Correlation between nasal airflow characteristics and clinical relevance of nasal septal deviation to nasal airway obstruction

Computational analysis of nasal airflow and its alteration by a nasal dilator

Nasal airflow obstruction correlates with several ailments, such as higher patency, increased friction at the mucosal wall or the so-called Little's area, improper air conditioning, and snoring. Nasal dilators are frequently employed, mainly due to their ease of access and use, combined with their non-permanent and non-surgical nature. Their overall efficacy, however, has not been clearly demonstrated so far, with some studies reporting conflicting outcomes, mainly because being based on subjective evaluations. This study employs Computational Fluid Dynamics simulations to analyze the flow inside a real nose, performs an objective assessment of a nasal dilator's effect in terms of airflow and air conditioning, reporting flow paths, friction levels, heat and water fluxes and detailed temperature and humidity distributions. Coincidentally, the studied nose presents a septal deviation, with one nostril being wider than the other. The tubes of the dilator used in both nostrils are identical, as with any standard commercial dilator. Consequently, the dilator widens one nostril, as intended, but results in an obstruction in the other. This allows simultaneously addressing two situations, the nominal function of the dilator, as well as an off-design case. Results indicate a 24 % increase in nasal patency in the design situation. The effect, however, is limited, as quantified by appropriate measures, such as the flow-generated friction at the nose surfaces and the temperature fluxes. Hence, the effect of such a dilator in nominal conditions is perhaps not as large as might be hoped. In the off-design situation, nasal resistance increases by 62 %, an undesirable effect, illustrating the consequences of using an inappropriate dilator.

Algorithm for Nasal Breathing Impairment Evaluation

Assessing patients with complaints of nasal obstruction has traditionally been done by evaluation of the nasal airway looking for fixed or dynamic obstructive locations that could impair nasal airflow. Not infrequently, however, symptoms of nasal obstruction do not match the clinical examination of the nasal airway. Addressing this subset of patients may be a challenge to the surgeon. Evaluation of patients with symptoms of nasal obstruction should include a combination of a patient-reported assessment of nasal breathing and at least one objective method for measuring nasal airflow or nasal airway resistance or dimensions. This will allow distinction between patients with symptoms of nasal obstruction and low airflow or high nasal airway resistance and patients with similar symptoms but whose objective evaluation demonstrates normal nasal airflow or normal airway dimensions or resistance. Patients with low nasal airflow or high nasal airway resistance will require treatment to increase nasal airflow as a necessary step to improve symptoms, whereas patients with normal nasal airflow or nasal airway resistance will require a multidimensional assessment looking for less obvious causes of impaired nasal breathing sensation.

Automated surgery planning for an obstructed nose by combining computational fluid dynamics with reinforcement learning

Septoplasty and turbinectomy are among the most common interventions in the field of rhinology. Their constantly debated success rates and the lack of quantitative flow data of the entire nasal airway for planning the surgery necessitate methodological improvement. Thus, physics-based surgery planning is highly desirable. In this work, a novel and accurate method is developed to enhance surgery planning by physical aspects of respiration, i.e., to plan anti-obstructive surgery, for the first time a reinforcement learning algorithm is combined with large-scale computational fluid dynamics simulations. The method is integrated into an automated pipeline based on computed tomography imaging. The proposed surgical intervention is compared to a surgeon's initial plan, or the maximum possible intervention, which allows the quantitative evaluation of the intended surgery. Two criteria are considered: (i) the capability to supply the nasal airway with air expressed by the pressure loss and (ii) the capability to heat incoming air represented by the temperature increase. For a test patient suffering from a deviated septum near the nostrils and a bony spur further downstream, the method recommends surgical interventions exactly at these locations. For equal weights on the two criteria (i) and (ii), the algorithm proposes a slightly weaker correction of the deviated septum at the first location, compared to the surgeon's plan. At the second location, the algorithm proposes to keep the bony spur. For a larger weight on criterion (i), the algorithm tends to widen the nasal passage by removing the bony spur. For a larger weight on criterion (ii), the algorithm's suggestion approaches the pre-surgical state with narrowed channels that favor heat transfer. A second patient is investigated that suffers from enlarged turbinates in the left nasal passage. For equal weights on the two criteria (i) and (ii), the algorithm proposes a nearly complete removal of the inferior turbinate, and a moderate reduction of the middle turbinate. An increased weight on criterion (i) leads to an additional reduction of the middle turbinate, and a larger weight on criterion (ii) yields a solution with only slight reductions of both turbinates, i.e., focusing on a sufficient heat exchange between incoming air and the air-nose interface. The proposed method has the potential to improve the success rates of the aforementioned surgeries and can be extended to further biomedical flows.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

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.

Airway Resistance and Respiratory Distress in Laryngeal Cancer: A Computational Fluid Dynamics Study

BACKGROUND

Obstructive upper airway pathologies are a great clinical challenge for the airway surgeon. Protection against acute obstruction is critical, but avoidance of unnecessary tracheostomy must also be considered. Decision-making regarding airway, although supported by some objective findings, is largely guided by subjective experience and training. This investigation aims to study the relationship between clinical respiratory distress and objective measures of airway resistance in laryngeal cancer as determined by computational fluid dynamic (CFD) and morphometric analysis.

METHODS

Retrospective CT and clinical data were obtained for series of 20 cases, defined as newly diagnosed laryngeal cancer patients who required admission or urgent airway surgery, and 20 controls. Cases and controls were matched based on T-staging. Image segmentation and morphometric analysis were first performed. Computational models based on the lattice Boltzmann method were then created and used to quantify the continuous mass flow, rigid wall, and constant static pressure inlet boundary conditions.

RESULTS

The analysis demonstrated a significant relationship between airway resistance and acute obstruction (OR 1.018, 95% CI 1.001-1.045). Morphometric analysis similarly demonstrated a significant relationship when relating measurements based on the minimum cross-section, but not on length of stenosis. Morphometric measurements also showed significance in predicting CFD results, and their relationship demonstrated that airway pressures increase exponentially below 2.5 mm. Tumor subsite did not show a significant difference, although the glottic subgroup tended to have higher resistances.

CONCLUSION

Airway resistance analysis from CFD computation correlated with presence of acute distress requiring emergent management. Morphometric analysis showed a similar correlation, demonstrating a radiologic airway assessment technique on which future risk estimation could be performed.

LEVEL OF EVIDENCE

4 (case-control study) Laryngoscope, 133:2734-2741, 2023.

The Effect of Segmentation Threshold on Computational Fluid Dynamic Analysis of Nasal Airflow

BACKGROUND

The objective analysis of nasal airflow stands to benefit greatly from the adoption of computational fluid dynamic (CFD) methodologies. In this emerging field, no standards currently exist in regard to the ideal modeling parameters of the nasal airway. Such standards will be necessary for this tool to become clinically relevant.

METHODS

Human nasal airways were modeled from a healthy control, segmented, and analyzed with an in-house immersed boundary method. The segmentation Hounsfield unit (HU) threshold was varied to measure its effect in relation to airflow velocity magnitude and pressure change.

FINDINGS

Surface area and volume have a linear relationship to HU threshold, whereas CFD variables had a more complex relationship.

INTERPRETATION

The HU threshold should be included in nasal airflow CFD analysis. Future work is required to determine the optimal segmentation threshold.

Maxillary sinus aeration analysis using computational fluid dynamics

The maxillary sinus aeration using the computational fluid dynamics (CFD) method based on individual adult patients’ computed tomography (CT) scans were analyzed. The analysis was based on CT images of 4 patients: one with normal nose anatomy and three with nasal septal deviation (NSD) and concha bullosa (CB). The CFD simulation was performed using the Reynolds-Average Simulation approach and turbulence closure based on linear eddy viscosity supplemented with the two-equation k-\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\omega$$\end{document}ω SST model. As a result, it was found that the lower part of NSD has the most significant impact on the airflow change within the maxillary sinuses compared to CB and the upper part of NSD. In a healthy nose, the airflow in the sinuses is continuous, while NSD and CB change this flow into pulsatile. Multiple changes in the direction of flow during one respiratory phase were observed. The flow intensity within the maxillary sinus opening is lower on the NSD side. The concept of vorticity measure is introduced to evaluate and compare various patients qualitatively. Typically, the lowest values of such measures are obtained for healthy airways and the highest for pathological changes in the nasal cavity.

Clinical perspectives on nasopharyngeal morphology in humans

The nasopharynx is an integral component of the upper aerodigestive tract, whose morphologic features share an intimate relationship with a vast array of clinical, functional, and quality of life conditions related to contemporary humans. Its composite architecture and central location amidst the nasal cavity, pharyngotympanic tube, palate, and skull base bears implications for basic physiologic functions including breathing, vocalization, and alimentation. Over the course of evolution, morphological modifications of nasopharyngeal anatomy have occurred in genus Homo which serve to distinguish the human upper aerodigestive tract from that of other mammals. Understanding of these adaptive changes from both a comparative anatomy and clinical perspective offers insight into the unique blueprint which underpins many clinical pathologies currently encountered by anthropologists, scientists, and otorhinolaryngologists alike. This discussion intends to familiarize readers with the fundamental role that nasopharyngeal morphology plays in upper aerodigestive tract conditions, with consideration of its newfound clinical relevance in the era of the COVID-19 pandemic.

CFD SIMULATIONS AND ANALYSES OF ASYMPTOMATIC AND SYMPTOMATIC NASAL AIRWAY OBSTRUCTIONS

The numerical simulations of the flow in nasal airways were performed for two different clinical cases. The results comprised the distributions of scalars at five different sections and included contours of pressure, velocity magnitude, turbulent kinetic energy and vorticity magnitude. Simulations showed the air branching occurring at the inferior meatus is unaffected by the variations in the volumetric flow rate or the changes in the flow regime through the olfactory cleft. However, the contractions and the following rapid change in the cross-section of the nasopharynx preclude the upward penetration of the vacuum field set by the lungs during the inhalation process. As a result, considerably low velocities and significant cross-sectional nonuniformities are observed, which lead to the appearances of the secondary flow structures and strong unsteadiness. Increased interactions between the airflow and the walls of the nasal cavity resulted in an increase in the vorticity on the right middle meatus and upper inferior meatus. The vorticity was also very high in the nostrils, where the flow was not fully developed.

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

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

Toward automatic atlas-based surgical planning for septoplasty

PURPOSE

Surgery for nasal airway obstruction (NAO) has a high failure rate, with up to 50% of patients reporting persistent symptoms postoperatively. Virtual surgery planning has the potential to improve surgical outcomes, but current manual methods are too labor-intensive to be adopted on a large scale. This manuscript introduces an automatic atlas-based approach for performing virtual septoplasties.

METHODS

A cohort of 47 healthy subjects and 26 NAO patients was investigated. An atlas of healthy nasal geometry was constructed. The automatic virtual septoplasty method consists of a multi-stage registration approach to fit the atlas to a target NAO patient, automatically segment the patient's septum and airway, and deform the patient image to have a non-deviated septum.

RESULTS

Our automatic virtual septoplasty method straightened the septum successfully in 18 out of 26 NAO patients (69% of cases). In these cases, the ratio of the higher to the lower airspace cross-sectional areas in the left and right nasal cavities improved from 1.47 ± 0.45 to 1.16 ± 0.33 in the region surrounding the septal deviation, showing that the nasal airway became more symmetric after virtual septoplasty.

CONCLUSION

This automated virtual septoplasty technique has the potential to greatly reduce the effort required to perform computational fluid dynamics (CFD) analysis of nasal airflow for NAO surgical planning. Future studies are needed to investigate if virtual surgery planning using this method is predictive of subjective symptoms in NAO patients after septoplasty.

The Relationship Between Degree of Nasal Septum Deviation With Sinonasal Structures and Variations

ABSTRACT

We aimed to evaluate whether the nasal septum deviation affects the development of sinonasal structures. Patients who had undergone paranasal sinus computed tomography (PNS-CT) imaging due to nasal obstruction were divided into 3 groups according to the septal deviation angle; group I: 0° to 9°, group II: 10° to 15°, and group III: >15°. The features of sinonasal structures were recorded when evaluating PNS-CT. There were totally 234 patients, 119 patients in group I, 68 in group II, and 47 in group III. On the opposite side of the deviation, keros 3 was significantly more in group III (P < 0.001). Although the incidence of concha bullosa and agger nasi cell were not affected by the degree of deviation (P > 0.05), the incidence of Haller and Onodi cells were significantly higher in group III (P < 0.001). In addition, all cells were observed more in the opposite side of the deviation in each group (P < 0.001). Maxillary sinus retention cysts and hypoplasia of maxillary and frontal sinuses, as an indicator of the low pneumatization of the sinuses, are seen more on the same side of nasal septum deviation, increasing with the degree of deviation increases (P < 0.001). Nasal septum deviation affects the development of sinonasal structures by affecting the pneumatization. Preoperative PNS-CT evaluation is important in order to be aware of the situations that we may encounter during surgery and to provide adequate treatment.

Effect of septal deviation on nasomaxillary shape: A geometric morphometric study

Nasal cavities in their primitive stage communicate with the oral cavity until the 8th week of intrauterine life where the posterior palate initiates its development. Hence, starting from the initial growth phases, a significant connection lays between the nasal structures and the maxillary bone and witnessing key functional roles, among which the respiration. Proper nasal breathing has been proven to be a crucial factor for the maturity of the craniofacial complex, and obstruction of the respiratory airway due to nasal septum deviation can generate clinically significant reduction of the nasal airflow. This situation will imply irreversible repercussions that hinders the harmonious development of the craniofacial complex. In order to understand such potential impacts of septal deviation, our first objective was to materialize the relation between septum deviation, and both nasal cavity and maxillary structures. For the second objective, we used Procrustes analysis to assess the shape variation of these two anatomical regions, the bivariate plots of Principal Components to evaluate their shape space, and a two-block Partial Least Square (PLS) to explore their covariation. We analysed, in this cross-sectional study, 62 posteroanterior cephalometric radiographs of adult subjects from both sexes (23 males, 39 females; mean age 25.3 years) collected from the database of the Department of Orthodontics at Lebanese University. Landmarks were plotted and variables were calculated and divided into nasal septum, nasal cavity and maxillary ones. The sample was further divided into two groups based on septal deviation severity (a septal deviation is considered minor if <6). The results suggested that nasal septum deviation was correlated to reduced nasal cavity area and a reduced maxillary area. Moreover, the comparison of the two groups concluded that the difference between all variables was statistically significant with higher scores in the minor septal deviation group. These findings were corroborated with the shape analysis where the mean centroid size of nasal cavity and that of the maxilla in the group of reduced septal deviation were significantly greater than those of the group with increased angle of deviation. Results of PLS analysis concluded to a strong covariation between nasal septum and nasomaxillary complex. These conclusions support the early septoplasty in growing patients as a solution to redirect the normal course of growth and re-establish a good function of the nasomaxillary complex.

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

Nasal adhesions are a known postoperative complication following surgical procedures for nasal airway obstruction (NAO); and are a common cause of surgical failure, with patients often reporting significant NAO, despite relatively minor adhesion size. Division of such nasal adhesions often provides much greater relief than anticipated, based on the minimal reduction in cross-sectional area associated with the adhesion. The available literature regarding nasal adhesions provides little evidence examining their quantitative and qualitative effects on nasal airflow using objective measures. This study examined the impact of nasal adhesions at various anatomical sites on nasal airflow and mucosal cooling using computational fluid dynamics (CFD). A high-resolution CT scan of the paranasal sinuses of a 25-year-old, healthy female patient was segmented to create a three-dimensional nasal airway model. Virtual nasal adhesions of 2.5 mm diameter were added to various locations within the nasal cavity, representing common sites seen following NAO surgery. A series of models with single adhesions were created. CFD analysis was performed on each model and compared with a baseline no-adhesion model, comparing airflow and heat and mass transfer. The nasal adhesions resulted in no significant change in bulk airflow patterns through the nasal cavity. However, significant changes were observed in local airflow and mucosal cooling around and immediately downstream to the nasal adhesions. These were most evident with anterior nasal adhesions at the internal valve and anterior inferior turbinate. Postoperative nasal adhesions create local airflow disruption, resulting in reduced local mucosal cooling on critical surfaces, explaining the exaggerated perception of nasal obstruction. In particular, anteriorly located adhesions created greater disruption to local airflow and mucosal cooling, explaining their associated greater subjective sensation of obstruction.

Nasal airflow of patient with septal deviation and allergy rhinitis

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

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

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

Role of nasal vestibule morphological variations on olfactory airflow dynamics

BACKGROUND

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

METHODS

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

FINDINGS

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

INTERPRETATION

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

Rapid Maxillary Expansion Has a Beneficial Effect on the Ventilation in Children With Nasal Septal Deviation: A Computational Fluid Dynamics Study

Nasal septal deviation (NSD) is one of the most common nasal diseases. Different from common clinical examination methods, computational fluid dynamics (CFD) can provide visual flow information of the nasal cavity. The dimension and volume of the nasal cavity are easily affected by rapid maxillary expansion (RME). The purpose of this study was to use CFD to evaluate the effect of RME on the aerodynamics of the nasal cavity in children with maxillary transverse deficiency and NSD. Computational fluid dynamics was implemented after 3D reconstruction based on the CBCT of 15 children who have completed RME treatment. After treatment, the volume increases in the nasal cavity, nasopharynx, oropharynx, and pharynx were not statistically significant. The wall shear stress of the nasal cavity after RME, 1.749 ± 0.673 Pa, was significantly lower than that before RME, 2.684 ± 0.919 Pa. Meanwhile, the maximal negative pressure in the pharyngeal airway during inspiration was smaller after RME (-31.058 Pa) than before (-48.204 Pa). This study suggests that RME has a beneficial effect on nasal ventilation. The nasal airflow became more symmetrical in the bilateral nasal cavity after RME. Pharyngeal resistance decreased with the reduction in nasal resistance and the increase in the volume of oropharynx after RME.

Three-dimensional modeling and automatic analysis of the human nasal cavity and paranasal sinuses using the computational fluid dynamics method

PURPOSE

The goal of this study was to develop a complete workflow allowing for conducting computational fluid dynamics (CFD) simulation of airflow through the upper airways based on computed tomography (CT) and cone-beam computed tomography (CBCT) studies of individual adult patients.

METHODS

This study is based on CT images of 16 patients. Image processing and model generation of the human nasal cavity and paranasal sinuses were performed using open-source and freeware software. 3-D Slicer was used primarily for segmentation and new surface model generation. Further processing was done using Autodesk^® Meshmixer TM. The governing equations are discretized by means of the finite volume method. Subsequently, the corresponding algebraic equation systems were solved by OpenFOAM software.

RESULTS

We described the protocol for the preparation of a 3-D model of the nasal cavity and paranasal sinuses and highlighted several problems that the future researcher may encounter. The CFD results were presented based on examples of 3-D models of the patient 1 (norm) and patient 2 (pathological changes).

CONCLUSION

The short training time for new user without a prior experience in image segmentation and 3-D mesh editing is an important advantage of this type of research. Both CBCT and CT are useful for model building. However, CBCT may have limitations. The Q criterion in CFD illustrates the considerable complication of the nasal flow and allows for direct evaluation and quantitative comparison of various flows and can be used for the assessment of nasal airflow.

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

OBJECTIVES

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

DESIGN

Computational fluid dynamics (CFD) study.

SETTING

The study was conducted in a tertiary medical centre.

PARTICIPANTS

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

MAIN OUTCOME MEASURES

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

RESULTS

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

CONCLUSIONS

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

The frequencies of different types of nasal septum deviation and their effect on increasing the thickness of maxillary sinus mucosa

Background. Diseases of the paranasal sinuses are very prevalent in East Azerbaijan Province, Iran, which is attributed to various reasons, including environmental and anatomical factors. This study investigated the prevalence of anatomical variations of nasal septum deviation and evaluated the effect of this factor on increasing the mucosal thickness of the sinuses.

Methods. The samples included all the patients referred to Tabriz Faculty of Dentistry, and the frequency of nasal septum deviation in the sample population was evaluated. The samples were re-examined to select the samples with a thickened mucosa of the maxillary sinus. The results were reported using descriptive statistical methods.

Results. Deviation of the nasal septum was seen in 75% of the cases. The results showed that 31.76 % of males and 56.67% of females had an increased maxillary sinus mucosa thickness.

Conclusion. There was a significant relationship between nasal septum deviation and thickening of the maxillary sinus mucosa.

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

BACKGROUND

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

OBJECTIVE OF THE REVIEW

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

TYPE OF REVIEW

Systematic literature review using PRISMA guidelines.

SEARCH STRATEGY

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

EVALUATION METHOD

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

RESULTS

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

CONCLUSIONS

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

Correlations between computational fluid dynamics and clinical evaluation of nasal airway obstruction due to septal deviation: An observational study

OBJECTIVES

The primary objective of this study was to determine how computational fluid dynamics (CFD) could be correlated to clinical evaluation of nasal airway obstruction (NAO) in a population of patients with symptomatic septal deviation (SD). The secondary objective was to determine whether CFD could define which side was the more obstructed.

DESIGN

This was an observational study.

SETTINGS

Few publications have attempted to correlate CFD with clinical evaluation of NAO. This correlation would permit validation and improved interpretation. This study was performed in a university research laboratory specialised in fluid mechanics.

PARTICIPANTS

We included patients referred for septal surgery at our centre. Age range was 19-58 years. Preoperative CT scans were performed. All patients with non-structural causes of NAO such as rhinitis, sinusitis or tumoral/autoimmune processes (ie, not due to anatomic obstruction) were excluded.

MAIN OUTCOME MEASUREMENT

For each nasal fossa, we compared CFD data (total pressure, heat flux, wall shear stress, temperatures, velocity and nasal resistances) with both patient perception scores and rhinomanometry using the Spearman correlation test (r_s ). Perception scores were graded from 0/4 to 4/4 on each side, based on the patient interview. We also compared CFD-derived nasal resistances with rhinomanometry-derived nasal resistances.

RESULTS

Twenty-two patients complaining of NAO with SD were analysed, and 44 analyses were performed comparing each side with its CFD data. Regarding correlations with patient perception scores, the best values we found were heat flux measures (r_s  = 0.86). Both rhinomanometry and CFD-calculated nasal resistances had strong correlations with subjective perception scores (r_s  = 0.75, P < 0.001 and r_s  = 0.6, P < 0.001, respectively). We found a statistically significant difference between RMM-NR and CFD-NR (P = 0.003). Heat flux analysis allowed us to distinguish the more obstructed side (MOS) and the less obstructed side (LOS) in 100% of patients.

CONCLUSION

This study aimed to enhance our ability to interpret CFD-calculated data in the nasal airway. It highlights and confirms that heat flux measures are very closely correlated to patient perception in cases of SD. It also helps to distinguish the more obstructed side from the less obstructed side and could contribute to further CFD studies.

Computational Analysis of the Mature Unilateral Cleft Lip Nasal Deformity on Nasal Patency

Background

Nasal airway obstruction (NAO) due to nasal anatomic deformities is known to be more common among cleft patients than the general population, yet information is lacking regarding severity and variability of cleft-associated nasal obstruction relative to other conditions causing NAO. This preliminary study compares differences in NAO experienced by unilateral cleft lip nasal deformity (uCLND) subjects with noncleft subjects experiencing NAO.

Methods

Computational modeling techniques based on patient-specific computed tomography images were used to quantify the nasal airway anatomy and airflow dynamics in 21 subjects: 5 healthy normal subjects; 8 noncleft NAO subjects; and 8 uCLND subjects. Outcomes reported include Nasal Obstruction Symptom Evaluation (NOSE) scores, cross-sectional area, and nasal resistance.

Results

uCLND subjects had significantly larger cross-sectional area differences between the left and right nasal cavities at multiple cross sections compared with normal and NAO subjects. Median and interquartile range (IQR) NOSE scores between NAO and uCLND were 75 (IQR = 22.5) and 67.5 (IQR = 30), respectively. Airflow partition difference between both cavities were: median = 9.4%, IQR = 10.9% (normal); median = 31.9%, IQR = 25.0% (NAO); and median = 29.9%, IQR = 44.1% (uCLND). Median nasal resistance difference between left and right nasal cavities were 0.01 pa.s/ml (IQR = 0.03 pa.s/ml) for normal, 0.09 pa.s/ml (IQR = 0.16 pa.s/ml) for NAO and 0.08 pa.s/ml (IQR = 0.25 pa.s/ml) for uCLND subjects.

Conclusions

uCLND subjects demonstrated significant asymmetry between both sides of the nasal cavity. Furthermore, there exists substantial disproportionality in flow partition difference and resistance difference between cleft and noncleft sides among uCLND subjects, suggesting that both sides may be dysfunctional.

Analysis of the development of human foetal nasal turbinates using CBCT imaging

PURPOSE

The morphological structure of the nasal cavity (NC) is important for endoscopic surgical treatment. The location of nasal turbinates, including the superior turbinate (ST), middle turbinate (MT) and inferior turbinate (IT), are well presented during the formation of the human NC in cone beam CT (CBCT) images. There is a complex relationship between the nasal sinuses, the maxillary sinus (MS), ethmoidal sinus and sphenoid sinus, during formation of the NC structure at the morphological level. There is a need to clearly define the relationships of these nasal elements at the ossification level, during development.

METHODS

We investigated the three-dimensional construction of human foetal NC elements, including ST, MT, IT and vomer, using CBCT images from 16 weeks gestation (E16) to E31 (25 foetuses) and compared it to histochemical observations (E25).

RESULTS

At the stage of ossification, the studied elements are elongated in the posterior region near the sphenoidal bone, showing that the locations of the ST, MT, and IT are important during formation of the NC. CBCT analysis revealed that the horizontal and vertical directions of nasal turbinates affect the formation of the human NC.

CONCLUSION

The location and elongated development of the MT is one of the most important elements for NC formation. The relationship between the nasal sinus and nasal turbine at the level of ossification may provide useful information in clinical treatment of children.

NASAL INTERNAL AND EXTERNAL AERODYNAMICS FOR HEALTHY AND BLOCKED CAVITIES

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

Effects of changes in nasal volume on voice in patients after endoscopic endonasal transsphenoidal surgery

OBJECTIVE

To investigate a potential correlation between changes in voice and changes in nasal volume.

METHODS

The endoscopic endonasal transsphenoidal approach (EETSA) was performed on 120 patients between February 2009 and August 2016 by using the bilateral modified nasoseptal rescue flaps method. All the patients were subjected to pre- and postoperative paranasal computed tomography (CT) and voice evaluations by using acoustic analyses, a nasometer to measure the nasalance, and determination of the voice handicap index (VHI). Paranasal CT and the medical image processing software were used to calculate changes in nasal cavity volume in three nasal sections.

RESULTS

Enlargement of the nasal cavity after surgery was evident in all three areas (anteronasal, p < 0.001; midnasal, p = 0.005; postnasal, p = 0.025). In addition, EETSA resulted in significantly higher mean nasalance scores for the oronasal passage (p < 0.001) and nasal passage (p < 0.001); more frequency perturbation (jitter) (p < 0.001) and amplitude perturbation (shimmer) (p < 0.001); and higher grade, roughness, breathiness, asthenia, and strain scores (p < 0.001), and VHI (p = 0.01). However, only changes in the nasal volume after EETSA correlated with postnasal hypernasality (r = 0.2; p = 0.029).

CONCLUSION

Although changes in nasal volume, voice, and speech may develop after EETSA, we found that changes in nasal volume were not correlated with changes in any voice-quality measure. However, the postnasal cavity was the region most dramatically affected by EETSA, and postnasal volume changes after surgery may be associated with hypernasal speech.

Numerical simulation of two consecutive nasal respiratory cycles: toward a better understanding of nasal physiology

BACKGROUND

Computational fluid dynamic (CFD) simulations have greatly improved the understanding of nasal physiology. We postulate that simulating the entire and repeated respiratory nasal cycles, within the whole sinonasal cavities, is mandatory to gather more accurate observations and better understand airflow patterns.

METHODS

A 3-dimensional (3D) sinonasal model was constructed from a healthy adult computed tomography (CT) scan which discretized in 6.6 million cells (mean volume, 0.008 mm³ ). CFD simulations were performed with ANSYS©FluentTMv16.0.0 software with transient and turbulent airflow (k-ω model). Two respiratory cycles (8 seconds) were simulated to assess pressure, velocity, wall shear stress, and particle residence time.

RESULTS

The pressure gradients within the sinus cavities varied according to their place of connection to the main passage. Alternations in pressure gradients induced a slight pumping phenomenon close to the ostia but no movement of air was observed within the sinus cavities. Strong movements were observed within the inferior meatus during expiration contrary to the inspiration, as in the olfactory cleft at the same time. Particle residence time was longer during expiration than inspiration due to nasal valve resistance, as if the expiratory phase was preparing the next inspiratory phase. Throughout expiration, some particles remained in contact with the lower turbinates. The posterior part of the olfactory cleft was gradually filled with particles that did not leave the nose at the next respiratory cycle. This pattern increased as the respiratory cycle was repeated.

CONCLUSION

CFD is more efficient and reliable when the entire respiratory cycle is simulated and repeated to avoid losing information.

Estimates of nasal airflow at the nasal cycle mid-point improve the correlation between objective and subjective measures of nasal patency

INTRODUCTION

The nasal cycle represents a significant challenge when comparing pre- and post-surgery objective measures of nasal airflow.

METHODS

Computational fluid dynamics (CFD) simulations of nasal airflow were conducted in 12 nasal airway obstruction patients showing significant nasal cycling between pre- and post-surgery computed tomography scans. To correct for the nasal cycle, mid-cycle models were created virtually. Subjective scores of nasal patency were obtained via the Nasal Obstruction Symptom Evaluation (NOSE) and unilateral visual analog scale (VAS).

RESULTS

The correlation between objective and subjective measures of nasal patency increased after correcting for the nasal cycle. In contrast to biophysical variables in individual patients, cohort averages were not significantly affected by the nasal cycle correction.

CONCLUSIONS

The ability to correct for the confounding effect of the nasal cycle is a key element that future virtual surgery planning software for nasal airway obstruction will need to account for when using anatomic models based on single instantaneous imaging.

Characterizing human nasal airflow physiologic variables by nasal index

Although variations in nasal index (NI) have been reported to represent adaptation to climatic conditions, assessments of NI with airflow variables have not been rigorously investigated. This study uses computational fluid dynamics modeling to investigate the relationship between NI and airflow variables in 16 subjects with normal nasal anatomy. Airflow simulations were conducted under constant inspiratory pressure. Nasal resistance (NR) against NI showed weak association from nostrils to anterior inferior turbinate (R(2)=0.26) and nostril to choanae (R(2)=0.12). NI accounted for 38% and 41% of the respective variation in wall shear stress (WSS) and heat flux (HF) at the nasal vestibule, and 52% and 49% of variability in WSS and HF across the entire nose. HF and WSS had strong correlation with NI<80, and weakly correlated with NI>80; these differences in HF and WSS for NI<80 and NI>80 were not statistically significant. Results suggest strong relationship between NI and both WSS and HF but not NR, particularly in subjects with NI<80.

A computational analysis of nasal vestibule morphologic variabilities on nasal function

Although advances in computational modeling have led to increased understanding of nasal airflow, not much is known about the effects of normal sinonasal anatomic variabilities on nasal function. In this study, three distinct variations in the human nasal vestibule airspace that have not been previously described were identified. Computational fluid dynamics modeling of nasal airflow profile in each identified variation of nasal vestibule phenotype was conducted to assess the role of these phenotypes on nasal physiology. Three-dimensional reconstructions of the nasal geometry in sixteen subjects with normal radiographic sinonasal images were created and each respective unilateral nasal cavity was classified as Notched, Standard, or Elongated phenotype based nasal vestibule morphology. Steady state, laminar and incompressible flow simulations were performed in the nasal geometries under physiological, pressure-driven conditions with constant inspiratory pressure. Results showed that at localized regions of the unilateral nasal cavity, average resistance was significantly different among nasal vestibule phenotypes. However, global comparison from nostril to choana showed that average resistance was not significantly different across phenotypes; suggesting that with normal anatomic variations, the nose has a natural compensatory mechanism that modulates localized airflow in order to achieve a desired amount of global airflow.

Effect of Septal Deviation, Concha Bullosa and Haller's Cell on Maxillary Sinus's Inferior Pneumatization; a Retrospective Study

Purpose: Maxillary sinus’s inferior pneumatization is a physiological process, which increase with time and accelerates following extraction. The aim of this study was to determine the prevalence of nasal septal deviation (NSD), concha bullosa (CB), and Haller’s cells (HC) and to examine the correlation of maxillary sinus inferior pneumatization (MSIP) with these anatomical variations. Material and Methods : 300 (150 m, 150 f) CBCT scans taken at the Marmara University School of Dentistry from 2011 to 2014 were retrospectively reviewed for the presence of CB, NSD, HC and MSIP. The correlation between pneumatization to the anatomic variants was then compared. Data were analyzed with a Chi-square test. Results : Of the 300 CBCT scans, 44.3% have CB, 37.3% NSD, 19.3% HC and 27.7% MSIP. There was no statistical significancewhen comparing the relationship of patients with CB, NSD, HC and pneumatization. Conclusion : NSD, CB and HC do not have a definite role on sinus’s inferior pneumatization. Further studies should be conducted including potential factors related pneumatization with more sample size for further correlation with NSD, CB,HC.