The ventilation distribution of helium–oxygen mixtures and the role of inertial losses in the presence of heterogeneous airway obstructions

A Patient-Specific Airway Branching Model for Mechanically Ventilated Patients

“…Head loss is defined as a pressure drop along the branching system which consists of major and minor losses [13]. The major loss is defined as the pressure drop in the straight section of the airway branching system [13]: $\begin{array}{c}\mathrm{\Delta }{P}_{\text{major}}=f\frac{L{V}^{\mathrm{2}}}{\mathrm{2}D}.\end{array}$ The model thus assumes that laminar flow exists in the branches since the diameter for all branches is less than 30 mm with Reynolds number being less than 2000 [10, 11, 21].…”

“…The major loss is defined as the pressure drop in the straight section of the airway branching system [13]: $\begin{array}{c}\mathrm{\Delta }{P}_{\text{major}}=f\frac{L{V}^{\mathrm{2}}}{\mathrm{2}D}.\end{array}$ The model thus assumes that laminar flow exists in the branches since the diameter for all branches is less than 30 mm with Reynolds number being less than 2000 [10, 11, 21]. Thus, the laminar flow friction factor ( f ) is defined as $\begin{array}{c}f=\frac{\mathrm{64}}{\mathrm{Re}},\end{array}$ where Re is the Reynolds number based on the branch diameter: $\begin{array}{c}\mathrm{Re}=\frac{\rho VD}{\mu },\end{array}$ where V is the velocity of the flow of the airway branch.…”

“…In practice, the ABM has been used to estimate respiratory pressure-flow responses in noncritically ill subjects [7, 8, 12, 13]. However, ABM models are very general, using a set of global airway dimensions that do not reflect patient-specific conditions and have not been validated in critically ill patients with respiratory failure.…”

Hélium en réanimation : de la mécanique des fluides à la clinique

“…En effet, les altérations des résistances dans la BPCO sont d'origine complexe, le site prédominant d'obstruction et, par extension, le régime d'écoulement variable [45,46], ce qui peut rendre compte d'une réponse variable elle aussi. Des travaux de modélisation récents ouvrent la voie vers une compréhension approfondie de ces mécanismes et laissent entrevoir la possibilité d'identifier les meilleurs répondeurs potentiels à l'inhalation d'He-O 2 [47]. Finalement, dans les deux études, la VNI était appliquée par intermittence et la durée des séances parfois brève, alors que les patients respiraient un mélange classique air-O 2 en dehors de ces séances [43,44].…”

Calculated ventilation and effort distribution as a measure of respiratory disease and Heliox effectiveness

“…In (Katz et al, 2011) a resistance model accounting for gas density effect on pressure drops in a bifurcation is proposed and applied to Heliox mixtures. In (Katz et al, 2014) the impact of breathing HeO 2 on particle deposition is studied, CFD, in-vivo imaging and bench study suggest deeper deposition compared to air.…”