Abstract
Background: The pathogenesis of empty nose syndrome (ENS) has not been elucidated so far. Though postulated, there remains a lack of experimental evidence about the roles of nasal aerodynamics on the development of ENS. Objective: To investigate the nasal aerodynamic features of ENS andto explore the role of aerodynamic changes on the pathogenesis of ENS. Methods: Seven sinonasal models were numerically constructed, based on the high resolution computed tomography images of seven healthy male adults. Bilateral radical inferior/middle turbinectomy were numerically performed to mimic the typical nasal structures of ENS-inferior turbinate (ENS-IT) and ENS-middle turbinate (ENS- MT). A steady laminar model was applied in calculation. Velocity, pressure, streamlines, air flux and wall shear stress were numerically investigated. Each parameter of normal structures was compared with those of the corresponding pathological models of ENS-IT and ENS-MT, respectively. Results: ENS-MT: Streamlines, air flux distribution, and wall shear stress distribution were generally similar to those of the normal structures; nasal resistances decreased. Velocities decreased locally, while increased around the sphenopalatine ganglion by 0.20±0.17m/s and 0.22±0.10m/s during inspiration and expiration, respectively. ENS-IT: Streamlines were less organized with new vortexes shown near the bottom wall. The airflow rates passing through the nasal olfactory area decreased by 26.27%±8.68% and 13.18%±7.59% during inspiration and expiration, respectively. Wall shear stresses, nasal resistances and local velocities all decreased. Conclusion: Our CFD simulation study suggests that the changes in nasal aerodynamics may play an essential role in the pathogenesis of ENS. An increased velocity around the sphenopalatine ganglion in the ENS-MT models could be responsible for headache in patients with ENS-MT. However, these results need to be validated in further studies with a larger sample size and more complicated calculating models. Citation: Di M-Y, Jiang Z, Gao Z-Q, Li Z, An Y-R, et al. (2013) Numerical Simulation of Airflow Fields in Two Typical Nasal Structures of Empty Nose Syndrome: A Computational Fluid Dynamics Study. PLoS ONE 8(12): e84243. doi:10.1371/journal.pone.0084243 Editor: Timothy W. Secomb, University of Arizona, United States of America Received May 24, 2013; Accepted November 13, 2013; Published December 18, 2013 Copyright: © 2013 Di et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: Funding was provided by National Science and Technology Infrastructure Program. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing interests: The authors have declared that no competing interests exist. * E-mail: [email protected]. (WL); [email protected] (ZJ) leading symptoms in patients with ENS-IT or ENS-both[1], Introduction while pain associated with breathing is predominant among Empty Nose Syndrome (ENS) was initially proposed by those with ENS-MT[4]. The different manifestations label ENS- Eugene Kern and Monika Stenkvist in 1994, to name a group MT as a controversial subtype[1-4]. of syndromes relevant to turbinate injuries or losses[1,2]. The pathogenesis of ENS has not been elucidated yet[1-4]. According to the Anglo-American usage[3], there are three The changes of nasal aerodynamic features are postulated to subtypes of ENS: ENS-inferior turbinate (ENS-IT), ENS-middle be responsible for the development of syndromes of ENS[1]. turbinate (ENS-MT) and ENS-both, due to the pathological However, till now there is a lack of evidence to support the changes of the inferior, middle, and both turbinates, hypothesis. As far as we know, only three computational fluid respectively. Typical manifestations differ among subtypes. dynamic (CFD) studies[5-7] have been conducted to explore Paradoxical nasal obstruction, dryness and crusting are the the changes of aerodynamic features in the postoperative PLOS ONE | www.plosone.org 1 December 2013 | Volume 8 | Issue 12 | e84243 A Computational Fluid Dynamics Study nasal structures of inferior turbinectomy- the typical ENS nasal structures pathological structure of ENS-IT. The changes reported in The nasal structures of bilateral radical inferior turbinectomy these studies were not all consistent with each other. For and bilateral radical middle turbinectomy were chosen to mimic instance, the velocities and the wall shear stresses widely ENS-IT and ENS-MT, respectively. In the latter structures, the decreased with inferior turbinectomy in two of the studies[5,6], horizontal parts of the middle turbinates were removed, while the vertical parts were preserved. All the virtual operations while increased in the third study[7]. Additionally, since those previous studies only included one or two subjects, the were performed by one otorhinolaryngologist by following the standardized procedures, to ensure the relative consistency extrapolation of the results would be greatly impaired by the among different models. potentially great nasal anatomical variations among individual The unstructured tetrahedral cells were generated by the people. As mentioned previously, patients with ENS-MT usually mesh generator, ICEM CFD (ANSYS, Inc.). In consideration of present atypical symptoms, compared to those with ENS-IT or the complicated structures in the nasal cavity and relatively low ENS-both, which makes the investigation on the nasal airspeeds corresponding to quiescent respiratory airflow, prism aerodynamic changes in ENS-MT especially compelling and layers were not created near the walls, which might lead to a meaningful. However, few such studies have been carried out poor mesh quality and increase the time and memory so far in the typical nasal structures of middle turbinectomy, consumption. The ENS-IT model during inspiration of No. 3 leaving a knowledge gap on the nasal airflow features in ENS- was taken as a representative for the convergence test. MT[1]. Analysis of grid convergence was performed by comparing the Further evidence on the aerodynamic features in the nasal velocity profiles for an arbitrary line in the geometry for a structures of ENS patients is in great need to help doctors to constant inhalation flow rate of 15 L/min, for each of four get a better understanding of the pathogenesis of ENS and to different grid sizes (approximately 435 000, 1 100 000, 2 000 make proper therapeutic plans for the patients. Therefore, this 000 and 3 000 000 tetrahedral elements). Similar profiles were study aims to investigate the common airflow characteristics in obtained for the two higher grid sizes. The convergence trend the typical nasal structures of ENS-IT and ENS-MT in 7 was clear and the 2 000 000 element grid was thought to be different individuals. sufficient to resolve the relative change tendency in flow fields in the nasal cavity. The total number of cells, ranging from 1 Methods 619 000 to 2 066 000 for different cases in our study, was at the same grid level. Ethics statement The protocol of the study has been approved by the ethical Numerical simulation committee of Peking Union Medical College Hospital. Each The aerodynamic parameters (pressure, velocity, subject signed informed consent before recruited in the study. streamlines and wall shear stress) were obtained by solving Navier-Stokes equations and continuity equations, using a Study subjects commercial CFD code of FLUENT. The second-order upwind scheme was used in spatial discretization. The pressure- Seven healthy male adults (age range: 29-41) without history velocity coupling was resolved through the SIMPLE method. In of chronic nasal or sinus diseases (atrophic rhinitis, nasal all the calculations carried out, the airflows were assumed to be septum deviation, turbinate hypotrophy, etc.) were included in incompressible and steady. The inlet plane was extracted this study and were sequentially numbered as 1-7. None of below the nasopharynx, and the outlet plane close to the them had experienced any acute upper respiratory infections nostril. A uniform velocity normal to the inlet plane was three months before the study. All the 7 subjects were scored 0 specified by the quiescent cyclic respiratory airflow rate of 15 L/ in both the Visual Analogue Scale (VAS) and the Sino-nasal min[6,7] through the entire nasal cavity. The inlet velocity was Outcome Test-20 (SNOT-20). Nasal structures and mucosa of negative value during the period of inspiration, and positive were normal in nasal inspection in all the subjects. during expiration. The gauge pressure at the outlet was set equal to one atmosphere pressure. The sino-nasal wall Normal nasal structures boundary condition was assumed as rigid and no-slip[6]. The The nasal cavity geometry was obtained through a computed Reynolds number based on the inlet velocity and the tomography (CT) scan. High-resolution CT (Siemens, German) nasopharynx diameter was approximately 1300, indicating that of sino-nasal areas was performed in each of the 7 subjects. the flow was predominantly laminar. To make it reasonably The layer interval of the CT scan was 0.6 mm. CT scan for simple, the laminar model was used in the simulation. each subject was finished within 30 minutes, to reduce the Most of the solutions were well-converged after 2000 influence of nasal period on the shape of the turbinates. The iterations with 8 CPUs. All residuals were below 1e-06 and the boundaries of the nasal cavities and all the sinuses were surface monitor of mass flow rate at the inlet almost numerically extracted. Smoothing of the extracted surfaces was unchanged. performed to facilitate mesh generation of the three- Eight cross sections (Figure 1) were extracted in the 21 dimensional models and reduction of computational effort as models. All the cross sections were approximately well as the increase of computational efficiency. perpendicular to the local airflow directions. The aerodynamic PLOS ONE | www.plosone.org 2 December 2013 | Volume 8 | Issue 12 | e84243 A Computational Fluid Dynamics Study Table 1. Nasal resistances, velocities around sphenopalatine ganglion, and airflow rates through nasal olfactory area in normal, ENS-MT and ENS-IT models. Normal ENS-MT ENS-IT ( mean±SD) ( mean±SD) ( mean±SD) * * 1 -2 3 Nasal Resistance , 10 Pa·s/cm 2.19±1.09 1.51±0.61 0.84±0.29 * * 2 -2 3 Nasal Resistance , 10 Pa·s/cm 2.27±0.90 1.71±0.49 0.99±0.20 1† * ¶ Velocities , m/s 1.14±0.27 1.34±0.26 -- 2† * ¶ 1.52±0.44 Velocities , m/s 1.74±0.44 -- 1§ * * Airflow rates , % 49.76±7.44 63.56±4.66 23.49±11.10 2§ * * Airflow rates , % 52.43±5.61 70.21±6.32 39.24±10.34 The corresponding values of inspiration; The corresponding values of expiration; Airflow rates around olfactory nerve endings in the nasal cavities; Velocities around the sphenopalatine ganglion; Statistically significant in paired-t test (two-tailed, P<0.05); Not calculated (for reasons refer to the result part). doi: 10.1371/journal.pone.0084243.t001 Figure 1. Representative planes in the noses. A: Nasal vestibule, B: Nasal valve, C: Head of the inferior turbinate, D: calculated as the total pressure difference divided by the flow Head of the middle turbinate, E: Middle of the inferior turbinate, rate); 2. Velocity; 3. Streamlines and air flux; 4. Wall shear F: Posterior portion of the inferior turbinate, G: choanal, H: stress distribution, in each of the 8 planes in the 21 models (7 Nasopharynx. The model in the figure is of the No. 3 subject. normal structures, 7 ENS-IT, and 7 ENS-MT). The parameters doi: 10.1371/journal.pone.0084243.g001 of the pathological structures of ENS-MT and ENS-IT were compared respectively with the corresponding normal ones. parameters of the 8 planes were calculated and compared The inspiratory phase is more essential for the nasal between the normal and the pathological structures. respiratory function. Additionally, the changes of the In the initially obtained aerodynamic features, the maximum aforementioned parameters were similar in the two phases in velocities noticeably increased within the choanal planes in the our study. Thus, we mainly illustrated the changes in the ENS-MT nasal structures (but not in the ENS-IT structures, see inspiratory phase in this part. details in the result part), which approached the sphenopalatine The differences in the values of the parameters (nasal ganglion- the suspected origin of headache in ENS-MT[1]. In resistance, maximum velocity and airflow rate) between groups order to get the maximum velocities around the sphenopalatine (normal and ENS-MT/ENS-IT) approximately satisfied the ganglion more accurately, the space around pteryopalatine normal distribution. Thus, paired t-test (two tailed) was applied fossa was extracted, surrounded by the lateral nasal wall, lower to calculate the t and P values by SPSS 17.0 software (IBM, portion of the anterior wall of sphenoid sinus, and the back USA). P<0.05 was defined as statistical significance. parts of the (previous) middle and superior turbinates and the 1. Nasal resistances changed proportionally with the total (previous) middle meatus. The inner sidewall of the extracted pressure differences in our study, due to the fixed airflow rate. space was 5.51±0.95mm apart from the nasal septum on Nasal resistances decreased significantly in both ENS-MT average in the 7 subjects. A relatively broader scope was used -3 (nasal resistance decrease=0.0067±0.0059Pa·s/cm ) and in our study, as there are potential anatomical variations in the -3 ENS-IT (nasal resistance decrease=0.0134±0.0100Pa·s/cm ) location of sphenopalatine ganglion in different individuals and models, when compared with the corresponding normal the stimulations to both the ganglion and its accessory nerves structures (Table 1). Nasal resistance of ENS-IT was would lead to headache. Maximum velocities were measured significantly lower than that of ENS-MT (P=0.007). by the aforementioned method in that area. 2. In the ENS-MT models, velocity distributions changed little A decreased airflow rate was qualitatively observed in the in the velocity contours, only with relatively low velocities middle and superior meatuses as well as the upper portion of shown in the areas where the middle turbinate previously the common meatus in the ENS-IT nasal structures (see details resided (Figure 2 and 3). Correspondingly, the means of the in the result part). We extracted a representative coronal plane, maximum velocities in the eight typical cross sections, plane of F in each model and calculated the airflow rates in the compared with those in normal structures, changed little within abovementioned area. a broad area of the nasal valve, head of inferior turbinate, inferior meatus, and the nasopharynx areas. The maximum Results velocities decreased significantly at the middle-posterior cross sections of the middle turbinate (P =0.036, 0.008) (Figure The aerodynamic parameters were illustrated as follows: 1. ENS-MT Total pressure difference and nasal resistance (the latter one is 4). PLOS ONE | www.plosone.org 3 December 2013 | Volume 8 | Issue 12 | e84243 A Computational Fluid Dynamics Study Figure 2. Velocity distribution during inspiration in normal (a), ENS-MT (b) and ENS-IT (c) models (No. 3). doi: 10.1371/journal.pone.0084243.g002 Figure 3. Velocity distribution during inspiration in normal (a), ENS-MT (b) and ENS-IT (c) models (No.2). doi: 10.1371/journal.pone.0084243.g003 In the ENS-IT models, velocities decreased more broadly obtain the velocities in that area in the ENS-IT models, since and more greatly in the velocity contours than ENS-MT, with there was no evidence of increased velocities either low velocities shown in the areas where the inferior turbinate qualitatively in the contours or quantitatively in the choanal previously resided (Figure 2). The maximum velocities planes. decrease significantly on the anterior-middle cross sections of 3. Changes of the air flux distributions and the streamlines the inferior turbinate and choanal (P =0.031, 0.021, 0.014) ENS-IT were similar in all the 7 ENS-MT/ENS-IT models. Both the (Figure 4). (The velocity profile of model No. 3 was taken as a ENS-MT and ENS-IT structures of model No. 3 were representative of the changes of velocity distribution in Figure representatively illustrated in Figure 7. 2). In the normal models, most of the airflow passed through the Noticeably, velocities increased in the upper-posterior area middle-upper part of the common meatus and the middle behind the inferior turbinate in 4 of the ENS-MT models during meatus. In the ENS-MT models, air flux distributions changed inspiration, and increased in 6 models during expiration, as slightly, compared to the normal ones, only with more fluxes shown in the velocity contours (Figure 5). Consistently, the shown in the middle-upper portion of where the middle means of the maximal velocities within the choanal planes turbinate previously resided. In the ENS-IT models, most increased in both phases, but the increase was only significant airflow passed through the middle-upper portion of where the during expiration (P=0.020) (Figure 4 and 6). As the area with inferior turbinate previously resided. Air fluxes decreased increased velocities was close to sphenopalatine ganglion, a greatly in the other parts of the nasal cavity. When we reasonable suspect would be an increase in velocities around calculated the overall airflow rates in both middle and superior the ganglion. The suspect was proved in our calculations that meatuses and upper portion of the common meatuses in all the the means of the 7 subjects significantly increased during both 7 subjects, the rate significantly decreased by 26.27%±8.68% phases in ENS-MT (velocity increase during and 13.18%±7.59%, respectively, during inspiration and inspiration=0.20±0.17m/s, velocity increase during expiration=0.22±0.10m/s) (Table 1). We did not attempt to expiration in the ENS-IT nasal structures (Table 1). PLOS ONE | www.plosone.org 4 December 2013 | Volume 8 | Issue 12 | e84243 A Computational Fluid Dynamics Study Figure 4. Average of maximum velocities on cross sections in 7 normal, ENS-MT and ENS-IT models during inspiration. doi: 10.1371/journal.pone.0084243.g004 Figure 5. Velocity distributions during expiration in normal and ENS-MT models (No. 1 and 4). 1(a) Normal model of No. 1, 1(b) ENS-MT model of No. 1. 2(a) Normal model of No. 4, 2(b) ENS-MT model of No. 4. doi: 10.1371/journal.pone.0084243.g005 In the normal models, laminar flows were predominant, with middle turbinates. In the ENS-IT models, wall shear stresses vortexes mainly found in the sinuses. In the ENS-MT models, decreased widely, and the areas with larger wall shear stresses streamlines changed little, while in the ENS-IT models, shrinked greatly (No. 1, 3-7). streamlines became chaotic, with new vortexes found in the lower portion of the previous locations of inferior turbinate and Discussion inferior meatus (No. 2-4 and 6) (Figure 7). 4. Changes of the wall shear stress were similar in all the 7 In our study, the nasal aerodynamic features of the typical ENS-IT and ENS-MT models have been obtained by CFD ENS-MT/ENS-IT models, respectively. The structures of the No. 1 model were representatively illustrated in Figure 8. simulation. The changes in the ENS-IT models are generally In the normal models, wall shear stresses were higher in the consistent with the results in most previous studies[5,6]: decreased nasal resistance, velocities and wall shear stresses, nasal valve and head of the inferior turbinate. In the ENS-MT models, wall shear stress distributions changed slightly- and more chaotic streamlines. In the ENS-MT models, the decreased in the middle-posterior portions of the (previous) changing trends of the measured parameters are similar to, PLOS ONE | www.plosone.org 5 December 2013 | Volume 8 | Issue 12 | e84243 A Computational Fluid Dynamics Study Figure 6. Average of maximum velocities on cross sections in 7 normal, ENS-MT and ENS-IT models during expiration. doi: 10.1371/journal.pone.0084243.g006 Figure 7. Air fluxes distributions and trajectories in normal (a), ENS-MT (b) and ENS-IT (c) models (No. 3). doi: 10.1371/journal.pone.0084243.g007 while less remarkable than those in the ENS-IT models. frequently found in patients with ENS-IT. More water vapors Velocities increased significantly around sphenopalatine are taken away by the chaotic airflows and vortexes[8-11], thus ganglion in the ENS-MT nasal structures during both inspiration the feeling of dryness is more likely to generate and the and expiration. To fill the knowledge gap by obtaining the crusting is more easily formed. aerodynamic features in the typical ENS-MT nasal structures is 2. Paradoxical nasal obstruction. It is the most characteristic one of the major contributions of our study. manifestation in ENS-IT patients. Meanwhile it is the most As speculated by other researchers[1], the occurrence of confusing one for otorhinolaryngologists, due to the ENS can be explained or at least partially explained by the inconsistency between patients’ complaint of nasal obstruction aerodynamic changes in the ENS-IT/ENS-MT models. In the and the wide-open nasal cavities in the inspection[1,12]. This following part, we are going to mainly focus on finding the makes it more meaningful to better understand the aerodynamic origins of the development of ENS symptoms, corresponding pathogenesis. In our study, the velocities based on the findings in our study. decrease widely in both phases of respiration in the ENS-IT 1. Dryness and crusting. In the ENS-IT models, more chaotic nasal structures, compared to those in the normal noses streamlines and new vortexes were shown near the bottom (Figure 2, 4 and 6). As the velocities of airflows are one of the wall of the nasal cavities (Figure 7), where crusting is specific stimulations to mechanoreceptors in nasal mucous- a PLOS ONE | www.plosone.org 6 December 2013 | Volume 8 | Issue 12 | e84243 A Computational Fluid Dynamics Study Figure 8. Wall shear stress distributions in the normal (a), ENS-MT (b) and ENS-IT (c) models (No. 1). doi: 10.1371/journal.pone.0084243.g008 receptor participating in the nasal airflow sensation[1,3-17], a ENS-IT. Similarly, increased velocities around sphenopalatine reduction in velocity would lead to decreased sensation of ganglion in the ENS-MT nasal structures were not found in the airflow. It is exactly a frequent description of paradoxical nasal ENS-IT ones, which is coherent with that headache is obstruction by patients with ENS-IT[1]. predominantly seen in patients with ENS-MT. On the other hand, higher temperatures on thermoreceptors Inter-individual variances of the aerodynamic changes in the nasal mucous, which participate together with demonstrated in our study would be a reasonable basis of mechanical receptors in the nasal airflow sensation, have been heterogeneity in clinical manifestations among patients with the shown to contribute to the subjective nasal obstruction[13,18]. same subtypes of ENS. For instance, the aerodynamic Although we did not obtain the temperature gradients directly in changes were less remarkable in the ENS-IT model of the No. our study, they can be satisfactorily reflected by the wall shear 2 subject, compared to the other individuals, who might not stress distribution- areas with higher shear stresses have lower develop ENS after the radical inferior turbinectomy, or only temperatures, and vice versa[19]. In our study, wall shear have mild symptoms in the long-term follow-up. Additionally, stresses decrease broadly in the ENS-IT models (Figure 8), velocities around the sphenopalatine ganglion did not increase which indicates a wide increase of the nasal temperatures, thus in all the ENS-MT models, or new vortexes did not appear in all may lead to the subjective nasal obstruction in this group of the ENS-IT models. These would explain why some people do patients not have headache after middle turbinectomy, or others do not 1. Hyposmia or anosmia. In ENS-IT models, air fluxes in the suffer that much from a dry nose or crusting after inferior olfactory areas significantly decreased (Figure 7, Table 1) turbinectomy, etc. From the comparison of ENS-IT and ENS- (upper middle turbinate, superior turbinate and their MT, and the analyses of inter-individual variations, we can be corresponding portions on the septum[20-22]). The more confident about the essential function of nasal correspondingly decreased “olfactory particles” transported by aerodynamics in the pathogenesis of ENS. the airflows would reduce the stimulation to olfactory sensors, Though the aerodynamic changes would be able to explain a leading to hyposmia, or even anosmia. number of phenomena in ENS, it is difficult to explain the 4. Headache in ENS-MT. It is the most typical complaint of occurrence of ENS-type[13], in which the aerodynamic features patients of this subtype, characterized by its association with change little due to the relatively normal nasal structures. It respiration[2,12]. Some authors speculated that headache indicates that there might be other factors responsible for the might be caused by the changed or increased stimulation to the occurrence of ENS, such as nerve injury with impaired sphenopalatine ganglion[1]. Noticeably, in our study, velocities regeneration, etc., where further studies are needed and significantly increased around the sphenopalatine ganglion in combined with the aerodynamic studies when possible and the ENS-MT models (Figure 3-6, Table 1), thus the stimulation necessary. to the ganglion and its accessory nerves by the airflows would There are several limitations in our study, as illustrated increase, which was likely to be the cause of headache below. Firstly, the calculations in our study were based on associated with respiration. several assumptions- laminar airflow in the nasal cavities and The aforementioned common changes of aerodynamic rigid wall, etc., which were not exactly the real situation. features in ENS-IT were less prominent in ENS-MT, which Though they were reasonable simplifications based on our were possibly responsible for those typical symptoms of ENS prior calculation, and have been accepted and applied by other (dry nose, crusting, paradoxical nasal obstruction, and researchers[5-7] before, it remains worthy of trying to make hyposmia or anosmia) from the above analyses. That was more accurate estimation by using more complicated models in consistent with the fact that patients with ENS-MT are less the future studies, such as the sine-analog one[23] with further likely to develop those symptoms, compared to people with refined boundary conditions. Secondly, restricted by the PLOS ONE | www.plosone.org 7 December 2013 | Volume 8 | Issue 12 | e84243 A Computational Fluid Dynamics Study resources available, we did not simulate other nasal structures pathogenesis of ENS. Importantly, a new hypothesis has been of ENS, such as the postoperative ones of unilateral radical proposed that the increased velocities around the turbinectomy or partial turbinectomy, etc. Thirdly, although the sphenopalatine ganglion in the ENS-MT models would be sample size in our study (n=7) is larger than most published responsible for headache in ENS-MT. However, the results and CFD studies (n=1 or 2), it remains small for generating hypothesis developed need to be validated in further studies undisputed conclusions on the relationship between the with larger sample size and more complicated calculating aerodynamic features and clinical manifestations of ENS. The models in the future. result or hypothesis developed should be further tested in the Acknowledgements future studies with larger sample size. Fourthly, the research subjects in our study were all male adults. Nasal aerodynamic Acknowledgement would be given to Dr. Jie Song, Department changes in female patients need be explored in the future. of Anesthesia, China-Japan Friendship Hospital, for her suggestions on the study design and for sharing her Conclusions experiences on data analysis. Acknowledgement would also go to Dr. Zhuo Li, Department of Radiology, Peking Union Medical Based on 7 different nasal structures, we obtained the College Hospital, for participating in modifying the extracted aerodynamic features in the two typical nasal structures of boundaries of the nasal models. ENS-IT and ENS-MT, the latter of which was little known before our study. The changes of nasal aerodynamic features Author Contributions are able to explain a number of typical symptoms of ENS. 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