Comparison of airway conductance and FEV₁ as measures of airway responsiveness to methacholine

Abstract

When defining bronchial responsiveness in healthy, non-asthmatic, subjects exposed in different working situations, it is not clear whether different outcome measures yield similar results. Therefore, the concentration and dose of methacholine that caused a 20% decrease in forced expiratory volume in 1 s (FEV(1)) (PC20(FEV(1)) and PD20(FEV(1))), the corresponding change in Gaw and the relationship between the dose-response slope (DRS) for FEV(1) and Gaw was studied in different working populations and healthy control subjects (n=1038). The two outcome measures were compared in groups of subjects in whom differences in bronchial responsiveness could be anticipated [atopics (n=72) and non-atopics (n= 207) and subjects exposed (n=54) and not exposed (n=32) to saw dust]. A bronchial challenge was also made before and after exposure in a swine confinement building, an exposure known to increase bronchial responsiveness (n=37). PD20(FEV(1)) was 1.7 mg in atopics and 4.9 mg in non-atopics, 7.1 mg in saw dust exposed and >20 mg in non-exposed subjects and 5.3 mg before and 0.79 mg after exposure to organic dust. There was a correlation between DRS(FEV(1)) and DRS(Gaw), r=0.87 (P<0.001). In subjects who were highly sensitive to methacholine a 20% change in FEV(1) corresponded to <40% change in Gaw, while a 20% decrease in FEV1 corresponded to none or a minor decrease in Gaw in subjects with less methacholine-sensitive airways. The ability to detect differences in bronchial responsiveness between groups, or to detect changes in bronchial responsiveness following exposure was approximately the same for FEV(1) and Gaw. The reproducibility was similar for both variables and a second measurement was within one doubling of the methacholine concentration of the first provocation in approximately 95% of all measurements (n=41). In conclusion, with our methacholine provocation method, FEV(1) and Gaw had similar sensitivity in detecting small differences in bronchial responsiveness in healthy subjects.

Comparison of FEV1 and specific airway conductance in assessing airway response to occupational agents

“…Discordance between measurements of SGaw and FEV 1 could theoretically result from several factors. Deep inspiration can reduce bronchoconstriction provoked by nonspecific stimuli in healthy individuals and in asthmatic subjects with mild to moderate bronchial hyperresponsiveness, whereas it can enhance induced bronchoconstriction in asthmatics with marked hyperresponsiveness (9–11, 21). In addition, it has been postulated that SGaw and FEV 1 assess different portions of the airways, with SGaw reflecting primarily the flow‐resistive properties of large, central airways (22, 23), although this concept has been subsequently questioned (24).…”

Small airways disease and severe asthma

“…This may be underestimated in individuals with elevated TLC. The provocative concentration of methacholine causing a 20% fall in FEV1 (PC 20 ) has also been described by several investigators as being a useful marker of air trapping [25], while greater sensitivity has been reported when both FEF 25-75 and FEV1 were used together to evaluate the response to methacholine. Finally, the difference between slow inspiratory vital capacity (SVC) and FVC and the FVC to SVC ratio may be surrogate markers of the collapsibility of small airways [26].…”

What Does Airway Resistance Tell Us About Lung Function?

“…In adults, Sundblad and colleagues have shown that a 20% change in FEV 1 following methacholine corresponds to different levels of change of G aw (reciprocal of R int ) determined by the interrupter technique, depending on the underlying degree of bronchial responsiveness, in this case, to a 39% change in G aw in all subjects, but a 66% change in less responsive subjects and a 27% change in more responsive subjects. 75 Thus, the range of cutoff of a positive test varies widely, depending on the nature of the underlying bronchial responsiveness.…”