[HN Gopher] Heart rate variability differs between smartwatch an...
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Heart rate variability differs between smartwatch and clinical
testing
Author : zdw
Score : 99 points
Date : 2024-10-10 01:05 UTC (3 days ago)
(HTM) web link (wvutoday.wvu.edu)
(TXT) w3m dump (wvutoday.wvu.edu)
| naveen99 wrote:
| Heart rate variability is just normal sinus arrhythmia that
| varies with inspiration and expiration. The relative variation is
| higher with a lower heart rate... I don't think there is any
| independent information in it aside from lower heart rate in
| endurance athletes...
| l33t7332273 wrote:
| > Researchers found the method Apple uses, standard deviation of
| normal-to-normal, or SDNN, is the most accurate. Other brands
| implement a system called root mean square standard deviation,
| RMSSD, which Tenan said produces a wider range of error in the
| measurement
|
| This is interesting for a couple of reasons. Firstly, I have one
| so it's cool to know Apple designed it well in that respect, and
| that I shouldn't lose confidence in the readings I get.
|
| The second reason it's interesting is that this kind of decision,
| which time-domain measure of heart rate variability metric to
| use, is the kind of super small design decision that really makes
| a system special.
|
| Having really good developers and designers really shines through
| for moments like these.
| raverbashing wrote:
| That's an interesting assessment
|
| I was curious about this and curious if the measurements made
| by my smart watch were "good" or "bad", and it does calculate
| RMSSD (allegedly)
|
| Though it seems while they have some correlation they're all
| over the place https://www.researchgate.net/figure/Scatterplot-
| for-SDNN-A-B...
|
| SDNN also might apply to a different time range than RMSSD
| drilbo wrote:
| As pointed out by someone further down the thread, the value
| of HRV really only seems to appear in comparing to your own
| baseline.
| yourabstraction wrote:
| Just got the latest Apple Watch, so also glad to hear they
| perform better on HRV. It seems they get a lot of the little
| details better than competitors in the wearables space. I read
| previously about how they likely had the most accurate sleep
| tracking and also had some special sauce in their GPS handling
| code that made it outperform Garmin.
| smallerfish wrote:
| I would love to know from somebody with an Apple watch how you
| use HRV.
|
| I wear a Garmin, which I mostly like. The HRV measurement is
| predictive enough to be useful. Two occasions from the past 18
| months are worth noting:
|
| 1) The measure dropped from green through yellow and into red.
| It was in yellow 7 days. On the first day it was in red, I was
| hit with covid symptoms. It stayed in red 2 1/2 weeks before
| starting to climb again; my symptoms had mostly cleared by the
| end of the first week, but I still felt sluggish for some time
| after. The kicker is that I hadn't looked at the HRV at all
| until sometime during the week of symptoms.
|
| 2) I went on a trip to a location +8 hours off my usual
| timezone, and jet lag symptoms were brutal. HRV dropped into
| yellow on day one of the trip, and stayed there during the 2
| weeks of travel. A couple days after I returned it dropped into
| red, exactly coinciding with the onset of flu/covid symptoms.
| Again, it stayed in red throughout the illness, and then as I
| started to get fit again on the other side it ramped up through
| yellow and into green.
|
| So even with 20% accuracy (if that is the case), it's a useful
| data point! What does 90% accuracy give you?
| micadep wrote:
| That sounds useful ! Apple have the best sensors and
| algorithms, but they are terrible at _presenting_ your data.
| egwor wrote:
| Is this true? Do you have a source? I thought that the pros
| tended to make use of polar's technology and that their
| heart rate monitoring (via strap) was considered the most
| accurate / baseline. (My sources are from what I remember
| dcrainmaker saying who I consider a well researched
| reviewer)
| hombre_fatal wrote:
| They are talking about wrist wearables with optical
| sensors, not EKG chest straps.
|
| Though Polar's apps are another good example of good data
| in a horrible app.
| gregoryl wrote:
| Pros use whomever is currently sponsoring or donating
| adamgordonbell wrote:
| Yeah, for heart rate, polar chest strap is most accurate.
| But for heart rate, running watch is almost exactly the
| same for me.
|
| Others report huge differences. It could be size of
| wrist, or who knows what throwing off measurements in
| some?
| mzhaase wrote:
| Usually people will use it to see if they recover well. If
| your recovery is bad HRV tends to dip.
|
| btw. in health snapshot Garmin will report both sdnn and
| rmssd.
| jdechko wrote:
| Exactly my experience. After my last couple races or long
| workouts, my HRV dipped a few ms for a few days before
| coming back to normal. In this case, it's not telling me
| anything I don't already know. But in other instances, a
| lower HRV would make me consider slowing down a bit.
| ycombinete wrote:
| About two weeks after I started wearing my wife's old Apple
| Watch, my average heart rate jumped up by ~10bpm about a week
| before I became sick enough to test myself for Covid, which I
| did indeed have!
|
| Subsequent to getting through the symptoms my heart rate went
| back down to normal.
| CrazyStat wrote:
| I have an Apple Watch. I don't pay attention to my HRV on a
| daily basis, but if I look at it I can often see in
| retrospect--for example I had a cold at the beginning of the
| month which clearly shows up as a ~30ms drop in HRV.
|
| Maybe I should pay more attention to it.
| cj wrote:
| Adding in my anecdata:
|
| I've been tracking HRV since 2018 (I wear an Apple Watch
| 24/7, aside from charging).
|
| Over 6 years between 2018-2024, I went from being 70 lbs
| overweight / very out of shape, I then lost all of the
| weight in 12 months, started going to the gym, became
| physically fit, and I continue to exercise by cycling 3-4
| days a week (sustained heart rate 165 for at least an
| hour).
|
| Despite going from basically an overweight couch potato to
| someone very physically fit and strong cardio system from
| cycling, there has been virtually zero noticeable trend
| with HRV.
|
| On the flip side, I've noticed resting heart rate
| correlates extremely closely with cardio fitness and
| stress. Resting heart rate tends to go up in stressful
| months or months I don't workout as much. HRV seems to just
| always be a flat line.
|
| I'm also very skeptical of Vo2 max. For some reason, the
| watch only records maybe 2 or 3 data points per month at
| most. Sometimes it doesn't record anything for an entire
| month even though I'm doing high intensity cardio weekly.
| Apple rates my Vo2 max as "below average" and similar to
| HRV, it's a flat line. Seems to not be correlated with my
| perceived fitness level.
|
| I haven't noticed any correlations with being sick. My
| impression of all of these metrics (including resting heart
| rate) is they're maybe useful, but only in the long-term to
| see trends over time. They aren't very useful for
| predicting short-term health events, in my experience.
| covercash wrote:
| VO2 max is only measured when you do a "brisk walk, hike
| or run outdoors" according to the Health app. So if
| you're doing any other workout type it won't measure this
| metric.
| SoftTalker wrote:
| Apple had goals to make their these health monitoring features
| in their watch medically approved, to open up additional
| markets. For other watch makers, it was a checkbox on a feature
| list.
| dxbydt wrote:
| > root mean square standard deviation, RMSSD
|
| This is incorrect. RMSSD means root mean square successive
| differences. Interestingly, if you actually compute what you
| wrote ie root mean square standard deviation, you will get the
| same result as sdnn.
| BiteCode_dev wrote:
| Sure, the statistical method matters, but I think it's missing
| the forest for the tree.
|
| Any metric will differ: bpm, sleep phases, body temp, etc.
|
| Because those devices are not super accurate, and the context you
| wear them in doesn't allow them to be anyway.
|
| If you were to do a respiratory polygraph with proper medical
| equipment you'll find different values from your Apple Watch or
| Oura ring for the times you wake up. But you'll also notice a gap
| between getting the values at home and in a hospital, because in
| the hospital the nurses will check your equipment setup.
|
| Those devices are great to give you a big picture, follow general
| trends and understand your own body. That's it.
| Madmallard wrote:
| i have wildly high HRV and my cardiologist says it doesn't really
| mean anything
|
| 815 ms average HRV when normal is like 50-200 ms
| nradov wrote:
| Everyone has a different baseline. For athletic training and
| recovery they usually look at variations from the baseline
| rather than the absolute value.
| eps wrote:
| Wouldn't this be closer to arrhythmia then?
| lazide wrote:
| Technically, any value > 0 is 'closer to arrythmia', but yeah
| that is a pretty high value. 60 bpm == 1 beat per second (if
| everything is perfect), so if the HRV is 850 ms and their
| heart rate is around 60 bpm that is what - 85% variation?
|
| If that is 'consistent', I'm not even sure what that EKG
| would even look like, but 'regular' seems unlikely. I'm
| honestly not even actually sure what 'beat' would mean when
| it's > 50% variation.
| Zanni wrote:
| For what it's worth, I loathe this sort of thing (damning by
| vague questioning): "But, if a composite is full of a measure
| that's biased, how accurate is it going to be?"
|
| Well, I don't know, and you haven't told me. Is it a consistent
| high bias? Low? Variable? How biased? How accurate?
|
| What you're trying to say, without accepting responsibility for
| actually saying it, is "It's an inaccurate composite because it's
| based on biased measurements." But you don't _know_ that, or you
| 'd say it without weasel words.
| drilbo wrote:
| From the study linked
| [https://link.springer.com/article/10.1007/s40279-024-02066-5]
| (with acronym meanings added inline for readability): "The
| lowest pulse arrival time standard deviation (PAT s) at 2.0
| times the standard deviation corresponded to 88.4% of the
| Region of Practical Equivalence (ROPE) for SDNN (Standard
| Deviation of Normal-to-Normal intervals), and 21.4% for RMSSD
| (Root Mean Square of Successive Differences). As the standard
| deviation of PAT increases, the equivalence between
| photoplethysmography-derived "heart rate variability" (PRV) and
| electrocardiography-derived heart rate variability (HRV)
| decreases for both SDNN and RMSSD. The width of the highest
| density interval (HDI), which encompasses 95% of the posterior
| distribution, increases with increasing PAT s. This increase
| occurs at a higher rate for RMSSD than for SDNN."
|
| So for "how accurate?", grossly and irresponsibly
| oversimplifying, the Apple method is roughly 90% accurate, and
| devices using the inferior method are roughly 20% accurate.
|
| I would be really interested to know of any devices not locked
| down to Apple ecosystem that also use this approach, if anyone
| has any insight.
| stavros wrote:
| And your comment was much more informative than the article.
| Etheryte wrote:
| This is such a ridiculously wide divide that I'm surprised
| Apple hasn't used this, or something similar to this, as a
| marketing tactic. Imagine being able to say your medical
| insights are 70 percentage points more accurate than your
| competitors. I do understand this is apples to oranges, since
| these are often devices in a completely different price
| range, but still. I was surprised to hear this and I have
| been loosely following the medical wearables space for
| awhile.
| willis936 wrote:
| I would imagine would be quite happy saying as little as
| possible about their sensors in their watches. It seems
| like their largest surface area for licensing litigation.
| Touting performance today is fuel in court tomorrow.
|
| https://time.com/6692718/apple-watch-masimo-alivecor-
| patent-...
| drilbo wrote:
| I _believe_ there are non-Apple devices that use this
| approach as well, but they 're certainly failing in making
| that information easy to find.
|
| That being said, being the only watch with FDA blessing is
| a pretty effective point to market
|
| https://www.apple.com/healthcare/apple-watch/
| hansvm wrote:
| I mean, they'll definitely market it as 4.5x more accurate.
| Or, for nice round numbers, 5x -- and while we're within
| orders of magnitude it's not unreasonable to say "up to 10x
| more accurate."
| naasking wrote:
| The Quantified Scientist has tested a while buttload of smart
| watches against a chest strap heart rate monitor:
|
| https://youtube.com/@thequantifiedscientist?si=4u-u1VI7eMrXD.
| ..
|
| Apple Watches are at the top, but there are many other
| watches that are almost as good.
| brnt wrote:
| Is there a searchable text version of this resource?
| dyauspitr wrote:
| If you do Apple's mindfulness breathing exercise it always takes
| a reading after that which tends to be closer to an accurate HRV.
| gloflo wrote:
| How do you know?
| formerly_proven wrote:
| Health > Heart Rate Variability > Show All Data lets you see
| the exact timestamp and source for any stored data point. And
| for HRV specifically it will give you the list of
| millisecond-timestamped heartbeats it considered for that
| measurement as well.
| gloflo wrote:
| But how do you know that this is (more) accurate?
| ID1452319 wrote:
| "But, if a composite is full of a measure that's biased, how
| accurate is it going to be?"
|
| Does it matter if the measure is biased, if you're measuring over
| time and looking for comparative differences?
| lloeki wrote:
| When I read the article, this exact question came out as borne
| out of genuine curiosity justifying the need for measuring and
| comparing stuff, not a rhetorical question aiming to dismiss
| the thing.
|
| And indeed, down the road, the article says:
|
| > "There's a lot going on between when the heart beats and when
| the blood gets all the way to the arm or wrist, what's called
| pulse arrival time," Tenan explained. "By simulating that and
| knowing what's happening at the heart, we determined what's
| being measured with the consumer wearable is different. It's
| not to say the consumer wearable is bad or not useful, it's
| just not the same."
|
| As in, electric signal ECG/EKG at chest level and blood flow
| PPG at finger/wrist level _factually_ are not the same
| measurement, and asking "do they somehow relate in any way?"
|
| Then the question is about the difference between RMSSD and
| SDNN/SDRR, and here this article (2022) explains it well:
|
| https://tryterra.co/blog/measuring-hrv-sdnn-and-rmssd-3a9b96...
|
| And answers TFA's question:
|
| > "I don't fundamentally see any reason why any of the wearable
| companies should be using the RMSSD measure
|
| with:
|
| > RMSSD is considered the best measure for short-term
| variations of HRV, but still a robust measure for longer-term
| analyses, with typical use cases for tracking stress, sickness,
| training, and recovery.
|
| > SDNN is more useful for longer term cardiac health trends and
| analysis.
| system2 wrote:
| This is why I use a chest strap heart rate monitor as a cyclist.
| I see the difference between when my hands are down on the
| handlebar. It varies around 10-15 bpm (the watch is lower than
| the chest strap in this scenario). Also, while hiking I see the
| difference after 2-3 hours. Hikers know the hands swell after 2-3
| hours of hiking (you will see people raising both hands while
| running, that's normal) and this affects my watch heart rate
| calculations. There is always a discrepancy between the strap and
| wristwatch.
|
| Watch tracks if my heart rate is high or not but for intense
| sports like mountain biking I don't expect it to be accurate at
| all.
|
| I am using a Garmin Instinct 2X Solar Tactical (watch) and a
| Garmin heart rate chest strap.
| Mistletoe wrote:
| How much is the discrepancy?
| system2 wrote:
| Easily 10 bpm and if it gets more intense around 150 bpm
| levels it is over 25 bpm. The watch is lower most of the time
| or delayed by 10 seconds at least. This is consistent with
| the 3 different brands I used. I just use the watch as a
| "your heart is getting faster" notification.
| byyoung3 wrote:
| you have to measure during periods of deep sleep to get accurate
| results
| byyoung3 wrote:
| this is why you a whoop, not an apple watch
| petesergeant wrote:
| I don't follow your reasoning here, what's the Whoop got that
| the Apple Watch does not that's relevant here?
| vadansky wrote:
| The whoop measures and averages your HRV over your deep
| sleep to give you one number.
|
| The AppleWatch, at last time I researched, just gives you
| your HRV, NOW. And my impression is it's not really a
| useful number as a snapshot, since it varies so much during
| the day it's not really useful to know what it is at 10:40
| AM EST.
| petesergeant wrote:
| My Apple Watch appears to have taken HRV measurements at
| 2 hour intervals last night overnight -- is it a
| granularity difference then?
| vadansky wrote:
| I think the idea is it has to during your deep sleep
| specifically, which may or may not overlap with those 2
| hour intervals.
| thenerdhead wrote:
| Seems odd to compare a machine like a 12 lead EKG to a smartwatch
| with a single lead EKG support.
|
| Of course variability will differ, that's why they invest to much
| into improving the technology and ml algorithms to make up for
| the difference to personalize the data.
|
| The watch could encourage you to go to a doctor and the doctor
| can use a more accurate instrument to diagnose.
| varsock wrote:
| I find it incredibly puzzling why Polar is left out of these
| conversations when it comes to wearable health tech when Polar
| pioneered a lot of the technology and releases white papers for
| all their functions.
|
| For example, Garmin has "body battery" which is a pseudo science
| measure of who knows what and Polar does orthostatic tests (based
| on HRV). Polar won't even let you do that test with a watch, you
| need a chest strap because of a lot of similar reasons outlined
| in this paper
| beepbooptheory wrote:
| I eventually stopped wearing my Coros running watch because I
| started to not trust the heart rate thing. Whenever it got cold,
| the readings shot up! Now I'm just trying to train myself to
| remember the right tempo from touch.
| ck2 wrote:
| You cannot get HRV from an optical sensor accurately.
|
| Not even at idle, but definitely useless in motion.
|
| And definitely not at the wrist.
|
| Optical at the wrist is all manipulated data via the watch
| software that is guessing what it is seeing or not.
|
| The only real way is via a heartrate strap that is electrical.
|
| And the next generation of sensors is going to be even more
| amazing with EKG
|
| https://www.movesense.com/movesense-flash/
| mannyv wrote:
| Note that the article states that they created a simulation to
| test. It's unclear how they validated that simulation from the
| abstract.
| rubatuga wrote:
| I don't like using smartwatches for HR tracking during exercise.
| If for any reason blood flow to your wrist decreases it becomes
| inaccurate
| sadcherry wrote:
| But when it's inaccurate then it's usualy blatantly obvious.
| For example if you are out on an easy jog and it shows 188 bpm
| then that's your cadence, not your heart, unless something is
| going down really badly and then you don't need the watch to
| tell you that.
|
| It's not like it will show 147 when the actual value is 134.
| wslh wrote:
| There's nothing new here, most athletes are aware of these
| issues, and there are plenty of discussions on Reddit. For
| instance, you can check out the Garmin subreddit. I've even had
| problems with fitness bands like Polar.
|
| My recommendation is to be cautious with extreme inaccuracies and
| interpretations, especially for health-related reasons. It's also
| helpful to develop greater awareness of your body as part of your
| training.
| jlarocco wrote:
| I agree, and IIRC, Garmin has a warning and disclaimer in their
| documentation stating the HR isn't guaranteed to be accurate,
| and it's easy to see in a graph that it's using a moving
| average.
|
| I still use mine a lot, because I'm not too worried about the
| exact numbers while excercising, and I feel like it's probably
| okay for comparing against previous activities. That's to say
| if the watch shows ~180 bpm for 10 minutes on a run, it's
| probably similar exertion to the last time I hit ~180 bpm for
| 10 minutes on a run, but I don't trust that it's exactly 180
| bpm, and I definitely don't trust the "ramp up" and "cool down"
| measurements from 180 bpm.
|
| As you said, everybody I know who cares about accuracy already
| uses a chest strap.
| guerrilla wrote:
| This is a weird post. I'm by no means an expert but I've read
| some papers on HRV and this is extremely well known in HRV
| research. So much so that these facts (and others) are basically
| copypasta at the beginning of a lot of papers. People have
| definitely quantified this before, like a lot. Also, the general
| advice is that it isn't expected to be "accurate" and the
| measurements are relative anyway (both to the individual and to
| the standard of measurement.)
|
| There weren't a bunch of researchers (or even biohackers) walking
| around who thought SDNN or RMSSD could be substituted for EKG.
| ineedaj0b wrote:
| we had patients come in complaining their smart watch had high
| readings. after testing they usually had something unusual or
| indicative. but they were also large... or had other signs.
|
| running an EKG is cheap and easy (might not be cheap to pay for,
| but it's not an MRI!). i still like patients having more access
| to health data - legibly - for them. if they were doctors they'd
| see signs by skin health, etc. the watchs are overall a net
| positive imo.
|
| .mris are cheap too but a headache to schedule cause everyone
| needs the machine and there might only be 1 or 2 in a hospital.
| lencastre wrote:
| O'rly????
|
| Every owner of Garmin I know complains of the absolute useless
| POS it is to rely on the optical HR for HRV. A HRM on a strap
| will get you good/very good readings for HRV. Finally there is a
| good podcast from Attia which he talks with an HRV expert behind
| an HRV dedicated product.
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