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Exhaled breath condensate pH standardised for CO₂ partial pressure

¹ Dept of Pathophysiology and, ³ Clinical Laboratory, National Korányi Institute for Tuberculosis and Pulmonology, and ² Institute of Human Physiology and Clinical Experimental Research, Semmelweis University, Budapest, Hungary.

CORRESPONDENCE: I. Horváth, Dept of Human Physiology and Clinical Experimental Research, Semmelweis University, 1082 Budapest Üllüi u. 78/a Hungary. Fax: 36 13343162. E-mail: kiss.horvath{at}t-online.hu

Keywords: Airway biology, airway inflammation, breath test, exhaled biomarkers, exhaled breath condensate

Received: June 27, 2006
Accepted October 23, 2006

Exhaled breath condensate (EBC) pH is considered to reflect the acid-base balance of the airways. Current pH measurements do not take into account the effect of CO₂. The aim of the present study was to determine the effect of condensate CO₂ partial pressure on pH and to provide a more precise mode of EBC pH determination.

Condensate pH and CO₂ partial pressure were measured in parallel from 12 healthy volunteers and 12 asthmatics using a blood gas analyser in neat, argon de-aerated and CO₂-loaded samples. The regression analysis was used to test the relationship between pH and CO₂, and to calculate the pH at a CO₂ level of 5.33 kPa (physiological alveolar CO₂ partial pressure). Reproducibility of different pH readings was compared using the Bland–Altman test.

Condensate CO₂ concentration was variable both in neat and argon de-aerated samples. There was a close negative logarithmic relationship between CO₂ and pH. Calculation of pH at a CO₂ level of 5.33 kPa provided reproducibility approximately six times as good as that of the currently used measurements.

Condensate CO₂ partial pressure influences pH measurements. Determination of pH at a standard CO₂ level provides the most reproducible condensate pH values to date.

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