The Connection Between Heart-Rate Variability (HRV) and Vagal Tone

Heart-rate variability (HRV) — the time between individual heartbeats — is one of the best measures of vagal tone. A healthy heart doesn’t beat like a metronome; its rhythm varies by hundreds of milliseconds as the sympathetic and parasympathetic systems engage in a dynamic push and pull.

Chronically stressed people tend to have low HRV, writes Sara Mednick, PhD, in The Power of the Downstate. “This represents a system stuck on overdrive and unable to flexibly respond to life’s demands and then appropriately calm the system down.”

Our HRV and vagal tone are highly responsive to daily experience, and we can influence them positively when we take good care of ourselves. Several lifestyle habits have an outsized impact, including time in nature; regular, high-quality sleep; a varied whole-foods diet; regular exercise; and routine social connection.

When these interventions are not available — or are not enough on their own to regulate the nervous system, as with illness or the aftereffects of trauma — vagal tone can also be enhanced through direct stimulation of the nerve.

Physicians first used modern electrical VNS in the 1980s to treat epileptic seizures; the U.S. Food and Drug Administration approved implantable electrical stimulation devices for epileptic patients in 1997. In recent years, research into noninvasive versions of this technology has expanded.

“The technology is not a cure for any particular condition at all,” explains functional-medicine provider Navaz Habib, DC. “It is a device meant to help create a state shift.”

Studies of VNS suggest it can effectively treat symptoms of depression, anxiety, migraine, stroke, traumatic brain injury, PTSD, Parkinson’s disease, and Alzheimer’s disease. Long COVID clinics have deployed VNS to help relieve fatigue, brain fog, and anxiety.

Because the vagus nerve is central to the gut–brain connection, VNS may be a promising treatment for gut-related conditions, such as irritable bowel syndrome and IBD. “When gut function is compromised, the vagus nerve tends to be the first area that needs to be turned on in order to regulate and support overall health,” says Habib.

A 2023 report published in Bioelectronic Medicine found transcutaneous auricular vagus nerve stimulation — a type of tVNS via the ear — improved symptoms and inflammatory markers in a small group of children and young adults with mild to moderate IBD. A 12-month pilot study looking at surgically implanted VNS found that it restored healthy vagal tone and reduced inflammation in a group of seven patients with Crohn’s disease.

Noninvasive VNS devices are increasingly available without a prescription. Some are designed to be used on the ear, where electrical pulses stimulate the vagus nerve in the brainstem. Others can be held directly against the neck, where a substantive part of the vagus nerve sits near the surface.

“Noninvasive VNS results in a quick improvement in vagus-nerve signaling,” says Habib. He’s seen a startlingly fast response in his patients who were previously unable to shift from sympathetic to parasympathetic states.

Though not a cure-all, VNS can help restore a sense of balance and calm, says functional-­medicine physician Gregory Plotnikoff, MD. Particularly for those with low vagal tone, who may have struggled with chronic stress and inflammation for years, it can provide a kick-start to the body’s relaxation response. This offers proof to the body and mind that another state is possible.

VNS can even be used during an acute stress response or panic attack, says functional neurologist Jeremy Schmoe, DC, DACNB. By activating the parasympathetic nervous system, VNS helps the body counteract the surge of adrenaline and cortisol. This enables the return to a regulated state.

The one time to avoid using VNS, says Habib, is when the body is in a freeze response. This is signaled by fainting, low heart rate, or a general lack of affect. These symptoms are a clue that the parasympathetic system is overactivated, and VNS could make matters worse.