MULTIDIMENSIONAL POST-BRONCHODILATOR RESPONSE PHENOTYPES BEYOND THE FEV₁/FVC RATIO IN NIGERIAN PATIENTS WITH CHRONIC OBSTRUCTIVE PULMONARY DISEASE

Background: Bronchodilator responsiveness in chronic obstructive pulmonary disease (COPD) is heterogeneous, and assessment centred on forced expiratory volume in one second (FEV₁) may overlook changes in forced vital capacity (FVC) and mid-expiratory flow. We evaluated post-bronchodilator response patterns in Nigerian adults with COPD.
Methods: This cross-sectional study included 59 adults aged ≥35 years with post-bronchodilator FEV₁/FVC <0.70. Spirometry was performed before and 15 minutes after 400 µg salbutamol. Mutually exclusive patterns were combined flow–volume, flow-dominant, volume-dominant, exploratory FEF₂₅–₇₅-defined response, or non-response. Conventional FEV₁ and FVC responses required increases of ≥12% and ≥200 mL; the exploratory FEF₂₅–₇₅ response required an increase ≥20% without an FEV₁ or FVC response. The updated ERS/ATS definition was examined in a sensitivity analysis.
Results: Mean age was 61.7±12.5 years, and 36 participants (61.0%) were men. Changes were 0.158 L for FEV₁, 0.190 L for FVC, and 0.209 L/s for FEF₂₅–₇₅ (all p<0.001). Patterns were combined flow–volume in 12 (20.3%), flow-dominant in eight (13.6%), volume-dominant in 13 (22.0%), exploratory FEF₂₅–₇₅-defined in five (8.5%), and non-response in 21 (35.6%). Changes were correlated (Spearman ρ = 0.746–0.847; all p<0.001). Under the updated ERS/ATS definition, FEV₁ or FVC responsiveness decreased from 33/59 (55.9%) to 25/59 (42.4%); eight participants (13.6%) had an FVC-only response. Phenotype distribution differed across GOLD grades (Monte Carlo p<0.001), but not by biomass or tobacco exposure.
Conclusions: Bronchodilator-related changes extended beyond FEV₁. Joint assessment of FEV₁ and FVC identified complementary flow and volume responses, whereas FEF₂₅–₇₅ provided an exploratory signal that requires validation. These patterns are descriptive and should not direct treatment without clinical validation.