Dilution of respiratory solutes in exhaled condensates

Most exhaled water is produced as gaseous water vapor, which can be collected in cooled condensers. The presence of nonvolatile solutes in these condensates suggests that droplets of respiratory fluid (RF) have also been collected. However, calculation of RF solute concentrations from condensates requires estimation of the dilution of RF droplets by water vapor. We used condensate electrolyte concentrations to calculate the dilution of RF droplets in condensates from 20 normal subjects. The total ionic concentration (conductivity) was 497+/-68 (mean+/-SEM) muM. Of this, 229+/-43 muM was NH4+, but little NH4+ was collected from subjects with tracheostomies, indicating oral formation. The Na+ concentration in condensate ([Na+](cond)) averaged 242+/-43 muM. Large variations in [Na+](cond) correlated well with variations of K+ in condensate ([K+](cond)) and Cl- in condensate ([Cl-](cond)), and were attributed to differences in respiratory droplet dilution. Dividing condensate values of ([Na+] + [K+]) by those of plasma indicated that RF represented between 0.01% and 2.00% of condensate volumes. Calculated values for Na+, K+, Cl-, lactate, and protein in RF were [Na+](RF) = 91+/-8 mM, [K+](RF) = 60+/-11 mM, [Cl-](RF) = 102+/-17 mM, [lactate](RF) = 44+/-17 mM, and [protein](RF) = 7.63+/-1.82 g/dl, respectively.