Lighter than air: heliox breathing improves exercise tolerance in COPD.

D yspnoea and reduced exercise tolerance are the hallmarks of chronic obstructive pulmonary disease (COPD). In the advanced phases of the disease the ability to exercise is mainly limited by the combination of a reduced ventilatory capacity, increased ventilatory requirement and lung dynamic hyperinflation. Importantly, the aforementioned respiratory mehanical abnormalities are well recognised causes of exertional dyspnoea in COPD [1]. However, in a substantial number of patients a heightened perception of leg effort may reduce tolerance to cycle-ergometer exercise, while dyspnoea appears to be the main symptom limiting the ability to walk [2]. Regardless of this, there would be little question that, in patients with severe COPD and particularly in those subjects with predominant emphysema, maximal exercise tolerance is markedly reduced because of ventilatory limitation, dynamic hyperinflation and dyspnoea sensation.