Figure 1

A , Scatterplot diagram of the percent change in forced expiratory volume in 1 second (FEV ₁ ) after inhalation of ipratropium bromide versus the natural logarithm of PC ₂₀ FEV ₁ (provocative concentration of methacholine that results in a 20% fall in FEV ₁ ) for methacholine challenge ( r = .169, p > .05). B, Scatterplot diagram of the percent change in FEV₁ after inhalation of salbutamol versus the natural logarithm of PC₂₀FEV₁ for methacholine challenge (r = .314, p = .049). Dashed lines represent the 95% confidence interval for linear regression.