The various methods of aerosol generation and inhalation have been compared: the Chai method with the Cockcroft method, the Yan method with the Cockcroft and Chai methods. These studies indicate that bronchial responsiveness can be measured reliably with any of the 3 methods. There are significant differences in the time required to conduct these various methods of measuring airway responsiveness: the Cockcroft and Chai methods take up to 45 minutes to complete, whereas the Yan method may be completed in less than 15 minutes. A modified protocol for methacholine challenge (Chai method) has been evaluated that reduces the test time to approximately 35 minutes without compromising safety or sensitivity.
The modification involves the omission of low doses in individuals whose history suggests they never had asthma. A similar shortened protocol for histamine challenge produced significant distortion of PDao, suggesting that histamine is less suitable than methacholine for use in such protocols. The incidence of side effects is slightly lower with methacholine than with histamine, particularly at higher concentrations.’
The method of calculating PC*, from the dose-response curve is another aspect of the determination of bronchial hyperresponsiveness that requires standardization. It is customary to use the last 2 points of the dose-response curve, that is, the 2 points on either side of the 20% fall in FEV,, to calculate the PC*,.