Quantitative evaluation of aerosol deposition in constricted tubes

Inhaled particles are known to deposit at sites of airways narrowing. Using an orifice model, we measured the influence of different mechanisms of deposition in situations that parallel the in vivo state. By relating deposition to dimensionless numbers the contributions of turbulence (Reynolds number), intrinsic particle inertia (Stokes number), and flow-limitation (Mach number) were determined. At Mach numbers below the level of flow-limitation we found that deposition could be accurately described for all conditions using Reynolds and Stokes numbers originally defined for a single orifice. When Mach numbers were in the range of flow-limitation, deposition significantly exceeded values predicted by Reynolds and Stokes numbers, indicating an important additional effect of compressible flow on particle deposition.