Computational Fluid Dynamics in the assessment of nasal obstruction in children.

OBJECTIVES: Nasal obstruction is a highly subjective symptom. It can be evaluated by combining clinical examination, imaging and functional measurements such as active anterior rhinomanometry (AAR). In pediatrics, AAR is often impossible because it requires the participation of the child. Airflow modeling by Computational Fluid Dynamics (CFD) has been developed since the early 1990s, mostly in adults. This study is the first to describe a methodology of "numerical rhinomanometry" in children using CFD and to evaluate the feasibility and the clinical interest of this new tool. MATERIALS AND METHODS: Five children aged from 8 to 15 years, complaining of nasal obstruction, underwent routine management including clinical evaluation, AAR, and CT-scanning. CT acquisitions were used for CFD calculations and numerical rhinomanometry. RESULTS AND CONCLUSIONS: In the 5 children, the results of CFD were concordant with clinical complaints and examination. In 3 children, AAR and CFD were concordant. In one patient, CFD corrected the results of AAR. In one patient, AAR was not feasible, unlike CFD, which contributed to diagnosis. This study highlighted the feasibility of CFD in children and that it can support or refute diagnosis of nasal obstruction with good reliability. These results indicate that CFD modeling could be widely used for functional exploration in pediatric rhinology.

Validation of the newborn larynx modeling with aerodynamical experimental data.

BACKGROUND: Many authors have studied adult's larynx modelization, but the mechanisms of newborn's voice production have very rarely been investigated. After validating a numerical model with acoustic data, studies were performed on larynges of human fetuses in order to validate this model with aerodynamical experiments. MATERIAL AND METHODS: Anatomical measurements were performed and a simplified numerical model was built using Fluent((R)) with the vocal folds in phonatory position. The results obtained are in good agreement with those obtained by laser Doppler velocimetry (LDV) and high-frame rate particle image velocimetry (HFR-PIV), on an experimental bench with excised human fetus larynges. RESULTS: It appears that computing with first cry physiological parameters leads to a model which is close to those obtained in experiments with real organs.

The osmotic migration of cells in a solute gradient.

The effect of a nonuniform solute concentration on the osmotic transport of water through the boundaries of a simple model cell is investigated. A system of two ordinary differential equations is derived for the motion of a single cell in the limit of a fast solute diffusion, and an analytic solution is obtained for one special case. A two-dimensional finite element model has been developed to simulate the more general case (finite diffusion rates, solute gradient induced by a solidification front). It is shown that the cell moves to regions of lower solute concentration due to the uneven flux of water through the cell boundaries. This mechanism has apparently not been discussed previously. The magnitude of this effect is small for red blood cells, the case in which all of the relevant parameters are known. We show, however, that it increases with cell size and membrane permeability, so this effect could be important for larger cells. The finite element model presented should also have other applications in the study of the response of cells to an osmotic stress and for the interaction of cells and solidification fronts. Such investigations are of major relevance for the optimization of cryopreservation processes.