Particle Retention in Airways by Surfactant

Abstract

ABSTRACT

With each breath thousands of particles may enter the lungs where they are deposited. They may be retained for various periods of time in the conducting airways, before being removed. The deposition of particles is, by definition, terminated, as soon as the particles touch the airway wall. Following deposition, retention and clearance begin. For both mechanisms structure and surface properties of the coating of the airway wall are important. In some recent studies it has been reported that clearance from the conducting airways may take longer than the postulated 24 hours. Our own recent structural studies with hamster lungs showed that a considerable number of particles initially deposited in the conducting airways of the lungs can be found retained in the airways in close association with the epithelium. These particles were coated with an osmiophilic film owing to phospholipids related to surfactant. This film may be responsible for the displacement of particles from the air to the aqueous (gel and sol) phases. Surface tension measurements in sheep lung bronchi and on surfaces of excised sheep tracheae not only confirmed the existence of a surfactant film in the conducting airways of the lungs but also led us to the conclusion that the surface tensions in these airways may be responsible for the observed particle displacement into the mucus.