Measurements of electrodynamic effects on the deposition of MDI and DPI aerosols in a replica cast of human oral-pharyngeal-laryngeal airways.

Metered dose inhalers (MDIs) and dry powder inhalers (DPIs) are popular drug delivery devices used in the treatment of respiratory diseases such as asthma and chronic obstructive pulmonary disease (COPD). Integrated effects of electrostatic charges and aerodynamic sizes on the deposition of MDI and DPI particles in a replica cast of human oral-pharyngeal-laryngeal (OPL) airways were examined. Experimental aerosols were generated from commercially available MDI and DPI devices. They are the trademarked brands of the same pharmaceutical company, and contain the same amounts of different drugs. Inhalations were administered as boluses and characterized with an Electronic Single Particle Aerodynamic Relaxation Time (ESPART) analyzer before and after passing through the cadaver-based OPL cast. The MDI and DPI aerosols were not only of different sizes but also carried different positive, negative and zero electrostatic charges; 42.2% of the total number of DPI particles was charged in comparison to 6% of those produced by the MDI. Electrodynamic properties (e.g., charges and sizes) played significant roles on the behavior and deposition of aerosols in the OPL airways. As detailed herein, deposition fractions of the total (charged and uncharged) DPI aerosols were 21.5% in contrast to 2.8% for the MDI aerosols, whereas the charged particle deposition for the DPI was 46.7% in contrast to 22.5% for the MDI. Particle losses in the OPL passages were greater for the DPI than the MDI as the former generated more charged particles than the latter. This finding is consistent with results reported by other researchers but contradicts the observation of another investigator where MDI losses were reported as being higher than those for DPIs. The chief reason for this difference may be that the latter study did not account for the electrical properties of aerosol particles, but only for their mechanical properties. Because the measured deposition efficiencies of MDI and DPI aerosols were different, the data have important implications to inhalation therapy protocols.