Bronchial responsiveness to histamine and methacholine measured with forced expirations and with the forced oscillation technique

AbstractThe objective of this study was to compare bronchial challenge tests with two substances [histamine (H) and methacholine (M)] and two methods of measuring the effect parameter FEV1 and pulmonary impedance [with the forced oscillation technique (FOT)] in order to determine which test is the shortest, and gives the least (drug) load to the patient. Furthermore, it was considered whether the result of one type of challenge test could be transferred to the result of another type of test. It was hypothesized that, since the FOT technique requires no forced manoeuvres of the subjects and therefore does not affect the airway patency, there must be differences in the provocation concentrations for reaching the conventional thresholds of 20% decrease in FEV1 (PC20 FEV1) and 40% increase in airway resistance measured at 8 Hz oscillation frequency (PC40 Rrs8). It was further hypothesized that the interindividual correlations between thresholds for both drugs will be low, because both drugs set off different mechanisms for bronchoconstriction. Bronchial challenge tests were performed in 23 stable asthmatics (15 males and 8 females; mean ± sd age 30·3 ± 11·6 years). Their mean control FEV1 was 85·2 ± 12·6% predicted. For both drugs, PC40 Rrs8 was three-fold lower than PC20 FEV1.The within-drug correlation between log PC20 FEV1 (H,M) and log PC40 Rrs8 (H,M) was quite good [r(H)=0·73, r(M)=0·68]. The between-drug correlation of log PC20 FEV1 (H) and log PC20 FEV1 (M) was equally good. However, the ‘between-drug’ correlation of log PC40 Rrs8 (H) and log PC40 Rrs8 (M) was low (r=0·36).It is concluded that the PC40 Rrs8 for histamine is the shortest test for bronchial responsiveness, with the lowest drug load for the patient. The results from one type of challenge test cannot be recalculated into the result of another type of test