Sylvia Verbanck

Distribution of Air: Ventilation Distribution and Heterogeneity

As air is breathed in, it follows a complex pathway of branching airways on its way to the alveolar spaces of the lung. Two basic regions of ventilation are recognized, one that participates in gas exchange, the alveolar ventilation, and one that serves as the conduit for air to reach the gas exchange region, the dead space ventilation. Ventilation is not evenly distributed throughout the lung. First, because of the weight of the lung, the more dependent regions of the lung are more compliant and therefore receive more ventilation than less dependent regions. Secondly, topographic ventilation heterogeneity also exists because of the varying time constants (resistance x compliance) scattered throughout the lung, resulting in fast and slow filling and emptying of different regions. This unevenness of ventilation can be detected by a variety of methods, but inert gas washout techniques, including single and multiple-breath nitrogen washout, are most common. This chapter will explore in more detail the physiology of ventilation heterogeneity, how it is measured, and what its implications may be for clinical medicine.

Numerical Study of Local Deposition Mechanisms of Nanoparticles in a Human Upper Airway Model

We carried out large-eddy simulation to study turbulent air flow and local deposition of inhaled nanoparticles with a 10nm diameter in an idealized human upper airway model for a steady inspiratory flow rate of \(30\frac{l}{min}\). We described the particles in an Eulerian framework and accounted for their Brownian motion by a diffusion coefficient calculated from the Stokes-Einstein relation. We calculated the turbulence subgrid-scale stresses and the subgrid-scale particle mass flux by a localized dynamic Smagorinsky subgrid-scale model. Predicted mean velocity and turbulent kinetic energy profiles were in good agreement with particle image velocimetry measurements and slightly superior to Reynolds-averaged Navier-Stokes simulations in the same model. We further showed that the most pronounced particle deposition hot-spots are located in the vicinity of intense turbulent structures and that their shapes are strongly correlated.