Cardiopulmonary exercise testing (CPET)
The patients completed an incremental maximal cardiopulmonary exercise testing until they reached exhaustion on a cycloergometer (Cybex™ cycle ergometer, USA) by an exercise physiologist. The patients were tested utilizing the Astrand modified protocol with an initial load of 25 watts and an increment of 25 watts every two minutes with a constant speed between 60 and 70 rpm. A breath-by-breath analysis was performed on the was measured by a computerized system (CPX-Ultima Medical Graphics™ Metabolic System, St. Paul, Minnesota, USA). Peak oxygen uptake (VO