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We investigated (1) how nasal septal perforations (NSPs) modify nasal airflow and air-conditioning characteristics and (2) how the modifications of nasal airflow are influenced by the size and location of the NSP. Computed tomography scans of 14 subjects with NSPs were used to generate nasal cavity models. Virtual repair of NSPs was conducted to examine the sole effect of NSPs on airflow. The computational fluid dynamics technique was used to assess geometric and airflow parameters around the NSPs and in the nasopharynx. The net crossover airflow rate, the increased wall shear stress (WSS) and the surface water-vapor flux on the posterior surface of the NSPs were not correlated with the size of the perforation. After the virtual closure of the NSPs, the levels in relative humidity (RH), air temperature (AT) and nasal resistance did not improve significantly both in the choanae and nasopharynx. A geometric parameter associated with turbinate volume, the surface area-to-volume ratio (SAVR), was shown to be an important factor in the determination of the RH and AT, even in the presence of NSPs. The levels of RH and AT in the choanae and nasopharynx were more influenced by SAVR than the size and location of the NSPs., (© 2024. The Author(s).)

The dynamic characteristics of air-conditioning in the human nasal cavity during a respiratory cycle were investigated using unsteady numerical simulations to assess whether inhaled air is sufficiently conditioned by the nasal cavity. Variations in the epithelial surface temperature, surface heat, and water vapor fluxes were found to vary significantly during inspiration while providing substantial air conditioning to the inhaled air, but variations and magnitudes were significantly reduced during the expiration period. Air temperature (31.3-35.3 °C) and relative humidity (85.1-100 %) in the nasopharynx exhibited significant variations during inspiration. Flow rate-weighted average values of the air temperature and relative humidity during inspiration were estimated to be 32.0 °C and 89.1 %, respectively. Inhaled air did not attain alveolar conditions before reaching the nasopharynx, and was therefore thought to be insufficiently conditioned by the nasal cavity alone. A steady flow of approximately 250 mL/s appears to be useful for evaluating the accumulated thermal state of air in the nasopharynx during inspiration., (Copyright © 2021 Elsevier B.V. All rights reserved.)

The characteristics of the thermal field in the human nasal cavity during the expiration period were investigated using computational fluid dynamics. Heat and water-vapor recovery features were quantitatively investigated under realistic distributions of the epithelial surface and air temperature. A constant expiratory flow rate of 250 mL/s was assumed. The epithelial surface temperature was approximately 34.3-34.4 °C in the nasopharynx and 33.5-33.6 °C in the vestibule region, and these values are in good agreement with the measurement data in the literature. We observed that heat-recovery from the exhaled air mostly occurred in the posterior turbinate region, and the amount of heat recovered is estimated to be approximately 1/3 of the heat supply during inspiration. Because of this heat transfer from the exhaled air to the epithelial surface, the temperature of the epithelial surface increased in this region, and the exhaled air temperature dropped through the turbinate airway. Water-vapor recovery primarily occurs in the posterior segments of the turbinates; however, the amount of water-vapor transfer was approximately 1/5 of that in inspiration. Accordingly, the relative humidity of the exhaled air remained constant throughout the airway., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

The air-conditioning characteristics in nasal cavity models obtained from two subjects exhibiting different degrees of the nasal cycle states in terms of the airflow partition were investigated using computational fluid dynamics. A constant inspiratory flow rate of approximately 250 mL/s was considered, and the air temperature and relative humidity at the inlet were assumed to be 25 °C and 35%, respectively. The air-conditioning capacities of the congested and decongested sides were assessed by the amounts of epithelial heat and water vapor transferred to the inhaled air through the airway from the nostrils to the end of the septum. The results revealed that the air temperature and relative humidity near the end of the septum, respectively, reached approximately 31.4-32.5 °C and 81.4-88.0% in the decongested sides and 34.0-35.9 °C and 95.3-100% in the congested sides. The differences seen in the air temperatures and relative humidity between the congested and decongested sides were found to be larger in the cavity model that showed a larger degree of reciprocal change in the airflow rate. From a fluid mechanics perspective, while the congested side is in a rest period during the nasal cycle such that a lower amount of airflow is transported through it, this side, in effect, works to provide assistive air-conditioning capacity to the nasal cavity and aids when insufficiently conditioned airflow passes through the decongested side so that the inhaled air merging after the septum can approach the alveolar condition favorably through the nasopharynx., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

The air-conditioning characteristics of the human nasal cavity were investigated using computational fluid dynamics. The wall layer was modeled as a heat conducting layer consisting of water with constant thickness placed on top of epithelial cells. By assuming constant tissue temperature, prescribed to be 36  ° C, which is close to the alveolar condition, the proposed wall model yielded a spatially varying surface temperature distribution that is in reasonable agreement with the measurement studies in the literature. The results show that the regions of the main airway between the nasal valve, and the anterior of the middle turbinate were shown to have relatively low temperatures, whereas the superior meatus exhibited relatively high temperature. Water vapor flux evaluated at the surface of the mucus layer was found to be quite large in the region between the posterior of the vestibule and the anterior of the middle turbinate. Comparing the results obtained from the present model to those obtained with a constant surface temperature boundary condition of 32.6 °C or 34 °C revealed that temperature, and absolute humidity of the airflow increased faster through the turbinated airway passage. Even in the presence of sizable differences in the distributions of surface temperature and water vapor concentration, distributions of relative humidity of the air were found to be quite similar regardless of temperature boundary conditions., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

We used computational fluid dynamics to study the effects of the nasal cycle on the modification of unilateral nasal resistance using nasal cavity models from 2 different patients with chronic rhinosinusitis. A steady airflow field with an inspiratory flow rate of 250 mL/s was simulated using ANSYS-FLUENT v14.5. The distribution of local unilateral nasal resistance showed different shapes of variation and magnitudes of resistance depending on the distribution of cross-sectional area in the nasal cavity models. The highest local resistance on the congested side was found near the nasal valve area in the first patient, whereas the highest value was found in the nasal vestibule for the second patient. The relative importance of nasal resistance in the turbinated air passage differed for the 2 patients. The unilateral resistance of the congested state was in the range of 0.0229-0.221 Pas/mL. In the inferior meatus, greater flow rate was allowed during the congested state than during the decongested state if an extensive backflow developed., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Since the imbalance of the nasal cavities due to nasal septal deviation (NSD) is a commonly observed anatomic variation in healthy adults, clinicians must often decide whether or not it is clinically relevant to the symptoms of nasal airway obstruction (NAO). Main reason for this is a lack of data correlating the symptoms of NAO with objective findings. The aim of our study is to find the correlation between fluid dynamic parameters and the anatomy of nasal cavity with NSD by numerical simulation. We generated 6 computational models of nasal cavities with NSD were created from computed tomographic images: 3 symptomatic patients with NAO and 3 asymptomatic patients. Computational fluid dynamics (CFD) was used to simulate steady inspiratory airflows in each nasal cavity model and compare the fluid dynamic properties of each. In the symptomatic cases, the pressure drop from the naris to the end of the septum was larger, and more uneven flow partitioning was observed. Local maximum velocity and wall shear stress were higher in the symptomatic group than in the asymptomatic group. The symptoms of NAO seem to be related more to the nasal resistance from the naris to the end of the septum than to the total nasal resistance from naris to nasopharynx. Factors correlated with NAO by CFD can be used as elements in patient-specific objective diagnostic tools for NAO in the presence of NSD., (Copyright © 2013 Elsevier B.V. All rights reserved.)

Respiratory physiology and pathology are strongly dependent on the airflow inside the nasal cavity. However, the nasal anatomy, which is characterized by complex airway channels and significant individual differences, is difficult to analyze. Thus, commonly adopted diagnostic tools have yielded limited success. Nevertheless, with the rapid advances in computer resources, there have been more elaborate attempts to correlate airflow characteristics in human nasal airways with the symptoms and functions of the nose by computational fluid dynamics study. Furthermore, the computed nasal geometry can be virtually modified to reflect predicted results of the proposed surgical technique. In this article, several computational fluid mechanics (CFD) issues on patient-specific three dimensional (3D) modeling of nasal cavity and clinical applications were reviewed in relation to the cases of deviated nasal septum (decision for surgery), turbinectomy, and maxillary sinus ventilation (simulated- and post-surgery). Clinical relevance of fluid mechanical parameters, such as nasal resistance, flow allocation, wall shear stress, heat/humidity/NO gas distributions, to the symptoms and surgical outcome were discussed. Absolute values of such parameters reported by many research groups were different each other due to individual difference of nasal anatomy, the methodology for 3D modeling and numerical grid, laminar/turbulent flow model in CFD code. But, the correlation of these parameters to symptoms and surgery outcome seems to be obvious in each research group with subject-specific models and its variations (virtual- and post-surgery models). For the more reliable, patient-specific, and objective tools for diagnosis and outcomes of nasal surgery by using CFD, the future challenges will be the standardizations on the methodology for creating 3D airway models and the CFD procedures., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

The airflow and gas exchange behaviors of the human maxillary sinus were quantified to better understand the effect of an accessory ostium (AO). An anatomically correct numerical domain was constructed using CT data from a male patient with mild nasal obstruction. For the purpose of comparison, a numerical model without an AO was also generated by artificially removing the AO from the original model using CAD software. A steady-flow field through the nasal cavity was simulated using ANSYS-FLUENT v13.0 with a target flow rate of 250 ml/s. The Volume of Fluid (VOF) method was used to investigate the concentration field of nitric oxide (NO) initially filled in the maxillary sinus. The simulation results showed that a transit flow through the maxillary sinus developed in the presence of an AO. As the flow entered the sinus through either a natural or accessory ostium from the middle meatus, the velocity was significantly reduced to a local maximum of approximately 0.034 m/s inside the sinus. This by-pass flow rate through the sinus of 2.186×10(-1) to 3.591×10(-1) ml/s was a small fraction of the total flow rate inhaled from the nostril, but it effectively changed the local flow topology and led to a larger reduction in NO concentration in the maxillary sinus. This more rapid reduction in NO concentration was due to enhanced ventilation activity afforded by convective transport of the transit stream through the flow path connecting the natural ostium and the AO. The inspiration and expiration phases were qualitatively similar in flow pattern except for the flow direction in the maxillary sinus, suggesting that the AO plays a similar physiological role during both inspiration and expiration in terms of ventilation., (Copyright © 2012 Elsevier B.V. All rights reserved.)

Time-dependent characteristics of the flow in a human nasal airway constructed from the CT image of a healthy volunteer were investigated using a computational fluid dynamics (CFD) technique. To capture the time-varying nature of the flow as well as pressure and temperature fields, the large eddy simulation (LES) technique instead of the RANS (Reynolds Averaged Navier-Stokes) approach was adopted. To make the present analysis more relevant to a real human breathing cycle, the flow was designed to be induced by the pressure difference and the time-varying pressure at the end of trachea was described to reproduce the flow rate data from the measurement. Comparison of the present results with those of typical steady simulations showed that the difference in flow characteristics is magnified in the expiration phase. This fact may suggest that the inertial effect associated with unsteady flow is more important during the expiration period. Also, the fact that the distribution of the flow rate in a given cross-section of the airway changes significantly with time implies the importance of unsteady data for clinical decision. The wall shear stress was found to have relatively high values at the locations near nasopharynx and larynx but the magnitude changes with time during the whole respiratory cycle. Analysis of the temperature field showed that most of the temperature change occurs in the nasal cavity when the air is incoming and thus, the nasal cavity acts as a very efficient heat exchanger during an inspiration period., (Copyright 2010 Elsevier B.V. All rights reserved.)

The location of nasal septal deviation (NSD) directly impacts nasal physiology. The objective is to examine, using computational fluid dynamics (CFD), the difference in the airflow and air conditioning characteristics according to the location of NSD. Twenty patients with septal deviation were divided into two: 10 caudal septal deviation (CSD) and 10 posterior septal deviation (PSD). Physiological variables were compared and numerical models for nasal cavity were created with CT scans. Cases with CSD had distinctive features including restricted airflow partition, larger nasal resistance, and decreased surface heat flux in the more obstructed side (MOS), and lower humidity and air temperature in the lesser obstructed side (LOS). Physiological differences were observed according to the location of septal deviation, CSD cases exhibit significantly more asymmetric airflow characteristics and air conditioning capacity between LOS and MOS. [ABSTRACT FROM AUTHOR]

In the presence of nasal septal deviation, the airflow can be skewed to the convex side of the airway. Asymmetry of the airflow partition can be aggravated if the decongestion phase of the nasal cycle occurs on the same side. This numerical study investigates the variation in the airflow partition over time during inspiration and the corresponding changes in relative humidity when septal deviation is combined with the nasal cycle. In the nasal cavities with a decongested convex side, the variation in the airflow partition ratio observed over time was larger than that in the nasal cavities not influenced by the nasal cycle. In addition, the decrease in the relative humidity of the convex side was larger, resulting in a relative humidity of as low as 76.3 %. Therefore, the convex side of the deviated cavity was more prone to nasal dryness under the influence of the nasal cycle. [ABSTRACT FROM AUTHOR]

The air conditioning capacity of the nasal cavity is influenced by nasal septal deviations. As corrective surgery for septal deviation alters the anatomical structure of the nasal cavity, modification of the airflow behavior after surgery is likely to also change the heat recovery characteristics. The present study investigated the improvement in heat recovery characteristics after septoturbinoplasty using computational fluid dynamics techniques with realistic cavity models constructed from computed tomography scans. The results indicated that the mucosal surface heat transfer rate was strongly correlated with the airflow rate in both the inspiration and expiration phases (Pearson correlation coefficient greater than 0.9). Because the increase in the airflow rate was greater during expiration, the heat recovery rate with the same breathing effort improved by more than 30 % after surgery. [ABSTRACT FROM AUTHOR]

Flow kinematics was investigated in the regions located in the superior (region P) and inferior (region N) meatuses of the human nasal cavity where flow recirculation develops during the respiration period. The region P represents the posterior part of the ethmoidal sinus ostium, which several studies have reported as a frequent site for the development of nasal polyps. Region N located in the airflow passage in the inferior meatus, where polyp rarely form, was also investigated for comparison. Wall shear stress was found to be significantly reduced in both regions due to the development of flow separation, indicating a mechanical irritation of the epithelium by wall shear is likely to be quite suppressed. Even though the region P had a relatively smaller separation bubble, this region was found to have a longer particle residence time, which may increase the exposure time of foreign particles (e.g. allergens, pollen, and various pathogens) to the epithelium of the nasal airway. [ABSTRACT FROM AUTHOR]

We used computational fluid dynamics to study airflow characteristics in the space between the bulla and the middle turbinate (Region P1) and the superior meatus (Region P2) of the human upper airway, which exhibit intermittent flow separation. For comparison, we examined airflow passage in the inferior meatus (Region N), where large-scale flow separation develops. We assessed six different flow rates, based on realistic human respiration data representing one full period of respiration, in an anatomically correct numerical model. The simulation results showed that airflow in regions P1 and P2 had a relatively smaller separation bubble with a larger variation of bubble size with time, whereas region N exhibited a more gradually changing, two-dimensional rotation-like motion. Distinctive features of flow characteristics in regions P1 and P2 were relatively low Reynolds number, higher curvature of streamlines of the local main flow, with the existence of locations exhibiting intermittent occurrence of relatively quite high level of wall shear during inspiration. [ABSTRACT FROM AUTHOR]

Abstract: Knowledge of airflow characteristics in the nasal cavity is essential to understanding the physiologic and pathologic aspects of nasal breathing. Airflows inside post-surgery models were investigated both experimentally and numerically to simulate the inferior turbinectomy. The left cavities of all three models are normal and right cavity is modified by (1) excision of the head of the inferior turbinate, (2) resection of the lower fifth of the inferior turbinate, and (3) resection of almost the entire inferior turbinate. Thin-slice CT (computed tomography) data (0.6mm deep) and meticulous refinement of the model surface by over a decade-long collaboration between engineers and an experienced ENT doctor resulted in the creation of sophisticated nasal cavity models. After numerical experiments and validation by comparison with the PIV results, the CFD code using the Reynolds stress turbulent model and variable temperature boundary condition on the mucosal wall was chosen as the proper numerical framework. Both global quantities (pressure drop, flow rate ratio, total wall heat transfer) and local changes (velocity, temperature, humidity, pressure gradient, and wall shear stress) were numerically investigated. The turbinectomy obviously altered the main stream direction. The flow rate in the upper airway near the olfactory slit decreased in models (1) and (3). This may weaken the olfactory function of the nose. Fluid and thermal properties that are believed to be related with physiology and prognosis are dependent on turbinate resection volume, position, and manner. Widening of the inferior airway does not always result in decreased flow resistance or wall heat transfer. The gains and losses of inferior turbinectomy were considered by analysis of the post-surgery model results. Nasal resistance was increased in model (1) due to sudden airway expansion. Nasal resistance increased and the wall heat transfer decreased in model (3) due to sudden airway expansion and excessive reduction of the mucosal wall surface area. Local shear stress and pressure gradient levels were increased in models (1) and (3). [Copyright &y& Elsevier]

In this study, we examined the effect of uncinectomy on the alteration in local airflows and on the resulting effect on gas exchange in the maxillary sinus, by using computational fluid dynamics in two nasal cavity models: one with a preserved uncinate process, and the other with the uncinate process removed virtually. Uncinectomy distinctively changed the local flow topology by triggering the formation of counter-rotating vortices in the ostiomeatal complex, except for the instants with relatively low airflow rate when the respiration phase changed, ultimately leading to a change in the velocity field inside the ostium and maxillary sinus. Despite a significant increase in the maximum air velocity through the maxillary ostium, ventilation was found to increase only slightly when the uncinate process was removed. Furthermore, the degree of maxillary sinus ventilation by inhaled air was comparable to that by exhaled air. This was true to both models and was independent of the presence of the uncinate process. [ABSTRACT FROM AUTHOR]