Exhaled breath condensate-site and mechanisms of formation.

Exhaled breath condensate (EBC) analysis is a promising tool for diagnosis and management of pulmonary diseases. Its clinical usefulness is still limited however due to unresolved issues around e.g. reproducibility, anatomical site of origin of EBC solutes and mechanisms of EBC formation. To gain some knowledge on these issues, three different airway deposition patterns of an aqueous aerosol containing technetium-99m were studied in eight healthy non-smoking subjects. EBC was collected 20 min after each radioaerosol administration and analyzed for gamma radiation and electrolytes. Radioaerosol deposition in preferentially central lung compared with preferentially peripheral lung resulted in 3.8 times higher EBC radioactivity. EBC concentrations of Na(+) and K(+) correlated significantly indicating dilution by water vapor to be a major source of variability. Since Na(+)/K(+)- and Na(+)/S(2-)-concentration ratios, but not Na(+)/Cl(-)- or Na(+)/Ca(2+)-, were comparable to those previously reported for alveolar lining fluid (ALF), some mechanisms other than dilution are likely also to be involved. In conclusion, our findings indicate that EBC derives mainly from the central airways, that the electrolyte composition of EBC does not consistently reflect that of ALF, and that EBC concentrations of electrolytes are determined not only by ALF dilution with water vapor but also by other mechanisms.