THE DIAGNOSTIC CAPACITY OF FORCED OSCILLATION AND FORCED EXPIRATION TECHNIQUES IN IDENTIFYING ASTHMA BY ISOCAPNIC HYPERPNEA OF COLD-AIR

The measurement of forced expiratory volume in one second (FEV1) is of ten used to assess the effect of bronchial provocations, and deep insp iration is required beforehand, This may briefly alter the bronchial t one in a variable way in some subjects, The forced oscillation techniq ue (FOT) is a test used to characterize the mechanical impedance of th e respiratory system, and prior deep inspiration is not required, We t ested the hypothesis that measurable bronchoconstriction would occur i n all asthmatic subjects stimulated with isocapnic hyperventilation of dry cold air (IHCA), Twenty patients with mild asthma and nine health y controls were exposed to IHCA, at 70% of their maximal voluntary ven tilatory capacity for 4 min and the results were assessed both by appl ying the FOT and by measuring FEV1, Optimal cut-off levels were define d by receiver operating characteristic (ROC) curve analyses of the cha nges in respiratory resistance and reactance at 5-35 Hz, resonant freq uency (fres) and FEV1, A positive result was present in the asthmatics when measured by FOT, and using ROC analyses the discriminative capac ity to correctly diagnose asthma was greatest for responses in fres; t he sensitivity was 89% and the specificity 100%, The sensitivity of FE V1 to correctly diagnose asthma was only 73%, and the specificity 88%, In conclusion, the results of this study suggest that the use of forc ed expiratory volume in one second for bronchial provocation tests by isocapnic hyperventilation of dry cold air may be misleading and that the bronchoconstriction thus elicited is measured with greater sensiti vity and specificity by the forced oscillation technique than by force d expiratory volume in one second.