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Exhaled breath condensate (EBC) pH is low in several lung diseases and it normalises with therapy.The current study examined factors relevant to EBC pH monitoring. Intraday and intraweek variability were studied in 76 subjects. The pH of EBC collected orally and from isolated lower airways was compared in an additional 32 subjects. Effects of ventilatory pattern (hyperventilation/hypoventilation), airway obstruction after methacholine, temperature (-44 to z13uC) and duration of collection (2-7 min), and duration of sample storage (up to 2 yrs) were examined. All samples were collected with a disposable condensing device, and de-aerated with argon until pH measurement stabilised.Mean EBC pH (n=76 subjects, total samples=741) was 7.7¡0.49 (mean¡SD). Mean intraweek and intraday coefficients of variation were 4.5% and 3.5%. Control of EBC pH appears to be at the level of the lower airway. Temperature of collection, duration of collection and storage, acute airway obstruction, subject age, saliva pH, and profound hyperventilation and hypoventilation had no effect on EBC pH.The current authors conclude that in health, exhaled breath condensate pH is slightly alkaline, held in a narrow range, and is controlled by lower airway source fluid. Measurement of exhaled breath condensate pH is a simple, robust, reproducible and relevant marker of disease. Eur Respir J 2003; 22: 889-894.

Fluid condensed from the breath of patients with acute asthma is acidic. Several features of asthma pathophysiology can be initiated by exposure of the airway to acid. In renal tubular epithelium, glutaminase produces ammonia to buffer urinary acid excretion. We hypothesized that human airway epithelium could also express glutaminase. Here, we demonstrate that human airway epithelial cells in vitro have biochemical evidence for glutaminase activity and express mRNA for two glutaminase isoforms (KGA and GAC). Glutaminase activity increased in response to acidic stress (media pH 5.8) and was associated with both increased culture medium pH and improved cell survival. In contrast, activity was inhibited by interferon-gamma and tumor necrosis factor-alpha. Glutaminase protein was expressed in the human airway in vivo. Further, ammonia levels in the breath condensate of subjects with acute asthma were low (30 microM [range: 0-233], n = 18, age 23 +/- 2.5 yr) compared with control subjects (327 microM [14-1,220], n = 24, age 24 +/- 2.4 yr, p < 0.001), and correlated with condensate pH (r = 0.58, p < 0.001). These data demonstrate that glutaminase is expressed and active in the human airway epithelium and may be relevant both to the regulation of airway pH and to the pathophysiology of acute asthmatic airway inflammation.

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Exposure to cat or dog allergen airborne in homes with an animal can be up to 100 times higher than exposure to mite allergen. The results are in keeping with a model where immunological tolerance to animal dander allergens results from high exposure.

Denitrifying bacteria metabolize nitrogen oxides through assimilatory and dissimilatory pathways. These redox reactions may affect lung physiology. We hypothesized that airway colonization with denitrifying bacteria could alter nitrogen balance in the cystic fibrosis (CF) airway. We measured airway nitrogen redox species before and after antimicrobial therapy for Pseudomonas aeruginosa in patients with CF. We also studied ammonium (NH(4)(+)) and nitric oxide (NO) metabolism in clinical strains of P. aeruginosa in vitro and in CF sputum ex vivo. Ammonium concentrations in both sputum and tracheal aspirates decreased with therapy. Nitric oxide reductase (NOR) was present in clinical strains of P. aeruginosa, which both produced NH(4)(+) and consumed NO. Further, NO consumption by CF sputum was inhibited by tobramycin ex vivo. We conclude that treatment of pseudomonal lung infections is associated with decreased NH(4)(+) concentrations in the CF airways. In epithelial cells, NH(4)(+) inhibits chloride transport, and nitrogen oxides inhibit amiloride-sensitive sodium transport and augment chloride transport. We speculate that normalization of airway nitrogen redox balance could contribute to the beneficial effects of antipseudomonal therapy on lung function in CF.