#193 - AMA #31： Heart rate variability (HRV), alcohol, sleep, and more
Episode Stats
Words per Minute
168.98405
Summary
In this episode, Dr. Bob Kaplan joins Dr. Atia to talk about heart rate variability (HRV) and the effects of alcohol on sleep. Dr. Kaplan discusses the importance of HRV and the role of ethanol in these phenomena.
Transcript
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hey everyone welcome to a sneak peek ask me anything or ama episode of the drive podcast
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i'm your host peter atia at the end of this short episode i'll explain how you can access
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the ama episodes in full along with a ton of other membership benefits we've created
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or you can learn more now by going to peter atia md.com forward slash subscribe so without further
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delay here's today's sneak peek of the ask me anything episode
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hey everyone welcome to ask me anything episode number 31 i'm joined once again by bob kaplan
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although as you'll learn at the end of this episode this will be the last time we're joined by bob
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kaplan but let's not get ahead of ourselves in today's episode we talk about really two things
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in detail one is hrv heart rate variability we've had so many questions on this subject for the past
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couple of years and we've just been slowly kind of collecting questions until we thought we had
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enough to do kind of one of our thematic shows on it and the second thing we talk about is ethanol
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all things related to ethanol so how does it affect hrv is really our segue but then also what are the
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effects of alcohol on sleep and we really go after mortality probably where we spend most of our time
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and we talk about it through the lens of all of the epidemiology as most of you or may some of you know
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there's a confusing body of literature out there that suggests that maybe some alcohol is good for
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you and no alcohol is not as good for you and so we go really deep on this subject matter so
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again if you have any questions about alcohol or if you drink at all and if you or if you don't drink
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and you're wondering if you should be drinking i think this episode will be very helpful for you
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so one thing i want to point out for this episode this episode was just due to some limitations of
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timing when we recorded this was not recorded in video so we will only be doing this in audio that
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might make the show notes a little more important although we didn't really have a lot of content here
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that necessitated being able to see so i think you're going to be fine listening to this in audio but
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obviously the show notes will have any of the graphs and other images that we talk about now if you're not a
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subscriber of course you can get a sneak peek of this as usual and then you'll have to obviously
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subscribe if you want to enjoy the full content so without further delay i hope you enjoy ama number 31
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hey bob how's it going today going well peter how are you it's good it's a little unusual today we're
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doing this a little bit on the old school tip no video today we're gonna have to be a little bit
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more descriptive in our terms since people can't watch our facial expressions although that somehow
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provided any value we won't do any screen sharing i think we can manage what do you have in store for
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us today so i aggregated a whole bunch of questions around hrv heart rate variability and alcohol many
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questions on both those topics i know this has been something you've been asking me about for a year
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when are we going to do one on hrv when are we going to do one on hrv so i think the answer is
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now all right we'll dive in first question seems relevant what is hrv and it's funny this is a tougher
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question to answer without an image but i'll do my best so as you pointed out a second ago hrv stands
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for heart rate variability and that's a pretty descriptive term because what it measures is the variation in
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time between heartbeats and that's measured in milliseconds so a thousand milliseconds is one
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second so if a person's heart is beating 60 times per minute you might say well there's a thousand
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milliseconds between every beat but it turns out that it's not really that way you see even if your
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heart is beating 60 times per minute or once per second between the first beat and the second beat
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it might be a thousand ten milliseconds and between that beat and the next beat it might be 960 milliseconds
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and between that beat and the beat thereafter it might be a thousand 27 milliseconds when you start
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looking at this thing at the level of thousandths of a second you realize that there is actually some
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variability if anybody has ever seen an ekg which i'm sure everybody has seen but maybe you haven't
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thought so much about what all the little squiggly lines mean without going into the details of what the
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p wave and the q r s and t waves mean i think most people will recognize that there is a very big
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spike for each of those beats and that's actually the r spike if you now measure the distance between
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the r's we call that the rr interval and you take the root mean square of the successive differences
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between the heartbeats so that means you calculate the time difference between each rr interval each of
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those values is squared so multiplied by itself then the result is averaged before the square root of
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the total is obtained so this is kind of a mathematical method for trying to approximate
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differences you get what's called the rmssd again if you just think about that in units you took
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something that was in milliseconds you squared it so it became milliseconds squared you added them all up
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it was still milliseconds squared you took the square root of it it's back to milliseconds so
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rmssd is reported in milliseconds if anybody's been paying attention to wearables a number of
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these things will calculate your heart rate variability typically while you're sleeping
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and you'll notice it gives you a number in milliseconds i think prior to the advent of wearables this
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was typically just done with an ekg or another sort of chest strap like device that was very accurately
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measuring the electrical activity of the heart the next question is probably why do we measure hrv so
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you talked about heart rate i think people would understand measuring heart rate and maybe why that
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matters why you might want to lower heart rate in general why do we measure hrv what does it tell us
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or what can it tell us possibly as i alluded to above the heart even when your heart rate is not changing
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and if you're at rest which is when we measure hrv so we don't really measure hrv
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when you're out and about moving around because just the movement itself that you're undergoing is
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going to change your heart rate so if i stand up from my desk and go and walk over to the kitchen and
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do something well that's going to increase my heart rate just because i stood up and if i'm exercising
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obviously my heart rate is changing quite a bit so this is really something that we care about when
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you're at rest but as i said there is variability between those beats and it turns out that that
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variability is heavily influenced by which of the autonomic nervous systems is most dominant so this
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probably warrants a slight detour so we have broadly broadly speaking two nervous systems we have one that
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is under our control and one that is not under our control and that's a very good thing if you want to
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reach for and grab a pencil or walk obviously that requires voluntary control you want to be in
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control of those nerves firing and making muscles do their thing but you certainly don't want to have
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to be thinking and consciously making things happen that need to happen constantly you certainly wouldn't
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want to have to think about breathing you certainly wouldn't want to have to think about your heart
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beating you certainly wouldn't want to have to think about digesting food you certainly wouldn't want to
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have to think about a lot of things that take place beneath the surface. So all of those things
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are regulated by this thing called the autonomic nervous system. We further divide this autonomic
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nervous system into two branches. One is called the sympathetic system and the other is called
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the parasympathetic system. The parasympathetic system, the way we would always learn to remember
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this in medical school was this was the rest and digest system. So this is the down-regulating
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system. It conserves energy. It aids in digestion. It slows heart rate. Our favorite little fact was
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it was responsible for erections, but not ejaculation. Ejaculation somehow came from the sympathetic
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system. So the sympathetic system, of course, is the fight or flight system. So it's making energy
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more available. It's dilating the pupils, right? It's getting you ready to see as much information
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as possible. It's slowing digestion and peristalsis, meaning it's slowing down anything that's not
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essential and it's increasing heart rate. Let's just think about what this looks like from a
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practical standpoint. If you're laying in bed and you hear a loud bang in your house, you have no
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idea if it's an intruder or if a picture fell off the wall, but you don't even have to worry about
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your brain isn't going to even force you to make that decision. It's going to make the decision for
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you, which is this is a threat. And so your heart rate's going to shoot up. Your pupils will dilate.
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Any amount of digestive energy going on right now will cease and your liver is going to start
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cranking out glucose and making you available for fight or flight. Okay. So what does this have to do
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with HRV? It turns out when the sympathetic system is revved up, HRV goes down. And when the
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parasympathetic system is in control, HRV goes up. And I think it's easy to think about this, right?
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As the heart rate speeds up, which is what's happening under sympathetic tone,
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there's less variability between the beats. When the heart rate slows down, when the body is
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relaxing, there's more variability between beats. I don't know if that's intuitive or not. I was
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thinking about that. If you have over the course of a minute and your beats per minute is say,
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you're, I don't know, Lance Armstrong when he's at the height of his powers. I don't even know what
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that is. Yeah, probably 30 beats per minute. Yeah. 30. And then you've got somebody else who
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has a hundred beats per minute, just the R, R intervals, whatever you call it. There's just
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less time between them. Intuitively, I would think there would be less room for variation between
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each beat. If that makes sense. Yeah. I mean, I don't know how strong the correlation is between
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resting heart rate and HRV. It's almost undoubtedly positive, but I don't know what the R squared is
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on that. Is that a fair explanation, Bob? Does that make sense on why we would care about HRV?
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Yes, I think so. As a knock on to that, when you get your HRV output, if it's high or low,
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what is that telling us? Or how does that inform us? What do we do with that information?
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