Deviated nasal septum hinders intranasal sprays: a computer simulation study

C, Farzal Z, Basu S, Zanation A, Thorp B, Kimbell J, Senior B, Kimple A. Intranasal corticosteroids: patient administration angles and impact of education

INTRODUCTION: Intranasal corticosteroids sprays (INCS) are first line treatment for allergic rhinitis and are frequently used for chronic rhinosinusitis. Improperly aiming INCS increases the risk of epistaxis and may decrease the efficacy of the medication. The goal of this study was to determine how patients position INCS for drug delivery and if verbal or written instructions improve their positioning. METHODS: Patients in rhinology clinics were photographed while administering a generic spray bottle. The angle of the spray bot- tle relative to the patients’ head and a fixed background was determined. RESULTS: A total of 46 participants were included. The average spray angle for the right naris was 10.1o towards the septum and 67.2o below the Frankfurt Horizontal plane. The average spray angle for the left naris was 4.5o towards the septum and 62.2o below the Frankfurt horizontal plane. The angle of the spray bottle ranged from 50o toward the septum to 43o away from the sep- tum. Only 8 patients aimed away from the septum for both nares. Patients who recalled receiving verbal and written instructions aimed the INCS bottle at the lateral wall and inferior turbinate in contrast to patients who only received one form of instruction or no instructions. CONCLUSIONS: Most patients (83%) incorrectly aim INCS when compared to current guidelines. There was statistically significant improvement in the positioning of patients who reported receiving both verbal and written instruction; however, this study high- lights a greater need for patient education.

Computational Analysis of the Mature Unilateral Cleft Lip Nasal Deformity on Nasal Patency

Background

Nasal airway obstruction (NAO) due to nasal anatomic deformities is known to be more common among cleft patients than the general population, yet information is lacking regarding severity and variability of cleft-associated nasal obstruction relative to other conditions causing NAO. This preliminary study compares differences in NAO experienced by unilateral cleft lip nasal deformity (uCLND) subjects with noncleft subjects experiencing NAO.

Methods

Computational modeling techniques based on patient-specific computed tomography images were used to quantify the nasal airway anatomy and airflow dynamics in 21 subjects: 5 healthy normal subjects; 8 noncleft NAO subjects; and 8 uCLND subjects. Outcomes reported include Nasal Obstruction Symptom Evaluation (NOSE) scores, cross-sectional area, and nasal resistance.

Results

uCLND subjects had significantly larger cross-sectional area differences between the left and right nasal cavities at multiple cross sections compared with normal and NAO subjects. Median and interquartile range (IQR) NOSE scores between NAO and uCLND were 75 (IQR = 22.5) and 67.5 (IQR = 30), respectively. Airflow partition difference between both cavities were: median = 9.4%, IQR = 10.9% (normal); median = 31.9%, IQR = 25.0% (NAO); and median = 29.9%, IQR = 44.1% (uCLND). Median nasal resistance difference between left and right nasal cavities were 0.01 pa.s/ml (IQR = 0.03 pa.s/ml) for normal, 0.09 pa.s/ml (IQR = 0.16 pa.s/ml) for NAO and 0.08 pa.s/ml (IQR = 0.25 pa.s/ml) for uCLND subjects.

Conclusions

uCLND subjects demonstrated significant asymmetry between both sides of the nasal cavity. Furthermore, there exists substantial disproportionality in flow partition difference and resistance difference between cleft and noncleft sides among uCLND subjects, suggesting that both sides may be dysfunctional.

Investigating the effects of laryngotracheal stenosis on upper airway aerodynamics

OBJECTIVE

Very little is known about the impact of laryngotracheal stenosis (LTS) on inspiratory airflow and resistance, especially in air hunger states. This study investigates the effect of LTS on airway resistance and volumetric flow across three different inspiratory pressures.

METHODS

Head-and-neck computed tomography scans of 11 subjects from 2010 to 2016 were collected. Three-dimensional reconstructions of the upper airway from the nostrils to carina, including the oral cavity, were created for one subject with a normal airway and for 10 patients with LTS. Airflow simulations were conducted using computational fluid dynamics modeling at three different inspiratory pressures (10, 25, 40 pascals [Pa]) for all subjects under two scenarios: 1) inspiration through nostrils only (MC), and 2) through both nostrils and mouth (MO).

RESULTS

Volumetric flows in the normal subject at the three inspiratory pressures were considerably higher (MC: 11.8-26.1 L/min; MO: 17.2-36.9 L/min) compared to those in LTS (MC: 2.86-6.75 L/min; MO: 4.11-9.00 L/min). Airway resistances in the normal subject were 0.051 to 0.092 pascal seconds per milliliter (Pa.s)/mL (MC) and 0.035-0.065 Pa.s/mL (MO), which were approximately tenfold lower than those of subjects with LTS: 0.39 to 0.89 Pa.s/mL (MC) and 0.45 to 0.84 Pa.s/mL (MO). Furthermore, subjects with glottic stenosis had the greatest resistance, whereas subjects with subglottic stenosis had the greatest variability in resistance. Subjects with tracheal stenosis had the lowest resistance.

CONCLUSION

This pilot study demonstrates that LTS increases resistance and decreases airflow. Mouth breathing significantly improved airflow and resistance but cannot completely compensate for the effects of stenosis. Furthermore, location of stenosis appears to modulate the effect of the stenosis on resistance differentially.

LEVEL OF EVIDENCE

NA. Laryngoscope, 128:E141-E149, 2018.

Creation of an idealized nasopharynx geometry for accurate computational fluid dynamics simulations of nasal airflow in patient-specific models lacking the nasopharynx anatomy

Virtual surgery planning based on computational fluid dynamics (CFD) simulations has the potential to improve surgical outcomes for nasal airway obstruction patients, but the benefits of virtual surgery planning must outweigh the risks of radiation exposure. Cone beam computed tomography (CT) scans represent an attractive imaging modality for virtual surgery planning due to lower costs and lower radiation exposures compared with conventional CT scans. However, to minimize the radiation exposure, the cone beam CT sinusitis protocol sometimes images only the nasal cavity, excluding the nasopharynx. The goal of this study was to develop an idealized nasopharynx geometry for accurate representation of outlet boundary conditions when the nasopharynx geometry is unavailable. Anatomically accurate models of the nasopharynx created from 30 CT scans were intersected with planes rotated at different angles to obtain an average geometry. Cross sections of the idealized nasopharynx were approximated as ellipses with cross-sectional areas and aspect ratios equal to the average in the actual patient-specific models. CFD simulations were performed to investigate whether nasal airflow patterns were affected when the CT-based nasopharynx was replaced by the idealized nasopharynx in 10 nasal airway obstruction patients. Despite the simple form of the idealized geometry, all biophysical variables (nasal resistance, airflow rate, and heat fluxes) were very similar in the idealized vs patient-specific models. The results confirmed the expectation that the nasopharynx geometry has a minimal effect in the nasal airflow patterns during inspiration. The idealized nasopharynx geometry will be useful in future CFD studies of nasal airflow based on medical images that exclude the nasopharynx.

A Computational Study of Nasal Spray Deposition Pattern in Four Ethnic Groups

BACKGROUND

Very little is known about the role of nasal morphology due to ethnic variation on particle deposition pattern in the sinonasal cavity. This preliminary study utilizes computational fluid dynamics (CFD) modeling to investigate sinonasal airway morphology and deposition patterns of intranasal sprayed particles in the nose and sinuses of individuals from four different ethnic groups: African American (Black); Asian; Caucasian; and Latin American.

METHODS

Sixteen subjects (four from each ethnic group) with "normal" sinus protocol computed tomography (CT) were selected for CFD analysis. Three-dimensional reconstruction of each subject's sinonasal cavity was created from their personal CT images. CFD simulations were carried out in ANSYS Fluent(™) in two phases: airflow phase was done by numerically solving the Navier-Stokes equations for steady state laminar inhalation; and particle dispersed phase was solved by tracking injected (sprayed) particles through the calculated airflow field. A total of 10,000 particle streams were released from each nostril, 1000 particles per diameter ranging from 5 μm to 50 μm, with size increments of 5 μm.

RESULTS

As reported in the literature, Caucasians (5.31 ± 0.42 cm(-1)) and Latin Americans (5.16 ± 0.40cm(-1)) had the highest surface area to volume ratio, while African Americans had highest nasal index (95.91 ± 2.22). Nasal resistance (NR) was highest among Caucasians (0.046 ± 0.008 Pa.s/mL) and Asians (0.042 ± 0.016Pa.s/mL). Asians and African Americans had the most regions with particle deposition for small (5 μm-15 μm) and large (20 μm-50 μm) particle sizes, respectively. Asians and Latin Americans individuals had the most consistent regional particle deposition pattern in the main nasal cavities within their respective ethnic groups.

CONCLUSIONS

Preliminary results from these ethnic groups investigated showed that Caucasians and Latin Americans had the least patent nasal cavity. Furthermore, Caucasians and African Americans had the lowest inter-subject consistency in regional particle deposition pattern; this may be due to greater inter-subject variability in their respective nasal vestibule morphology.

Influence of Mesh Density on Airflow and Particle Deposition in Sinonasal Airway Modeling

BACKGROUND

There are methodological ambiguities in the literature on mesh refinement analysis for computational fluid dynamics (CFD) modeling of physiologically realistic airflow dynamics and particle transport in the human sinonasal cavity. To investigate grid independence in discretization of the (sino)nasal geometry, researchers have considered CFD variables such as pressure drop, velocity profile, wall shear, airflow, and particle deposition fractions. Standardization in nasal geometry is also lacking: unilateral or bilateral nasal cavities with and without paranasal sinuses have been used. These methodological variants have led to inconsistencies in establishing grid-independent mesh densities. The aim of this study is to provide important insight in the role of mesh refinement analysis on airflow and particle deposition in sinonasal airway modeling.

METHODS

A three-dimensional reconstruction of the complete sinonasal cavity was created from computed tomography images of a subject who had functional endoscopic sinus surgery. To investigate airflow grid independence, nine different tetrahedral mesh densities were generated. For particle transport mesh refinement analysis, hybrid tetrahedral-prism elements with near-wall prisms ranging from 1 to 6 layers were implemented. Steady-state, laminar inspiratory airflow simulations under physiologic pressure-driven conditions and nebulized particle transport simulations were performed with particle sizes ranging from 1-20 μm.

RESULTS

Mesh independence for sinonasal airflow was achieved with approximately 4 million unstructured tetrahedral elements. The hybrid mesh containing 4 million tetrahedral cells with three prism layers demonstrated asymptotic behavior for sinonasal particle deposition. Inclusion of boundary prism layers reduced deposition fractions relative to tetrahedral-only meshes.

CONCLUSIONS

To ensure numerically accurate simulation results, mesh refinement analyses should be performed for both airflow and particle transport simulations. Tetrahedral-only meshes overpredict particle deposition and are less accurate than hybrid tetrahedral-prism meshes.

A computational study of functional endoscopic sinus surgery and maxillary sinus drug delivery

BACKGROUND

Topical medication is increasingly used following functional endoscopic sinus surgery (FESS). Information on particle sizes that maximise maxillary sinus (MS) delivery is conflicting, and the effect of antrostomy size on delivery is unclear. The purpose of this study was to estimate antrostomy and particle size effects on topical MS drug delivery.

METHODOLOGY

Sinonasal reconstructions were created from a pre- and a post-FESS CT scan in each of four chronic rhinosinusitis patients. Additional models were created from each post-FESS reconstruction representing four alternative antrostomy sizes. Airflow and particle deposition were simulated in each reconstruction using computational fluid dynamics for nebulised and sprayed delivery.

RESULTS

MS ventilation and drug delivery increased following FESS, the largest virtual antrostomy led to greatest delivery, and MS delivery was sensitive to particle size. Particles within a 5-18 μm and 5-20 μm size range led to peak MS deposition for nebulised and sprayed particles, respectively. Post-FESS increases in drug delivery varied across individuals and within individuals by the type of antrostomy created.

CONCLUSION

Our findings suggest that FESS, particularly with larger antrostomies, improves topical drug delivery, and that certain particle sizes improve this delivery. Further research is needed to contextualise these findings with other post-surgical effects.

A computational study of functional endoscopic sinus surgery and maxillary sinus drug delivery

BACKGROUND

Topical medication is increasingly used following functional endoscopic sinus surgery (FESS). Information on particle sizes that maximise maxillary sinus (MS) delivery is conflicting, and the effect of antrostomy size on delivery is unclear. The purpose of this study was to estimate antrostomy and particle size effects on topical MS drug delivery.

METHODOLOGY

Sinonasal reconstructions were created from a pre- and a post-FESS CT scan in each of four chronic rhinosinusitis patients. Additional models were created from each post-FESS reconstruction representing four alternative antrostomy sizes. Airflow and particle deposition were simulated in each reconstruction using computational fluid dynamics for nebulised and sprayed delivery.

RESULTS

MS ventilation and drug delivery increased following FESS, the largest virtual antrostomy led to greatest delivery, and MS delivery was sensitive to particle size. Particles within a 5-18 μm and 5-20 μm size range led to peak MS deposition for nebulised and sprayed particles, respectively. Post-FESS increases in drug delivery varied across individuals and within individuals by the type of antrostomy created.

CONCLUSION

Our findings suggest that FESS, particularly with larger antrostomies, improves topical drug delivery, and that certain particle sizes improve this delivery. Further research is needed to contextualise these findings with other post-surgical effects.

Quantification of airflow into the maxillary sinuses before and after functional endoscopic sinus surgery

BACKGROUND

The effects of increases in maxillary sinus (MS) airflow following functional endoscopic sinus surgery (FESS) are unknown. The goal of this study was to quantify the effects of FESS on airflow into the MS in a cohort of patients with chronic rhinosinusitis, and compare MS flow rate with patient-reported outcome measures.

METHODS

A pilot study was conducted in which preoperative and postoperative computed tomography scans of 4 patients undergoing bilateral or unilateral FESS were used to create 3-dimensional (3D) reconstructions of the nasal airway and paranasal sinuses using Mimics™ (Materialise, Inc.). The size of the maxillary antrostomies post-FESS ranged from 107 to 160 mm(2). Computational meshes were generated from the 3D reconstructions, and steady-state, laminar, inspiratory airflow was simulated in each mesh using the computational fluid dynamics (CFD) software Fluent™ (ANSYS, Inc.) under physiologic, pressure-driven conditions. Airflow into the MS was estimated from the simulations and was compared preoperatively and postoperatively. In addition, patients completed preoperative and postoperative Rhinosinusitis Outcome Measure-31 (RSOM-31) questionnaires and scores were compared with MS airflow rates.

RESULTS

CFD simulations predicted that average airflow rate into post-FESS MS increased by 18.5 mL/second, and that average flow velocity into the MS more than quadrupled. Simulation results also showed that MS flow rate trended with total RSOM-31 and all domain scores.

CONCLUSION

CFD simulations showed that the healed maxillary antrostomy after FESS can greatly enhance airflow into the MS. Our pilot study suggests that to some extent, increasing airflow into the MS may potentially improve chronic rhinosinusitis patients' quality of life pre-FESS and post-FESS.