Caltech Develops First Noninvasive Method to Continually Measure Blood Pressure

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.

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.

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/

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

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.

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/

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!

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.

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.

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

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?

> 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?

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.

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.

> 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.

When will my apple watch support this ?

So cool!

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