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Exhaled Breath Condensate pH

In an editorial (1) that accompanied our article on the effect of volatile acids and bases released from the mouth (2), Dr. Hunt has acknowledged that these can have a significant influence on exhaled breath condensate (EBC) pH, but believes that EBC pH primarily reflects pulmonary rather than oral buffering. Since the EBC pH approach was designed to detect pH changes in the lungs, it was hoped that most of the acids and bases found in oral EBC samples are derived from the lungs rather than saliva. Unfortunately, we found that represents greater than 80% of the cations in the EBC, and most of this is generated from NH₃ in the mouth, even though the surface area of the mouth is much smaller than that of the lungs (3). Furthermore, titrimetry showed that NH₃ produced in the mouth is largely neutralized by ambient CO₂ to form concentrations of that approach those of (2). Had we flushed the samples with dry argon to remove CO₂, as recommended by Hunt, we would have increased EBC pH and found titrimetric evidence for or even OH^– rather than acids unrelated to CO₂. We avoided "degassing" the samples because we found this was neither effective nor selective: much CO₂ remained, some water and were lost, and losses of other volatile constituents (e.g., acetic acid) would be expected.

Our studies indicate that the pH of oral EBC is usually governed by high concentrations of volatile contaminants from the mouth ( and ) rather than pulmonary constituents. However, acidification of saliva (e.g., by gastroesophageal reflux or periodontal disease) can lower the EBC pH by reducing release of NH₃ and increasing release of acetic acid from saliva. It should be noted that, contrary to Dr. Hunt's editorial, we used relative and cation concentrations as well as amylase to rule out direct salivary contamination, indicating that both acetic acid and NH₃ reach the EBC as vapor rather than droplets.

Although inflammation can presumably acidify intrapulmonary airways, the predominant effects of EBC contamination with volatile salivary acids and bases call into question the reliability of oral EBC pH as a measure of pulmonary acidification. Major discrepancies between bronchial EBC and bronchial surface pH measurements also suggest that EBC pH values can be misleading (4).

Richard M. Effros

Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, Torrance, California

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

1. Hunt J. Exhaled breath condensate pH: reflecting acidification of the airway at all levels [editorial]. Am J Respir Crit Care Med 2006;173:366–367.[Free Full Text]
2. Effros RM, Casaburi R, Su J, Dunning M, Torday J, Biller J, Shaker R. The effects of volatile salivary acids and bases on exhaled breath condensate pH. Am J Respir Crit Care Med 2006;173:386–392.[Abstract/Free Full Text]
3. Effros RM, Hoagland KW, Bosbous M, Castillo D, Foss B, Dunning M, Gare M, Lin W, Sun F. Dilution of respiratory solutes in exhaled condensates. Am J Respir Crit Care Med 2002;165:663–669.[Abstract/Free Full Text]
4. Gessner C, Hammerschmidt S, Kuhn H, Seyfarth H-J, Sack U, Engelmann L, Schauer J, Wirtz H. Exhaled breath condensate acidification in acute lung injury. Respir Med 2003;97:1188–1194.[CrossRef][Medline]

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