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

Abstract

Background: 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.

Methods: 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.

Results: 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.

Conclusions: 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.

Keywords: Bronchodilator response; Pulmonary function testing; Spirometry.

Fig. 1

Effects of referencing a bronchodilator-induced increase in airway radius (r) relative to the pre-bronchodilator radius (r₁ and r₂) or the radius of a normal airway (r_n) in two constricted airways

Fig. 2

Plot of bronchodilator-induced change in FEV₁ relative to pre-bronchodilator FEV₁ (∆FEV_1(%Pre−B); top left panel) and relative to predicted normal FEV₁ (∆FEV_1(%PN); top right panel) as a function of pre-bronchodilator FEV₁ in patients with a positive change in FEV₁ (N = 1,040). The horizontal dashed line indicates a 12% change. The bottom left panel is the scatter plot of ∆FEV_1(%Pre−B) vs. ∆FEV_1(%PN) with the diagonal dashed line as the line of identity.

Fig. 3

Plot of bronchodilator-induced change in FEV₁ relative to pre-bronchodilator FEV₁ (∆FEV_1(%Pre−B); top left panel) and relative to predicted normal FEV₁ (∆FEV_1(%PN); top right panel) as a function of pre-bronchodilator FEV₁ in patients with a ΔFEV₁ ≥ 0.2 L (N = 213). The horizontal dashed line indicates a 12% change. The bottom left panel is the scatter plot of ∆FEV_1(%Pre−B) vs. ∆FEV_1(%PN) with the diagonal dashed line as the line of identity

Fig. 4

Plot of bronchodilator-induced change in FVC relative to pre-bronchodilator FVC (∆FVC_(%Pre−B); top left panel) and relative to predicted normal FVC (∆FVC_(%PN); top right panel) as a function of pre-bronchodilator FVC in patients with a ∆FVC ≥ 0.0 L (N = 928). The horizontal dashed line indicates a 12% change. The bottom left panel is the scatter plot of ∆FVC_1(%Pre−B) vs. ∆FVC_(%PN) with the diagonal dashed line as the line of identity

Fig. 5

Plot of bronchodilator-induced change in FVC relative to pre-bronchodilator FVC (∆FVC_(%Pre−B); top left panel) and relative to predicted normal FVC (∆FVC_(%PN); top right panel) as a function of pre-bronchodilator FVC in patients with a ∆FVC ≥ 0.2 L (N = 220). The horizontal dashed line indicates a 12% change. The bottom left panel is the scatter plot of ∆FVC_1(%Pre−B) vs. ∆FVC_(%PN) with the diagonal dashed line as the line of identity