MDI - The Pressurised Metered Dose Inhaler is the early System of inhalers. It is more and more exchanged by the environment friendly Dry Powder Inhaler.
At the MDI the drug is dosed by the unit itself. For this reason in addition to particle size the accuracy of the dosing process of the unit itself has to be checked.
The lung is simulated by a vacuum pump. For all kind of tests different testing devices can be connected to the pump.

DPI - The more modern kind of Inhaler is the so called Dry Powder Inhaler (DPI).
In contrast to the Metered Dose Inhaler (MDI) it is environment friendly.
Because the unit is not pressurised the lung acts to serve the pressure.
For this reason in addition to the vacuum pump a Dry Powder Controller is needed which serves to control the air-flow of the system, simulating the human lung.