A comparison or lung function methods for assessing dose-response effects of salbutamol

Pulmonary function methods which are able to detect small pharmacological effects may be useful for assessing the full dose-response curve of bronchodilatators. We compared the ability of impulse oscillometry (R5, R20, X5, RF), plethysmography (sGaw) and spirometry [forced expiratory volume in 1 s (FEV1), maximal mid expiratory flow rate (MMEF)] to measure the dose-response effects of salbutamol in 12 healthy subjects, 12 mild asthmatics (mean FEV1 96% predicted) and 12 moderate asthmatics (mean FEV 1 63% predicted). The techniques were performed twice to assess variability. Then salbutamol 10, 20, 100, 200 and 800 μg was administered. The sensitivity of the methods were compared by determining the lowest dose that caused changes greater than variability. In healthy subjects significant changes (p ≤ 0.05) were observed only in FEV1 (4.1%) and MMEF (14.6%) at 100 μg and sGaw (25.6%) and R20 (8.3%) at 200 μg. In mild asthmatics significant changes were observed in sGaw (15.9%) at 10 μg, X5 (23%), RF (20.3%) and MMEF (15.70/0) at 20 μg, R5 (13.9%) and R20 (9.4%) at 100 μg and FEV1 (7.1%) at 200 μg. All measurements except R20 demonstrated significant changes at 10 μg in moderate asthmatics. The most sensitive test for assessing bronchodilatation is different in healthy subjects and asthmatics, and varies with seventy of airflow obstruction.