ackground : Methacholine inhalation test was known to be a good method for assessing
the nonspecific bronchial hyperresponsiveness(NSBH). And a decline in forced expiratory
volume in 1 second(FEVI) of more than 20% indicates the presence of NSBH. But there are
some difficulties in determination of NSBH objetively as the results of spirometry are
influenced by patients mechanisms of airway narrowing between natural bronchial asthma and
methacholine induced bronchial spasm.
Methods : We measured spirometric and body plethysmographic parameters both before
and after inhalation of methacholine in 30 cases of mild asthmatics. To better understan the
mechanism of the methacholine induced bronchospam, spirometric and plethysmographic
parameters of methacholine induced bronchospasm(MIBS, n=18) were compared with natural
bronchial asthma(n=18). The MIBS and natural bronchial asthma groups were matched with
same predict value of FEV1(65 vs 67%)
Results : After the inhalation of methacholine, maximal expiratory flow volume at 50% of
total lung capacity(Vmax50) was decreased more than 20% compared to baseline value in all
30 cases and the Vmax25 was decreased more than 20% 27 of the 30 cases. Inhalation of
methaholine produced an 175% increase in airway resistance(Raw)and 239% increase in
specific airway resistance(Sraw), and all of the 30 cases had an increase in Raw of more
than 35 percent. Methacholine inhalation produced a 33.5% increase in residual volume (RV),
however the RV was decreased or remained unchange after inhalation of methacholine in 7
out of 30 cases. There were no differences in total lung capacity and effective residual
volume between before and after inhalation of methacholine. Vital capacity and diffusing
capacity of CO after challenge were significantly decreased 15.1% and 8.7% respectively.
With comparison of MIBS(n=18) and natural bronchial asthma(n=18), Sraw was significantly
higher in MIBS than natural bronchial asthma (380.±43.7 vs 247.8±02.0% of pred.) and no
significant difference was found in all spirometric and other plethysmographic parameters.
Conclustion : For assessing the NSBH, Raw, Vmax50 and Vmax25 are useful and
objective parameters. And even though there are some pathophysologic differences between
MIBS and natural bronchial asthma, we could not fin significant differences in most
parameters of spirometer and plethysmographic parameters except Sraw between MIBS and
natural asthma.
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