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

McSharry CP, McKay IC, Chaudhuri R, Livingston E, Fraser I, Thomson NC

Department of Immunology, Division of Immunology, Infection and Inflammation, University of Glasgow, United Kingdom. cms4q@clinmed.gla.ac.uk

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 - 0.58 e -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.

Published 1 July 2005 in J Allergy Clin Immunol, 116(1): 88-93.
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