BBC article about vagus nerve stimulation study

Here's the paper.
https://www.aging-us.com/article/102074/text

Effects of transcutaneous vagus nerve stimulation in individuals aged 55 years or above: potential benefits of daily stimulation
Beatrice Bretherton 1 , Lucy Atkinson 1 , Aaron Murray 1 , Jennifer Clancy 2 ,Susan Deuchars 1 , Jim Deuchars
Aging, 2019

They talk about three studies. I haven't got past the first one:

Study 1
14 participants aged ≥ 55 years with no previous medical history of hypertension, cardiac disease, diabetes mellitus or epilepsy were enrolled on the study (see Supplementary Table 1).

tVNS vs. sham effects on cardiac baroreflex and HRV
Change in baroreflex sensitivity (BRS) between baseline and tVNS significantly differed between the tVNS and sham visits (p = 0.028): there was a significantly greater increase in BRS during the tVNS visit (3.28 ± 0.59 ms/mmHg) compared to the sham visit (0.81 ± 0.68 ms/mmHg). Baseline heart rate variability (HRV), measured as ratio of LF/HF power, significantly predicted response to tVNS (R2 = 0.772, p < 0.001, see Figure 1), where higher resting LF/HF ratio was associated with greater decreases during tVNS. Removing the potential outlier with a baseline LF/HF ratio > 5 had a slight impact on the regression (R2 = 0.480, p = 0.009). This HRV analysis revealed that the LF/HF ratio response of four participants was greater than a 20% increase, corresponding to a definition of responders previously applied [11].
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So, 14 participants - pretty small.

They found that those with a higher LF/HF ratio were most likely to have a relatively large reduction during electrical stimulation by the ear. Sounds like a regression to the mean result - for whatever reason some people were first measured during a moment when their LF/HF ratio was high. (I haven't looked into the physiology, but maybe if they were stressed about finding a park, or getting to the clinic on time?)

And, using their predefined definition of a response, only 4 of the 14 were classified as responders. (!)

Note also this was all just during the stimulation, so it says nothing about long or even medium term effects.
 
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I've found vagal stimulation genuinely helpful if I've accidentally overdone it and can't switch off at night, though. Resistance breathing (forcing air out whilst partly closing my nose with my fingers), or using a TENs machine (before I managed to tread on the wretched ear clip and snap it, anyway :rolleyes:) reduce my heart rate and allow my mind to relax.

I rarely need the strategy now that I'm retired and able control my activity levels – but it felt like a lifesaver when work was making me more and more exhausted, and less and less able to sleep.
 
Just reading that Study 1 description again, they wanted the LF/HF ratio to increase with the stimulation (LF/HF being a measure of heart rate variability and high variability seeming to be a good thing). But it looks like 8 of the 14 participants actually had a lower LF/HF ratio after stimulation! So, I think, according to their aim of increasing the LF/HF ratio by 20%, the trial was a failure. (?)


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And then there's the assumption that the HF/LF ratio actually tells us anything about sympathetic and parasympathetic nerve activities. Looks like that is disputed. e.g.
https://www.frontiersin.org/articles/10.3389/fphys.2013.00026/full

Based upon these assumptions, Pagani and co-workers proposed that the ratio of LF to HF (LF/HF) could be used to quantify the changing relationship between sympathetic and parasympathetic nerve activities (i.e., the sympatho-vagal balance) (Pagani et al., 1984, 1986; Malliani et al., 1991) in both health and disease. However, this concept has been challenged (Kingwell et al., 1994; Koh et al., 1994; Hopf et al., 1995; Eckberg, 1997; Houle and Billman, 1999; Billman, 2011). Despite serious and largely under-appreciated limitations, the LF/HF ratio has gained wide acceptance as a tool to assess cardiovascular autonomic regulation where increases in LF/HF are assumed to reflect a shift to “sympathetic dominance” and decreases in this index correspond to a “parasympathetic dominance.”
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As we have seen, the hypothesis that LF/HF quantifies “sympatho-vagal balance” depends upon four interrelated assumptions, all of which can be proven to be false. The facts are in direct opposition to the assumptions. In particular, the complex nature of LF power, its exceedingly poor relationship to sympathetic nerve activation, and the non-linear (and often non-reciprocal) interactions between sympathetic and parasympathetic nerve activity that are confounded by the mechanical effects of respiration and prevailing heart rate, make it impossible to delineate the physiological basis for LF/HF with any degree of certainty. Thus, the LF/HF sympatho-vagal balance hypothesis has been disproven—the preponderance of evidence confirms that LF/HF data cannot accurately quantify cardiac “sympatho-vagal balance” either in health or disease.
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I could have things wrong (among other reasons for wrongness, I still haven't got past Study 1). But taking the extra leap to suggest that this ear stimulation is going to bring benefits of
the paper said:
reduced risk of mortality and reductions in the need for medication and/or hospitalisation.
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or
the article said:
Aging effects could be slowed down
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seems unwarranted.

But don't let that stop the ear tickling @TiredSam.
 
From study 1:
the paper said:
This HRV analysis revealed that the LF/HF ratio response of four participants was greater than a 20% increase, corresponding to a definition of responders previously applied [11].
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From study 2:
the paper said:
Using the response definition employed in study 1 (20% decrease in LF/HF ratio), 16 responders and 32 non-responders were identified.
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:confused:I'm confused. Time for a cup of tea.
 
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