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The Effects of Volatile Salivary Acids and Bases on Exhaled Breath Condensate pH

Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, Torrance, California; and Department of Medicine, Medical College of Wisconsin, Milwaukee, Wisconsin

Correspondence and requests for reprints should be addressed to Richard M. Effros, M.D., LABiomed–Harbor–UCLA Medical Center, 1124 West Carson Street, RB2, Torrance, CA 90502-2064. E-mail: reffros{at}labiomed.org

Rationale: Recent studies have reported acidification of exhaled breath condensate (EBC) in inflammatory lung diseases. This phenomenon, designated "acidopnea," has been attributed to airway inflammation.

Objectives: To determine whether salivary acids and bases can influence EBC pH in chronic obstructive pulmonary disease (COPD).

Methods: Measurements were made of pH, electrolytes, and volatile bases and acids in saliva and EBC equilibrated with air in 10 healthy subjects and 10 patients.

Results: The average EBC pH in COPD was reduced (normal, 7.24 ± 0.24 SEM; range, 6.11–8.34; COPD, 6.67 ± 0.18; range, 5.74–7.64; p = 0.079). EBCs were well buffered by NH₄⁺/NH₃ and CO₂/HCO₃^– in all but four patients, who had NH₄⁺ concentrations under 60 µmol/L, and acetate concentrations that approached or exceeded those of NH₄⁺. Saliva contained high concentrations of acetate ( 6,000 µmol/L) and NH₄⁺ ( 12,000 µmol/L). EBC acetate increased and EBC NH₄⁺ decreased when salivary pH was low, consistent with a salivary source for these volatile constituents. Nonvolatile acids did not play a significant role in determining pH of condensates because of extreme dilution of respiratory droplets by water vapor ( 1:12,000). Transfer of both acetic acid and NH₃ from the saliva to the EBC was in the gas phase rather than droplets.

Conclusions: EBC acidification in COPD can be affected by the balance of volatile salivary acids and bases, suggesting that EBC pH may not be a reliable marker of airway acidification. Salivary acidification may play an important role in acidopnea.

Key Words: acetate • ammonium • bicarbonate • buffer • exhaled breath condensate

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