Disorders of the nasal cavity are closely linked to its structure and function. Correction of morphological abnormalities of the nasal cavity is fundamental to the treatment of diseases. Secondary atrophic rhinitis (AR) is commonly caused by destructive nasal surgery [
Medical treatments provide only symptomatic relief. With the developments in tissue engineering, surgical reconstruction of the nasal structure is a promising treatment to effect radical cure. But, simultaneous implantation of materials or tissues may cause problems like infection and nonhealing. Staging surgery is often used to prevent these problems. For patients with secondary atrophic rhinitis with nasal septum perforation, the cavity-narrowing operation and nasoseptal perforation repair operation are two common choices [
With the development of the biological simulation methods, computational fluid dynamics (CFD) is increasingly gaining popularity as a powerful tool for performing virtual surgeries to test various scenarios and for selecting the proper procedure to achieve the optimal outcome. Rhinologists use this approach to simulate surgeries for deviation of the nasal septum, turbinectomy [
In this study, three operation plans have been simulated using CFD models (Virtual surgery 1: nasoseptal perforation repair operation, Virtual surgery 2: cavity-narrowing operation, Virtual surgery 3 = 1 + 2: both nasoseptal perforation repair and cavity narrowing). By analyzing the aerodynamic changes after different operations and comparing them with those in height- and weight-matched healthy volunteers, the effects of the three operations have been evaluated by the optimal sequence of operations. In addition, we implemented the surgical closure of the nasal septum perforation in a patient, based on CFD modeling. We summarize this clinical experience in this paper.
The subject in our study was a 62-year-old Chinese woman who was a known case of atrophic rhinitis. The patient required repeated hemostatic laser treatment at the local hospital for frequent epistaxis, but without any symptom relief. The patient complained of nasal dryness and hyposmia with no purulent nasal discharge, nasal obstruction, nasal itching, sneezing, and whistling. Figure
(a) Preoperative horizontal slice of CT data; (b) preoperative nasal endoscopy; (c) preoperative visualization of the respiratory airways in a midsagittal cut; (d) postoperative nasal CT scan after 1 month; (e) intraoperative nasal endoscopy; and (f) postoperative visualization of the respiratory airways in a midsagittal cut. Red circles indicate preoperative positions of nasal septal perforation. Green circles indicate the positions of nasal septal perforation, the postoperation.
There was no history of allergic rhinitis, chronic heart and lung disease, or nasal trauma. The patient requested a nasoseptal perforation repair operation. After an effective control of nasal dryness, an autograft comprising three layers of temporal fascia, tragus cartilage, and artificial dura was fixed into the nasal septum using the “sandwich” technique (Figure
A height- and weight-matched healthy volunteer served as the control. We measured her nasal resistance using a six-phase rhinomanometer (GM) in inspiration and expiration. The result was 0.131 Pa ∗ s/mL in inspiration. All subjects provided written informed consent for participation in this study. The study was approved by the institutional review board and the medical ethics committee at the second affiliated hospital of the Xi’an Jiaotong University.
Figure
Operations and characteristics of models A, B, C, D, and E. Red circles indicate preoperative positions of nasal septal perforation. Green circles indicate the positions of nasal septal perforation, the postoperation. Black arrows indicate the positions of the cavity-narrowing operation.
Here, the 3D geometry of human nasal airways was reconstructed in four steps [
Technical route of the research.
Mesh sensitivity tests were conducted to ensure grid independence for all results; data reported here were obtained in meshes of 600,000–1,200,000 tetra cells. The air flow is modelled by using the steady, laminar, incompressible, and isothermal Navier–Stokes equations. The second-order upwind scheme was used for spatial discretization.
Pressure-velocity coupling was resolved using the SIMPLE method. For all calculations, the airflows were assumed to be incompressible and steady. The inlet plane was below the nasopharynx and the outlet plane close to the nostril. A uniform velocity normal to the inlet plane was specified by the quiescent cyclic respiratory airflow rate of 250 mL/s [
The objectives of surgery are to reduce nasal cavity volume so as to increase nasal resistance, to reduce mucosal wall shear stress so as to decrease epistaxis, and to deviate airflow from the surgical site toward a healthy or nonoperated area [
Nasal resistance (
CFD-calculated total nasal resistance, resistance ratio, and airflow allocation.
Model A | Model B | Model C | Model D | Model E | Model F | |
---|---|---|---|---|---|---|
Total nasal resistance (Pa ∗ s/mL) | 0.050 | 0.066 | 0.082 | 0.080 | 0.076 | 0.117 |
Nasal resistance ratio (%) | 43.2% | 56.8% | 70.2% | 68.8% | 65.1% | 100% |
Airflow allocation (olfactory area) | 13.1% | 19.1% | 21.5% | 19.4% | 14.2% | 22.6% |
Airflow allocation indicates the percentage of total air passing through the olfactory area. As is shown in Table
Comparison of airflow density path lines.
It implied that Virtual surgery 2 > Virtual surgery 3 > Virtual surgery 1 > Postoperation > Preoperation.
Vortex: Model F > Model C > Model D > Model B > Model E > Model A. (Figure
It implied that Virtual surgery 2 > Virtual surgery 3 > Virtual surgery 1 > Postoperation > Preoperation.
There are large vortexes before operation (Model A). Thick nasal crusts appeared at this site. There are still large vortexes after virtual and real closure of perforation operation (Model B and Model E). However, there are few vortexes in healthy control and after virtual surgery 2 and 3 (models F, C, and D).
Wall shear stress is the tangential drag force produced by air moving across the mucosal surface. It is a function of the velocity gradient of air near the mucosal surface. The higher the wall shear force is, the greater damage the mucosa may suffer.
As is shown in Figure Preoperation: the mucosal shear stress on the posterior inferior edge of the septal perforation is relatively higher than that at other edges of the septal perforation, which is consistent with the site of epistaxis and erosion (Figures Virtual surgery 1 reduced the maximum mucosal wall shear stress at the nasal floor by 85% (0.253 Pa to 0.037 Pa) Virtual surgery 2 reduced the maximum mucosal wall shear stress in the original epistaxis area by 82% (0.330 Pa to 0.059 Pa) and reduced the maximum mucosal wall shear stress at the nasal floor by 77% (0.253 Pa to 0.059 Pa) In all models, the highest mucosal wall shear stress areas appeared on the nasal valve and the nasopharynx.
Comparison of mucosal wall shear stress contours (Pa).
CFD-calculated wall shear stress.
Maximum wall shear stress (Pa) | Model A | Model B | Model C | Model D | Model E | Model F |
---|---|---|---|---|---|---|
Nasal floor | 0.253 | 0.037 | 0.059 | 0.041 | 0.047 | 0.110 |
Septal perforation | 0.330 | — | 0.059 | — | 0.095 | — |
In our study, both pre- and postoperations’ nasal aerodynamics were obtained by CFD simulation. The changes in the models are generally consistent with the results from previous studies [
As speculated by other researchers [
In this study, the preoperative nasal resistance was found to be 43.2% of the healthy nasal resistance, which increased to 56.8%, 70.2%, and 68.8% after nasoseptal perforation repair, cavity-narrowing operation, and that after both operations, respectively. In an earlier study, nasal resistance reportedly decreased to 64% of the healthy nasal resistance after resection of the inferior turbinate [
Therefore, cavity-narrowing surgery is better than nasoseptal perforation repair for increasing nasal resistance.
In our case, the preoperative airflow reaching the olfactory area was very limited. In addition, pathological dryness in nasal cavity and dry crust formation in the olfactory area also impaired the smell sensation (preoperative score: 2.8 points, T&T olfactometer). Virtual surgery 1, 2, and 3 were associated with increased vortexes and airflow reaching the olfactory area, thus increasing the deposition of odorants in the olfactory area. This presumably resulted in an improved smell sensation (postoperative score, 1.6 points).
Stream flow in the olfactory area: Model C > Model B; therefore, cavity-narrowing surgery led to a greater increase in nasal olfaction as compared with that observed after nasoseptal perforation repair.
In the Model A, more chaotic streamlines and new vortexes were observed near the bottom of the nasal cavity (Figure
After surgical closure of septal perforation, large vortexes were still observed. Cavity-narrowing surgery is more effective in eliminating vortexes. Therefore, the cavity-narrowing surgery is better than the nasoseptal perforation repair operation in decreasing nasal crusting.
The anteroinferior part of the nasal septum, also referred to as Little’s area, is susceptible to epistaxis [
The cavity-narrowing surgery reduced the mucosal wall shear stress and vortexes at the edges of the septal perforation, so it can be concluded that the epistaxis can be eased after this surgery.
Perforations in the septum do not typically heal on their own, and surgical treatment of nasal septal perforation remains a challenging field of rhinology. High mucosal wall shear stress at the open edge of the perforation may be a reason why it does not easily heal. Furthermore, after surgical closure of perforation, the mucosal wall shear stress over the site of perforation is still high, which impacts graft survival. However, cavity-narrowing surgery can reduce the mucosal wall shear stress and provide favorable conditions for graft survival, thus reducing the probability of reperforation.
Based on 6 different nasal structures, we examined the aerodynamic features in three typical nasal structures associated with secondary AR after different surgeries, which has not been studied and compared before. The observed changes in nasal aerodynamics can explain the underlying mechanisms involved in causing the typical symptoms in patients with secondary AR. Nasal aerodynamics appear to be instrumental in the pathogenesis of secondary AR. Thus, restoration of nasal aerodynamics should be a key consideration in the selection of the surgical approach.
Simultaneous cavity-narrowing operation and nasoseptal perforation repair operation can not only improve the flow field but also prevent the deterioration of the saddle nose. However, simultaneous implantation of materials or tissues may result in complications such as infection and nonhealing. Staged surgical approach may be beneficial wherein the cavity-narrowing operation should take precedence over the septal repair. If only one surgery is to be chosen, the cavity-narrowing operation is better. The exponential advancements in computing technology raise the hope that CFD analysis may be a viable and practical adjunct to nasal airway surgery in the near future.
Atraphic rhinitis
Computational fluid dynamics
Computed tomography
Three dimensional
Virtual surgery
Preoperation
Postoperation
The CT data used to support the findings of this study are restricted by the institutional review board and the medical ethics committee at the second affiliated hospital of the Xi’an Jiaotong University in order to protect patient privacy. Data are available from (Guoxi Zheng,
No outside interest was paid for any part of this study.
The authors declare that they have no conflicts of interest.
This work was financially supported by the National Natural Science Foundation of China (no. 81271057) and Interdiscipline Subject of Xi’an Jiaotong University (no. 08143039).