Two Doctors, One Nerve | The Angry Gut, Chapter 3

Vagus nerve and anxiety · HRV

Vagus Nerve and Anxiety: What a Heart Reading Shows About Your Gut

Heart rate variability records the vagus nerve’s effect on your heartbeat, and in studies of people with gut disorders, low vagal tone tracked inflammation and adrenaline rather than anxiety or mood scores. It is a stand-in for the gut, not a window into it.

The nerve that joins your gut and your brain cannot be sampled like blood. It can be measured where it touches the heart, and that reading is useful once you know its limits.

The vagus nerve, anxiety and calm are usually discussed as a chain in which soothing the nerve soothes the mood. The measurements tell a more specific story: vagal tone tracks inflammation and adrenaline more closely than it tracks mood. The nerve cannot be sampled like blood, but its effect on the heart can be measured, and knowing what that number does and does not mean separates a useful reading from a misleading one.

In the video Two Doctors, One Nerve, Dr. Gurpreet Singh Padda, MD, MBA, MHP, who wrote The Angry Gut with Ami Michelle Grimes, describes a thirty-four-year-old woman whose bowel trouble came first and whose panic followed a month later. One specialist manages her gut and another manages her anxiety. Measura [Cardiometabolic and Autonomic Health Analysis] is a testing service, and what follows is the measurement side of her situation.

What does the vagus nerve connect?

The book calls the gut the first brain and the brain in the skull the second brain. The vagus nerve is the cable between them. Below the diaphragm it is made mostly of thin, slow sensory fibers, so the bulk of what it carries is information flowing up from the abdomen rather than commands flowing down.

No clinic test reads that abdominal traffic directly. Every practical measurement of vagal activity is taken somewhere else, usually at the heart, and then interpreted. The wiring itself is laid out in the first post in this series. That limit is the first thing to understand before anyone puts a number in front of you.

What does heart rate variability measure?

Your heart rate rises a little as you breathe in and eases as you breathe out. The size of that rhythm is set largely by the vagus nerve, and it is captured as heart rate variability. The two standard vagal measures are RMSSD, the root mean square of successive differences between beats, and high-frequency power. A lower value means less vagal influence on the heart at the time of the recording. The Measura heart rate variability test records this from the heartbeat.

Two limits keep that reading honest. The balance ratio many consumer apps display went from 1.1 to 8.4 when researchers took away most of the nerve input to the heart, so it is not a nerve measurement at all. And heart rate variability reflects cardiac vagal tone; a review of inflammatory bowel disease studies noted it may not reflect vagal tone in the abdomen. It is a stand-in for the gut, not a window into it. For more on the number itself, read heart rate variability: what the number means.

Is low vagal tone linked to anxiety or to the gut?

Healthy controls averaged 39.99 ms on the vagal index across 24-hour recordings in a study of 253 people. Those with functional dyspepsia, a painful stomach with a normal scope, averaged 16.87 ms. Poor sleep, not mood, was the stronger predictor of a low reading in that group. A separate study of people with Crohn’s disease and irritable bowel syndrome found lower vagal tone tracking higher tumor necrosis factor, an inflammatory messenger, in Crohn’s (r = -0.48) and higher epinephrine in irritable bowel syndrome (r = -0.39). Vagal tone showed no link to mood scores in any group.

Put those findings together and her two diagnoses start to look like one picture with three drivers. Inflammatory signals from an irritated lining travel up the nerve and feed metaflammation. Sympathetic overdrive, the adrenaline side of the system, stays switched on while vagal tone sits low. And a care system that sends the bowel to one office and the panic to another never measures the connection between them. Her anxiety is unlikely to settle while her gut keeps sounding the alarm.

What can a vagus nerve test measure, and what can it not?

A Measura autonomic assessment looks at the heart side of the nerve with more than one number:

Cardiac autonomic reflex tests record how heart rate and blood pressure respond to simple, standardized challenges, adding a structured response to a resting reading.
Autonomic nervous system testing looks at the wider balance of the automatic nervous system in one visit.
Laboratory panels describe the metabolic terrain, including markers related to blood sugar and fats, that sits under the inflammation.

Some tests belong elsewhere. Stool tests, capsule studies and scopes are gastrointestinal tests ordered through your physician, not Measura tests. Stool also has a timing problem: in healthy volunteers sampled inside the small intestine, roughly 95% of the bile acids arriving at its far end were taken back up before stool formed. Ear clips and nerve stimulators are treatments, not tests, and Measura offers neither. No Measura result, and no other test, reads what the vagus is carrying up from your gut in real time.

Does breathing training strengthen the vagus nerve?

Dr. Padda was taught that the vagus calms inflammation by signaling the spleen, and he repeated it for years. A 2026 study that used four separate anatomical methods in male mice found the vagal motor fibers do not supply the spleen to any significant degree. The reflex exists, but it runs through sympathetic nerves. That correction matters to readers, because wellness marketing still sells the old route.

The same caution applies to what changes the reading. In randomized trials of people with heart disease, breathing biofeedback lowered blood pressure by about 3.08 mmHg but did not change high-frequency power, the vagal index it is named after. Breathing still earns a place: diaphragm training helped resolve reflux-related cough in 94% of patients against 77%. It simply is not proof of a stronger nerve. That is why a trend inside one person, measured the same way each time, beats a single number or a before-and-after taken minutes apart.

Taking this to your physician

Describe the order your symptoms began in, including any change in sleep.
Ask whether an autonomic baseline would help, and how it would be repeated.
Bring wearable readings as a trend, not a verdict.
List every medication, since drugs that act on heart rate can change the result.
Keep both your gut specialist and your mental health clinician informed.

The studies behind these numbers, graded one by one, are in the Deep Dive companion. What happens on the day is covered in what to expect at your appointment. The gut’s inputs start with the medicine cabinet, in what nine bottles hide from your numbers, and continue with what crosses a damaged gut wall.

Frequently asked questions

How do I get my vagus nerve checked?

Ask your physician whether an autonomic baseline would help. No clinic test reads the traffic on the vagus nerve in your abdomen, so it is measured where it touches the heart. Measura records heart rate variability, runs cardiac autonomic reflex tests that track heart rate and blood pressure during simple, standardized challenges, and offers wider autonomic nervous system testing. Results go to your physician.

Can you reset the vagus nerve to calm anxiety?

Be careful with that promise. In randomized trials of people with heart disease, breathing biofeedback lowered blood pressure by about 3.08 mmHg but did not change high-frequency power, the vagal index it is named after. Breathing still earns a place; it simply is not proof of a stronger nerve. Ear clips and nerve stimulators are treatments, not tests. A trend measured the same way each time shows what actually moved.

Can a test show whether my vagus nerve is behind my anxiety?

Not directly. No test reads the traffic on the abdominal vagus. Heart rate variability and cardiac autonomic reflex tests measure how the nerve and the rest of the automatic nervous system act on the heart, which is an indirect view. Results go to your physician, who puts them next to your symptoms and history. See autonomic symptoms.

What is a normal heart rate variability?

There is no single normal value. Readings change with recording length, breathing rate, posture, device and analysis method, and the measure is stronger for tracking change within one person than for ranking people against each other. Your own baseline, repeated under the same conditions, is the most useful comparison to discuss with your physician. See understanding your results.

Can IBS or functional dyspepsia lower heart rate variability?

In studies, yes. In one group of 253 people, those with functional dyspepsia averaged 16.87 ms on the vagal index against 39.99 ms in healthy controls. Lower vagal tone has also tracked higher epinephrine in irritable bowel syndrome. That is an association in groups, not a diagnosis for any one person. See cardiac autonomic reflex tests.

Does a low vagal tone reading mean I have anxiety?

Not necessarily. In the Crohn’s disease and irritable bowel syndrome research, vagal tone tracked inflammatory and adrenaline markers but showed no link to anxiety or depression scores, and in another cohort sleep quality predicted it better than mood. A low reading is a reason to look at inflammation and sleep, not a label. See questions worth asking your doctor.

How should I prepare for autonomic testing?

Follow the instructions you receive when the appointment is booked, and bring a complete list of your medications, because drugs that act on heart rate can affect the readings. Tell the staff about recent illness or poor sleep. Consistent conditions make a repeat test comparable with the first one. See how to prepare.

Get a baseline for the nerve between gut and brain

If gut symptoms and anxiety arrived together, ask about Measura heart rate variability and autonomic testing, with results sent to your physician.

Send a message

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References

Shaffer, F., & Ginsberg, J. P. (2017). An overview of heart rate variability metrics and norms. Frontiers in Public Health, 5, 258. https://doi.org/10.3389/fpubh.2017.00258
Billman, G. E. (2013). The LF/HF ratio does not accurately measure cardiac sympatho-vagal balance. Frontiers in Physiology, 4, 26. https://doi.org/10.3389/fphys.2013.00026
Kim, K.-N., Yao, Y., & Ju, S.-Y. (2020). Heart rate variability and inflammatory bowel disease in humans: a systematic review and meta-analysis. Medicine, 99(48), e23430. https://doi.org/10.1097/MD.0000000000023430
Du, L., Yang, J., Jiang, L., Zeng, G., Shu, Y., & Bi, B. (2026). Postprandial attenuation of gastric slow waves in anxiety-depression, with and without functional dyspepsia: associations with heart rate variability and sleep quality. Frontiers in Medicine, 13, 1890716. https://doi.org/10.3389/fmed.2026.1890716
Pellissier, S., Dantzer, C., Mondillon, L., Trocme, C., Gauchez, A.-S., Ducros, V., Mathieu, N., Toussaint, B., Fournier, A., Canini, F., & Bonaz, B. (2014). Relationship between vagal tone, cortisol, TNF-alpha, epinephrine and negative affects in Crohn’s disease and irritable bowel syndrome. PLoS One, 9(9), e105328. https://doi.org/10.1371/journal.pone.0105328
Khan, A., Tinajero, A., Moresco, J. J., Yang, J., & Gautron, L. (2026). Anatomical reappraisal of the relationship between vagal preganglionic motor neurons and the spleen in the male mouse. Autonomic Neuroscience: Basic & Clinical, 264, 103394. https://doi.org/10.1016/j.autneu.2026.103394
Kaneko, K., Aikawa, G., Sakuramoto, H., Ota, Y., Oyama, Y., Tomooka, M., Naya, K., Fukunaga, T., Sugishima, K., & Yamada, T. (2026). Effects of heart rate variability biofeedback on cardiac autonomic function in patients with cardiovascular disease: a systematic review and meta-analysis. Applied Psychophysiology and Biofeedback. https://doi.org/10.1007/s10484-025-09765-3
Niu, S., Zhang, T., Li, W., Wen, S., Dong, L., Wang, S., Shi, W., Shi, C., Shen, Y., Huang, Q., Tan, Y., Xu, X., & Yu, L. (2024). Positive effect of deep diaphragmatic breathing training on gastroesophageal reflux-induced chronic cough: a clinical randomized controlled study. Respiratory Research, 25(1), 169. https://doi.org/10.1186/s12931-024-02783-5
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