Background: Noninvasive monitoring of airway inflammation is important for diagnosis and treatment intervention of lung disease. Mediators of interest are often nonvolatile molecules that are exhaled as aerosols and captured by breath condensation. Because analysis of exhaled breath condensate has been troublesome in the past, partly due to poor standardization and unknown dilution, we investigated in detail the influence of respiratory variables on exhaled particle number and size distribution during tidal breathing in healthy volunteers.
Methods: Particle number was detected by a condensation nuclei counter, and size distribution was determined by a laser spectrometer online with high time resolution while subjects underwent a defined protocol of normal and deep tidal breathing. Intra- and intersubject variability of particle emission was analyzed and physical properties of exhaled aerosols were correlated to pulmonary function variables obtained by body-plethysmography.
Results: The particle size distribution was in the submicron range and stable during tidal breathing. Increasing tidal volumes dominantly influenced particle number emission while flow rates had only little effect. Reproducibility within subjects was high, but there was a large variation of particle emission between subjects. The ratio of functional residual capacity to total lung capacity was found to correlate with exhaled particle numbers. This indicates that particle generation is caused by reopening of terminal airways and is dependent on functional residual capacity.
Conclusion: We conclude that online determination of exhaled aerosols from the human lungs is a prerequisite to standardize the assessment of nonvolatile mediators by normalization to the aerosol emission rate.