Expert Q&A: What your HRV says about your nervous system, with Jane Ollis

The following interview is a transcript excerpt from The Heallist Podcast episode. Listen to the full audio version below and subscribe to get notified of new episodes.

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In this episode of The Heallist Podcast, we unpack heart rate variability (HRV) — the number your Oura ring or wearable gives you — and what it actually says about your nervous system, how it's coping, and how to read it in context rather than as a daily verdict. Our guest, Jane Ollis, is the founder of Sona, a neurotech company developing AI-guided vagus nerve stimulation to help people regulate their nervous systems. She's a biochemist by training, a former NASA intern, and an Oxford University Business Fellow who has spent her career at the intersection of heart science and human health.

Jane writes the newsletter Precision Recovery and chairs the Health Innovation Network for Cancer in Sussex. In this conversation, she explains what HRV actually measures, why it's tied to your autonomic nervous system, what causes it to drop, how to benchmark it against yourself rather than population averages, and simple tools — from breathing to vagus nerve stimulation — that can help raise it.

What HRV Really Measures

Jane: I was interested in the ear as a place for measuring stress biomarkers — you can get a lot of data from the ear. What I learned fairly early on is that there's a metric called heart rate variability, which is the interbeat intervals between your heartbeats. Most of us think our heart beats like a metronome, but it's actually a lot more clever than that — it speeds up and slows down all the time. This variation between each heartbeat is your heart rate variability, and it's a measure of how stressed you are at quite a simple level. The lower your HRV, the more likely you are stressed. The higher it is — and normally we think high is bad, like high cholesterol — but with HRV, high is good. Higher means your nervous system is more balanced, and the more ability you have to recover.

We have two arms of our autonomic nervous system. The sympathetic system is our fight and flight — the brain releases adrenaline, sends off cues to release cortisol. The parasympathetic nervous system is responsible for activating systems to do with growth, repair, and recovery, and it's made up of 80% of your vagus nerve. Your heart rate variability is a really good metric of how balanced these two systems are, and how well you're able to move between them. Stress gets a bit of a bad rap — actually it's a very powerful tool for us as humans, and we need cortisol. But having the ability to toggle nicely between these two arms of the nervous system is your heart rate variability. It's a good broad indicator of how well balanced your autonomic nervous system is, though not always perfectly accurate.

Wearables measure HRV overnight because it just gets a longer sample where you're not doing anything. During the day you're moving around, life is happening to you, and your nervous system is responding to that in real time. At night, it removes all that noise so it can get a more consistent measure — that's often why overnight HRV reads higher than daytime HRV.

What Drops HRV Day To Day

Jane: We are complex. Your average might be a certain number, but things that tip it down are stresses that happen in your life. The first deep research we did into HRV was during COVID — we were funded by the UK government to look at whether HRV changes could be an early indicator of viral infection. We were able to show that HRV drops when the body is under attack by a virus. Getting ill, or your immune system trying to fight things off, will often send your HRV down. Other things that can send it down: a stressful week, or alcohol.

Life is constantly happening to us. Our nervous system is constantly toggling between the sympathetic and parasympathetic arms, depending on what's going on in our external world and within our body. So it's never going to be constant, it's a variable. What I've learned is it's going to change depending on what life throws at you — the real question is how quickly can you recover. Seeing when it drops, and asking what's happening that you could change, is a valuable signal worth paying attention to. That correlates exactly to what we found in the long COVID study — generally two to three days before symptoms, you could see a signal, though it can be noisy and other things can mask it, so treat it with a little caution. As I've gotten older, I've noticed it's harder to keep HRV at a high level — it's a really valuable longevity marker, and it's important to focus on what tools you have to keep it from dropping over time.

A really interesting piece of research I read for the first time last year was around mitochondria levels — for the first time there's evidence of a seasonal shift in mitochondrial activity, the batteries of every cell in our body. The thinking is that during winter they're much more in repair mode, and during summer they're much more in power-up mode. It's interesting to see how that might correlate with how our nervous system is driving some of that too. It feels like we need to start taking more notice of these important signals and rhythms, and not pushing against them so hard. But it's a real challenge.

Benchmarks And Device Differences

Jane: I would always say benchmark against your own data, whatever that is. People always ask me what's a good HRV, and I push back and say it's an incredibly personal signal. HRV is measured in a time domain, in milliseconds. I did a measure just before we came on, because I'd had a really busy day, and it was around 25 milliseconds. Luckily I have a product that can help drive it up, and it can go up to around 100. It's less about the low point and more about how quickly you can move it, how responsive it is when you ask it to rise.

Every wearable has a different algorithm to calculate HRV, because they need to remove noise from the signal — particularly wrist-based devices with a lot of hand movement. That's why a Whoop, a Garmin, and an Apple Watch might all give you different values. Don't expect one device to match another. What's more important is your trend line — whether it goes up or down, how quickly you can move it around. A long-term increase is always the aim.

Another anecdote: we do a lot of demoing of my product, so I'm always looking at HRV scores. I had two men, identical age, identical physique — one single, the other a new dad whose sleep was completely messed up. The single man had an HRV around 80 milliseconds; the new dad's was around 20, and I couldn't get it to nudge up. He was chronically sleep deprived, like many young parents, so his body wasn't recovering during the night. It's about taking a whole view of what's happening in someone's life, and what's happened before they arrived at today, to understand where their HRV might land.

Sleep Loss And Chronic Stress

Jane: It puts your body under a lot of stress, especially sleep. Sleep is one of the most precious commodities we have for health, well-being, and longevity, and wherever that's compromised, that's always the first thing I try to focus on.

Jane 18:38 It does go down. I see quite a lot of people living with autoimmune dysfunction, whether that's chronic fatigue, ME, or long COVID, and that also seems to correlate with low heart rate variability. It feels like that constant stress on your nervous system, that inability to strengthen the vagus nerve, which can help lift you out of it — that just seems to take a long time to nudge back up.

Breathing To Raise HRV

Jane: The best way to lift it is to use your vagus nerve, since it makes up 80% of your parasympathetic nervous system. That's often the reason you've got an overactivated, over-dominant sympathetic response — we're turning our stress system on too many times a day. The simplest tool is breathing — using your respiratory apparatus, and therefore your heart, at a specific rate to increase your heart rate variability. It costs nothing, it's a mechanical hack, you don't need to meditate or think about it, you just need to do slow breathing. I recommend four seconds in and a longer six-second exhale, as much as you can from your diaphragm. The reason for that timing is an effect called respiratory sinus arrhythmia — when you breathe at that rate, your heart rate variability starts to synchronize with it, and that's when you see a beautiful increase.

Jane: Isn't it interesting that you don't see it immediately? I think we're quite impatient — we want to try something and have it be instant. When it comes to regulating a nervous system that's been operating the same way for years, these shifts take a while. Our chief scientific officer always says the body pushes against it to start off with — it wants to rebound back to where it's used to being. So getting that HRV needle to move upward takes time and consistency of practice.

Vagus Nerve Tech And Real-Time Feedback

Jane: We seem to have landed at a time when there's a lot of interest in this nerve. The great news about the vagus nerve is it shows up externally in two places in the body. One is in the ear — a bit of evolutionary pipework from when we had fish gills. It's called the auricular branch of the vagus nerve, going from the ear into the back of the brain stem. From there, the vagus nerve branches down the side of the neck to all of your organs, like a communication superhighway. The other place you can access it is on the skin, on the cervical branch in the neck. But accessing it isn't always straightforward — we're all different, with different ear shapes and where the nerve shows up, different placement on the neck, different skin. If you want to activate it with an electrical pulse, you need to know what shape of wave you're sending.

The reason I'm excited about what we've built is that we measure heart rate variability in real time, which gives us a feedback loop — is it working, how do we optimize it, what happens if we change the pulse shape. We're at an early stage, so I'm not saying we've found the magical solution for everybody, but it's about using heart rate variability to guide how you stimulate the vagus nerve.

You put it on your ear. On the back of the device we have a PPG sensor, the same type you'd find in an Oura ring, measuring in real time, plus two little electrodes that stimulate the ear. This form of bioelectronic medicine is about to evolve. In the US, it's now regulated for opioid withdrawal, and we're starting to see real clinical efficacy for hard-to-treat depression too. Unless you've got real-time data to know how it's working, it gets a bit hard to gauge — that's why I'm interested in how heart rate variability can drive that. We're all different, and there's no point sending the same signal to everyone — it's got to meet you where you're at and learn with you. That's the future.

I use it as a sleep ritual. I'm a menopausal woman whose sleep disappeared — when estrogen levels drop in your brain, you become more stress-reactive. I do 10 minutes within an hour of going to sleep, and that works for me. I see results within five minutes. Again, it comes back to using the data to drive how you use it.

It discharges a small electrical pulse across the surface of the skin, and we measure the impedance to know how well it's discharging, getting that current across the skin. All we're trying to do with any of these devices is mimic the firing of the nerve's action potentials — artificially get that neuron firing and get that cascade happening. The big caveat is everyone's ears or necks are different — skin's different, ear shapes are different. There's an enormous amount of variability in human anatomy. Everyone thinks they have weird ears — nope, we all just have a weird ear shape.

None that I've seen, in terms of concerns about using it before bed. I always say within an hour of bedtime, it doesn't need to be literally as you're climbing into bed. What we're trying to do is give you the right sleep architecture — melatonin levels rising during the day, cortisol levels coming down, and we need these two systems working well together to fall asleep. Doing it before sleep is about driving down the sympathetic system and getting the parasympathetic pedal up and running, so you're in the best position to fall asleep.

There's a US company now cleared by the FDA for opioid withdrawal, and also recently approved for reduction of menstrual bleeding. Research that just came out this week from the Feinstein Institute looked at stopping hemorrhaging in the brain during severe trauma. We've also done studies in Parkinson's disease where we've seen improvement in gait and cognition. There's a lot still to learn, but we're at the beginning of understanding how these tools could help across a whole range of health conditions.

The Future Of Nervous System Care

Jane: I think there's a very clear future around improving nervous system balance. If our body is operating with optimal balance between these two arms of the nervous system, that sits upstream of nearly every chronic condition we have — cardiovascular disease, migraine, arthritis — because we can see a change in the inflammatory markers driving those. Nervous system regulation opens up an enormous possibility for healing and optimal health moving forward, and it's an area that's still under-covered in conventional medicine.

We need stress. I really believe stress is a human superpower — it allows us to focus, it was designed to let us move, to run fast, tipping glucose into our bloodstream. It gets a bad rap. What we need is to switch it on a little less, but to have better recovery — if we can build more headroom before the amygdala switches on our stress response, and bounce back faster from a stressful episode. Can we build headroom? Can we bounce back faster? That's the critical bit.

A good female response is to actually talk to someone about it, or to yourself. Part of the female stress response is tend-and-befriend — a built-in drive to communicate whatever is making us anxious, because there's something about turning those thoughts into words and sharing them that can relieve that stress. It is a part of the female brain being wired slightly differently, with this tend-and-befriend element as part of our stress response.

Absolutely, and it just helps keep you in the better space. I think the future is bright. Last words of wisdom: enjoy every day that we are blessed to live and walk on this planet.

Want to go deeper? Your HRV number isn't a grade to chase — it's a conversation with your own nervous system, and the most useful thing you can do with it is get to know your own pattern rather than someone else's average. Whether it's a slow exhale, a full night of uninterrupted sleep, or simply noticing what season your body thinks it's in, the smallest, most consistent habits tend to move the needle more than any single hack ever will. Some of the most powerful recovery tools cost nothing at all.

Disclaimer: This article is for education, not medical advice. Talk to a qualified healthcare professional before making health decisions. Heallist doesn't provide medical services or verify practitioners.

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