Influence of insoluble aerosol deposits on the surface activity of the pulmonary surfactant: A possible mechanism of alveolar clearance retardation?

Pulmonary surfactant is believed to be involved in the alveolar clearance b oth due to its direct influence on the flow of the liquid alveolar hypophas e and due to the stimulating effect on the alveolar macrophages activity. I n the present work, interaction between aerosol particles and liquid materi al containing pulmonary surfactant was investigated in a model physicochemi cal system. Interfacial activity of the surfactant material used in clinica l practice (Infasurf) was evaluated with the Pulsating Bubble Surfactometer (PBS). Dynamic surface properties were compared for the surfactant before and after contact with soot particles (MMAD: 0.3 microns, GSD: 1.56). Conce ntration of soot in the surfactant suspension was adjusted to 0.2 mg per ml and 1 mg per ml based on the calculations of maximum alveolar deposition f or the particles of that size during 6 h inhalation at 2 harmful occupation al concentrations: 750 mu g/m(3) and 3.7 mg/m3, respectively. The average m inimum surface tension measured under dynamic conditions was 3.2 mN/m for c ontrol surfactant, while for the surfactant mixed with soot it was equal to 4.5 and 6.8 mN/m for 0.2 mg soot per mi and 1 mg soot per mi, respectively . Other surfactant properties (hysteresis, stability index) determined from the experimental data confirmed surfactant inactivation. Results of the st udies indicate that the amount and activity of the surfactant in the suspen sions were reduced after contact with soot particles, probably due to adsor ption of the surfactant molecules on solid particles characterized by a lar ge interfacial area. Reduction of the activity of the surfactant in the pre sence of a significant number of airborne insoluble particles (e.g., soot), as suggested by this study, can lead to disturbance of the physiological r ole of the surfactant, including alveolar clearance. This physicochemical p henomenon can be considered as a contributing factor to alveolar clearance retardation in the overloaded lungs.