Numerical modeling of nasal obstruction and endoscopic surgical intervention: outcome to airflow and olfaction

Computational Fluid Dynamics and Its Potential Applications for the ENT Clinician

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

Value of Opening the Middle Meatus in Patients With Nasal Airway Obstruction

OBJECTIVES

While surgeries to correct the anatomical malformations that cause nasal airway obstruction (NAO) are generally successful, the outcomes of such procedures are often unsatisfactory. The aim of the present study was to assess the value of opening the middle meatus in patients with NAO.

METHODS

Thirty-four patients with nasal obstruction due to nasal septal deviation were included in this study. After randomization, the middle meatus was either opened or not opened during septoplasty. The patients were evaluated through pre- and postoperative rhinomanometry and acoustic rhinometry. The Visual Analog Scale (VAS) scores of subjective symptoms along with responses to the 20-item Sinonasal Outcome Test (SNOT-20) were obtained before surgery and three months after surgery.

RESULTS

The VAS scores and SNOT-20 responses improved significantly in both groups after surgery. The effective treatment rate based on the nasal congestion score (NCS) was 64.7% in the single group (septoplasty alone) and 100% in the combined group (septoplasty in conjunction with opening the middle meatus), and the difference was statistically significant (P = .018). In both groups, surgery significantly improved nasal flow, resistance, minimal cross-sectional area, cross-sectional area 6 cm (CA6) from the anterior nostril and nasal volume. Nasal volume and CA6 after surgery were statistically different between the 2 groups (P = .004 and .019, respectively).

CONCLUSIONS

Opening the middle meatus may further improve the subjective perception of patency on the basis of septoplasty.

Olfaction Now and in the Future in CRSwNP

BACKGROUND

Chronic rhinosinusitis (CRS) is the leading cause of olfactory dysfunction in the general population. Olfactory dysfunction is more common in patients with CRS with nasal polyposis (CRSwNP) compared to those without polyps.

PURPOSE

The present review aims to summarize the current literature on the mechanism behind olfactory dysfunction in CRSwNP and the impact of therapy on olfactory outcomes in this patient population.

METHODS

A comprehensive review of the available literature on olfaction in CRSwNP was performed. We evaluated the most recent evidence from studies on the mechanisms behind smell loss in CRSwNP and the impact of medical and surgical therapy for CRS on olfactory outcomes.

RESULTS

The mechanism behind olfactory dysfunction in CRSwNP is not completely understood, but evidence from clinical research and animal models suggests both an obstructive component causing conductive olfactory loss and an inflammatory response in the olfactory cleft leading to sensorineural olfactory loss. Oral steroids and endoscopic sinus surgery have both shown efficacy in improving olfactory outcomes in CRSwNP in the short term; however, the long-term response of these treatments remains uncertain. Newer targeted biologic therapies, such as dupilumab, have also shown remarkable and durable improvement in smell loss for CRSwNP patients.

CONCLUSION

Olfactory dysfunction is highly prevalent in the CRSwNP population. Although significant advances have been made in our understanding of olfactory dysfunction in the setting of CRS, additional studies are needed to elucidate cellular and molecular changes mediated by type 2-mediated inflammation in the olfactory epithelium with potential downstream effects on the central olfactory system. Further identification of these underlying basic mechanisms will be vital for developing future therapies targeted to improve olfactory dysfunction in patients with CRSwNP.

Beyond aroma: A scoping review on the impact of chronic rhinosinusitis on retronasal olfaction

Background

Retronasal olfaction (RNO) refers to the perception of odorants inhaled through the mouth and carried through the nasopharynx to olfactory receptors within the olfactory cleft, enabling the perception of flavor. Although orthonasal olfactory dysfunction in chronic rhinosinusitis (CRS) has been widely described, the impact of CRS on RNO is less clear. In this study, we systematically review available literature to provide an update on RNO in the setting of CRS.

Methods

We systematically searched PubMed, Ovid Embase, Web of Science, and the Cochrane Library for studies examining RNO in patients with documented CRS. The primary outcome of interest was objective psychophysical measurement of olfaction, including characterization of RNO.

Results

We identified 404 unique references that underwent title and abstract review by two independent reviewers, with 52 articles undergoing full-text review, where 10 relevant studies underwent data extraction. Although outcome measures varied, all included studies demonstrated diminished RNO in patients with CRS. Of six studies evaluating the relationship between retronasal and orthonasal olfactory test scores in CRS patients two out of six (33%) demonstrated a correlation between both forms of olfaction and CRS, and two out of six studies (33%) found significantly lower orthonasal olfactory test scores compared to retronasal olfactory test scores. Two of three found significant improvement in RNO with treatment of underlying CRS. Of three studies examining patient reported outcome measures (PROMs) in CRS, two found significant associations between retronasal olfactory test scores and PROMs.

Conclusions

Based on the current literature, CRS patients appear to have diminished RNO, which may be associated with orthonasal olfactory dysfunction and decreased quality of life in this population. Higher level of evidence studies are required to further elucidate these relationships and the impact of medical and surgical CRS management on RNO.

International consensus statement on allergy and rhinology: Olfaction

BACKGROUND

The literature regarding clinical olfaction, olfactory loss, and olfactory dysfunction has expanded rapidly over the past two decades, with an exponential rise in the past year. There is substantial variability in the quality of this literature and a need to consolidate and critically review the evidence. It is with that aim that we have gathered experts from around the world to produce this International Consensus on Allergy and Rhinology: Olfaction (ICAR:O).

METHODS

Using previously described methodology, specific topics were developed relating to olfaction. Each topic was assigned a literature review, evidence-based review, or evidence-based review with recommendations format as dictated by available evidence and scope within the ICAR:O document. Following iterative reviews of each topic, the ICAR:O document was integrated and reviewed by all authors for final consensus.

RESULTS

The ICAR:O document reviews nearly 100 separate topics within the realm of olfaction, including diagnosis, epidemiology, disease burden, diagnosis, testing, etiology, treatment, and associated pathologies.

CONCLUSION

This critical review of the existing clinical olfaction literature provides much needed insight and clarity into the evaluation, diagnosis, and treatment of patients with olfactory dysfunction, while also clearly delineating gaps in our knowledge and evidence base that we should investigate further.

Non-food odors and the duality of smell: Impact of odorant delivery pathway and labeling convention on olfactory perception

The olfactory system encompasses two perceptual pathways (orthonasal and retronasal) that activate the same receptors in the olfactory epithelium yet are thought to elicit different perceptions. Presently, a novel matching paradigm was employed using a non-food flavor set with low retronasal familiarity (honeysuckle, lavender, rose, and jasmine) to evaluate the effect of odor type on the Duality of Smell. Additionally, the influence of cognitive strategies used by subjects was assessed by manipulating the naming convention seen by the subjects: familiar (Honeysuckle, Lavender, Rose, Jasmine), unfamiliar (Inodora, Pedunculata, Beggeriana, Didymum), and generic (A, B, C, D). Subjects were presented with a reference, either in a vial (orthonasal delivery, ON) or a 2 oz. cup (retronasal delivery, RN) and instructed to match the same aroma from four unknowns, evaluated either by the same delivery route (congruent, e.g., ON-ON, RN-RN) or different route (incongruent, e.g., ON-RN, RN-ON) than the reference evaluation. All possible combinations of orthonasal and retronasal delivery for the reference and unknowns (e.g. ON-ON, RN-RN, ON-RN, RN-ON) were assessed by all subjects. Matching performance and signal detection measures indicated that, on average, subjects performed significantly better in the congruent conditions than in the incongruent conditions. These results suggest perceptual quality of aromas is route dependent and extend the Duality of Smell hypothesis to samples with low retronasal familiarity such as non-food odors. Labeling convention also had an impact on performance but, surprisingly, not in the direction anticipated. Indeed, as the information contained in the label decreased from familiar to generic reference names, performance increased. Moreover, depending on the labeling convention used, certain aromas were easier to match than others. The present research suggests odorant matching is a function of stimulus quality, cognitive strategy, and labeling convention.

Computational modeling of nasal nitric oxide flux from the paranasal sinuses: Validation against human experiment

BACKGROUND

Nitric oxide (NO) is important in respiratory physiology and airway defense. Although the paranasal sinuses are the major source of nasal NO, transport dynamics between the sinuses and nasal cavities are poorly understood.

METHODS

Exhaled nasal NO tracings were measured in two non-asthmatic subjects (one with allergic rhinitis, one without) using NO analyzer connected via face mask. We subsequently performed computational fluid dynamics NO emission simulations based on individual CT scans and compared to the experimental data.

RESULTS

Simulated exhaled NO tracings match well with experimental data (r > 0.84, p < 0.01) for both subjects, with measured peaks reaching 319.6 ppb in one subject (allergic-rhinitis), and 196.9 ppb in the other. The CFD simulation accurately captured the peak differences, even though the initial sinus NO concentration for both cases was set to the same 9000 ppb based on literature value. Further, the CFD simulation suggests that ethmoid sinuses contributed the most (>67%, other sinuses combined <33%) to total nasal NO emission in both cases and that diffusion contributes more than convective transport. By turning off diffusion (setting NO diffusivity to ~0), the NO emission peaks for both cases were reduced by >70%.

CONCLUSION

Historically, nasal NO emissions were thought to be contributed mostly by the maxillary sinuses (the largest sinuses) and active air movement (convection). Here, we showed that the ethmoid sinuses and diffusive transport dominate the process. These findings may have a substantial impact on our view of nasal NO emission mechanisms and sinus physiopathology in general.

Outcomes of olfaction in patients with empty nose syndrome after submucosal implantation

BACKGROUND

Olfactory dysfunction, such as hyposmia, is a significant symptom of empty nose syndrome (ENS). The efficacy of surgical intervention in olfaction improvements for ENS has not been investigated extensively.

OBJECTIVE

The aim of this study was to evaluate changes in olfaction after surgical treatment for ENS.

METHODS

This prospective cohort study at a tertiary medical center enrolled patients with ENS indicated for surgical treatment between June 2015 and June 2019. The Sniffin' Sticks 12-items odor identification test (SS-12) and subjective olfaction rating were completed by patients before and after surgery to assess olfaction.

RESULTS

A total of 40 patients completed the survey both before and after surgical treatment. Prior to surgery, 25% of the patients had olfactory dysfunction detected by SS-12, whereas 80% of the patients reported a reduction in olfactory function by subjective rating. The degree of olfactory dysfunction by both assessments significantly improved following surgery. The age was a significant predictor of postoperative improvement.

CONCLUSION

Surgical treatment is helpful in improving olfaction in patients with ENS who commonly suffer from olfactory dysfunction. Younger patients may benefit more from surgical intervention in aspect of olfaction.

Computational fluid dynamic modelling of maxillary sinus irrigation after maxillary antrostomy and modified endoscopic medial maxillectomy

OBJECTIVE

For recalcitrant chronic maxillary sinusitis, modified endoscopic medial maxillectomy has been shown to be clinically beneficial after failed maxillary antrostomy as endoscopic medial maxillectomy may offer improved topical therapy delivery. This study compared irrigation patterns after maxillary antrostomy versus endoscopic medial maxillectomy, using computational fluid dynamic modelling.

CASE REPORT

A 54-year-old female with left chronic maxillary sinusitis underwent maxillary antrostomy, followed by endoscopic medial maxillectomy. Computational fluid dynamic models were created after each surgery and used to simulate irrigations.

RESULTS

After maxillary antrostomy, irrigation penetrated the maxillary sinus at 0.5 seconds, initially contacting the posterior wall. The maxillary sinus was half-filled at 2 seconds, and completely filled at 4 seconds. After endoscopic medial maxillectomy, irrigation penetrated the maxillary sinus at 0.5 seconds and immediately contacted all maxillary sinus walls. The maxillary sinus was completely filled by 2 seconds.

CONCLUSION

Computational fluid dynamic modelling demonstrated that endoscopic medial maxillectomy allowed faster, more forceful irrigation to all maxillary sinus walls compared with maxillary antrostomy.

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.

Computational Fluid Dynamics to Evaluate the Effectiveness of Inferior Turbinate Reduction Techniques to Improve Nasal Airflow

Importance

Inferior turbinate reduction (ITR) is a commonly performed procedure for the treatment of nasal obstruction. Which portion of the inferior turbinates should be surgically addressed to improve nasal airflow has yet to be determined.

Objective

To use computational fluid dynamics (CFD) analysis to evaluate the airflow changes after reduction along different portions of the inferior turbinate.

Design, Setting, and Participants

Computed tomographic scans of 5 patients were selected. Seven CFD models were created for each patient: 1 unaltered and 6 various ITRs, including 3 one-third ITRs (anterior, middle, and posterior one-third); 2 two-thirds ITRs (anterior and posterior two-thirds); and 1 full-length ITR model. Total airflow rate and nasal resistance was obtained through CFD analysis, and regression analysis was performed on the increased nasal volume, locations, and nasal resistance for all 5 patients.

Main Outcomes and Measures

Total airflow rate and nasal resistance was obtained through CFD analysis, and regression analysis was performed on the increased nasal volume, locations, and nasal resistance for all 5 patients.

Results

Full ITR over the whole length was consistently most effective to improve nasal airflow and resistance for all 5 patients (2 men and 3 women), adjusted for the volume. Regression analysis showed a strong linear (R2≥0.79) relationship between nasal volume changes and nasal airflow. However, the most effective location of partial turbinate reduction was not consistent among patients. Surprisingly, for some patients, posterior ITRs were more effective than anterior ITRs. The site of most effective partial ITR differed from 1 side to the other even in the same individual.

Conclusions and Relevance

The effectiveness of partial ITR and target location likely depends on individual patient anatomy. The fact that full ITRs were consistently most effective and the linear regression between flow and nasal volume changes may indicate that the entire length of the IT has a functional impact on nasal airflow and resistance.

Level of Evidence

NA.

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.

Different Olfactory Percepts Evoked by Orthonasal and Retronasal Odorant Delivery

The Duality of Smell hypothesis suggests odorants delivered orthonasally elicit different sensations compared with those delivered retronasally despite activating the same receptors in the olfactory epithelium. Presently, we investigated this further using a matching paradigm free from odorant or semantic memory bias. Subjects were asked to evaluate an aroma delivered in one condition (orthonasal or retronasal delivery) and match the same aroma from 4 unknowns evaluated in the same or different delivery conditions. Panelists matched flavors in 4 delivery conditions: orthonasal-orthonasal, retronasal-retronasal, retronasal-orthonasal, and orthonasal-retronasal. For orthonasal presentation, panelists smelled samples using their nostrils, and for retronasal presentation, panelists swallowed aqueous flavors. In Experiment 1, panelists were instructed to match familiar flavors (banana, grape, orange, raspberry). In Experiments 2 and 3, panelists used the same experimental design with either 4 unfamiliar flavors (kinnow, longan, pawpaw, prunus) or 4 distinct subtypes of a strawberry flavor (woody, green, ripe, candy). In Experiment 1, the number of correct matches in each condition did not significantly differ suggesting stability in the perceptual construct across delivery routes. However, in Experiments 2 and 3, significantly more samples were correctly matched in the orthonasal-orthonasal and retronasal-retronasal conditions compared with the retronasal-orthonasal or orthonasal-retronasal conditions suggesting aroma perception is dependent on delivery route. Additionally, across the 4 delivery methods, the ability to correctly match flavors decreased as flavor familiarity decreased or similarity increased and may reflect the different cognitive strategies employed by subjects when matching these stimuli. Our results suggest odorant percepts are route-dependent and consistent with the Duality of Smell phenomenon.

Geometry and airflow dynamics analysis in the nasal cavity during inhalation

BACKGROUND

A major issue among computational respiratory studies is the wide variety of nasal morphologies being studied, caused by both inter-population and inter-subject variations.

METHOD

Six nasal cavity geometries exhibiting diverse geometry variations were subjected to steady inhalation flow rate of 15L/min. to determine if any consistent flow behaviour could be found.

FINDINGS

Despite vastly different geometries we were able to identify consistent flow patterns including relatively high velocity in the nasal valve region, followed by flow continuing predominantly in the inferior half of the airway. We also found conformity among models where the inhaled air reached a near-conditioned state by the middle of the nasal cavity. Air from the front of the face reached the olfactory regions while air from the lateral sides of the face moved through the inferior half of the nasal cavity.

INTERPRETATION

The ability to predict gross flow features provides a baseline flow field to compare against. This contributes towards establishing well defined flow predictions and be used as a comparison for future larger studies.

Nasal Structural and Aerodynamic Features That May Benefit Normal Olfactory Sensitivity

Nasal airflow that effectively transports ambient odors to the olfactory receptors is important for human olfaction. Yet, the impact of nasal anatomical variations on airflow pattern and olfactory function is not fully understood. In this study, 22 healthy volunteers were recruited and underwent computed tomographic scans for computational simulations of nasal airflow patterns. Unilateral odor detection thresholds (ODT) to l-carvone, phenylethyl alcohol (PEA) and d-limonene were also obtained for all participants. Significant normative variations in both nasal anatomy and aerodynamics were found. The most prominent was the formation of an anterior dorsal airflow vortex in some but not all subjects, with the vortex size being significantly correlated with ODT of l-carvone (r = 0.31, P < 0.05). The formation of the vortex is likely the result of anterior nasal morphology, with the vortex size varying significantly with the nasal index (ratio of the width and height of external nose, r = -0.59, P < 0.001) and nasal vestibule "notch" index (r = 0.76, P < 0.001). The "notch" is a narrowing of the upper nasal vestibule cartilage region. The degree of the notch also significantly correlates with ODT for PEA (r = 0.32, P < 0.05) and l-carvone (r = 0.33, P < 0.05). ODT of d-limonene, a low mucosal soluble odor, does not correlate with any of the anatomical or aerodynamic variables. The current study revealed that nasal anatomy and aerodynamics might have a significant impact on normal olfactory sensitivity, with greater airflow vortex and a narrower vestibule region likely intensifying the airflow vortex toward the olfactory region and resulting in greater olfactory sensitivity to high mucosal soluble odors.

Olfactory Adaptation is Dependent on Route of Delivery

Odorants are perceived orthonasally (nostrils) or retronasally (oral cavity). Prior research indicates route of delivery impacts odorant perception, pleasantness, and directed behaviors thus suggesting differential processing of olfactory information. Adaptation is a form of neural processing resulting in decreased perceived intensity of a stimulus following prolonged and continuous exposure. The present study objective was to determine whether route of delivery differentially impacts olfactory adaptation and whether cross-adaptation occurs between orthonasal and retronasal pathways. Linalool (12%) or vanillin (25%) were delivered orthonasally [6 L/min (LPM)] and retronasally (8 LPM) in air phase through a custom-built olfactometer. Perceived odorant intensity was collected every 5 min over 10-min exposure. Immediately following the exposure period, cross-adaptation was assessed by shunting the delivery of the odorant from the nostrils to the oral cavity, or vice versa. A control study was also completed in which subjects underwent the orthonasal adaptation protocol using stimulus concentrations matched to the intensity of restronasal stimuli (e.g., 1.5% linalool and 6.25% vanillin). Following orthonasal delivery of both high and low vanillin concentrations, results showed perceived intensity decreased significantly at 5 and 10 min. High concentrations of orthonasal linalool similarly decreased significantly whereas lower concentrations decreased but did not reach statistical significance. Linalool and vanillin delivered retronasally did not adapt as perceived intensity actually increased significantly following a 10-min exposure. In addition, evidence of cross-adaptation was not obvious following extended odorant exposure from either delivery pathway. This study suggests that olfactory processing may be affected by the route of odorant delivery.

Voxel-based modeling of airflow in the human nasal cavity

This paper describes the simulation of airflow in human nasal airways using voxel-based modeling characterized by robust, automatic, and objective grid generation. Computed tomography scans of a healthy adult nose are used to reconstruct 3D virtual models of the nasal airways. Voxel-based simulations of restful inspiratory flow are then performed using various mesh sizes to determine the level of granularity required to adequately resolve the airflow. For meshes with close voxel spacings, the model successfully reconstructs the nasal structure and predicts the overall pressure drop through the nasal cavity.

Modeling congenital nasal pyriform aperture stenosis using computational fluid dynamics

OBJECTIVES

Congenital nasal pyriform aperture stenosis (CNPAS) is a rare cause of airway obstruction in the neonate. Computational airway modeling has not been done in neonates and young infants to understand the impact of stenosis on functional nasal airflow. In this study, we 1) applied computational fluid dynamics (CFD) model to the airway of a neonate with CNPAS and 2) compare airflow dynamics of a normal and CNPAS airway.

METHODS

Three-dimensional models of the nasal airway of a normal neonate and a neonate with CNPAS were created using computed tomography scans of the facial bones. Measured anatomic parameters included volume, surface area, and cross-sectional area. CFD simulation was then performed. Simulated flow parameters included pressure, average velocity, and resistance.

RESULTS

The neonate with CNPAS had a lesser volume (2.74 cm³ vs. 4.50 cm³) and surface area (18.8 cm² vs. 45.5 cm²) than the normal airway. The CNPAS airway had a lesser bilateral cross-sectional area and average cross-sectional velocity throughout the length of the model. While there is a large pressure drop in the normal airway immediately after the entry point, the pressure drop in the CNPAS airway occurs more posteriorly. The total nasal resistance was approximately eight-fold greater in the CNPAS airway than the normal.

CONCLUSIONS

CFD analysis can be performed on airways of neonates with nasal obstruction, such as in CNPAS. A CFD model may help characterize severity of airway obstruction as it can predict the three-dimensional pattern of airflow. Determining the role of CFD in clinical management of CNPAS requires further investigation.

Influence of the location of nasal polyps on olfactory airflow and olfaction

BACKGROUND

Chronic rhinosinusitis with nasal polyps (CRSwNP) often results in decreased olfaction. In this study, we examined the relationship between nasal polyp location and olfactory airflow and odorant transport changes using virtual nasal polyp models at different locations and computational fluid dynamics (CFD) analysis. We also compared olfactory airflow and olfaction between patients with nasal polyps at different locations using CFD analysis and an olfactory test.

METHODS

Nasal computed tomography images were used to generate a normal model and 4 virtual nasal polyp models based on polyp locations, including the olfactory region (all-olfactory model), the region anterior to the olfactory region (preolfactory model), the middle meatus (middle-meatus model), and the superior meatus (superior-meatus model). Various airflow parameters were compared between these models and a normal model without polyps. We then performed a similar comparison between the 3-dimensional (3D) reconstruction models of patients with nasal polyps, and retrospectively investigated the correlation between olfaction and nasal polyp location in those patients.

RESULTS

Virtual nasal polyp analysis revealed dispersion of olfactory airflow in the all-olfactory model. Olfactory airflow and odorant transport showed maximum decrease in the preolfactory model and a slight decrease in the superior-meatus model. Olfactory airflow by polyps was further decreased by blockade of the olfactory airflow inlet than of the outlet. The findings obtained by patients corresponded well to those of the virtual polyp analysis.

CONCLUSION

Olfactory airflow and olfaction are differentially affected by nasal polyp location. This finding is important for planning polyp-removal surgeries from the perspective of improving patient olfaction.

The Influence of Sniffing on Airflow and Odorant Deposition in the Canine Nasal Cavity

Nasal airflow plays a critical role in olfaction by transporting odorant from the environment to the olfactory epithelium, where chemical detection occurs. Most studies of olfaction neglect the unsteadiness of sniffing and assume that nasal airflow and odorant transport are "quasi-steady," wherein reality most mammals "sniff." Here, we perform computational fluid dynamics simulations of airflow and odorant deposition in an anatomically accurate model of the coyote (Canis latrans) nasal cavity during quiet breathing, a notional quasi-steady sniff, and unsteady sniffing to: quantify the influence of unsteady sniffing, assess the validity of the quasi-steady assumption, and investigate the functional advantages of sniffing compared to breathing. Our results reveal that flow unsteadiness during sniffing does not appreciably influence qualitative (gross airflow and odorant deposition patterns) or quantitative (time-averaged olfactory flow rate and odorant uptake) measures of olfactory function. A quasi-steady approximation is, therefore, justified for simulating time-averaged olfactory function in the canine nose. Simulations of sniffing versus quiet breathing demonstrate that sniffing delivers about 2.5 times more air to the olfactory recess and results in 2.5-3 times more uptake of highly- and moderately-soluble odorants in the sensory region per unit time, suggesting one reason why dogs actively sniff. Simulations also reveal significantly different deposition patterns in the olfactory region during inspiration for different odorants, and that during expiration there is little retronasal odorant deposition in the sensory region. These results significantly improve our understanding of canine olfaction, and have several practical implications regarding computer simulation of olfactory function.

Robust nondimensional estimators to assess the nasal airflow in health and disease

There are significant variations of both human nose shapes and airflow patterns inside nasal cavities, so it is difficult to provide a comprehensive medical identification using a universal template for what otolaryngologists consider normal breathing at rest. In addition, airflow patterns present even more random characteristics in diseased nasal cavities. To give a medical assessment to differentiate the nasal cavities in health and disease, we propose 2 nondimensional estimators obtained from both medical images and computational fluid dynamics. The first mathematical estimator ϕ is a function of geometric features and potential asymmetries between nasal passages, while the second estimator R represents in fluid mechanics terms the total nasal resistance that corresponds to the atmosphere-choana pressure drop. These estimators only require global information such as nasal geometry and magnitudes of flow determined by simulations under laminar conditions. We find that these estimators take low and high values for healthy and diseased nasal cavities, respectively. Our study, based on 24 healthy and 25 diseased Caucasian subjects, reveals that there is an interval of values associated with healthy cavities that clusters in a small region of the plane ϕ-R. Therefore, these estimators can be seen as a first approximation to provide nasal airflow data to the clinician in a noninvasive method, as the computed tomography scan that provides the required images is routinely obtained as a result of the preexisting naso-sinusal condition.

New CFD tools to evaluate nasal airflow

Computational fluid dynamics (CFD) is a mathematical tool to analyse airflow. As currently CFD is not a usual tool for rhinologists, a group of engineers in collaboration with experts in Rhinology have developed a very intuitive CFD software. The program MECOMLAND^® only required snapshots from the patient's cross-sectional (tomographic) images, being the output those results originated by CFD, such as airflow distributions, velocity profiles, pressure, temperature, or wall shear stress. This is useful complementary information to cover diagnosis, prognosis, or follow-up of nasal pathologies based on quantitative magnitudes linked to airflow. In addition, the user-friendly environment NOSELAND^® helps the medical assessment significantly in the post-processing phase with dynamic reports using a 3D endoscopic view. Specialists in Rhinology have been asked for a more intuitive, simple, powerful CFD software to offer more quality and precision in their work to evaluate the nasal airflow. We present MECOMLAND^® and NOSELAND^® which have all the expected characteristics to fulfil this demand and offer a proper assessment with the maximum of quality plus safety for the patient. These programs represent a non-invasive, low-cost (as the CT scan is already performed in every patient) alternative for the functional study of the difficult rhinologic case. To validate the software, we studied two groups of patients from the Ear Nose Throat clinic, a first group with normal noses and a second group presenting septal deviations. Wall shear stresses are lower in the cases of normal noses in comparison with those for septal deviation. Besides, velocity field distributions, pressure drop between nasopharynx and the ambient, and flow rates in each nostril were different among the nasal cavities in the two groups. These software modules open up a promising future to simulate the nasal airflow behaviour in virtual surgery intervention scenarios under different pressure or temperature conditions to understand the effects on nasal airflow.

Computational fluid dynamics evaluation of posterior septectomy as a viable treatment option for large septal perforations

BACKGROUND

Numerous surgical techniques exist to treat nasal septal perforation (NSP). The surgical closure of large NSPs (>2 cm) is still challenging. Posterior septectomy has been reported as a simple alternative to treat large NSP, yet its mechanisms for symptom relief are not clear, and if failed, its consequence cannot be easily reversed.

METHODS

Ten NSP patients were recruited: 5 underwent posterior septectomy and 5 underwent conventional flap or button repair. Computational fluid dynamics (CFD) simulated the nasal aerodynamics based on computed tomography (CT) scans. All patients had preoperative CT; however, only 4 had postoperative CT: 2 underwent posterior septectomy and the other 2 underwent flap repair. We examined surgical outcomes and the nasal airflow features among the 2 treatment options.

RESULTS

Both groups of patients had good outcomes based on chart review. Patients undergoing septectomy had significantly larger perforation size (2.32 ± 0.87 vs 1.21 ± 0.60 cm), higher flow rate across the perforation (47.8 ± 28.6 vs 18.3 ± 12.2 mL/second), and higher wall shear stress (WSS) along the posterior perforation margin (1.39 ± 0.52 vs 1.15 ± 0.58 Pa). The posterior WSS significantly correlated with crossover flow velocity (r = 0.77, p = 0.009) and was reduced by almost 67% postseptectomy, and by 29% postrepair.

CONCLUSION

This is the first CFD analysis on an NSP patient cohort. NSP resulted in flow disturbance and increased WSS that potentially led to symptomatology. The removal of high stress points along the posterior margin may explain why posterior septectomy can be an effective treatment option. Aerodynamic abnormalities, in addition to perforation size and location, could serve as basis for future treatment decisions.

Computational fluid dynamics and trigeminal sensory examinations of empty nose syndrome patients

OBJECTIVE

The precise pathogenesis of empty nose syndrome (ENS) remains unclear. Various factors such as nasal aerodynamics and sensorineural dysfunction have been suspected, although evidence is limited. This study reported the first examination of both nasal aerodynamics and trigeminal sensory factors in actual ENS patients.

STUDY DESIGN

Prospective case control.

METHODS

We enrolled six patients diagnosed with ENS. Three patients had pre- and post-inferior turbinate (IT) reduction computed tomography scans, which allowed comparison of their nasal aerodynamics changes through computational fluid dynamic (CFD) simulation. Their symptoms were confirmed through Sino-nasal Outcome Test-22, ENS 6-item Questionnaire, acoustic rhinometry, and rhinomanometry findings. Nasal trigeminal sensitivity that potentially mediates their perception of airflow was assessed via menthol lateralization detection thresholds (LDT) and compared with 14 healthy controls.

RESULTS

Post-surgical reductions in nasal resistance were observed and significantly lower than normal (P < 0.05). Computational fluid dynamic analysis showed that, paradoxically for all ENS patients, IT reduction did not draw more airflow to the airway surrounding the ITs, but rather resulted in nasal airflow forming into a narrow jet toward the middle meatus region, leaving the airway surrounding the IT with significantly reduced airflow intensity and air-mucosal interactions (inferior region flow percentage reduced from 35.7% ± 15.9% to post-surgery 17.7% ± 15.7%, P < 0.05; inferior wall-shear-stress reduced from 7.5 ± 4.2 × 10^-2 Pa to 3.4 ± 3.1 × 10^-2 Pa, P < 0.01). Empty nose syndrome patients also had significantly impaired menthol LDT compared to healthy controls (P < 0.005).

CONCLUSION

The results indicated that a combinatory of factors, including paradoxically distorted nasal aerodynamic, impaired sensorineural sensitivity, and potential predisposing conditions, may contribute to the development of ENS.

LEVEL OF EVIDENCE

3b. Laryngoscope, 127:E176-E184, 2017.

Ethmoidectomy combined with superior meatus enlargement increases olfactory airflow

OBJECTIVES

The relationship between a particular surgical technique in endoscopic sinus surgery (ESS) and airflow changes in the post-operative olfactory region has not been assessed. The present study aimed to compare olfactory airflow after ESS between conventional ethmoidectomy and ethmoidectomy with superior meatus enlargement, using virtual ESS and computational fluid dynamics (CFD) analysis.

STUDY DESIGN

Prospective computational study.

MATERIALS AND METHODS

Nasal computed tomography images of four adult subjects were used to generate models of the nasal airway. The original preoperative model was digitally edited as virtual ESS by performing uncinectomy, ethmoidectomy, antrostomy, and frontal sinusotomy. The following two post-operative models were prepared: conventional ethmoidectomy with normal superior meatus (ESS model) and ethmoidectomy with superior meatus enlargement (ESS-SM model). The calculated three-dimensional nasal geometries were confirmed using virtual endoscopy to ensure that they corresponded to the post-operative anatomy observed in the clinical setting. Steady-state, laminar, inspiratory airflow was simulated, and the velocity, streamline, and mass flow rate in the olfactory region were compared among the preoperative and two postoperative models.

RESULTS

The mean velocity in the olfactory region, number of streamlines bound to the olfactory region, and mass flow rate were higher in the ESS-SM model than in the other models.

CONCLUSION

We successfully used an innovative approach involving virtual ESS, virtual endoscopy, and CFD to assess postoperative outcomes after ESS. It is hypothesized that the increased airflow to the olfactory fossa achieved with ESS-SM may lead to improved olfactory function; however, further studies are required.

LEVEL OF EVIDENCE

NA.

Hemostasis in sinus surgery

PURPOSE OF REVIEW

Optimization of the surgical field involves a complex interplay of many factors. Although it is agreed that hemostasis is critical to safe, efficient, and successful sinus surgery, a lack of consensus exists as to the best way to achieve it. This review examines the current body of evidence supporting many of the practices surgeons believe to influence hemostasis.

RECENT FINDINGS

Although many of the practices discussed in this article have long been considered to influence hemostasis, it is not until recently that high-level evidence supporting their use has been available. Well designed studies now exist supporting the preoperative use of oral steroids in polyp patients, the importance of adequate reverse trendelenburg positioning, the use of flexible laryngeal mask ventilation during general anesthesia, and the increased safety and comparable efficacy of topical epinephrine over other topical and injectable agents. Controversy still exists as to the ideal method of achieving controlled hypotensive anesthesia, although new evidence has emerged as to what hemodynamic parameters should be adhered to, to reduce the risk of cerebral hypoperfusion.

SUMMARY

Numerous factors influence hemostasis and so it is important that ENT surgeons have a sound understanding of the evidence supporting their everyday surgical practice. Improved standardization of scoring and reporting of bleeding may increase the power of research studies to draw more definitive conclusions about the role that certain factors have on hemostasis.

Effect of Nasal Obstruction on Continuous Positive Airway Pressure Treatment: Computational Fluid Dynamics Analyses

Objective

Nasal obstruction is a common problem in continuous positive airway pressure (CPAP) therapy for obstructive sleep apnea and limits treatment compliance. The purpose of this study is to model the effects of nasal obstruction on airflow parameters under CPAP using computational fluid dynamics (CFD), and to clarify quantitatively the relation between airflow velocity and pressure loss coefficient in subjects with and without nasal obstruction.

Methods

We conducted an observational cross-sectional study of 16 Japanese adult subjects, of whom 9 had nasal obstruction and 7 did not (control group). Three-dimensional reconstructed models of the nasal cavity and nasopharynx with a CPAP mask fitted to the nostrils were created from each subject’s CT scans. The digital models were meshed with tetrahedral cells and stereolithography formats were created. CPAP airflow simulations were conducted using CFD software. Airflow streamlines and velocity contours in the nasal cavities and nasopharynx were compared between groups. Simulation models were confirmed to agree with actual measurements of nasal flow rate and with pressure and flow rate in the CPAP machine.

Results

Under 10 cmH₂O CPAP, average maximum airflow velocity during inspiration was 17.6 ± 5.6 m/s in the nasal obstruction group but only 11.8 ± 1.4 m/s in the control group. The average pressure drop in the nasopharynx relative to inlet static pressure was 2.44 ± 1.41 cmH₂O in the nasal obstruction group but only 1.17 ± 0.29 cmH₂O in the control group. The nasal obstruction and control groups were clearly separated by a velocity threshold of 13.5 m/s, and pressure loss coefficient threshold of approximately 10.0. In contrast, there was no significant difference in expiratory pressure in the nasopharynx between the groups.

Conclusion

This is the first CFD analysis of the effect of nasal obstruction on CPAP treatment. A strong correlation between the inspiratory pressure loss coefficient and maximum airflow velocity was found.

Cadaveric validation study of computational fluid dynamics model of sinus irrigations before and after sinus surgery

BACKGROUND

Investigations into the distribution of sinus irrigations have been limited by labor-intensive methodologies that do not capture the full dynamics of irrigation flow. The purpose of this study was to validate the accuracy of a computational fluid dynamics (CFD) model for sinonasal irrigations through a cadaveric experiment.

METHODS

Endoscopic sinus surgery was performed on 2 fresh cadavers to open all 8 sinuses, including a Draf III procedure for cadaver 1, and Draf IIb frontal sinusotomies for cadaver 2. Computed tomography maxillofacial scans were obtained preoperatively and postoperatively, from which CFD models were created. Blue-dyed saline in a 240-mL squeeze bottle was used to irrigate cadaver sinuses at 60 mL/second (120 mL per side, over 2 seconds). These parameters were replicated in CFD simulations. Endoscopes were placed through trephinations drilled through the anterior walls of the maxillary and frontal sinuses, and sphenoid roofs. Irrigation flow into the maxillary, frontal, and sphenoid sinuses was graded both ipsilateral and contralateral to the side of nasal irrigation, and then compared with the CFD simulations.

RESULTS

In both cadavers, preoperative and postoperative irrigation flow into maxillary, frontal, and sphenoid sinuses matched extremely well when comparing the CFD models and cadaver endoscopic videos. For cadaver 1, there was 100% concordance between the CFD model and cadaver videos, and 83% concordance for cadaver 2.

CONCLUSION

This cadaveric experiment provided potential validation of the CFD model for simulating saline irrigation flow into the maxillary, frontal, and sphenoid sinuses before and after sinus surgery.

Sinus irrigations before and after surgery-Visualization through computational fluid dynamics simulations

OBJECTIVES/HYPOTHESIS

Topical sinus irrigations play a critical role in the management of sinonasal disease, and the improvement in irrigant penetration into the sinuses postoperatively greatly contributes to the success of endoscopic sinus surgery. Prior investigations on postoperative sinus irrigations have been mostly limited to cadaver studies, which are labor intensive and do not capture the full dynamics of the flows. A pilot study was conducted to investigate the impact of surgery on sinus irrigation through computational fluid dynamics (CFD) simulations.

STUDY DESIGN

Retrospective computational study.

METHODS

Pre- and postoperative computed tomography (CT) scans were obtained on a patient who underwent standard endoscopic surgeries for all sinuses, including a Draf III frontal sinusotomy. CT-based pre- and postoperative CFD models then simulated irrigations of 120 mL saline per nostril at 12 mL/s (typical of Sinugator) and 60 mL/s (SinusRinse Bottle), in two head positions: face parallel and at a 45° angle to the ground.

RESULTS

Overall, surgery most significantly improved frontal sinus irrigation, but surprisingly resulted in less maxillary and ethmoid sinuses penetration. This may due to the partial removal of the septum during the Draf III, causing most fluid to exit prematurely across the resected septum. Higher flow rate slightly improved ethmoid sinus irrigation, but resulted in less preoperative contralateral maxillary sinus penetration.

CONCLUSIONS

CFD modeling of sinonasal irrigations is a novel technique for evaluating irrigant penetration of individual sinus cavities. It may prove useful in determining the optimal degree of surgery or the ideal irrigation strategy to allow for maximal and targeted sinus irrigant penetration.

LEVEL OF EVIDENCE

NA Laryngoscope, 126:E90-E96, 2016.

Computational fluid dynamics as surgical planning tool: a pilot study on middle turbinate resection

Controversies exist regarding the resection or preservation of the middle turbinate (MT) during functional endoscopic sinus surgery. Any MT resection will perturb nasal airflow and may affect the mucociliary dynamics of the osteomeatal complex. Neither rhinometry nor computed tomography (CT) can adequately quantify nasal airflow pattern changes following surgery. This study explores the feasibility of assessing changes in nasal airflow dynamics following partial MT resection using computational fluid dynamics (CFD) techniques. We retrospectively converted the pre- and postoperative CT scans of a patient who underwent isolated partial MT concha bullosa resection into anatomically accurate three-dimensional numerical nasal models. Pre- and postsurgery nasal airflow simulations showed that the partial MT resection resulted in a shift of regional airflow towards the area of MT removal with a resultant decreased airflow velocity, decreased wall shear stress and increased local air pressure. However, the resection did not strongly affect the overall nasal airflow patterns, flow distributions in other areas of the nose, nor the odorant uptake rate to the olfactory cleft mucosa. Moreover, CFD predicted the patient's failure to perceive an improvement in his unilateral nasal obstruction following surgery. Accordingly, CFD techniques can be used to predict changes in nasal airflow dynamics following partial MT resection. However, the functional implications of this analysis await further clinical studies. Nevertheless, such techniques may potentially provide a quantitative evaluation of surgical effectiveness and may prove useful in preoperatively modeling the effects of surgical interventions.

Neurotoxic exposure and impairment of the chemical senses of taste and smell

The chemical senses of taste and smell determine the flavor of foods and beverages, guide appropriate food intake, and warn of such environmental hazards as spoiled or poisonous food, leaking natural gas, smoke, and airborne pollutants. This chapter addresses the influences of neurotoxic exposures on human chemoreception and provides basic information on the adverse influences of such exposures on rodent epithelia. The focus of the chapter is in olfaction, given dearth of empiric research on the effects of neurotoxic chemical exposures on the sense of taste, i.e., sweet, sour, bitter, salty, and savory sensations. As will be apparent from the chapter, numerous neurotoxins--many of which are encountered in industrial workplaces--alter the ability to smell, including solvents, metals, and particulate matter. The olfactory system is particularly vulnerable to such agents since its receptors are more or less directly exposed to the outside environment. Importantly, some such agents can enter the brain via the olfactory nerve or surrounding perineural spaces, bypassing the blood-brain barrier and damaging central nervous system structures and inducing pathologic processes that appear to be similar to those seen in neurodegenerative diseases such as Alzheimer's and Parkinson's.

Numerical investigation of the flow field in realistic nasal septal perforation geometry

The computational fluid dynamics (CFD) are used to evaluate the physiological function of the nose. We evaluated the aerodynamics of the nasal cavity in a patient with septal perforation (SP), pre- and postvirtual repair. Three-dimensional nasal models were reconstructed, and then a wide range of the pressure drops and flow rates were analyzed. The airflow velocity is higher in the central region and is lower around the boundary of the SP. The air velocity in the SP increases as the pressure drop increases. Furthermore, at the anterior part of the SP, the shear stress is higher in the upper part. In addition, the repair of SP does not affect the total nasal airflow rate and the velocity contour patterns. The potential usage of the CFD technique as a predictive technique to explore the details and a preoperative assessment tool to help in clinical decision making in nasal surgery is emphasized.

What is normal nasal airflow? A computational study of 22 healthy adults

BACKGROUND

Nasal airflow is essential for the functioning of the human nose. Given individual variation in nasal anatomy, there is yet no consensus what constitutes normal nasal airflow patterns. We attempt to obtain such information that is essential to differentiate disease-related conditions.

METHODS

Computational fluid dynamics (CFD) simulated nasal airflow in 22 healthy subjects during resting breathing. Streamline patterns, airflow distributions, velocity profiles, pressure, wall stress, turbulence, and vortical flow characteristics under quasi-steady state were analyzed. Patency ratings, acoustically measured minimum cross-sectional area (MCA), and rhinomanometric nasal resistance (NR) were examined for potential correlations with morphological and airflow-related variables.

RESULTS

Common features across subjects included: >50% total pressure drop reached near the inferior turbinate head; wall shear stress, NR, turbulence energy, and vorticity were lower in the turbinate than in the nasal valve region. However, location of the major flow path and coronal velocity distributions varied greatly across individuals. Surprisingly, on average, more flow passed through the middle than the inferior meatus and correlated with better patency ratings (r = -0.65, p < 0.01). This middle flow percentage combined with peak postvestibule nasal heat loss and MCA accounted for >70% of the variance in subjective patency ratings and predicted patency categories with 86% success. Nasal index correlated with forming of the anterior dorsal vortex. Expected for resting breathing, the functional impact for local and total turbulence, vorticity, and helicity was limited. As validation, rhinomanometric NR significantly correlated with CFD simulations (r = 0.53, p < 0.01).

CONCLUSION

Significant variations of nasal airflow found among healthy subjects; Key features may have clinically relevant applications.

Conductive olfactory losses in chronic rhinosinusitis? A computational fluid dynamics study of 29 patients

BACKGROUND

Besides sensorineural factors, conductive impediments likely contribute to olfactory losses in chronic rhinosinusitis (CRS) patients, yet no conclusive evidence exists. We aimed to examine possible conductive factors using computational fluid dynamics (CFD) models.

METHODS

A total of 29 CRS patients were assessed via odorant detection thresholds (ODTs), rhinomanometry (nasal resistance [NR]), acoustic rhinometry (minimum-cross-sectional area [MCA]) and computed tomography (CT) staging. CFD simulations of nasal airflow and odorant absorption to olfactory region were carried out based on individual CTs. Biopsies of olfactory epithelium (OE) were collected, cryosectioned, stained, and scored for erosion.

RESULTS

Significant correlations to ODTs were found for 3 variables: odor absorption in the olfactory region (r = -0.60, p < 0.01), MCA (r = -0.40, p < 0.05), and CT staging (r = 0.42, p < 0.05). However, significant findings were limited to ODTs of the highly soluble l-carvone. Multiple regression analysis revealed that these variables combined, with the addition of NR, can account for 65% of the total variance in ODTs. CT staging correlated significantly with OE erosion (r = 0.77, p < 0.01) and can replace the latter in the regression with comparable outcomes. Partial correlations suggest the contributions of both conductive and sensorineural variables are more prominent if adjusted for the effects of the other. Olfactory loss and inflammatory factors have strong bilateral involvement, whereas conductive factors are independent between sides. As validation, CFD-simulated NRs significantly correlated with rhinomanometrically assessed NRs (r = 0.60, p < 0.01).

CONCLUSION

Both conductive and sensorineural mechanisms can contribute to olfactory losses in CRS. CFD modeling provides critical guidance in understanding the role of conductive impediments in olfactory dysfunction in CRS.

Particle transport and deposition: basic physics of particle kinetics

The human body interacts with the environment in many different ways. The lungs interact with the external environment through breathing. The enormously large surface area of the lung with its extremely thin air-blood barrier is exposed to particles suspended in the inhaled air. The particle-lung interaction may cause deleterious effects on health if the inhaled pollutant aerosols are toxic. Conversely, this interaction can be beneficial for disease treatment if the inhaled particles are therapeutic aerosolized drugs. In either case, an accurate estimation of dose and sites of deposition in the respiratory tract is fundamental to understanding subsequent biological response, and the basic physics of particle motion and engineering knowledge needed to understand these subjects is the topic of this article. A large portion of this article deals with three fundamental areas necessary to the understanding of particle transport and deposition in the respiratory tract. These are: (i) the physical characteristics of particles, (ii) particle behavior in gas flow, and (iii) gas-flow patterns in the respiratory tract. Other areas, such as particle transport in the developing lung and in the diseased lung are also considered. The article concludes with a summary and a brief discussion of areas of future research.

Quantification of airflow into the maxillary sinuses before and after functional endoscopic sinus surgery

BACKGROUND

The effects of increases in maxillary sinus (MS) airflow following functional endoscopic sinus surgery (FESS) are unknown. The goal of this study was to quantify the effects of FESS on airflow into the MS in a cohort of patients with chronic rhinosinusitis, and compare MS flow rate with patient-reported outcome measures.

METHODS

A pilot study was conducted in which preoperative and postoperative computed tomography scans of 4 patients undergoing bilateral or unilateral FESS were used to create 3-dimensional (3D) reconstructions of the nasal airway and paranasal sinuses using Mimics™ (Materialise, Inc.). The size of the maxillary antrostomies post-FESS ranged from 107 to 160 mm(2). Computational meshes were generated from the 3D reconstructions, and steady-state, laminar, inspiratory airflow was simulated in each mesh using the computational fluid dynamics (CFD) software Fluent™ (ANSYS, Inc.) under physiologic, pressure-driven conditions. Airflow into the MS was estimated from the simulations and was compared preoperatively and postoperatively. In addition, patients completed preoperative and postoperative Rhinosinusitis Outcome Measure-31 (RSOM-31) questionnaires and scores were compared with MS airflow rates.

RESULTS

CFD simulations predicted that average airflow rate into post-FESS MS increased by 18.5 mL/second, and that average flow velocity into the MS more than quadrupled. Simulation results also showed that MS flow rate trended with total RSOM-31 and all domain scores.

CONCLUSION

CFD simulations showed that the healed maxillary antrostomy after FESS can greatly enhance airflow into the MS. Our pilot study suggests that to some extent, increasing airflow into the MS may potentially improve chronic rhinosinusitis patients' quality of life pre-FESS and post-FESS.

Size of nostril opening as a measure of intranasal volume

The anatomy of the human intranasal cavity is complex and anatomical variations are known to affect olfactory functions. Measurement of anatomical variations via delineation of intranasal volume is, however, technically complicated as well as time-consuming. It is well documented that size of various body parts tends to correlate within the same individual. Therefore, in the current study, we explored the relationship between intranasal volume and the size of the nares, with the aim of using the area of the nostril opening as a potential predictor of intranasal volume. Structural whole-brain T1-weighted MR images of 69 healthy volunteers (35 women) were obtained using a 1.5 T standard clinical MRI scanner. The intranasal volume, as well as the area of the nostril opening, were delineated. Our results suggest that the intranasal volume is positively correlated with the area of the nostril opening. Intranasal volume did not differ significantly between men and women although men had significant larger nostril openings. However, the correlation between intranasal volume and nostril opening was not influenced by the subject's gender. In conclusion, it is possible to obtain a good estimate of the intranasal volume using measurements of the nares.

Impacts of fluid dynamics simulation in study of nasal airflow physiology and pathophysiology in realistic human three-dimensional nose models

During the past decades, numerous computational fluid dynamics (CFD) studies, constructed from CT or MRI images, have simulated human nasal models. As compared to rhinomanometry and acoustic rhinometry, which provide quantitative information only of nasal airflow, resistance, and cross sectional areas, CFD enables additional measurements of airflow passing through the nasal cavity that help visualize the physiologic impact of alterations in intranasal structures. Therefore, it becomes possible to quantitatively measure, and visually appreciate, the airflow pattern (laminar or turbulent), velocity, pressure, wall shear stress, particle deposition, and temperature changes at different flow rates, in different parts of the nasal cavity. The effects of both existing anatomical factors, as well as post-operative changes, can be assessed. With recent improvements in CFD technology and computing power, there is a promising future for CFD to become a useful tool in planning, predicting, and evaluating outcomes of nasal surgery. This review discusses the possibilities and potential impacts, as well as technical limitations, of using CFD simulation to better understand nasal airflow physiology.

Recording odor-evoked response potentials at the human olfactory epithelium

Electro-olfactogram (EOG) represents the sum of generator potentials of olfactory receptor neurons in response to an olfactory stimulus. Although this measurement technique has been used extensively in animal research, its use in human olfaction research has been relatively limited. To understand the promises and limitations of this technique, this review provides an overview of the olfactory epithelium structure and function, and summarizes EOG characteristics and conventions. It describes methodological pitfalls and their possible solutions, artifacts, and questions of debate in the field. In summary, EOG measurements provide a rare opportunity of recording neuronal input from the peripheral olfactory system, while simultaneously obtaining psychophysical responses in awake humans.

Aerodynamic characteristics inside the rhino-sinonasal cavity after functional endoscopic sinus surgery

BACKGROUND

The aim of this study was to evaluate effects of functional endoscopic sinus surgery (FESS) on transient nasal aerodynamic flow patterns using computational fluid dynamics (CFD) simulations.

METHODS

A three-dimensional model of the nasal cavity was constructed from CT scans of a patient with FESS interventions on the right side of the nasal cavity. CFD simulations were then performed for unsteady aerodynamic flow modeling inside the nasal cavity as well as the sinuses.

RESULTS

Comparisons of the local velocity magnitude and streamline distributions inside the left and right nasal cavity and maxillary sinus regions were presented. Because of the FESS procedures in the right nasal cavity, existences and distributions of local circulations (vortexes) were found to be significantly different for the same nasal airflow rate but at different acceleration, deceleration, or quiet phases in the maxillary sinus region on the FESS side. Because of inertia effects, local internal airflow with circulation existences was continuous throughout the whole respiration cycle. With a larger peak inspiration flow rate, the airflow intensity inside the enlarged maxillary sinus increased significantly. Possible outcomes on functional performances of the nose were also examined and discussed.

CONCLUSION

Surgical enlargements of natural ostium of the maxillary sinus will change the aerodynamic patterns inside the main nasal cavity and maxillary sinus regions, which may affect normal nasal physiological functions. Local inertia effects play more important roles for the internal nasal airflow pattern changes and thus such conventional FESS procedures should be carefully planned.

COMPUTATIONAL FLUID DYNAMICS (CFD) APPLIED IN THE DRUG DELIVERY DESIGN PROCESS TO THE NASAL PASSAGES: A REVIEW

Computer fluid dynamics (CFD) has for many years now been employed to study and solve fluid problems in the industry and offers an attractive method for accurately describing systems at a reasonable cost. Computer-aided methods are becoming increasingly important in medicine. Due to a combination of increased computer efficiency and advanced numerical techniques, the realism of these simulations has been enhanced in recent years. Over the past decade, computer-aided design has emerged as a method that is both sufficiently rigorous and efficient to be used for studies of the fluid dynamics in complex airway structures like the nasal airway. Physical experiments in vitro and in vivo are often expensive and time-consuming, and CFD has gained increasing attention as a tool in the design process of devices delivering drugs to the respiratory tract. This paper provides a review of the development of CFD in the studies of nasal airway fluid dynamics, particle and filtering properties in health and disease. Special emphasis is given to studies related to CFD studies used in the development of nasal drug delivery devices. The accuracy and value of CFD for the study of drug delivery design to the nose is reviewed in comparison to experimental results with other methods. Some important challenges when dealing with grid generation and flow simulations in these complex geometries with variable multiphase flow patterns in alternate directions are discussed.

Drug delivery in the nasal cavity after functional endoscopic sinus surgery: a computational fluid dynamics study

BACKGROUND

Intranasal medication is commonly used for nasal disease. However, there are no clear specifications for intranasal medication delivery after functional endoscopic sinus surgery.

METHODS

A three-dimensional model of the nasal cavity was constructed from computed tomography scans of an adult Chinese male who had previously undergone functional endoscopic sinus surgery in the right nasal cavity. Computational fluid dynamic simulations modelled airflow and particle deposition, based on discrete phase models.

RESULTS

In the right nasal cavity, more particles passed through the upper dorsal region, around the surgical area, and streamed into the right maxillary sinus region. In the left cavity, particles were distributed more regularly and uniformly in the ventral region around the inferior turbinate. A lower inspiratory airflow rate and smaller initial particle velocity assisted particle deposition within the right maxillary sinus cavity. In the right nasal cavity, the optimal particle diameter was approximately 10(-5) m for maxillary sinus cavity deposition and 3 × 10(-6) m for bottom region deposition. In the right nasal cavity, altered back head tilt angles enhanced particle deposition in the top region of the surgical area, and altered right side head tilt angles helped enhance maxillary sinus cavity deposition.

CONCLUSION

This model indicates that a moderate inspiratory airflow rate and a particle diameter of approximately 10(-5) m should improve intranasal medication deposition into the maxillary sinus cavity following functional endoscopic sinus surgery.

Numerical simulation and nasal air-conditioning

Heating and humidification of the respiratory air are the main functions of the nasal airways in addition to cleansing and olfaction. Optimal nasal air conditioning is mandatory for an ideal pulmonary gas exchange in order to avoid desiccation and adhesion of the alveolar capillary bed. The complex three-dimensional anatomical structure of the nose makes it impossible to perform detailed in vivo studies on intranasal heating and humidification within the entire nasal airways applying various technical set-ups. The main problem of in vivo temperature and humidity measurements is a poor spatial and time resolution. Therefore, in vivo measurements are feasible only to a restricted extent, solely providing single temperature values as the complete nose is not entirely accessible. Therefore, data on the overall performance of the nose are only based on one single measurement within each nasal segment. In vivo measurements within the entire nose are not feasible. These serious technical issues concerning in vivo measurements led to a large number of numerical simulation projects in the last few years providing novel information about the complex functions of the nasal airways. In general, numerical simulations merely calculate predictions in a computational model, e.g. a realistic nose model, depending on the setting of the boundary conditions. Therefore, numerical simulations achieve only approximations of a possible real situation. The aim of this review is the synopsis of the technical expertise on the field of in vivo nasal air conditioning, the novel information of numerical simulations and the current state of knowledge on the influence of nasal and sinus surgery on nasal air conditioning.

Olfactory event-related potential in patients with rhinosinusitis-induced olfactory dysfunction

BACKGROUND

Olfactory disorders are a common syndrome in the rhinology clinic. Olfactory event-related potential (OERP) has been considered as an important alternative method to evaluate olfactory function. The aim of this study was to find the consistency of OERP and the psychophysics olfactory test (T&T olfactometry assessment) in rhinosinusitis patients with or without nasal polyposis.

METHODS

Both the psychophysics olfactory test and the OERP were performed in all patients before functional endoscopic sinus surgery (FESS). Detailed information including demographic, comorbidity, subjective symptoms, CT, and endoscopic examination were recorded. Six months later, the T&T test and OERP were reexamined in patients with preoperative identified OERP.

RESULTS

Preoperative OERP was identified in 26 patients of the nonpolyp group and 12 patients of the polyp group. Good correlation existed between T&T scores and amplitude and latency of N1 and P2 in 26 nonpolyp patients (p < 0.05). No meaningful correlation was apparent in 12 polyp patients (p > 0.05). Significant correlation existed in 7 polyp patients with a free olfactory cleft (OC) according to CT (p < 0.05). The other 5 patients with partial OC obstruction were anosmic according to the psychophysics olfactory test; however, OERP was present. Six months later, T&T scores decreased significantly only in these five patients (p < 0.05). Significant correlation was obtained between postoperative T&T scores and OERP in both polyp and nonpolyp groups (p < 0.05).

CONCLUSION

OERP can be used to investigate olfactory function of rhinosinusitis patients. Nasal polyp obstruction in specific parts of the OC might influence the consistency between the psychophysics olfactory test and OERP.

A computational fluid dynamics model for drug delivery in a nasal cavity with inferior turbinate hypertrophy

BACKGROUND

Intranasal medications are commonly used in treating nasal diseases. However, technical details of the correct usage of these medications for nasal cavity with obstruction are unclear.

METHODS

A three-dimensional model of nasal cavity was constructed from MRI scans of a healthy human subject. Nasal cavities corresponding to healthy, moderate, and severe nasal obstruction (NO) were simulated by enlarging the inferior turbinate geometrically, which was documented by approximately one-third reduction of the minimum cross-sectional area for the moderate and two-thirds for the severe obstruction. The discrete phase model based on steady-state computational fluid dynamics was used to study the gas-particle flow. The results were presented with drug particle (from 7 x 10⁻⁵ to 10⁻⁷ m) deposition distribution along the lateral walls inside these three nasal cavities, and comparisons of the particle ratio escaping from the cavity were also presented and discussed.

RESULTS

Nasal patency is an essential condition that had the most impact on particle deposition of the factors studied; the particle percentage escaping the nasal cavity decreased to less than a half and one-tenth for the moderately and severely blocked noses. Decreasing of flow rate and particle diameter increased the escaping ratio; however, zero escaping percentage was detected with the absence of air flow and the effect was less noticeable when the particle diameter was very small (<10⁻⁶ m). The existence of inspiratory flow and head tilt angle helped to improve the particle escaping ratio for the healthy nose; however, such changes were not significant for the moderately and severely blocked noses.

CONCLUSION

When using an intranasal medication, it is advisable to have a moderate inspiratory air-flow rate and small size particles to improve particle escaping ratio. Various head positions suggested by clinicians do not seem to improve the drug escaping ratio significantly for the nasal cavities with inferior turbinate hypertrophy.

Objective measures in aesthetic and functional nasal surgery: perspectives on nasal form and function

The outcomes of aesthetic and functional nasal surgery are difficult to assess objectively because of the intricate balance between nasal form and function. Despite historical emphasis on patient-reported subjective measures, objective measures are gaining importance in both research and the current outcomes-driven health care environment. Objective measures currently available have several shortcomings that limit their routine clinical use. In particular, the low correlation between objective and subjective measures poses a major challenge. However, advances in computer, imaging, and bioengineering technology are now setting the stage for the development of innovative objective assessment tools for nasal surgery that can potentially address some of the current limitations. Assessment of nasal form after aesthetic surgery is evolving from two-dimensional analysis to more sophisticated three-dimensional analysis. Similarly, assessment of nasal function is evolving with the introduction of computational fluid dynamics techniques, which allow for a detailed description of the biophysics of nasal airflow. In this article, we present an overview of objective measures in both aesthetic and functional nasal surgery and discuss future trends and applications that have the potential to change the way we assess nasal form and function.

Septal deviation and nasal resistance: an investigation using virtual surgery and computational fluid dynamics

BACKGROUND

Septal deviation is an extremely common anatomic variation in healthy adults. However, there are no standard criteria to determine when a deviated septum is clinically relevant. Presently, selection of patients for septoplasty is based on mostly clinical examination, which is prone to observer bias and may lead to unsuccessful treatment. The objective of this article is twofold. First, we investigate whether the location of a septal deviation within the nasal passages affects nasal resistance. Second, we test whether computer simulations are consistent with rhinomanometry studies in predicting that anterior septal deviations increase nasal resistance more than posterior deviations.

METHODS

A three-dimensional computational model of a healthy nose was created from computed tomography scans. Geometry-deforming software was used to produce models with septal deviations. Computational fluid dynamics techniques were used to simulate nasal airflow and compute nasal resistance.

RESULTS

Our results revealed that the posterior nasal cavity can accommodate significant septal deviations without a substantial increase in airway resistance. In contrast, a deviation in the nasal valve region more than doubled nasal resistance. These findings are in good agreement with the rhinomanometry literature and with the observation that patients with anterior septal deviations benefit the most from septoplasty.

CONCLUSION

In the model, anterior septal deviations increased nasal resistance more than posterior deviations. This suggests, in agreement with the literature, that other causes of nasal obstruction (dysfunction of the nasal valve, allergy, etc.) should be carefully considered in patients with posterior septal deviations because such deviations may not affect nasal resistance. This study illustrates how computational modeling and virtual manipulation of the nasal geometry are useful to investigate nasal physiology.

Allergic rhinitis and aspirin-exacerbated respiratory disease as predictors of the olfactory outcome after endoscopic sinus surgery

BACKGROUND

Unlike the functional outcomes of endoscopic sinus surgery, which have been thoroughly studied, the effect of the surgery on olfactory performance and the relative predictive factors have not been adequately assessed by literature. Allergic rhinitis and aspirin-exacerbated respiratory disease (AERD) are examined as potential confounding factors of the olfactory outcome in patients with extensive nasal polyposis and rhinosinusitis treated with functional endoscopic sinus surgery (FESS).

METHODS

A population of 116 adults with severe nasal polyposis was subjected to FESS after failure of the appropriate medical treatment. The olfactory outcome was quantified by Sniffin' Sticks at the 1st, 3rd, and 6th postoperative month in relation to the concomitant presence of allergic rhinitis (n = 62) or AERD (n = 18).

RESULTS

Allergic patients seemed to perform worse than nonallergic patients at all time frames. However, when patients with similar olfactory acuity, age, and medical history are compared, allergic rhinitis does not seem to affect the postoperative improvement of the composite threshold-discrimination-identification scores. The same seems to apply for the likelihood of acquiring normosmia after surgery. On the contrary, AERD significantly limits the recovery of olfactory function at all follow-up examinations and patients with AERD are unlikely to become normosmic.

CONCLUSION

The olfactory recovery after FESS for nasal polyposis is significantly affected by the concomitant presence of AERD. Although allergy seems to have a general negative effect on olfactory acuity, it was not found to affect the extent of the olfactory improvement, when patients with comparable preoperative characteristics are addressed.

Endoscopic sinus surgery in the management of nasal obstruction

Nasal obstruction is the leading symptom observed among patients who have chronic rhinosinusitis (CRS) with or without nasal polyposis. After failure of medical therapy, functional endoscopic sinus surgery (FESS) has emerged as the preferred treatment of CRS. Interestingly, although patient-reported outcomes show unequivocal relief of nasal obstruction after FESS, studies measuring nasal airflow and resistance demonstrate more modest improvements. This article provides an overview of the physiology of nasal airflow sensation, the burden of nasal obstruction in patients who have CRS, and the efficacy of FESS in addressing nasal obstruction in this population. Additionally, advances in airflow modeling that may enable improved preoperative planning for the relief of nasal obstruction after FESS are discussed.