Development of a theoretical model to predict pMDI spray force, using alternative propellant systems

Continued success in the treatment of asthma and COPD requires new pMDI propellants for delivering aerosols with good patient comfort and acceptable levels of oral cavity deposition. The purpose of this work is to develop a theoretical model capable of predicting pMDI spray force as a function of metering valve geometric parameters and different propellant systems: HFA134a, HFA227ea and HFA152a. Such theoretical tool can be used in combination with lab-based measurements for device characterisation and potentially to reduce the number of experimental trials. The outcome of the model is compared against measurements of plume force with Copley Scientific Spray Force Tester SFT 1000. Results suggest that the size of the spray orifice has a significant direct effect on the spray force. We have also observed HFA134a and HFA152a generates similar magnitude of spray force and velocity where HFA227ea generates the lowest velocity and force values. These findings could potentially mean HFA152a sprays are expected to show similar levels of mouth-throat deposition to HFA134a sprays rather than HFA227ea sprays.