Respiratory tract, collection efficiency

Inertial impaction has many inaccuracies and limitations and there are also some relevant differences between deposition in vitro (impactor) and in vivo (respiratory tract) which cause poor correlation between impactor data and lung deposition data. The most important difference is that deposition in vitro is by inertial impaction only, whereas deposition in vivo is by sedimentation and diffusional deposition as well. Except for the possible passage of the final stage (by the finest particles), particle collection in vitro is almost 100% efficient. In con-... 

Considering a sphere of unit density, p, and diameter, d, for which (p = (pd ), its transport properties are identical with those of all particles characterized by the same value of (pd ). Its diameter is called the aerodynamic diameter. The behavior of this fictitious sphere is representative of all particles collected with the same efficiency by the respiratory tract regardless of their density. Or, in other words, this sphere represents aU these particles as far as then-transport properties are concerned. However, it does not represent them as far as their physical properties are concerned (particle diameter, particle density, and consequently particle mass). 

Airway and airspace dimensions of these individuals estimated from deposition of l-pm particles due to gravitational transport during end-inspiratory breathholding are closely correlated with the total deposition of the individuals. The respiratory tract of individuals with wide airways collects particles less efficiently than that of individuals with narrow airways. 

If the suspected contaminants are particulates, membrane filters are frequently used which have collection efficiencies of 100% for particles most likely to enter the deep respiratory tract... 

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