Background: The pH of exhaled breath condensate (EBC) of adolescent athletes engaged in vigorous physical activity is low compared to healthy controls; however, the ionic determinants of EBC pH and the acute effects of exercise on those determinants have not been definitively established.
Objectives: This study had two purposes: (1) to identify the ionic composition of EBC before and after exercise, and (2) to examine the effects of sample deaeration on EBC pH and composition.
Methods: EBC ionic composition was determined by ion chromatography and correlated with pH measured before and after deaeration. Bicarbonate concentration was calculated from the ion balance of other measured species and pH.
Results: EBC pH displayed a bimodal distribution, included values lower than expected for healthy individuals, and was correlated exclusively with volatile species, namely ammonia (mean concentration = 215 microM) and acetic (31.7 microM) and propionic acids (10.0 microM). Following exercise, raw EBC pH and ammonia concentration increased while propionic acid concentration fell. Following deaeration, EBC pH increased by one unit on average; however, the pH of samples with unusually low pH did not change significantly, and the concentrations of several ionic species were altered in a manner that cannot be explained in terms of volatility.
Conclusions: We conclude that in healthy adolescents, exercise results in an acute increase in raw EBC pH in association with an increase in ammonium and a decrease in propionate concentration. Since exercise increases systemic ammonia and urea (which is hydrolyzed by oral bacteria to form ammonia), we propose that the likely source of these changes is gas-phase diffusion from epithelial and oral surface liquids and to a lesser extent, from pulmonary circulation.