Three 20‐Minute Interspaced Salbutamol Inhalations as a Test for the Diagnosis of Reversible Airflow Limitation in Adult Asthmatics

Reversible airflow limitation represents an important parameter for the diagnosis of bronchial asthma. The aim of this study was to design a simple and useful test for the detection of reversible airflow limitation. The subjects were 29 patients with asthma and forced expiratory volume in 1 second (FEV1) < 80% predicted. Following baseline spirometry, subjects inhaled 1.5 mg of salbutamol by a nebulizer and then spirometry was performed 20 min later. The procedure was repeated three times. Subsequently, 13 patients received 30 mg of predonisolone orally once daily for 1 week. Spirometry was performed before and after the oral predonisolone therapy, and results were compared with those of salbutamol inhalation test. The mean increase in FEV1 over the baseline was 18.3% after the first salbutamol inhalation, 26.4% after the second inhalation, and 30.2% after the third inhalation. The increases in FEV1 were significant after each inhalation. The mean increases in the maximum expiratory flow rate at 50% (V50) and that at 25% (V25), measured from the flow volume loop, were 53.5% and 46.9% after the first inhalation, but there were no significant changes by repeated inhalations. A significant reversal of airflow limitation was demonstrated in 18 subjects after the first inhalation, 22 subjects after the second inhalation, and 27 subjects after the third inhalation. Improvement in FEV1 after oral predonisolone was equivalent to that after the third inhalation of salbutamol. A test composed of three 20-min interspaced salbutamol inhalations is useful for the diagnosis of asthma by demonstrating the presence of reversible airflow limitation.