Reliability of graded treadmill testing in patients with intermittent claudication

Aim. The purpose of this study was to examine the reliability of maximal walking time (MWT), peak oxygen consumption, maximal heart rate (MHR), respiratory exchange ratio (RER), rating of perceived exertion and claudication pain scale in these patients. Methods. Eleven patients underwent two graded progressive treadmill exercise tests. The exercise test commenced with an initial speed of 2 mph and a 0% gradient for two min. During subsequent stages the gradient was increased by two percent every two minutes, and the speed kept constant. During each test, patients were instructed to walk for as long as they could endure the pain (maximum walking time). Peak oxygen uptake was assessed on a breath-by-breath basis by online expiratory gas analysis (CardiO 2, Medical Graphics Corp., St Paul, MN, USA). Results. Repeated tests were obtained within 5±3 days. Paired t-tests demonstrated that measurements of peak oxygen consumption, maximal walking time, maximal heart rate, RER, RPE and pain were reproducible between tests. The coefficient of variation and intraclass correlation coefficient values confirmed the reliability. Bland-Altman analysis revealed that peak oxygen consumption varied within 3 mL kg min-1; however, maximum walking distance varied by up to 158 seconds. Conclusion. The graded exercise test is reliable. It allows differentiation between patients' walking ability and allows magnitude of improvement to be analysed post intervention. Metabolic measures taken during the test show similar repeatability, giving the clinician confidence in the interpretation of the values.