Study On Small Airway Function In Asthmatics With Fractional Exhaled Nitric Oxide And Impulse Oscillometry

BackgroundAsthma is a very common condition of respiratory system,which affects estimated 300 million population.Asthma is characterized by chronic airway inflammation and remodeling.It is now widely accepted that airway inflammation and remodeling occur not only in the central airways but also in the small airways.The forced expiratory volume in one second(FEV1)is deemed a core pulmonary physiology outcome for monitoring asthma control and assessing response to treatment.However,FEV1 is considered to mainly reflect the large airways but be not sensitive to small airway obstruction.Although small airways account for less than 10%of airflow resistance in normal conditions,evidence shows that their abnormalities significantly contribute to increasing airflow resistance in asthmatic patients.As a result,the small airway dysfunction may dramatically affect the clinical manifestations and lung function in asthma.The mid-forced expiratory flow(FEF25-75)is believed to be a marker of small airways.However,traditional spirometry requires participators to perform forced expiratory maneuvers,which is difficult for young children and old subjects and hampers reproducibility.The invasive techniques such as surgical resection,transbronchial biopsy and optical coherence tomography(OCT)can be direct and objective to assess small airway function,but they have significant risks and inconveniences for patients and cannot be repeated often.Some sophisticated techniques including fractional exhaled nitric oxide(FeNO)and impulse oscillometry(IOS)may surmount such restrictions.Therefore,we investigated the relation among FeNO,IOS and small airway function in asthmatic patients,which will provide suggestions to new and more convenient methods to diagnose small airway dysfuntion.ObjectiveTo investigate the relation between exhaled nitric oxide(FeNO),impulse oscillometry(IOS)and small airway function in asthmatic patients.MethodsWe recruited 140 patients with asthma in the Respiratory Clinic of Qilu Hospital,Shandong University from July 2014 to July 2015,including 69 patients with small airway normal function and 71 patients with small airway dysfunction.FeNO,eosinophil(EOS)count and total immunoglobulin E(IgE)in peripheral blood and pulmonary function,as well as IOS were measured.Results1.The levels of FeNO,IgE,EOS the reactance area(AX)and the resonant frequency(Fres)were significantly increased in small airway dysfunction group compared with small airway normal function group and the difference was statistically significant,(t =-7.24,p<0.001;t =-12.42,p<0.001;t =-3.20,p =0.002;t =-7.82,p<0.001;t =-7.43,p<0.001,respectively).2.FeNO,AX,Fres and EOS were correlative factors of mid forced expiratory flow of percentages of predicted values(FEF25-75%pred)in small airway dysfunction group(r =-0.856,p<0.00];r =-0.851,p<0.001;r =-0.398,p = 0.001;r =-0.288,p = 0.014,respectively).3.A multiple regression model showed that the strongest independent predictors of small airway dysfunction were FeNO,AX and Fres,(t =-3.906,p<0.001;t =-3.065,p = 0.003;t =-2.442,p = 0.017,respectively).The turns of standard errors of partial regression coefficient were that FeNO>AX>Fres>EOS(0.407;0.363;0.161;0.087,respectively).4.The turns of predictive value in diagnosis of small airway dysfunction were that FeNO combining AX and Fres>FeNO>AX>Fres>EOS(AUC = 0.881,p<0.001;AUC = 0.830,p<0.001;AUC = 0.822,p<0.001;AUC = 0.816,p<0.001;AUC =0.673,p<0.001,respectively).Conclusion1.FeNO and IOS may be helpful in diagnosis of small airway dysfunction with high sensitivity and specificity.2.FeNO level combined with IOS can better evaluate the function of small airway in asthmatic patients.