Effects of partial middle turbinectomy with varying resection volume and location on nasal functions and airflow characteristics by CFD

Highlights

• We created one pre-surgery and sixvirtual surgery models, which simulate variations of partial middle turbinectomy (MT) with varying resection volume /location.

• We identified the tendency of changes in nasal functions with respect to resection volume/location,by comparing CFD results of pre- and post-surgery models.

• We attempt to investigate impacts of partial MT on mucosal secretion.

• We postulated that the removal of anterior inferior part of middle turbinate while preserving posterior margin will not alter airflow characteristics extensively.

ABSTRACT

The surgical term “turbinectomy” encompasses many variations in the location and extent of removal. As a systemic approach to consider the negative impact of middle turbinectomy(MT), such as the excessive removal of turbinate, airflows inside a pre-surgery model and a series of virtual surgery models were numerically analyzed and compared. These models simulate three variations of partial MT(three bilateral and three unilateral) with varying resection volume and location. Each middle turbinectomy results in alterations of flow and thermal parameters, such as nasal resistance (NR), velocity, temperature, wall shear stress(WSS) and wall heat transfer(WHT). WSS distributions were also considered in connection with mucosal secretion. The tendency of changes in nasal functions and airflow characteristics was identified with respect to resection volume and location. A counter-rotating vortical structure was seen in the region of widened middle airway for the case of total resection of middle turbinate. Maximum velocity and WSS near sphenopalatine ganglion, which was a possible explanation for headache after total resection of middle turbinate, was increased. Changes in NR and WHT for bi-lateral resection cases were greater than those for unilateral resection cases. While the physiological changes in four partial MT models were insignificant, changes in near total resection model was prominent. Although our surgical simulation was done for a single case, we postulate that the removal of the anterior inferior part of middle turbinate while preserving posterior margin will not alter airflow characteristics extensively. These findings will help designing surgical plans for partial MT.

Introduction

Respiratory physiology and pathology are strongly dependent on the airflow inside the nasal cavity. Since nasal airflow is heavily affected by the geometry of the flow passage, changes in the anatomical shape of the nasal cavity, due to diseases or surgical treatments, alter the nasal resistance and functions of nose.

One of the surgical modifications is the partial middle turbinectomy (MT). Usually the partial resection is done during endoscopic sinus surgeries (ESS) for the patients with chronic sinusitis with polyps and endoscopic endonasal skull base surgeries. There still exist controversies regarding the resection or preservation of the middle turbinate during functional endoscopic sinus surgery [14,28]. Although it is generally accepted by rhinologists that a diseased or flail middle turbinate should be excised, air-conditioning, filtration functions, possible loss of olfaction, and empty nose syndrome (ENS) after MT are of concern [14]. Radical resection of middle turbinate seems to be associated with an increased incidence of complication. The effect of partial MT was investigated experimentally by using the particle image velocimetry(PIV) technique with unilateral nasal cavity models [4], [19]. The change in velocity field according to the extent of resection volume was investigated and the change of main flow direction and root mean square velocity was observed. The effect of the presence of inferior and middle turbinate was investigated by PIV and CFD techniques with simplified models [17]. They concluded that the presence of inferior turbinate was more important than the middle turbinate on the flow during inspiration.

In the last decade, CFD has become a fast and convenient research tool to study airflow in the human airway [1], [6], [7], [20], [23], [24], [27], [29], especially when investigating heat and humidity transfer, which is not easy to study by using other experimental techniques. There had been numerical studies on partial inferior turbinectomy [2], [15], [24].

Zuber et al. [29] studied the impact of middle turbinate in flow behavior and air conditioning ability of the nose by CFD. They concluded that turbinates play a vital role in conditioning of the inspired air and therefore alteration of turbinate structure would seriously hamper its air-conditioning ability. Di et al. [5] investigated nasal airflows in two virtual bilateral turbinectomy models (total resection of middle and inferior turbinate) by CFD, in connection with the pathogenesis of ENS. They correlated nasal aerodynamic changes with two different symptoms of ENS and proposed a new hypothesis that the increased velocities around the sphenopalatine ganglion (medial and lateral portion of the posterior part of the nasal cavity before nasopharynx or medial and lateral part before posterior choana) in the ENS-MT model is responsible for headache in ENS-MT patients. Zhao et al. [28] studied airflow in pre- and post-MT(partial) models of a specific patient by CFD to find the effect of the presence of middle turbinate. Streamlines, air flux distribution, and wall shear stress distribution for middle turbinectomy model were generally similar to those of the normal structures and the nasal resistances decreased by 20% after radical middle turbinectomy. Dayal et al. [8] studied the effects of total middle (TMT) and inferior (TIT) turbinectomy on nasal aerodynamics by comparing CFD results for pre- and virtual surgery models of 10 patients with hypertrophy. They investigated changes in nasal resistance and air-conditioning efficiency post-operatively, and concluded that TIT yields greater increases in nasal airflow but also impairs the nasal air-conditioning capacity to a greater extent than TMT. Yet, the effect of partial turbinectomy, especially according to the extent of removal, has not been evaluated up to now.

Recent studies indicate that nasal secretion from the mucosa/mucous membrane of the nasal cavity is not only important for air conditioning, brain cooling, and defense, but also for olfactory function [16]. Even-Tzur et al. [11] conjectured that wall shear stress (WSS) on epithelial cells caused by airflow activates nasal secretion by in-vitro experiments in cultured human nasal epithelial cells, and this was cited by Hildebrandt et al. [16]. Therefore the wall shear stress distribution in the olfactory region might be related with nasal secretion and nasal functions, such as air-conditioning, filtration and olfaction.

In this article, airflows inside a normal (pre-surgery) model and six kinds of virtual partial MT (post-surgery) models including near total MT were investigated by CFD. Using comparative study of CFD results for pre- and post-MT models, we extracted the tendency of post-surgical changes in nasal functions and resistance with respect to turbinate resection volume, location, and surgical technique. Furthermore, we closely examined flow-rate and WSS distributions in connection with nasal secretion. Since secretion substances act as a solvent for odors and enable their adhesion to the surface of olfactory cells [16], WSS may affect the olfactory function of nose. Therefore, we hypothesized that WSS on epithelial cells in the olfactory region is likely correlated with mucus secretion and possibly olfaction function of nose. The spatial and temporal changes of WSS distribution in the olfactory region were examined to investigate the influence of a series of virtual MT on the nasal secretion and functions.

Although the surgical simulation was done for a single case, we postulate that removal of the anterior inferior part of middle turbinate while preserving posterior margin will not disturb the airflow characteristics and physiological functions of nose excessively.