Exhaled breath condensate pH standardised for CO2partial pressure

Abstract

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 CO₂partial pressure on pH and to provide a more precise mode of EBC pH determination.Condensate pH and CO₂partial 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 CO₂level of 5.33 kPa (physiological alveolar CO₂partial pressure). Reproducibility of different pH readings was compared using the Bland–Altman test.Condensate CO₂concentration was variable both in neat and argon de-aerated samples. There was a close negative logarithmic relationship between CO₂and pH. Calculation of pH at a CO₂level of 5.33 kPa provided reproducibility approximately six times as good as that of the currently used measurements.Condensate CO₂partial pressure influences pH measurements. Determination of pH at a standard CO₂level provides the most reproducible condensate pH values to date.