Heart rate as a measure of ME/CFS-relevant exertion/severity

[forestglip]

I'm wondering whether average heart rate, acting as a measure of total exertion, might be a good measure of ME/CFS severity.

Step count and upright time don't really disambiguate between type of activity performed. For example, slow walking, normal walking, and running all count the same when tracking steps. Heart rate changes are more directly proportional to the magnitude of exertion - walking fast for 10 steps would count more than walking slowly for 10 steps.

And more forms of exertion would be factored into a single metric. Sitting upright and walking would both increase heart rate. And while the increase from cognitive exertion, such as reading, might be minimal at best [1], studies have at least shown that chess increases heart rate [2,3]. I'm not sure whether this is due to the high intellectual demand or the stress of the activity, but I think people report that both of these can result in PEM so it might be relevant either way.

It probably wouldn't be very useful to directly compare average heart rate between different people because people vary in their baseline heart rate. Thus, I would propose that instead of tracking average daily heart rate, one would track average heart rate above each person's baseline.

Maybe for each day in each person, one would determine the baseline HR by averaging two hours worth of the lowest consecutive HR values, which presumably would be during sleep and correspond to HR during zero exertion. For a given day, if the baseline is 60 bpm and the daily average is 70 bpm, then the person performed 10 bpm of "excess exertion" on average during this day. They would count as more severe than someone with, say, an excess of 15 bpm on average.

I'm interested in whether this "excess exertion" based on HR might act as a more accurate measure for trial outcomes and severity stratification than using step count or subjective severity scales.

Spoiler: References

1. Thissen, Birte A. K., et al. “At the Heart of Optimal Reading Experiences: Cardiovascular Activity and Flow Experiences in Fiction Reading.” Reading Research Quarterly, Oct. 2021, https://doi.org/10.1002/rrq.448.

2. Leone, María J., et al. “The Tell-Tale Heart: Heart Rate Fluctuations Index Objective and Subjective Events during a Game of Chess.” Frontiers in Human Neuroscience, vol. 6, 2012, https://doi.org/10.3389/fnhum.2012.00273. Accessed 2 Nov. 2019.

3. Troubat, Nicolas, et al. “The Stress of Chess Players as a Model to Study the Effects of Psychological Stimuli on Physiological Responses: An Example of Substrate Oxidation and Heart Rate Variability in Man.” European Journal of Applied Physiology, vol. 105, no. 3, Nov. 2008, pp. 343–49, https://doi.org/10.1007/s00421-008-0908-2.

 

[Yann04]

I think the exertion strain for outcomes is definitely an interesting way to look at this. Maybe it could be a useful measure.

severity stratification

I don’t understand how that would work.

For example my anecdotal experience:
My RHR is about 40-45 when I’m not in PEM and 50-55 when I’m in PEM. My heart rate might increase upto 90 bpm, maybe 100 if im pushing myself, like if I sit up for over a minute it goes to 110 bpm, but I don’t sit anymore for PEM avoidance. Most of my day itll be between 40-80.

When I was mild. I’d say my RHR was around 50, standing up would bring it to 80. And the sports I did brought it easily to maybe 150.

But say if I had not been doing sports or biking to commute and walking up the stairs my max heart rate mightve been around 100-110 thats what I got when stress walking and holding a conversation back then. So a similar difference of like ~50 bpm between RHR and most active heart rate.

I’m not sure I understand how that could stratify my severity.

 

[Utsikt]

Wouldn’t there be too many possible confounders?

 

[forestglip]

I don’t understand how that would work.

For example my anecdotal experience:
My RHR is about 40-45 when I’m not in PEM and 50-55 when I’m in PEM. My heart rate might increase upto 90 bpm, maybe 100 if im pushing myself, like if I sit up for over a minute it goes to 110 bpm, but I don’t sit anymore for PEM avoidance. Most of my day itll be between 40-80.

When I was mild. I’d say my RHR was around 50, standing up would bring it to 80. And the sports I did brought it easily to maybe 150.

But say if I had not been doing sports or biking to commute and walking up the stairs my max heart rate mightve been around 100-110 thats what I got when stress walking and holding a conversation back then. So a similar difference of like ~50 bpm between RHR and most active heart rate.

I’m not sure I understand how that could stratify my severity.

I think the disconnect might be that you're talking about a simple difference between resting heart rate and maximum heart rate during the day. I'm talking about averages. If you get your HR up to 150 bpm for a minute, that won't increase your average bpm as much as increasing to 90 bpm for an hour.

Instead of averages, it might be easier to think of it as total heart beats.

If your RHR is 60, and if you did zero exertion all day, your heart would have beat 60 beats/minute * 1440 minutes/day = 86,400 heart beats during the day (of course with some variability due to other things).

If you bring your HR up to 150 bpm for a single minute then back to 60 immediately, that's an extra 90 beats for the day. The average bpm would barely change (60.063). If you instead increase to 90 bpm for an hour, that's 1800 extra heart beats, which would increase the average to 61.3 bpm - a difference of 1.3 bpm.

Of course, the amount of change in average bpm depends on how much exertion you would choose/need to do, even if mild. But it's the same for step count. I'm proposing that an increase in heart rate says more about the actual amount of exertion than an increase in step count.

For comparing severities between different people, it might not work as well depending on the differences in how much exertion a person chooses/has to do (e.g. work from home in bed versus do a physical job). But I think we might be able to assume that most people with ME/CFS generally do the maximum amount of exertion they can handle given their severity.

 

[Yann04]

For comparing severities between different people, it might not work as well depending on the differences in how much exertion a person chooses/has to do (e.g. work from home in bed versus do a physical job). But I think we might be able to assume that most people with ME/CFS generally do the maximum amount of exertion they can handle given their sever

I don’t understand how you think this would work?
Mild people have more extra beats?
Less extra beats?

I think mine would have looked pretty similar when I was mlld and now.

I guess you could use visible band data to test this theory?

 

[forestglip]

Wouldn’t there be too many possible confounders?

Could you give an example(s) of what you mean?

For example, in the dara trial, I'm suggesting that average heart rate might have better captured how much more people were actually doing, versus average step count.

And insofar as we can at least get a rough idea of a person's severity from their average step count (e.g. ~100 would probably indicate severe and ~5000 would probably indicate mild or moderate at most), I think it might be more accurate with an average heart rate above resting. I'm sure many factors will influence heart rate that will make it imperfect, but it seems to me that the same would apply to steps.

 

[MrMagoo]

I already do heart rate monitoring via Fitbit and visible. They also measure HRV and the RHR daily average changes most days.

I know when I’m exerting above normal, or resting below normal. I can measure my time upright through this. But not cognitive exertion, which tends to buildup then slow down, rather than stay at a peak.

I also have sleep which is generally at normal, and only occasionally shows rest.

 

[OrganicChilli]

I'm not convinced heart rate tells us anything about ME/CFS. When I was moderate I could shower every day without issues and my heart rate would be between 110-120 for up to 15 mins.

But if I took a beta blocker and walked 100m with a heart rate of 85, I still got PEM the next day.

 

[forestglip]

I don’t understand how you think this would work?
Mild people have more beats?
Less beats?

Yes, it's very simple: mild people's hearts would beat more times throughout the day because they are participating in more exertion than severe people.

Only slightly more complicated when considering only those heart beats that are in excess of resting heart beats to normalize between people.

 

[forestglip]

I'm not convinced heart rate tells us anything about ME/CFS. When I was moderate I could shower every day without issues and my heart rate would be between 110-120 for up to 15 mins.

But if I took a beta blocker and walked 100m with a heart rate of 85, I still got PEM the next day.

Good point about the beta blocker. Heart rate wouldn't be considered a direct measure of exertion, it would just be a proxy marker. If you take a beta blocker to decrease the correlation between exertion and heart rate, then it wouldn't act as a good proxy anymore.

Any studies that used this would probably have to control for HR-modulating medications.

 

[OrganicChilli]

Good point about the beta blocker. Heart rate wouldn't be considered a direct measure of exertion, it would just be a proxy marker. If you take a beta blocker to decrease the correlation between exertion and heart rate, then it wouldn't act as a good proxy anymore.

My point isn't really the beta blocker. It's that walking large chunks has always been more exhausting than walking the same distance while taking breaks or just standing. I can't explain while walking a short distance with a low heart rate was more exhausting than taking a shower with a high heart rate. Equally, if I split those 100m into 4 x 25m across 4h it wouldn't have caused a problem regardless of heart rate.

 

[forestglip]

It's that walking large chunks has always been more exhausting than walking the same distance while taking breaks or just standing. I can't explain while walking a short distance with a low heart rate was more exhausting than taking a shower with a high heart rate.

Thanks, maybe this would in fact show a disconnect between HR and the types of exertion that can lead to PEM.

Equally, if I split those 100m into 4 x 25m across 4h it wouldn't have caused a problem regardless of heart rate.

For this scenario, step count presumably wouldn't be a good indicator either since it would be the same number of steps. Yet people use step count for trying to get a rough measure of severity or for trial outcomes.

 

[Utsikt]

Could you give an example(s) of what you mean?

For example, in the dara trial, I'm suggesting that average heart rate might have better captured how much more people were actually doing, versus average step count.

And insofar as we can at least get a rough idea of a person's severity from their average step count (e.g. ~100 would probably indicate severe and ~5000 would probably indicate mild or moderate at most), I think it might be more accurate with an average heart rate above resting. I'm sure many factors will influence heart rate that will make it imperfect, but it seems to me that the same would apply to steps.

Yes, it's very simple: mild people's hearts would beat more times throughout the day because they are participating in more exertion than severe people.

Only slightly more complicated when considering only those heart beats that are in excess of resting heart beats to normalize between people.

I get a higher HR from being on S4ME on my phone while lying flat (with betablockers), than what my sister gets from walking at a fast pace for an hour.

According to this logic, if I reached her level of physical functioning my HR would show me as worse off.

 

[OrganicChilli]

For this scenario, step count presumably wouldn't be a good indicator either since it would be the same number of steps. Yet people use step count for trying to get a rough measure of severity or for trial outcomes.

True. Step count for me wasn't a good way to predict PEM.

 

[Clio]

Just concentrating hard while laying in bed completely still (like solving a puzzle or trying to do some drawing) is enough to raise my heart rate by 30-40BPM

 

[Yann04]

Yes, it's very simple: mild people's hearts would beat more times throughout the day because they are participating in more exertion than severe people.

My experience is that for similar exertion your severity changes how fast your heart beats. Ie. watching a video on a computer at rest with sound would have been 50 bpm for me when mild and would be around 100bpm now that I’m severe.

There may still be a correlation in there though. But I would want to actually have some data to test it.

 

[Utsikt]

My experience is that for similar exertion your severity changes how fast your heart beats. Ie. watching a video on a computer at rest with sound would have been 50 bpm for me when mild and would be around 100bpm now that I’m severe.

There may still be a correlation in there though. But I would want to actually have some data to test it.

This is my experience from wearing a smartwatch for two years while going from moderate to severe.

 

[forestglip]

I get a higher HR from being on S4ME on my phone while lying flat (with betablockers), than what my sister gets from walking at a fast pace for an hour.

According to this logic, if I reached her level of physical functioning my HR would show me as worse off.

My experience is that for similar exertion your severity changes how fast your heart beats. Ie. watching a video on a computer at rest with sound would have been 50 bpm for me when mild and would be around 100bpm now that I’m severe.

There may still be a correlation in there though. But I would want to actually have some data to test it.

Thanks for the counter examples. I think worth at least a look. Maybe if people do end up improving from dara and they run more trials based on step count and subjective scales, they could measure heart rate as well and see how much it correlates to the other metrics.

 

[Yann04]

Thanks for the counter examples. I think worth at least a look. Maybe if people do end up improving from dara and they run more trials based on step count and subjective scales, they could measure heart rate as well and see how much it correlates to the other metrics.

I liked your idea but maybe applied to the same activity and same person. Like say we’re doing the 6 minute walking test.

If someone scores better after GET but theyre heart’s also beating much faster than the original try — have they just learnt to push themselves more?

 

[poetinsf]

I'm wondering whether average heart rate, acting as a measure of total exertion,

I've done some study on this years ago with fitbit and I couldn't extract anything useful out of HR. It wasn't much better than a noise in predicting fatigue/PEM. But I did extract some signal in10-40% range from minute-by-minute data of calorie expenditure. I'm not sure how cal/min data differs from HR, but I assume that activity trackers incorporate motion data as well HR to refine cal/min.

The exertion should really be measured in watts. The Pandolf equation developed by the US army does that in terms of walking speed (V), load (W) and incline grade (G):
Ṁw=1.5⋅W+2.0⋅(W+L)⋅(L/W)2+η⋅(W+L)⋅(1.5⋅V2+0.35⋅V⋅G)

Or the LDCA equation that highlights the speed being the real killer:
M = 1.44 + 1.94S^0.43 + 0.24S^4

The most common way of measuring exertion for activities is with MET (metabolic equivalent of tasks), which measures the power like watts. They define the intensity of activities with MET (https://www.health.state.mn.us/diseases/asthma/schools/documents/physicalactivity.pdf) or professions (https://epi.grants.cancer.gov/physical/met/ocs-met.php).

For hypersensitive conditions like ME/CFS, even cal/min, let alone cal/hr, may be too crude. Ideally, you'd need an instantaneous measure. You'd think that instantaneous HR would be useful there, but HR smooths out the impulse. So even that may not be an accurate enough.

Personally, I never had success with HR to control my PEM. I had much better luck with measuring my speed. I understand though, that some people had success controlling PEM by monitoring HR. Maybe HR is more useful for more severe cases. Then again, there is so much noise in HR that it may be hard to extract a useful signal even in severe cases.