Exhaled breath condensates have been widely used to detect inflammatory mediators in the fluid that covers airway surfaces of patients with inflammatory lung disorders. This approach is much less invasive than bronchoalveolar lavage, but respiratory droplets are markedly diluted by large and variable amounts of water vapor. We estimated the dilution of respiratory droplets by comparing concentrations of nonvolatile, reference indicators (total nonvolatile cations, urea or conductivity) in 18 normal subjects with normal plasma concentrations by assuming similar concentrations in the respiratory fluid and plasma. The volatile cation, NH4+ (most of which is delivered as NH3 gas from the mouth), represented 93 +/- 3% (SEM) of the condensate cations. More than 99% of the NH4+ was removed by lyophilization, making it possible to use conductivity to estimate total nonvolatile ionic concentrations and facilitating analysis of urea. Conductivity was significantly correlated with electrolyte and urea concentrations. Estimates of dilution based on total cations, conductivity, and urea were not significantly different (cations: 20,472 +/- 2,516; conductivity: 21,019 +/- 2,427; and urea: 18,818 +/- 2,402). These observations suggest that the conductivity of lyophilized samples can be used as an inexpensive, simple, and reliable method for estimating dilution of nonvolatile, hydrophilic mediators in condensates.

The exhaled breath condensate (EBC) approach provides a convenient and noninvasive approach for sampling the pulmonary epithelial lining fluid (ELF). Increased EBC concentrations of more than a dozen inflammatory markers and hydrogen ions have been reported in lung diseases associated with inflammation. However, the usefulness of EBC is compromised by uncertainties concerning the sources of the EBC droplets and by the extreme and variable dilution of ELF droplets with condensed water vapor (ϳ20,000-fold). Reported increases in EBC concentrations may reflect proportionate increases in the total volume rather than the concentration of ELF droplets in the collected samples. Conclusions regarding ELF concentrations can only be made if this dilution is estimated with a dilutional indicator (e.g., conductivity of lyophilized EBC). In normal EBC samples, pH is effectively set by oral contamination with NH 3, and EBC pH cannot provide reliable information regarding ELF pH in normal subjects. Acidification of EBC observed in asthma and other conditions may reflect acidification of ELF, decreases in NH 3 added to the EBC, and/or the presence of gastric droplets in the EBC.

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. In 2000, Hunt and colleagues reported that exhaled breath condensates (EBCs) are acidified during asthmatic exacerbations (1). They referred to this phenomenon as "acidopnea" and suggested that it reflected excess acid produced in the airways by inflammation. These observations were confirmed in studies of chronic obstructive pulmonary disease (COPD) and other inflammatory lung disorders (2-10). Subsequently, Hunt and colleagues found that EBC NH 4 ϩ concentrations were reduced in many patients with asthma (11). They postulated that production of NH 3 in the airways was reduced because of impaired glutaminase activity, and suggested that reductions in airway NH 3 production reduced local buffering, thereby promoting airway acidification. They also argued that concentrations of NH 4 ϩ in EBCs did not influence the pH of the EBC samples, which represented an accurate marker of airway acidification (12, 13). This study has analyzed the acid and base concentrations in saliva and EBC from 10 healthy subjects and 10 patients with COPD to determine whether EBC pH is influenced by volatile or nonvolatile constituents in the saliva. METHODSEleven healthy subjects and 10 subjects with COPD were initially selected but condensate from one healthy subject was deleted because high amylase concentrations indicated salivary contamination (Table 1). Spirometry was performed in all subjects (Sensormedics, Yorba Linda, CA). The patients had COPD (FEV 1 Ͻ 75% predicted, FEV 1 /FVC Ͻ 70%) (14) and an average smoking history of 59 Ϯ 43 (SD) pack-yr. None smoked within an hour of the study. All were taking prescribed maintenance bronchodilators, which were not used during the hour before collections.Patients exhaled for 1 h into an insulated 66-cm polycarbonate condenser cooled with recirculated ice water. One-way valves were used to ensure that subjects inhaled fresh air and exhaled into the condenser. Nose clips were not used. The mouthpiece and condenser were connected by a 450-ϫ 22-mm ID ventilator tubing (Corr-a-Flex 2; Hudson RCI, Temecula, CA) inclined upward to minimize salivary contamination. Condensate was collected using polycarbonate tubes. Collection and analysis of capillary plasma and saliva are described in the online supplement.All samples were stored at Ϫ80ЊC. Before analysis, all samples were allowed to thaw in room air for about 30 min. To minimize potential losses of volatile acids and bases, no attempt was made to remove ambient CO 2 from the EBC or saliva with inert gas (see the online supplement). The buffering capacity of th...