Characterization of exhaled particles from the human lung in airway obstruction

Background: Human breath contains small particles which might be useful for non-invasive diagnosis of lung disease. In this study, the impact of peripheral and central airway obstruction on particle emission characteristics was investigated. Methods: Particle number flux and particle size distribution were recorded for healthy non-smokers (n = 16), healthy smokers (n = 13), patients with chronic obstructive pulmonary disease (COPD, n = 28, GOLD-stage I - IV), and patients with asthma following methacholine challenge (n = 10) by means of a condensation nucleus counter (TSI 3760) and a laser spectrometer (PMT LASAIR II-110). Results: Particle number per breath showed high intra-subject reproducibility. However, there was a large inter-subject variability of emitted particle number in the order of about two magnitudes, with no influence of airway obstruction on emission level. Similarly, methacholine-induced airway obstruction in subjects with allergic asthma did not change the exhaled particle number when compared to pre-challenge values. For the droplet size distribution averaged per breath, there was no difference between healthy subjects and subjects with airway obstruction. Conclusion: Airway obstruction does not change the number flux or size distribution of particles in exhaled breath. Due to the high inter-subject variability of particle emission, only the on-line determination of aerosol properties, primarily number flux, during exhaled breath condensate sampling would allow for a normalization procedure for the results of biochemical analysis. As high and variable dilution is the main challenge of biomarker assessment in exhaled breath condensate, normalization would significantly add to the value of this technique