Potential confounding factors in measurement of exhaled nitric oxide

Nitric oxide is present in the exhaled air. Factors affecting the level of exhaled nitric oxide (exNO), except for smoking, are not well defined. In this study we seek to determine whether age, gender, body mass index (BMI), part of the day, or time after a meal could modulate exNO levels. exNO was examined by the use of a chemiluminescence method in 100 subjects - 31 women (19 nonsmokers and 12 smokers) and 69 males (55 nonsmokers and 14 smokers). Forty four subjects took medications due to stable coronary disease, 22 were after heart transplantation, and 34 did not take any drugs. We found that exNO levels did not differ either between the whole groups of women and men or between smokers and nonsmokers of either respective group (4.91 +/-2.38 vs. 6.27 +/-4.23 ppb; 3.21 +/-1.16 vs. 3.71 +/-1.55 ppb; 5.98 +/-2.35 vs. 6.92 +/-4.45 ppb). The correlation of exNO with age in the whole population was weak (r=0.23; P=0.02) and insignificant in the smoking and nonsmoking subgroups. Likewise, correlations of exNO with BMI, part of the day, or time after a meal were insignificant in whole population as well as the subgroups. We conclude that the aforementioned factors are not able to confound the measurement of exNO in the population studied.