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Heart-rate Variability: What it means as a measure of autonomic nervous system health

I used to blog about heart-rate monitoring as a pacing tool in ME/CFS about five years ago on this blog but the newer devices also monitor heart-rate variability so I wanted to know more about it.  The following is a Note published by one of my Facebook Friends.  Unlike the timeline posts, Notes are easily saved and readily accessible via a menu option that people rarely check. This one was Posted by Karyn Crimmin on Tuesday, June 7, 2016

Heart Rate Variability (HRV) – An Under-Utilised ME/CFS Management Tool

Reposted with permission from Karyn

About Me
Although I have a health background (in Optometry), I have no experience whatsoever in exercise science. I'm an ordinary patient with diagnoses of Myalgic Encephalomyelitis (ME), Postural Orthostatic Intolerance (POTS), Neurally Mediated Hypotension (NMH), Mast Cell Activation Syndrome (MCAS) and autoimmune disease. Among others!

This blog is about my experience with HRV tracking and what I have learned along the way. I can’t cover all there is to know about HRV, but hopefully it will be sufficient to demonstrate what HRV tracking has to offer, and how to get started.

I've been bedridden for 7 years and I struggle to read much of anything, or to do significant amounts of research. My point is this: HRV tracking looks daunting at first but it's very doable, and in my experience it has a lot to offer the ME/CFS patient. If I can do it anyone can. My advice is to just dip your toe in and learn as you go along.

What is Heart Rate Variability (HRV)?

Heart Rate Variability (HRV) is the term used to describe moment-to-moment variations in our heart rate. It does not refer to the variations of heart rate that occur with activity, illness or other factors. HRV variation is much more subtle and transitory. When we breathe in our heart rate speeds up slightly and when we breathe out our heart rate slows down slightly.

This variation is normal. In fact a higher variation is healthier than a lower variation, and is an indication of a healthy autonomic nervous system, and good stress resilience. Low HRV is associated with increased Sympathetic (fight/flight) Nervous System (SNS) activity, and/or decreased Parasympathetic (rest/digest) Nervous System (PNS) activity, and is associated with chronic inflammatory disease, cardiovascular disease, stroke, diabetes, and indeed ME/CFS.

 The Parasympathetic Nervous System’s effect on the heart occurs primarily during expiration, and this is what causes slowing of the heart rate as we breathe out. This effect makes HRV a convenient measure of the function of the autonomic nervous system.

HRV measurements are often used by athletes to determine when they can train harder, and when they need to ease back. And it seems to me that ME/CFS patients can use their measurements in a similar way.

How Can HRV Tracking Help ME/CFS Patients?

Because many studies suggest that autonomic nervous system problems are present in ME/CFS, having a way of measuring and tracking the function of our ANS, via HRV, on a day to day basis can be a useful adjunct to our management of illness. HRV tracking is not a treatment though – it is a management tool that can help you manage your illness more effectively. It can be used to track your day to day progress and long term trends, determine a sustainable level of activity and pace effectively, objectively assess the impact of some treatments, and demonstrate to your Doctor or others how you're progressing. It also helps me make sense of what is happening in my body and what various symptoms or symptom clusters mean.

All of that is amazingly helpful, but the most surprising benefit I found from HRV tracking has been being able to objectively demonstrate ‘crashes’ to others. For me, qualitative descriptions of how you’re feeling from day to day always feel whingey. And – let’s face it - descriptors cannot adequately convey how you feel to people who have no direct experience of our illnesses. However, I’ve found that when you can show graphs of your heart numbers, or can simply say, ‘My heart numbers have plummeted today’, people actually get it! They really do. My husband now asks me almost every day how my numbers are – and it makes sense to him. That makes HRV an amazing tool as far as I am concerned!  

HRV vs HR

HRV tracking is different from heart rate (HR) tracking. If you are unaware of the benefits of pacing using a heart rate monitor, I’d recommend that you look into that as well. HR tracking helps you pace, and stay within your anaerobic threshold throughout the day. It is an important tool for monitoring activity as it happens. HRV on the other hand tracks your recovery status, long term trends, sympathetic/parasympathetic nervous system balance, and helps you plan your day. Wrist band monitors like FitBit and Mio Alpha are fine for HR tracking, but you need a good chest strap monitor for accurate HRV monitoring. There tends to be an inverse relationship between HR and HRV - when your HR is up your HRV will tend to be down - so to some extent, morning resting heart rate can be used in a similar way to HRV, but it is a more crude measure, and will miss a lot of the subtleties that HRV readings will pick up.

HRV Terminology There is a lot of (daunting) terminology that comes with tracking HRV. Don’t let that put you off. My advice would be to just start tracking, and with a little experience, it will all begin making sense. There are many more, but the most basic terms that a beginner should get to know are:

• HRV (Heart Rate Variability) - refers to the variation in time intervals between heart beats. As noted earlier our heart rate should be fluctuating constantly and that is reflected in changing time intervals between your heart beats. Low HRV indicates a lack of autonomic nervous system flexibility. Instead of a continually fluctuating heart rate (as the PNS rhythmically increases and decreases its effect on the heart), the heart rate is constant and inflexible.

• HF (High Frequency): relates to the level of parasympathetic (vagal nerve) activity – this is the body’s rest and digest system. HF decreases with stress, anxiety and emotional strain.

• LF (Low Frequency): was initially believed to relate to the level of sympathetic activity – the body’s fight/flight system – but is now known to reflect both sympathetic and parasympathetic activity.

• LF/HF (Low Frequency / High Frequency ratio) is an indicator of balance between the sympathetic and parasympathetic systems. A higher number is believed to indicate higher sympathetic nervous system activation in comparison to parasympathetic. The SweetBeat app claims that a healthy well-balanced result is approx. 1.5:1.

Apps and Hardware

HRV is calculated using various algorithms, which vary between apps. Therefore HRV results obtained using one app are not directly comparable to those measured with a different app. Comparisons can only be made between readings using the same app, in the same conditions. Usually apps will use algorithms which give HRV on a 1 – 100 scale. HRV can be measured most easily using inexpensive and readily available apps, in combination with a good quality (chest strap type) heart rate sensor. HRV measurement is very sensitive to error – so it’s important to make sure you have a good quality sensor and app. Unfortunately strapless optical sensors (such as Mio Alpha) or camera flashes do not (in my experience) give the accuracy required to get reliable HRV measurements.

Sensors

To accurately measure HRV, a chest strap sensor is needed. The Polar H7 seems to be considered the gold standard as far as sensors go - I started with it but had endless problems. Eventually I worked out that it was my small frame size that was the problem. So if you are at the lower end of their strap’s recommended size range I’d steer clear of it. I switched to the Wahoo Tickr and I love it. It has a centre front clasp which also makes it much easier for someone with ME/CFS to put on! However there are plenty of other sensors that will do the job well. Just be sure to check compatibility with whatever apps you want to try. Cost is reasonably affordable – the Wahoo Tickr RRP is $89.99AU, the Polar H7 is around $119AU.  

Apps

I'd recommend trying a variety of apps - because there are significant differences between them. Some apps will give you specific results for factors like LF, HF etc. Others give fewer specific results, but do the interpretation for you. (Keep in mind any interpretation is geared towards athletes wanting to know how hard they can train on a particular day). Some are nicer to use, or more intuitive, or allow recording of other variables like sleep and exercise. Some examples of available HRV apps: SweetBeat, Elite HRV, ithlete, Bioforce, and HRV4training. There are apps available for both iOS (iPhone) and Android devices. The app I personally prefer is SweetBeat. As well as HRV numbers, it also provides HF, LF and LF/HF numerical results, and it correlates extremely well with my day to day perceived energy. Elite is also a very nice app. I particularly like the weekly and monthly averages it provides, but it does not give specific HF and LF numbers, only a sympathetic-parasympathetic scale (though I believe HF and LF numbers may be coming in the future).

SweetBeat: the ‘geek screen’ gives actual numerical results. This LF/HF result of 10.5 shows sympathetic dominance

Elite HRV: gives sympathetic/parasympathetic balance on a scale

This result with the pointer in green zone in centre of scale indicates balanced sympathetic/parasympathetic systems (compared to previous results). It also gives a ‘readiness’ number (10) indicating good ability to exercise that day. However the readiness number can lead you astray at times, and I have found it more useful to make my own interpretation of readiness from the actual HRV scores.

Ithlete summary screen includes variables such as sleep, fatigue, stress & diet

I also recommend purchasing a separate graphing app. I use LogsAll, and most of the graphs I will show in these blogs will be from that app. It is exceptionally simple to use, costs only a few dollars, and for me, has been worth its weight in gold. It can produce trend lines, and statistics such as averages and standard deviations. I enter all my daily HRV data into LogsAll each morning, and that enables me to do a lot more with my data. (More about that in my next blog).

  

Taking Measurements

HRV is a tool for determining your capacity for exercise/activity/stress resilience from day to day, or alternatively your need for increased rest, and all that is required is a 5 minute recording each morning when you wake.

To validly compare readings from different days, they should be recorded at about the same time of day, under the same conditions. Your HRV recordings should be done on waking – preferably before you do anything else in the morning e.g. drinking fluid, going to the bathroom, conversation, brain activity {not that too much of that happens in my brain in the mornings :) }

 Body position is important. Readings can be taken lying, sitting, or standing – but you must stick to the same body posture for all your waking readings so that you have valid comparisons from day to day. For ME/CFS patients, being upright can (sometimes dramatically) increase heart rate, and cause the SNS to kick in, so I always do supine (lying) readings. There is an argument to be made for seated or standing readings if you are not too ill – as that puts your body under a little stress, and gives some indication of how the body is coping with that stress.

HF and LF are very influenced by breathing rate, so I like to use a breathing pacer (which most apps provide) in order to eliminate breathing rate as a factor in my results. However there is some difference of opinion on this. I have tried both paced and un-paced methods, and found little difference other than a higher HRV result with paced breathing. The important thing is to choose one method and stick with it.

LogsAll graph showing HRV results with paced breathing (blue line) vs un-paced (red line)

Although short readings (of at least 1 minute) can be used reasonably successfully for HRV readings, a recording of 5 minutes is needed to reliably assess LF and HF components. Therefore, if you want the benefit of readings for LF and HF as well as HRV, I would recommend a 5 minute reading. But if you are only interested in tracking HRV, 1 – 3 minute readings are fine.

Aside from all that, it’s simply a matter of putting on your sensor, starting up your app, and lying quietly for 5 minutes while the measurements are taken. Then save your readings, enter results into LogsAll (if using), and you’re done!

Interpreting Results

Seeing the numbers and graphs will make everything more real for you. And to be honest it was a bit of a shock for me to see how low my numbers were. But it was also validating for me to see that how I feel each day physically is reflected in these objective numbers.

When I do too much I see a drop in my HRV the next morning. If I continue to do too much, or try to push through, a downward trend takes shape. These downward trends should not be ignored – it is a hole which becomes more and more difficult to dig yourself out of.

 Start recording your data and see it take shape, and begin to make sense, before your very eyes.

Elite HRV trends screen: The blue line is HRV and shows a significant dip (crash) in late April. The crash is also evident in the readiness (green, yellow and red) bars

LogsAll graph of SweetBeat HRV daily scores showing a deep crash in Nov 2015. When you show someone objective heart measurement data like this, they cannot help but understand the devastating effects of a crash

As well as levels of activity, you will need to consider other factors that can cause drops in HRV e.g. sleep, diet, medications, and stress. I find the HRV apps a bit limited in their ability to clearly identify the influence of these types of contributing factors. For me this is where LogsAll app comes in to its own.

  

 

Legs come, legs go

My legs stop working unless I take 5mg Prednisolone a day. The problem was that I was only prescribed tablets for the "emergency" treatment of 1 or 2 weeks after which I would stop taking the tablet. On the third cycle of that happening this year, I become so loathe at the idea of losing my legs again that I didn't stop taking them. That was June sometime. It took a little while but by this month I was ready to tackle all the medical appointments that I had let accumulate since before Christmas last year. I WON'T DELIBERATELY PUSH MYSELF INTO RELAPSE any more when I know for sure that it is going to happen. It's not hard to tell when it is going to happen for sure and going out for any reason for even tiny amounts of time has been enough to cause payback all year and I don't see why I should have to line up for it especially if these are my last days....relatively speaking. I'm not inclined to do it for anyone else any more either and I think that is the point when friendships reveal themselves as "fair weather" friendships. People question my love for them possibly because I am not prepared to pay the price of putting up with discomfort which to my body is akin to stress. It could be just the cold wind that my body hates or it could be the energy of "talking" or the light intensity or the fact that I have to wear clothes of a certain calibre. Ban the bra! I say. When I take the prednisolone I feel more alive and more able to distract myself from environmental stress and yeah, my legs work and I can think more clearly and feel more in control because of it. I have not had a nice time of trying to imagine myself any more sick than I already am so now the pressure is off and I can enjoy myself within my limitations. I can potter around the house slowly getting things organised and I can make it to appointments with far less dread. I've had my hearing aid checked and adjusted and I changed providers for the better. I had my eyes checked for everything in a particular effort to find a reason for the "eye headaches" but there was none. I had a home sleep study which I have not got the results of yet and a lung CT which I have got the results of in a watered-down fashion - the nodule has changed!

Now that the news has digested I have more questions but on the day I was just as keen to secure a long-term supply of prednisolone (before discussing the lung lumps)  so that I could take it daily and keep my legs working which I did. She agreed to daily.  She obviously does not want me to lose my walking again either but the only thing she said was that we will try to lower the dose as soon as possible. But now I want to know if taking steroids makes lung nodules grow? All the steroid sprays this year and it grows and none last year and it doesn't? I have not researched this so it is just my thoughts. If I think about it from another angle, I could ask, what is likely to grow faster in the presence of steroids? The answer to that one is fungus. Fungus has been on my mind since the antibiotics seemed to trigger that familiar itch as well as the most worrisome burning mouth I have had all year. It was so intense.

Living my life is kinder to me when I take both the Targin pain killers and now the low-dose steroids as well. I spend too much time feeling ill, and in pain even with these bandaids in my opinion and I do have trouble with side effects, although fewer now that my body is getting a consistent dose. I do wonder how long it will last as being something I am grateful for. Back in my high-dose steroid days (the Crohn's days) the benefit seemed to wear off over time (years). And right now the benefit does not feel as good as it did because I can still get that lead legs feeling that I once used to ignore. However rather than "poop-out", it could be the fact that I have been taking both Amoxycillin and Clarithromycin antibiotics because there is a chance that the lung nodule change is just the result of an infection. But her prescription was only for a week and that seems such a short time to try and rid me of an infection that has been causing lung-snoring noises, sinus problems and a  cough to clear the mucus all year. I'd like it to prove that it is not asthma or COPD as she diagnosed already this year and it is a flare up of say mycoplasma pneumonia (a past infection of mine) by getting better while I am on the antibiotics, but I feel terrible while taking these antibiotics. I've actually finished taking them but I still feel bad.  I was feeling so much better on a regular dose of steroid alone, but I wouldn't even know I am taking an energy-giving steroid right now because I feel yuk and "coma sleep" kind of tired again and if anything, it seems to have stirred up the coughing and lung rattles and mucus squeak sounds even more. I wonder if any of that got picked up on in the sleep study? The extra sore throat I have would not have been noticed by anyone because no-one has actually asked me about my symptoms. I've also been feeling feverish again and I've complained of mini-fevers coming and going all year too.  Needless to say, I hate antibiotic treatments.......even if they work long term to reduce an unproven bug load (which they did in 2012).  But this little one week application won't even do that. My gut is now trying to pay me back with my stomach not letting my food go down.  I am taking a couple of different kinds of probiotics and prebiotics in an attempt to avoid candida and thrush but that has not been something I can count on working.

Anyway, it is starting to sound more like lung cancer as I write about coughing and squeaking and even fevers so I think I will stop writing. It feels like I've been threatened with lung cancer all my smoking life and even when I stopped for 2 years the medical people still treated me like a smoker so it is sort of like "you deserve cancer you idiot". It's nice to know I may get a chance to keep everyone happy in their illusion of life's predictability. The Lyme and CFS and fibromyalgia and crazy autoimmune markers and 100 symptoms (yes I've counted) will be forgotten about if I have cancer. That worries me.  My life and death is now for the purpose of validating all the promising research into multi-systemic chronic disease and to have lung cancer put down on my death certificate will ruin everything!!!!