Heart Rate Variability: What You Need To Know

Each time our heart beats we live a little longer.

There isn’t a better measure of our overall mortality than heart health.  And there are few better indicators of heart health than heart rate variability (HRV).

Heart rate variability is the interval between heartbeats—the duration of the R–R interval—and how those intervals vary over time. If your heartbeats were doughnuts, then the interval between each beat would be the doughnut hole. Are each of these doughnut holes the same size? Or are some larger than others? Smaller? The measure of these ‘doughnut holes’, and how they compare in size to the ones that precede or follow them, is the measure of heart rate variability.

A variable heart rate is a normal, health response to changes in our bodies and environment including breathing, exercise, stress, blood flow, and any metabolic changes. The measure of HRV has emerged as a key tool to measure health and the viability of health interventions over time.

Pulse rates have been observed and studied since ancient Greece. In 1707 a “Physician’s Pulse Watch” was invented that could accurately measure changes in pulse. 1898 brought the electrocardiogram (ECG) which can measure fluctuations in milliseconds. In 1965 doctors discovered they could predict fetal distress by observing reduced changes in beat-to-beat variation, even before measurable changes in  heart rate occurred.

The digital revolution of the late 20th century expedited advances in the science of cardio measurement, culminating in today’s affordable wearable tech.  The advance of wearable tech has brought non-invasive measurement of heart rate variability into the home, into the gym. But what are the benefits of measuring HRV? What are the advantages and implications for health, well-being, and training peak athletic performance?

The reason we care about HRV is that the more responsive our heart is to changes in our environment the better equipped we are to survive.

It’s counterintuitive. One might think that the steadier the heartbeat and the more fixed the intervals,  the better off we are.  But HRV is an indicator of a flexible, resilient heart. A healthy heart at rest actually has greater variability.

How it works

Healthy people at rest have normal periodic variation in heartbeat intervals. Reduced HRV is a marker of reduced vagal activity and waning health.

Allostasis is our bodies’ response to stress and the method by which we return to balance or homeostasis. HRV is a marker of robust allostasis, our bodies’ ability to bounce back.

Over time, repeated stressors increase our allostatic load and can diminish our health.  Allostatic Load has been called the ‘wear and tear’ on the body over time.

What is normal?

How can we measure HRV, and when should we be worried?  What IS normal when it comes to our heart?  There is currently no standardized scale of normalcy for HRV.  And  as with resting heart rate (BPM) or blood pressure, demographics impact what’s ’normal’.

HRV also naturally decreases with age, perhaps a function of allostatic load or perhaps just a reflection of wear and tear. The resting heart (beats per minute) remains the same but HRV analysis shows diminished variability.

What affects HRV?

HRV is sensitive to acute stress, including daily work stress such as making complex decisions, or public speaking.  Daily worry, lingering impact of PTSD, medication all can decrease HRV. So can stress or illness.

The beauty of our bodies is that our most essential functions, breathing, heartbeat, blood flow, digestion, take no thought whatsoever. Our autonomic nervous system (ANS) controls our breathing, our heartbeat, our digestion, without our lifting a finger. NS  is comprised of two independent systems, the sympathetic nervous system (fight-or-flight response) and our parasympathetic nervous system which occurs at rest.  These two systems work together to help us attain homeostasis ( balance)  It’s an elaborately choreographed danced wherein each part of the whole functions, or malfunctions, together. HRV is a function of the parasympathetic system.

Even when our heart rate appears steady there can be considerable variance between each beat.

Consider two individuals each at rest with a heart rate of 60 beats per minute. They would appear of comparable health.  But an assessment of their HRV might show two very different stories.

Take two streams of equal breadth, each with ten rocks across it. The rocks are heartbeats. In stream A the rocks are equally spaced. In stream B the rocks are uneven. The first few rocks are close together. There’s a wider gap between rocks 3 and 4.  An especially large gap between 8 and 9.  Each stream has ten equal rocks, ten equal heartbeats. But the intervals between rocks vary.  Such is the measure of HRV. Although their heart rate per minute is the same, their contrasting HRV point to very different survival outcomes over time.

HRV measurement can be a significant tool in ongoing health and athletic performance. It has also been linked to better foods, reactions, and cognitive functions.  Changes in HRV can assess health interventions such as diet, exercise, sleep hygiene and biofeedback.

The Good News

Optimal HRV is associated with positive outcomes across all measures of health and well-being.

The benefits aren’t merely physical, but extend to executive functioning including attention, concentration, and working memory.

The good news? There are multiple research-based  interventions which can increase our HRV.

Can we increase or bolster our HRV?

The exact mechanisms of how exercise modifies HRV are unknown, but one needn’t understand the cause to get the benefit of the effect.

Exercise increased HRV in healthy people and regular exercise has been shown to slow aging and raise HRV, perhaps by increasing vagal tone.

Vagal tone impacts heart health and can be improved. Vagal health reduces resting heart rate, which decreases how hard the heart has to work how much oxygen is it has to use. HRV is one measure of vagal health.

Thought initially developed to assess cardio health, HRV is a burgeoning field of research. It’s implications have been studied across heart patients, schizophrenics, firefighters, soldiers, the concussed, elite athletes; HRV’s been used to quantify compassion and to determine if motor vehicle patient could survive an airlift to a trauma center.  HRV biofeedback is an emerging treatment for sports and military-related concussion. It’s also being used to study self-regulation and biobehavior, the relationship between biology and behavior. It’s being used to foster peak performance in athletes and modulate depression and anxiety.

Wearable tech doesn’t take the place of a health provider and we can’t carry a cardiologist in our pocket. But it can augment treatment between visits with a valuable tool to lead our best healthiest lives.

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