The impact of nasal adhesions on airflow and mucosal cooling – A computational fluid dynamics analysis
Introduction
One of the most common complications arising from nasal airway obstruction surgery is the formation of nasal adhesions, also known as synechiae or scar bands. Nasal adhesions are abnormal tissue bridges between adjacent mucosal surfaces, particularly between the septum and components of the lateral nasal wall, such as the inferior and middle turbinates. The adhesions most commonly form post-operatively following sinonasal surgery or can form following trauma. Less common causes of adhesions include chronic inflammatory conditions such as granulomatosis with polyangiitis (Wegener's granulomatosis), sarcoidosis, systemic lupus erythematosus, tuberculosis or following radiotherapy (Vartiainen and Nuutinen, 1992, Jones, 1999).
Nasal adhesions are thought to form when two opposing raw or inflamed mucosal surfaces heal inappropriately, forming a mucosal bridge (Choi et al., 2017). The location of post-operative nasal adhesions typically depends primarily upon specific patient anatomy and the area of surgical intervention (Nayak et al., 1998). The adhesions are most commonly found at the internal nasal valve following septoplasty or the middle meatus following endoscopic sinus surgery but can occur at other locations (Chandra et al., 2009). The reported incidence of adhesions following septoplasty with submucous turbinate surgery estimates 0–19.7% occurrence (Naghibzadeh et al., 2011, Deniz et al., 2014, Chen and Huang, 2019, Joshi et al., 2019).
Patients who develop nasal adhesions after surgery often complain of persistent nasal airway obstruction (Young et al., 1997, Stewart et al., 2004, Joe Jacob et al., 2011, Derin et al., 2016). In particular, the degree of perceived nasal airway obstruction that patients report following nasal adhesion formation appears out-of-proportion compared to the relatively small size of the adhesion and minimal reduction in the cross-sectional area typically seen (Becker et al., 2010). Furthermore, the division of such small adhesions is often accompanied by significantly greater relief of nasal airway obstruction than would be anticipated from what appears to be a relatively minor increase in cross-sectional area (Henriquez et al., 2013). More anterior adhesions appear to have an even greater impact on perceived nasal airway obstruction than posterior adhesions (Rettinger and Kirsche, 2006). In anterior adhesions, the effect on cross-sectional area is at least partly explained by the relatively narrower dimensions at the internal nasal valve. Despite the observed significant impact of post-operative adhesions, there remains a lack of objective evidence in the literature that examines the cause for this disproportionate symptom profile, nor the physiological mechanism by which this occurs. To the best of our knowledge, there have been no studies assessing nasal adhesions with traditional objective measures of nasal airflow, such as rhinomanometry, acoustic rhinometry or peak nasal inspiratory flow (PNIF).
In recent years, the development of Computational Fluid Dynamics (CFD) has facilitated reliable assessment of airflow within the sinonasal cavity. In contrast to traditional objective measures of airflow, CFD provides highly detailed, reproducible and quantifiable results, where multiple variables can be rapidly assessed while avoiding many of the challenges of physical experiments. CFD has been validated and utilised in the assessment of nasal airflow in various physiological conditions, including septal deviation, sinus ventilation, nasal cycling, and examining the efficacy of nasal irrigation and sprays (Lindemann et al., 2013, Nishijima et al., 2018, Alam et al., 2019, Frank-Ito et al., 2019, Abouali et al., 2012, Garcia et al., 2015, Tian et al., 2017, Inthavong, 2020, Dong et al., 2018, Kim et al., 2014, Salati et al., 2021, Gaberino et al., 2017, Zhu et al., 2012, Jo et al., 2015).
This study used CFD to examine the effect of nasal adhesions on nasal airflow in locations commonly seen following NAO surgery (i.e. septoplasty and turbinate reduction). We hypothesise that the disproportionally excessive NAO observed with postoperative nasal adhesions may be more related to key alterations in local nasal airflow and mucosal cooling downstream to the adhesion, rather than due to the relatively minor reduction in cross-sectional area. Furthermore, we hypothesise that anterior nasal adhesions create greater local disruption in airflow in the critical internal valve region and that reduction in cross-sectional area may have a proportionally greater impact in this already narrow region.
Section snippets
Normal nasal airway model
A high-resolution Computed Tomography (CT) scan of a healthy 25-year-old female patient was used to create the nasal airway computational model. The patient had no history of previous sinonasal pathology, trauma or surgery and no anatomical abnormalities. CT scanning of the nasal airway was conducted using a Siemens Dual Source CT Scanner (Siemens Healthcare, Erlangen, Germany) with the following imaging parameters: 0.39 × 0.39 mm pixel size, 512 × 512 pixel image dimensions and slice thickness
Flow streamlines
The effect of adhesions on nasal airflow was explored through streamlines in the right lateral view shown in Fig. 2. The baseline ‘no adhesion’ model demonstrated initial oblique high-velocity flow at the nasal vestibule, followed by a decrease in airflow velocity occurring in the middle meatus region, and further decreasing in the curvature down to the nasopharynx. All models demonstrated flow re-circulation in the nasal vestibule which corresponds to the scroll region between the upper and
Discussion
The presence of adhesions in different locations of the nasal cavity lead to different effects on the flow behaviour in the nasal cavity. The results showed that anteriorly located adhesions were more influential in altering the flow field, and the heat transfer, with the anterior-most adhesion being the internal nasal valve which exhibited the most significant changes in all flow parameters. It is established that the anterior portion of the nasal cavity is responsible for up to 80% of the air
Conclusion
This study used CFD analysis on a single patient with virtual nasal adhesions, located at the sites commonly seen in clinical practice following nasal airway surgery (septoplasty with turbinate reduction), to demonstrate that the presence of postoperative nasal adhesions results in no significant change in overall airflow but does result in localised downstream disruption to airflow. This localised disruption creates reduced local mucosal cooling on critical surfaces, resulting in the
Acknowledgements
The authors gratefully acknowledge the financial support provided by the Garnett Passe and Rodney Williams Foundation Conjoint Grant 2019-22.
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