A comparative study of bronchodilator response: utilizing pre-bronchodilator versus predicted normal values

A positive bronchodilator response has been defined as a 12% increase in the forced expiratory volume in one second (FEV₁) or forced vital capacity (FVC) from their respective pre-bronchodilator values, combined with at least a 0.2 L absolute change. Recent recommendations suggested the use of the percent change in FEV₁ and FVC relative to their predicted normal values without having applied them in patients with airflow obstruction. The aim of the current study was to compare the two approaches over a wide range of pre-bronchodilator FEV₁ and FVC values.

A retrospective review of consecutive patients undergoing spirometry and bronchodilator testing was completed. The change in FEV₁ and FVC with a bronchodilator was expressed relative to the pre-bronchodilator and predicted normal FEV₁ and FVC.

In 1,040 patients with a non-paradoxical change in FEV₁, 19.0% had a ≥ 12% change in FEV₁ using their pre-bronchodilator value compared to 5.7% using their predicted normal value. For FVC, the respective values were 12.7% vs. 5.8%. The difference was retained in patients with a ≥ 0.2 L change in FEV₁ or FVC. In unobstructed patients, the upper threshold (two standard deviations above the mean) of the bronchodilator response was 14% for FEV₁ and 10% for FVC using predicted normal values.

Expressing the percent change in FEV₁ and FVC relative to predicted normal values reduces the over-estimation of the bronchodilator response, especially in patients with a very low pre-bronchodilator FEV1, including in those with a ≥ 0.2 L change in FEV₁. Irrespective of pre-bronchodilator values, a ≥ 14% change in FEV₁ and ≥ 10% change in FVC relative to the predicted normal values could be considered a positive bronchodilator response.