The effect of temperature on exhaled breath condensate collection

Exhaled breath condensate (EBC) collection is an innovative method of non-invasively sampling the lung, and can detect a variety of volatile and non-volatile biomarkers, but the disadvantage is the small volume of sample collected. It was hypothesized that a collection system at a lower temperature would increase the volume collected, but may alter the relative concentration of the biomarkers of interest. EBC was collected in a cross-over study using a custom-made collection system, cooled using either wet (4 °C) or dry ice (-20 °C) in randomized order in normal non-smoking volunteers. The volume of the EBC collected per unit time was determined as were conductivity, the concentrations and total amount of protein, hydrogen peroxide, and nitrite/nitrate concentrations. Dry ice was associated with a 79% greater volume of EBC than the wet ice (1387 ± 612 µL; 773 ± 448 µL respectively, p < 0.0001). Conductivity was influenced by the temperature of collection (18.78 ± 6.71 µS cm(-1) for wet ice and 15.32 ± 6.28 µS cm(-1) for dry ice, p = 0.02) as was hydrogen peroxide (1.34 ± 0.88 µg mL(-1) for wet ice and 0.68 ± 0.32 µg mL(-1) for dry ice, p = 0.009) while the concentrations and total values for protein and nitrate/nitrite were not significantly different (p > 0.05). This pilot study suggests that lower collection temperatures facilitate the collection of a larger sample volume. This larger volume is not simply more dilute, with increased water content, nor is there a simple correction factor that can be applied to the EBC biomarkers to correct for the different methods.