Stability of nitric oxide in stored exhaled gases of healthy individuals

Nitric oxide (NO), a highly reactive gas, is formed by cleavage of the guanido group on arginine. NO plays an important role in many pathophysiological processes. NO has been observed in the exhaled gases in normal humans and animals. Measurement of exhaled NO levels may be useful in the clinical management of diseases including asthma and chronic obstructive pulmonary disease. No data are available regarding the stability of NO in stored exhaled gases. This study was designed to determine, in healthy individuals, the stability of NO in exhaled gases stored for up to 24 hours in a balloon. After Institutional Review Board (IRE) approval, nitric oxide levels were measured both directly and in stored samples of exhaled gases of 15 healthy individuals using a chemiluminescence analyzer. Data were analyzed using repeated analysis of variance (ANOVA) and plotted using the Bland and Altman technique. NO levels measured when exhaled directly into the NO analyzer were 10.1 +/- 2.0 parts per billion (ppb). NO levels when measured in stored exhaled gases at two minutes, two hours, six hours, 12 hours and 24 hours after sample collection were 9.8 +/- 2.0, 10.0 +/- 2.0, 9.9 +/- 1.9, 9.8 +/- 1.9 and 10.2 +/- 2.1 ppb respectively There was no statistically significant difference between NO levels measured directly into the NO analyzer and levels measured over 24 hours in stored samples. The mean difference between NO levels when exhaled directly into the analyzer and two min, two hours, six hours, 12 hours and 24 hours after collection of exhaled gas samples were: 0.13 +/- 0.27, 0.04 +/- 0.24, 0.04 +/- 0.20, 0.13 +/- 0.23, and 0.02 +/- 0.57 ppb respectively. The 95% confidence intervals of the difference of NO levels measured directly into the analyzer and analyzed at 2 min, 2, 6, 12 and 24 hours were -0.41 to 0.67, -0.46 to 0.41, -0.35 to 0.45, -0.33 to 0.59 and -1.16 to 1.12 ppb respectively.