Aerosol Inhalation and Depth of Deposition in the Human Lung

Abstract

Ten patients with chronic bronchitis, whose FEV-_1.0 varied between 0.48 and 3.00 1, inhaled uniform 5-μm particles tagged with technetium-99 in tidal volumes (VT) varying between 750 and 1830 ml. Their chests were scanned after inhalation to ascertain depth of deposition of the particles, and clearance from the lungs was monitored for 5 hr by serial whole-lung gamma counting. A significant inverse relationship (P < .05) was found between depth of deposition after inhalation (D), measured horizontally across the lung as percentage per inch, and rate of clearance of the particles (5-hr retention [%] = 100 - % cleared at 5 hi = 69.12 − 3.02D). This confirmed previous findings. The depth of deposition depended directly on the FEV_1.0 and VT (5-hr retention [%] = 0.026VT + 12.67FEV_1.0 -4.13); this resulted in a 14%-75% range for 5-hr retention. Regression slopes for VT and FEV_1.0 were independently significant (P <.05). The findings suggest that, as commonly administered at present, the therapeutic efficiency of most drugs given by aerosol will be reduced in proportion to the degree of airway obstruction as measured by the FEV_1.0.The efficiency can be enhanced by increasing the depth of inspiration of the aerosol.