CLEARANCE OF PARTICLES FROM SMALL CILIATED AIRWAYS

In recent years, there has been a debate on whether a considerable fra ction of particles is retained after 24 h in the tracheobronchial regi on. In the present study, 8 healthy subjects inhaled 6.2-mu m monodisp erse Teflon particles labeled with In-111 twice, at flow rates of 0.45 and 0.045 L/s. According to theoretical calculations, tile particles inhaled at 0.45 L/s should deposit mainly in large bronchi and in the alveolar region, whereas the particles inhaled at 0.045 L/s should be deposited mainly in small ciliated airways. Twenty-four hours after in halation, about half of the particles inhaled with both modes of inhal ation had cleared. Clearance during the period from 1 to about 30 days after inhalation, could, for both modes of inhalation, be described b y the sum of two exponential functions. For the inhalation rate of 0.4 5 L/s, 15% cleared with a half-time of 3.4 days and 85% with a half-ti me of 190 days. For the inhalation at 0.045 L/s, 20% cleared with a ha lf-lime of 2.0 days and 80% with a half-time of 50 days. The results s trongly indicate (1) that a considerable fraction of particles deposit ed in small ciliated airways had not cleaved within 24 h, and (2) that these particles cleared differently from particles deposited in the a lveolar region. The experimental data agree quite well with the IRTM p redictions made using its default slow clearance fractions.