Decreased oxygen extraction during cardiopulmonary exercise test in patients with chronic fatigue syndrome.

Abstract

BACKGROUND: The insufficient metabolic adaptation to exercise in Chronic Fatigue Syndrome (CFS) is still being debated and poorly understood. METHODS: We analysed  the cardiopulmonary exercise tests of CFS patients, idiopathic chronic fatigue  (CFI) patients and healthy visitors. Continuous non-invasive measurement of the  cardiac output by Nexfin (BMEYE B.V. Amsterdam, the Netherlands) was added to the  cardiopulmonary exercise tests. The peak oxygen extraction by muscle cells and  the increase of cardiac output relative to the increase of oxygen uptake  (ΔQ'/ΔV'O₂) were measured, calculated from the cardiac output and the oxygen  uptake during incremental exercise. RESULTS: The peak oxygen extraction by muscle  cells was 10.83 ± 2.80 ml/100ml in 178 CFS women, 11.62 ± 2.90 ml/100 ml in 172  CFI, and 13.45 ± 2.72 ml/100 ml in 11 healthy women (ANOVA: P=0.001), 13.66 ±  3.31 ml/100 ml in 25 CFS men, 14.63 ± 4.38 ml/100 ml in 51 CFI, and 19.52 ± 6.53  ml/100 ml in 7 healthy men (ANOVA: P=0.008).The ΔQ'/ΔV'O₂ was > 6 L/L (normal  ΔQ'/ΔV'O₂ ≈ 5 L/L) in 70% of the patients and in 22% of the healthy group.  CONCLUSION: Low oxygen uptake by muscle cells causes exercise intolerance in a  majority of CFS patients, indicating insufficient metabolic adaptation to  incremental exercise. The high increase of the cardiac output relative to the  increase of oxygen uptake argues against deconditioning as a cause for physical  impairment in these patients.