[00:00:00] Speaker A: Welcome to the Heart Rate Variability Podcast. Each week we talk about heart rate variability and how it can be used to improve your overall health and wellness.
Please consider the information in this podcast for your informational use and not medical advice. Please see your medical provider to apply any of the strategies outlined in this episode. Heart Rate Variability Podcast is a production of Optimal LLC and Optimal HRV. Check us out at optimalhrv.com Please enjoy the show. All right, welcome friends to Heart Rate Variability Podcast. I am Matt Bennett, back here with my good friend, HRV nerd and favorite podcast guest, Dr. Ina Hazan. Dr. Ina Hazan, welcome back to the show.
It's great to see you again. I'm excited to nerd out with you a little bit about low frequency heart rate variability.
[00:00:51] Speaker B: Thanks so much for having me back, Matt. Always a pleasure.
[00:00:55] Speaker A: Awesome. And if you're new to the podcast, you'll also see this week in HRV episodes hitting on Tuesday.
We throw in these interviews every once in a while, but I'm excited to get back to this format as well. So we want to focus just on what is my favorite HRV biometric. And I know it's at least near and dear to your heart as well, low frequency. So, you know, I would love to kind of slow walk us up to really understanding the power of low frequency and why we focus on it for HRV biofeedback. What's it tell us about our autonomic nervous system?
But one of the things that I get and hear from people is I still don't really understand what a frequency domain is. And so let's kind of slow walk me and everybody else up to what are we talking about when we're talking about a frequency domain. A little bit more complicated, I think for a lot of folks than maybe, hey, we're measuring over a specific period of time, which is the time domain.
Let's again slow walk up to what is a frequency domain and then we can talk about what specific, specifically low frequency is.
[00:02:13] Speaker B: Sure thing.
It is not an intuitive concept for.
[00:02:19] Speaker A: Sure, which makes all of us feel a little bit better right off the bat.
[00:02:27] Speaker B: Okay, so your heart rate signal, we think of it as one signal. If we look at an ekg, there is like one line, or you know, a medical EKG has a bunch of lines, but it's one line.
So we think of it as one signal. But in reality, the heart rate signal is actually composed of a bunch of different frequency of a bunch of different signals, each one having a different frequency.
So that you can think of as Just like looking at white light. Right. If you look at white light, it looks like white light. Right. And that's it. But we know that in reality, white light is composed of a bunch of different color frequencies mixed up together.
So if we take a prism and look at white light through that prism, you will see the seven colors of the rainbow. The prism would break down that white light into the blue and the orange and the purple and the yellow and the red, et cetera, et cetera, even though without the prism, we just see the white light. But there is a lot more that we don't see with the naked eye. The same thing is happening with your heart rate signal. If you just look at an EKG tracing, if you just look at the BBP tracing, which is what you're seeing on, you know, on most of your HRV biofeedback screens, it's just one line.
But again, in reality, what we don't see with the naked eye is that the heart rate signal is composed of a bunch of different signals, each one at a different frequency. And the reason that's important is because we have these ranges of frequencies that are attributed to different parts of the nervous system. We know where they come from, we know what they mean, we know how to interpret them, we know what to do with them, how to train them.
Is that a good place to start?
[00:04:17] Speaker A: Yeah. So I guess just to again, keep us slow walking up, up to the definition so we're, we can take a heartbeat and separate that out. Are we breaking down different parts of the ekg? Is it like, where do these frequencies sort of come from that we're kind of getting in a beats per minute sort of data set?
[00:04:50] Speaker B: Okay, good question. So you need to have at least a minute, at least a minute of data. If you have one heartbeat that tells you absolutely nothing. You need to have a bunch of consecutive heartbeats. You need to have a bunch of interbeat intervals in order to be able to determine frequencies. Because a frequency is a signal that's continuously running.
For that, you have to have enough data.
So our fast Fourier transform algorithm, which is the one that breaks down your heart rate signal into these component frequencies, works by first gathering at least a minute's worth of data. So there's going to be a lot of intermediate intervals in that original initial data set, and that's going to keep running and analyzing minute by minute. Right. So in that moving a long way, it's going to start incorporating new data into it.
But it's always going to be working with a bunch of Data, Right. Just one or two or three intermediate intervals will not tell us anything about the frequency of any particular signal.
So once we have that minute of data, then the fast forward transform can look at how is this signal showing up?
It's looking at the intermediate interval. It's almost like building a histogram.
How much of this kind of interbit interval we have and how many of these and how many it's creating almost like a curve and then it's actually calculating area under the curve. So if you are, if you want to think back to your calculus times, if it's not giving you hives, I mean, it's calculating area under the curve and looking at how much of that area is due to the high frequency signal, how much of that area is it? So is in the high frequency range, right? How much of the area is in the high frequency range? How much of the area is in the low frequency range? How much of the area under that curve is in the very low frequency range? Right. And it's going to give you a number, I don't know, 600 milliseconds squared, right?
So that tells you how much like what is the power? That 600 millisecond square is the power of that signal in that frequency range.
[00:07:22] Speaker A: Okay, so we got that.
It's so like, is like we, we talk a lot about high frequency, low frequency also. There's very low frequency and ultra low frequency and who knows what else lies out there in the universe.
So what are we like talking about is, are you either in high frequency or low frequency?
You know, are we major, are you always in a little bit of high frequency and a little bit of low frequency? Like, how does all this kind of come together and what, what are they sort of telling us about our autonomic nervous system?
[00:08:06] Speaker B: So all three of these frequency frequency ranges are really important.
Let me also add a caveat. There is an ultra low frequency, just so we're aware, we don't use it in biofeedback because that signal is so slow that it requires at least 24 hours of data to do anything with. So we're not going to get into the ultra low frequency. But. But it exists. Just so you know, we primarily in biofeedback deal with high frequency, low frequency, very low frequency, and we need all of these, right? So when we are just walking around going about our day, we want that signal to be mixed up and distributed among all three of these frequencies. We don't want to walk around in any one where most of our signal is in any one of these frequencies, we want to have a healthy distribution, distribution of all, because they're all important.
They're all signals of important function of your nervous system. So we really don't want to eliminate any of them when we are purely at rest. Right. You know, just kind of, you know, kind of chilling, you know, with not a whole lot going on. We want to be dominant in the high frequency, which is the signal that is indicative of the vagal tone or the parasympathetic nervous system, nervous system activity.
So, you know, most of our daily activities, you know, we do want to have more high frequency power than any of the others, but we still want the other two as well. Right? We don't want to eliminate them. We don't want just high frequency. We want all three to be present and the distribution is going to fluctuate throughout the day depending on what's happening.
[00:09:51] Speaker A: So high frequency, if I get this right, please correct me if I'm wrong. You know, sort of seems to trend and I won't, unless we can use the word, you know, stronger than trend. I'll let you tell me that with RMSSD and SDNN for those time domains, for the most part. So are we measuring similar things when we see like high frequency and rmssd? I know when I look at my charts, they usually trend together.
Am I correct in making that, that assumption?
[00:10:26] Speaker B: They are generally. Yes, they're not exactly the same thing, but so high frequency power is almost prime, almost, almost exclusively the vagal nerve function, the parasympathetic rmssd, which is a time domain measure, it is considered a general measure of all autonomic nervous system functioning, but it does skew towards the vagal nerve.
That's why you see them trending together. Yes, RMSSD does tell us a bit more about vagal functioning than any other part of nervous system.
Sdnn, for example, which is another time domain measurement, is much more general. It takes everything into consideration about equally.
So it does not skew towards the Vegas. So there it's not going to trend as much with a high frequency. But because RMSSD is skewed more towards vagal function, it will trend more with a high frequency power.
[00:11:29] Speaker A: Excellent. So we got a definite working definition of high frequency.
So let's move down to low frequency. So I'd love to compare and contrast the two of them, you know, what are we talking about? You know, because everything I've learned about heart rate variability, that that vagal break, the vagal tone is really so powerful in our overall health and wellness so when we shift to low frequency, what are we looking at there specifically?
[00:11:59] Speaker B: So low frequency power is an indicator of the two main sources of heart rate variability.
At low frequency we're looking at the baroreflex, which is your autonomic nervous system's ability to regulate blood pressure, it's a blood pressure regulatory system.
And the vagus, it's the parasympathetic influences.
When your heart rate signal is concentrated in the low frequency range, you are maximizing the activity of the two main sources of heart variability, the baroreflex and the vagus.
Which is why we use low frequency power for biofeedback training, for hrv. Biofeedback training. Right, because that's the frequency where we're maximizing the two main sources of hrv.
So you know, this is a really good place to exercise those two, they get stronger, right? So this, if you do get 20 minutes a day of breathing, shifting your signal into the low frequency range, you do that through resonance frequency breathing, right? So when you do your breathing 20 minutes a day, you're exercising the two main sources of HRV, they're getting stronger. And then when you get over time, as you get back to normal breathing, your HRV starts increasing, right? So if you've been doing your 20 minutes a day of breathing for say four, six, eight weeks, your daily HRV at normal breathing is going to start trending up because you've exercised that self regulatory muscle, right? So this is very much akin to going to the gym, right? When you go to the gym and you lift some dumbbells and swing some kettlebells, you know you are do some squats and some planks, etc, whatever you're gonna do, you are strengthening your muscles, right? Um, and then you know, you might not notice a big change in your muscle strength after any one workout. But if you've been working out for a couple of months, you will notice that change, right? So if you know after a couple of months of working out, a friend asks you to help them move a couch, you'll notice that it's a lot easier to lift that couch than it would have been a couple months earlier, right? That's because you've been strengthening those like your literal muscles and now it's easier to lift heavy things.
With HIV biofeedback, you're exercising the proverbial muscle, although heart is a muscle, so technically you're also exercising a muscle, but you are exercising the primary sources of heart rate variability. So then a couple months down the road, when you encounter a Stressful situation, you might notice that it's just easier to respond to that situation in a healthier way because your self regulatory mechanism is better and you know, more ready to help you do that.
[00:14:55] Speaker A: I love that. So I guess you know, is like why then? I guess question would be so high frequency will drop, I think, and correct me if I'm wrong, during HRV biofeedback, low frequency goes up. So if high frequency is measuring vagal tone, are we through like resonance frequency, breathing practice, kind of pulling the vagal break off or why are those two things?
Like I would think just logically they would both kind of spike during training sections, but obviously that's not what we see happening.
[00:15:40] Speaker B: Really, really good question.
So the frequency range for the vagal tone is, spans a wider, it's a wider range. It actually falls into the low frequency and then all the way into the high frequency.
[00:15:54] Speaker A: Okay.
[00:15:55] Speaker B: But it is also very breathing dependent. Right? So it's not just the frequency of the vagal tone. It, where that frequency lies is very much breath dependent. So when you're breathing at a normal breathing rate of say, you know, 11 breaths a minute or higher, most of your vagal tone is going to be reflected in the high frequency range. There's still going to be a little bit in the low frequency, but most of it at normal breathing rate is going to be in the high frequency range.
But then as you slow down your breathing, that shifts the vagal tone power into the low frequency range where the baroreflex resides as well. All right, so this is where you're going to exercise both of them together.
[00:16:44] Speaker A: Okay, so next question is how you describe low frequency. I think the natural thing for obsessive people like myself is, well, it sounds so amazing. I should breathe in that all the time, right? Or I want to like, you know, be in low frequency because I got all these systems synced up. You know, obviously if I want big biceps, I'm not going to do curls for 24, seven. But what, what would, why wouldn't I want to breathe in low frequency for two, three hours a day? So like just as an example, because.
[00:17:23] Speaker B: When you are in the low, when you are shifting your, your breath into, well, a resonance frequency and maximizing your low frequency power, you are greatly reducing the high frequency and the very low frequency activity. They are, they don't disappear, but they're very, they're barely there, right.
And, but, but we really do need them, right. So we don't want to suppress them for too long. So when you do 20 minutes a day or 20 minutes twice a day if you're so motivated.
First of all, that is sufficient. That is sufficient to train your nervous system. That is sufficient to give your vagal nerve that bit of extra oomph over time to help you self regulate better and better.
So there is no need to keep doing that. You can overdo it. Just like you can overdo it with exercise, you can overdo it with this. So you don't want to be suppressing the high frequency and the very low frequency power for too long because there are other mechanisms involved here that you don't want to be eliminating from your.
[00:18:33] Speaker A: Everyday functioning and being in high frequency during. Well, I don't know, Performance is a. But let's just say at work after this I have to go return some emails and do some website edits, stuff like that. That's where I really want. High frequency is going to be probably where I want to be to perform at my best on, on task. I don't want to say performance overall because if you're in an athletic performance, I'm assuming that, you know, you're going to get more sympathetic energy. Hey, HRV is going to track. So you know, I want to kind of perform in high frequency with that and train at low frequency. Am I, am I close to right with that?
[00:19:20] Speaker B: Yes. So through training, so through doing your 20 minutes a day, when you maximize your low frequency, what will happen when you are sitting at your computer working on the website, you are going to increase your high frequency power.
We do want to be careful. Most of what we get from the HRE distribution is parasympathetic. There is not a lot of actually sympathetic activity that we're capturing, especially in those shorter recordings.
You know, that may be a conversation for, for, for another time.
But when you are, you know, let's say you're working on your website and then you realize that, you know, you gotta run to the post office because it's about to close and you need to mail, you know, a reader to somebody.
There you go.
What you're getting is you will get a spike in the very low frequency.
Your high frequency will decrease, you'll get a spike in the very low frequency and that is prim due to vagal withdrawal.
[00:20:25] Speaker A: Oh, interesting.
[00:20:26] Speaker B: Right. So in order for your activity level to go up, the vagus has to take its foot off the brake.
[00:20:31] Speaker A: Okay.
[00:20:32] Speaker B: It has to allow the activation to go up. So that's why you'll see a decrease in high frequency and increase in very low frequency. It's a Vagal withdrawal.
[00:20:42] Speaker A: So with normal breathing, increased low frequency is a sign of a demand on you, you know, stress, one way of good stress, bad stress. But you'll see that elevated low frequency when I need to get off my butt and run to the post office to mail a reader or something like that, that's we're getting, I don't know, does the like break going off? I know the sympathetic's just there. So sympathetic activations, the wrong way to use, but you get more of that, that sympathetic energy as measured by low frequency when you're not doing resonance frequency breathing.
[00:21:24] Speaker B: Well, low frequency does not measure sympathetic activity at all.
This is the really confusing part. It's also contradictory. What you'll find in the literature is up until maybe 10 years ago, literature predominantly considered low frequency to be a balance between sympathetic and parasympathetic.
All right? So if you're reading all the research, you're going to see that everywhere or.
[00:21:50] Speaker A: Three articles I read last week that are still kind of getting it wrong.
[00:21:53] Speaker B: Well, yeah, so that's the thing. Yes. So a lot of the newer research is still citing the older research, Right. Or the older articles.
What we know, you know, in the last 10, 12 years, and there's a number of papers on this, so I'm, I'm quite convinced that low frequency has no sympathetic input at all. It is the baroreflux and parasympathetic, and that's it.
So what you might be seeing, you know, is, you know, if you are more activated, right? You're not, you may not be seeing sympathetic activation, but you're seeing, you know, you're seeing activation.
So if the low frequency goes up in these situations, it's simply happening because you're getting vagal withdrawal, right? So vagal engagement decreases. So your high frequency is going to go down and your very low frequency might go up just a bit, might not be going up a ton.
And it just because those two.
Because the vagal withdrawal is happening, so high frequency is decreasing. You'll just see the low frequency rising because high frequency is decreasing.
[00:23:01] Speaker A: Interesting.
[00:23:02] Speaker B: Okay, so I would be careful in interpreting low frequency at normal breathing.
The fact that low frequency might be higher normal breathing may not be a problem in and of itself. It's just that it usually happens because high frequency is low and that may be a problem.
[00:23:20] Speaker A: Okay, so that, that makes a lot of sense. So just that the high frequency is less dominant in a way. So we'll see maybe an increase in low frequency, but, you know, a different sort of increase than we See during residence frequency, intentional increasing of low frequency.
[00:23:39] Speaker B: Exactly, exactly. So breathing rate matters, the context matters. Plus, you know, a lot of our displays are percentage based, right? So if you have less, if the, if your vagus is withdrawing, if it's taking its foot off the brake to allow more activation to go up, like to activate. To allow activation to go up, percentage wise, you're going to have a lot less high frequency.
So low frequency becomes higher percentage wise. It may not even be changing much. It's just now taking up more of the space because less of that area under the curve is due to high frequency. So your low frequency is gonna. Low frequency percentage is gonna go up.
[00:24:20] Speaker A: Gonna go up.
You'll see low frequency slash high frequency as a now outdated metric that you still see peaking out.
[00:24:31] Speaker B: Yeah, the LFHF ratio is problematic.
It does not tell us what we used to think. It tells us. Right. It does not. It's not a sympath of vagal balance measure that we used to think it is.
[00:24:47] Speaker A: Okay. Because you still see that. Like I said, I think I saw three in three articles last week. So that still is sort of an artifact of the field, so to speak. Because yeah, you Google it and that becomes, you know, ChatGPT wants to throw it in everything as well, I find. Which is an interesting phenomena that I'd say us HRV nerds need to be careful about if we're using AI because AI loves that ratio for whatever reason.
[00:25:16] Speaker B: It's sometimes it's the only. Some papers report only on that ratio. It's the only HRV variable they're looking at, which is very sad.
Yeah.
[00:25:25] Speaker A: So real quick because I got a couple questions. I want to make sure we get to anything we need to say about very low frequency in this. I see it as kind of like the third stepchild. We don't really care that much about it, but should we, do we need to care about it? Is it telling us anything?
[00:25:42] Speaker B: It is actually very important in our short term biofeedback recordings. It doesn't tell us a ton. Only because very low frequency means it's slow.
So if we have a short term recording, we're not getting a ton of data.
Doesn't mean it's not important.
Especially if somebody's getting like a 24 hour recording. If they are wearing a hole to monitor and their cardiologist is monitoring. Right. That very low frequency measurements are very important. We want them there, we need them there. If they're suppressed, it's a problem. Right. It's like, you know, we do need to have some very low frequency. We don't want to be very low frequency dominant, right, for long periods of time.
But we do need a healthy very low frequency in a normal state. Very low frequency is going to be the lowest of the three power wise, right? Just for daily activities.
But we do need it. It's there for a good reason.
Now the reason we don't attempt to it as much in biofeedback is because again, our recordings are short, we don't see it as much. But fluctuations in very low frequency can be meaningful moment to moment.
You know, when we get vagal withdrawal, that's going to manifest in increase in very low frequency nerve taking its foot off the brake, allowing activation to go up, right? So when that's happening in a healthy way, right, let's say you suddenly realize I need to run to that post office, right?
Hurry, hurry, hurry, hurry. The vagal nerve needs to quickly take its foot off the brake and allow activation to go up. So you can make it.
So you'll see a decrease in high frequency and a rise in very low frequency. And that's good and healthy and that's how it should be.
If on the other hand, at rest, that's what's happening. The high frequency power is low and very low frequency power is high. And that's addressed when they're not doing anything in particular. That's a problem that means that the vagus is not strong enough to regulate on a daily basis. That made me and you know, it's not a diagnostic tool, but you know, you know, I do see this frequently with folks who have chronic anxiety, chronic pain, you know, things like that.
Be careful. This is not a diagnostic tool. I'm just talking about correlations and associations.
But that's not a healthy state to be in all the time.
Great.
[00:28:06] Speaker A: All right, so a couple of questions to wrap us up here. So, and these are a little bit more optimal HRV specific, but they're, they're questions we get from users sometimes. So we've got the, the optimal zone scale which you know, as I tell people, again, correct me here, I think I'm aligned with everything we've said. It's out of the last 60 seconds. How many of those, what percentage of time did you spend low frequency dominant.
I think I'm using the word dominant there, but in low frequency with that. And so it gives you a really great scale and it's been just a game changer. Like as I like to say, using your gym analogy, that that low frequency scale is like not only just going to the gym but doing it on steroids because I feel like I'm just healthy steroids. Healthy steroids? Yes. The kind with no side effects. Maybe creatine is a better example.
[00:28:59] Speaker B: There you go. Yeah.
[00:29:01] Speaker A: Nowadays sometimes there there's a phenomenon that I know I'm not. The only one that that's seen is one. Is there any relationship between low frequency and max min? Because it's another number that we give post biofeedback session and sometimes we'll see our max min numbers maybe even be below the average where we've spent almost all of our time in low frequency during the practice. So are those two connected in any way? Like I find when I really give a good exhale I can see max min coming up. But it's sometimes doesn't really impact my ability to stay in optimal zone or low frequency during the practice.
[00:29:47] Speaker B: They are related but it's not a one to one correlation as you just described.
So max min is very strongly vaguely influenced.
Not barore reflex, it's vagal.
It is a very good indicator of being in your resonance frequency breathing rate. It is a very good indicator of are you training your vagus to to get stronger.
So that's why we do look at max min during HRV biofeedback exercises.
Now you might sometimes see this discrepancy where your optimal zone meaning that your low frequency power is 80% of your heart rate signal or more. Right. So it's not just dominant but like really dominant. Right. 80% of your heart rate signal or more is in the low frequency range.
But max min is a little lower than typical. That's happening because we're looking at low frequency in that situation as percentage.
What you will see much better correlation with is absolute power of low frequency and max min. Right. So max minus a percentage wise percentage base is just a number on a day. Let's say you're having a day when your HRV is just a little lower. You know you didn't sleep as well, your jet lag, the other ton going on your HRV is generally just a little lower.
So your absolute numbers during your biofeedback training are going to be lower. So your total power of low frequency, absolute power blow frequency is going to be lower. Max min is going to be lower than your than typical. They'll still go up compared to where you are at baseline that day.
Right. But they'll be lower than typical. But you, but percentage wise you can spend, you know you can be 100% on the optimal Zone. That's because you're looking at percentages, not absolute numbers.
[00:31:44] Speaker A: Because that was my second question is I do see the max min number and the total low frequency, that big number. We give those trend together.
I'm not gonna say perfectly because I'd have to do a lot of math to come to that conclusion, but that I can have a really. And it's for me. And maybe again we have to always.
This could just be a math thing like when I'm tired, but I still can have enough focus to get into low, like, you know, 80% of my time in, you know, the optimal zone, I can see my total power low frequency, my max min actually be lower than my average. So that would explain both those phenomena that people often can confuse people because, well, why am I above my average for optimal zone time but below my average for these two things? And that's. We're just measuring kind of different aspects and ideally, I guess we'd want to be above our average on all three.
But still getting that time in training in optimal zone, you know, is, is the best thing to, to pay attention to.
[00:32:52] Speaker B: Exactly right. So the optimal zone just tells you kind of like about the efficiency of your practice.
[00:32:58] Speaker A: Yes.
[00:32:59] Speaker B: And you can, you can be very efficient on days when you have very high hrv. So your low frequency and maximum are going to be high during training. Just like, you know, you had high RMSSD in the morning, you're likely to have higher low frequency and max min during your training times.
And you can have very high optimal zone or maybe not. Right. You might have high RMSSD in the morning.
And so your HRV is doing well. So you'll have higher than, you know, higher than typical low frequency and max min. But your optimal zone may not be as high because you might be just a little bit distracted during that time.
That's possible too.
They are measuring slightly different aspects and that's why we give you all of that information because it's important and gives you slightly different information on the days when you're waking up with lower rmssd.
Your low frequency and maximin might be lower than typical during a training, but you might be able to get really focused and really into the training and be at a very high optimal zone.
[00:34:11] Speaker A: I can't believe you ran this masterclass in a half hour. So my friend, thank you so much.
I've been on a five year journey to fully understand this. I will listen to this episode probably 20 times to get some of your wisdom into these synapses in my own head. But I appreciate this because I think, you know, a lot of times we'll just throw around heart rate variability and we can get in trouble if we don't know what we're really talking about. And, you know, I think part of the struggle is we really have to have these conversations to understand what these metrics and what these numbers are really telling us. And I just appreciate you to, I think, answer a lot of questions.
Not only the users of optimal HRV have, but one of the things I try to get a lot is what is low frequency? And you know, it is. I get to sit at the feet of some of the most brilliant people in this field and it's still a really complicated thing to come to an answer to. So I thank you for your time today and walking us through this and, you know, helping us all interpret our scores and get the most out of our biofeedback practice.
[00:35:19] Speaker B: This Always a pleasure to talk about this. It's fun.
[00:35:23] Speaker A: And as always, you can find show notes and everything
[email protected] and again, if you haven't listened to the this Week in HRV episodes, highly encourage you to do so.
It has been a we, we do a deep dive into research and news around heart rate variability and I think you will enjoy it as much as I do. So everybody have a great week. Ena, thanks so much. Always a pleasure, my friend.
