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.

The very first cry: a multidisciplinary approach toward a model.

OBJECTIVES: In previous work, we showed that a rigid larynx-like geometry can generate a sound by itself. However, very little is known about the exact mechanisms and control of the larynx during the first cry of life. The goal of this work was to understand how the very first cry is generated. METHODS: Simultaneous high-speed imaging and sound recording on 2 excised 38-week term human fetus larynges were performed. The behaviors of the vocal folds and the false vocal folds were studied separately. The behavior of the vocal folds after resection of the supraglottic structures was also analyzed. A comparative acoustic analysis of the first cry and of the sound generated by the excised organs was performed. RESULTS: Our data showed that the vocal folds in a larynx with the pressure conditions of the first cry do not generate sound themselves, but induce aerodynamic conditions leading to vibrations of other parts of the larynx. CONCLUSIONS: The similarities between the sound generated by an excised larynx and the first cry suggest a lack of neurologic control of the larynx during production of the first cry. A model-algorithm is proposed.