Single breath particle characterization to detect small airway alterations
Rationale: Breath aerosols are generated during the reopening of collapsed terminal airways and therefore provide information directly from the lung periphery. Thus, physical breath aerosol characterization might be useful for detection of small airways disease, which is primarily located in the lung periphery. Hitherto, there is a lack in systematic data on exhaled particle characteristics, especially on single breath basis. The aim of our study was to investigate the potential of single breath aerosol characterization as a novel method for diagnosis of airway disease. Methods: Exhaled particle number, size distribution and airflow rates were recorded simultaneously using a condensation nucleus counter (TSI 3760) and a laser spectrometer (LASAIR II-110, range 0.1 -5 µm). For 11 healthy non-smokers, 13 healthy smokers, and 22 subjects with mild-to-severe COPD, breath aerosol properties were recorded highly time-resolved during a standardized slow exhalation manoeuvre at large tidal volume. Results: The analysis of the size distribution measured during the exhalation phase of a single breath shows a decreasing size-reduction towards end-expiration with increasing severity of COPD compared to healthy non-smokers. Using a particle size index, defined as number of particles larger than 0.5 ?m to total particle number for the exhalation process, healthy non-smokers and COPD-patients can be well separated (e.g. 0.17 for healthy non-smokers, 0.23 for COPD I and 0.34 for COPD II at a vital capacity of 5 litres). Most importantly, part of the healthy smokers show a size distribution pattern like subjects with mild COPD, while others display results typically observed for healthy non-smokers. For the time-resolved exhaled particle concentration profile, no significant differences were found between healthy and diseased subjects. Discussion and Conclusions: The exhaled particle size distribution is determined by the size of the droplets generated in the lung and by size-dependent gravitational re-deposition during exhalation, controlled by the relevant airway structures. Since, according to further investigations, the particle size generated is assumed to be the same for healthy and diseased subjects, the differences in exhaled particle size indicate small airway alterations. COPD and early stages of airway diseases are known to be associated with structural changes in the lung periphery. Therefore, single breath particle characterization might be a suitable non-invasive method for early detection of small airway alterations.