Heow Pueh Lee

Assessment of septal deviation effects on nasal air flow: A computational fluid dynamics model

The purpose of this article is to analyze the effects of septal deviation on the aerodynamic air flow pattern compared with that of a normal nose by computational fluid dynamics (CFD) tools.

A review of the implications of computational fluid dynamic studies on nasal airflow and physiology.

BACKGROUND Computational fluid dynamics has been adapted to studying nasal aerodynamics. AIM To review current literature on CFD studies, with an emphasis on normal nasal airflow, the impact of sinonasal pathology on airflow, and implications on nasal physiology. The objective is to provide the rhinologists with a greater understanding of nasal airflow and how symptomatology of sinonasal disease may be explained via CFD simulations. RESULTS The nasal valve region redirects inspiratory airstreams over the inferior turbinate in a high turbulent kinetic energy, which is important in heat and moisture exchange. The bulk of airflow occurs in the common meatus with small streams traversing the olfactory groove, increasing during sniffing. Septal deviation and enlarged inferior turbinate causes redistribution of airflow, changes in intranasal pressure and increased turbulence. High velocity airflow and wall shear stress at the septal perforation causes desiccation and mucosal damage. The airflow within an atrophic nasal cavity is predominantly laminar with minimal contact with nasal mucosa. The inferior turbinate is an important organ for air conditioning and preservation during surgery is highlighted. CONCLUSIONS Despite some limitations of CFD simulations, this technology has improved understanding of the complex nasal anatomy and the implications of disease and surgery on physiology.

Changes of airflow pattern in inferior turbinate hypertrophy : A computational fluid dynamics model

Background Nasal obstruction (NO) is a very common symptom, but its effect on nasal physiology has not been fully understood. We performed this study to determine the effect of severity of NO due to inferior turbinate hypertrophy on airflow pattern using the computational fluid dynamics simulations. Methods A three-dimensional nasal cavity model was constructed from the MRI scans of a healthy human subject. Nasal cavities corresponding to healthy, moderate, and severe NO was simulated by enlarging the inferior turbinate geometrically, which can be documented by approximately one-third reduction of the minimum cross-sectional area (1.453 cm2 in the healthy nose) for the moderate (0.873 cm2) and two-thirds (0.527 cm2) for the severe obstruction. Results Total negative pressure through the nasal cavity increased during the inspiratory phase by almost twofold (-19 Pa) and threefold (-33 Pa) for moderate and severe blockage, respectively, compared with the increase of total negative pressure of -10 Pa in a healthy nose. In cases of moderate and severe blockage, a higher velocity and shear stress was observed at the nasopharynx and dorsal region of the nasal cavity. Moreover, nasal valve function will not exist in severe NO because of the changes of airflow pattern at the original nasal valve location. Conclusion Impairment of nasal airflow and physiology is evidenced in NO caused by inferior turbinate hypertrophy. Data of this study may help in predicting the aerodynamic effects of surgical correction of the inferior turbinate hypertrophy.

Aerodynamic effects of inferior turbinate surgery on nasal airflow - a computational fluid dynamics model

BACKGROUND Turbinate reduction surgery may be indicated for inferior turbinate enlargement when conservative treatment fails. The aim of this study was to evaluate the effects of inferior turbinate surgery on nasal aerodynamics using computational fluid dynamics (CFD) simulations. METHODS CFD simulations were performed for the normal nose, enlarged inferior turbinate and following three surgical procedures: (1) resection of the lower third free edge of the inferior turbinate, (2) excision of the head of the inferior turbinate and (3) radical inferior turbinate resection. The models were constructed from MRI scans of a healthy human subject and a turbulent flow model was used for the numerical simulation. The consequences of the three turbinate surgeries were compared with originally healthy nasal model as well as the one with severe nasal obstruction. RESULTS In the normal nose, the bulk of streamlines traversed the common meatus adjacent to the inferior and middle turbinate in a relatively vortex free flow. When the inferior turbinate was enlarged, the streamlines were directed superiorly at higher velocity and increased wall shear stress in the nasopharynx. Of the three surgical techniques simulated, wall shear stress and intranasal pressures achieved near-normal levels after resection of the lower third. In addition, airflow streamlines and turbulence improved although it did not return to normal conditions. As expected, radical turbinate resection resulted in intra-nasal aerodynamics of atrophic rhinitis demonstrated in previous CFD studies. CONCLUSION There is little evidence that inspired air is appropriately conditioned following radical turbinate surgery. Partial reduction of the hypertropic turbinate results in improved nasal aerodynamics, which was most evident following resection of the lower third. The results were based on a single individual and cannot be generalised without similar studies in other subjects.

Numerical simulation of the effects of inferior turbinate surgery on nasal airway heating capacity.

Background The aim of this study was to evaluate the effects of inferior turbinate surgery on nasal airway heating capacity using computational fluid dynamics (CFD) simulations. Methods Heat transfer simulations were performed for a normal nasal cavity and others with severely enlarged inferior turbinates, before and after three simulated surgical procedures: (1) resection of the lower third free edge of the inferior turbinate, (2) excision of the head of the inferior turbinate, and (3) radical inferior turbinate resection. The models were run with three different environmental temperatures. Results The changes of airflow pattern with the reduction of inferior turbinate affected heat transfer greatly. However, the distribution of wall heat flux showed that the main location for heat exchange was still the anterior region. Under the cold environment, the nasal cavities with the head of inferior turbinate reduction were capable of heating the inspired air to 98.40% of that of the healthy one; however, for the case with lower third of inferior turbinate excised, the temperature was 11.65% lower and for the case with radical inferior turbinate resection, 18.27% lower temperature compared with the healthy nasal cavity. Conclusion The healthy nasal cavity is able to warm up or cool down the inspiratory airflow under different environmental temperature conditions; for the nasal cavities with turbinate surgeries, partial inferior turbinate reduction can still sustain such heating capacity. However, too much or total turbinate resection may impair the normal function of temperature adjustment by nasal mucosa.

Aerodynamic characteristics inside the rhino-sinonasal cavity after functional endoscopic sinus surgery.

Background The aim of this study was to evaluate effects of functional endoscopic sinus surgery (FESS) on transient nasal aerodynamic flow patterns using computational fluid dynamics (CFD) simulations. Methods A three-dimensional model of the nasal cavity was constructed from CT scans of a patient with FESS interventions on the right side of the nasal cavity. CFD simulations were then performed for unsteady aerodynamic flow modeling inside the nasal cavity as well as the sinuses. Results Comparisons of the local velocity magnitude and streamline distributions inside the left and right nasal cavity and maxillary sinus regions were presented. Because of the FESS procedures in the right nasal cavity, existences and distributions of local circulations (vortexes) were found to be significantly different for the same nasal airflow rate but at different acceleration, deceleration, or quiet phases in the maxillary sinus region on the FESS side. Because of inertia effects, local internal airflow with circulation existences was continuous throughout the whole respiration cycle. With a larger peak inspiration flow rate, the airflow intensity inside the enlarged maxillary sinus increased significantly. Possible outcomes on functional performances of the nose were also examined and discussed. Conclusion Surgical enlargements of natural ostium of the maxillary sinus will change the aerodynamic patterns inside the main nasal cavity and maxillary sinus regions, which may affect normal nasal physiological functions. Local inertia effects play more important roles for the internal nasal airflow pattern changes and thus such conventional FESS procedures should be carefully planned.

Effects of septal perforation on nasal airflow: computer simulation study

BACKGROUND Nasal septal perforation is a structural or anatomical defect in the septum. The present study focused on the effects of septal perforation on nasal airflow and nasal patency, investigated using a computer simulation model. METHODS The effect of nasal septal perforation size on nasal airflow pattern was analysed using computer-generated, three-dimensional nasal models reconstructed using data from magnetic resonance imaging scans of a healthy human subject. Computer-based simulations using computational fluid dynamics were then conducted to determine nasal airflow patterns. RESULTS The maximum velocity and wall shear stress were found always to occur in the downstream region of the septal perforation, and could potentially cause bleeding in that region, as previously reported. During the breathing process, there was flow exchange and flow reversal through the septal perforation, from the higher flow rate to the lower flow rate nostril side, especially for moderate and larger sized perforations. CONCLUSION In the breathing process of patients with septal perforations, there is airflow exchange from the higher flow rate to the lower flow rate nostril side, especially for moderate and large sized perforations. For relatively small septal perforations, the amount of cross-flow is negligible. This cross-flow may cause the whistling sound typically experienced by patients.

Drug delivery in the nasal cavity after functional endoscopic sinus surgery: a computational fluid dynamics study.

BACKGROUND Intranasal medication is commonly used for nasal disease. However, there are no clear specifications for intranasal medication delivery after functional endoscopic sinus surgery. METHODS A three-dimensional model of the nasal cavity was constructed from computed tomography scans of an adult Chinese male who had previously undergone functional endoscopic sinus surgery in the right nasal cavity. Computational fluid dynamic simulations modelled airflow and particle deposition, based on discrete phase models. RESULTS In the right nasal cavity, more particles passed through the upper dorsal region, around the surgical area, and streamed into the right maxillary sinus region. In the left cavity, particles were distributed more regularly and uniformly in the ventral region around the inferior turbinate. A lower inspiratory airflow rate and smaller initial particle velocity assisted particle deposition within the right maxillary sinus cavity. In the right nasal cavity, the optimal particle diameter was approximately 10(-5) m for maxillary sinus cavity deposition and 3 × 10(-6) m for bottom region deposition. In the right nasal cavity, altered back head tilt angles enhanced particle deposition in the top region of the surgical area, and altered right side head tilt angles helped enhance maxillary sinus cavity deposition. CONCLUSION This model indicates that a moderate inspiratory airflow rate and a particle diameter of approximately 10(-5) m should improve intranasal medication deposition into the maxillary sinus cavity following functional endoscopic sinus surgery.

Assessments of nasal bone fracture effects on nasal airflow: A computational fluid dynamics study.

Background The aim of this study was to evaluate effects of nasal bone fractures on nasal aerodynamic flow patterns using computational fluid dynamics (CFD) simulations. Methods A three-dimensional model of nasal cavity with a nasal bone fracture was constructed from computerized tomography (CT) scans of a patient with use of software Mimics 13.0 (The Materilize Group, Leuven, Belgium). CFD simulations were performed using Fluent 6.3 (ANSYS, Inc., Canonsburg, PA) with a turbulent flow model. Numerical results were presented with velocity, streamline, and pressure contour distributions in left and right nasal cavities and were compared with those of a healthy one. Possible outcomes on functional performances or patencies of the nose were also examined and discussed. Results For the nose with a nasal bone fracture, distributions of velocity contours showed there was more airflow in the right nasal cavity than in the left one, especially for inspiration status. In the left cavity, the airflow was redirected irregularly and there were also more circulations with larger sizes, higher pressure jumps, and greater wall shear stresses. Flow partitioning in the right and left cavities was noticeable with a larger nasal resistance compared with the healthy one. When the inspirational flow rate was increased, pressure jump from the nostril to the nasopharynx increased faster. Conclusion The aerodynamic flow was redistributed greatly for the nose with a nasal bone fracture compared with the healthy one, which might affect local normal nasal functions. Such physical assessments of nasal airflow based on a model from the patients’ CT scans may help clinicians determine the best treatment in advance.

Numerical simulation of septal deviation effects in nasal flow

The purpose of this article is to analyze the effects of septal deviation on the aerodynamic flow pattern compared with a normal nose by Computational Fluid Dynamics (CFD) tools. The software MIMICS 12.0 was used to perform the image segmentation and meshed model generation from CT scans. Thereafter high resolution 3D volume meshes comprising boundary layer effect and computational domain exterior to the nose were constructed. Numerical simulations were then carried out using FLUENTS for computational fluid dynamics simulations. The overall flow was assumed to be incompressible, quasi-steady and laminar. The same oxygen (flow rate) amount with a normal nose for a deviated one was also assumed. The results were shown with the contours of velocity for exhalation and inhalation. The distribution of wall shear stress and flow partitioning were also investigated. It was found that the existence of “dead space” might cause turbulence due to the deviated nasal septal structures.