[The effects of dose of salbutamol and observation time on bronchodilation test].

Objective: To evaluate the effects of different doses of salbutamol and observation times on bronchodilation test.

Methods: Three groups of subjects (30 patients with asthma, 29 patients with COPD, and 30 normal controls) were included in this study. The forced expiratory volume in the first second (FEV1) was evaluated in the positive rates at 15, 20, and 30 min after inhaling 200 microg or 400 microg salbutamol. On day 2, another dose of salbutamol was inhaled, and FEV1 measurement was performed repeatedly. SPSS 10.0 was used for statistical analysis. The positive rates after inhaling 200 microg and 400 microg salbutamol at the 15, 20 and 30 min were compared with chi-square test.

Results: Using absolute change of FEVY1 > 200 ml and improving rate of FEV1 > or = 12% as the positive standard, the positive rate of the asthmatic subjects at 15, 20, and 30 min after inhaling 200 microg salbutamol was 28/30 (93.3%), 28/30 (93.3%) and 28/30 (93.3%, chi2 = 0.00, P > 0.05). The positive rate of the asthmatic subjects at 15, 20 and 30 min after inhaling 400 microg salbutamol was 28/30 (93.3%), 29/30 (96.7%), 27/30 (90.0%, chi2 = 1.07, P > 0.05). The positive rate at 15, 20 and 30 min were not significantly different between patients inhaling 200 microg and 400 microg salbutamol (chi2 = 0.00, 0.00, 0.00, all P > 0.05). In the patients with COPD and in normal controls, the positive rate was not significantly different between patients inhaling 200 microg and 400 microg salbutamol. There was also no difference in the positive rate at different time. If using absolute change of FEVY1 > 200 ml and improving rate of FEV1 > or = 12% as the positive standard, the best combination of sensitivity and specificity of diagnosing asthma was achieved. The sensitivity was 93.3% and the specificity was 98.3%.

Conclusions: FEV1 at 15 min after inhaling 200 microg salbutamol is the best choice as it is highly efficient and causes less side effects. We suggest that an absolute increase of FEV1 > 200 ml and improving rate of FEV1 > or = 12% to be the positive standard of diagnosing asthma.