BRONCHIAL RESPONSIVENESS TO HISTAMINE AND METHACHOLINE MEASURED WITH FORCED EXPIRATIONS AND WITH THE FORCED OSCILLATION TECHNIQUE

The objective of this study was to compare bronchial challenge tests w ith two substances [histamine (H) and methacholine (M)] and two method s of measuring the effect parameter FEV(1) and pulmonary impedance [wi th 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 chal lenge 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 pa tency, there must be differences in the provocation concentrations for reaching the conventional thresholds of 20% decrease in FEV(1) (PC20 FEV(1)) and 40% increase in airway resistance measured at 8 Hz oscilla tion frequency (PC40 Rrs(8)). It was further hypothesized that the int erindividual correlations between thresholds for both drugs will be lo w, because both drugs set off different mechanisms for bronchoconstric tion. 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 FEV(1) was 85.2 +/- 12.6% predicted. For both drugs, PC40 Rrs(8) was three-fold lower than PC20 FEV(1). The within-drug correla tion between log PC20 FEV(1) (H,M) and log PC20 Rrs(8) (H,M) was quite good [r(H)=0.73, r(M)=0.68]. The between-drug correlation of log PC20 FEV(1) (H) and log PC20 FEV(1) (M) was equally good. However, the 'be tween-drug' correlation of log PC40 Rr(8), (M) and log PC40 Rrs(8) (M) was low (r=0.36). It is concluded that the PC40 Rr(8), for histamine is the shortest test for bronchial responsiveness, with the lowest dru g load for the patient. The results from one type of challenge test ca nnot be recalculated into the result of another type of test.