What Is Heart Rate Variability (HRV) and How Does the Vagus Nerve Control It?

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As a wellbeing coach and health psychology specialist, I've worked with hundreds of clients — executives running global teams, athletes preparing for competition, busy working parents spinning a dozen plates — and one of the most common things I hear, in slightly different words each time, is: "I just feel a bit off, not myself, but I don't really know why."

What strikes me is how rarely people connect that feeling to their nervous system.

It's not their fault. Nervous system regulation isn't something we're taught about in school, and the symptoms often don't feel serious enough to bring to a healthcare professional.

So when something feels off, most people don't know where to look for answers. And they end up tolerating a low-grade version of themselves for months, sometimes years, before joining the dots.

So before we get into this further, let’s do a simple check-in to see if your nervous system might be a little out of sorts.

A few questions to ask yourself

Sit with these for a moment. There's no scoring system, and this isn’t a diagnosis. Just be really honest about whether any of these describe you right now, and if there’s a pattern across more than one area.

1. Do you find it hard to fall asleep even when you're exhausted? Do you wake at 2 or 3 am with a busy mind? Or, do you get a full night’s sleep yet wake unrested?
2. Do you feel "tired but wired", too depleted to do much and too revved up to rest? Do you crash in the afternoons, then get a second wind late at night?
3. Is your concentration patchier than it used to be? Are you losing words mid-sentence, walking into rooms and forgetting why, or finding tasks that used to be easy harder?
4. Are you more reactive than usual — tearful, snappy, anxious — over things that wouldn't normally land that hard? Or the opposite: flat, numb, a little disconnected from yourself and the people around you?
5. Is your jaw tight? Shoulders up by your ears? Heart occasionally racing for no clear reason? Has your digestion become unpredictable? Do bloating, reflux, irregular bowels, sensitivities seem to be multiplying?
6. When something stressful happens, how long does it take you to genuinely come back down? Hours? Days? Or does it feel like you never quite return to baseline at all?

If you're nodding along to several of these — particularly across more than one category — it's worth taking seriously. This is what a dysregulated nervous system tends to look like in real life. Not dramatic. Not always alarming. Just a steady accumulation of small signals.

Why this happens — even when you're coping

Here's the part that often lands hardest with my clients: you can be coping and be dysregulated at the same time. In fact, that's the most common presentation I see.

You're still showing up, still hitting deadlines, still being a good parent, a reliable friend, a strong performer. From the outside — and often from the inside too — it looks like things are working. And they are, but your body is keeping score. And it's beginning to show you, in quiet ways, that the system needs some help.

To understand why, it helps to know a little about how your autonomic nervous system works.

Your autonomic nervous system has two main branches, the sympathetic (fight-or-flight) and the parasympathetic (rest-and-digest). A balanced system switches fluidly between the two throughout the day. You ramp up for a meeting, then come back down. You handle a stressful conversation, then return to baseline. That movement between states is what we mean by regulation.

Dysregulation isn't about being stressed. It's about losing the ability to come back down. When the body lives in a state of low-grade activation for long enough — from demanding work, caring responsibilities, illness, unresolved emotional load, or simply years of pushing through — the system stops returning to baseline between stressors.

Your sleep gets lighter. Your digestion gets touchier. Your mood gets thinner. Your thinking gets foggier. None of it is dramatic in isolation. All of it points to the same underlying issue.

The symptoms above, while seemingly random and tied to character flaws, are just your physiology responding to you running hot for too long without a proper reset.

Where to go from here

The first piece of work is recognition, which is what this article has really been about. And it is what asking yourself those questions at the top will help ignite. And if they have helped you identify something worth addressing, there is good news.

Your nervous system can relearn any flexibility it may have lost.

Quitting your job, ditching your caring responsibilities, or running away to a tropical island won’t help you rebalance your nervous system long-term. Teaching your system that it's safe to come down will. Consistently engaging in small daily rituals that activate your rest-and-digest response helps your body to learn how to switch back into this mode more easily and fast-track you back to feeling more like yourself.

By André P. Boezaart, MD, PhD, FASRA

It helps to think of the human nervous system as four connected parts, each with its own job.

The central nervous system (CNS) is the brain and spinal cord. It is the command center. It handles thoughts, feelings, and decisions.

The autonomic nervous system (ANS) runs the jobs you never think about but can't live without: your heartbeat, your breathing, digestion, and blood flow.

The somatic nervous system (SNS) controls the movements you choose to make and facilitates your senses. It is your link to the outside world.

The enteric or "gut" nervous system (GUT) lives in your digestive tract. It has more nerve cells than your spinal cord, and it acts like a mind of its own, talking to the brain all day through nerve and chemical signals.

Together, these four systems work like a piece of music. Each part matters. Harmony is the goal. When one section plays too loudly, the whole piece falls out of tune.

When the stress system gets stuck

Inside the autonomic nervous system are two branches that keep each other in check.

The sympathetic system is the accelerator (fight-or-flight). The parasympathetic system is the brake (rest-and-digest).

In modern life, the accelerator often gets stuck. Alerts, deadlines, and worry keep the sympathetic system running hard, all the time.

What was meant for short bursts of alertness becomes prolonged hypervigilance. What was meant to be a useful alarm turns into slow harm.

A gland called the adrenal medulla releases catecholamines (stress hormones like adrenaline) and doesn’t stop. And another system, the hypothalamic–pituitary–adrenal (HPA) axis, releases cortisol, and doesn’t stop.

The immune system slips into a low, simmering, inflamed state. Inflammatory signals called cytokines rise, blood vessel linings work less well, and the gut wall becomes leakier and weaker.

The nervous and immune systems, which are meant to be partners, start working against each other.

Calming the body through the senses

You wouldn’t think it, but your senses play a role in spreading calm throughout your nervous system. Each of the five senses offers a direct path to the parasympathetic system. These paths evolved to tell the body one thing: you are safe.

Sight. When your eyes rest on something wide and open, like mountains or the ocean, the visual part of the brain sends calming signals inwards. This lowers activity in the amygdala, the brain's alarm center. A soft, wide gaze actually slows your heart.

Hearing. Gentle, patterned sounds calm us. Think of a mother's sing-song voice to a baby, a soft hum, ocean waves, or soothing music. These sounds work the tiny muscles in the middle ear and activate the vagus nerve. Your body tunes toward connection instead of defense.

Smell. Scent has a direct line to the brain's emotion centers. Aromas like lavender, bergamot, and frankincense lower stress activity and lift vagal tone (the strength of the calming vagus nerve).

Taste. Eating mindfully wakes up taste nerves that run along cranial nerves VII, IX, and X. This releases feel-good chemicals like dopamine and endorphins and gets digestion moving, which is part of the vagus nerve's territory.

Touch. Massage, firm pressure, and gentle skin contact switch on special nerve fibers called C-tactile afferents. These signal safety and belonging. They raise oxytocin (a bonding hormone) and boost the calming system.

Put together, these signals tell the body you are safe and free to heal.

The vagus nerve: the body's anti-inflammation highway

At the center of all this calming is the vagus nerve, the tenth cranial nerve. It is a two-way highway linking the brain, the organs, and the immune system.

About 80% of its fibers are afferent, meaning they carry information up to the brain. They send sensory signals from the organs and body, including from parts of the outer ear called the cymba and cavum conchae, back to the brainstem.

Its efferent fibers carry signals the other way, down from the brain. They switch on the cholinergic anti-inflammatory reflex.

Here's how that works: the vagus nerve releases a chemical called acetylcholine. It attaches to receptors on immune cells called macrophages. This lowers inflammatory signaling.

This link between the nervous and immune system is what allows thought, emotion, and inflammation to "talk" to each other in real time.

Bundling the senses at the ear

When we stimulate the part of the vagus nerve in the outer ear, in the cymba and cavum conchae, we tap straight into those calming afferent (sensory) pathways.

Transcutaneous auricular vagus nerve stimulation (taVNS) sends gentle electrical pulses to the very same circuits that music, touch, scent, and beauty stir up on their own.

It's as if all five senses were bundled into a single clear signal, all arriving together at a hub in the brainstem called the nucleus tractus solitarius.

Then, using the vagus nerve, the brain sends calming signals back down into the body. It steadies the heart, settles the gut, and quiets inflammation through that same acetylcholine pathway.

taVNS does not replace the senses. It amplifies their message. It reminds the nervous system what safety feels like.

Closing thought

At its heart, the path from stress to healing is a shift from sympathetic noise to parasympathetic calm.

Beautiful views, gentle sounds, soothing scents, delicious meals shared with loved ones, and a caring touch all send the same message the vagus nerve carries in every heartbeat: Be still.