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I didn't reverse-engineer the protocol for my blood pressure monitor in 24 hours

https://james.belchamber.com/articles/blood-pressure-monitor-reverse-engineering/
68•jamesbelchamber•2h ago

Comments

cestith•2h ago
Regarding white coat hypertension, the shot isn’t always necessary. Some people’s blood pressure just goes up from the stress of the clinical setting.
pavel_lishin•1h ago
I have an intense phobia of dentists; if I were wearing a constant monitor, I bet you could tell when I was at the dentist just by watching the blood pressure and heart rate spikes. (You'd have to find some way of differentiating them from me being in a car accident, or being attacked by a werewolf.)
6LLvveMx2koXfwn•1h ago
It's interesting that you have a baseline for 'being attacked by a werewolf'.
gregdeon•52m ago
I wonder if it would show up on the heart rate (or heart rate variability) tracking from an Apple Watch or similar. My Garmin picks up stressful events all the time.
SchemaLoad•1h ago
If you've got one of these machines at home it seems you really want to run it a couple of times. Often I find the first reading I get is quite alarming but then if I sit for a bit longer and run it another 1-2 times I get a very normal reading.
loeg•1h ago
Also, they can read high if the batteries are low.
llm_nerd•1h ago
A big reason people's first measurement is often high is the positioning while putting the cuff on, adjusting to the pose, and then settling in place, a process which can spike pressure. Ideally you prepare yourself (cuff on, in place with your arms at rest, etc) and sit there and relax for five minutes before you take the first measurement, making it legitimately reflective of the at-rest state.

This is often isn't possible, but it's a reason doctor visits usually drop you in a room by yourself with a machine that will take multiple measurements with a lengthy delay between. Though that's where the white coat thing comes into play and people are stressed about a doctor coming in, etc.

OxO4•49m ago
FWIW, some "smarter" machines (e.g., [0, 1]) support taking three readings with a minute pause in-between and then spit out a single reading.

[0] https://www.garmin.com/en-US/p/716808/ [1] https://www.withings.com/us/en/bpm-connect

jeena•43m ago
Actually that is what my doctor told me to do, this seems standard procedure to measure twice every time with 1-2 minutes in between.
lysace•1h ago
Taking a BP in person during a medical consultation, while stressed out because I know I have a very limited amount of time to do a verbal data dump of a large amount of information in a good way never fails to give me extreme values.

It also never helps to explain that this has happened many times before and that I have a reasonably high quality BP measurement device at home (most recently the exact same Braun model) that gives me decent measurements when I'm at rest/relaxed. They just look at me like I'm an idiot. How could a civilian conceivably perform such a complex measurement?

Then I get the predictably insanely high measurement and they look satisfied. Gotcha!

Please bring on the AI doctors.

alexfoo•1h ago
White coast hypertension isn't just about a clinical setting, it's more generally about the worry about the results of having your BP measured. [EDIT] OK, well maybe there's another type of hypertension which is related to anxiety about a high result regardless of the measurement setting.

I have to take daily BP measurements during titration for ADHD medication. (Using an _A&D UA-611 Plus_ machine at home.)

I can put the cuff on my arm and sit at my desk for 20 minutes to be nicely rested and calm, and then take 5 different measurements with a few minutes between each one. They'll vary quite wildly (anything from, say, 115/75 to 135/90) despite not moving between measurements or having any reason to be more or less agitated. I generally just ignore the low/high outliers and average the others. There's no pattern either, sometimes the outliers are first, sometimes last.

Also it's not just the monitor I have at home, the same is true of a probably more trustworthy machine in a clinical setting. I mentioned this to my doctor when I last visited and we saw the same thing with multiple measurements using a more sophisticated machine at the clinic.

mh-•58m ago
I check my BP a lot for reasons, too, and this matches my experience as well. A few tips to reduce the variance (but it'll never go away):

* the position of both of your arms, and the angle your elbows are bent at matters. make sure the edge of your desk isn't pushing into your forearm.

* same goes for both of your legs. make sure you're sitting with legs uncrossed, relaxed angles, make sure the edge of your chair isn't pushing into the back of your thighs excessively.

* control your posture. slouching seems to have an effect too, but I'm unclear on the mechanism.

Anecdotally, the nurses at the doctor's offices I go to rarely (~never) bother to control for any of this other than telling me not to cross my legs. So while I fully believe white coat hypertension is a thing, I also think there's a lot of poor control of variables here. If you look up the AMA/AHA guidelines for blood pressure, the ranges they offer are predicated on some very prescriptive protocols for measurement.. which I virtually never see adhered to.

wpollock•3m ago
> I can put the cuff on my arm and sit at my desk for 20 minutes to be nicely rested and calm, and then take 5 different measurements with a few minutes between each one. ...

Doesn't it take more than a few minutes for one's circulation to return to normal after a BP measurement?

hansvm•39m ago
Yep. My heart-rate is normally pretty low (45bpm or so, 55 if I'm walking around), and my BP is on the high end of normal, but white-coat syndrome reliably brings it up to a fluttery 110bpm and 155/125 pressure. I was just in a wreck last week, so I got to see the before-and-after measurements from a few medical providers, and it's shocking how the act of talking to a new person in an unfamiliar environment spikes my BP even when I "know" that it's fine, and also how quickly it falls back down to normal.
dhosek•11m ago
I got it when an eye clinic wanted to do my blood pressure (which is kind of weird in itself), which they did shortly after the glaucoma test which never works for me because I have an overdeveloped blink reflex and it turned up high.

It really amazes me how people whose job it is to take blood pressure don’t recognize the stress situations that people are in might result in abnormal readings.

lifeisstillgood•1h ago
So I did something similar (well less cool), but as old Software devs start finding our bodies don’t work as well after a while we will see more and more of this sort of “taking control”

https://mikado-aktiia.readthedocs.io/en/latest/

jamesbelchamber•1h ago
That's very cool. I wonder if sniffing the Bluetooth connection directly might be easier than reading the PDF (although not because it's easy).

At least you have more than 24 hours to find out!

olalonde•40m ago
nRF Connect for Mobile[0] could be handy here.

https://www.nordicsemi.com/Products/Development-tools/nRF-Co...

lifeisstillgood•15m ago
I did wonder but I keep downloading to the app to “see how I am doing” Throughout the day so I would not be easily able to sniff it - and I assumed that as a highly engineered professional “medical device” it would of course be encrypted with unbreakable … oh it’s probably base64
lagosfractal42•1h ago
you missed a closing parenthesis
Arainach•1h ago
Testing blood pressure after a shot seems weird.

I have high blood pressure, managed with a low dose of medication. I've had plenty of advice from my PCP and other actual doctors on how to take blood pressure - how to sit, how long to sit still, how to position your arm, etc.

It is remarkable how many medically-adjacent professionals are bad at this. My dentist starts my sessions with a blood pressure reading - theoretically in case they have to numb me or something, probably because it's billable or whatever. What always seems to happen is that I get in for my appointment (driving, which can be stressful even if I'm not running late), they take me to the chair within 2 minutes max, immediately put some sort of wrist cuff on me, hold my arm at an angle that is not what most actual doctors have recommended to me and take a reading that is often high enough to surprise both the hygenist and myself.

The thing is that I have two sufficiently-calibrated Omron units, one at home and one at the office. I take my blood pressure often enough to know what it usually is (and my real doctor takes it at least twice a year). That is to say that no, it's not 200/160 or whatever nonsense the dentist thinks it is and you'd think that with a very small amount of reading they'd know better.

quickthrowman•51m ago
> Testing blood pressure after a shot seems weird.

I was at the Dr last week and my first BP reading was 154/95, a second reading a few minutes later was 141/89. The doctor asked for one more reading before I left.

The medical assistant gave me my vaccines and then took my BP, 130/81 right after a Hep B and COVID vaccine. I told the tech that needles didn’t bother me at all, she believed me after she saw my blood pressure :)

Arch-TK•1h ago
Would be fun to see the traffic dumps, I would love to try to figure out the protocol offline with them.

Just spent half a day reverse engineering a Windows virtual printer driver (for work) and had to force myself to stop spending the rest of the day doing it.

ck2•1h ago
I have three blood pressure cuffs

They all give me different numbers, by a lot sometimes

btw you think they ever clean those devices?

you think healthy people go to pharmacies?

I won't even touch the signature pen, imagine what's on that

kotaKat•1h ago
If you think that's bad, just think about what's in those finger-holes in bowling balls, between rounds of beer, bowling, and greasy bar food :)
ErroneousBosh•1h ago
I had my blood pressure tested several times over the course of the month and each time it was high, weirdly high, like 160/100. If I drove in, weirdly high. If I cycled in, weirdly high. If I got another reading after sitting quietly in the waiting room reading my book for half an hour, weirdly high.

They wanted me to start on all sorts of medications immediately.

The second-last time, they got a reading of 220/130, and were going to get an ambulance to take me into hospital immediately.

Er, hang on a minute, folks.

That's beyond "hypertension crisis" and well into "incompatible with life" levels. That's the kind of pressure I see in hydraulic servo feedback channels, not living things.

They grudgingly agreed that someone with high blood pressure probably ought not to be making as much sense as I was, although what would I know about it, they're the professionals, etc etc.

The next time I noticed the automatic blood pressure cuff had a fresh new calibration sticker on it.

130/90. Not bad, for a reading taken at the doctor's surgery.

I wonder how many people are on medication they just plain don't need because of a plainly faulty sphyg though?

aDyslecticCrow•48m ago
I have a family member working in hospital setting. Electronics bairly survive a year from the amount of disinfectant they're exposed to. Everything is wiped so constantly that anything not made for the environment has its lettering stripped and rubber dissolved and cracked within short notice.
thaumasiotes•47m ago
> btw you think they ever clean those devices?

Maybe? Do they clean the shelves? Arm-to-arm contact isn't exactly a big threat.

> you think healthy people go to pharmacies?

Yes. Of course. Those free blood pressure machines are generally found in drug stores that have a small pharmacy section. The vast majority of people there are there because they're shopping. There are probably more people who come in to buy mascara than people who come in because they're sick. If you're sick, someone else goes to the pharmacy for you.

pinkmuffinere•57m ago
> I tried feeding a lot of this into various Als (Kagi gives you access to a few with a nice interface) and I found that they mostly were stupid in ways that made me think

"stupid in ways that made me think" is (IMO) a really good summary of how AI is useful, as well as its pitfalls.

senectus1•29m ago
yup, its a decent "Rubber duck" and an ok search engine.
mctt•11m ago
https://en.wikipedia.org/wiki/Rubber_duck_debugging

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I didn't reverse-engineer the protocol for my blood pressure monitor in 24 hours

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