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Re: Normal range of exhaled breath condensate pH

Dear Editor,

We read with interest the recent paper by Ojoo et al. [1] showing dissociation between exhaled breath condensate (EBC) pH and FENO in patients with asthma and cystic fibrosis. We note that EBC pH was measured without prior deaeration of the sample using argon gas, in common with other studies [2,3]. An alternative method is to pass argon gas through or over EBC samples in order to remove dissolved carbon dioxide [3,4,5]. Argon deaeration has been shown to be highly reproducible [4,5]. Both methods have demonstrated differences in pH between disease and control samples [1,2,3,5], but their relative benefits have not been established.

There is currently no consensus definition of the range of “normal” airway pH. Defining this range is hindered by the lack of standardisation regarding the use of argon e.g. in healthy controls, mean pH values in studies without argon deaeration have ranged from 6.08 [1] to 7.46 [2], and from 7.7 [4] to 8.3 [3] in studies using argon deaeration. We suggest that standardization of EBC methodology with respect to the use of argon is required. This will enable comparable data from different studies to be obtained, so that the range of pH values in controls and disease can be fully understood.

References

1. Ojoo JC, Mulrennan SA, Kastelik JA, Morice AH, Reddington. Exhaled breath condensate pH and exhaled nitric oxide in allergic asthma and cystic fibrosis. Thorax 2005;60:22-26.

2. 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.

3. Niimi A, Nguyen LT, Usmani O, Mann B, Chung KF. Reduced pH and chloride levels in exhaled breath condensate of patients with chronic cough. Thorax 2004; 59: 608-612.

4. Vaughan J, Ngamtrakulpanit L, Pajewski TN, Turner R, Nguyen T-A, Smith A, Urban P, Horn S, Gaston B, Hunt J. Exhaled breath condensate pH is a robust and reproducible assay of airway acidity. Eur Respir J 2003; 22: 889-894.