Effects of forced exhalations and cough on surfactant content and size distribution of exhaled particles

We exhale endogenous particles during breathing that may carry information on the status of the respiratory tract. The aim of the study was to investigate particle formation during forced exhalations and cough, by evaluating particle size distribution and surfactant content. A reference maneuver that emits a minimum number of particles, was compared with a forced exhalation, a cough maneuver and an airway opening maneuver. These maneuvers were studied in a group of 11 healthy subjects using the PExA method. Particle size distribution and number concentrations in the range of 0.41-4.55 µm in diameter were measured using an optical particle counter before sampling by inertial impaction. Concentration of the main surfactant lipid dipalmitoylphosphatidylcholine (DPPC) was determined by mass spectrometry. The exhaled particle mass for the forced and cough maneuvers were 2.5 (95% CI 1.1-5.7, p=0.03) and 7.4 (95% CI 3.3-16.7, p The results are consistent with particle formation in central airways during forced exhalation and in the upper airways during cough. There was no increase in exhaled DPPC by forced exhalations or cough, despite the increase in exhaled particles, these particles have a very low concentrations of surfactant compared to particles from small airways.