We have been asked by the UK Government to test the hypothesis that HRV may be a powerful diagnostic tool for Covid-19. This article will explain the relationship between HRV and Covid, focusing particularly on the implications for people who exercise regularly and contains a call to action for how you can help make this a success.
Those of you that have been monitoring your heart rate variability (HRV) for a while will know that it is a great general barometer of the stress your body is experiencing. This stress can come from multiple sources including:
- Physical stress i.e. physical work & training
- Chemical stress e.g. poor nutrition, alcohol
- Mental & emotional stress
The Total Load caused by the sum of all these stresses needs to be balanced in the form of recovery from good quality nutrition, sleep and relaxation. We can use HRV as a tool primarily to detect when physical stress from training is out of balance with our ability to recover, and the body is starting to break down.
Why might HRV be able to tell us about COVID-19?
What is not so well known is that as well as showing when someone is stressed, HRV can also tell us about the body’s reaction to sickness caused by bacteria and viruses and in particular about the level of inflammation. That’s because the vagus nerve, responsible for controlling the changes in heart rate via the so-called parasympathetic or ‘rest and digest’ nervous system also controls the body’s immune reaction (via the cholinergic anti-inflammatory pathway).
Put simply, when an invading microbe (bacteria or virus) is detected, the body produces cytokines which mobilise the immune response consisting of B cells, and the appropriately named ‘killer T cells’ which latch on to the cells the invader has occupied and literally explode them.
Left unchecked, cytokine production can go crazy, causing more damage to the body than the invading pathogens. This is known as the cytokine storm, and the resulting inflammation is what often kills very sick COVID-19 patients, rather than the virus itself.
The vagus nerve determines the strength of the immune reaction, and by measuring the vagus nerve using HRV, we can see how strongly this is going on. Our earlier blog post discusses this more, but in short, higher HRV = less inflammation, lower HRV = more inflammation.
The body’s nervous system can detect small increases in inflammation, and some previous research has shown that HRV changes may be able to predict regular colds several days in advance of when the person becomes sick.
It does seem as though some athletes are getting what starts as mild to moderate cases of COVID-19, but by carrying on training near the start, they actually draw out the symptoms for many weeks, if not months. At the end of May, the Royal Society of Medicine gave an online webinar on the dangers of novel coronavirus for athletes, where it was explained that bad cases could lead to heart muscle damage (myocarditis) requiring up to 6 months rest from sports participation as well as long term consequences such as Chronic Fatigue Syndrome.
Let’s look at some examples
This chart shows the course of a short, but reasonably intense viral illness – likely caused by one of the 4 corona viruses already in existence before COVID-19 came along. You can see from the red dots and emojis that this athlete became sick quite rapidly, and their HRV dropped for a period of 5-6 days before recovering above their baseline (the thick blue line). You can also see that their resting heart rate started to rise after their HRV had dropped, and that they stopped training (sensibly) whilst their body was fighting the infection. The drop in HRV, before raised HR or symptoms presenting, allowed this athlete to reduce his training, focus on eating and sleeping well in order to give his body a head start on fighting off the virus.
Let’s contrast this now with the ithlete Pro timeline chart for an athlete who had a case of suspected coronavirus:
The athlete first became sick on March 14th, and developed a range of typical COVID-19 symptoms, including a cough, muscle weakness and a tingling in his hands that he compared to altitude sickness (AMS). Although he reduced training, his condition continued to get worse, and soon he was forced to stop altogether. To the end of this timeline, mid May, he remained unwell, and his HRV baseline was still falling. That is a solid 6/7 weeks of illness, so far, which may have been significantly reduced by stopping training and lowering his total load earlier.
HRV and COVID study
This and similar reports led us to apply for a UK Government grant program funding short term projects intended to help mitigate the effects of the COVID-19 pandemic. We are supported on this project by some specialist physiology researchers and an experienced medical statistician.
What we intend to discover is whether changes in heart rate variability are able to predict:
- The start / onset of COVID-19 before a person develops symptoms
- How severe the illness is likely to become
- When it is safe to resume training
If HRV was able to predict COVID infection during the 5-7 days a person has the virus before they show symptoms, they could self-isolate much sooner. This would significantly reduce the spread of the disease, whilst also giving the individual better opportunity reduce their Total Load and give their body the best chance of fighting the infection (i.e. stop training, sleep & eat as well as possible).
We are very happy to say our project was selected for funding, the required resources are in place, and are now conducting the study via the following steps:
- An appeal to HRV users to send in their data from any app or system (not just ithlete)
- Sending a link to a professionally designed symptom questionnaire
- Anonymising the data in a GDPR compliant manner to ensure it cannot be personally identified
- Statistical analysis to test whether our ideas are supported by the data
- Writing up the findings into a report and making them public so that everyone can benefit
The key point here is that we need HRV users who have had (or think they may have had) COVID-19 to support the initiative and spend 10 mins to fill in the questionnaire and send in their data. This can be from any app or system, not only ithlete, for example, Bioforce and Elite HRV (who have kindly agreed to support the initiative), HRV4Training, Oura, Whoop, etc.
The benefits of doing this are that we might be able to detect the onset of COVID, reducing infection rates, saving healthcare costs, and importantly for athletes, reducing or eliminating long post-infection periods of ill health that can scupper not only race plans but general wellbeing!
For those who support and spend the few minutes needed to fill out the survey and send in the data, grateful thanks, not only from us, but from fellow athletes that may be able to avoid a severe illness for themselves and others around them!
If you have any questions about taking part, or would like to discuss your suitability, please don’t hesitate to contact us on firstname.lastname@example.org