Variability in Measures of Exhaled Breath Na+, Influence of Pulmonary Blood Flow and Salivary Na+

The assessment of inflammatory markers and ions in exhaled breath condensate (EBC) is being utilized more frequently in diseases such as asthma and cystic fibrosis with marked variability in EBC measures, including those of exhaled Na+. We sought to determine if variability in exhaled Na+ was due to differences in pulmonary blood flow (PBF) or Na+ in the mouth (salivary Na+). We measured exhaled Na+ three times with coinciding sampling of salivary Na+ and assessment of PBF (using acetylene rebreathing) in 13 healthy subjects (54% female, age = 27 ± 7 yrs., ht. = 172 ± 10 cm, wt. = 70 ± 21 kg, BMI = 22 ± 7 kg/m2 mean ± SD). Exhaled Na+ averaged 2.7 ± 1.2 mmol/l, and salivary Na+ averaged 5.51 ± 4.58 mmol/l. The coefficients of variation across all three measures in all 13 subjects averaged 30% for exhaled Na+ and 83% for salivary Na+, within subjects the variability across the three measures averaged 30% for exhaled Na+ and 38% for salivary Na+. Across all three measures in all 13 subjects the relationship between PBF and exhaled Na+ averaged 0.027 (P = 0.87), and the relationship between salivary Na+ and exhaled Na+ concentrations averaged 0.59 (P = 0.001). Also, we sought to determine the relationship between exhaled Na+ and serum Na+ in an addition 20 subjects. There was a moderate and significant relationship between serum Na+ and exhaled Na+ (r = 0.37, P = 0.04). These findings suggest there that the variability in exhaled Na+ is caused, at least in part, by droplet formation from within the mouth as turbulent air passes through and that there is a flux of ions from the pulmonary blood into the airways.