This was a blinded, randomized crossover study. At Visit 1 we assessed pulmonary function, exercise capacity and 6MWT distance. Visits 2 and 3 consisted of four 6MWT with different inspired gases: room air by mask (RA), 100% O2 by mask (Mask O2), 100% O2 by nasal prongs (Nasal O2), and 70% He/30% O2 by mask (HeO2). Walking distance, shortness of breath, leg fatigue, O2 saturation and heart rate (HR) were assessed