Oxygen and inhaled or oral corticosteroids are even less suitable than theophylline for a patient with stable COPD (without a reversible component)

I agree concerning the oral corticosteroids, though oxygen is helpful for hypoxemia, "Two randomized trials evaluated the use of oxygen therapy in patients with severe COPD and persistent hypoxemia...Oxygen therapy proved beneficial: there was an absolute reduction in the rate of death from any cause of about 20 percentage points in both trials." NEJM 2010 Niewoehner

Smoking is the most significant risk factor for COPD (likelihood ratio=8.3)

Emphysema is an obstructive airway disease characterized by formation of bullae or large sacs by dilation and destruction of airspaces distal to the terminal bronchiole. Significant pressures are required in the airway in order to prevent collapse of these remodelled airways. Pursed lips enables patients with severe obstructive symptoms to prevent closure of these dilated airways by preventing the significant drop in pressure normally encountered during expiration.