Diagnostic sensitivity of 2-day cardiopulmonary exercise testing in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome Nelson et al. 2019

The Workwell studies showed that the anaerobic threshold was reached at a much lower heart rate on the 2nd day. From the data in the trials, and presumably the data they have from the people they test outwith the trials Mark Van Ness has said that people with ME go into anaerobic respiration at a much lower level than healthy people.

This finding is consistent with patient's symptoms and with other research done by the likes of Julia Newton on cell cultures.

Aerobic exercise (when the body goes from relying on aerobic to anaerobic respiration) is only meant to be an emergency system but people with ME use it for the activities of daily living as their aerobic respiration cannot meet their needs. The level is different for everyone and at different times.

The big problem for CPET testing as a diagnosis is that many people will exceed their maximum effort by getting to the centre so we need another way to test for it.

The heart rate at which we go cross AT can be measured by CPET testing but if you can't do the test for any reason you can do a rough and ready calculation which many of us have done. To my amazement the times when I felt worse my heart rate was higher.

 

Sure, but elevated heart rate can have a variety of causes and does not necessarily indicate that anerobic respiration is becoming predominant, which is dependent on muscular drive.

Heart rate in general depends on cardiac drive (and balance between parasympathetic and sympathetic drive) and is based on a variety of physiological needs.

A graded CPET is a special case as it requires a stepped ramping up in power and therefore a regular increase in metabolic demands. The increase in heart rate in this case actually lags slightly behind muscular drive and metabolic demands. This is why the 2 day CPET has given mostly consistent results whereas other attempts to measure the actual fatigue as a result of PEM have failed.

The ventilatory threshold is associated with a variety of physiological factors, the transition from predominantly aerobic to anerobic metabolism itself is not the interesting part. The interesting part is why? In the case of a graded CPET, at some point the muscle fibres which predominantly rely on aerobic metabolism ("slow-twitch" fibres) reach their limits, so to increase the power, more (less efficient) muscle fibres must be recruited at this point. Hence not only are there non linearities in the graphs comparing VCO2 vs VO2 (consumed), or ventilation vs VO2 or lactate accumulation, but also in the in the electromyogram signal (EMG), indicating the initial ventilatory threshold. Exercise physiologists debate which happens first, but I think the answer is "it depends" and once one of these events is initiated (lactate threshold or EMG threshold), the other aspects will occur due to feedback.
The increase in the EMG signal is also associated with a stronger EEG signal in the brain, which in turn is the determining factor in effort perception (short term effort perception is primarily in the brain and ignores afferent signals)

My personal experience of the 2 Day CPET is on the second day, my legs felt like they had significantly less power than the previous day, I needed to ramp up my pedalling effort sooner to maintain the same power, hence an earlier ventilatory threshold and corresponding non linear increase in perception of effort as measured by the Borg scale.

This is not true if you are careful (don't go for a jog) and are not a severely affected patient.

 

There is already a wealth of information on how people with other illnesses respond to a CPET. It has long been known that the CPET is reliable and repeatable with little difference between tests on consecutive days for healthy people and those with a range of illnesses. That’s what makes it a useful test for evaluating different conditions over time. It’s also what made the findings in ME/CFS so unique. We don’t need CPET studies comparing us to other illnesses. They really just need a few controls to verify that the equipment is functioning normally so that the unusual results for ME/CFS patients cannot be explained away.

 

Yes and no... If this is going to be used to determine specificity of diagnosis for example (when used in scientific studies investigating the illness), comparisons with other fatiguing neurological conditions for example is necessary, otherwise this may be a non-specific association of fatiguing conditions, rather than specific to ME.