Study objective: To evaluate exhaled nitric oxide (eNO) during exercise in patients with stable COPD.
Setting: Outpatient evaluation in a rehabilitation center.
Patients: Eleven consecutive male patients with stable COPD (age, 65 +/- 6 years; FEV(1), 56 +/- 10% predicted). Eight healthy (six men; age, 51 +/- 16 years) nonsmoking, nonatopic volunteers served as control subjects.
Methods: In each subject, a symptom-limited cycle ergometry test was performed by monitoring eNO with the tidal-breath method to assess eNO concentration (FENO) and output (VNO) at rest, peak exercise, and recovery time.
Results: Resting FENO (9.8 +/- 5.1 and 14.1 +/- 6.3 parts per billion, respectively) and VNO (4.2 +/- 2.0 and 5.9 +/- 3.4 nmol/min, respectively) were lower, although not significantly, in COPD patients than in control subjects. In both groups, FENO significantly decreased whereas VNO significantly increased during exercise. Both variables returned to baseline during the recovery time. Peak exercise VNO, but not FENO, was significantly lower in COPD patients than in control subjects (7.9 +/- 5.4 and 12.7 +/- 6.0 nmol/min, respectively, p < 0.05). The rise in VNO was weakly correlated to oxygen consumption VO(2)) both in control subjects (r = 0.31, p = 0. 002) and in COPD patients (r = 0.22, p = 0.03). FENO showed an inverse correlation to VO(2) in both groups (r = -0.53, p = 0.000; r = -0.31, p = 0.003 in control subjects and COPD patients, respectively).
Conclusions: In patients with mild and moderate COPD, eNO during exercise parallels that observed in normal control subjects. VNO, but not FENO, is significantly reduced at peak exercise in COPD patients as compared with control subjects. The long-term effects of exercise training on eNO has to be evaluated by further studies.