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Methodological implications in pH standardization of exhaled breath condensate
F Hoffmeyer1, H Berresheim, A Beine
1Institute for Prevention and Occupational Medicine of the German Social Accident Insurance, Institute of the Ruhr-University Bochum (IPA), Bochum, Germany.
Journal of Breath Research
|May 15, 2015
Summary
Dissolved carbon dioxide significantly affects exhaled breath condensate (EBC) pH. Adjusting for carbon dioxide (CO2) in EBC samples ensures accurate pH measurements, crucial for detecting respiratory changes.
Area of Science:
- Respiratory Physiology
- Analytical Chemistry
Background:
- Accurate pH measurement of exhaled breath condensate (EBC) is vital for respiratory diagnostics.
- Dissolved carbon dioxide (CO2) is a major confounder in EBC pH analysis, necessitating effective standardization methods.
Purpose of the Study:
- To assess the correlation between pH and partial pressure of carbon dioxide (pCO2) in neat EBC samples.
- To reevaluate CO2 standardization for valid EBC pH measurements after deaeration.
- To investigate the impact of deaeration on the acid-base balance of EBC samples.
Main Methods:
- Collected EBC from 38 subjects (7 female, 31 male).
- Measured pH and pCO2 in untreated EBC samples.
- Performed deaeration using argon and re-measured pH and pCO2.
- Utilized a regression function to calculate pH based on pCO2.
Main Results:
- A strong negative correlation (rp = -0.723) was found between pH and pCO2 in untreated EBC.
- This correlation disappeared after argon deaeration (rs = 0.264).
- Calculated pH at 5.33 kPa pCO2 was 6.07 (IQR 5.99, 6.20), with no significant difference from neat samples when adjusted for pCO2.
Conclusions:
- pCO2 is the primary confounder affecting EBC pH measurements.
- Deaeration does not significantly alter the acid-base balance of EBC when pCO2 is accounted for.
- Standardizing EBC pH measurements for pCO2 using a blood-gas analyzer enables sensitive detection of airway pH changes relevant to respiratory conditions.
