Biomedical Engineering Reference
In-Depth Information
Fig. 1.3 Typical grouping of API mass collected in full-resolution CI; group 1 is the aggregated
mass collected by the non-sizing components; groups 2, 3, and 4 defi ne the coarse, fi ne, and extra-
fi ne mass components of the CI size-fractionated aerosol, respectively; the symbol “F” on the stages
identifi es full resolution CI confi guration
In EDA, consideration of the API deposition data from the CI is limited to the
total API mass that is size-fractionated, defi ned as the impactor-sized mass ( ISM ).
Mathematically, ISM represents the area under the curve ( AUC ) of the differential
mass-weighted APSD. However, it should be noted that in the traditional defi nition
of AUC , this quantity is estimated from the best fi t of a model describing a process
that results in a continuous curved relationship between two independent variables.
In contrast, individual values of API mass are assigned to separate stages of the CI,
each possessing a small number (no more than eight with the compendial appara-
tuses) of different and discrete size bounds that are contiguous in the represented
differential mass-weighted APSD. In this topic, AUC will, however, be used as an
approximation to the quantity. ISM , in the context of EDA, can be conveniently
thought of as defi ning the total mass of API from the OIP aerosol that is sized-
fractionated and represented by the continuous form of the APSD.
ISM is further subdivided into large particle mass ( LPM ) and small particle mass
( SPM ) with the boundary ideally fi xed at a size close to or identical with the mass
median aerodynamic diameter ( MMAD ), representing the central moment of the
APSD (Fig. 1.4 ). The MMAD is therefore a function of the distribution of API mass
across all stages of the CI. The ratio metric LPM / SPM is independent of ISM , con-
ferring a powerful advantage for EDA for the detection of small shifts in APSD
either to fi ner or coarser sizes.
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