Cockcroft Method. This method utilizes the same doubling dosage regimen of histamine and methacholine. The aerosol is generated using a Wrights nebulizer primed with 5 ml of test solution and an oxygen flow rate of 7 L/min. It is delivered direcdy into a face mask and inhaled through the mouth (the nose is closed by a clip) by quiet tidal breathing for 2 minutes. Challenges are conducted at 5-minute intervals.
Yan Method. This is a rapid, simple method for measuring bronchial responsiveness. A hand-held De Vilbiss no 40 nebulizer is used to generate the aerosol. The nebulizers are standardized to produce an output of 0.003 ml per puff (0.0018 to 0.0042 ml). Each nebulizer is primed with 1 ml of saline or histamine in concentrations of 0.3, 0.6, 2.5, or 5.0 g/100 ml. Histamine is administered in a regimen that achieves cumulative doubling doses of 0.03 to 7.8 itmol. Inhalations are administered by expressing 1 or more puffs from the nebulizer direcdy in front of the subject s open mouth, at the beginning of a near maximal inspiration from functional residual capacity. The inspiration is held for 3 s.
Comparisons of Methods and Results
A number of studies have been carried out comparing responsiveness to histamine and to methacholine, intrasubject day-to-day variability, and techniques of aerosol generation. In practically all studies using similar aerosol generation methods, responsiveness to histamine correlates closely with methacholine. Under carefully controlled conditions, responses to histamine and methacholine are highly reproducible.- The 95% confidence intervals of PCM histamine is a ± 1.6-fold difference in PC*, from 1 visit to another.