Development of airflow limitation according to smoking history and underlying disease.

<p><i>(A)</i> Plots of FEV₁/FVC according to smoking intensity and its 50th percentile prediction line show lower levels of smoking are required for airflow limitation in participants with asthma or inactive TB than in those without. <i>(B</i>, <i>C)</i> FEV₁ was lower in participants with asthma or inactive TB than in those without. The gray region represents the 95% confidence interval of FEV₁. FVC = forced vital capacity, FEV₁ = forced expiratory volume in one second.