USEFULNESS OF THE FORCED OSCILLATION TECHNIQUE IN THE DIAGNOSIS OF COUGH VARIANT ASTHMA WITH PROLONGED OR CHRONIC COUGH

BACKGROUND: Usefulness of carrying out the reversibility test after inhaling bronchodilator by forced oscillation technique (FOT) in addition to spirometry was investigated in the diagnosis of bronchial asthma (BA), cough variant asthma (CVA) and allergic rhinitis (AR) with prolonged or chronic cough. METHODS: The subjects were the 622 patients at Idaimaeminamiyojo Clinic in Sapporo who complained cough over three weeks, and underwent bronchial reversibility test with salbutamol by using spirometry and FOT. We divided them into 5 groups; BA, BA+AR, CVA, CVA+AR, AR, and examined their lung functions. RESULTS: The mean of improvement of FEV1 after inhalation of salbutamol was significantly different (p<0.001); 465ml (26%) of BA, 136ml (5.5%) of CVA, and 44ml (1.6%) of AR. However, in CVA, the mean reversibility value was not over the diagnostic criteria of BA; 200ml (12%). Improvement of respiratory resistant at 5Hz (R5) using FOT in BA/CVA were 25.7%/24.1%, and significantly higher (p<0.001) than that in AR, and these results were alike even in cases accompanied by AR; BA+AR, CVA+AR, and AR. AUC value in the ROC curve for diagnosis of CVA from AR with R5 was 0.870, and highest among with R5, R20, R35 and Fres. When the cut off value of R5 improvement was 15%, sensitivity was 74% and specificity was 81%. CONCLUSION: It was suggested that the additional bronchial reversibility test using FOT may be useful especially in the diagnosis of cough variant asthma where the reversibility in spirometry alone is not sufficient.