Evidence for Airway Acidity and Oxidative Stress in Exhaled Breath Condensates from Grain Workers

Abstract

In their article, Dr. Do and colleagues described exhaled breath condensate (EBC) studies that they interpret to indicate airway acidity and oxidative stress (8-isoprostane) in grain workers (1). Unfortunately, neither of these conclusions can be drawn on the basis of the data they have collected. With regard to pH, the species NH4 1 and HCO3 2 represent approximately 90% of the acids and bases found in most samples of EBC (2). Generation of approximately 90% of the NH4 1 is in the mouth rather than the airways, much of it from bacterial degradation of urea (3). Low concentrations of volatile organic acids (e.g., acetic acid) may be found in EBC, but these may also represent oral contamination. Abnormal EBC pH probably reflects oral rather than airway metabolism (3), and the pH and constituents of saliva should have been measured. Furthermore, the investigators did not measure amylase concentrations in the EBC to detect direct salivary contamination, which is more likely because the condenser they used is close to the mouth during collection. Filtering the EBC is not well justified in the article and had no effect. Furthermore, exposure of the samples to argon leaves behind much of the CO2/HCO3 2 and may cause loss of other volatile acids and bases. Interpretation of EBC pH is problematical because the buffering capacity of the EBC was not measured. Condensates should not be used to collect volatile constituents such as NH3 since recovery of these solutes in the aqueous phase can be influenced by local pH, temperature, airflow, and turbulence in airways and condensers. With regard to isoprostane, EBC concentrations of isoprostane cannot be reliably used to estimate either concentrations or changes in concentrations of isoprostane in the airways unless a dilutional indicator is also measured (e.g., conductivity of lyophilized samples, which is readily measured with simple equipment) (4). Increased 8-isoprostane concentrations may reflect the production of more respiratory droplets in the airways rather than increased concentrations in the airway fluid. EBC concentrations of nonvolatiles are approximately 1% those in bronchoalveolar lavage (BAL) and 0.01% those in respiratory fluids. It is therefore puzzling that EBC 8-isoprostane levels in the normals of Do and coworkers (z10 pg/mL) are nearly the same as those reported in BAL by others (5). The EBC approach holds the promise that airway constituents may be measured noninvasively, but oral contamination with volatile solutes and extreme and variable dilution by water vapor from the airways must be experimentally addressed in all studies of this sort.