ME/CFS is a complex and debilitating condition characterised by profound fatigue, post-exertional malaise (PEM), cognitive difficulties, sleep dysfunction and other symptoms. Assessing PEM, the cardinal feature of ME/CFS, is crucial for gaining a deeper understanding of the condition. The primary method for assessing PEM is through cardiopulmonary exercise testing (CPET).
Purpose of CPET
CPET is a widely used tool in various fields, including cardiology, respiratory, sports medicine, and perioperative assessment. It provides valuable information about cardiovascular and respiratory function, exercise capacity, and the physiological response to exertion. In diagnostic settings, CPET can help clinicians evaluate patients with suspected heart- or lung-related conditions, assess exercise tolerance, and determine appropriate treatment strategies.
CPET allows researchers to study physiological responses to exertion in individuals with ME/CFS, and how PEM relates to this. Although, ME/CFS is usually diagnosed through self-report measures and exclusion of other conditions, CPET is sometimes used for diagnostic purposes in ME/CFS e.g. within the context of disability testing.
CPET protocol and types of CPET
1-day CPET involves individuals partaking in maximal exercise whereby peak levels of effort are reached. During testing there is comprehensive assessment of how well the cardiovascular and respiratory systems perform under stress, monitoring aspects such as oxygen consumption, blood pressure and heart rate. 2-day CPET adds a second day to assess whether the day one performance can be reproduced.
There is usually a distinction between 1-day and 2-day CPET findings in ME/CFS research. Whilst 1-day CPET may not distinguish ME/CFS participants from others in some cases, the second day of CPET often demonstrates significant reductions in measured variables in individuals with ME/CFS, indicating impaired recovery coinciding with PEM. This interesting response pattern on the second day distinguishes ME/CFS patients from both healthy controls and individuals with other fatiguing conditions.
Dr Betsy Keller and colleagues stated in their study that ‘ME/CFS patients currently represent a unique class of ill patients who do not reproduce maximal CPET measures, unlike individuals with cardiovascular disease, lung disease, end-stage renal disease, pulmonary arterial hypertension and cystic fibrosis.’ Essentially this implies that individuals with certain other fatiguing illnesses do not experience PEM, therefore despite exercising to the maximum on one day they can still reproduce a similar performance the next day. Note: As many individuals with long COVID report having PEM, it is worth noting this study was conducted prior to the COVID-19 pandemic.
Ethical Considerations
Despite its utility, CPET in ME/CFS research and diagnostics is not without risks. Deliberately inducing PEM through maximal exertion contradicts ME/CFS management advice, which typically emphasises pacing and avoiding overexertion. Barbara Stussman and colleagues explored experiences of PEM in 43 individuals who reported having ME/CFS, finding that PEM following CPET is potentially more immediate, intense, and longer in duration than PEM in daily life.
In the Bateman Horne PEM video series, Dr Lucinda Bateman states, ‘Serial two-day CPET testing has been clinically used to establish objective measurements supporting eligibility for disability benefits, in some cases it may be crudely used to measure disease progression or severity. Despite these utilities, providers must weigh the benefits of CPET testing against its potential harm, which could include the induction of a prolonged worsening of an individual’s ME/CFS as a result of the provocation of an extended episode of PEM.’
ME/CFS research involving CPET is typically subject to ethics approval from institutional review boards or ethics committees. This approval ensures that research protocols adhere to ethical principles, protect participants’ rights and well-being, and minimise risks. Usually, informed consent is obtained from all participants, and studies are conducted in accordance with established ethical guidelines, such as the Declaration of Helsinki.
