Andy's attempt to create a reasonable descriptive model of ME.

Title, which was originally "Published evidence for a minimum calorie/energy expenditure?", really says it all but the background to the question is that I'm trying to come up with some graphical/pictorial way to explain more easily our experience with a reduced sustainable exertion limit, over exertion and PEM.

So I'm wondering if there are any studies out there that establish a typical baseline minimum amount of energy expenditure? With the idea that if a severe ME patient has a sustainable exertion limit below this level then they are going to be in constant PEM.

A lot of what I'm intending will only be subjective and unproven, but if there is anything that is established and published then it will be helpful.

ETA: Added original thread title in the text after changing thread title.

 

Have you tried searching under Basal Metabolic Rate, used to be the term used for the metabolism/energy needed to keep the body going?

 

@Andy, I hope you find some answers.

It would be a great help if we were ultimately able to establish the physiological parameters of what triggers PEM:

- is it the total amount of calories burnt in a specific time period?
- is it the rate of calories being burnt?
- is it the heart rate?
- is the total number of heart beats in a specific time period?
- is it the build up of a metabolic waste product, such as lactic acid?
- is it the over consumption of a specific chemical, enzyme or even neurotransmitter or insufficient production of this as of yet unidentified substance?
- is it blood pressure?
- is it build up of something inappropriate in the blood stream, the brain or elsewhere (eg leaky gut hypothesis)?
- etc

Then how do superficially very different triggers, such as physical exertion or sensory overload apparently trigger a similar biochemical response? Is it that they somehow indirectly act on the same underlying system?

Certainly defining triggers would be a great help. Before I was aware that I had orthostatic intolerance I struggled to make senses of my crashes in terms of physical exertion, though I had got to the point of speculating about the different calorie demands of lying, sitting and standing. A clearer pattern only began to emerge when I distinguished between energy use/consumption/exertion (just based on subjective perception) and the amount of time I spent upright. Exceeding the limit in either triggers PEM. Once PEM has been triggered the result is the same, though interestingly I suspect the two do not interact if below the level of the trigger points.

That is the level of exertion for example sitting in a chair versus walking whilst carrying a load does not seem to reduce the amount of time I have upright as long as it does not in itself trigger PEM, similarly the amount of time I have already spent upright, as long as it is below the PEM trigger point does not seem to reduce the trigger point of exertion induced PEM.

 

Good question, that's very weird to me

 

It is definitely not the heart rate, otherwise all the people with POTS and ME would be in big trouble, and the people with ME and a low heart rate would be protected.

I think it could be the result of a tipping point reached due to a faster accumulation of x due to deficient mechanisms to dispose or deal with x. Where x could be something like oxidative stress or some metabolite involved in energy production, or some signal in the brain (or it could be the increased absence of something, like good blood flow).

 

Thanks, this is interesting

Especially

https://en.wikipedia.org/wiki/Basal_metabolic_rate

 

OK, I've changed the thread title to more reflect where the content of this thread is headed. See the next post for my first attempt at a descriptive 'model' of ME.

 

[Initial public draft]

This model is not an attempt to capture every symptom that all patients experience, but is an attempt to explain the patient experience of what many patients see as being the core issue of ME, Post Exertional Malaise (PEM). It is also NOT an attempt to accurately explain what is happening biologically, it is merely an attempt to set out a logical description of the patient experience.

*******
Introduction

ME patients have both a reduced sustainable exertion limit, and an abnormal reaction to overexertion, both levels of which are individual to the patient and may change over time.

Sustainable exertion limit (SEL) is the maximum level of exertion that a patient can reliably replicate without overexerting. This is no different to a healthy person, who too will have a sustainable exertion limit, only for an ME patient this limit is considerably reduced.

For many patients it is not impossible for them to exert themselves above their SEL, however the question then is, what is their individual tolerance to overexertion at the time that they overexert.

Too much overexertion, that exceeds the individual patient's tolerance to it, without sufficient rest to counteract it, results in PEM. The severity of PEM is often closely related to the severity of a patient’s condition, as the lower a patient’s SEL is, the more likely it is that overexertion will accumulate.

This suggests that the mechanism in the body that, in healthy people, leads to increased fitness is, in some way, broken in ME patients. This also could be related to Delayed Onset Muscles Soreness (DOMS) which seems to share some elements of PEM.

Overexertion and/or PEM may be the main reasons why a patient’s condition might deteriorate over time, however there are reports from patients of declines despite avoiding overexertion to the best of their abilities.


Descriptions and explanations of ME patients mildly, moderately and severely affected, within the context of this model.

For descriptive purposes, the SEL of an average healthy person is assigned the ‘score’ of 100, and the average basal metabolic rate is scored at 30.

Note - no attempt has been made to align the mild/moderate/severe categories used here with any other scale used elsewhere. Also, it is not the intention to suggest that the categories used are distinct phenotypes, they are used for descriptive purposes only.


“Mild” sufferers

This description likely represents the majority of the patients that medical professionals will see. While their SEL has been reduced, through overexertion they may still be able to maintain much of their previous lifestyle. Typically this may present as working a typical week, but using weekends as rest periods in which they dramatically reduce their activity.

The activity of a mildly affected suffer might be represented by the chart below, where the patient’s activity during the working week is at 95, and at the weekend 75.




As long as the reduction in activity at the weekend is sufficient to counterbalance the overexertion during the week, this activity pattern might be long term sustainable.


“Moderate” sufferers

This group will have made significant changes in their lives in order to maintain as much activity as is possible for them. They are unlikely to be working, almost certainly they won’t be working full time.



Here the patient, whose SEL is 50, has two days in which they exert themselves to a level of 75. In an attempt to recover/avoid PEM, they reduce their activity to a level of 40. Again, this activity pattern might be sustainable but, as can be seen, the patient’s life is dramatically limited.


“Severe” sufferers

[Note: I have a graph for this but didn't feel it added anything.]

Severe patients could well find themselves in a situation where the SEL is below their basal metabolic rate (i.e less than a score of 30 in this model). If this is the case, it would mean that they are in constant PEM, with no way of escaping from it.


End thoughts
One quirk of the above might explain the concept of why and how mild and severe sufferers might be in constant PEM, whereas moderate sufferers might be able to manage their exertion enough to avoid PEM altogether.
[End]

Comments and improvement suggestions welcome.

ETA: "End thoughts" paragraph added.

 

I think this is great Andy! Very well explained.

Perhaps you could add after this sentence that it's not only that ME patients have a lower SEL, but that it has greater consequences if they exceed it than when healthy persons exceed their SEL. At least that's what I think is happening: ME patients not only have a lower energy budget, they also have to pay more for overexertion than healthy controls (and perhaps other patient groups). But maybe that's not how you see it. One could argue that there isn't actually a larger payback, just that ME patients are above their SEL in a way that is highly unusual in controls and that this alone is sufficient to explain PEM.

I think the resting will be mostly a necessity here rather than a decision in the hope that this will help them avoid PEM.

Personal note: I don't know if I'm alone or an exception in this regard, but what Andy has written better explains my situation than the word 'crash', which is often used in relation to PEM. 'Crash' makes it sound like it's a very abrupt mechanism. In my case, PEM isn't that sudden or dramatic, it's more like an excessive payback that is spread out over a period of a couple of days, usually more than a week. And if I try to push through it, I only make it worse.

 

Thanks Michiel. I've attempted to cover that point with this text, but I assume that it's not sufficient/not clear enough?

I also note

but I don't specify that I mean PEM here, so certainly that could be clarified.

Absolutely, but I'm also trying to describe to an interested non-patient what our experience might be, and I certainly have used resting after an over-exertion as an attempt to avoid PEM. Again, perhaps this could be worded better, or at least more comprehensively.

 

This is roughly how I think about it. Exertion is a bit narrow as there seem to be other less obvious things that also affect the orange curve.

 

Yeah sort of. There might be some ambiguity because one could argue that PEM is not unique to ME but that it is simply a consequence of going above a persons' SEL and that this is unusual but not impossible in healthy people. For example, if they exercise and get fitter, that is because they are still below their SEL. But if they were to go beyond their SEL (as perhaps happens in athletes who overtrain) they could get PEM as well.

Personally, I don't think this is the case and that PEM isn't simply the consequence of an extremely low SEL in ME patients. I think there is a combination of (1) having a low SEL and (2) having a low tolerance to exceeding SEL. So perhaps, if you agree, you could add a small sentence to make this somewhat clearer. For example:

Could be changed into :"For many patients, it is possible to temporarily exert themselves above their SEL. What happens next, however, is determined by their individual tolerance to overexertion at the time that they overexert. In patients with ME this tolerance to overexertion seems significantly reduced.

Yes I think that's a good point as well. Here's how I see it:

If you overexert, you don't just temporarily experience more symptoms that make life more difficult. Outsiders might misinterpret PEM this way. As Trish suggested during PEM, the SEL lowers as well. That means that you have to do much less to overexert yourself again. So in a sense, you are forced to reduce your activity level/energy expenditure, to make sure you don't keep making things worse. (theoretically, this could create a snowball effect, but I think symptoms quickly get so severe that patients are automatically forced to reduce their activity level so that this doesn't happen).

 

Here's my mental model of PEM. This seems to be able to predict several important qualities: the ability to accumulate an "energy debt", the delay in onset of PEM, the delayed recovery. The "Signal" is whatever it is that ultimately pushes the body into PEM, which could be something like a metabolite, exosome or immune signal or even a combination of things.



The signal would also not be able to go below a certain value as otherwise it implies that months of resting should enable months of what would otherwise be overtexertion and that doesn't seem to be case.

 

I would like to add a short note to this discussion.

Because PEM is now often regarded as the most characteristic symptom of ME/CFS, debate about it and how we all experience it can be intense. If a patient describes his experience and that doesn’t match up with what others experience, he/he might get the impression that his condition is not ME/CFS, while we don’t actually, know that for sure.

The patient in question might feel excluded or his experience and contributions to the discussion might be undervalued if others think that his/her condition doesn’t represent ME/CFS. I hope we can find a way to value each other's contribution and avoid confirmation bias. What PEM is and how characteristic it is to ME/CFS is sort of what we trying to find out, it's not a given.

I think it is useful to go deeper into what we mean by PEM and how we experience it, whether that is the same or not. It could be interesting to work out different descriptions of PEM (for example a more sudden crash-like one versus a more accumulative one) and see what % of patients agree with it. Perhaps this could lead to a better definition and description of PEM or to some interesting subgroups that might tell us more about the underlying mechanism. Just an example, suppose that there’s a subgroup with a more sudden and abrupt form of PEM and that they have significantly more food sensitivities and gut problems. Or that there is a subgroup where muscle weakness and automatic issues stand out. That could lead to interesting perspectives.

So I think it’s worth working out descriptions of PEM, even if this is most likely going to be a contentious subject to debate. I hope we can value each other’s input and that everyone feels invited to contribute to the discussion, even if their experience of PEM would turn out to be unusual. Sorry for this rather annoying (and a little patronizing) interlude. Just think this is an important discussion and I hope we can all delve into it some more.

 

And that obviously is the issue with using categories of ME severity, they create artificial phenotypes that don't actually exist. I used the example of a very 'high-functioning' patient so that it was more relatable to healthy readers.

I do state

which is my attempt to prevent this sort of comparison. Improving the wording of it would probably help.

Which seems to be you saying that PEM causes a drop in SEL, which I'm not arguing against but in the model above that is lumped into PEM itself.

I strongly believe that tolerance to overexertion is an important aspect to take into account. For the vast majority of us on the forum, our tolerance is going to be pretty low, so we will feel ill effects far more quickly but can, I feel, explain part of the difference in experience between those "mild" and those more affected.

And, as has been noted on the forum before, "mild" as a description is awful anyway, given the level of impact ME has on anyone affected.

I think my comments to Trish cover this. I'm certainly not disagreeing with any of it, just that I think it is going beyond what the model is trying to currently do, which is effectively to be an Idiots guide to our experiences.

 

I don't mean a gradual onset PEM, just the phenomenon where a certain dose of exertion is tolerated if preceded and followed by days of low activity or rest, but not if repeated several days in a row. There seems to be something like an "energy debt" that can accumulate. Whatever it is that is accumulating, I call the signal. Once the signal is strong enough it triggers PEM.

 

I'd suggest that minimum level would be that which is involved in the basal metabolic rate for the individual.

Which could perhaps be best on seperate thread? I'm trying to build a "broad strokes" model, which certainly could use a crowd-validated description of PEM, but if possible I'd like to keep in depth discussion here to be about the model, rather than individual components of it.

 

Ok, sorry. I might have misinterpreted. Your text, using the term SEL, was quite thought-provoking.

Perhaps moderators could duplicate the posts starting with Andy's text and post them on another thread that tries to work out descriptions of PEM?