SURFACTANT AND INHALED PARTICLES IN THE CONDUCTING AIRWAYS - STRUCTURAL, STEREOLOGICAL, AND BIOPHYSICAL ASPECTS

We have investigated the displacement into the sol phase of inhaled pa rticles deposited in the intrapulmonary conducting airways. Hamsters i nhaled an aerosol of monodisperse polystyrene particles of 6 mum diame ter. Their lungs were fixed by intravascular perfusion, and light and electron microscopy was used to study the epithelial coating. The surf actant film at the wall-air interface was investigated by measuring it s surface tension. The number of particles retained was determined ste reologically. In addition we investigated the displacement of spherica l particles in vitro on a DPPC monolayer in a Langmuir-Wilhelmy surfac e balance and determined the surface tension in vivo in the horse trac hea by video bronchoscopy, applying the droplet spreading method. We f ound that particles deposited onto a surfactant film were pulled into the aqueous subphase, and we concluded that surface forces due to the airway surfactant likely displace deposited particles into the pericil iary fluid (sol phase). Comparing lungs fixed immediately after inhala tion with lungs fixed 24 hr after inhalation revealed that 86% of the particles retained in the intrapulmonary conducting airways immediatel y after inhalation had been cleared within 24 hr. One-third of the par ticles of the lungs fixed immediately after inhalation was phagocytize d. The combination of structural and stereological analyses with in vi tro and in vivo measurements has led to new insights into the role of airway surfactant with respect to the fate of inhaled particles, which may have important consequences regarding the effects of hazardous pa rticles. These studies may also help to evaluate the deposition patter n and clearance of therapeutic particles, with important implications for their therapeutic use. (C) 1993 Wiley-Liss, Inc.