Levels of sustainable aerobic workload in dialysis patients

The aerobic performance of a heterogeneous group of 89 ambulatory medically stable patients on chronic hemodialysis was studied to define individual levels of the most acceptable metabolic workload. The patients performed a step test protocol (3 steps) with a cycle ergometer. Each step (25 Watt) lasted 6 min. Heart rate (HR), oxygen consumption (VO2), ventilation (VE), respiratory exchange ratio (RER), blood pressure (BP) and subjective ratings of dyspnea (CRd) and fatigue (CRf) levels were monitored throughout the test. The test was continued to exhaustion or to values of systolic arterial blood pressure (SABP) >240 mmHg, heart rate (HR) > or = 85% max, or ST changes in ECG. In eleven patients (12.5% of the whole group) the test was interrupted within the first two minutes of exercise. In the remaining 78 patients, the maximum workload sustained for at least 3 min (MSW) was 25 Watts for 43 (48.5%), 50 Watts for 27 (30%), and 75 Watts for 8 (9%) patients. Performance was affected in a statistically significant manner by the subjects' anagraphic age, but not by their dialytic age, hemoglobin (Hb) level or weight. Individual levels of tolerable workload were estimated for 60% of the group from the stability of physiological variables during 3 min, and from subjective ratings at a "moderate" level. This level corresponded to an average of 3.5+/-0.9 METs, at 60% of the HRmax, with a mean BP of 167+/-21/98+/-14 mmHg. This could become a safe starting point for a program of physical retraining.