Heart Rate Variability
What is HRV?
- HRV stands for heart rate variability
- HRV measures the variation in time between heartbeats, and that’s measured in milliseconds (1,000 milliseconds is one second)
- So if a person’s heart is beating 60 times per minute, you think there’s 1,000 milliseconds between every beat…but it turns out that it’s not really the case
- Even if your heart is beating 60 times per minute (i.e., once per second) between the first beat and the second beat, it might be 1,010 milliseconds
- And between that second beat and the third beat, it might be 960 milliseconds
- And between that beat and the beat thereafter, it might be 1,027 milliseconds.
- In other words, there is actually some variability
- If you has ever seen an EKG, you will recognize that there is a very big spike for each of those beats (known as the spike in the R wave)
- If you now measure the distance between the Rs—the RR interval—and you take the RMSSD (The Root Mean Square of Successive Differences between normal heartbeats)…that means you calculate the time difference between each RR interval
- The RMSSD is obtained by first calculating each successive time difference between heartbeats (RR intervals) in ms.
- Then, each of the values is squared and the result is averaged before the square root of the total is obtained.
- So RMSSD is reported in milliseconds
- If using wearables that calculate HRV while you’re sleeping, you’ll notice it gives you a number in milliseconds
What can it tell us, possibly?
- HRV provides a snapshot into how your body is balancing between the two branches of your autonomic nervous system: sympathetic (“fight-or-flight”), and parasympathetic (“rest-and-digest”).
- The heart is not a metronome – it’s actually erratic
- A healthy nervous system has a balanced but strong push and pull between Sympathetic and Parasympathetic causing high Heart Rate Variability
- It turns out that that variability is heavily influenced by which of the autonomic nervous systems is most dominant
What is the autonomic system, and what’s the difference between sympathetic and parasympathetic?
- The Autonomic system handles the unconscious processes (and even effects conscious behavior)
- Autonomic contains two branches – the Parasympathetic and the Sympathetic
Sympathetic is activated in times of stress
- Fight or Flight
- Sacrifice long term to get through the short term
- Flood energy, dilate pupils, slow digestion/peristalsis, increase heart rate
- It’s slowing digestion and peristalsis, meaning it’s slowing down anything that’s not essential, and it’s increasing heart rate
Parasympathetic is activated in times of recovery
- Rest and digest
- Conserves energy, constricts pupils, aids digestion, slows heart rate
What does this have to do with HRV?
- when the sympathetic system is revved up, HRV goes down
- when the parasympathetic system is in control HRV goes up
- As the heart rate speeds up, which is what’s happening under sympathetic tone, there’s less variability between the beats
- When the heart rate slows down, when the body is relaxing, there’s more variability between beats.
- High HRV means you’re getting both strong “on” and “off” outputs and your body is highly responsive to your environment. It can quickly shift its energy from “fight or flight” to “rest and digest” to easily match its surroundings.
- Low HRV is sympathetic dominant and means the body is under some form of stress.
NOTE: comparing your HRV to another person’s HRV might not be the most helpful thing in the world, but knowing how your HRV, your heart rate, your respiratory rate, your body temperature change over time, and assimilating all of that data is probably a more useful biomarker.
Factors that lower HRV
- Alcohol – I’ve never seen anything that lowers my HRV as much as alcohol does.
- stress
- when you go to bed and you’re stressed out
- Smoking
- lack of physical activity
- lousy diet
- caffeine consumption in the evening
- high blood pressure
- high triglycerides
- metabolic syndrome
- apparently even air pollution can lower a person’s HRV
Things that raise HRV
- endurance exercise
- yoga
- meditation
- Biofeedback
- Good sleep hygiene
The Gold standard in measuring HRV is EKG but now a days many wearables also show your HRV.
What’s a good HRV?
Science still does not have a specific answer to this. HRV declines with age so whenever you talk about HRV, you have to talk about it in the context of age.
Middle 50% of HRV by age
You’ll notice it’s actually quite a steep drop with age. The most important thing to be thinking about is how do you stack up to yourself over time. Don’t compare your HRV to others.
(Excerpts from Peter Attias Podcast )s
