The cut-off diameters generated by each stage of any cascade impactor are dependent on a steady, fixed flow of air passing through it.
In contrast, the in vivo inhalation profiles of breathing cycles generated by patients produce a continually varying flow rate far removed from the fixed, steady-state flow rates employed in in vitro testing.
For this reason, there have been various attempts to link cascade impactors directly to breathing simulators in order to reproduce actual clinical conditions more closely. Any such system must be capable of varying the flow rate through the inhaler whilst ensuring that the aerosol generated is sampled at a fixed rate through the impactor.
The Mixing Inlet fits between the USP Induction Port (or Alberta Idealised Throat) and the inlet of the impactor used to carry out the test.
It is designed to permit the cascade impactor to be operated at a constant flow rate (e.g. 100 L/min), whilst allowing a lower fixed or variable rate, such as a breathing pattern generated by a breathing simulator, to pass through the inhaler itself.
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