Biomedical Engineering Reference
In-Depth Information
Fig. 8.1 EDA concept illustrated for a hypothetical CI using the ACI at 28.3 L/min to represent
the full-resolution measurement system; the pre-separator, if used, would provide a data bar
between the induction port and S0
The sum ( LPM + SPM ) is numerically equal to the total mass collected on all
stages of the impactor, which have an upper-bound size, and is termed the impactor-
sized mass ( ISM ). The values of these two metrics, ISM and ratio , defined as LPM/
SPM , can be mathematically independent: thus, the total mass of API collected in
the CI can change without affecting the relative masses contained in the large- and
small-sized fractions. Even though there could be physical causes that lead the two
metrics to change “in synchrony” and thus to appear correlated, mathematically,
the ratio can vary without ISM being changed, and vice versa. In other words, a
change in one metric does not require a concomitant variation in the other. This
means that the effects detected by these metrics can be measured independently
(i.e., a shift of the entire profile or a shift of mass between stages—by the ratio and
total area under the curve—by the value of ISM ).
Even when there is physical correlation between the two effects, a change in one
does not affect the ability to measure or interpret the other. This is not the case for
the grouped-stage approach, in which there is a mathematical relationship that, for
any change in total mass, requires a change in mass assigned to one or more of the
stage groupings. However, it is possible for there to be changes in two or more
groupings due to a shift that may or may not affect the total mass collected.
Furthermore, since decisions for grouped stages are made for each grouping sepa-
rately, it may be difficult to correctly interpret the meaning of a change in a stage
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