Ammonia in breath and emitted from skin

Ammonia concentrations in exhaled breath (eNH(3)) and skin gas of 20 healthy subjects were measured on-line with a commercial cavity ring-down spectrometer and compared to saliva pH and plasma ammonium ion (NH4+), urea and creatinine concentrations. Special attention was given to mouth, nose and skin sampling procedures and the accurate quantification of ammonia in humid gas samples. The obtained median concentrations were 688 parts per billion by volume (ppbv) for mouth-eNH(3), 34 ppbv for nose-eNH3, and 21 ppbv for both mouth-and nose-eNH(3) after an acidic mouth wash (MW). The median ammonia emission rate from the lower forearm was 0.3 ng cm(-2) min(-1). Statistically significant (p < 0.05) correlations between the breath, skin and plasma ammonia/ammonium concentrations were not found. However, mouth-eNH(3) strongly (p < 0.001) correlated with saliva pH. This dependence was also observed in detailed measurements of the diurnal variation and the response of eNH(3) to the acidic MW. It is concluded that eNH(3) as such does not reflect plasma but saliva and airway mucus NH4+ concentrations and is affected by saliva and airway mucus pH. After normalization with saliva pH using the Henderson-Hasselbalch equation, mouth-eNH(3) correlated with plasma NH4+, which points to saliva and plasma NH4+ being linked via hydrolysis of salivary urea.