8 ms·

Caltech Develops First Noninvasive Method to Continually Measure Blood Pressure

269 points by crhulls 2y ago

kekeblom 2y ago
Aktiia has a product on the market which supposedly already does this https://aktiia.com/uk/ https://aktiia.com/uk/. It is based on an optical method though.
- trentnix 2y 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.
  - benterix 2y ago
    I wonder if things changed by now.
- ryeights 2y ago
  The Aktiia bracelet takes measurements automatically but not continuously. It produces about 1 measurement point every hour.
dredmorbius 2y 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-softky 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 2y 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.
  - dredmorbius 2y 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 2y ago
  Paper: https://academic.oup.com/pnasnexus/article/3/7/pgae252/7717708?login=false 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 2y ago
    The article mentions getting it down to an arm band or patch.
- Mistletoe 2y 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.
  - dredmorbius 2y 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.
coldcode 2y 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 2y 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.
  - delichon 2y ago
    [flagged]
  - pkaye 2y 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.
jkid 2y ago
[dead]
- oezi 2y ago
  This isn't measuring blood pressure, isn't it?
  - barbazoo 2y ago
    And it’s not continuous either.
- deleted 2y ago
  [deleted]
ck2 2y 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://scholar.google.com/scholar?q=earlobe+blood+pressure https://www.todaysmedicaldevelopments.com/article/wearable-blood-pressure-monitoring-technology/ 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 2y 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 2y ago
meowdoesnt the apple watch do this already? or was that just heart rate?
- rrrix1 2y 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 2y 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 2y ago
  It’s one of my favorite procedures! To each their own I guess.
- dredmorbius 2y 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.
robomartin 2y 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.
ryukoposting 2y 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/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6912522/
pkaye 2y 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/ https://aktiia.com/
- benterix 2y ago
  I wonder how do you calibrate it in practice.
  - pkaye 2y ago
    They include a blood pressure cuff with the watch. https://aktiia.com/uk/blood-pressure-monitor https://aktiia.com/uk/blood-pressure-monitor
- ryeights 2y 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-calibration 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 2y 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!
ruckfool 2y ago
When will my apple watch support this ?
amelius 2y 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?
deleted 2y ago
[deleted]
bjornsing 2y 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 https://www.bio-beat.com/cuffless-blood-pressure-monitoring
ggm 2y 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 2y 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 2y ago
So cool!
2-3-7-43-1807 2y 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.
deleted 2y ago
[deleted]

269 points by crhulls 2y ago

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

trentnix 2y 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.
- benterix 2y ago
  I wonder if things changed by now.
ryeights 2y ago
The Aktiia bracelet takes measurements automatically but not continuously. It produces about 1 measurement point every hour.

dredmorbius 2y 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-softky 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 2y 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.
- dredmorbius 2y 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 2y ago
Paper: https://academic.oup.com/pnasnexus/article/3/7/pgae252/7717708?login=false 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 2y ago
  The article mentions getting it down to an arm band or patch.
Mistletoe 2y 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.
- dredmorbius 2y 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.

coldcode 2y 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 2y 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.
- delichon 2y ago
  [flagged]
- pkaye 2y 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.

jkid 2y ago

[dead]

oezi 2y ago
This isn't measuring blood pressure, isn't it?
- barbazoo 2y ago
  And it’s not continuous either.
deleted 2y ago
[deleted]

ck2 2y 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://scholar.google.com/scholar?q=earlobe+blood+pressure https://www.todaysmedicaldevelopments.com/article/wearable-blood-pressure-monitoring-technology/ 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 2y 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 2y ago

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

rrrix1 2y 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 2y 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 2y ago
It’s one of my favorite procedures! To each their own I guess.
dredmorbius 2y 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.

robomartin 2y 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.

ryukoposting 2y 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/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6912522/

pkaye 2y 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/ https://aktiia.com/

benterix 2y ago
I wonder how do you calibrate it in practice.
- pkaye 2y ago
  They include a blood pressure cuff with the watch. https://aktiia.com/uk/blood-pressure-monitor https://aktiia.com/uk/blood-pressure-monitor
ryeights 2y 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-calibration 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 2y 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!

ruckfool 2y ago

When will my apple watch support this ?

amelius 2y 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?

deleted 2y ago

[deleted]

bjornsing 2y 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 https://www.bio-beat.com/cuffless-blood-pressure-monitoring

ggm 2y 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 2y 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 2y ago

So cool!

2-3-7-43-1807 2y 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.

deleted 2y ago

[deleted]