Bronchodilator Response in Patients with COPD, Asthma-COPD-Overlap (ACO) and Asthma, Evaluated by Plethysmographic...

Airflow reversibility criteria in COPD are still debated - especially in situations of co-existing COPD and asthma. Bronchodilator response (BDR) is usually assessed by spirometric parameters. Changes assessed by plethysmographic parameters such as the effective, specific airway conductance (sG_eff), and changes in end-expiratory resting level at functional residual capacity (FRC_pleth) are rarely appreciated. We aimed to assess BDR by spirometric and concomitantly measured plethysmographic parameters. Moreover, BDR on the specific aerodynamic work of breathing (sWOB) was evaluated.

From databases of 3 pulmonary centers, BDR to 200 g salbutamol was retrospectively evaluated by spirometric (∆FEV₁ and ∆FEF_25-75), and plethysmographic (∆sG_eff, ∆FRC_pleth, and ∆sWOB) parameters in a total of 843 patients diagnosed as COPD (478 = 57%), asthma-COPD-overlap (ACO) (139 = 17%), or asthma (226 = 27%), encountering 1686 BDR-measurement-sets (COPD n = 958; ACO n = 276; asthma n = 452).

Evaluating z-score improvement taking into consideration the whole pre-test z-score range, highest BDR was achieved by combining ∆sG_eff and ∆FRC detecting BDR in 62.2% (asthma: 71.4%; ACO: 56.7%; COPD: 59.8%), by ∆sG_eff in 53.4% (asthma: 69.1%; ACO: 51.6%; COPD: 47.4%), whereas ∆FEV₁ only distinguished in 10.6% (asthma: 21.8%; ACO: 18.6%; COPD: 4.2%). Remarkably, ∆sWOB detected BDR in 49.4% (asthma: 76.2%; ACO: 47.8%; COPD: 46.9%).

BDR largely depends on the pre-test functional severity and, therefore, should be evaluated in relation to the pre-test conditions expressed as ∆z-scores, considering changes in airway dynamics, changes in static lung volumes and changes in small airway function. Plethysmographic parameters demonstrated BDR at a significant higher rate than spirometric parameters.