What's Heart Rate Variability (HRV) got to do with chronic pain?

Heart Rate Variability (HRV) is quickly becoming a popular biometric to measure wellness, with several watches tracking this data and numerous apps analyzing it. But what is HRV?

Understanding HRV

HRV denotes the relationship and synchrony between the heart and the brain. It measures the “differences in the length of time between consecutive heartbeats, resulting from the natural rise and fall of the heart rate in response to breathing, blood pressure, hormones, and emotions” (Rosenberg, 2017, p. 69). In essence, the amount of time between each of your heart beats is supposed to adapt and change depending on your environment, as described in The Heartmath Solution:

Contrary to the earlier belief that a steady heart rate was an indicator of health, we now know that a loss of the naturally occurring variability in heart rate is actually a sign of disease and a strong predictor of future health problems. (p. 35)

Correspondingly, the more variable the length of time between the heart beats, the higher the HRV reading. Likewise, small or even non-detectable changes in the time interval between heart beats will cause a lower HRV reading. This is significant if you have chronic pain because studies have found that people with chronic pain tend to have lower HRV readings (Rampazo et al, 2024). Thus, raising HRV could relieve chronic pain. Similar to the theme of last month’s blog, how this works has to do with feelings of safety/relaxation or threat/stress in the nervous system.

HRV and the Autonomic Nervous System (ANS)

HRV “is indicative of the state of the autonomic nervous system and might be a biomarker of general stress and health” (Dana, 2020, p. 5). In short, your HRV reading provides direct bodily feedback in numerical form about the condition of your nervous system. Further, HRV provides a way for you to listen in on the conversations within the body between the heart and brain. 

Specifically, HRV indicates whether you are predominately operating in either the stress response, which is the sympathetic nervous system (SNS), or the relaxation response, which is the parasympathetic nervous system (PNS), or if you are balanced between the two. (Refer to this blog for a review on how the body responds when functioning in the SNS vs the PNS.) 

Consequently, if we consider the lesson from last month’s blog,

Threat = Pain

Safety = No Pain

And add in the ANS and HRV relationships,

SNS = low HRV

PNS = high HRV

It follows that ultimately,

Threat = Pain = SNS = low HRV

Safety = No Pain = PNS = high HRV

Within these equations is the answer to this blog’s question, What's Heart Rate Variability (HRV) got to do with chronic pain? Answer: HRV is low when we have chronic pain. Basically, when we feel threatened, the stress response dominates our ANS. To reduce chronic pain, then, we need to feel safe, which happens when we are relaxed and our PNS is activated. This results in a high HRV reading. Bottom line: chronic pain can be eased by raising our HRV. Let’s dig a little deeper into the connection between the heart and brain.

Heart-Brain Connection and the Vagus Nerve

The heart has its own nervous system. This system communicates with the brain through four pathways: neurological, biophysical, energetic, and biochemical (Childre, 1999, pp. 28-34). Although all of these pathways are fascinating and deserve mention, I am going to focus on the neurological track, specifically the vagus nerve. What follows gives you an anatomical reference for how these structures are coupled in the body.

As you can see in the picture below, the vagus nerve is the 10th cranial nerve and is part of the PNS. You’ll notice that this nerve has two branches. One branch terminates at the heart, called the ventral vagus, and one extends to the lower organs, called the dorsal vagus. The discovery of this split of the vagus nerve into two pathways was made by Steven Porges and was the impetus for the development of the Polyvagal Theory (Porges, 2018, p.52). As you look at the image, pay particular attention to the ventral vagus, which connects the heart to the brain. This is the branch that influences HRV. Furthermore, the ventral vagus exerts its effect on the heart through the breath.

Porges discovered a link between breathing patterns and inhibition of the heart, essentially slowing down heart rate, via fibers of the ventral vagus. And HRV measures this relationship (Porges, 2017, p.3). Not surprisingly, then, practices to raise HRV are often centered around breathing, with practices such as resonance frequency breathing, which is described below. But before we go there, you need to know about entrainment.

The Heart Sets the Rhythm

The Heartmath Solution defines entrainment as “A phenomenon seen throughout nature, whereby systems or organisms exhibiting periodic behavior come into sync, oscillating with the same frequency and phase” (p. 267). The heart creates the strongest oscillations in the body from which the other organs, including the brain, set their rhythm. Heartmath research has found, “When brain waves entrain with heart rhythms at 0.1 Hz, subjects in our studies report heightened intuitive clarity and a greater sense of well-being” (Childre, 1999, p. 38). 

Therefore, how the heart beats impacts the rest of the body all the way up to our cognitive functioning, including our stress. Here’s a final motivating thought before moving into working with your HRV: “It’s heart intelligence, working in consort with the head, that gives us the ability to eliminate stress. The best prescription for stress reduction is this: heart + head = coherence” (Childre, 1999, p. 58).

How to Measure HRV

A baseline HRV reading is best accessed when you are still and are breathing normally. You can sit or lie down and breathe for a few minutes while your watch or heart rate monitor takes a continuous reading. For best results, measure your HRV at a similar time every day for several consecutive days. When you receive your results, rather than focusing only on the number for that day, you’ll want to notice how your HRV numbers are trending over several days, weeks, and months.

Resonance Breathing to Raise HRV

The first exercise in the book Heart, Breath, Mind by Leah Legos is to determine your resonance breathing frequency. This is the rate of breathing that most raises your HRV. It is characterized by a longer exhale than inhale because the exhale phase of the breath stimulates the PNS. Legos recommends the basic resonance frequency of a 4 count inhale and 6 count exhale. However, she encourages experimenting with this ratio to the tenth of a second to find the best rate for you. 

Resonance breathing is often done for 20 minutes. However, you might opt to start with a shorter session. Some apps like Elite HRV, which I have used, give you continuous mapping of your heart rate and HRV readings and help you maintain your breathing frequency using a visual on the screen. As a data person, I appreciated this feedback and felt that it kept me motivated and engaged with the practice for longer. Give it a try!

Summary

HRV measures the state of your nervous system. It provides insight into how the heart and brain are communicating. Information between these organs is relayed through various channels, including a physical connection via the ventral vagus nerve. The ventral vagus is part of the parasympathetic nervous system. When it is stimulated, it can slow heart rate and raise HRV, which is associated with feeling safe and free of pain.

The heart is the most powerful pacemaker in the body to which all the other organs set their rhythm. When the bodily systems are in sync, there is greater efficiency and harmony throughout, resulting in greater wellness. The heartbeat oscillates with the breath. Hence, practices like resonance frequency breathing can bring the heart in a synchronous pattern, thus raising HRV while simultaneously lowering stress and pain.

Rosenberg, S. (2017). Accessing the Healing Power of the Vagus Nerve: Self-Help Exercises for Anxiety, Depression, Trauma, and Autism. North Atlantic Books.

Childre, D., & Martin, H. (1999). The Heartmath Solution. HarperOne.

Rampazo, É. P., Rehder-Santos, P., Catai, A. M., & Liebano, R. E. Heart rate variability in adults with chronic musculoskeletal pain: A systematic review. Pain Pract. 2024 Jan;24(1):211-230. doi: 10.1111/papr.13294. Epub 2023 Sep 3. PMID: 37661339.

Dana, D. (2020). Polyvagal Exercises for Safety and Connection. W. W. Norton & Company.

Porges, S. W. (2018). Polyvagal Theory: A Primer. Clinical Applications of the Polyvagal Theory: The Emergence of Polyvagal-Informed Therapies. (pp. 50-69). W. W. Norton.

Porges, S. W., (2017). Chapter 1: The Pocket Guide to the Polyvagal Theory: The Transformative Power of Feeling. (pp. 1-11). W. W. Norton.

Lagos, L. (2020) Heart, Breath, Mind: Train Your Heart to Conquer Stress and Achieve Success [Audiobook]. Houghton Mifflin Harcourt. https://www.audible.com/pd/Heart-Breath-Mind-Audiobook/0358172292