Diminished Ventilatory Responses During Post-Exertional Malaise Contributes to Exercise Intolerance in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome.

Reduced functional capacity and post-exertional malaise following physical activity are hallmark symptoms of Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS). The mechanisms producing exercise intolerance in the post-exertional state have not been adequately described. Purpose: To compare the ventilatory response to repeated exercise stress in control and ME/CFS subjects. Methods: 40 female subjects were recruited for the study, 20 ME/CFS patients and 20 age and weight matched controls. All underwent two maximal exercise tests 24 hours apart. Oxygen consumption, ventilation (VE), tidal volume (TV), respiratory rate (RR), end-tidal oxygen and carbon dioxide (ET02/ETCO2) were measured at rest, at the anaerobic threshold, and at maximal exercise. Multivariate analysis was performed for group (ME/CFS vs control), test (exercise test 1 vs test 2), and condition (rest vs anaerobic threshold vs maximal exertion) with univariate follow up. Results: 15 ME/CFS subjects and 18 control subject reached criteria for maximal effort. The overall multivariate was significant for group and condition. Follow up univariate and post-hoc showed VO2, VE and TV were lower in the ME/CFS group only on exercise test 2. Post hoc for condition was significant for ventilation at maximal exercise only. Respiratory rate, ETO2, and ETCO2 were not different between tests or groups. Conclusion: In the absence of a second exercise test, the lack of any significant differences for the first test would appear to suggest no functional impairment in ME/CFS patients. However, the results from the second test indicate the presence of exercise intolerance and post-exertional malaise. Diminished ventilatory responses accompany reductions in work output and oxygen consumption during post exertional malaise