Aerosol Therapy of Particle Behavior in the Respiratory Tract

Consequences for Aerosol Therapy of Particle Behavior in the Respiratory Tract 

In aerosol therapy, particles are used to carry pharmaceuticals into the respiratory tract, where they become available upon deposition for the treatment of topical or systemic diseases. It must, however, be recognized that particle deposition in the human respiratory tract discussed so far is confined to particles with hydrophobic surfaces and fuUy entrained in the inspired air. However, in aerosol therapy, these ideal conditions are often not fulfilled. It must also be recognized that the deposited mass (dose) or the mass deposited per unit surface area (surface dose) rather than the number of deposited particles is of interest in aerosol therapy. Therefore, particles are suitable for therapy only if they deliver a sufficient dose of a pharmaceutical to the respiratory tract. These particles are usually larger than 1 pm in diameter. 

Mabcel Dekker, Inc. 270 Madison Avenue, New York, New York 10016 

Mass Deposition of Poiydisperse Particies (Deposited Dose) 

These data are confined to particles fully entrained in the inspired air. When particles are, however, inspired from propellant-based metered-dose or dry-powder inhalers, their velocity is much greater than that of the inspired air, and only a small mass fraction (nonballistic fraction) escapes inertial deposition in the oropharynx and enters the trachea. The mass fraction of particles deposited in the oropharynx (ballistic fraction) can be determined experimentally. It comprises more than 50% of the mass released from inhaler devices and therefore is much larger than that deposited in the larynx. It is usually assumed that the ballistic fraction is equal to the mass fraction collected in an induction port placed in front of a cascade impactor. Collection of particles in the impactor allows the estimation of the mass distribution of particles entering the respiratory tract. Finally, these distributions can be used to calculate regional mass depositions with a deposition model. 

---