Functional Respiratory Imaging Study (DARWiIN)

The objective of this clinical study was to evaluate the tolerability, safety, and efficacy of stepping up from fluticasone propionate (FP)/salmeterol (SLM) dry-powder inhaler (DPI) (SERETIDE™ DISKUS™) to extrafine beclometasone dipropionate (BDP)/formoterol fumarate (FF)/glycopyrronium bromide (GB) DPI (CHF5993) and to assess its effect on airway geometry and lung ventilation in subjects with advanced Chronic Obstructive Pulmonary Disease (COPD). Primary Objectives: * Untrimmed siVaw for distal region at TLC - actual value for V2 pre-dose and V3 pre-dose * Trimmed siRaw for distal region at TLC - actual value for V2 pre-dose and V3 pre-dose Secondary Objectives: * Untrimmed siVaw for distal region at TLC and FRC - actual value for V2 pre-dose, V2 post-dose, V3 pre-dose and V3 post-dose * Trimmed siRaw for distal region at TLC and FRC - actual value for V2 pre-dose, V2 post-dose, V3 pre-dose and V3 post-dose * Safety assessment through the evaluation of treatment-emergent adverse events (TEAEs).