Difference Between Slow and Forced Vital Capacity and Its Relationship with Dynamic Hyperinflation in Patients with Chronic Obstructive Pulmonary Disease

The aim of the study was to investigate the relationship between slow and forced vital capacity (SVC–FVC) difference with dynamic lung hyperinflation (DH) during the 6-min walking test (6MWT) in subjects with chronic obstructive pulmonary disease (COPD). Twenty-four subjects with COPD (12 males; 67 ± 6 years; forced expiratory volume in first second [FEV₁] 56 ± 18% predicted) performed lung function tests by spirometry and plethysmography. DH was assessed by serial measurements of inspiratory capacity (IC) performed during the 6MWT and defined as ∆IC ≥ 150 mL or 10%. IC decrease significantly during the 6MWT (ΔCI: − 0.48 ± − 0.40 L; P < 0.0001), and 18 individuals (75%) presented DH. There was significant difference when comparing IC measured at rest with the other serial IC measurements (P < 0.0001). Correlation between the SVC–FVC difference and DH during the 6MWT was r = − 0.38; P = 0.06. The SVC–FVC difference presented only weak correlation with the development of DH during the 6MWT in patients with COPD.