Cardiopulmonary exercise test
Symptom-limited incremental CPET was performed according to the ERS guidelines on an electronically braked cycle ergometer (Ergometrics 900; Ergoline; Bitz, Germany) [After a steady-state resting period, a 3 min warm-up was conducted at about 20% of individually estimated maximal workload. A progressive increase in workload was then applied every minute (10 to 20 W/min) depending on the patient’s physical condition, medical history and according to a total exercise time between 8 and 12 min. Tests were terminated at the point of symptom limitation (peak exercise) or in the presence of electrocardiographic changes. Subjects rated the magnitude of their perceived breathing and leg discomfort by pointing to a number on the 10-point Borg scale [Breath-by-breath gas exchange values were measured using a Masterscreen CPX metabolic cart (MGC-CPX System; MGC Diagnostics Corporation) and were expressed as 30 s averages, according to recommended guidelines. Minute ventilation (V′E), oxygen uptake (V′ODuring CPET, arterialized earlobe blood samples were drawn by a nurse at rest, at anaerobic threshold (AT) and at peak exercise. Partial pressure of oxygen (PaOTests were considered maximal if a plateau of the V′ONormal predicted values for V′O