New insights into pMDI operation using synchrotron X-ray techniques

This article describes synchrotron x-ray measurement techniques to study the internal and external flow of aerosols produced by pressurized metered dose inhalers (pMDIs). Application of phase contrast imaging, x-ray radiography and x-ray fluorescence techniques have revealed the internal flow within the pMDI nozzle expansion chamber to be comprised of a bubbly multiphase mixture. Bubble size was found to vary with time and pMDI formulation. Atomization of the mixture was shown to be initiated in the nozzle itself, with exit flow dominated by vapor. Measurement of drug concentration within the spray followed a similar trend to droplet distribution, suggesting the drug is well mixed within the spray. New x-ray techniques under development promise to expand measurement capacity to droplet size, which when combined with these three techniques, may deliver spatial and temporal data on drug particle formation in the spray.