Short and long-term effects of cigarette smoking independently influence exhaled nitric oxide concentration in asthma

Background: The fractional concentration of nitric oxide in exhaled breath (FeNO) is elevated in asthma. FeNO measurement has been proposed as a noninvasive index of disease activity. Cigarette smoking suppresses FeNO, which limits its use in smokers. Objective: To identify and model short-term and long-term influences of cigarette smoking on FeNO. Methods: The smoking history, FeNO, and fractional concentration of carbon monoxide in exhaled breath (FeCO) were measured in 53 subjects with asthma and 51 control subjects. A mathematical model of the short-term and long-term effects of cigarette smoking on FeNO was derived. Results: Subjects with asthma had higher FeNO than controls (P < .001). Smokers had increased FeCO (P < .001). The short-term effect (hours since last cigarette) was associated with increased FeNO (P < .01) and decreased FeCO (P < .05). The long-term effect (years smoked) was associated with decreasing FeNO only in the subjects with asthma (r = -0.62; P = .005). These short-term and long-term effects were independent and were combined in a model predicting FeNO, predicted log(10) FeNO = 1.23 - 0.58e(-0.34t) - 0.00000103 X (lifetime cigarettes), where t = hours since the last cigarette. This gave a convincing prediction of FeNO (r = 0.83; P < .0001). Conclusion: Short-term and long-term effects of smoking influenced the measurement of FeNO. We defined a model that describes these effects. The use of this formula may improve the value of FeNO measurements in smokers with asthma.