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

Abstract

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.