Computational Fluid Dynamics in the assessment of nasal obstruction in children

Assessment of high-flow nasal cannula efficacy in humidification of infant airways: A computational fluid dynamics approach

INTRODUCTION

High-flow nasal cannula therapy has garnered significant interest for managing pathologies affecting infants' airways, particularly for humidifying areas inaccessible to local treatments. This therapy promotes mucosal healing during the postoperative period. However, further data are needed to optimize the use of these devices. In vivo measurement of pediatric airway humidification presents a challenge; thus, this study aimed to investigate the airflow dynamics and humidification effects of high-flow nasal cannulas on an infant's airway using computational fluid dynamics.

METHODS

Two detailed models of an infant's upper airway were reconstructed from CT scans, with high-flow nasal cannula devices inserted at the nasal inlets. The airflow was analyzed, and wall humidification was modeled using a film-fluid approach.

RESULTS

Air velocities and pressure were very high at the airway inlet but decreased rapidly towards the nasopharynx. Maximum relative humidity-close to 100%-was achieved in the nasopharynx. Fluid film development along the airway was heterogeneous, with condensation primarily occurring in the nasal vestibule and larynx.

CONCLUSION

This study provides comprehensive models of airway humidification, which pave the way for future studies to assess the impact of surgical interventions on humidification and drug deposition directly at operative sites, such as the nasopharynx or larynx, in infants.

Nasal airway obstruction in patients with cleft lip nasal deformity: A systematic review

BACKGROUND

Cleft lip nasal deformity (CLND)-associated nasal airway obstruction (CL-NAO) may be inadequately characterized, with its functional implications subsequently underappreciated and neglected. The purpose of this systematic review is to (1) summarize the available assessment results in CL-NAO, (2) evaluate the reliability of current assessment tools, and (3) identify ongoing gaps and inconsistencies for future study.

METHODS

A systematic search of the MEDLINE, EMBASE, and Scopus databases was performed for articles studying CL-NAO. Articles focusing on noncleft populations or surgical techniques were excluded. Extracted data included information about study design, patient demographics, medical history, and assessment scores.

RESULTS

Twenty-six articles met criteria for inclusion. Assessments included patient-reported outcome measures (PROMs), anatomic characterizations of CLND, and nasal airflow and resistance studies. Objective assessments were generally more reliable than subjective assessments in CLND. Unilateral CLND was better represented in the literature than bilateral CLND. For unilateral CLND, the cleft side was more obstructed than the noncleft side, with stereotyped patterns of anterior nasal deformity but varied middle and posterior deformity patterns. Overall, there was considerable heterogeneity in study design regarding stratification of CLND cohorts by age, cleft phenotype and laterality, and surgical history.

CONCLUSIONS

A wide range of subjective and objective assessment tools were used to characterize CL-NAO, including PROMs, anatomic measurements, and airflow and resistance metrics. Overall, objective assessments of CL-NAO were more reliable than subjective surveys, which may have resulted from variable expectations regarding nasal patency in the CLND population combined with large heterogeneity in study design.

The influence of flowmeters on rhinomanometry results and detection of nasal airflow asymmetry

<b><br>Introduction:</b> Rhinomanometry is an otolaryngological diagnostic method used to determine airflow as a function of the pressure drop through the left and right nasal cavities. Airflow is measured using orifice flowmeters that attenuate the flow.</br> <b><br>Aim:</b> This paper describes the results of a study into the effects of flowmeter design on rhinomanometry results and detection of nasal airflow asymmetry.</br> <b><br>Material and methods:</b> Four flowmeters were examined using a 3D printed model of a human nose.</br> <b><br>Conclusions:</b> Each flowmeter interfered with the rhinomanometry results.</br>.

Heliox simulations for initial management of congenital laryngotracheal stenosis

OBJECTIVES

Congenital laryngotracheal stenosis is rare, potentially severe, and difficult to manage. Heliox is a medical gas effective in obstructive airway pathologies, given its physical properties. This study aims to model the interest of Heliox in reducing the respiratory work in congenital laryngotracheal stenosis, using numerical fluid flow simulations, before considering its clinical use.

DESIGN

This is a retrospective study, performing Computational Fluid Dynamics numerical simulations of the resistances to airflow and three types of Heliox, on 3D reconstructions from CT scans of children presenting with laryngotracheal stenosis.

PATIENTS

Infants and children who were managed in the Pediatric ENT department of a tertiary-care center and underwent CT scanning for laryngotracheal stenosis between 2008 and 2018 were included.

RESULTS

Fourteen models of congenital laryngotracheal stenosis were performed in children aged from 16 days to 5 years, and one model of the normal trachea in a 5-year-old child. Tightest stenosis obtained the highest airway resistances, ranging from 40 to 10 kPa/L/s (up to 800 times higher than in the normal case). Heliox enabled a decrease in pressure drops and airway resistances in all stenosis cases, correlated to increasing Helium concentration.

CONCLUSIONS

Heliox appears to reduce pressure drops and airway resistances in 3D models of laryngotracheal stenosis. It may represent a supportive treatment for laryngotracheal stenosis, while waiting for specialized care, thanks to the reduction of respiratory work.

Numerical modelling of micron particle inhalation in a realistic nasal airway with pediatric adenoid hypertrophy: A virtual comparison between pre- and postoperative models

Adenoid hypertrophy (AH) is an obstructive condition due to enlarged adenoids, causing mouth breathing, nasal blockage, snoring and/or restless sleep. While reliable diagnostic techniques, such as lateral soft tissue x-ray imaging or flexible nasopharyngoscopy, have been widely adopted in general practice, the actual impact of airway obstruction on nasal airflow and inhalation exposure to drug aerosols remains largely unknown. In this study, the effects of adenoid hypertrophy on airflow and micron particle inhalation exposure characteristics were analysed by virtually comparing pre- and postoperative models based on a realistic 3-year-old nasal airway with AH. More specifically, detailed comparison focused on anatomical shape variations, overall airflow and olfactory ventilation, associated particle deposition in overall and local regions were conducted. Our results indicate that the enlarged adenoid tissue can significantly alter the airflow fields. By virtually removing the enlarged tissue and restoring the airway, peak velocity and wall shear stress were restored, and olfactory ventilation was considerably improved (with a 16∼63% improvement in terms of local ventilation speed). Furthermore, particle deposition results revealed that nasal airway with AH exhibits higher particle filtration tendency with densely packed deposition hot spots being observed along the floor region and enlarged adenoid tissue area. While for the postoperative model, the deposition curve was shifted to the right. The local deposition efficiency results demonstrated that more particles with larger inertia can be delivered to the targeted affected area following Adenoidectomy (Adenoid Removal). Research findings are expected to provide scientific evidence for adenoidectomy planning and aerosol therapy following Adenoidectomy, which can substantially improve present clinical treatment outcomes.

CFD SIMULATIONS AND ANALYSES OF ASYMPTOMATIC AND SYMPTOMATIC NASAL AIRWAY OBSTRUCTIONS

The numerical simulations of the flow in nasal airways were performed for two different clinical cases. The results comprised the distributions of scalars at five different sections and included contours of pressure, velocity magnitude, turbulent kinetic energy and vorticity magnitude. Simulations showed the air branching occurring at the inferior meatus is unaffected by the variations in the volumetric flow rate or the changes in the flow regime through the olfactory cleft. However, the contractions and the following rapid change in the cross-section of the nasopharynx preclude the upward penetration of the vacuum field set by the lungs during the inhalation process. As a result, considerably low velocities and significant cross-sectional nonuniformities are observed, which lead to the appearances of the secondary flow structures and strong unsteadiness. Increased interactions between the airflow and the walls of the nasal cavity resulted in an increase in the vorticity on the right middle meatus and upper inferior meatus. The vorticity was also very high in the nostrils, where the flow was not fully developed.

Clinical parameters influencing the results of anterior rhinomanometry in children

BACKGROUND

Nasal obstruction is a frequent symptom in both adults and children and it is a common reason to see an otorhinolaryngologist. Endoscopy of the nasal cavity and the epipharyngeal space along with anterior rhinomanometry is regarded the gold standard since many years to estimate the severity of nasal obstruction in the particular patient. Endoscopy shows anatomical reasons for an obstruction, whereas the nasal flow volume and nasal resistance can be determined using anterior rhinomanometry. Currently, there are only few data available for rhinomanometry results in children. The purpose of the present study was to evaluate the application of this technique in the pediatric population for objective evaluation of nasal flow. Whether it achieves reproducible results and which clinical parameters have some influence on the results were studied.

PATIENTS AND METHODS

427 children (average age of 8.5 years, range 7 months through 17 years) who were admitted to evaluate nasal patency or for allergy testing were examined. After clinical examination and endoscopy of the nasal cavity and epipharyngeal space, anterior rhinomanometry was performed before and after application of decongestant nose drops separately for each nose side in 334 children. The nasal flow with a pressure of 150 Pasc was measured and served for statistical evaluation. Flow values were correlated to clinical and endoscopic parameters along with results of allergy tests (prick tests).

RESULTS

Reproducible rhinomanometric measurements were possible in children age 3 years and older. However, the standard deviation and variation of measurements were significant in this cohort of patients. Statistically highest significant correlations were found between flow measurements and body height along with the age of the children (p < 0.01) and status following adenoidectomy (p < 0.05). No statistically significant correlations were found between rhinomanometry and results of prick tests.

CONCLUSIONS

The study demonstrates that rhinomanometry can be applied in the pediatric population for objective evaluation of nasal obstruction and for determining the effects of decongestant nose drops. The highest correlation was found between nasal flow and children's body height, children's age and status following adenoidectomy. The correlation between nasal flow and clinically/endoscopically determined degree of nasal obstruction was lower. However, definition of normal flow values for particular age groups is challenging since the results showed high variation and standard deviation. Yet with regard to individual patient, the technique achieves reliable results in nasal provocation tests, which are widely used for allergy testing in children. When performed in children it should always be considered that there are age-specific requirements for the examination and interpretation of results in this patient cohort.

Nasal ventilation and rapid maxillary expansion (RME): a randomized trial

OBJECTIVE

To assess three rapid maxillary expansion (RME) appliances in nasal ventilation.

TRIAL DESIGN

Three-arm parallel randomized clinical trial.

METHODS

Sixty-six growing subjects (10-16 years old) needing RME as part of their orthodontic treatment were randomly allocated (1:1:1 ratio) to three groups of 22 patients receiving Hyrax (H), Hybrid-Hyrax (HH), or Keles keyless expander (K). The primary outcome of nasal ventilation (pressure and velocity) and secondary outcomes (skeletal, dental, soft tissue, and nasal obstruction changes) were blindly assessed on the initial (T0) and final (T1, 6 months at appliance removal) cone-beam computed tomography (CBCT) data by applying computational fluid dynamics (CFD) method. Differences across groups were assessed with crude and adjusted for baseline values and confounders (gender, age, skeletal maturation, expansion amount, mucosal/adenoid hypertrophy, nasal septum deviation) regression models with alpha = 5%.

RESULTS

Fifty-four patients were analysed (19H, 21HH, 14K). RME reduced both nasal pressure (H: -45.8%, HH: -75.5%, K: -63.2%) and velocity (H: -30%, HH: -58.5%, K: -35%) accompanied with nasal obstruction resolution (H: 26%, HH: 62%, K: 50%). Regressions accounting for baseline severity indicated HH expander performing better in terms of post-expansion maximum velocity (P = 0.03) and nasal obstruction resolution (P = 0.04), which was robust to confounders. Mucosal/adenoid hypertrophy and nasal septum deviation changes were variable, minimal, and similar across groups. The HH resulted in significantly greater increase in the nasal cross-sectional area (62.3%), anterior (14.6%), and posterior (10.5%) nasal widths. Nasal obstruction resolution was more probable among younger (P = 0.04), skeletally immature (P = 0.03), and male patients (P = 0.02) without pre-treatment mucosal hypertrophy (P = 0.04), while HH was associated with marginal greater probability for obstruction resolution.

CONCLUSIONS

RME resulted in improvement of nasal skeletal parameters and simulated ventilation with the former being in favour of the HH and the latter not showing significant differences among the three appliances.

LIMITATION

Attrition in the K group due to blocked activation rods possibly leading to limited sample to identify any existing group differences.

HARMS

Replacement of blocked Keles expanders for finalizing treatment.

PROTOCOL

The protocol was not published before the trial commencement.

REGISTRATION

Australian and New Zealand Clinical Trial Registry; ACTRN12617001136392.

Three-dimensional modeling and automatic analysis of the human nasal cavity and paranasal sinuses using the computational fluid dynamics method

PURPOSE

The goal of this study was to develop a complete workflow allowing for conducting computational fluid dynamics (CFD) simulation of airflow through the upper airways based on computed tomography (CT) and cone-beam computed tomography (CBCT) studies of individual adult patients.

METHODS

This study is based on CT images of 16 patients. Image processing and model generation of the human nasal cavity and paranasal sinuses were performed using open-source and freeware software. 3-D Slicer was used primarily for segmentation and new surface model generation. Further processing was done using Autodesk^® Meshmixer TM. The governing equations are discretized by means of the finite volume method. Subsequently, the corresponding algebraic equation systems were solved by OpenFOAM software.

RESULTS

We described the protocol for the preparation of a 3-D model of the nasal cavity and paranasal sinuses and highlighted several problems that the future researcher may encounter. The CFD results were presented based on examples of 3-D models of the patient 1 (norm) and patient 2 (pathological changes).

CONCLUSION

The short training time for new user without a prior experience in image segmentation and 3-D mesh editing is an important advantage of this type of research. Both CBCT and CT are useful for model building. However, CBCT may have limitations. The Q criterion in CFD illustrates the considerable complication of the nasal flow and allows for direct evaluation and quantitative comparison of various flows and can be used for the assessment of nasal airflow.

Rhinomanometry Versus Computational Fluid Dynamics: Correlated, but Different Techniques

BACKGROUND

Past studies reported a low correlation between rhinomanometry and computational fluid dynamics (CFD), but the source of the discrepancy was unclear. Low correlation or lack of correlation has also been reported between subjective and objective measures of nasal patency.

OBJECTIVE

This study investigates (1) the correlation and agreement between nasal resistance derived from CFD (R_CFD) and rhinomanometry (R_RMN), and (2) the correlation between objective and subjective measures of nasal patency.

METHODS

Twenty-five patients with nasal obstruction underwent anterior rhinomanometry before and after mucosal decongestion with oxymetazoline. Subjective nasal patency was assessed with a 0-10 visual analog scale (VAS). CFD simulations were performed based on computed tomography scans obtained after mucosal decongestion. To validate the CFD methods, nasal resistance was measured in vitro (R_EXPERIMENT) by performing pressure-flow experiments in anatomically accurate plastic nasal replicas from 6 individuals.

RESULTS

Mucosal decongestion was associated with a reduction in bilateral nasal resistance (0.34 ± 0.23 Pa.s/ml to 0.19 ± 0.24 Pa.s/ml, p = 0.003) and improved sensation of nasal airflow (bilateral VAS decreased from 5.2 ± 1.9 to 2.6 ± 1.9, p < 0.001). A statistically significant correlation was found between VAS in the most obstructed cavity and unilateral airflow before and after mucosal decongestion (r = -0.42, p = 0.003). Excellent correlation was found between R_CFD and R_EXPERIMENT (r = 0.96, p < 0.001) with good agreement between the numerical and in vitro values (R_CFD/R_EXPERIMENT = 0.93 ± 0.08). A weak correlation was found between R_CFD and R_RMN (r = 0.41, p = 0.003) with CFD underpredicting nasal resistance derived from rhinomanometry (R_CFD/R_RMN = 0.65 ± 0.63). A stronger correlation was found when unilateral airflow at a pressure drop of 75 Pa was used to compare CFD with rhinomanometry (r = 0.76, p < 0.001).

CONCLUSION

CFD and rhinomanometry are moderately correlated, but CFD underpredicts nasal resistance measured in vivo due in part to the assumption of rigid nasal walls. Our results confirm previous reports that subjective nasal patency correlates better with unilateral than with bilateral measurements and in the context of an intervention.

Numerical simulation of nasal airflows and thermal air modification in newborns

Warming, filtering, and humidification of inspired air are major functions of the upper airway, which can be negatively altered by local disorders or surgical interventions. These functions have not been described in neonates because of ethical and technical problems difficult to solve. Numerical simulations can get around these limitations. The objective of this study was to analyze physiological nasal airflow and thermal distribution using computational fluid dynamics (CFD) techniques in neonates. CT imaging of neonates was collected from the Pediatric Radiology Department of our center. CFD has been used to simulate nasal airflow numerically, with ambient air set at 19 °C, following the recommendations for a neonate's bedroom. Thermal distribution within the nasal cavity was analyzed and coupled with airflow patterns over complete respiratory cycles. Sixteen patients have been included in the study. During inspiration, important air warming is noticed in the first centimeter of the nasal cavity (+ 8 °C at the anterior end of the inferior turbinate). During the expiration phase, the temperature decreases slightly (- 3 °C) between the pharynx and the nostrils. A model with asymmetric nasal fossae showed that nasal obstruction leads to decreased airflow and abnormally high temperatures in the obstructed side (+ 2 °C at the nasal valve, + 4 °C at the choana). According to our results, the nasal valve area is of crucial importance in air warming in neonates, when ambient air is 19 °C, since about 70% of air warming is performed in this area. When needed, surgical interventions should respect the anatomy of this zone and restore normal airflows and warming. Graphical abstract .