© 2008 American Thoracic Society
Metabolomics in Exhaled Breath CondensatesTo the Editor:The intriguing article by Dr. Carraro and colleagues (1) concerning nuclear magnetic resonance (NMR) measurements of exhaled breath condensate (EBC) for distinguishing patients with asthma from normal subjects suggests that this procedure may be used as an "artificial nose" for detecting airway disease. Further studies of this novel approach should be encouraged, but two caveats are warranted. In Carraro and colleagues' study, the EBC samples were not fully dried out, and they may have contained volatile substances derived from extrapulmonary sources. For example, more than 80% of exhaled NH3 and vapors responsible for halitosis are derived from the upper aerodigestive structures (tongue, periodontal tissues, nose, sinuses, etc.) (2, 3), and contamination by volatile salivary compounds can have a profound effect on EBC pH (4). Volatile organic substances may reflect local bacterial metabolism and inflammation rather than abnormalities in the lungs. At the very least, NMR measurements should also be made in saliva. Additional studies are needed in subjects with tracheostomies or endotracheal tubes. The EBC approach is particularly unsuitable for collecting volatile solutes since recovery of these substances in EBC is dependent on their distribution between the saliva, exhaled air and droplets, and the condensate, which can be altered by multiple factors including minute ventilation, salivary pH, solubility, temperature, and sample preparation.
Harbor–UCLA Medical Center FOOTNOTES Conflict of Interest Statement: R.M.E. does not have a financial relationship with a commercial entity that has an interest in the subject of this manuscript. REFERENCES
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