Inability of myalgic encephalomyelitis/chronic fatigue syndrome
patients to reproduce VO2peak indicates functional impairment
Betsy A Keller, John Luke Pryor and Ludovic Giloteaux
Journal of Translational Medicine 2014, 12:104 doi:10.1186/1479-5876-12-104
Published: 23 April 2014
Background: Myalgic Encephalomyelitis/Chronic Fatigue Syndrome
(ME/CFS) is a multi-system illness characterized, in part, by
increased fatigue following minimal exertion, cognitive impairment,
poor recovery to physical and other stressors, in addition to other
symptoms. Unlike healthy subjects and other diseased populations who
reproduce objective physiological measures during repeat
cardiopulmonary exercise tests (CPETs), ME/CFS patients have been
reported to fail to reproduce results in a second CPET performed one
day after an initial CPET. If confirmed, a disparity between a first
and second CPET could serve to identify individuals with ME/CFS, would
be able to document their extent of disability, and could also provide
a physiological basis for prescribing physical activity as well as a
metric of functional impairment.
Methods: 22 subjects diagnosed with ME/CFS completed two repeat CPETs
separated by 24 h. Measures of oxygen consumption (VO2), heart rate
(HR), minute ventilation (Ve), workload (Work), and respiratory
exchange ratio (RER) were made at maximal (peak) and ventilatory
threshold (VT) intensities. Data were analyzed using ANOVA and
Wilcoxon's Signed-Rank Test (for RER).
Results: ME/CFS patients showed significant decreases from CPET1 to
CPET2 in VO2peak (13.8%), HRpeak (9 bpm), Ve peak (14.7%), and
Work@peak (12.5%). Decreases in VT measures included VO2@VT (15.8%),
Ve@VT (7.4%), and Work@VT (21.3%). Peak RER was high (>=1.1) and did
not differ between tests, indicating maximum effort by participants
during both CPETs. If data from only a single CPET test is used, a standard classification of functional impairment based on VO2peak or VO2@VT results in over-estimation of functional ability for 50% of ME/CFS participants in this study.
Conclusion: ME/CFS participants were unable to reproduce most physiological measures at both maximal and ventilatory threshold intensities during a CPET performed 24 hours after a prior maximal
exercise test. Our work confirms that repeated CPETs warrant
consideration as a clinical indicator for diagnosing ME/CFS.
Furthermore, if based on only one CPET, functional impairment
classification will be mis-identified in many ME/CFS participants.