Characterisation of Aerosols Generated by Pressurised Metered Dose Inhalers
For over half a century, pressurised metered dose inhalers (pMDIs) have been the most sold inhaler devices for the treatment of lung diseases. However, they suf- fer from signicant drug deposition in the mouth and throat, mainly due to the aerosolisation of large and fast-moving droplets. This causes a high occurrence of side eects and is wasteful of drug. They are also aected by a low consistency of dosing and as a result users might not benet from maximal device eciencies. The hypothesis of this work was that the performance of pMDIs is dependent on numerous factors which might alter the characteristics of their particles and their deposition location within the respiratory tract. For example, it was thought that the variations in actuation forces of pMDIs and temperatures at which they are used might contribute to their low consistency. A one-dimensional Matlab computational model was developed in order to calcu- late spray properties at the exit of the device where experimental measurements are dicult to conduct. The model simulated the discharge of pure HFA134a formulations and HFA134a-based suspension formulations containing uticasone propionate; the latter representing a commercially available formulation. The results showed that the actuation force of a\healthy" adult led to a higher valve opening rate and to the aerosolisation of smaller droplets than the actuation force provided by a \weak" adult. The model also showed that an increase of temperature led to the aerosolisation of smaller droplets. The model was validated using impaction measurements and laser techniques. The next generation impactor (NGI) experiments revealed the importance of actu-ation forces on the throat deposition. Automated actuation forces with high valve opening rates led to a lower throat deposition than a manual actuation force with low valve opening rate.
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