Study objectives: To investigate whether exhaled
carbon monoxide (CO) and nitric oxide (NO) could be used as noninvasive
in vivo biomarkers of oxidative stress in the lungs of
patients with COPD.
Patients: Ten healthy
nonsmokers, 12 smokers, 15 stable ex-smokers with COPD, and 15 stable
current smokers with COPD.
attended the outpatient clinic on one occasion for pulmonary function
tests and exhaled CO and NO measurements.
results: Mean (± SEM) CO levels in ex-smokers with COPD were
higher (7.4 ± 1.9 ppm; p < 0.05) than in nonsmoking control
subjects (3.0 ± 0.3 ppm) but were lower than in current smokers with
COPD (20.0 ± 2.6 ppm; p < 0.001). There was no correlation
between exhaled CO and NO. There was no correlation between CO and lung
function tests in any group of patients. Exhaled NO was higher in
ex-smokers with COPD (12.0 ± 1.0 parts per billion [ppb];
p < 0.001) than in healthy nonsmokers (6.5 ± 0.6 ppb) and in
current smokers with COPD (7.6 ± 1.1 ppb; p < 0.01) compared to
healthy smokers (3.3 ± 0.4 ppb). Ex-smokers with COPD had higher
exhaled NO levels than did current smokers with COPD (p < 0.001)
There was a negative correlation between exhaled NO and
FEV1 in both ex-smokers with COPD
(r = −0.60; p < 0.02) and current smokers with
COPD (r = −0.59; p < 0.02).
Conclusion: The measurement of exhaled CO and NO may
represent a new method for the noninvasive monitoring of airway
inflammation and oxidant stress in COPD ex-smokers. Exhaled CO and NO
are strongly affected by cigarette smoking, which limits their
usefulness as biomarkers in current smokers.