A computational fluid dynamics model for drug delivery in a nasal cavity with inferior turbinate hypertrophy

Recent In Vitro and In Silico Advances in the Understanding of Intranasal Drug Delivery

BACKGROUND

Many drugs are delivered intranasally for local or systemic effect, typically in the form of droplets or aerosols. Due to the high cost of in vivo studies, drug developers and researchers often turn to in vitro or in silico testing when first evaluating the behavior and properties of intranasal drug delivery devices and formulations. Recent advances in manufacturing and computer technologies have allowed for increasingly realistic and sophisticated in vitro and in silico reconstructions of the human nasal airways.

OBJECTIVE

The study aims to perform a summary of advances in the understanding of intranasal drug delivery based on recent in vitro and in silico studies.

CONCLUSION

The turbinates are a common target for local drug delivery applications, and while nasal sprays are able to reach this region, there is currently no broad consensus across the in vitro and in silico literature concerning optimal parameters for device design, formulation properties and patient technique which would maximize turbinate deposition. Nebulizers can more easily target the turbinates, but come with the disadvantage of significant lung deposition. Targeting of the olfactory region of the nasal cavity has been explored for the potential treatment of central nervous system conditions. Conventional intranasal devices, such as nasal sprays and nebulizers, deliver very little dose to the olfactory region. Recent progress in our understanding of intranasal delivery will be useful in the development of the next generation of intranasal drug delivery devices.

An Overview of Computational Fluid Dynamics Preoperative Analysis of the Nasal Airway

Evaluation of the nasal airway is crucial for every patient with symptoms of nasal obstruction as well as for every patient with other nasal symptoms. This assessment of the nasal airway comprises clinical examination together with imaging studies, with the correlation between findings of this evaluation and symptoms reported by the patient being based on the experience of the surgeon. Measuring nasal airway resistance or nasal airflow can provide additional data regarding the nasal airway, but the benefit of these objective measurements is limited due to their lack of correlation with patient-reported evaluation of nasal breathing. Computational fluid dynamics (CFD) has emerged as a valuable tool to assess the nasal airway, as it provides objective measurements that correlate with patient-reported evaluation of nasal breathing. CFD is able to evaluate nasal airflow and measure variables such as heat transfer or nasal wall shear stress, which seem to reflect the activity of the nasal trigeminal sensitive endings that provide sensation of nasal breathing. Furthermore, CFD has the unique capacity of making airway analysis of virtual surgery, predicting airflow changes after trial virtual modifications of the nasal airway. Thereby, CFD can assist the surgeon in deciding surgery and selecting the surgical techniques that better address the features of each specific nose. CFD has thus become a trend in nasal airflow assessment, providing reliable results that have been validated for analyzing airflow in the human nasal cavity. All these features make CFD analysis a mainstay in the armamentarium of the nasal surgeon. CFD analysis may become the gold standard for preoperative assessment of the nasal airway.

Positional Installation of Intranasal Corticosteroids in the Treatment of Chronic Rhinosinusitis: A Systematic Review of the Literature

OBJECTIVES

First-line treatment of chronic rhinosinusitis includes topical corticosteroids aimed at decreasing inflammation of sinonasal mucosa. No guidelines exist regarding the effect of head position during administration of corticosteroids. We hypothesize certain positions enhance delivery to the paranasal sinuses, with further improvement in delivery after sinus surgery.

METHODS

A systematic review of the literature was conducted using Medline Ovid, Embase, Scopus, and Cochrane databases. All studies evaluating intranasal medications administered in 2 or more head positions were included. Study population, head position(s), method/volume of delivery, and outcome metrics were recorded.

RESULTS

Twenty-four studies compared head positions and their role in distribution of intranasal medication. Of 12 papers studying surgically naive subjects, 6 found improvement in delivery to specific sinonasal regions (middle meatus; lateral, superior, or posterior nasal cavity) and/or symptomatic improvement, in the lying head back (LHB) or head down and forward (HDF) positions, but only 3 reached statistical significance. Of 12 papers studying surgically altered patients, 10 found delivery improved in the HDF, LHB, and head forward 45° or 90° positions. Of 5 studies of extended frontal sinus procedures (Draf IIb/III), a majority found distribution to the frontal sinus improved with the head forward 90° position. Patients found the HDF position most uncomfortable.

CONCLUSIONS

Studies found no statistically significant difference in distribution to unoperated sinuses among different head positions. A minority of studies supported the use of the LHB and HDF positions. This suggests that in surgically naive patients, intranasal corticosteroid delivery to sinonasal regions and/or symptomatic improvement may be best achieved with the sinuses positioned inferior to the delivery device. Surgery improved distribution to the paranasal sinuses regardless of head position, although tilting the head forward 90° was particularly effective in delivery to the frontal sinus after extended frontal sinus procedures.

The effect of nasal shape on the thermal conditioning of inhaled air: Using clinical tomographic data to build a large-scale statistical shape model

In this paper, we investigate the heating function of the nasal cavity qualitatively, using a high-quality, large-scale statistical shape model. This model consists of a symmetrical and an asymmetrical part and provides a new and unique way of examining changes in nasal heating function resulting from natural variations in nasal shape (as obtained from 100 clinical CT scans). Data collected from patients suffering from different nasal or sinus-related complaints are included. Parameterized models allow us to investigate the effect of continuous deviations in shape from the mean nasal cavity. This approach also enables us to avoid many of the compounded effects on flow and heat exchange, which one would encounter when comparing different patient-specific models. The effects of global size, size-related features, and turbinate size are investigated using the symmetrical shape model. The asymmetrical model is used to investigate different types of septal deviation using Mladina's classification. The qualitative results are discussed and compared with findings from the existing literature.

Predicting drug delivery efficiency into tumor tissues through molecular simulation of transport in complex vascular networks

Efficient delivery of anticancer drugs into tumor tissues at maximally effective and minimally toxic concentrations is vital for therapeutic success. At present, no method exists that can predict the spatial and temporal distribution of drugs into a target tissue after administration of a specific dose. This prevents accurate estimation of optimal dosage regimens for cancer therapy. Here we present a new method that predicts quantitatively the time-dependent spatial distribution of drugs in tumor tissues at sub-micrometer resolution. This is achieved by modeling the diffusive flow of individual drug molecules through the three-dimensional network of blood-vessels that vascularize the tumor, and into surrounding tissues, using molecular mechanics techniques. By evaluating delivery into tumors supplied by a series of blood-vessel networks with varying degrees of complexity, we show that the optimal dose depends critically on the precise vascular structure. Finally, we apply our method to calculate the optimal dosage of the cancer drug doxil into a section of a mouse ovarian tumor, and demonstrate the enhanced delivery of liposomally administered doxorubicin when compared to free doxorubicin. Comparison with experimental data and a multiple-compartment model show that the model accurately recapitulates known pharmacokinetics and drug-load predictions. In addition, it provides, for the first time, a detailed picture of the spatial dependence of drug uptake into tissues surrounding tumor vasculatures. This approach is fundamentally different to current continuum models, and reveals that the target tumor vascular topology is as important for therapeutic success as the transport properties of the drug delivery platform itself. This sets the stage for revisiting drug dosage calculations.

Examining mesh independence for flow dynamics in the human nasal cavity

Increased computational resources provide new opportunities to explore sophisticated respiratory modelling. A survey of recent publications showed a steady increase in the number of mesh elements used in computational models over time. Complex geometries such as the nasal cavity exhibit sharp gradients and irregular curvatures, leading to abnormal flow development across their surfaces. As such, a robust method for examining the near-wall mesh resolution is required. The non-dimensional wall unit y⁺ (often used in turbulent flows) was used as a parameter to evaluate the near-wall mesh in laminar flows. Mesh independence analysis from line profiles showed that the line location had a significant influence on the result. Furthermore, using a single line profile as a measure for mesh convergence was unsuitable for representing the entire flow field. To improve this, a two-dimensional (2D) cross-sectional plane subtraction method where scalar values (such as the velocity magnitude) on a cross-sectional plane were interpolated onto a regularly spaced grid was proposed. The new interpolated grid values from any two meshed models could then be compared for changes caused by the different meshed models. The application of this method to three-dimensional (3D) volume subtraction was also demonstrated. The results showed that if the near-wall mesh was sufficiently refined, then narrow passages were less reliant on the overall mesh size. However, in wider passages, velocity magnitudes were sensitive to mesh size, requiring a more refined mesh.

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.

A computational analysis of nasal vestibule morphologic variabilities on nasal function

Although advances in computational modeling have led to increased understanding of nasal airflow, not much is known about the effects of normal sinonasal anatomic variabilities on nasal function. In this study, three distinct variations in the human nasal vestibule airspace that have not been previously described were identified. Computational fluid dynamics modeling of nasal airflow profile in each identified variation of nasal vestibule phenotype was conducted to assess the role of these phenotypes on nasal physiology. Three-dimensional reconstructions of the nasal geometry in sixteen subjects with normal radiographic sinonasal images were created and each respective unilateral nasal cavity was classified as Notched, Standard, or Elongated phenotype based nasal vestibule morphology. Steady state, laminar and incompressible flow simulations were performed in the nasal geometries under physiological, pressure-driven conditions with constant inspiratory pressure. Results showed that at localized regions of the unilateral nasal cavity, average resistance was significantly different among nasal vestibule phenotypes. However, global comparison from nostril to choana showed that average resistance was not significantly different across phenotypes; suggesting that with normal anatomic variations, the nose has a natural compensatory mechanism that modulates localized airflow in order to achieve a desired amount of global airflow.

A Method for Accurate Reconstructions of the Upper Airway Using Magnetic Resonance Images

Objective

The purpose of this study is to provide an optimized method to reconstruct the structure of the upper airway (UA) based on magnetic resonance imaging (MRI) that can faithfully show the anatomical structure with a smooth surface without artificial modifications.

Methods

MRI was performed on the head and neck of a healthy young male participant in the axial, coronal and sagittal planes to acquire images of the UA. The level set method was used to segment the boundary of the UA. The boundaries in the three scanning planes were registered according to the positions of crossing points and anatomical characteristics using a Matlab program. Finally, the three-dimensional (3D) NURBS (Non-Uniform Rational B-Splines) surface of the UA was constructed using the registered boundaries in all three different planes.

Results

A smooth 3D structure of the UA was constructed, which captured the anatomical features from the three anatomical planes, particularly the location of the anterior wall of the nasopharynx. The volume and area of every cross section of the UA can be calculated from the constructed 3D model of UA.

Conclusions

A complete scheme of reconstruction of the UA was proposed, which can be used to measure and evaluate the 3D upper airway accurately.

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.

Current understanding of nasal morphology and physiology as a drug delivery target

The nasal cavity is both a target for locally and systemically acting medications. An adequate treatment for rhinosinusitis continues to be an unmet need. With the recent approval of intranasal medications for the treatment of pain, the nasal cavity continues to be a viable route for rapid uptake into the systemic circulation. Despite the opportunities, there is still a void in the knowledge of how therapeutic entities interact with the nasal epithelium. In addition, new opportunities in mucosal immunity via nasal vaccination as well as the elusive nose to brain uptake continue to drive innovation. To facilitate understanding of the issues involved that facilitate drug delivery in the nose, a review of nasal morphology and physiology is presented.

Deviated nasal septum hinders intranasal sprays: a computer simulation study

BACKGROUND

This study investigates how deviated nasal septum affects the quantity and distribution of spray particles, and examines the effects of inspiratory airflow and head position on particle transport.

METHODS

Deposition of spray particles was analysed using a three-dimensional computational fluid dynamics model created from a computed tomography scan of a human nose with leftward septal deviation and a right inferior turbinate hypertrophy. Five simulations were conducted using FluentTM software, with particle sizes ranging from 20-110 μm, a spray speed of 3 m/s, plume angle of 68(deg), and with steady state inspiratory airflow either present (15.7 L/min) or absent at varying head positions.

RESULTS

With inspiratory airflow present, posterior deposition on the obstructed side was approximately four times less than the contralateral side, regardless of head position, and was statistically significant. When airflow was absent, predicted deposition beyond the nasal valve on the left and right sides were between 16% and 69% lower and positively influenced by a dependent head position.

CONCLUSION

Simulations predicted that septal deviation significantly diminished drug delivery on the obstructed side. Furthermore, increased particle penetration was associated with presence of nasal airflow. Head position is an important factor in particle deposition patterns when inspiratory airflow is absent.

Impacts of fluid dynamics simulation in study of nasal airflow physiology and pathophysiology in realistic human three-dimensional nose models

During the past decades, numerous computational fluid dynamics (CFD) studies, constructed from CT or MRI images, have simulated human nasal models. As compared to rhinomanometry and acoustic rhinometry, which provide quantitative information only of nasal airflow, resistance, and cross sectional areas, CFD enables additional measurements of airflow passing through the nasal cavity that help visualize the physiologic impact of alterations in intranasal structures. Therefore, it becomes possible to quantitatively measure, and visually appreciate, the airflow pattern (laminar or turbulent), velocity, pressure, wall shear stress, particle deposition, and temperature changes at different flow rates, in different parts of the nasal cavity. The effects of both existing anatomical factors, as well as post-operative changes, can be assessed. With recent improvements in CFD technology and computing power, there is a promising future for CFD to become a useful tool in planning, predicting, and evaluating outcomes of nasal surgery. This review discusses the possibilities and potential impacts, as well as technical limitations, of using CFD simulation to better understand nasal airflow physiology.

Computed nasal resistance compared with patient-reported symptoms in surgically treated nasal airway passages: a preliminary report

BACKGROUND

Nasal airway obstruction (NAO) is a common health condition impacting mood, energy, recreation, sleep, and overall quality of life. Nasal surgery often addresses NAO but the results are sometimes unsatisfactory. Evaluating surgical treatment efficacy could be improved if objective tests were available that correlated with patient-reported measures of symptoms. The goal of this study was to develop methods for comparing nasal resistance computed by computational fluid dynamics (CFD) models with patient-reported symptoms of NAO using early data from a 4-year prospective study.

METHODS

Computed tomography (CT) scans and patient-reported scores from the Nasal Obstruction Symptom Evaluation (NOSE) scale and a visual analog scale (VAS) measuring unilateral airflow sensation were obtained pre- and postoperatively in two NAO patients showing no significant mucosal asymmetry who were successfully treated with functional nasal surgery, including septoplasty. Pre- and postsurgery CFD models were created from the CT scans. Numerical simulation of steady-state inspiratory airflow was used to calculate bilateral and unilateral CFD-derived nasal resistance (CFD-NR).

RESULTS

In both subjects, NOSE and VAS scores improved after surgery, bilateral CFD-NR decreased, and unilateral CFD-NR decreased on the affected side. In addition, NOSE and VAS scores tracked with unilateral CFD-NR on the affected side.

CONCLUSION

These preliminary results suggest a possible correlation between unilateral NR and patient-reported symptoms and imply that analysis of unilateral obstruction should focus on the affected side. A formal investigation of unilateral CFD-NR and patient-reported symptoms in a series of NAO patients is needed to determine if these variables are correlated.

Computed intranasal spray penetration: comparisons before and after nasal surgery

BACKGROUND

Quantitative methods for comparing intranasal drug delivery efficiencies pre- and postoperatively have not been fully utilized. The objective of this study is to use computational fluid dynamics techniques to evaluate aqueous nasal spray penetration efficiencies before and after surgical correction of intranasal anatomic deformities.

METHODS

Ten three-dimensional models of the nasal cavities were created from pre- and postoperative computed tomography scans in 5 subjects. Spray simulations were conducted using a particle size distribution ranging from 10 μm to 110 μm, a spray speed of 3 m/second, plume angle of 68 degrees, and with steady state, resting inspiratory airflow present. Two different nozzle positions were compared. Statistical analysis was conducted using Student t test for matched pairs.

RESULTS

On the obstructed side, posterior particle deposition after surgery increased by 118% and was statistically significant (p = 0.036), while anterior particle deposition decreased by 13% and was also statistically significant (p = 0.020). The fraction of particles that bypassed the airways either pre- or postoperatively was less than 5%. Posterior particle deposition differences between obstructed and contralateral sides of the airways were 113% and 30% for pre- and postsurgery, respectively. Results showed that nozzle positions can influence spray delivery.

CONCLUSION

Simulations predicted that surgical correction of nasal anatomic deformities can improve spray penetration to areas where medications can have greater effect. Particle deposition patterns between both sides of the airways are more evenly distributed after surgery. These findings suggest that correcting anatomic deformities may improve intranasal medication delivery. For enhanced particle penetration, patients with nasal deformities may explore different nozzle positions.

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.

Effects of anatomy and particle size on nasal sprays and nebulizers

OBJECTIVE

To study the effects of nasal deformity on aerosol penetration past the nasal valve (NV) for varying particle sizes using sprays or nebulizers.

STUDY DESIGN

Computed mathematical nasal airway model.

SETTING

Department computer lab.

SUBJECTS AND METHODS

Particle deposition was analyzed using a computational fluid dynamics model of the human nose with leftward septal deviation and compensatory right inferior turbinate hypertrophy. Sprays were simulated for 10 µm, 20 µm, 50 µm, or particle sizes following a Rosin Rammler particle size distribution (10-110 µm), at speeds of 1, 3, or 10 meters per second. Nebulization was simulated for 1, 3.2, 6.42, or 10 µm particles. Steady state inspiratory airflow was simulated at 15.7 liters per minute.

RESULTS

Sprays predicted higher NV penetration on the right side for particle sizes >10 µm, with comparable penetration on both sides at 10 µm. Nearly 100% deposited in the nasal passages for all spray characteristics. Nebulizer predictions showed nearly 100% of particles <6.42 µm and more than 50% of 6.42 µm bypassing both sides of the nose without depositing. Of the nebulized particles that deposited, penetration was higher on the right at 10 µm, with comparable penetration on both sides at 6.42 µm. Spray penetration was highest at 10 µm, with more than 96% penetrating on both sides at 1 and 3 meters per second. Nebulization penetration was also highest at 10 µm (40% on the left, >90% on the right).

CONCLUSION

In the presence of a septal deviation, sprays or nebulizers containing 10-µm particles may have good penetration beyond the NV. Nebulized particles <10 µm are likely to be respirable. Additionally, spray speeds above 3 meters per second may limit penetration.