Assessing the relationship between movement and airflow in the upper airway using computational fluid dynamics with motion determined from magnetic resonance imaging

A novel method to generate dynamic boundary conditions for airway CFD by mapping upper airway movement with non‐rigid registration of dynamic and static MRI

“…At the beginning of the solution to each timestep, these control points were moved to their new location, and the mesh morphed to account for this motion. An in‐house Java script was used to control the motion of these control points within Star‐CCM+, as described previously . As the mesh moved through the simulation, mesh quality metrics including face validity, cell volume, and the change in cell volume size were monitored, and a new mesh was created when these values fell below certain limits (cell quality [a function of the relative distribution of surrounding cell centroids and their face orientations] < 0.001, face validity [area‐weighted measure of the correctness of the face normals relative to their attached cell centroid] < 0.55, change in cell volume from one cell to its neighbors <0.003, cell volume < 0).…”

“…In addition to solving the equations for the conservation of mass and momentum, large eddy simulation (LES) was employed to model sub‐grid scale turbulence as previous studies have shown this technique to be effective at modeling the turbulent and transitional flow regimes within the airway . The procedure to solve the Navier‐Stokes equations in a moving mesh was implemented as previously described . At each time step, the residuals of the equations for continuity and the three components of momentum were reduced by three orders of magnitude, and measures of pressure loss between planes along the airway converged to within 0.1% of a stable value before moving to the next timestep.…”

Quantitative Assessment of Regional Dynamic Airway Collapse in Neonates via Retrospectively Respiratory‐Gated 1H Ultrashort Echo Time MRI

“…Previously, CFD simulations have been used to calculate the increased tracheal work of breathing in adult subjects with goiters and a transplanted trachea . These simulations rely on high‐resolution imaging to provide the anatomical boundaries of the airway structure, and there is increasing recognition that the accuracy of CFD simulations suffers when airway wall motion is ignored and simplified into a static model …”

“…Future studies could use this additional data to infer further information about the trachea at other respiratory stages, such as the duration of tracheal narrowing and how collapse metrics relate to respiratory flow rates or pleural pressures. Moving airway wall CFD simulations could utilize data acquired throughout the breath in order to capture the necessary tracheal motion for boundary conditions, as has been done previously on real‐time cine imaging . Therefore, the techniques detailed here can generate respiratory‐gated image reconstructions throughout the whole breathing cycle at no additional data acquisition cost.…”

Molecular Binding Contributes to Concentration Dependent Acrolein Deposition in Rat Upper Airways: CFD and Molecular Dynamics Analyses

“…Therefore, molecular binding can only explain part of the deposition decrease, while the limited Michaelis–Menten metabolism rate is still the major reason. The influences of tidal breathing [30,31,32], dynamic airways [33,34,35,36], polydisperse aerosols [37,38], hygroscopic growth [39,40,41], electric charges [42,43], and intersubjective variability [44,45,46] on acrolein deposition are also important and should be considered in future studies. Imaging techniques such as phase-contrast MRI (magnetic resonance imaging) with hyperpolarized 3 He can be used to visualize respiratory flows [47,48].…”