[Evaluating the efficacy of fractional exhaled nitric oxide and impulse oscillometry in screening out cough variant asthma from patients with subacute cough].

Objective: To evaluate the clinical value of fractional exhaled nitric oxide (FeNO) and impulse oscillometry (IOS) in screening out cough variant asthma (CVA) from patients with subacute cough. Methods: Patients with subacute cough were included from the outpatient department of Respiratory Medicine of Zhujiang Hospital of Southern Medical University from May to October in 2016. Based on "the guidelines for the diagnosis and treatment of cough (2015 edition)" , patients were classified into CVA group, and non CVP group with other causes of subacute cough. Lung function, bronchial provocation test, FeNO and IOS were measured. The diagnostic efficiency and optimal cut-off points of FeNO and IOS indicators to diagnose CVA from subacute cough were respectively assessed by the receiver operating characteristic (ROC) curves. Results: A total of 85 patients with subacute cough were included. Among them, 35 patients were diagnosed with CVA (CVA group), the others are classified as non CVP group ( n =50). In CVA group, the levels of FeNO and total respiratory impedance (Zrs) were significantly higher, while maximal mid expiratory flow (MMEF)%pred, and mid expiratory flow (MEF)75/50/25%pred, reactance at 5 Hz (X5) levels were significantly lower than those in non CVP group (all P <0.05). Furthermore, the FeNO had a positive correlation with Zrs and Fres (ρ=0.312, P =0.003 and ρ=0.318, P =0.003, respectively), had a negative correlation with X5 (ρ=-0.288, P =0.007). A ROC analysis indicated that the area under ROC curve (AUC) of FeNO in diagnosis of CVA was 0.786 (95% CI: 0.684-0.889), the best cut-off point of FeNO volume ratio was 24.5×10(-9). When FeNO volume ratio=24.5×10(-9,) the sensitivity of in diagnosing CVA was 77.8%, specificity was 70.0%. The AUC for Zrs and X5 were 0.679 and 0.687, respectively. The combination of FeNO and X5 had a greater AUC than other indicators (AUC: 0.817, 95% CI : 0.726-0.908), the sensitivity and specificity were 80.6% and 66.0%, respectively. Conclusion: Both FeNO level and IOS index can be used to screen CVA in patients with subacute cough, and the combination of both have better value in diagnosing CVA.