The primary objective is to comparatively evaluate the isolated effects of a long-acting beta2-adrenergic (formoterol fumarate 12µg b.i.d. via Aeroliser) and combined with a long-acting anti-cholinergic (tiotropium bromide 18µg o.d via Handihaler) on breathlessness, dynamic hyperinflation and exercise tolerance in patients with advanced, but stable, chronic obstructive pulmonary disease. The study hypothesis is that combining long acting bronchodilators with different action mechanisms would promote synergistic effects on clinical outcomes.