Objective: To explore the change of fractional exhaled nitric oxide (FeNO) and its correlation with forced expiratory volume in the first second (FEV1), the first second forced expiratory volume percentage of forced vital capacity (FEV1/FVC) in bronchial asthma and chronic obstructive pulmonary disease (COPD).
Methods: FeNO, FEV1 and FEV1/FVC were measured in 57 suspected asthmatics (21 acute onsets, 12 non-acute and 24 non-asthma), 38 COPD patients (25 acute exacerbations and 13 stable stages) and 26 healthy subjects.
Results: In the 57 suspected asthmatic patients, when the optimal cut off value of FeNO was 20.15 PPb, which was used to diagnose asthma and differentiate asthma and non-asthma, the positive predictive value, the negative predictive value, the sensitivity and the specificity was 94.1%, 95.7%, 97.0%, and 91.7% respectively. There was significant difference in the FeNO level between the 33 asthmatics and 26 healthy subjects (P<0.05). There was also significant difference in the FeNO level between the acute onset and the non-acute (P<0.05), but not in the FEV1 and FEV1/FVC level (both P>0.05). There was no significant correlation between FeNO and FEV1, FEV1/FVC in patients with asthma (r=-0.186, -0.236, both P>0.05). There was significant difference in the levels of FeNO, FEV1 and FEV1/FVC between the 38 COPD patients and the 26 healthy subjects (all P<0.05), and also between the 25 acute exacerbations and 13 stable COPDs (all P<0.05), but not between the 13 stable COPDs and 26 healthy subjects (all P>0.05). FeNO was not correlated with FEV1 and FEV1/FVC level in COPD patients (r=-0.167, -0.285, both P>0.05).
Conclusion: FeNO level is increased obviously in patients with asthma. The optimal cut off value of FeNO at 20.15 PPb can differentiate asthma and non-asthma with high sensitivity and specificity. FeNO is higher for the acute onset than non-acute, which may be useful to evaluate the control degree. FeNO level is increased in COPD patients in the acute exacerbations, but there is no change in stable COPD patients compared with the healthy subjects.