Physiological Responses to Incremental Exercise in Patients With Chronic Fatigue Syndrome

The purpose of this investigation was to characterize the physiological response profiles of patients with chronic fatigue syndrome (CFS), to an incremental exercise test, performed to the limit of tolerance. Fifteen patients (12 women and 3 men) who fulfilled the case definition for chronic fatigue syndrome, and fifteen healthy, sedentary, age- and sex-matched controls, performed an incremental progressive all-out treadmill test (CPET). As a group, the CFS patients demonstrated significantly lower cardiovascular as well as ventilatory values at peak exercise, compared with the control group. At similar relative sub-maximal exercise levels (% peakVO2), the CFS patients portrayed response patterns (trending phenomena) characterized, in most parameters, by similar intercepts but either lower (VCO2, HR, O2pulse, ERE, VE, Vt, PETCO2) or higher (Bf, VE/VCO2, Vd/Vt) trending kinetics in the CFS compared with the control group. It is suggested that the primary exercise-related physiological difference between the CFS and the control groups was their significantly lower heart rate at any equal relative and maximal work level. Assuming maximal effort by all (indicated by RER, PETCO2, and subjective exhaustion), these results could indicate either cardiac or peripheral insufficiency embedded in the pathology of CFS patients. We conclude that indexes from cardiopulmonary exercise testing may be used as objective discriminatory indicators for evaluation of patients complaining of chronic fatigue syndrome.