Heart rate variability (HRV) is everywhere. This is because it is nowadays so easy to measure in non-invasive ways via the personal self-optimisation devices (aka wearables). But just because something is available does not make it useful, does it?

So what is HRV good for? More particularly, when it comes to emotional wellbeing, how much of it is real deal and how much is hype?

The evidence is mounting to show that we are more resilient – physically and emotionally – when HRV amplitudes are higher and more complex.

HRV is a reflection of complex processes and all manners of biological systems influence HRV in complex ways. For example, the immune system changes affect HRV and when we have a flu or have another inflammatory condition the HRV is suppressed by the cytokines.

But to answer the question of the relationship between HRV and emotional and psychological resilience and stress, I’ve got to cover the basics first so that we know what we are talking about.

Because answering my initial question in one go would make this piece intractable, I am making it a two-parter:

• Part 1: HRV and RSA ( ResHRV) definitions and basic mechanisms of ANS control and impact of breathing patterns

• Part 2: HRV and psychosocial stress, emotion and resilience

In this piece I will:

1. Define HRV

2. Recap of the basic concepts and principles of the ANS

3. Explain how the ResHRV (RSA) is the main component of HRV

4. Look at the mechanism of ANS cardiac control

5. Why and how changing breathing pace and pattern influences HRV

6. Is HRV a measure of the total vagal tone?

7. Is HRV a reflection of the sympathetic and parasympathetic balance?

All of this is extremely pertinent not only for those of you interested in understanding HRV but also those who are interested in use of ANS in psychotherapy and gaining a better insight into what we know and what we don’t know about the complex web of influence of the inter-dynamics of the sympathetic and parasympathetic systems on our emotional wellbeing.

In this piece, I do not discuss the difficulty and the many levels of approximation and heuristics that come with using HRV measures obtained through the commercially available wearables and the short term measurements that those usually provide. It is a minefield and I would love to see it discussed by another author expertly.

Note on Epistemic Humility

Right off the bat, let’s start with a healthy dose of epistemic humility:

Ok, so now we established that, let’s see what, at my level of understanding, we actually can know.

HRV

“A healthy heart is not a metronome”. Heart rate is variable, from one heartbeat to another. In other words, the time interval between two heart beats is not equal and depends on many things - breathing, physical effort, emotional state, health status, circadian rhythm, to name just a few. In a nutshell, heart rate variability (HRV) is the measure of the variability of the interval between two heartbeats.

Terms and definitions to know before we continue:

• Heart rate: the average number of heartbeats in a minute ( optimal range between 60 to 80)

• R-R interval: the between two consecutive R-waves in an electrocardiogram (ECG) signal (peaks in the graph below)

• HRV: beat-to-beat variations of heart rate or the heart period (R-R interval)

  

If we use the graph above as illustration, first beat-to-beat interval is 859ms, second is 793ms and the third is 726ms, the HRV between the second and the first interval is 66ms and between the third and the second is 33ms.

More about this later, but HRV is calculated as an average over a certain amount of time - it can be over a 24h, or 5 min or shorter (ultra-short term). 24 h HRV recordings represent the “gold standard” because they can account for all the fluctuations in metabolism and activity that happen over 24h cycle.

But what causes these fluctuations in heart rate and why should you care?

It turns out that a major contributor to the HRV is in fact another process with a well known acronym: the respiratory sinus arrhythmia or the RSA.

What Is ResHRV (aka RSA)?

You might have heard about RSA? We have seen it a lot in relation to Polyvagal theory, as some crucial claims of the theory pertain to the purported properties of the RSA.

It stands for respiratory sinus arrhythmia (RSA). RSA has been recently been renamed ResHRV (respiratory heart rate variability) - see below.

HRV and RSA are not the same but the terms are often used interchangeably.

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Here, I will go into little nitty gritty of the neurobiology of stress and autonomic nervous system (ANS) responses such as the fight-or-flight and freeze. Not too little, not too much, but just right for psychotherapists.

Additionally, I am sharing some of my essential reads and I touch on a recent critical reappraisal of the idea of the ANS response itself.

In this post I will share:

• Basics of how stress response is enacted in the body (sympathoadrenal and HPA axis)

• Beyond buzzwords: definitions, differences, overlaps and hierarchy between different ANS responses (e.g freeze, fight-or-flight, tonic immobility, tend-and-befriend)

• Why fawn is not an ANS response

• Is framing and conceptualization of ANS response to stress fundamentally outdated? A critical perspective in the light of new brain paradigms.

• References around the fundamentals of neurobiology of stress (including impact on wellbeing)

• References around classic ANS responses

• References tend-and-befriend hypothesis

OK, let’s start with what is stress response and what are the two major brain/body pathways for enacting it.

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I speak an awful lot about the need for a body of evidence in order to accept something as bona fide neuroscience in psychotherapy, don’t I? So what, then, is the body of evidence that links autonomic nervous system functioning and regulation to psychotherapy? Today I am sharing my treasure chest of references on all things ANS and mental health.

The list is not exhaustive, and I will be updating it over time. It covers references around:

• Autonomic nervous system (ANS) basics

• ANS and mental health

• ANS and trauma (and ACEs)

• ANS and emotional regulation

• On measures of ANS activity

• Breathwork/mindfulness effects on ANS

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