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Muscle oxygenation [as assessed by NIRS - Near Infra-Red Spectroscopy]

Discussion in 'Cardiovascular and exercise physiology (CPET)' started by Hutan, Sep 8, 2023.

  1. Hutan

    Hutan Moderator Staff Member

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    This study found reduced oxygen extraction in the thigh muscles of people with ongoing symptoms after Covid-19 infections as compared to healthy controls:
    Structural and functional impairments of skeletal muscle in patients with [PASC], 2023, Colosio et al.

    The measure is "Δ[HHbMb]peak (% ischemia)" and it is essentially a measure of the level of oxygen in the blood relative to that that occurs when the blood supply to the muscle is stopped for a few minutes. When the blood supply is stopped (the ischemia), the oxygen in the blood in the muscle eventually comes to an equilibrium, where no more oxygen is diffusing out of the blood. That's the baseline, the 100%.

    The technique used is Near Infra-Red Spectroscopy. It involves a sensor being placed in a specified part of the muscle, taped securely to ensure there is no movement, and with an opaque barrier placed over it to prevent ambient light affecting the results. The thickness of epidermal fat affects the results, so that needs to be controlled for. I don't know, but perhaps the colour of skin, the density of melanin, might also have a confounding effect?

    The specific thigh muscle that seems to be used is the Vastus lateralis.

    Here's a chart of how Δ[HHbMb]peak changes over the course of exercise tests that continue on to VO2max (source: Oxygenation Threshold Derived from Near-Infrared Spectroscopy: Reliability and Its Relationship with the First Ventilatory Threshold, 2016)

    Screen Shot 2023-09-09 at 6.10.39 am.png

    This was for male cyclists. There's a plateauing at around the 60% mark. If I'm understanding that correctly, that plateauing begins at around ventilatory threshold, with some minor decline through to the point of VO2max when the exercise test is stopped.

    The Colosio paper looking at people with Long Covid linked above reported that the healthy controls had a mean value of 61% (SD 13) - that is in line with the chart above - see the plateau on the y axis. However, the people with Long Covid had a mean value of only 45% (SD 9). They didn't get close to extracting more oxygen from the blood during a time of high demand in the way that the healthy controls did. The study was small, but the standard deviations are also relatively small and the separation of the results from each group is substantial. It suggests that the tissue is not receiving enough oxygen for optimal performance.

    The 2016 paper noted that the oxygen extraction values as determined by NIRS were reproducible, so, if the measures are done carefully and the confounding of epidermal fat is taken into account, it sounds as though this is a measure that we can have confidence in.

    I'd like to know a bit more about what this might means for the physiology. The baseline (under a situation of ischemia for a few minutes) is determined for each person, and the reported peak measure during exercise is relative to that. I wonder, does the baseline vary much from person to person? Could repeated exposure to hypoxic conditions alter that baseline? So, is it the baseline that changes or the actual oxygen extraction during exercise?

    I'd also like to know - has oxygen extraction during exercise been measured in people with ME/CFS or related conditions?
     
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  2. bobbler

    bobbler Senior Member (Voting Rights)

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    I'm noting your description of the method not involving anything 'invasive' for the muscle and to me that seems like it could be a potentially significant thing if it can be something which could be used as a measure where perhaps other methods which might involve biopsy or something invasive might normally be used?

    And also, whilst we are looking at V02 max then is there a possible of that being measured for those who are less severe, and if there were more replications finding that there is an indicator regarding oxygen at that point it could be calibrated to include those more severe with the very tiny exertions that might trigger the equivalent for them? ie just lifting a leg, arm or a small walk if that might be what causes 'PEM'?
     
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  3. SNT Gatchaman

    SNT Gatchaman Senior Member (Voting Rights)

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    I've purchased a Moxy monitor (https://www.moxymonitor.com/). It's a commercial system aimed at athletes. It's expensive (USD 900) but I purchased one and have been trialling it for 24 hours. On very early indications I think this could prove very interesting. I've posted some more papers under the moxy tag.

    IMG_9744 copy Small.jpeg


    This is a pilot observation and I may be doing things wrong. But... it appears that I am not at all normal, with a very unstable trace. By this I don't mean there's a technical problem with sensing — instead my SmO2 level falls with minimal exertion and does not recover properly. I benchmarked against my wife, measuring left vastus lateralis. At rest she had a stable reading around 85% (females tend to be a bit higher I believe). With 20 rapid gym squats, her SmO2 did not move. She's lost a bit of fitness after a back injury last year, but will also try out more intense exercise on her static trainer over Easter.

    I had been resting, reading in a chair for an hour and had a higher baseline - high 80s with an apparently stable trace, where I would expect low 70s as a male (if healthy).

    Standing up led to a prompt drop of a few % points, reducing to ~70% with a few steps to the kitchen. I then took a few more steps to the deck and did 3 slow and creaky gym squats. After <1 minute delay the reading dropped quite steeply to 30% and stayed there for over 6 hours (during mostly desk work). If I moved to stand, make a coffee etc it could drop to the low 20s. At 8 hours post it's in the low 50s and varies between 40s and 60s with standing and a few paces in the house.

    By comparison an athlete would expect to start at 70% and bottom out at 10-30% after 10 mins of intense exertion and maintain that until exhaustion. See The use of muscle near-infrared spectroscopy NIRS to assess the aerobic training loads of world-class rowers (2021, Biology of Sport)

    The key question is what would a sedentary control look like. I'm looking for data on this but my suspicion is that a completely unfit person doing what I did might drop 10-20% and recover within minutes, at most. A reasonable approximation is probably Muscle oxygenation of the paretic and nonparetic legs during and after exercise in chronic stroke: Implications for mobility (2023, PM&R)

    I'll post more findings in this thread in time. Early days obvs, but if anyone is in the position to access/purchase one of these devices, please do and post independent observations here. It just might be that this is a useful way to look at mild, moderate and even more severely affected ME (non-invasively) that might correlate with historical and recent muscle spectroscopy and biopsy findings.
     
  4. Hutan

    Hutan Moderator Staff Member

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    CovidSpice, Kitty, Wonko and 6 others like this.
  5. EndME

    EndME Senior Member (Voting Rights)

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    Thanks for sharing @SNT Gatchaman! If things hold up well it might be possible to motivate an organisation to buy a handful of devices that can be tested and then sent around to different people to reduce costs.
     
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  6. SNT Gatchaman

    SNT Gatchaman Senior Member (Voting Rights)

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    So it's 12 hours since my "exercise session" (reminder this was just 3 slow squats and total step count for the day is currently a mere 458). I'm now back to SmO2 80%, having been sitting on the couch for a couple of hours after dinner. Tomorrow I will not do any additional "exercise" to check that it's not due simply to some diurnal variation. I have the POTS crazy HR situation that has me at my best at the end of the day.
     
  7. chillier

    chillier Senior Member (Voting Rights)

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    Interesting @Hutan and @SNT Gatchaman. Trying to get my head around what you're both saying correct me if I'm misunderstanding.

    [O2HbMb]-[HHbMb] is measuring roughly the same thing as SmO2 which is [O2Hb]/([O2Hb]+[HHB])x100.

    @SNT Gatchaman you are maybe suggesting you are having a more extreme reduction in SmO2 than you would expect for a healthy person.

    The y axis in the plot @Hutan shows is the change in [O2HbMb]-[HHbMb] as a proportion the maximum negative change in [O2HbMb]-[HHbMb] measured under ischaemic conditions. It's argued that in long covid there is less of a reduction as a proportion of the maximum reduction at the ventilatory threshold.

    So what @SNT Gatchaman is seeing is sort of the opposite of what you'd expect if that's the case right? Unless the maximum reduction in ischaemic conditions is much lower in pwME, such that despite the absolute decrease in SmO2 being more extreme, as a percentage of it's ischaemic minimum it's lower. Either way that would not suggest a problem with oxygen extraction.

    What do you guys think? I admit I'm out of my depth in this area
     
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  8. Jonathan Edwards

    Jonathan Edwards Senior Member (Voting Rights)

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    I cannot make head nor tail of this. It is time these physiologists explained things more clearly and stopped using impenetrable jargon. I strongly suspect that you cannot deduce much from NIR spectroscopy because so many parameters may shift - much as others have suggested.
     
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  9. SNT Gatchaman

    SNT Gatchaman Senior Member (Voting Rights)

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    @chillier I'm going to have to gather a bit more data to make sure this isn't spurious in me; and compare with both @Kiwipom and a healthy sedentary who has kindly volunteered (matched age/sex/BMI). I think the machine can't distinguish between Hb and Mb, and gives SmO2 as the percentage according to the formula exactly as you gave.

    From Near-infrared spectroscopy-derived muscle oxygen saturation on a 0% to 100% scale: reliability and validity of the Moxy Monitor (2019, Journal of Biomedical Optics) —

    Screenshot 2024-03-26 at 10.46.22 PM copy.jpg

    I'll defer the rest of your questions until I've done more reading and got more understanding. The machine gives tHb in g/dL which I presume is total Hb and Mb, whether oxy- or deoxy- for both. Concentration in muscle Mb shouldn't change (albeit oxy- <-> deoxy) so I'm guessing any change indicates the component of Hb in capillaries?
     
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