Critical Flow Controller
During the use of Dry Powder Inhalers (DPI’s) the emitted and fine particle dose are affected by the strength and duration of the patient's inspiration particulalry noticeable in the lederly and in small children.
Furthermore, different inhaler designs provide various degrees of resistance to inhalation.
The Pharmacopoeia have defined the factors governing the performance, and therefore, the test criteria for Dry Powder Inhalers.
1. The pressure drops of the air drawn through the inhaler during inspiration.
2. The appropriate flow rate (Q) to give a pressure drop of 4kPa across the device during the test
3. The duration of in-vivo inspiration to give a volume of 4 litres
4. Flow rate stability in terms of critical (sonic) flow
The main features of the Critical Flow Controller as required by the Pharmacopoeia to fulfill its requirments are:
1. Built in Differential Pressure Meter for measuring pressure drop (P1)
2. Flow Control Valve to adjust flow rate
3. Timer controlled two-way solenoid valve to adjust flow duration
4. Absolute Pressure Meters for measuring sonic flow (P2 and P3)
5. Membrane keypad control
6. LCD display of differential and absolute pressure valves
7. Illuminated LC display of Set and Elapsed Times
8. Printer port