1Occupational and Environmental Medicine, 2Respiratory Medicine and Allergology, Sahlgrenska Academy at University

nique of sampling exhaled air is attractive because it is noninvasive and so allows repeated sampling with ease and no risk for the patient. Knowledge of the biomarkers ’ origin is important to correctly under-stand and interpret the data. Endogenous particles, formed in the airways, are exhaled and reflect chemical composition of the respira-tory tract lining fluid. However, the formation mechanisms and formation sites of these particles are unknown. We hypothesize that airway opening following airway closure causes production of air-borne particles that are exhaled. The objective of this study was to examine production of exhaled particles following varying degrees of airway closure. Ten healthy volunteers performed three different breathing maneuvers in which the initial lung volume preceding an inspiration to total lung capacity was varied between functional residual capacity (FRC) and residual volume (RV). Exhaled particle number concentrations in the size interval 0.30–2.0 m were re