Changes of airflow pattern in inferior turbinate hypertrophy: a computational fluid dynamics model

Comparing Patient-Reported Outcomes with Computational Fluid Dynamics-Derived Nasal Airflow After Nasal Airway Surgery: Prioritizing the Patient's Perception of Nasal Obstruction

Background: Some patients report persistent nasal obstruction after surgical treatment despite objective improvement. Objective: To compare patients' perceptions of nasal obstruction after surgery with objective nasal airflow as determined by computational fluid dynamics (CFD) modeling: (1) Is perception driven by a more symptomatic side? (2) Can symptom improvement be predicted with CFD modeling? Methods: Pre/postoperative Nasal Obstruction Symptom Evaluation (NOSE) and visual analog scale (VAS) score were collected for patients undergoing nasal obstruction surgery. Pre/postoperative computed tomography was used to generate patient-specific airway models for CFD simulation at 15 L/min resting inspiration. Results: Ten patients (22-53 years, seven men and three women) underwent septoplasty, turbinate reduction, and/or rhinoplasty. Postoperative NOSE was most correlated with postoperative VAS score from the "affected" side (R2 = 0.59, p < 0.01), and postoperative NOSE was strongly predicted by a two-parameter model using parameters only from the "affected" side (R2 = 0.84, adjusted R2 = 0.80, p < 0.01). Conclusion: The postoperative state of the initially "affected" side drives outcomes after nasal obstruction surgery. Surgeries should prioritize improving the "affected" side. A two-parameter model using the VAS and nasal airflow from only the "affected" side strongly predicts NOSE and is promising for the future using virtual planning to individualize procedures to optimize outcome.

Olfactory drug delivery with intranasal sprays after nasal midvault reconstruction

Conductive olfaction and nose to brain drug delivery are important processes that remain limited by inadequate odorant or drug delivery to the olfactory airspace. Primary challenges include anatomic barriers and poor targeting to the olfactory region. This study uses computational fluid dynamics to investigate the effects of nasal midvault surgery on olfactory drug delivery with intranasal sprays. Soft tissue elevation, spreader flaps, and spreader grafts were performed on two fresh cadaveric specimens, using computed tomography for airway reconstruction. Nasal airflow and drug particle transport simulations were performed under these conditions: inhalation rate (15, 30 L/min), spray velocity (1, 5, 10 m/s), spray location (top, bottom, center, medial, lateral), head position (upright, supine, forward, backward), and particle size (1-100 µm). Simulation results were used to calculate drug particle deposition to the olfactory airspaces and bulbs. Total olfactory deposition was < 5% but attained a maximum of 36.33% when sorted by particle size. There was no association between nasal midvault surgery and olfactory deposition. No single parameter or technique demonstrated superior olfactory deposition, but smaller particle size, slower spray velocity, and higher inhalation rate tended to optimize olfactory deposition, providing important implications for future intranasal spray and drug design to target the olfactory airspace.

Computational Fluid Dynamics Could Enable Individualized Surgical Treatment of Nasal Obstruction (A Preliminary Study)

Passage of nasal airflow during breathing is crucial in achieving accurate diagnosis and optimal therapy for patients with nasal disorders. Computational fluid dynamics (CFD) is the dominant method for simulating and studying airflow. The present study aimed to create a CFD nasal airflow model to determine the major routes of airflow through the nasal cavity and thus help with individualization of surgical treatment of nasal disorders. The three-dimensional nasal cavity model was based on computed tomography scans of the nasal cavity of an adult patient without nasal breathing problems. The model showed the main routes of airflow in the inferior meatus and inferior part of the common meatus, but also surprisingly in the middle meatus and in the middle part of the common nasal meatus. It indicates that the lower meatus and the lower part of the common meatus should not be the only consideration in case of surgery for nasal obstruction in our patient. CFD surgical planning could enable individualized precise surgical treatment of nasal disorders. It could be beneficial mainly in challenging cases such as patients with persistent nasal obstruction after surgery, patients with empty nose syndrome, and patients with a significant discrepancy between the clinical findings and subjective complaints.

The Biomechanical Mechanism of Upper Airway Collapse in OSAHS Patients Using Clinical Monitoring Data during Natural Sleep

Obstructive sleep apnea hypopnea syndrome (OSAHS) is a common sleep disorder characterized by repeated pharyngeal collapse with partial or complete obstruction of the upper airway. This study investigates the biomechanics of upper airway collapse of OSASH patients during natural sleep. Computerized tomography (CT) scans and data obtained from a device installed on OSASH patients, which is comprised of micro pressure sensors and temperature sensors, are used to develop a pseudo three-dimensional (3D) finite element (FE) model of the upper airway. With consideration of the gravity effect on the soft palate while patients are in a supine position, a fluid–solid coupling analysis is performed using the FE model for the two respiratory modes, eupnea and apnea. The results of this study show that the FE simulations can provide a satisfactory representation of a patient’s actual respiratory physiological processes during natural sleep. The one-way valve effect of the soft palate is one of the important mechanical factors causing upper airway collapse. The monitoring data and FE simulation results obtained in this study provide a comprehensive understanding of the occurrence of OSAHS and a theoretical basis for the individualized treatment of patients. The study demonstrates that biomechanical simulation is a powerful supplementation to clinical monitoring and evaluation.

Computational Fluid Dynamics Modeling of Nasal Obstruction and Associations with Patient-Reported Outcomes

BACKGROUND

Nasal obstruction is a common problem, with significant impact on quality of life. Accurate diagnosis may be challenging because of the complex and dynamic nature of the involved anatomy. Computational fluid dynamics modeling has the ability to identify specific anatomical defects, allowing for a targeted surgical approach. The goal of the current study is to better understand nasal obstruction as it pertains to disease-specific quality of life by way of a novel computational fluid dynamics model of nasal airflow.

METHODS

Fifty-three patients with nasal obstruction underwent computational fluid dynamics modeling based on computed tomographic imaging. Nasal resistance was compared to demographic data and baseline subjective nasal patency based on Nasal Obstructive Symptom Evaluation scores.

RESULTS

Mean Nasal Obstructive Symptom Evaluation score among all patients was 72.6. Nasal Obstructive Symptom Evaluation score demonstrated a significant association with nasal resistance in patients with static obstruction (p = 0.03). There was a positive correlation between Nasal Obstructive Symptom Evaluation score and nasal resistance in patients with static bilateral nasal obstruction (R2 = 0.32) and poor correlation in patients with dynamic bilateral obstruction caused by nasal valve collapse (R2 = 0.02). Patients with moderate and severe bilateral symptoms had significantly higher nasal resistance compared to those with unilateral symptoms (p = 0.048).

CONCLUSIONS

Nasal obstruction is a multifactorial condition in most patients. This study shows correlation between simulated nasal resistance and Nasal Obstructive Symptom Evaluation score in a select group of patients. There is currently no standardized diagnostic algorithm or gold standard objective measure of nasal airflow; however, computational fluid dynamics may better inform treatment planning and surgical techniques on an individual basis.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Risk, V.

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

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

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

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

Endoscopic maxillectomy: anatomo-radiological description of the "double" maxillary sinus window

OBJECTIVES/HYPOTHESIS

To present a modified endoscopic medial maxillectomy (MEMM) approach to control maxillary sinus pathologies.

METHODS

MEMM was completed in 13 fresh-frozen specimens. An MEMM includes cutting the nasolacrimal duct, inferior meatus flap, and repositioning the inferior turbinate (IT). The following measurements were obtained: length of IT, height from the nasal floor to valve of Hasner, height of the IT at the level of valve of Hasner, height of the IT at the insertion of the middle turbinate, and distance from the piriform aperture to the posterior wall of maxillary sinus and to the posterior border of palatine bone. Similar measurements were also performed on craniofacial computed tomography (CT) scans (n = 50). The surgical technique was performed in a case series (n = 8).

RESULTS

The mean of the specimens was 82 (range 70-95) years old. The average area of the harvested inferior meatus flap area was 9.6 ± 1.0 cm². In the radiologic study, the mean maximum antrostomy area was 8.8 ± 1.7 cm² and the IT area overlapping the antral window was 5.8 ± 1.1 cm², the area allowing a double window control was 3.1 ± 1.9 cm², the posterior IT insertion length was 0.7 ± 0.4 cm, and the inferior meatus flap covering the inferior meatotomy had an area measuring 6.7 ± 1.7 cm². Eight patients underwent MEMM for various benign conditions showing no recurrence after 26 month follow-up.

CONCLUSION

The proposed modifications of MEMM provide a "double" window maxillary sinus control with access to all maxillary walls and preservation of the IT.

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.

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.

Investigation on the nasal airflow characteristics of anterior nasal cavity stenosis

We used a computational fluid dynamics (CFD) model to study the inspiratory airflow profiles of patients with anterior nasal cavity stenosis who underwent curative surgery, by comparing pre- and postoperative airflow characteristics. Twenty patients with severe anterior nasal cavity stenosis, including one case of bilateral stenosis, underwent computed tomography (CT) scans for CFD modelling. The pre- and postoperative airflow characteristics of the nasal cavity were simulated and analyzed. The narrowest area of the nasal cavity in all 20 patients was located within the nasal valve area, and the mean cross-sectional area increased from 0.39 cm² preoperative to 0.78 cm² postoperative (P<0.01). Meanwhile, the mean airflow velocity in the nasal valve area decreased from 6.19 m/s to 2.88 m/s (P<0.01). Surgical restoration of the nasal symmetry in the bilateral nasal cavity reduced nasal resistance in the narrow sides from 0.24 Pa^.s/mL to 0.11 Pa^.s/mL (P<0.01). Numerical simulation of the nasal cavity in patients with anterior nasal cavity stenosis revealed structural changes and the resultant patterns of nasal airflow. Surgery achieved balanced bilateral nasal ventilation and decreased nasal resistance in the narrow region of the nasal cavity. The correction of nasal valve stenosis is not only indispensable for reducing nasal resistance, but also the key to obtain satisfactory curative effect.

Impact of Middle versus Inferior Total Turbinectomy on Nasal Aerodynamics

OBJECTIVES

This computational study aims to (1) use virtual surgery to theoretically investigate the maximum possible change in nasal aerodynamics after turbinate surgery, (2) quantify the relative contributions of the middle and inferior turbinates to nasal resistance and air conditioning, and (3) quantify to what extent total turbinectomy impairs the nasal air-conditioning capacity.

STUDY DESIGN

Virtual surgery and computational fluid dynamics.

SETTING

Academic tertiary medical center.

SUBJECTS AND METHODS

Ten patients with inferior turbinate hypertrophy were studied. Three-dimensional models of their nasal anatomies were built according to presurgery computed tomography scans. Virtual surgery was applied to create models representing either total inferior turbinectomy (TIT) or total middle turbinectomy (TMT). Airflow, heat transfer, and humidity transport were simulated at a steady-state inhalation rate of 15 L/min. The surface area stimulated by mucosal cooling was defined as the area where heat fluxes exceed 50 W/m(2).

RESULTS

In both virtual total turbinectomy models, nasal resistance decreased and airflow increased. However, the surface area where heat fluxes exceed 50 W/m(2) either decreased (TIT) or did not change significantly (TMT), suggesting that total turbinectomy may reduce the stimulation of cold receptors by inspired air. Nasal heating and humidification efficiencies decreased significantly after both TIT and TMT. All changes were greater in the TIT models than in the TMT models.

CONCLUSION

TIT yields greater increases in nasal airflow but also impairs the nasal air-conditioning capacity to a greater extent than TMT. Radical resection of the turbinates may decrease the surface area stimulated by mucosal cooling.

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.

Coblation nasal septal swell body reduction for treatment of nasal obstruction: a preliminary report

In this paper, we present the results of coblation nasal septal swell body (NSB) reduction for the treatment of nasal obstruction in patients with abnormally thickened NSB. The study design was a retrospective clinical series conducted at a single tertiary medical center. Eight patients underwent coblation NSB reduction. Pre-operative and post-operative nasal functions were evaluated by acoustic rhinometry and subjective symptom scales. We also analyzed pre-operative CT scan images and nasal endoscopic findings. The mean maximal NSB width was 16.4 ± 2.2 mm on pre-operative coronal CT scan images. The mean visual analog scale score for nasal obstruction was decreased from preoperative 7.63 ± 0.99 points to 3.88 ± 0.92 points (postoperative 3 months), 4.16 ± 0.78 points (postoperative 6 months), and 4.63 ± 0.69 points (postoperative 1 year). Six out of the eight patients were satisfied with the clinical outcome at 1 year after the procedure. To the best of our knowledge, coblation NSB reduction has not yet been reported in the medical literature. Our results show that it can be an effective treatment modality for nasal valve narrowing in patients with abnormally thickened NSB.

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.

Update on surgical management of adult inferior turbinate hypertrophy

PURPOSE OF REVIEW

There are numerous surgical managements of hypertrophic inferior turbinate. Controversy still exists involving the optimal surgical technique for hypertrophic inferior turbinate. The current review will discuss the most commonly used techniques for turbinate surgery and highlight their recently published clinical outcomes.

RECENT FINDINGS

Microdebrider-assisted turbinoplasty, along with total removal of inferior turbinate mucosa, turned out to have no negative impact on healing time and no adverse postoperative events. The majority of recently published studies were focused on surgical outcomes of radiofrequency ablation. It appears that radiofrequency ablation could improve nasal resistance, sense of smell, and nasal mucociliary function. A 1470-nm diode laser was found superior to a conventional 940-nm diode laser in reducing scar formation. Ultrasonic bone aspirator was used to manage hypertrophic inferior turbinate caused by bone enlargement. Few recent literatures report turbinectomy.

SUMMARY

Inferior turbinate surgery offers benefit and improves nasal obstruction in patients with hypertrophic inferior turbinate refractory to medical treatment. Rigorously designed study including subjective and objective measurements, control or comparison group, and long-term follow-up should be carried out in the future.

Characterization of postoperative changes in nasal airflow using a cadaveric computational fluid dynamics model: supporting the internal nasal valve

IMPORTANCE

Collapse or compromise of the internal nasal valve (INV) results in symptomatic nasal obstruction; thus, various surgical maneuvers are designed to support the INV.

OBJECTIVE

To determine the effect on nasal airflow after various surgical techniques focused at the level of the INV and lateral nasal sidewall.

DESIGN AND SETTING

A fresh cadaver head was obtained and underwent suture and cartilage graft techniques directed at the level of the INV using an external approach. Preoperative and postoperative digital nasal models were created from the high-resolution, fine-cut, computed tomographic imaging after each intervention. Isolating the interventions to the level of the INV, we used computational fluid dynamic techniques to calculate nasal resistance, nasal airflow, and nasal airflow partitioning for each intervention.

INTERVENTION

Suture and cartilage graft techniques.

MAIN OUTCOMES AND MEASURES

Nasal airflow, nasal resistance, and partitioning of airflow.

RESULTS

Using the soft-tissue elevation model as baseline, computational fluid dynamic analysis predicted that most of the suture and cartilage graft techniques directed toward the nasal valve improved nasal airflow and partitioning while reducing nasal resistance. Specifically, medial and modified flare suture techniques alone improved nasal airflow by 16.9% and 15.1%, respectively. The combination of spreader grafts and modified flare suture improved nasal airflow by 13.2%, whereas spreader grafts alone only improved airflow by 5.9%. The largest improvements in bilateral nasal resistance were achieved using the medial and modified flare sutures, outperforming the combination of spreader grafts and modified flare suture.

CONCLUSIONS AND RELEVANCE

Techniques directed at supporting the INV have tremendous value in the treatment of nasal obstruction. The use of flare sutures alone can address dynamic valve collapse or upper lateral cartilage incompetence without gross disruption of the nasal architecture. Using computational fluid dynamic techniques, this study suggests that flare sutures alone may improve flow and reduce resistance when placed medially, surpassing spreader grafts alone or in combination with flare sutures. The longevity of these maneuvers can only be assessed in the clinical setting. Studies in additional specimens and clinical correlation in human subjects deserve further attention and investigation.

LEVEL OF EVIDENCE

NA.

Model demonstrates functional purpose of the nasal cycle

Background

Despite the occurrence of the nasal cycle being well documented, the functional purpose of this phenomenon is not well understood. This investigation seeks to better understand the physiological objective of the nasal cycle in terms of airway health through the use of a computational nasal air-conditioning model.

Method

A new state-variable heat and water mass transfer model is developed to predict airway surface liquid (ASL) hydration status within each nasal airway. Nasal geometry, based on in-vivo magnetic resonance imaging (MRI) data is used to apportion inter-nasal air flow.

Results

The results demonstrate that the airway conducting the majority of the airflow also experiences a degree of ASL dehydration, as a consequence of undertaking the bulk of the heat and water mass transfer duties. In contrast, the reduced air conditioning demand within the other airway allows its ASL layer to remain sufficiently hydrated so as to support continuous mucociliary clearance.

Conclusions

It is quantitatively demonstrated in this work how the nasal cycle enables the upper airway to accommodate the contrasting roles of air conditioning and the removal of entrapped contaminants through fluctuation in airflow partitioning between each airway.

Numerical simulation for the upper airway flow characteristics of Chinese patients with OSAHS using CFD models

OSAHS is a common disease with many factors related to the etiology. Airflow plays an important role in the pathogenesis of OSAHS. Previous research has not yielded a sufficient understanding of the relationship between airflow in upper airway and the pathophysiology of OSAHS. Therefore, a better understanding of the flow inside the upper airway in an OSAHS patient is necessary. In this study, ten Chinese adults with OSAHS were recruited. We used the software MIMICS 13.1 to construct 3-dimensional (3-D) models based on the computer tomography scans of them. The numerical simulations were carried out using the software ANSYS 12.0. We found that during the inhalation phase, the vortices and turbulences were located in both the anterior part of the cavity and nasopharynx. But there is no vortex in the whole nasal cavity during the expiratory phase. The airflow velocity is much higher than that of the normal models. The distributions of pressure and wall shear stress are different in two phases. The maximum velocity, pressure and wall shear stress (WSS) are located in velopharynx. It is notable that a strong negative pressure region is found in pharyngeal airway. The maximum velocity is 19.26 ± 12.4 and 19.46 ± 13.1 m/s; the average pressure drop is 222.71 ± 208.84 and 238.5 ± 218.56 Pa and the maximum average WSS is 0.72 ± 0.58 and 1.01 ± 0.61 Pa in inspiratory and expiratory, respectively. The changes of airflow due to the structure changes play an important role in the occurrence of collapse and obstruction of the upper airway, especially, the abnormal pressure changes in velopharyngeal during both inspiratory and expiratory phases. We can say that the airway narrowing in the pharynx may be one of the most important factors driving airway collapse. In addition, the most collapsible region of the pharyngeal airway of the patient with OSAHS may be the velopharynx and oropharynx. In spite of limitations, our results can provide a basis for the further research. On this basis, more about the secret of the pathogenesis of the OSAHS will be revealed.

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.

Computed nasal resistance compared with patient-reported symptoms in surgically treated nasal airway passages: a preliminary report

BACKGROUND

Nasal airway obstruction (NAO) is a common health condition impacting mood, energy, recreation, sleep, and overall quality of life. Nasal surgery often addresses NAO but the results are sometimes unsatisfactory. Evaluating surgical treatment efficacy could be improved if objective tests were available that correlated with patient-reported measures of symptoms. The goal of this study was to develop methods for comparing nasal resistance computed by computational fluid dynamics (CFD) models with patient-reported symptoms of NAO using early data from a 4-year prospective study.

METHODS

Computed tomography (CT) scans and patient-reported scores from the Nasal Obstruction Symptom Evaluation (NOSE) scale and a visual analog scale (VAS) measuring unilateral airflow sensation were obtained pre- and postoperatively in two NAO patients showing no significant mucosal asymmetry who were successfully treated with functional nasal surgery, including septoplasty. Pre- and postsurgery CFD models were created from the CT scans. Numerical simulation of steady-state inspiratory airflow was used to calculate bilateral and unilateral CFD-derived nasal resistance (CFD-NR).

RESULTS

In both subjects, NOSE and VAS scores improved after surgery, bilateral CFD-NR decreased, and unilateral CFD-NR decreased on the affected side. In addition, NOSE and VAS scores tracked with unilateral CFD-NR on the affected side.

CONCLUSION

These preliminary results suggest a possible correlation between unilateral NR and patient-reported symptoms and imply that analysis of unilateral obstruction should focus on the affected side. A formal investigation of unilateral CFD-NR and patient-reported symptoms in a series of NAO patients is needed to determine if these variables are correlated.

Correlation of nasal obstruction with nasal cross-sectional area measured by computed tomography in patients with nasal septal deviation

OBJECTIVES

The objective of the present study was to investigate the relationship between the subjective sensation of nasal obstruction and the corresponding cross-sectional area for nasal airflow in patients with a deviated septum.

METHODS

Seventy-one patients with a diagnosis of unilateral nasal obstruction due to a deviated nasal septum were evaluated by preoperative computed tomography. Anterior anatomic characteristics (the internal nasal valve angle and the cross-sectional areas at the external nasal valve, the head of the inferior turbinate, and the head of the middle turbinate) and posterior anatomic factors (the cross-sectional areas at the openings of the frontal sinus, maxillary sinus, and end of the nasal septum) were examined. Associations between the computed tomography measurements and the subjective severity of nasal obstruction were analyzed with a visual analog scale (VAS).

RESULTS

Anterior and posterior anatomic characteristics were associated with the subjective severity of nasal obstruction. Anterior anatomic factors were related to the VAS scores of patients with anterior septal deviation, and posterior anatomic factors were related to the VAS scores of patients with posterior septal deviation.

CONCLUSIONS

This study indicated that the anterior and posterior parts of the nasal cavity are both related to nasal obstruction. In some patients, the posterior part of the nasal cavity was more important than other locations in causing nasal obstruction.

Assessments of nasal bone fracture effects on nasal airflow: A computational fluid dynamics study

BACKGROUND

The aim of this study was to evaluate effects of nasal bone fractures on nasal aerodynamic flow patterns using computational fluid dynamics (CFD) simulations.

METHODS

A three-dimensional model of nasal cavity with a nasal bone fracture was constructed from computerized tomography (CT) scans of a patient with use of software Mimics 13.0 (The Materilize Group, Leuven, Belgium). CFD simulations were performed using Fluent 6.3 (ANSYS, Inc., Canonsburg, PA) with a turbulent flow model. Numerical results were presented with velocity, streamline, and pressure contour distributions in left and right nasal cavities and were compared with those of a healthy one. Possible outcomes on functional performances or patencies of the nose were also examined and discussed.

RESULTS

For the nose with a nasal bone fracture, distributions of velocity contours showed there was more airflow in the right nasal cavity than in the left one, especially for inspiration status. In the left cavity, the airflow was redirected irregularly and there were also more circulations with larger sizes, higher pressure jumps, and greater wall shear stresses. Flow partitioning in the right and left cavities was noticeable with a larger nasal resistance compared with the healthy one. When the inspirational flow rate was increased, pressure jump from the nostril to the nasopharynx increased faster.

CONCLUSION

The aerodynamic flow was redistributed greatly for the nose with a nasal bone fracture compared with the healthy one, which might affect local normal nasal functions. Such physical assessments of nasal airflow based on a model from the patients' CT scans may help clinicians determine the best treatment in advance.

Numerical simulation of normal nasal cavity airflow in Chinese adult: a computational flow dynamics model

Our purpose is to simulate the airflow inside the healthy Chinese nose with normal nasal structure and function by computational fluid dynamics (CFD) method and to analyze the relationship between the airflow and physiological function. In this study, we used the software MIMICS 13.0 to construct 20 3-dimensional (3-D) models based on the computer tomography scans of Chinese adults' nose with normal nasal structure and function. Thereafter, numerical simulations were carried out using the software FLUENT 6.3. Then the characteristics of airflow inside the airway and sinuses were demonstrated qualitatively and quantitatively in steady state. We found that during the inhalation phase, the vortices and turbulences were located at anterior part and bottom of the nasal cavity. But there is no vortex in the whole nasal cavity during the expiratory phase. The distributions of pressure and wall shear stress are different in two phases. The maximum airflow velocity occurs around the plane of palatine velum during both inspiratory and expiratory phases. After the airflow passed the nasal valve, the peak velocity of inhaled airflow decreases and it increases again at the postnaris. Vice versa, the exhaled airflow decelerates after it passed the postnaris and it accelerates again at nasal valve. The data collected in this presentation validates the effectiveness of CFD simulation in the study of airflow in the nasal cavity. Nasal airflow is closely related to the structure and physiological functions of the nasal cavity. CFD may thus also be used to study nasal airflow changes resulting from abnormal nasal structure and nasal diseases.

Comparison between effects of various partial inferior turbinectomy options on nasal airflow: a computer simulation study

Partial inferior turbinectomy is typically performed on patients suffering from chronic nasal obstruction due to hypertrophy of inferior turbinates and is refractory to other more conservative treatments. The effects of the various options of incision performed on the inferior turbinate in terms of the resulting nasal airflow pattern are examined using computational fluid mechanics. The pressure drops across the severely blocked nose and healthy nose models were found to be 32.3 and 12.3 Pa, respectively, whereas the pressure drops across the nasal cavity following one-third turbinate resection, total turbinate resection and front-end resection were obtained as 5.8, 6.1 and 30.5 Pa correspondingly. Based on the total pressure drop results, the one-third resection option seems to be better than the front-end surgery and the total turbinate resection.

Investigation on the structure of nasal cavity and its airflow field in Crouzon syndrome

OBJECTIVE

Setup computational fluid dynamics (CFD) model of the nasal cavity in patients with Crouzon syndrome analyze inspiratory airflow hydrokinetics of its nasal cavity. After changing the morphosis structure of the nasal cavity by operation, compare the preoperative and postoperative alteration of the airflow field of the nasal cavity and evaluate the effect of operation on the physiological function of nasal ventilation.

METHODS

Eleven patients with Crouzon syndrome were underwent spiral computed tomographic laminar scanning to obtain DICOM data and establish the CFD model. The field features of the nasal cavity with inspiratory static state phase were simulated and analyzed by the Fluent software. The changed data on preoperative and postoperative flow field in the nasal cavity in 5 of 11 patients were compared and analyzed.

RESULTS

The nasal cavity of a patient with Crouzon syndrome reflected the structural features of relatively short and high-vaulted anteroposterior diameter. The nasal valve was the narrowest region in the nasal cavity and was the key region of producing obvious pressure drop. The inspiratory static state phase reflected comparatively high local airflow rate (approximately 2.469 m/s) and sheer force of the nasal wall. With the distance increasing from the anterior naris, the pressure inside the nasal cavity was decreased gradually. The pressure drop in the nasal cavity before the front end of the concha nasalis inferior (approximately 2 cm from anterior naris) accounted for most of the pressure of the whole nasal cavity (69%-88% of the overall pressure in nasal cavity and 79.24% on average). Osteotomy advancement and distraction osteogenesis increased the anteroposterior diameter of the nasal cavity and the changed nasal resistance.

CONCLUSIONS

By analyzing the structure of the nasal cavity of patients with Crouzon syndrome and the CFD numerical simulation of patients after the procedure, airflow distribution in patients' nasal cavity and the effect of the surgery on the structure of the nasal cavity and airflow field were realized. Nasal valve played a pivotal role in the airflow field distribution of the nasal cavity. Operation changed the nasal resistance, improved the ventilation of nasal cavity, but did not affect the airflow field distribution of nasal cavity.

Numerical simulation of the effects of inferior turbinate surgery on nasal airway heating capacity

BACKGROUND

The aim of this study was to evaluate the effects of inferior turbinate surgery on nasal airway heating capacity using computational fluid dynamics (CFD) simulations.

METHODS

Heat transfer simulations were performed for a normal nasal cavity and others with severely enlarged inferior turbinates, before and after three simulated surgical procedures: (1) resection of the lower third free edge of the inferior turbinate, (2) excision of the head of the inferior turbinate, and (3) radical inferior turbinate resection. The models were run with three different environmental temperatures.

RESULTS

The changes of airflow pattern with the reduction of inferior turbinate affected heat transfer greatly. However, the distribution of wall heat flux showed that the main location for heat exchange was still the anterior region. Under the cold environment, the nasal cavities with the head of inferior turbinate reduction were capable of heating the inspired air to 98.40% of that of the healthy one; however, for the case with lower third of inferior turbinate excised, the temperature was 11.65% lower and for the case with radical inferior turbinate resection, 18.27% lower temperature compared with the healthy nasal cavity.

CONCLUSION

The healthy nasal cavity is able to warm up or cool down the inspiratory airflow under different environmental temperature conditions; for the nasal cavities with turbinate surgeries, partial inferior turbinate reduction can still sustain such heating capacity. However, too much or total turbinate resection may impair the normal function of temperature adjustment by nasal mucosa.

Endonasal endoscopic medial maxillectomy with preservation of the inferior turbinate

BACKGROUND

Endonasal endoscopic medial maxillectomy usually includes removal of the inferior turbinate (IT) even if it is not involved in the disease. A surgical approach is presented in which the IT is temporarily excised and then reinserted, followed by postoperative occlusion of the nose for at least 2 weeks.

METHODS

A retrospective case series of 12 patients with inverted papilloma (IP) of the maxillary sinus (Krouse II-III) and 2 patients with 3 mucoceles of the maxillary sinus after a Caldwell-Luc operation were reviewed. After a follow-up period of 12-80 months (28 months on average) all patients underwent endoscopy, and in four cases, additionally, an MRI was performed.

RESULTS

There was no recurrence of tumor or mucocele after 12-80 months. The IT and its important function for warming and humidifying the inhaled air could be preserved up to now in all 15 operated sides. The patients did not have any specific pain postoperatively and there was no postoperative bleeding. They all tolerated occlusion for 2-4 weeks. Two patients developed mucoceles due to the formation of scar tissue after endonasal tumor surgery. In three cases of endonasal endoscopic Denker operation patients reported some degree of numbness or irritation of the ipsilateral frontal teeth.

CONCLUSION

The IT can be preserved in endonasal endoscopic medial maxillectomy for treatment of IP without a higher incidence of tumor recurrence. Aftercare should specifically focus on preventing the development of mucoceles caused by scarring.

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.

Indicators for the correct usage of intranasal medications: A computational fluid dynamics study

OBJECTIVES/HYPOTHESIS

Intranasal medications are commonly used in treating nasal diseases. However, technical details of their correct administration are unclear.

METHODS

A three-dimensional model of nasal cavity was constructed from the magnetic resonance imaging scans of a healthy human subject. Nasal cavities corresponding to moderate and severe nasal obstruction were derived from the healthy nose by enlarging the inferior turbinate geometrically, which can be documented by approximately one third reduction of the minimum cross-sectional area in the moderate and two thirds in the severe obstruction. The discrete phase model based on computational fluid dynamics was used to study the gas particle flow. The percentage of discrete particles that pass through the minimum cross-sectional area in the nasal valve (NV) region is computed as the percentage of NV penetration rate.

RESULTS

The percentage of NV penetration is 10 to 20 times higher when nasal spray is accompanied by an inspiratory airflow than no flow, which can be as low as 4.69% to 8.81% in the healthy model, and 0% in moderate and severe blockage models. In the presence of inspiratory airflow, there is no significant difference in the percentage of NV penetration (80.97%-82.13%) among different head tilt angles (0 degrees -90 degrees ).

CONCLUSIONS

When using an intranasal medication, it is advisable to have an inspiratory flow to improve drug penetration. Various suggested head positions do not improve drug penetration significantly, even in the presence of uniform quiet breathing. Further studies that consider turbulence and unsteady airflow are needed to investigate the deposition distribution of discrete particles inside various nasal cavities.