Relationship Between Fractional Exhaled Nitric Oxide And Airway Responsiveness In Patients With Chronic Cough

Objective：To access the correlation between fractional exhaled nitric oxide(FeNO) and airway responsiveness in patients with chronic cough. Tostudy the value of FeNO test in distinguishing airway hyperresponsiveness(AHR) from patients with chronic cough. To access the same diagnosticvalue of the combination of FeNO, airway function and atopic status, andmake a comparison with each detection method apart as mentioned aboveto seek for a better diagnostic strategy of chronic cough.Methods：A total of90patients with chronic cough who visited our hospitalfrom August2013to January2014were enrolled in this study. FeNO test,a pulmonary function test and a bronchial provocation test (BPT) weregiven in order. a prospective follow-up was made later on.Results：1.30patients had an abnormal BPT result (the BPT positive group)while60patients had a normal BPT result (the BPT negative group). TheFeNO level of the positive group was significantly higher than that of thenegative group [51.60(21.23,123.35) ppb VS20.05(13.25,31.58) ppb,P<0.001].2. The consistency analysis showed a general consistency betweenFeNO and PD20-FEV1(Kappa=0.594, P<0.001). Numerically, there was anegative correlation (r=-0.517, P<0.001) with Spearman rank correlationanalysis. The classification of FeNO level was negatively correlated with the classification of airway responsiveness (r=-0.505, P<0.001).3. To diagnosis patients with AHR from patients with chronic cough,we chose the Receiver Operating Character (ROC) curve of FeNO toanalyze this issue, and the area under the ROC curve (AUC) was0.778（95%CI:0.678-0.859, P<0.001), with an optimal cutoff value of34.4ppbfor maximum Youden index of0.5, with sensitivity of66.67%, specificityof83.33%.4. FeNO test has no use when FeNO was under25ppb (P=0.068). TheAUC was0.811(95%CI：0.696-0.897，P=0.005) when FeNO was between25ppb and50ppb, while the AUC was0.990(95%CI：0.933-0.997,P<0.001) when FeNO>50ppb.5. As for airway dysfunction, there was a significant differencebetween the two groups in FEV1/FVC, MMEF, FEF75, FEF50and FEF25.6. To diagnosis patients with AHR from patients with chronic cough,we chose the combined model with airway inflammation(FeNO), airwayfunction (FEV1/FVC, MMEF, FEF75, FEF50, FEF25) and atopic status toanalyze the issue, the AUC of which was0.907（95%CI:0.841-0.973,P<0.001), with a maximum Youden index of0.67, sensitivity of80.00%,specificity of86.67%.7. The diagnostic efficacy of it was greater than any detection methodapart as mentioned in this article.Conclusions：Elevated FeNO level could be detected in patients with chronic cough,in which FeNO had shown good correlation with airway responsiveness.FeNO test was useful in the diagnosis of AHR, and the diagnostic abilityincreased with the FeNO level. A joint analysis of airway inflammation,airway function and atopic status was useful in the diagnosis of AHR inpatients with chronic cough. Probably, this was due to the complexity ofmechanisms leading to AHR in this common disease.