Dose-response slope of forced oscillation and forced expiratory parametersin bronchial challenge testing

In population studies, the provocative dose (PD) of bronchoconstrictor caus ing a significant decrement in lung function cannot be calculated for most subjects. Dose-response curves for carbachol were examined to determine whe ther this relationship can be summarized by means of a continuous index lik ely to be calculable for all subjects, namely the two-point dose response s lope (DRS) of mean resistance (Rm) and resistance at 10 Hz (R10) measured b y the forced oscillation technique (FOT), Five doses of carbachol (320 pg each) were inhaled by 71 patients referred for investigation of asthma (n=16), chronic cough (n=15), nasal polyposis ( n=8), chronic rhinitis (n=8), dyspnoea (n=8), urticaria (n=5), post-anaphyl actic shock (n=4) and miscellaneous conditions (n=7), FOT resistance and fo rced expiratory volume in one second (FEV1) were measured in close successi on. The PD of carbachol leading to a fall in FEV1 greater than or equal to 20% (PD20) or a rise in Rm or R10 greater than or equal to 47% (PD47,Rm and PD47,R10) were calculated by interpolation. DRS for FEV1 (DRSFEV1), Rm (DR SRm) and R10 (DRSR10) were obtained as the percentage change at last dose d ivided by the total dose of carbachol. The sensitivity (Se) and specificity (Sp) of DRSRm, DRS10 Delta%Rm and Delta%R10 in detecting spirometric bronc hial hyperresponsiveness (BHR, fall in FEV1 greater than or equal to 20%) w ere assessed by receiver operating characteristic (ROC) curves. There were 23 (32%) "spirometric" reactors. PD20 correlated strongly with D RSFEV1 (r=-0.962; p=0.0001); PD47,Rm correlated significantly with DRSRm (r =-0.648; p=0.0001) and PD47,R10 With DRSR10 (r=-0.552; p=0.0001), DRSFEV1 c orrelated significantly with both DRSRm (r=0.700; p=0.0001) and DRSR10 (r=0 .784; p=0.0001), The Se and Sp of the various FOT indices to correctly dete ct spirometric BHR were as follows: DRSRm: Se=91.3%, Sp=81.2%; DRSR10: Se=9 1.3%, SP=95.8%; Delta%Rm: Se=86.9%, Sp=52.1%; and Delta%R10: Se=91.3 %, Sp= 58.3 %, Dose-response slopes of indices of forced oscillation technique resistance, especially the dose-response slope of resistance at 10Hz are proposed as s imple quantitative indices of bronchial responsiveness which can be calcula ted for all subjects and that may be useful in occupational epidemiology.