Changes in aerodynamics during vocal cord dysfunction

Computational fluid dynamics of upper airway aerodynamics for exercise-induced laryngeal obstruction: A feasibility study

Objective

Use of computational fluid dynamic (CFD) simulations to measure the changes in upper airway geometry and aerodynamics during (a) an episode of Exercise-Induced Laryngeal Obstruction (EILO) and (b) speech therapy exercises commonly employed for patients with EILO.

Methods

Magnetic resonance imaging stills of the upper airway including the nasal and oral cavities from an adult female were used to re-construct three-dimensional geometries of the upper airway. The CFD simulations were used to compute the maximum volume flow rate (l/s), pressure (Pa), airflow velocity (m/s) and area of cross-section opening in eight planes along the vocal tract, separately for inhalation and exhalation.

Results

Numerical predictions from three-dimensional geometrical modeling of the upper airway suggest that the technique of nose breathing for inhalation and pursed lip breathing for exhalation show most promising pressure conditions and cross-sectional diameters for rescue breathing exercises. Also, if EILO is due to the constriction at the vocal fold level, then a quick sniff may also be a proper rescue inhalation exercise. EILO affects both the inspiratory and the expiratory phases of breathing.

Conclusions

A prior knowledge of the supraglottal aerodynamics and the corresponding upper airway geometry from CFD analysis has the potential to assist the clinician in choosing the most effective rescue breathing technique for optimal functional outcome of speech therapy intervention in patients with EILO and in understanding the pathophysiology of EILO on a case-by-case basis with future studies.

Level of Evidence

4.

A computational analysis on the impact of multilevel laryngotracheal stenosis on airflow and drug particle dynamics in the upper airway

Laryngotracheal stenosis (LTS) is a type of airway narrowing that is frequently caused by intubation-related trauma. LTS can occur at one or multiple locations in the larynx and/or trachea. This study characterizes airflow dynamics and drug delivery in patients with multilevel stenosis. Two subjects with multilevel stenosis (S1 = glottis + trachea, S2 = glottis + subglottis) and one normal subject were retrospectively selected. Computed tomography scans were used to create subject-specific upper airway models. Computational fluid dynamics modeling was used to simulate airflow at inhalation pressures of 10, 25, and 40 Pa, and orally inhaled drug transport with particle velocities of 1, 5, and 10 m/s, and particle size range of 100 nm-40 µm. Subjects had increased airflow velocity and resistance at stenosis with decreased cross-sectional area (CSA): S1 had the smallest CSA at trachea (0.23 cm2) and resistance = 0.3 Pa·s/mL; S2 had the smallest CSA at glottis (0.44 cm2), and resistance = 0.16 Pa·s/mL. S1 maximal stenotic deposition was 4.15% at trachea; S2 maximal deposition was 2.28% at glottis. Particles of 11-20 µm had the greatest deposition, 13.25% (S1-trachea) and 7.81% (S2-subglottis). Results showed differences in airway resistance and drug delivery between subjects with LTS. Less than 4.2% of orally inhaled particles deposited at stenosis. Particle sizes with most stenotic deposition were 11-20 µm and may not represent typical particle sizes emitted by current-use inhalers.

Computational fluid dynamics model of laryngotracheal stenosis and correlation to pulmonary function measures

3D models of airway lumens were created from CT scans of 19 patients with laryngotracheal stenosis. Computational fluid dynamics (CFD) simulations were completed for each, and results were compared to measured peak inspiratory flow rate, grade of lumen constriction, and measures of airway geometry. Results demonstrate flow resistance and shear stress correlate with degree of lumen constriction and absolute cross-sectional area as well as flow rate. Flow recirculation depends on airway constriction but does not vary with flow rate. Resistance and wall shear stress did not correlate well with functional measures. Flow recirculation did differ between subjects with higher functional measures and subjects with lower functional measures. This analysis provides mathematical models to predict airway resistance, wall shear stress, and flow reversal according lumen constriction and inspiratory flow rate. It suggests aerodynamic factors such as flow recirculation play a role in differences in functional performance between patients with similar airway measures.

Comparison of Inhaled Drug Delivery in Patients With One- and Two-level Laryngotracheal Stenosis

OBJECTIVES/HYPOTHESIS

Laryngotracheal stenosis (LTS) is a functionally devastating condition with high respiratory morbidity and mortality. This preliminary study investigates airflow dynamics and stenotic drug delivery in patients with one- and two-level LTS.

STUDY DESIGN

A Computational Modeling Restropective Cohort Study.

METHODS

Computed tomography scans from seven LTS patients, five with one-level (three subglottic, two tracheal), and two with two-level (glottis + trachea, glottis + subglottis) were used to reconstruct patient-specific three-dimensional upper airway models. Airflow and orally inhaled drug particle transport were simulated using computational fluid dynamics modeling. Drug particle transport was simulated for 1-20 μm particles released into the mouth at velocities of 0 m/s, 1 m/s, 3 m/s, and 10 m/s for metered dose inhaler (MDI) and 0 m/s for dry powder inhaler (DPI) simulations. Airflow resistance and stenotic drug deposition in the patients' airway models were compared.

RESULTS

Overall, there was increased airflow resistance at stenotic sites in subjects with two-level versus one-level stenosis (0.136 Pa s/ml vs. 0.069 Pa s/ml averages). Subjects with two-level stenosis had greater particle deposition at sites of stenosis compared to subjects with one-level stenosis (average deposition 2.31% vs. 0.96%). One-level stenosis subjects, as well as one two-level stenosis subject, had the greatest deposition using MDI with a spacer (0 m/s): 2.59% and 4.34%, respectively. The second two-level stenosis subject had the greatest deposition using DPI (3.45%). Maximum deposition across all stenotic subtypes except one-level tracheal stenosis was achieved with particle sizes of 6-10 μm.

CONCLUSIONS

Our results suggest that patients with two-level LTS may experience a more constricted laryngotracheal airflow profile compared to patients with one-level LTS, which may enhance overall stenotic drug deposition.

LEVEL OF EVIDENCE

NA Laryngoscope, 133:366-374, 2023.

Biaxial mechanical properties of the bronchial tree: Characterization of elasticity, extensibility, and energetics, including the effect of strain rate and preconditioning

Distal airways commonly obstruct in lung disease and despite their importance, their mechanical properties are vastly underexplored. The lack of bronchial experiments restricts current airway models to either assume rigid structures, or extrapolate the material properties of the trachea to represent the small airways. Furthermore, past works are exclusively limited to uniaxial testing; investigating the multidirectional tensile loads of both the proximal and distal pulmonary airways is long overdue. Here we present comprehensive mechanical and viscoelastic properties of the porcine airway tree, including the trachea, trachealis muscle, large bronchi, and small bronchi, via measures of elasticity, extensibility, and energetics to explore regional and directional dependencies, cross-examining strain rate and preconditioning effects using planar equibiaxial tensile tests for the first time. We find bronchial regions are notably heterogeneous, where the trachea exhibits greater stiffness, energy loss, and preconditioning sensitivity than the smaller airways. Interestingly, the trachealis muscle is similar to the distal bronchi, despite being anatomically located adjacent to the proximal ring. Tissues are anisotropic and axially stiffer under initial loading, losing more energy with greater stress relaxation circumferentially. Strain rate dependency is also noted, where tissues are more energetically efficient at the faster strain rate, likely attributable to the microstructure. Findings highlight assumptions of homogeneity and isotropy are inadequate, and enable the improvement of aerosol flow and dynamic airway deformation computational predictive models. These results provide much needed fundamental material properties for future explorations contrasting healthy versus diseased pulmonary airway mechanics to better understand the relationship between structure and lung function. STATEMENT OF SIGNIFICANCE: We present comprehensive multiaxial mechanical tensile experiments of the proximal and distal airways via measures of maximum stress, initial and ultimate moduli, strain and stress transitions, hysteresis, energy loss, and stress relaxation, and further assess preconditioning and strain rate dependencies to examine the relationship between lung function and structure. The mechanical response of the bronchial tree demonstrates significant anisotropy and heterogeneity, even within the tracheal ring, and emphasizes that contrary to past studies, the behavior of the proximal airways cannot be extended to distal bronchial tree analyses. Establishing these material properties is critical to advancing our understanding of airway function and in developing accurate computational simulations to help diagnose and monitor pulmonary diseases.

Evaluation of computational fluid dynamics models for predicting pediatric upper airway airflow characteristics

Computational fluid dynamics (CFD) has the potential for use as a clinical tool to predict the aerodynamics and respiratory function in the upper airway (UA) of children; however, careful selection of validated computational models is necessary. This study constructed a 3D model of the pediatric UA based on cone beam computed tomography (CBCT) imaging. The pediatric UA was 3D printed for pressure and velocity experiments, which were used as reference standards to validate the CFD simulation models. Static wall pressure and velocity distribution inside of the UA under inhale airflow rates from 0 to 266.67 mL/s were studied by CFD simulations based on the large eddy simulation (LES) model and four Reynolds-averaged Navier-Stokes (RANS) models. Our results showed that the LES performed best for pressure prediction; however, it was much more time-consuming than the four RANS models. Among the RANS models, the Low Reynolds number (LRN) SST k-ω model had the best overall performance at a series of airflow rates. Central flow velocity determined by particle image velocimetry was 3.617 m/s, while velocities predicted by the LES, LRN SST k-ω, and k-ω models were 3.681, 3.532, and 3.439 m/s, respectively. All models predicted jet flow in the oropharynx. These results suggest that the above CFD models have acceptable accuracy for predicting pediatric UA aerodynamics and that the LRN SST k-ω model has the most potential for clinical application in pediatric respiratory studies.

Fluid dynamics of the upper airway in pediatric patients with severe laryngomalacia

Laryngomalacia is the top cause of pediatric laryngeal wheeze. We used computational fluid dynamics to study the inspiratory airflow dynamics in severe pediatric laryngomalacia. Computed tomography was performed on the upper airways of two infants, one with severe laryngomalacia and one with normal airway, and 3D models were reconstructed. ANSYS CFD-POST software was used to simulate airflow in these models to compare the volumetric flow rate, flow velocity, pressure, wall shear, and vortex. The volume flow rate in the laryngomalacia model was significantly reduced compared with the control model. Under inspiratory pressures, the peak flow velocity, pressure, and shear force in the control model appeared at the soft palate stenosis, while that in the laryngomalacia model appeared at the supraglottis stenosis. In both models, the maximum flow velocity and shear force increased with decreasing inspiratory pressure, while the minimum pressure decreased with decreasing inspiratory pressure. In the control model, the airflow vortex appeared anteriorly below the posterior section of the soft palate. In the laryngomalacia model, the vortex appeared anteriorly below the posterior section of the soft palate and anteriorly below the vocal folds. Our methodology provides a new mechanistic understanding of pediatric laryngomalacia.

Analysis of the Effectiveness of Arytenoidectomy and Posterior Cordectomy with the Use of CFD Airflow Measurements in Patients with BVFP: A Retrospective Study

PURPOSE

Bilateral vocal fold paralysis (BVFP) is a rare larynx disease manifested by dyspnea, which often requires surgical treatment. The aim of the study is to determine the effectiveness of unilateral arytenoidectomy with posterior cordectomy in the treatment of BVFP using the computational fluid dynamics (CFD) method.

METHODS

This study included 33 patients with BVFP who underwent unilateral laser arytenoidectomy with posterior cordectomy. Glottis area measurements and spirometry, as well as a self-assessment of respiratory efficiency were performed before the surgery and after the recovery period. Using the CFD method, computer models of the glottis were made. Then, changes in air pressure gradient and maximum air velocity at the level of glottis were calculated, and local fields of pressure and air velocities were obtained.

RESULTS

The values of glottal surface area (S), spirometry parameters (forced expiratory volume in one second (FEV1), forced vital capacity (FVC), and peak expiratory flow (PEF)), inlet air velocity at the glottal level as well as patients self-assessment of respiratory efficiency turned out to be significantly higher after the operation. The values of maximum velocity at the glottal level, pressure gradient at the glottal level turned out to be significantly lower after the surgery. We observed that the greater the increase in glottal surface area, the greater the decrease in self-assessment scales (visual analogue scale (VAS) and Medical Research Council (MRC)). Increased levels of spirometry parameters after the surgery correlated with smaller decrease of PEF-dependent pressure gradient at the glottal level (PEFΔP CFD).

CONCLUSION

Unilateral laser arytenoidectomy with posterior cordectomy is an effective method for the treatment of BVFP. CFD is a useful tool to determine and visualize the effectiveness of surgical treatment in BVFP.

Orally Inhaled Drug Particle Transport in Computerized Models of Laryngotracheal Stenosis

OBJECTIVE

Adjuvant management for laryngotracheal stenosis (LTS) may involve inhaled corticosteroids, but metered dose inhalers are designed for pulmonary drug delivery. Comprehensive analyses of drug particle deposition efficiency for orally inhaled corticosteroids in the stenosis of LTS subjects are lacking.

STUDY DESIGN

Descriptive research.

SETTING

Academic medical center.

METHODS

Anatomically realistic 3-dimensional reconstructions of the upper airway were created from computed tomography images of 4 LTS subjects-2 subglottic stenosis and 2 tracheal stenosis subjects. Computational fluid dynamics modeling was used to simulate airflow and drug particle transport in each airway. Three inhalation pressures were simulated, 10 Pa, 25 Pa, and 40 Pa. Drug particle transport was simulated for 100 to 950 nanoparticles and 1 to 50 micron-particles. Particles were released into the airway to mimic varying inhaler conditions with and without a spacer chamber.

RESULTS

Based on smallest to largest cross-sectional area ratio, the laryngotracheal stenotic segment shrunk by 57% and 47%, respectively, for subglottic stenosis models and by 53% for both tracheal stenosis models. Airflow resistance at the stenotic segment was lower in subglottic stenosis models than in tracheal stenosis models: 0.001 to 0.011 Pa.s/mL vs 0.024 to 0.082 Pa.s/mL. Drug depositions for micron-particles and nanoparticles at stenosis were 0.06% to 2.48% and 0.10% to 2.60% for subglottic stenosis and tracheal stenosis models, respectively. Particle sizes with highest stenotic deposition were 6 to 20 µm for subglottic stenosis models and 1 to 10 µm for tracheal stenosis models.

CONCLUSION

This study suggests that at most, 2.60% of inhaled drug particles deposit at the stenosis. Particle size ranges with highest stenotic deposition may not represent typical sizes emitted by inhalers.

The effect of airway motion and breathing phase during imaging on CFD simulations of respiratory airflow

RATIONALE

Computational fluid dynamics (CFD) simulations of respiratory airflow can quantify clinically useful information that cannot be obtained directly, such as the work of breathing (WOB), resistance to airflow, and pressure loss. However, patient-specific CFD simulations are often based on medical imaging that does not capture airway motion and thus may not represent true physiology, directly affecting those measurements.

OBJECTIVES

To quantify the variation of respiratory airflow metrics obtained from static models of airway anatomy at several respiratory phases, temporally averaged airway anatomies, and dynamic models that incorporate physiological motion.

METHODS

Neonatal airway images were acquired during free-breathing using 3D high-resolution MRI and reconstructed at several respiratory phases in two healthy subjects and two with airway disease (tracheomalacia). For each subject, five static (end expiration, peak inspiration, end inspiration, peak expiration, averaged) and one dynamic CFD simulations were performed. WOB, airway resistance, and pressure loss across the trachea were obtained for each static simulation and compared with the dynamic simulation results.

RESULTS

Large differences were found in the airflow variables between the static simulations at various respiratory phases and the dynamic simulation. Depending on the static airway model used, WOB, resistance, and pressure loss varied up to 237%, 200%, and 94% compared to the dynamic simulation respectively.

CONCLUSIONS

Changes in tracheal size and shape throughout the breathing cycle directly affect respiratory airflow dynamics and breathing effort. Simulations incorporating realistic airway wall dynamics most closely represent airway physiology; if limited to static simulations, the airway geometry must be obtained during the respiratory phase of interest for a given pathology.

Is the healthy respiratory system built just right, overbuilt, or underbuilt to meet the demands imposed by exercise?

In the healthy, untrained young adult, a case is made for a respiratory system (airways, pulmonary vasculature, lung parenchyma, respiratory muscles, and neural ventilatory control system) that is near ideally designed to ensure a highly efficient, homeostatic response to exercise of varying intensities and durations. Our aim was then to consider circumstances in which the intra/extrathoracic airways, pulmonary vasculature, respiratory muscles, and/or blood-gas distribution are underbuilt or inadequately regulated relative to the demands imposed by the cardiovascular system. In these instances, the respiratory system presents a significant limitation to O₂ transport and contributes to the occurrence of locomotor muscle fatigue, inhibition of central locomotor output, and exercise performance. Most prominent in these examples of an "underbuilt" respiratory system are highly trained endurance athletes, with additional influences of sex, aging, hypoxic environments, and the highly inbred equine. We summarize by evaluating the relative influences of these respiratory system limitations on exercise performance and their impact on pathophysiology and provide recommendations for future investigation.

Investigation of inhalation and exhalation flow pattern in a realistic human upper airway model by PIV experiments and CFD simulations

In this study, flow field characteristics in the trachea region in a realistic human upper airway model were firstly measured by particle image velocimetry (PIV) in the air under three constant inhalation and exhalation conditions: 36 L/min, 64 L/min and 90 L/min, representing flow rates of 18 L/min, 32 L/min and 45 L/min in real human airway (the model was twice the size of a human airway). Computational fluid dynamics (CFD) analyses were performed on four turbulence models, with boundary conditions corresponding to the PIV experiments. The effects of flow rates and breathing modes on the airflow patterns were investigated. The CFD prediction results were compared with the PIV measurements and showed relatively good agreement in all cases. During inhalation, the higher the flow rates, the less significant the "glottal jet" phenomenon, and the smaller the area of the separation zone. The air in the nasal inhalation condition accelerated more dramatically after glottis. The SST-Transition model was the best choice for predicting inhalation velocity profiles. For exhalation condition, the maximum velocity was much smaller than that during inhalation due to the more uniform flow field. The exhalation flow rates and breathing modes had little effect on the flow characteristics in the trachea region. The RNG k - ε model and SST k - ω model were recommended to simulate the flow field in the respiratory tract during exhalation.

Exercise Induced Laryngeal Obstruction in Humans and Equines. A Comparative Review

Dynamic obstructions of the larynx are a set of disorders that occur during exercise in equines and humans. There are a number of similarities in presentation, diagnosis, pathophysiology and treatment. Both equines and humans present with exercise intolerance secondary to dyspnea. During laryngoscopy at rest, the larynx appears to function normally. Abnormalities are only revealed during laryngoscopy at exercise, seemingly triggered by increased ventilatory demands, and quickly resolve after cessation of exercise. Lower airway disease (asthma being the most prevalent condition), cardiac disease and lack of fitness are the major differentials in both species. Laryngoscopic examination during exercise should be performed from rest to peak exertion to allow for a comprehensive diagnosis, including where the airway collapse begins, and thereafter how it progresses. Dynamic disorders with most visual similarity between humans and equines are: aryepiglottic fold collapse (both species); equine dynamic laryngeal collapse (DLC) relative to some forms of human combined supraglottic/glottic collapse; and epiglottic retroversion (both species). Quantitative grading techniques, such as airway pressure measurement, that have proven effective in veterinary research are currently being piloted in human studies. Conditions that appear visually similar are treated in comparable ways. The similarities of anatomy and certain types of dynamic collapse would suggest that the equine larynx provides a good model for human upper respiratory tract obstruction during exercise. Thus, close collaboration between veterinarians and medical personal may lead to further advancements in understanding pathophysiologic processes, and enhance the development of improved diagnostic tests and treatments that will benefit both species.

Inducible laryngeal obstruction: Endoscopic quantitative analysis of glottic aperture

OBJECTIVES

Using a method developed for this study, the objective was to perform a quantitative analysis of glottic aperture during the respiratory cycle in subjects suspected of having inducible laryngeal obstruction (ILO) and to compare results to healthy individuals. Correlations between glottic aperture and spirometric parameters were assessed.

METHODS

Subjects with high clinical suspicion of ILO and atypical inspiratory findings in spirometry had the images of their laryngoscopy displayed alongside a respiratory flow chart and both were recorded simultaneously. This method allowed detailed analysis of the glottic aperture by measuring the angle of the anterior commissure during inspiration and expiration. Healthy volunteers who performed the same tests and agreed to provide data to this study were used as a control group.

RESULTS

All 15 subjects with ILO and 16 healthy participants were evaluated successfully using the proposed method. Measures of the anterior commissure angle in the ILO versus control group were significantly different in all observed parameters and just three ILO subjects had an anterior commissure closure greater than 50% during the respiratory cycle. Inspired volume (FIF₅₀ ) and mid-vital capacity ratio (FEF₅₀ /FIF₅₀ ) had a significant correlation with glottic aperture parameters when considering the evaluation of the subjects all together.

CONCLUSION

The proposed method provided precise and quantitative analysis of glottic aperture during the respiratory cycle thus indicating that the usage of equipment that allows for such assessment should be encouraged. Also, the threshold of vocal cords closure accepted as indicative of ILO should be reconsidered, especially during the intercritical period of the disease.

LEVEL OF EVIDENCE

4 Laryngoscope, 130:E349-E356, 2020.

Gasping for a Diagnosis: Pediatric Vocal Cord Dysfunction

Vocal cord dysfunction is an obstruction of the upper airway, primarily on inspiration, due to the paradoxical adduction of the vocal cords. Vocal cord dysfunction continues to be underdiagnosed as its own entity. The lack of diagnosis can be attributed to the overlap of symptoms between asthma and exercise-induced bronchospasm. It is possible for patients diagnosed with asthma and/or exercise-induced bronchospasm to have underlying vocal cord dysfunction, which needs to be considered when prescribing asthma medications. This article will review the history of vocal cord dysfunction, the differential diagnosis, diagnostic testing, and the role of the nurse practitioner in caring for these patients.

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.

Drug-Induced Paradoxical Vocal Fold Motion

Vocal cord dysfunction, also known as paradoxical vocal fold motion (PVFM), is a disorder characterized by abnormal vocal cord adduction during inspiration. PVFM is commonly misdiagnosed as asthma because of the similarity of symptoms: cough, wheezing, chest pain, and dyspnea. We present the clinical vignette of a 36-year-old woman with juvenile rheumatoid arthritis and multiple adverse drug reactions who presented with recurrent episodes of unrecognized PVFM during skin testing for drug allergy, omalizumab treatment, and tocilizumab desensitization. Before the diagnosis of PVFM, these episodes were treated as anaphylaxis, including the administration of epinephrine. Once diagnosed and treated for PVFM, the patient did not present any further events and continued treatment for drug allergy. PVFM may be underreported in hypersensitivity reactions because of the similarity to Type 1-mediated respiratory symptoms and comorbid asthma.

The forgotten cause of stridor in the emergency department

Paradoxical Vocal Fold Movement Disorder is where the larynx exhibits paradoxical vocal cords closure during respiration, creating partial airway obstruction. Causes of vocal fold movement disorder are multifactorial, and patients describe tightness of throat, difficulty getting air in, have stridor, and do not respond to inhalers. We propose using transnasal laryngoscopy examination, which will show narrowing of vocal cords on inspiration, and The Pittsburgh Vocal Cord Dysfunction Index with a cutoff score of ≥4 to distinguish vocal fold movement disorder from asthma and other causes of stridor. Management of paradoxical vocal fold movement disorder involves a combination of pharmacological, psychological, psychiatric, and speech training. Paradoxical vocal fold movement disorder is a very treatable cause of stridor, so long as it is identified and other organic causes are excluded.

Characterizing airflow profile in the postoperative maxillary sinus by using computational fluid dynamics modeling: A pilot study

BACKGROUND

Maxillary antrostomy is commonly performed during endoscopic sinus surgery. Little is known about the association surrounding recalcitrant maxillary sinusitis, antrostomy size, and intranasal airflow changes. Furthermore, the interaction between sinus mucosa and airflow is poorly understood. This study used computational fluid dynamics (CFD) modeling to investigate postoperative airflow characteristics between diseased and nondiseased maxillary sinuses in subjects with recurrent disease.

METHODS

A retrospective review of patients from a tertiary-level academic rhinology practice was performed. Seven subjects with endoscopic evidence of postoperative maxillary sinus disease that presented as chronic unilateral crusting at least 1 year after bilateral maxillary antrostomies were selected. A three-dimensional model of each subject's sinonasal cavity was created from postoperative computed tomographies and used for CFD analysis.

RESULTS

Although the variables investigated between diseased and nondiseased sides were not statistically significant, the diseased side in six subjects had a smaller antrostomy, and five of these subjects had both reduced nasal unilateral airflow and increased unilateral nasal resistance on the diseased side. The ratio of posterior wall shear stress (WSS) of the maxillary sinus to the total WSS was higher on the diseased side in six subjects. Results also showed strong correlations between antrostomy and CFD variables on the diseased side than on the nondiseased side.

CONCLUSION

This pilot study showed that the majority of the simulated sinonasal models exhibited common characteristics on the side with persistent disease, such as smaller antrostomy, reduced nasal airflow, increased nasal resistance, and increased posterior WSS. Although statistical significance was not established, this study provided preliminary insight into variables to consider in a larger cohort study.