Inhalation and deposition of spherical and pollen particles after middle turbinate resection in a human nasal cavity

https://doi.org/10.1016/j.resp.2021.103769Get rights and content

Highlights

  • Virtual middle turbinate resection surgery performed on nasal cavity.

  • Aerodynamic behaviour of pollen was compared with spherical particles.

  • Two constant flow rates of 5 L/min, and 15 L/min were performed.

  • An inhalation efficiency curve is proposed which introduced an inhalation parameter, dae2Q0.825.

  • Middle turbinate excision led to increased allergen deposition on the septum.

  • Middle turbinate plays a protective role in preventing allergen impaction on the septum.

Abstract

Middle turbinate resection significantly alters the anatomy and redistributes the inhaled air. The superior half of the main nasal cavity is opened up, increasing accessibility to the region. This is expected to increase inhalation dosimetry to the region during exposure to airborne particles. This study investigated the influence of middle turbinate resection on the deposition of inhaled pollutants that cover spherical and non-spherical particles (e.g. pollen). A computational model of the nasal cavity from CT scans, and its corresponding post-operative model with virtual surgery performed was created. Two constant flow rates of 5 L/min, and 15 L/min were simulated under a laminar flow field. Inhaled particles including pollen (non-spherical), and a spherical particle with reference density of 1000 kg/m3 were introduced in the surrounding atmosphere. The effect of surgery was most prominent in the less patent cavity side, since the change in anatomy was proportionally greater relative to the original airway space. The left cavity produced an increase in particle deposition at a flow rate of 15 L/min. The main particle deposition mechanisms were inertial impaction, and to a lesser degree gravitational sedimentation. The results are expected to provide insight into inhalation efficiency of different aerosol types, and the likelihood of deposition in different nasal cavity surfaces.

Introduction

Nasal airway obstruction can lead to significant impairment in quality-of-life, secondary to a myriad of potential sequelae, including chronic nasal obstruction, mouth breathing, chronic rhinosinusitis, sleep-disordered breathing and obstructive sleep apnoea. As the prevalence of nasal airway obstruction is high, surgery to relieve nasal obstruction is a commonly performed elective procedure. Post-surgery patients have significantly altered anatomy and simulating airflow will improve our understanding of how surgical strategies affect post-surgical airway ventilation, as well as the inhalation dosimetry caused by exposure to airborne pollutants. The removal of anatomical structures in the nose opens up the airway, redistributing the airflow and consequently the particle distribution.

There have been extensive computational studies investigating different nasal surgeries and their effect on nasal airflow (Xiong et al., 2008, Rhee et al., 2011, De Wang et al., 2012, Frank et al., 2013a, Hariri et al., 2015, Dayal et al., 2016, Maza et al., 2019, Inthavong et al., 2019, Siu et al., 2020a), which showed the ability of virtual surgery to guide surgical interventions to alleviate nasal airway obstruction. Previous CFD studies of middle turbinate resection (Zhao et al., 2014, Alam et al., 2019, Lee et al., 2016) have demonstrated shifts in airflow toward the area of middle turbinate resection and decreased airflow velocity, decreased wall shear stress, and increased local air pressure.

Chen et al. (2012) found that following functional endoscopic sinus surgery, a moderate inspiratory airflow rate and a particle diameter of approximately 10 μm improved intranasal deposition into the maxillary sinuses. Frank et al. (2013b) investigated surgical correction of nasal anatomic deformities on ten patients, and their simulation results showed posterior particle deposition after surgery increased by 118%. Bahmanzadeh et al. (2015) showed that sphenoidotomy increased the airflow and particle deposition into the sphenoid sinus, with the highest deposition occurring for resting breathing rate with 10μm. Siu et al. (2020b) studied drug delivery in post-operative sinonasal geometries of patients who underwent a comprehensive functional endoscopic sinus surgery and a modified endoscopic Lothrop procedure and found sinus deposition was more effective with inhalational transport of low-inertia particles outside of the range produced by many standard nasal sprays or nebulizer.

A recent outcome from DelGaudio et al. (2019)'s analysis of patients with middle turbinate resection suggested that the surgery removed the middle turbinate protective function in preventing inhaled allergen particles from depositing on the septum. Anatomical changes in the airway aimed at restoring airway ventilation or increased accessibility to the paranasal sinuses as the primary aims, may in fact be ignoring the secondary effects of persistent inhalation exposure to airborne particulates, such as dust (Tian et al., 2007), dust mites (Zhang et al., 2019), and fibres. Additionally, pollen has been implicated for initiating the onset of allergic rhinitis (such as hay fever) and sometimes has exacerbating asthma (Bousquet et al., 2001).

Modelling of non-spherical particles needs to account for the changes in particle motion due to the different drag coefficients leading to altered trajectories. While the discrete element method and immersed boundary methods can resolve more physics such as rotational degrees-of-freedom and inter-particle interactions, the Lagrangian approach remains popular for its computational efficiency and ability to easily integrate into finite-volume CFD codes. Drag correlations for non-spherical particles have been developed Hölzer and Sommerfeld (2008), Wang et al. (2018), Bagheri and Bonadonna (2016). This is in addition to inclusions of lift and torque components applied to oblate ellipsoidals or fibres (Sanjeevi et al., 2018, Zastawny et al., 2012, Tian et al., 2012, Tian and Ahmadi, 2013). Th authors used a simplified approach in earlier work Inthavong et al. (2013) by using shape factors and an overall drag coefficient to account for tumbling and rotational effects, but this does not allow for the interception deposition mechanism.

This study investigated the changes in deposition of inhaled pollutants in the nasal airways, and the proportion escaping through the nasopharynx towards the lungs. Spheres with aerodynamic equivalent diameters, dae, were used as a reference while pollen particles were investigated. A nasal airway model was used in pre-operative state, followed by a virtual middle turbinectomy surgery (post-operative state) with two constant inhalation flow rates of 5 and 15 L/min. The airway was separated into different regions allowing a detailed comparison of regional deposition changes.

Section snippets

Nasal cavity model

The nasal cavity geometry was reconstructed from high-quality CT scans of a healthy 25-year-old, Asian female (161 cm height, 53 kg mass) without any nasal obstructions. The CT data was scanned with a Siemens Dual Source CT Machine with parameters of 0.39×0.39 mm in pixel size, 512×512 in image dimension, and 0.5 mm in slice thickness. The images were imported into 3D Slicer, where the entire paranasal sinus model was determined and exported as a stereolithography (STL) file format for

Flow field

Velocity contours on ten coronal planes from the anterior, main nasal passage and the posterior regions are shown in Fig. 4. The highest velocities were found in the anterior planes, which exhibited the smallest cross-sectional areas. The white to red colours in the contours depict the main bulk flow paths which were located in the medial regions of the planes as the airflow is directed superiorly from the nostrils. The effect of surgery is evident in planes y4 to y8 where the removal of the

Discussion

Pollen particles exhibited higher drag coefficients, and a lower particle density compared to aerodynamic equivalent spheres. This suggests that pollen has greater mobility in its aerodynamic flight and greater potential to penetrate the nasal cavity. Middle turbinate resection in this study created a larger open space in the superior half of the main nasal passage where the inhaled air was directed into, thus transporting inhaled particles to the space. At 5L/min, smaller particles penetrated

Conclusion

An inhalation parameter was introduced to account for the multi-parameter scenario of inhaled particles from the surrounding air, given as dae2Q0.825. The drag coefficient for pollen and its lighter density led to greater inhalation efficiency compared to spherical particles at 1000 kg/m3. Correlations to curve fit the pollen, and spherical particle was produced to predict inhalation fractions. Deposition on local surfaces was obtained for Pre-Op and Post-Op models. The effect of surgery

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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