On the Formation and Physical Behaviour of Exhaled Particles

Aerosol particles are generated in human airways and leave the body with exhaled air. The particles originate from the respiratory tract and contain non-volatile com-pounds that potentially may be used as biomarkers for various medical conditions. To utilise any information provided by the particles, they must be characterised. The work performed in this thesis focuses on measuring concentrations and size distribu-tions of endogenous particles in exhaled air. The results give indications on how and where in the airways particles are formed. Number size distributions of exhaled particles, obtained from different individuals and breathing techniques, were measured. The results show that the inter-individual variation in number concentration is very high, while the size distribution peaks at about the same diameter for all subjects. The distribution peaks at a smaller particle diameter for tidal breathing than it does for breathing reaching airway closure. More-over, deep exhalations result in significantly higher particle concentrations than tidal breathing. Exhalation followed by a few seconds breath hold amplifies the number o