This is an observational study with a cross-over design performed in the Department of Nephrology and the Third Department of Cardiology in Hippokration Hospital of Thessaloniki in Greece. For the purposes of this study, hemodialysis patients fulfilling the inclusion/exclusion criteria, as well as controls without CKD, were invited to participate. All included patients signed a written informed consent form. The study protocol was approved by the Ethics Committee of the School of Medicine, Aristotle University of Thessaloniki. All procedures and evaluations are performed according to the Declaration of Helsinki 2013 Amendment.~Baseline evaluation includes the recording of demographics and anthropometric characteristics, medical history, concomitant medications and dialysis-related parameters, as well as physical examination and venous blood sampling for routine laboratory tests. Hemodialysis patients will be evaluated at two time points (at the end of the long and at the end of the short interdialytic interval), while controls at one time point. All the participants will undergo spirometry, CPET, cardiac ultrasound, lung ultrasound and bioelectrical impedance analysis.
Chronic kidney disease (CKD), especially end-stage kidney disease (ESKD), is associated with increased risk for cardiovascular events and all-cause mortality. Exercise intolerance as well as reduced cardiovascular reserve are extremely common in patients with CKD. Cardiopulmonary exercise testing (CPET) is a non-invasive, dynamic technique that provides an integrative evaluation of cardiovascular, pulmonary, neuropsychological and metabolic function during maximal or submaximal exercise, allowing the evaluation of functional reserves of these systems. CPET is currently considered to be the gold-standard for identifying exercise limitation and differentiating its causes. It has been widely used in several medical fields for risk stratification, clinical evaluation and other applications. However, the use of CPET in assessment of exercise intolerance in everyday nephrology practice is limited. Hence, this is the first study possible differences in CPET's parameters during long and short interdialytic intervals in hemodialysis patients.