A CASCADE IMPACTOR ENTRY PORT FOR MDI SPRAYS WITH COLLECTION CHARACTERISTICS IMITATING A PHYSICAL MODEL OF THE HUMAN THROAT

Purpose. This work was performed in order to compare and contrast resu lts obtained from cascade impactor measurements on metered dose inhale rs (MDIs) using a variety of inlet ports. Methods. The collection char acteristics of four cascade impactor ports (a physical model of the hu man throat, a simplified geometry intended to mimic the physical model , and two currently-used ports) were measured on a variety of MDI form ulations. Results. The portion of the MDI spray which collects on the entry port depends in a complicated fashion on the characteristics of the formulation; in these studies the fraction of the total dose which was collected on the port ranged between about 20% and 90% of the tot al emitted dose. The collection characteristics of the simplified geom etry closely corresponded to the physical model. The length of the flo w path between the port and the impactor was varied, and found not to have a strong effect on the measured size distribution passing the por t. Conclusions. Ranking of various MDI formulations according to perfo rmance criteria as measured with a cascade impactor should be expected to depend on the particular inlet port which is used.