiration flow). We found that, for each anatomy, the maximum amount of powder that can be deposited in the olfactory region is directly proportional to the total area of this region. More precisely, the results show that, whatever the instillation strategy, if the total area of the olfactory region is below 1500 mm2, no more than 25% of an instilled powder can reach this region. On the other hand, if the total area of the olfactory region is above 3000 mm2, the deposition efficiency reaches 50% with the optimal choice of parameters, whatever the other anatomical characteristics of the nasal cavity. Finally, if the relative difference between the areas of the two sides of the internal nasal valve is larger than 20%, it becomes important to carefully choose the side of instillation. This work, by predicting the amount of powder reaching the olfactory region, provides a tool to evaluate the adequacy of nose-to-brain treatment for a given patient. While the conclusions should be confirmed via in vivo studies, it is a first step towards personalised treatment of neurological pathologies.

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

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

A single‐sided trans‐nasal catheter for smooth and efficient oxygen delivery can improve the safety in patients undergoing pancreato‐biliary endoscopy under intravenous sedation: A randomized trial

Background

Pancreato‐biliary endoscopic procedures often need to be performed under deep intravenous sedation. The patients are at an increased risk of respiratory depression influenced by the anatomical dead space of the upper respiratory system. We aimed to evaluate the benefit of oxygen delivery through a single‐sided trans‐nasal catheter (TC) for patients undergoing pancreato‐biliary endoscopy.

Methods

Oxygen supplementation during the procedure was provided either by insertion of a single‐sided TC or insertion of a conventional nasal catheter (NC). A prospective, single‐blind, randomized controlled study was conducted in two groups.

Results

The number of patients who indicated a decrease in the peripheral transcutaneous oxygen saturation (SpO2; desaturation) was significantly lower in the TC group than in the counterpart (8/58; 13.8% vs. 26/58; 44.8% p < 0.001). The efficient oxygen delivery in the safe range was better conserved in the TC group than in the NC one. There was no adverse effect on both groups. The maximum SpO2 while the endoscopic procedure was significantly higher in the TC group (99.7% vs. 99.3% p = 0.016) and the minimum SpO2 was also significantly higher in the same group (97.7% vs. 94.1% p < 0.0001), which meant that the efficient oxygen delivery was better maintained in TC group than the NC group.

Conclusions

A single‐sided TC placed in the pharynx in patients undergoing pancreato‐biliary endoscopy prepares a superior condition of the patients for venous sedation, maintained hyper‐oxygen saturation and a relatively higher SpO2 level to be maintained in limited conditions to reduce the dead space with acceptable tolerance, as compared to the placement of a conventional NC.

Development of intranasal implantable devices for schizophrenia treatment

In this work the preparation and characterisation of intranasal implants for the delivery of risperidone (RIS) is described. The aim of this work is to develop better therapies to treat chronic conditions affecting the brain such as schizophrenia. This type of systems combines the advantages of intranasal drug delivery with sustained drug release. The resulting implants were prepared using biodegradable materials, including poly(caprolactone) (PCL) and poly(lactic-co-glycolic acid) (PLGA). These polymers were combined with water-soluble compounds, such as poly(ethylene glycol) (PEG) 600, PEG 3000, and Tween® 80 using a solvent-casting method. The resulting implants contained RIS loadings ranging between 25 and 50%. The obtained implants were characterised using a range of techniques including thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), attenuated total reflectance-Fourier transform infrared (ATR-FTIR), X-ray diffraction (XRD), and Scanning Electron Microscopy (SEM). Moreover, in vitro RIS release was evaluated showing that the addition of water-soluble compounds exhibited significant faster release profiles compared to pristine PCL and PLGA-based implants. Interestingly, PCL-based implants containing 25% of RIS and PLGA-based implants loaded with 50% of RIS showed sustained drug release profiles up to 90 days. The former showed faster release rates over the first 28 days but after this period PLGA implants presented higher release rates. The permeability of RIS released from the implants through a model membrane simulating nasal mucosa was subsequently evaluated showing desirable permeation rate of around 2 mg/day. Finally, following in vitro biocompatibility studies, PCL and PLGA-based implants showed acceptable biocompatibility. These results suggested that the resulting implants displayed potential of providing prolonged drug release for brain-targeting drugs.

Anatomically realistic nasal replicas capturing the range of nasal spray drug delivery in adults

To improve the relationships between commonly conducted in vitro studies for locally-acting nasal spray drug products with in vivo regional deposition, this study developed a set of in vitro adult nasal geometries that captured the range of nasal drug delivery to the region posterior to internal nasal valve (INV), also known as posterior delivery (PD), and evaluated their performance with existing in vivo data. The PD of fluticasone propionate (FP) and fluticasone furoate (FF) in 40 nasal cavities was statistically analyzed to identify three airway models representing the low, mean, and high PD in adults. The models were also externally validated by comparing the in vitro nasal deposition from a different drug product (mometasone furoate (MF)) with the relevant in vivo data. The three selected geometries represented the low, mean, and high PD with multiple nasal sprays. They were verified in terms of reproducibility of in vitro data and validated by showing a reasonable agreement with preexisting in vivo MF PD despite differences in administration and defining the regions. The three models are envisioned to potentially facilitate the development of locally-acting nasal sprays and provide a better understanding of how in vitro metrics relate to in vivo regional nasal deposition.

Simulation and Artificial Intelligence in Rhinoplasty: A Systematic Review

BACKGROUND

Rhinoplasty is one of the most popular cosmetic procedures. The complexity of the nasal structure and the substantial aesthetic and functional impact of the operation make rhinoplasty very challenging. The past few years have witnessed an increasing implementation of artificial intelligence (AI) and simulation systems into plastic surgery practice. This review explores the potential uses of AI and simulation models in rhinoplasty.

METHODS

Five electronic databases were searched: PubMed, CINAHL, EMBASE, Scopus, and Web of Science. We used the Preferred Reporting Items for Systematic Reviews and Meta-Analysis as our basis of organization.

RESULTS

Several simulation models were described to predict the nasal shape that aesthetically matches the patient's face, indicate the implant size in augmentation rhinoplasty and construct three-dimensional (3D) facial images from two-dimensional images. Machine learning was used to learn surgeons' rhinoplasty styles and accurately simulate the outcomes. Deep learning was used to predict rhinoplasty status accurately and analyze the factors associated with increased facial attractiveness after rhinoplasty. Finally, a deep learning model was used to predict patients' age before and after rhinoplasty proving that the procedure made the patients look younger.

CONCLUSION

3D simulation models and AI models can revolutionalize the practice of functional and aesthetic rhinoplasty. Simulation systems can be beneficial in preoperative planning, intra-operative decision making, and postoperative evaluation. In addition, AI models can be trained to carry out tasks that are either challenging or time-consuming for surgeons.

LEVEL OF EVIDENCE III

This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

In Vitro Nasal Tissue Model for the Validation of Nasopharyngeal and Midturbinate Swabs for SARS-CoV-2 Testing

Large-scale population testing is a key tool to mitigate the spread of respiratory pathogens, such as the current COVID-19 pandemic, where swabs are used to collect samples in the upper airways (e.g., nasopharyngeal and midturbinate nasal cavities) for diagnostics. However, the high volume of supplies required to achieve large-scale population testing has posed unprecedented challenges for swab manufacturing and distribution, resulting in a global shortage that has heavily impacted testing capacity worldwide and prompted the development of new swabs suitable for large-scale production. Newly designed swabs require rigorous preclinical and clinical validation studies that are costly and time-consuming (i.e., months to years long); reducing the risks associated with swab validation is therefore paramount for their rapid deployment. To address these shortages, we developed a 3D-printed tissue model that mimics the nasopharyngeal and midturbinate nasal cavities, and we validated its use as a new tool to rapidly test swab performance. In addition to the nasal architecture, the tissue model mimics the soft nasal tissue with a silk-based sponge lining, and the physiological nasal fluid with asymptomatic and symptomatic viscosities of synthetic mucus. We performed several assays comparing standard flocked and injection-molded swabs. We quantified the swab pickup and release and determined the effect of viral load and mucus viscosity on swab efficacy by spiking the synthetic mucus with heat-inactivated SARS-CoV-2 virus. By molecular assay, we found that injected molded swabs performed similarly or superiorly in comparison to standard flocked swabs, and we underscored a viscosity-dependent difference in cycle threshold values between the asymptomatic and symptomatic mucuses for both swabs. To conclude, we developed an in vitro nasal tissue model that corroborated previous swab performance data from clinical studies; this model will provide to researchers a clinically relevant, reproducible, safe, and cost-effective validation tool for the rapid development of newly designed swabs.

Advances and Challenges in Intranasal Delivery of Antipsychotic Agents Targeting the Central Nervous System

Treatment of central nervous system (CNS) disorders is challenging using conventional delivery strategies and routes of administration because of the presence of the blood–brain barrier (BBB). This BBB restricts the permeation of most of the therapeutics targeting the brain because of its impervious characteristics. Thus, the challenges of delivering the therapeutic agents across the BBB to the brain overcoming the issue of insufficient entry of neurotherapeutics require immediate attention for recovering from the issues by the use of modern platforms of drug delivery and novel routes of administration. Therefore, the advancement of drug delivery tools and delivering these tools using the intranasal route of drug administration have shown the potential of circumventing the BBB, thereby delivering the therapeutics to the brain at a significant concentration with minimal exposure to systemic circulation. These novel strategies could lead to improved efficacy of antipsychotic agents using several advanced drug delivery tools while delivered via the intranasal route. This review emphasized the present challenges of delivering the neurotherapeutics to the brain using conventional routes of administration and overcoming the issues by exploring the intranasal route of drug administration to deliver the therapeutics circumventing the biological barrier of the brain. An overview of different problems with corresponding solutions in administering therapeutics via the intranasal route with special emphasis on advanced drug delivery systems targeting to deliver CNS therapeutics has been focused. Furthermore, preclinical and clinical advancements on the delivery of antipsychotics using this intranasal route have also been emphasized.

Human Multi-Compartment Airways-on-Chip Platform for Emulating Respiratory Airborne Transmission: From Nose to Pulmonary Acini

The past decade has witnessed tremendous endeavors to deliver novel preclinical in vitro lung models for pulmonary research endpoints, including foremost with the advent of organ- and lung-on-chips. With growing interest in aerosol transmission and infection of respiratory viruses within a host, most notably the SARS-CoV-2 virus amidst the global COVID-19 pandemic, the importance of crosstalk between the different lung regions (i.e., extra-thoracic, conductive and respiratory), with distinct cellular makeups and physiology, are acknowledged to play an important role in the progression of the disease from the initial onset of infection. In the present Methods article, we designed and fabricated to the best of our knowledge the first multi-compartment human airway-on-chip platform to serve as a preclinical in vitro benchmark underlining regional lung crosstalk for viral infection pathways. Combining microfabrication and 3D printing techniques, our platform mimics key elements of the respiratory system spanning (i) nasal passages that serve as the alleged origin of infections, (ii) the mid-bronchial airway region and (iii) the deep acinar region, distinct with alveolated airways. Crosstalk between the three components was exemplified in various assays. First, viral-load (including SARS-CoV-2) injected into the apical partition of the nasal compartment was detected in distal bronchial and acinar components upon applying physiological airflow across the connected compartment models. Secondly, nebulized viral-like dsRNA, poly I:C aerosols were administered to the nasal apical compartment, transmitted to downstream compartments via respiratory airflows and leading to an elevation in inflammatory cytokine levels secreted by distinct epithelial cells in each respective compartment. Overall, our assays establish an in vitro methodology that supports the hypothesis for viral-laden airflow mediated transmission through the respiratory system cellular landscape. With a keen eye for broader end user applications, we share detailed methodologies for fabricating, assembling, calibrating, and using our multi-compartment platform, including open-source fabrication files. Our platform serves as an early proof-of-concept that can be readily designed and adapted to specific preclinical pulmonary research endpoints.

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.

In Vitro Nasal Tissue Model for the Validation of Nasopharyngeal and Mid-turbinate Swabs for SARS-CoV-2 Testing

Large-scale population testing is a key tool to mitigate the spread of respiratory pathogens, as in the current COVID-19 pandemic, where swabs are used to collect samples in the upper airways (e.g. nasopharyngeal and mid-turbinate nasal cavities) for diagnostics. However, the high volume of supplies required to achieve large-scale population testing has posed unprecedented challenges for swab manufacturing and distribution, resulting in a global shortage that has heavily impacted testing capacity world-wide and prompted the development of new swabs suitable for large-scale production. Newly designed swabs require rigorous pre-clinical and clinical validation studies that are costly and time consuming ( i . e . months to years long); reducing the risks associated with swab validation is therefore paramount for their rapid deployment. To address these shortages, we developed a 3D-printed tissue model that mimics the nasopharyngeal and mid-turbinate nasal cavities, and we validated its use as a new tool to rapidly test swab performance. In addition to the nasal architecture, the tissue model mimics the soft nasal tissue with a silk-based sponge lining, and the physiological nasal fluid with asymptomatic and symptomatic viscosities of synthetic mucus. We performed several assays comparing standard flocked and injection-molded swabs. We quantified the swab pick-up and release, and determined the effect of viral load and mucus viscosity on swab efficacy by spiking the synthetic mucus with heat-inactivated SARS-CoV-2 virus. By molecular assays, we found that injected molded swabs performed similarly or superiorly in comparison to standard flocked swabs and we underscored a viscosity-dependent difference in cycle threshold values between the asymptomatic and symptomatic mucus for both swabs. To conclude, we developed an in vitro nasal tissue model, that corroborated previous swab performance data from clinical studies, with the potential of providing researchers with a clinically relevant, reproducible, safe, and cost-effective validation tool for the rapid development of newly designed swabs.

The importance of pre-formulation studies and of 3D-printed nasal casts in the success of a pharmaceutical product intended for nose-to-brain delivery

This review aims to cement three hot topics in drug delivery: (a) the pre-formulation of new products intended for nose-to-brain delivery; (b) the development of nasal casts for studying the efficacy of potential new nose-to-brain delivery systems at the early of their development (pre-formulation); (c) the use of 3D printing based on a wide variety of materials (transparent, biocompatible, flexible) providing an unprecedented fabrication tool towards personalized medicine by printing nasal cast on-demand based on CT scans of patients. This review intends to show the links between these three subjects. Indeed, the pathway selected to administrate the drug to the brain not only influence the formulation strategies to implement but also the design of the cast, to get the most convincing measures from it. Moreover, the design of the cast himself influences the choice of the 3D-printing technology, which, in its turn, bring more constraints to the nasal replica design. Consequently, the formulation of the drug, the cast preparation and its realisation should be thought of as a whole and not separately.

Recent In Vitro and In Silico Advances in the Understanding of Intranasal Drug Delivery

BACKGROUND

Many drugs are delivered intranasally for local or systemic effect, typically in the form of droplets or aerosols. Due to the high cost of in vivo studies, drug developers and researchers often turn to in vitro or in silico testing when first evaluating the behavior and properties of intranasal drug delivery devices and formulations. Recent advances in manufacturing and computer technologies have allowed for increasingly realistic and sophisticated in vitro and in silico reconstructions of the human nasal airways.

OBJECTIVE

The study aims to perform a summary of advances in the understanding of intranasal drug delivery based on recent in vitro and in silico studies.

CONCLUSION

The turbinates are a common target for local drug delivery applications, and while nasal sprays are able to reach this region, there is currently no broad consensus across the in vitro and in silico literature concerning optimal parameters for device design, formulation properties and patient technique which would maximize turbinate deposition. Nebulizers can more easily target the turbinates, but come with the disadvantage of significant lung deposition. Targeting of the olfactory region of the nasal cavity has been explored for the potential treatment of central nervous system conditions. Conventional intranasal devices, such as nasal sprays and nebulizers, deliver very little dose to the olfactory region. Recent progress in our understanding of intranasal delivery will be useful in the development of the next generation of intranasal drug delivery devices.

Estimation of absorbed radiation doses to skin and S-values for organs at risk due to nasal administration of PET agents using Monte Carlo simulations

PURPOSE

The intranasal (IN) administration of radiopharmaceuticals is of interest in being a viable route for the delivery of radiopharmaceuticals that do not ordinarily cross the blood-brain barrier (BBB). However, to be viable in a patient population, good image quality as well as safety of the administration should be demonstrated. This work provides radiation dosimetry calculations and simulations related to the radiation safety of performing such experiments in a human cohort.

METHODS

We performed Monte Carlo (MC) simulations to estimate radiation dose to the skin inside a cylindrical model of the nasal cavity assuming a homogenous distribution layer of ¹¹ C and ¹⁸ F and calculated a geometry conversion factor (F_P-C ) which can be used to convert from a planar geometry to a cylindrical geometry using more widely available software tools. We compared radiation doses from our simulated cylindrical geometry with the planar dose estimates employing our geometry conversion factor from VARSKIN 6.1 software and also from an analytical equation. Furthermore, in order to estimate radiation dosimetry to surrounding organs of interest, we performed a voxelized MC simulation of a fixed radioactivity inside the nasal cavity and calculated S-values to organs such as the eyes, thyroid, and brain.

RESULTS

MC simulations of contamination scenarios using planar absorbed doses of 15.50 and 8.60 mGy/MBq for ¹⁸ F and ¹¹ C, respectively, and 35.70 and 19.80 mGy/MBq per hour for cylindrical geometries, leading to determination of an F_P-C of 2.3. Planar absorbed doses (also in units of mGy/MBq) determined by the analytical equation were 16.96 and 8.68 (¹⁸ F and ¹¹ C) and using VARSKIN were 16.60 and 9.26 (¹⁸ F and ¹¹ C), respectively. Application of F_P-C to these results demonstrates values with a maximum difference of 9.41% from the cylindrical geometry MC calculation, demonstrating that when accounting for geometry, more simplistic techniques can be utilized to estimate IN dosimetry. Voxelized MC simulations of radiation dosimetry from a fixed source of 1 MBq of activity confined to the nasal cavity resulted in S-values to the thyroid, eyes, and brain of 1.72 x 10^-6 , 1.93 x 10^-5 , and 3.51 x 10^-6  mGy/MBq·s, respectively, for ¹⁸ F and 1.80 × 10^-6 , 1.95 × 10^-5 , and 3.54 × 10^-6  mGy/MBq·s for ¹¹ C.

CONCLUSION

Dosimetry concerns about IN administrations of PET radiotracers should be considered before clinical use. Values presented in the simulations such as the S-values can be further used for assessment of absorbed doses in cases of IN administration, and can be used to develop and adapt specific study protocols. All three presented methods provided similar results when considering the use of a geometry conversion factor for planar to cylindrical geometry, demonstrating that standard tools rather than dedicate MC simulations may be used to perform dose calculations in nasal administrations.

In situ-gelling starch nanoparticle (SNP)/O-carboxymethyl chitosan (CMCh) nanoparticle network hydrogels for the intranasal delivery of an antipsychotic peptide

Existing oral or injectable antipsychotic drug delivery strategies typically demonstrate low bioavailability to targeted brain regions, incentivizing the development of alternative delivery strategies. Delivery via the nasal cavity circumvents multiple barriers for reaching the brain but requires drug delivery vehicles with very specific properties to be effective. Herein, we report in situ-gelling and degradable bulk nanoparticle network hydrogels consisting of oxidized starch nanoparticles (SNPs) and carboxymethyl chitosan (CMCh) that enable intranasal delivery via spray, high nasal mucosal retention, and functional controlled release of the peptide drug PAOPA, a positive allosteric modulator of dopamine D2 receptor. PAOPA-loaded SNP-CMCh hydrogels can alleviate negative symptoms like behavioural abnormalities associated with schizophrenia (i.e. decreased social interaction time) for up to 72 h in an MK-801-induced pre-clinical rat model of schizophrenia at a low drug dosage (0.5 mg/kg); in comparison, conventional PAOPA administration via the intraperitoneal route requires twice the PAOPA dose to achieve a therapeutic effect that persists for only a few hours. This strategy offers potential for substantially decreasing re-administration frequencies and overall drug doses (and thus side-effects) of a range of potential antipsychotic drugs via a minimally-invasive administration route.

Role of nasal casts for in vitro evaluation of nasal drug delivery and quantitative evaluation of various nasal casts

Background: Nasal casts may characterize intranasal drug deposition. Methodology: The Koken cast, described as 'anatomically correct', and the Optinose cast, derived from MRI of a healthy male during velum closure, were dimensionally compared and assessed for deposition assessment suitability. Results: Smallest vertical cross-sectional areas (valve region) for Koken and Optinose right/left: 2.55/2.75 and 1.18/1.18 cm², respectively, versus a 'normative' mean (range) of 0.85 cm² (0.2-1.6 cm²). Intranasal volumes differed (computed tomography/water fill): Koken, 35.8/38.6 cm³ and Optinose, 24.1/25.0 cm³, versus a 'normative' mean (range) of 26.4 cm³ (20.9-31.1 cm³). Conclusion: Koken cast dimensions are larger than the normal range and the Optinose cast. The validity of casts for regulatory drug deposition studies is suspect.

Characterization of the Airflow within an Average Geometry of the Healthy Human Nasal Cavity

This study's objective was the generation of a standardized geometry of the healthy nasal cavity. An average geometry of the healthy nasal cavity was generated using a statistical shape model based on 25 symptom-free subjects. Airflow within the average geometry and these geometries was calculated using fluid simulations. Integral measures of the nasal resistance, wall shear stresses (WSS) and velocities were calculated as well as cross-sectional areas (CSA). Furthermore, individual WSS and static pressure distributions were mapped onto the average geometry. The average geometry featured an overall more regular shape that resulted in less resistance, reduced WSS and velocities compared to the median of the 25 geometries. Spatial distributions of WSS and pressure of the average geometry agreed well compared to the average distributions of all individual geometries. The minimal CSA of the average geometry was larger than the median of all individual geometries (83.4 vs. 74.7 mm²). The airflow observed within the average geometry of the healthy nasal cavity did not equal the average airflow of the individual geometries. While differences observed for integral measures were notable, the calculated values for the average geometry lay within the distributions of the individual parameters. Spatially resolved parameters differed less prominently.

Review: The role of computational simulation in understanding the postoperative sinonasal environment

Nasal surgery improves symptoms in a majority of patients for whom medical treatment has failed. In rhinosinusitis patients, endoscopic sinus surgery aims to alleviate obstruction and re-establish mucociliary clearance. Surgery alters the structure-function relationship within the nasal passage, which is difficult to assess clinically. Computational modelling has been used to investigate this relationship by simulating air flow and environmental variables inside realistic three-dimensional models of the human nasal airway but many questions remain unanswered and need further investigation. The application of computational models to improve pre-surgical planning and post-surgical treatment may not be currently possible due to the absence of knowledge correlating the model-predicted parameters to physiological variables. Links between these parameters to patient outcomes are yet to be established. This article reviews the recent application of computational modelling to understand the nasal structure-function relationship following surgery in patients with sinusitis and nasal obstruction.

The complexities of nasal airflow: theory and practice

The objective of this study was to investigate the effects of nasal valve area, valve stiffness, and turbinate region cross-sectional area on airflow rate, nasal resistance, flow limitation, and inspiratory "hysteresis" by the use of a mathematical model of nasal airflow. The model of O'Neill and Tolley (Clin Otolaryngol Allied Sci 13: 273-277, 1988) describing the effects of valve area and stiffness on the nasal pressure-flow relationship was improved by the incorporation of additional terms involving 1) airflow through the turbinate region, 2) the dependence of the flow coefficients for the valve and turbinate region on the Reynolds number, and 3) effects of unsteady flow. The model was found to provide a good fit for normal values for nasal resistance and for pressure-flow curves reported in the literature for both congested and decongested states. Also, by showing the relative contribution of the nasal valve and turbinate region to nasal resistance, the model sheds light in explaining the generally poor correlation between nasal resistance measurements and the results from acoustic rhinometry. Furthermore, by proposing different flow conditions for the acceleration and deceleration phases of inspiration, the model produces an inspiratory loop (commonly referred to as hysteresis) consistent with those reported in the literature. With simulation of nasal flaring, the magnitude of the loop, the nasal resistance, and flow limitation all show change similar to that observed in the experimental results.NEW & NOTEWORTHY The present model provides considerable insight into some difficult conundrums in both clinical and technical aspects of nasal airflow. Also, the description of nasal airflow mechanics based on the Hagen-Poiseuille equation and Reynolds laminar-turbulent transition in long straight tubes, which has figured prominently in medical textbooks and journal articles for many years, is shown to be seriously in error at a fundamental level.

Normative ranges of nasal airflow variables in healthy adults

PURPOSE

Virtual surgery planning based on computational fluid dynamics (CFD) simulations of nasal airflow has the potential to improve surgical outcomes for patients with nasal airway obstruction (NAO). Virtual surgery planning requires normative ranges of airflow variables, but few studies to date have quantified inter-individual variability of nasal airflow among healthy subjects. This study reports CFD simulations of nasal airflow in 47 healthy adults.

METHODS

Anatomically accurate three-dimensional nasal models were reconstructed from cone beam computed tomography scans and used for steady-state inspiratory airflow simulations with a bilateral flowrate of 250 ml/s. Normal subjective sensation of nasal patency was confirmed using the nasal obstruction symptom evaluation and visual analog scale. Healthy ranges for several CFD variables known to correlate with subjective nasal patency were computed, including unilateral airflow, nasal resistance, airspace minimal cross-sectional area (mCSA), heat flux (HF), and surface area stimulated by mucosal cooling (defined as the area where HF > 50 W/m²). The normative ranges were targeted to contain 95% of the healthy population and computed using a nonparametric method based on order statistics.

RESULTS

A wide range of inter-individual variability in nasal airflow was observed among healthy subjects. Unilateral airflow varied from 60 to 191 ml/s, airflow partitioning ranged from 23.8 to 76.2%, and unilateral mCSA varied from 0.24 to 1.21 cm². These ranges are in good agreement with rhinomanometry and acoustic rhinometry data from the literature. A key innovation of this study are the normative ranges of flow variables associated with mucosal cooling, which recent research suggests is the primary physiological mechanism of nasal airflow sensation. Unilateral HF ranged from 94 to 281 W/m², while the surface area stimulated by cooling ranged from 27.4 to 64.3 cm².

CONCLUSIONS

These normative ranges may serve as targets in future virtual surgery planning for patients with NAO.

Review: The role of computational simulation in understanding the postoperative sinonasal environment

Nasal surgery improves symptoms in a majority of patients for whom medical treatment has failed. In rhinosinusitis patients, endoscopic sinus surgery aims to alleviate obstruction and re-establish mucociliary clearance. Surgery alters the structure-function relationship within the nasal passage, which is difficult to assess clinically. Computational modelling has been used to investigate this relationship by simulating air flow and environmental variables inside realistic three-dimensional models of the human nasal airway but many questions remain unanswered and need further investigation. The application of computational models to improve pre-surgical planning and post-surgical treatment may not be currently possible due to the absence of knowledge correlating the model-predicted parameters to physiological variables. Links between these parameters to patient outcomes are yet to be established. This article reviews the recent application of computational modelling to understand the nasal structure-function relationship following surgery in patients with sinusitis and nasal obstruction.

An idealized geometry that mimics average nasal spray deposition in adults: A computational study

This work describes the development of an idealized geometry that mimics average regional deposition of nasal sprays within realistic adult nasal geometries. Previous simulation results in seven realistic nasal airways (Kiaee et al. Int. J. Num. Methods Biomed. Eng. 34: e2968, 2018) were used to establish target values of regional deposition. Characteristic geometric features observed to be common to all the realistic nasal airway geometries studied were extracted and included in the idealized geometry. Additional geometric features and size scaling were explored, in order to enhance deposition in specific regions based on the results of simulations done in preliminary versions of the idealized geometry. In total, more than one hundred thousand simulation cases were conducted across a range of particle parameters and geometric shapes in order to reach the final idealized geometry presented herein. For droplet velocities of 0-20 m/s, droplet sizes of 5-40 μm and at an inhalation flow rate of 15 l/min, regional deposition in the final idealized geometry compares favourably with average deposition in each of the vestibule, valve, olfactory, turbinate, nasopharynx, and outlet regions in the realistic geometries. The proposed idealized nasal geometry has potential for use in the development and testing of nasal drug delivery systems, allowing researchers to estimate in vivo regional nasal deposition patterns using a simple benchtop test apparatus.

Three-dimensional endoscopy: The future of nasoendoscopic training

OBJECTIVES/HYPOTHESIS

Three-dimensional (3D) endoscopy is an emerging tool in surgery that provides real-time depth perception. Its benefits have been investigated in surgical training, but the current literature lacks significant objective outcome data. We aimed to objectively compare the efficacy of two-dimensional (2D) versus 3D high-definition endoscopes in novice users.

STUDY DESIGN

Prospective, randomized crossover study.

METHODS

Ninety-two novice medical students who used both 2D and 3D endoscopes to complete two validated tasks in a box trainer participated in the study. Time taken and error rates were measured, and subjective data were collected.

RESULTS

Wilcoxon tests showed 3D technology was significantly faster than 2D (78 vs. 95 seconds, P = .004), and errors per task were significantly lower (3 vs. 5, P < .001). Sixty-nine percent of participants preferred the 3D endoscope.

CONCLUSIONS

3D high-definition endoscopy could be instrumental in training the next generation of endoscopic surgeons. Further research is required in a clinical setting.

LEVEL OF EVIDENCE

2b Laryngoscope, 129:1280-1285, 2019.

A hierarchical stepwise approach to evaluate nasal patency after virtual surgery for nasal airway obstruction

BACKGROUND

Despite advances in medicine and expenditures associated in treatment of nasal airway obstruction, 25-50% of patients undergoing nasal surgeries complain of persistent obstructive symptoms. Our objective is to develop a "stepwise virtual surgery" method that optimizes surgical outcomes for treatment of nasal airway obstruction.

METHODS

Pre-surgery radiographic images of two subjects with nasal airway obstruction were imported into Mimics imaging software package for three-dimension reconstruction of the airway. A hierarchical stepwise approach was used to create seven virtual surgery nasal models comprising individual (inferior turbinectomy or septoplasty) procedures and combined inferior turbinectomy and septoplasty procedures via digital modifications of each subject's pre-surgery nasal model. To evaluate the effects of these procedures on nasal patency, computational fluid dynamics modeling was used to perform steady-state laminar inspiratory airflow and heat transfer simulations in every model, at resting breathing. Airflow-related variables were calculated for virtual surgery models and compared with dataset containing results of healthy subjects with no symptoms of nasal obstruction.

FINDINGS

For Subject 1, nasal models with virtual septoplasty only and virtual septoplasty plus inferior turbinectomy on less obstructed side were within the healthy reference thresholds on both sides of the nasal cavity and across all three computed variables. For Subject 2, virtual septoplasty plus inferior turbinectomy on less obstructed side model produced the best result.

INTERPRETATION

The hierarchical stepwise approach implemented in this preliminary report demonstrates computational fluid dynamics modeling ability to evaluate the efficiency of different surgical procedures for nasal obstruction in restoring nasal patency to normative level.

High quality statistical shape modelling of the human nasal cavity and applications

The human nose is a complex organ that shows large morphological variations and has many important functions. However, the relation between shape and function is not yet fully understood. In this work, we present a high quality statistical shape model of the human nose based on clinical CT data of 46 patients. A technique based on cylindrical parametrization was used to create a correspondence between the nasal shapes of the population. Applying principal component analysis on these corresponded nasal cavities resulted in an average nasal geometry and geometrical variations, known as principal components, present in the population with a high precision. The analysis led to 46 principal components, which account for 95% of the total geometrical variation captured. These variations are first discussed qualitatively, and the effect on the average nasal shape of the first five principal components is visualized. Hereafter, by using this statistical shape model, two application examples that lead to quantitative data are shown: nasal shape in function of age and gender, and a morphometric analysis of different anatomical regions. Shape models, as the one presented here, can help to get a better understanding of nasal shape and variation, and their relationship with demographic data.

Personalized Medicine in Nasal Delivery: The Use of Patient-Specific Administration Parameters To Improve Nasal Drug Targeting Using 3D-Printed Nasal Replica Casts

Effective targeting of nasal spray deposition could improve local, systemic, and CNS drug delivery; however, this has proven to be difficult due to the anatomical features of the nasal cavity, including the nasal valve and turbinate structures. Furthermore, nasal cavity geometries and dimensions vary between individuals based on differences in their age, gender, and ethnicity. The effect of patient-specific administration parameters was evaluated for their ability to overcome the barriers of targeted nasal drug delivery. The nasal spray deposition was evaluated in 10 3D-printed nasal cavity replicas developed based on the CT-scans of five pediatric and five adult subjects. Cromolyn sodium nasal solution, USP, modified with varying concentrations of hypromellose was utilized as a model nasal spray to evaluate the deposition pattern from formulations producing a variety of plume angles. A central composite design of experiments was implemented using the formulation with the narrowest plume angle to determine the patient-specific angle for targeting the turbinate region in each individual. The use of the patient-specific angle with this formulation significantly increased the turbinate deposition efficiency compared to that found for all subjects using an administration angle of 30°, around 90% compared to about 73%. Generally, we found turbinate deposition increased with decreases in the administration angle. Deposition to the upper regions of the replica was poor with any formulation or administration angle tested. Effective turbinate targeting of nasal sprays can be accomplished with the use of patient-specific administration parameters in individuals. Further research is required to see if these parameters can be device-controlled for patients and if other regions can be effectively targeted with other nasal devices.

Physical and geometric constraints shape the labyrinth-like nasal cavity

The nasal cavity is a vital component of the respiratory system that heats and humidifies inhaled air in all vertebrates. Despite this common function, the shapes of nasal cavities vary widely across animals. To understand this variability, we here connect nasal geometry to its function by theoretically studying the airflow and the associated scalar exchange that describes heating and humidification. We find that optimal geometries, which have minimal resistance for a given exchange efficiency, have a constant gap width between their side walls, while their overall shape can adhere to the geometric constraints imposed by the head. Our theory explains the geometric variations of natural nasal cavities quantitatively, and we hypothesize that the trade-off between high exchange efficiency and low resistance to airflow is the main driving force shaping the nasal cavity. Our model further explains why humans, whose nasal cavities evolved to be smaller than expected for their size, become obligate oral breathers in aerobically challenging situations.

Challenges in nasal drug absorption: how far have we come?

The nasal route is commonly used for local delivery of drugs to treat inflammatory conditions. It is also an attractive route for systemic delivery of some drugs. Irrespective of intended use, administered drugs must permeate the epithelial or olfactory membrane to be effective. The enthusiasm for potential use of the nasal route for systemic drug delivery has not been met by comparable success. In this paper, the anatomical and physiological attributes of the nasal cavity and paranasal sinuses important for drug delivery and challenges limiting drug absorption are discussed. Efforts made so far in improving nasal drug absorption such as overcoming restrictive nasal geometry and paranasal sinuses accessibility, mucociliary clearance, absorption barriers, metabolism and drug physicochemical challenges are discussed. Highlights on future prospects of nasal drug delivery/absorption were discussed.

Advances in Technology for Functional Rhinoplasty: The Next Frontier

Advances in computer modeling and simulation technologies have the potential to provide facial plastic surgeons with information and tools that can aid in patient-specific surgical planning for rhinoplasty. Finite element modeling and computational fluid dynamics are modeling technologies that have been applied to the nose to study structural biomechanics and nasal airflow. Combining these technologies with patient-specific imaging data and symptom measures has the potential to alter the future landscape of nasal surgery.

A deformable template method for describing and averaging the anatomical variation of the human nasal cavity

Background

Understanding airflow through human airways is of importance in drug delivery and development of assisted breathing methods. In this work, we focus on development of a new method to obtain an averaged upper airway geometry from computed tomography (CT) scans of many individuals. This geometry can be used for air flow simulation. We examine the geometry resulting from a data set consisting of 26 airway scans. The methods used to achieve this include nasal cavity segmentation and a deformable template matching procedure.

Methods

The method uses CT scans of the nasal cavity of individuals to obtain a segmented mesh, and coronal cross-sections of this segmented mesh are taken. The cross-sections are processed to extract the nasal cavity, and then thinned (‘skeletonized’) representations of the airways are computed. A reference template is then deformed such that it lies on this thinned representation. The average of these deformations is used to obtain the average geometry. Our procedure tolerates a wider variety of nasal cavity geometries than earlier methods.

Results

To assess the averaging method, key landmark points on each of the input scans as well as the output average geometry are located and compared with one another, showing good agreement. In addition, the cross-sectional area (CSA) profile of the nasal cavities of the input scans and average geometry are also computed, showing that the CSA of the average model falls within the variation of the population.

Conclusions

The use of a deformable template method for aligning and averaging the nasal cavity provides an improved, detailed geometry that is unavailable without using deformation.

Electronic supplementary material

The online version of this article (doi:10.1186/s12880-016-0154-8) contains supplementary material, which is available to authorized users.

First Steps to Develop and Validate a CFPD Model in Order to Support the Design of Nose-to-Brain Delivered Biopharmaceuticals

PURPOSE

Aerosol particle deposition in the human nasal cavity is of high interest in particular for intranasal central nervous system (CNS) drug delivery via the olfactory cleft. The objective of this study was the development and comparison of a numerical and experimental model to investigate various parameters for olfactory particle deposition within the complex anatomical nasal geometry.

METHODS

Based on a standardized nasal cavity, a computational fluid and particle dynamics (CFPD) model was developed that enables the variation and optimization of different parameters, which were validated by in vitro experiments using a constructed rapid-prototyped human nose model.

RESULTS

For various flow rates (5 to 40 l/min) and particle sizes (1 to 10 μm), the airflow velocities, the calculated particle airflow patterns and the particle deposition correlated very well with the experiment. Particle deposition was investigated numerically by varying particle sizes at constant flow rate and vice versa assuming the particle size distribution of the used nebulizer.

CONCLUSIONS

The developed CFPD model could be directly translated to the in vitro results. Hence, it can be applied for parameter screening and will contribute to the improvement of aerosol particle deposition at the olfactory cleft for CNS drug delivery in particular for biopharmaceuticals.

A Method for Accurate Reconstructions of the Upper Airway Using Magnetic Resonance Images

Objective

The purpose of this study is to provide an optimized method to reconstruct the structure of the upper airway (UA) based on magnetic resonance imaging (MRI) that can faithfully show the anatomical structure with a smooth surface without artificial modifications.

Methods

MRI was performed on the head and neck of a healthy young male participant in the axial, coronal and sagittal planes to acquire images of the UA. The level set method was used to segment the boundary of the UA. The boundaries in the three scanning planes were registered according to the positions of crossing points and anatomical characteristics using a Matlab program. Finally, the three-dimensional (3D) NURBS (Non-Uniform Rational B-Splines) surface of the UA was constructed using the registered boundaries in all three different planes.

Results

A smooth 3D structure of the UA was constructed, which captured the anatomical features from the three anatomical planes, particularly the location of the anterior wall of the nasopharynx. The volume and area of every cross section of the UA can be calculated from the constructed 3D model of UA.

Conclusions

A complete scheme of reconstruction of the UA was proposed, which can be used to measure and evaluate the 3D upper airway accurately.

Variability in Nose-to-Lung Aerosol Delivery

Nasal delivery of lung targeted pharmaceutical aerosols is ideal for drugs that need to be administered during high flow nasal cannula (HFNC) gas delivery, but based on previous studies losses and variability through both the delivery system and nasal cavity are expected to be high. The objective of this study was to assess the variability in aerosol delivery through the nose to the lungs with a nasal cannula interface for conventional and excipient enhanced growth (EEG) delivery techniques. A database of nasal cavity computed tomography (CT) scans was collected and analyzed, from which four models were selected to represent a wide range of adult anatomies, quantified based on the nasal surface area-to-volume ratio (SA/V). Computational fluid dynamics (CFD) methods were validated with existing in vitro data and used to predict aerosol delivery through a streamlined nasal cannula and the four nasal models at a steady state flow rate of 30 L/min. Aerosols considered were solid particles for EEG delivery (initial 0.9 μm and 1.5 μm aerodynamic diameters) and conventional droplets (5 μm) for a control case. Use of the EEG approach was found to reduce depositional losses in the nasal cavity by an order of magnitude and substantially reduce variability. Specifically, for aerosol deposition efficiency in the four geometries, the 95% confidence intervals (CI) for 0.9 and 5 μm aerosols were 2.3-3.1 and 15.5-66.3%, respectively. Simulations showed that the use of EEG as opposed to conventional methods improved delivered dose of aerosols through the nasopharynx, expressed as penetration fraction (PF), by approximately a factor of four. Variability of PF, expressed by the coefficient of variation (CV), was reduced by a factor of four with EEG delivery compared with the control case. Penetration fraction correlated well with SA/V for larger aerosols, but smaller aerosols showed some dependence on nasopharyngeal exit hydraulic diameter. In conclusion, results indicated that the EEG technique not only improved lung aerosol delivery, but largely eliminated variability in both nasal depositional loss and lung PF in a newly developed set of nasal airway models.

Surface mapping for visualization of wall stresses during inhalation in a human nasal cavity

Airflow analysis can assist in better understanding the physiology however the human nasal cavity is an extremely complicated geometry that is difficult to visualize in 3D space, let alone in 2D space. In this paper, an anatomically accurate 3D surface of the nasal passages derived from CT data was unwrapped and transformed into a 2D space, into a UV-domain (where u and v are the coordinates) to allow a complete view of the entire wrapped surface. This visualization technique allows surface flow parameters to be analyzed with greater precision. A UV-unwrapping tool is developed and a strategy is presented to allow deeper analysis to be performed. This includes (i) the ability to present instant comparisons of geometry and flow variables between any number of different nasal cavity models through normalization of the 2D unwrapped surface; (ii) visualization of an entire surface in one view and; (iii) a planar surface that allows direct 1D and 2D analytical solutions of diffusion of inhaled vapors and particles through the nasal walls. This work lays a foundation for future investigations that correlates adverse and therapeutic health responses to local inhalation of gases and particles.

Standardization of Malaysian adult female nasal cavity

This research focuses on creating a standardized nasal cavity model of adult Malaysian females. The methodology implemented in this research is a new approach compared to other methods used by previous researchers. This study involves 26 females who represent the test subjects for this preliminary study. Computational fluid dynamic (CFD) analysis was carried out to better understand the characteristics of the standardized model and to compare it to the available standardized Caucasian model. This comparison includes cross-sectional areas for both half-models as well as velocity contours along the nasal cavities. The Malaysian female standardized model is larger in cross-sectional area compared to the standardized Caucasian model thus leading to lower average velocity magnitudes. The standardized model was further evaluated with four more Malaysian female test subjects based on its cross-sectional areas and average velocity magnitudes along the nasal cavities. This evaluation shows that the generated model represents an averaged and standardized model of adult Malaysian females.

Frictional resistance sheds light on the multicomponent nature of nasal obstruction: a combined in vivo and computational fluid dynamics study

Exploring nasal flow contributes to better understanding of pathophysiological functions of nasal cavities. We combined the rhinomanometry measurements of 11 patients and computational fluid dynamics (CFD) simulations in 3 nasal airway models to dissect the complex mechanisms that determine nasal flow obstruction: spatial complexity and pressure-dependent deformability of nasal airways. We quantified spatial complexity by calculating longitudinal variations of hydraulic diameter, perimeter and area of nasal cavities, and their impact on flow characteristics by examining the longitudinal variations of the kinetic energy coefficient and the kinetic to potential energy ratio. Airway distensibility variably affected in vivo pressure-flow relationships through the appearance of flow-limitation patterns characterized by maximum flow and/or flow plateau. We quantified deformability and spatial complexity effects on nasal airway resistance by normalizing all data with averaged reference parameters. The results show that discrepancies in nasal flow resistances reflect airway deformability and geometrical complexity, and thereby constitute a framework to better characterize nasal obstruction.

Patient specific CFD models of nasal airflow: overview of methods and challenges

Respiratory physiology and pathology are strongly dependent on the airflow inside the nasal cavity. However, the nasal anatomy, which is characterized by complex airway channels and significant individual differences, is difficult to analyze. Thus, commonly adopted diagnostic tools have yielded limited success. Nevertheless, with the rapid advances in computer resources, there have been more elaborate attempts to correlate airflow characteristics in human nasal airways with the symptoms and functions of the nose by computational fluid dynamics study. Furthermore, the computed nasal geometry can be virtually modified to reflect predicted results of the proposed surgical technique. In this article, several computational fluid mechanics (CFD) issues on patient-specific three dimensional (3D) modeling of nasal cavity and clinical applications were reviewed in relation to the cases of deviated nasal septum (decision for surgery), turbinectomy, and maxillary sinus ventilation (simulated- and post-surgery). Clinical relevance of fluid mechanical parameters, such as nasal resistance, flow allocation, wall shear stress, heat/humidity/NO gas distributions, to the symptoms and surgical outcome were discussed. Absolute values of such parameters reported by many research groups were different each other due to individual difference of nasal anatomy, the methodology for 3D modeling and numerical grid, laminar/turbulent flow model in CFD code. But, the correlation of these parameters to symptoms and surgery outcome seems to be obvious in each research group with subject-specific models and its variations (virtual- and post-surgery models). For the more reliable, patient-specific, and objective tools for diagnosis and outcomes of nasal surgery by using CFD, the future challenges will be the standardizations on the methodology for creating 3D airway models and the CFD procedures.