Caltech Develops First Noninvasive Method to Continually Measure Blood Pressure

https://www.caltech.edu/about/news/caltech-team-develops-first-noninvasive-method-to-continually-measure-true-blood-pressure

by crhulls • 2 years ago

269 77 2 years ago

caltech.edu

dredmorbius4• 2 years ago

This approach has been tried before. Bill Softky describes a startup he'd worked for using a similar sound-transduction continuous non-invasive blood-pressure monitoring technique. It ... had problems:

Our non-invasive device was supposed to measure blood pressure just as accurately [as an arterial line], but without the cutting, using specially-sculpted sonic vibrations and fancy algorithmic analysis, which was my job. The overall challenge was like measuring the pressure inside a bottle without opening it. Our device worked fine, in that our algorithmically-estimated blood pressure moved up and down, beat to beat, in lockstep with the actual blood pressure. The problem was that our estimate also moved up and down at other times as well, say when the patient moved her fingers, rotated her arm, or took vaso-constricting drugs like nicotine. I spent most of a year understanding these problems, and understanding they couldn’t be solved before our funding ran out. That was when an old-timer taught me an important lesson of measurement: it’s fairly easy to calculate a signal which correlates with what you want to measure, the way our vibration-estimate correlated with actual blood pressure. It’s much harder, though, to calculate a signal which does NOT correlate with what you DON’T want to measure, like arm motion.

<https://www.linkedin.com/pulse/monster-monetization-bill-sof...>

I'd be exceedingly curious as to how the CalTech team have solved that non-correlation problem.

Timothy055• 2 years ago

Looking at the diagram I’d suspect they use accelerometer information from both the wrist watch and the upper arm mounted sensor to remove the effects of arm motion. At simplest it could only check when the arm is in a neutral position. But I’d expect they did something more complex/better than that.

dredmorbius4• 2 years ago

As I understand Softky's work, it's not that the measurements varied predictably with movements, it's that they varied unpredictably.

I'm obviously distant from the project, but a team of SWEs spending years trying to make nondeterministic data deterministic suggests a fairly deep problem.

mhb• 2 years ago

Paper: https://academic.oup.com/pnasnexus/article/3/7/pgae252/77177...

They tested on the carotid artery. I don't know whether they're concerned with addressing issues of wearing this while active. It seems more likely that it will be used in a clinical setting.

phkahler• 2 years ago

The article mentions getting it down to an arm band or patch.

Mistletoe• 2 years ago

It’s just a blurb from a college PR team. As someone that came from academia, they don’t have to have solved any of that because these are generally pretty worthless. It can be as small as someone in a lab discovered how to do the smallest thing and the college wants to run with it to look good.

dredmorbius4• 2 years ago

I'm aware. Which is why I'm pointing to someone who chased that "first" achievement for years, and has the scars to show for it.

CamperBob22• 2 years ago

There's a nicely-presented introductory paper: https://academic.oup.com/pnasnexus/article/3/7/pgae252/77177...

CamperBob22• 2 years ago

I guess it's not considered reasonable to keep your arm still when measuring BP, or to measure it only during intervals of minimal movement? Doesn't seem like a showstopper to me.

One of the key applications for this technology is during surgery, when (ideally) nothing is being moved.

coldcode• 2 years ago

As a person who had a hypertensive crisis late last year, nothing boils my blood (yes, a pun, I am fine now) more than how people measure blood pressure incorrectly in doctors offices and even hospitals. There are many different things than can increase a BP measurement above the "baseline" including talking, moving around, not having rested but also just waking up, not being in a supported position, only a single value, etc. Most of the major health agencies (AMA,AHA,CDC, etc in the US) have recommendations on how to do it properly, but in medical situations like doctors offices and hospitals, these are rarely done as they take too much time. A single measurement is not sufficient and can result in misdiagnosis.

A more reliable way to measure a continuum would make a difference, but I imagine it would still require time to collect as BP is a dynamic value that changes with behavior, posture and activity.

nulbyte• 2 years ago

As an adult with a congenital heart defect and white coat hypertension, I can relate. Once, a nurse took my blood pressure and immediately freaked out as I was sitting calmly on the exam table. She took it again in the same arm, then hurriedly took it in each of my other limbs before throwing her hands up.

Often, I would arrive at the cardiology office having made my way through downtown traffic to find a parking space and walk across the pedway. Then I'd find a seat as far away as possible from all the noisy children there to remind me that I should be dead. No wonder my BP is higher than usual. And you're the one freaking out?

I got so used to nurses tossing out every recommendation for measuring BP that I started taking it myself at home before visits just to prove the point. Eventually, as I grew older, my BP rose to a point where it actually needed to be addressed. I am now on medication. But I have yet to find a nurse anywhere that has taken time to follow even one recommendation for properly taking BP.

pkaye3• 2 years ago

When I was a dialysis patient with frequent office visits, I've had the same experiences myself. Two things I've ended up doing is get to the hospital 30 minutes early, sit in a quiet area and relax till 10 minutes before the appt. Secondly I've found deep and slow breathing can improve your blood pressure a lot. The problem of white coat syndrome still remain though.

dgacmu• 2 years ago

It's frustrating. I usually bike to the doctor's office, and every time I warn them that they're going to get a systolic 10 higher than if they'll wait until the end of the appointment. They don't wait. The tech-taken entry gets put in the EMR. The doctor takes my BP again at the end, says "oh, great" and that reading gets ignored. :p

As a sibling comment noted, I ended up deciding to just watch my BP at home every now and then. It turns out it's fine and it reduced my metaphorical blood pressure to monitor it myself.

benmanns• 2 years ago

However, as discovered during a family heart crisis, medical professionals will routinely ignore any kind of heart rate or blood pressure readings that you take at home. In my experience, it's not until they see the same measurement during the ($$$) ambulance ride that they take it seriously.

grogenaut• 2 years ago

I found that taking it at home helped a lot with white coat syndrome, I was more relaxed and more able to tell when I'd settled. I also just set a timer when walking and told the nurse "no not yet" when they tried to take my BP. They listened except the one nurse who insisted I was wrong and that I was 5'11" not 6'2" which was entered in by the urgent care the day before because people get shorter as they get older. You know, a day later, at 40, after being 6'2" since I was 18. no possible way she could be wrong, everyone else was. Also tried to mark me as an active smoker because I'd been in a resturant with smoking before, in the 90s and she had magically never been around smoke in her 50 years. The doctor corrected the smoker note but the height hung around in some SOT field even though the next 15 height measurements were 6'2" until I had an extra 10 minutes with a PA who went over all my records with me and corrected things.

I had trouble with 2 of the BPs drugs, one gave me head spins in the afternoon seated in my car sometimes, another gave me the dry cough (could feel a prickle in my thorat). My bp is actually high esp when I've had caffiene (what coder doesnt), move around, etc, but it's usually low pre-hyper tension. I also had it taken about 300 times in the last 6 months getting certified as an EMT. There's a LOT of variation in how the tools take the BP and just how close you're listening. I compared a manual cuff with one of the fancy automated ones and it's not that hard to hear your dystolic down 10 below what the automated reads. Same with systolic, you can hear it higher if you really listen before it starts sounding like a watch with another 10 spread, and you leave that cuff at 200 for 10 seconds and everyone's going to read higher and tense up more. I can feel my blood pressure surge any time an automated machine decides "nope I need to go higher on systolic" and it squeezes and I know I'm going to read high and have yet another conversation with the nurse and doctor. Just take it to 200 and come down stupid machine.

teamspirit• 2 years ago

I had hypertension for about 15 years and after quitting drinking and smoking no longer do. I still suffer from white cost hypertension regularly and frequently have to tell nurses to just press the button again - second time drops back to normal range with a drop of about 20/10.

hn727743• 2 years ago

I had it too. When I was under stress, sometimes I could hear my pulse in my ears like a whooshing sound.

I stopped drinking and my BP is now completely normal, and RHR is low 40's. Sleep is much better too.

mkoryak• 2 years ago

I stopped drinking and mine went up :p

Being sober is pretty stressful

xattt• 2 years ago

A single measurement is not sufficient and can result in misdiagnosis.

During an acute care stay, a single blood pressure is a drop in the bucket. It averages out on the long term, and it’s not taken out of context of a clinical presentation.

I would take pressures manually, question unusual values, repeat on the spot and after some time had passed.

blackeyeblitzar• 2 years ago

Totally agree and I think the malpractice comes from laziness and a lack of interest in their patients. If they cared, they would do it correctly per the guidelines they hand out to patients themselves! By which I mean these: https://www.heart.org/en/news/2020/05/22/how-to-accurately-m...

It is especially bizarre to me when they don’t listen to patients and make medical decisions like deciding prescriptions and dosage amounts based on false readings.

ineedaj0b2• 2 years ago

i don't think it matters too much. we don't want to take it right after you just exercised obviously, but even taking it once is indicative of things. 'i have white coat etc. i have nerves!' these are all things we don't mind seeing. all those those things connect.

using up time to double check blood pressure is so/so useful but generally a waste. a patient's labs tell much more, and are better to hedge suspicions against.

white coat hypertension at 320lbs!? alright sir we can check again if you like...

HPsquared• 2 years ago

I find doctors and nurses rush things too much in general. I guess they're paid flat-rate, like mechanics?

ineedaj0b2• 2 years ago

there's just no time. we have to write down everything you tell us, we have to come off genial, make you sure you aren't lying about something or mistaken, and fix you.

barbazoo• 2 years ago

They have a million patients. I bet no one on that moment thinks, oh I’m only paid $10.75 for this, I better rush this so I can earn more money.

dillydogg2• 2 years ago

If you had to see as many patients as your doctors do, you would be rushing around too.

hereme8882• 2 years ago

I'm a resident physician and I deny having my BP taken in outpatient clinics.

The techniques used are ridiculously inappropriate:

"Ok, Mr. So-and-so, come with me." calls the nurse, as the pt who is irritated for having to wait 30 minutes quickly gets up to walk along unknown hallways, while rushing to finish a phone conversation, stressed and not knowing where to turn next..."Ok, now we're going to weigh you on this scale" while the pt thinks 'oh man, I've probably gained weight', followed by "ok, now we're going to measure your blood pressure." 'I don't want BP meds...let me try to relax...breathe slooowly...but I don't want the nurse to notice I may be trying to cheat this sudden examination.'

That's why the most appropriate way nowadays is to measure it at home, and keep a BP log.

thelittleone• 2 years ago

People try to cheat BP tests? Because they dont want tp taks BP meds? Daaaang I'm trying to get my head around that. I guess I'm missing something because that sounds like an incredibly tangled way to be.

slaymaker1907• 2 years ago

One thing that I think would dramatically improve the routine screening numbers at doctors' offices would be to try and take it after the patient has been sitting down for a few minutes waiting for the doctor after the other vitals have been taken. If I'm going to sit around for 15m+ anyways, why not use some of that time to let BP stabilize?

WWLink3• 2 years ago

That's why the most appropriate way nowadays is to measure it at home, and keep a BP log.

"Oh yea those machines are junk and totally wrong"

And/or "WHY DO YOU TAKE YOUR OWN BLOOD PRESSURE?!" followed by accusations of being a hypochondriac.

Also the log is junk because I don't know how to properly take the blood pressure. Unlike the assistant who is also doing it wrong.

lolololol

dillydogg2• 2 years ago

One of my attendings has a running joke where he takes fresh interns in July and tells them "I will take you to <most expensive restaurant in my city> if you can take this patient's blood pressure correctly." He's been doing this for 30 years and no one has been treated to dinner yet. He's looking for the rest time, arm at heart level, everything.

HackerThemAll• 2 years ago

Not only the medical personnel is very often unable to properly measure the blood pressure, they also cannot properly take blood sample for potassium. They put tourniquet and order patients to pump their fist, so that the veins appear, but that cause muscles to release potassium into the bloodstream, causing elevated levels and misdiagnosis leading to incorrect treatment. I make people aware of that, and it should be widely spread so that doctors and nurses have the knowledge that they sometimes unwittingly cause harm.

samstave• 2 years ago

This would be the best use of the "AI Pin" fiasco of a device;

Create an AI pin that takes in all the activity associated with the BP monitoree, including telemtry for environment, movement, and diet. if I had a pin that did this (and recorded all audio for the day, and snapped pictures when I wanted and transcribed all audio via whisper and I had a full searchable day-runner...

Yay!

EDIT: The above desire is fully capable of a phone - except battery life...

I have a boatload of old phones. It would be interesting to just build a mini-build for an android phone to simply be a daily recorder. to capture audio/video only and run a slow app that will transcribe all audio to text on the device (even if it does so once its on lan, then it connects to an endpoint running locally on your docker desktop fast api to capture the audio that auto uploads as soon as on home lan. Sorts the files and pics and everything onto the NAS with simple txAI workflow to ffmpeg as needed.

bamboozled• 2 years ago

Yeah I was told I had high blood pressure, was about to be put on a bunch of medication and then I decided to get a second opinion. The hospital I went to gave me a 24 hour monitor and it came back I had perfectly fine blood pressure.

Turns was scared of doctors.

m463• 2 years ago

not being in a supported position

does this mean your arm is not relaxed when measuring?

They always measure my blood pressure in a jury-rigged way resting on not an armrest, but some uncomfortable bracket of the blood pressure device.

ck2• 2 years ago

No they didn't invent the first way

The first way has been done in studies for years, maybe even a decade ago.

Earlobes.

I'll search for the papers later and link them.

https://scholar.google.com/scholar?q=earlobe+blood+pressure

https://www.todaysmedicaldevelopments.com/article/wearable-b...

I've always wanted a Garmin linked ear-cuff device that uses the earlobe for heartrate and blood pressure and then doubles as music playback or alerts from the watch. You could even do body temperature from the earlobe reliably.

queuebert• 2 years ago

This is quite an old problem. A quick search of PubMed yields 4834 results for "noninvasive blood pressure monitoring". Caltech has a weird definition of "first".

Edit: To clarify, plenty of things have been tried besides the cuff, but most patients who need something more sophisticated than that are already sick enough to be in the ICU, where an a-line can be placed. This is really a solution in search of a problem.

anon115• 2 years ago

meowdoesnt the apple watch do this already? or was that just heart rate?

rrrix1• 2 years ago

Just heart rate and psuedo "EKG."

BP monitoring requires a pressurized cuff which restricts (stops) arterial flow. The readings are the pressure of the cuff as it deflates when the blood starts flowing and when it can no longer be detected.

Herodotus38• 2 years ago

Aside from the home use, If this could be proven to be just as accurate as arterial lines this would be a huge benefit to patients in the ICU or undergoing major surgery where continuous blood pressure is needed. I hate putting in A-lines.

_qua• 2 years ago

It’s one of my favorite procedures! To each their own I guess.

dredmorbius4• 2 years ago

Yes, the concept is sold as a huge benefit in patient quality-of-life.

A-lines mean you can't just get up and move, or even roll over in bed. Non-invasive measures can simply be unclipped, or made fully mobile in the first place.

The problem is having a non-invasive method which works, which has been the sticking point until now.

kekeblom• 2 years ago

Aktiia has a product on the market which supposedly already does this https://aktiia.com/uk/. It is based on an optical method though.

trentnix• 2 years ago

A year or two ago, I interviewed a developer who worked for one of the companies trying to build these types of optical blood pressure sensors. I have high blood pressure so I was keen to learn more. The gist of his message was that even in excellent conditions, it was very inaccurate.

benterix2• 2 years ago

I wonder if things changed by now.

ryeights2• 2 years ago

The Aktiia bracelet takes measurements automatically but not continuously. It produces about 1 measurement point every hour.

robomartin2• 2 years ago

I've been thinking a lot about continuos health parameter monitoring lately. For the last 100 days or so I have been running a personal health experiment and collecting multiple data points during the process. I guess some use the term "bio-hacking", not sure if it applies.

The experiment has included multiple fasting periods, with a maximum of 7 days as well as changing one variable at a time in categories such as diet and exercise. The results have been very interesting and I intend to continue on this path until at least the end of the year.

As part of the data collection I have been taking my blood pressure a minimum of twice a day, sometimes more. Also blood glucose, ketones and (consumer) EKG.

The first thing that jumped at me was the inaccuracy or variability of these measurements. I even got a Dexcom continuous glucose monitor. Interesting but useless for my purposes. The thing produced 20% error with respect to finger poke measurements. And, then again, when I got a calibration kit to check my finger poke meter, the calibration range is approximately +/- 18%. In other words, unless you hit extremes it feels like these measurements are almost useless. You can kind of tell you are going up or down, yet don't really know where you are.

The same, of course, has been true of blood pressure measurements. I went through three consumer machines. I can't say any of it is accurate because there are too many variables. I have run multiple experiments with regards to where and how to measure BP. All I can determine are relative changes by effectively measuring under as close to the same conditions as possible twice a day, morning and evening (both before meals).

During the last month or so I have been using a protocol I learned from one of Andrew Huberman's presentations (can't remember which one or I would post a link). I believe he was interviewing a researcher who explained the process they use during their studies. In simple terms, they take three measurements and then average. The first is after 15 minutes sitting, feet on the ground, back supported, no movement, no speaking, no activity. The second and third are at 5 minute intervals under the same conditions. In other words, the entire process takes at least 25 minutes.

After adopting this approach I have been seeing wildly different numbers with respect to the single measurement protocol I had been using for two months. In addition to that, the standard deviation of the computed values are much tighter now.

This experience, so far, has made me wonder about just how many people might be misdiagnosed and put on medication every year because of bad data. I can see the value in having more data, of course. Yet, continuous data is only good if it is accurate to within a reasonable margin.

lostlogin3• 2 years ago

how many people might be misdiagnosed and put on medication every year because of bad data

Another variable that causes this is the patient. They don't like the medication or don't take it properly but tell their prescriber that they are taking the medication correctly (age, culture, dementia etc). The prescriber then adjusts the dose.

robomartin2• 2 years ago

Very true. My wife is a doctor. This is one of the issues that comes out most frequently during conversations about healthcare.

ryukoposting• 2 years ago

Interesting. I recall working on some devices that implemented something called Pulse Arrival Time [1] which the biomeds on the team told me "isn't blood pressure, but it can be used for the same purposes."

Does this technique have an advantage over PAT? How true is the statement that "PAT can be used for the same purposes?"

[1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6912522/

pkaye3• 2 years ago

This believe this blood pressure watch has been approved in a few European countries. It requires you to calibrate against the normal approach every month. I think they are trying to get it approved in the US by next year.

https://aktiia.com/

benterix2• 2 years ago

I wonder how do you calibrate it in practice.

pkaye3• 2 years ago

They include a blood pressure cuff with the watch.

https://aktiia.com/uk/blood-pressure-monitor

ryeights2• 2 years ago

They’ve just received approval for a monitor that needs no calibration at all, although it’s not commercially available yet, and will probably take another half a decade to reach the US.

https://aktiia.com/uk/regulatory-approval-no-need-for-calibr...

Psst… the bracelet is available in the US if you use a UK freight forwarder, & download the app from the EU app store…

hm-nah• 2 years ago

Huge deal for humans moving forward. ~5-8yrs too late for me (2-5yrs for product dev, 3yrs since a hemorrhagic stroke that was likely caused by serious blood pressure).

I was 40 at the time and never measured my blood pressure (and certainly never when exercising). After the event I measured it all the time. During the 8th time of sitting in a chair, rolling up my sleeve, I thought, the Apple Watch has BP sensor, right?

That question sent me on a quest only to find that humans had not yet figured out a way to measure blood pressure on-the-go.

Congratulations on this effort!

amelius• 2 years ago

This measurement requires three parameters—a measurement of the artery's radius, the thickness of the artery's walls, and the tension or energy in the skin of the artery.

Ok, so now instead of 1 variable, there are 3?

ruckfool• 2 years ago

When will my apple watch support this ?

bjornsing• 2 years ago

There’s a company called Biobeat that sells a patch you put on your chest for continuous 24-hour blood pressure measurement [1]. From what I’ve heard it’s in clinical use and works.

1. https://www.bio-beat.com/cuffless-blood-pressure-monitoring

ggm• 2 years ago

I have reverse white coat hypertension: having a health professional care about me reduces my BP appreciably when they measure it. Placebos work very well on me, if delivered by an obvious competent authority like a nurse practitioner or GP.

I still take the hypertension meds: it's cheaper than paying somebody that highly trained to be nice to me.

spoonfeeder006• 2 years ago

So basically resonance frequency of an artery doesn't depend on the artery's radius or wall thickness?

Or perhaps is that enough the case on a certain lower frequency band, where variations in those quantities are much smaller than the wavelength?

patrickhogan1• 2 years ago

So cool!

2-3-7-43-1807• 2 years ago

The new patented technique, called resonance sonomanometry, uses sound waves to gently stimulate resonance in an artery and then uses ultrasound imaging to measure the artery's resonance frequency, arriving at a true measurement of blood pressure.

That's invasive - gently or not.

Caltech Develops First Noninvasive Method to Continually Measure Blood Pressure

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