Computational fluid dynamics (CFD), virtual rhinomanometry, and virtual surgery for neonatal congenital nasal pyriform aperture stenosis.

OBJECTIVES: Investigate the implications of Congenital Nasal Pyriform Aperture Stenosis (CNPAS) on neonatal nasal airflow through computational fluid dynamics (CFD), create a virtual rhinomanometry, and simulate the prospective outcomes post-virtual surgical intervention. METHODS: CT scanning of a neonate diagnosed with CNPAS and a control model were used to execute CFD simulations. The segmentation file of the CNPAS underwent manual modifications to simulate a virtual surgical procedure, resulting in a geometry that mirrors a post-operatively corrected patient. Virtual rhinomanometry was reconstructed, and airflow dynamics within the nasal cavity were systematically assessed. The results of the three models were compared. RESULTS: In the CNPAS model, airflow dynamics underwent discernible alterations, with the principal airflow corridor confined to the nasal cavity's upper region. There was a marked pressure drop around the nasal valve, and diminished velocities. This first model of virtual surgery has allowed us to observe that the airflow parameters trended toward the control model, reintroducing an airflow trajectory between the lower and middle turbinates. Virtual rhinomanometry presented near-complete nasal obstruction in the CNPAS model, which showed considerable improvement after the virtual surgery. CONCLUSION: CFD highlights the aerodynamic changes resulting from CNPAS. It also allows for the creation of virtual rhinomanometry and the performance of virtual surgeries. Virtual surgery confirms the therapeutic potential of pyriform aperture enlargement techniques used in clinical practice to improve nasal respiratory function. Future research will investigate additional surgical scenarios and the application of these findings to optimize surgical interventions for CNPAS.

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.

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 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 .

Functional relevance of computational fluid dynamics in the field of nasal obstruction: A literature review.

BACKGROUND: Nasal airway obstruction (nasal obstruction) is a common symptom affecting the quality of life of patients. It can be estimated by patient perception or physical measurements. Computational fluid dynamics (CFD) can be used to analyse nasal ventilation modalities. There is a lack of comparative studies investigating the correlations between CFD variables and patient perception or physical measurements. OBJECTIVE OF THE REVIEW: Our goal was to define correlations between CFD variables and patient perception and physical measurements. We also aimed to identify the most reliable CFD variable (heat flux, WSS, total pressure, temperature…) characterising nasal breathing perception. TYPE OF REVIEW: Systematic literature review using PRISMA guidelines. SEARCH STRATEGY: The selected studies were obtained from the US National Library of Medicine (PubMed) online database, MEDLINE (Ovid), Google Scholar and the Cochrane Library using a combination of MeSH terms (nose, paranasal sinus, fluid dynamics, rhinology) and non-MeSH terms (CFD, nasal airway, nasal airflow, numerical, nasal symptoms). Studies that did not incorporate objective or subjective clinical assessment were excluded. EVALUATION METHOD: We compared all results obtained by authors regarding CFD variables and assessment of nasal airway obstruction (clinical or physical). RESULTS: To compare nasal obstruction with CFD variables, most authors use CFD-calculated nasal resistances, airflow, heat flux, wall shear stress, total pressure, velocities and streamlines. We found that heat flux appears to be the CFD variable most closely correlated with patient perception. Total pressure, wall shear stress and velocities are also useful and show good correlations. Correlations between CFD-calculated nasal resistances and patient perception are stronger after correction of the nasal cycle. CONCLUSIONS: The growing number of CFD studies on the nose has led to a better understanding of nasal obstruction. The clinical interpretation of previously unknown data, such as WSS and heat flux, is opening up new horizons in the understanding of this symptom. Heat fluxes are among the best CFD values correlated with patient perception. More studies need to be performed including temperature and humidity exchanges.

Correlations between computational fluid dynamics and clinical evaluation of nasal airway obstruction due to septal deviation: An observational study.

OBJECTIVES: The primary objective of this study was to determine how computational fluid dynamics (CFD) could be correlated to clinical evaluation of nasal airway obstruction (NAO) in a population of patients with symptomatic septal deviation (SD). The secondary objective was to determine whether CFD could define which side was the more obstructed. DESIGN: This was an observational study. SETTINGS: Few publications have attempted to correlate CFD with clinical evaluation of NAO. This correlation would permit validation and improved interpretation. This study was performed in a university research laboratory specialised in fluid mechanics. PARTICIPANTS: We included patients referred for septal surgery at our centre. Age range was 19-58 years. Preoperative CT scans were performed. All patients with non-structural causes of NAO such as rhinitis, sinusitis or tumoral/autoimmune processes (ie, not due to anatomic obstruction) were excluded. MAIN OUTCOME MEASUREMENT: For each nasal fossa, we compared CFD data (total pressure, heat flux, wall shear stress, temperatures, velocity and nasal resistances) with both patient perception scores and rhinomanometry using the Spearman correlation test (rs ). Perception scores were graded from 0/4 to 4/4 on each side, based on the patient interview. We also compared CFD-derived nasal resistances with rhinomanometry-derived nasal resistances. RESULTS: Twenty-two patients complaining of NAO with SD were analysed, and 44 analyses were performed comparing each side with its CFD data. Regarding correlations with patient perception scores, the best values we found were heat flux measures (rs  = 0.86). Both rhinomanometry and CFD-calculated nasal resistances had strong correlations with subjective perception scores (rs  = 0.75, P < 0.001 and rs  = 0.6, P < 0.001, respectively). We found a statistically significant difference between RMM-NR and CFD-NR (P = 0.003). Heat flux analysis allowed us to distinguish the more obstructed side (MOS) and the less obstructed side (LOS) in 100% of patients. CONCLUSION: This study aimed to enhance our ability to interpret CFD-calculated data in the nasal airway. It highlights and confirms that heat flux measures are very closely correlated to patient perception in cases of SD. It also helps to distinguish the more obstructed side from the less obstructed side and could contribute to further CFD studies.

A preliminary study of computer assisted evaluation of congenital tracheal stenosis: a new tool for surgical decision-making.

OBJECTIVE: Congenital tracheal stenosis is a rare but severe condition with tracheal narrowing. There is no absolute correlation between luminal diameter and prognosis, and therapeutic decisions are difficult for intermediate cases. The aim of this study was to develop a dynamic model of the ventilatory consequences of congenital tracheal stenosis using computational fluid dynamics. METHODS: In 8 children with congenital tracheal stenosis and 1 healthy child, 3-dimensional geometries of the trachea were constructed with computed tomography images and specialized software (ITK-SNAP). Airflow simulations were performed for each geometry using 2 physiologic inhalation flow rates under steady and laminar flow conditions. Flow velocity, static and total airway pressure, and pressure drop across the entire trachea were determined. RESULTS: In the patients with congenital tracheal stenosis, the pressure drop from the tracheal inlet to outlet, at flow rate 3L/min, ranged from 14 to 430Pa; the pressure drop at flow rate 7.3L/min ranged from 60 to 1825Pa. The pressure drop enabled a classification based on the severity of stenosis. The classification based on pressure drop was retrospectively consistent with the classification based on clinical data from the patients. CONCLUSIONS: Simulations with computational fluid dynamics may provide an objective method to evaluate the severity of the symptoms in patients with congenital tracheal stenosis and may help guide treatment.