Comparison of two methacholine challenge methods using Spira-2 or Mefar dosimeter

Two bronchial challenge protocols with breath-actuated dosimeters, Spira El ektro-2 and Mefar, with similar cumulative dose steps were compared in 28 p atients with mild to moderate asthma. Methacholine challenges were performe d after two different protocols at the same time of day in random order 3 o r 4 days apart. The provocative dose of methacholine producing a 20% fall i n forced expiratory volume in 1 second (PD20) was lower when determined by Spira than with the Mefar dosimeter (P<0.05). Transition equations calculat ed by linear regression analysis were: PD20mefar, = exp(10)[0.897 + 0.678(l ogPD(20spira))] (P<0.05; r = 0.62) and PD20spira = exp(10)[0.759 + 0.559 (l og PD20mefar)] (P<0.05; r = 0.62). The slopes were calculated by regressing the percentage fall in FEV1 on log(10) (dose) and transformed as slope = 1 00/(regression coefficient + 10). The mean slope (95% CI) for Spira was 3.1 (2.6-3.7) and for Mefar 4.4 (3.6-5.1) (P<0.005). Regression equations calc ulated by linear regression analysis were: slope(mefar) = 2.126 + 0.712 slo pe(spira) (P<0.05; r=0.51) and slope(spira) = 1.551 + 0.365 slope(mefar) (P <0.05; r = 0.1). In conclusion, PD20 was smaller and the decline in FEV1/lo g(dose) curve steeper using the Spira compared with the Mefar protocol. The dose-response curves should be validated and transition equations calculat ed when bronchial reactivity to inhaled agents is compared, even while usin g apparently similar well-standardized dosimeter methods.