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POTS Is Actually Deconditioning

Discussion in 'General ME/CFS News' started by PhoenixDown, May 30, 2013.

  1. Simon

    Simon

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    Now looked at that full text, and it's bizarre that Joyner should cite it as evidence that deconditioning helps POTS because the study gave no information at all about the effect of exercise training on POTS. All it found was that, as is widely found in healthy people, a sustained moderate exercise programme led to modest gains in VO2max. No mention of any effect on POTS.

    It's hard to see how anyone could conceive of a study on POTS that didn't measure POTS as an outcome; perhaps they did measure this and chose not to publish the findings or perhaps they just came up with a bizarre study design. We don't know (will email the authors, for fun).

    Anyway, turns out a separate thread was set up the editorial last year (also turned out I had read and even contributed to that thread, but forgotten all about it..).
     
    alex3619, WillowJ, Shell and 2 others like this.
  2. Simon

    Simon

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    So, got a reply from the senior author and it turns out they have published POTS outcome data in another paper, and the results were quite good.

    There was improvement in objective measures of Heart Rate on Standing (main POTS criterion), plasma volume and heart stroke volume and VO2 max. Self-reported SF36 score showed an improvement from approx 28 to 43 on the 'Physical Component Score', where 50 is 'normal' and 43 is within 0.7SD of the mean.

    Median increase in heart rate on standing decreased from +32 to about +27 (from graph, couldn't see the data but didn't read thoroughly) vs +17 for controls. The authors claimed a 53% 'cure' rate though this appears to be based on people moving from a little above to a little below the POTS threshold of 30bpm increase in HR on standing.

    So I'm not sure the authors claim that deconditioning causes POTS totally stands up, but the evidence looks quite good on this small study (n=19 completers) that deconditioning plays a part. A larger study in clinical practice (n=250) showed a '75%' cure rate but with a higher and as yet unspecified drop-out rate (the paper hasn't been published yet).

    Also, not mentioned:
    • all subjects came off any POTS medication they were on before the trial started
    • there was no 'no treatment/placebo' control to at least measure any natural recovery rate, though over the short time-frame of 3 months there might not have been much natural progress
    • POTS symptoms were not measured "Patients with POTS often experience palpitations, light-headedness, dizziness, nausea, fatigue, exercise intolerance, or near syncope", though the SF36 functional score did improve substantially. As ever would have been good to know if the patients rated themselves as 'cured'.
    Nonetheless, this does look to me like evidence that reversible deconditioning can contribute to POTS
     
  3. PhoenixDown

    PhoenixDown Senior Member

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    Yes it's a very optimistic definition of cured, it's really a shame they don't interview patients to ask them in there own unconfined words, how much of a difference it made in their day to day life, something a bit more qualitative rather than the ubiquitous quantitative square-peg forcing SF36 scale (which in my opinion is trying to be something it's not).

    (I have gripes about a lot of common subjective scales used in all research, I'm not just picking on papers I dislike).

    http://www.anapsid.org/cnd/files/sf36.pdf
     
  4. Simon

    Simon

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    Yes, I think it should be mandatory for any researcher attempting to define 'cured' to compare their findings with the paitents' view of their health status. But what convinced me that there was something in this paper is the number of objective measures that showed significant improvement, even though I don't buy a 53% 'cure' rate.
     
  5. Simon

    Simon

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    POTS can be caused by a deficiency of a norepinepherine transporter protein

    So, while there seems to be decent evidence that deconditioning can play a role in POTS (or at least that exercise training can reduce it), there are other factors at play too. Cort's recent blog covers a recent mouse study where knocking out a norepinepherine transporter led to POTS-like symptoms in mice. This builds on an earlier study that found a human family with POTS had a defective gene for a norepinepherine transporter protein (though the same gene was not implicated in other cases of POTS). As is often the case, there isn't a simple answer...
     
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  6. SOC

    SOC Moderator and Senior Member

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    I'll buy that deconditioning can play a role in some cases of POTS, but I don't see that anything in this research supports that it is the only, or even a major, cause of POTS over the entire spectrum of patients. The research of the knock-in mice is one small bit of evidence that not all cases of POTS are due to deconditioning. I think it's extrapolating pretty far beyond their data to suggest that POTS is not a true medical diagnosis and medication is not warranted.
     

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