Deposition of pressurised aerosols in the human respiratory tract

Although the use of pressurised aerosol inhalers is widespread, little is known about the actual deposition of the aerosol in the respiratory tract, since this has previously been difficult to measure. We have incorporated Teflon particles (mean diameter 2 micrometer) with aerodynamic properties similar to those of bronchodilator drug crystals into pressurised aerosol canisters. Controlled inhalations by eight patients with obstructive airways disease showed that on average 8.8% of the dose was deposited in the lungs (3.0% in the alveoli and 5.8% on the conducting airways) and 80% in the mouth. These figures are in good agreement with previous indirect estimates of deposition based on metabolic studies. The remainder of the dose was either expired (1.0%) or deposited in the aerosol actuator (9.8%). This method should have wide application for measurement of deposition patterns under various conditions and for assessment of therapeutic effects.