Relative Importance of These Mechanisms Within the Respiratory Tract

6 Relative Importance of These Mechanisms Within the Respiratory Tract 

Under the humid conditions found with the respiratory tract, it is most likely that any charges on particles will be quickly dissipated and so electrostatic precipitation is unlikely to play a significant role in particle deposition anywhere in the airways. 

Deposition by interception is also not significant, since the particles of interest are far smaller than the airways. 

We will now consider the relative importance of the other three mechanisms, sedimentation, inertial impaction and diffusion, in the various parts of the respiratory tract. First, it is interesting to compare, for different particle sizes, the displacements due to sedimentation and diffusion under the conditions typically found within the respiratory tract. Table 14.2 makes this comparison for particles of density 1000 kg/m in air at a temperature of 30°C. 

Now we will consider the importance of inertial impaction as a mechanism for causing deposition. In Table 14.4 we have calculated [using Equation (14.4)] the Stokes numbers for particles of different sizes in the various areas of the respiratory duct, based on the information provided in Table 14.1. This calculation assumes that the particle velocity is the same as the air velocity in the relevant part of the respiratory tract. 

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