Continuous blood pressure monitoring has always been a major challenge for the biohacking community. Those giant arm cuffs aren’t exactly the kind of thing you want to wear all day and the wrist monitors aren’t super great either. So, [Kaan] and his research team set out to create a better continuous blood pressure monitor. This time as a ring.
When your heart beats, the volume of blood in the blood vessels increases ever so slightly. This increase in volume results in a decrease in electrical impedance because blood is fairly conductive. We’ve seen a similar volume measurement using light for detecting heart rate, but [Kaan] says with impedance, you won’t need to worry about the effect of skin tone on the accuracy of the measurement.
As far as the hardware is concerned, they inject a small, constant 10 kHz sinusoidal current into the finger through 2 current-injecting electrodes, and then measure the resulting voltage drop across the finger with two sensing electrodes, a standard 4-probe Kelvin approach. Their results seem pretty good. They are within 5.27 millimeters of mercury (mmHg) of the gold standard for systolic blood pressure and 3.87 mmHg for diastolic blood pressure across 10 subjects, which they say are within the American Association for the Advancement of Medical Instrumentation’s (AAMI) guidelines. That’s definitely something to catch your attention.
We’ve seen several attempts to measure blood pressure using the analogous photoplethysmography technique, but those generally don’t seem to work out. Will the impedance plethysmography approach overcome the optical technique’s shortcomings? Only time will tell.
How does it works around the difference in impedance caused by sweating?
I’m also wondering about the general variability of conductivity of different people. They solved one variables (skin tone), but they don’t address whether they have simply traded that for a different issue.
Maybe it’s not an issue.
Bioimpedance does change for various reasons over various timescales, including sweating from exercise, diet+weight gain/loss, health, and how excited the person is. Note that it is not only skin resistance that can affect a measurement but also the other intervening tissue, and changes in those tissues likely happen on different timescales. Measuring the impedance on a time scale (pulse to pulse) short enough to use it for changes caused by blood pressure would mostly not be affected by skin impedance changes since the timescale would be much shorter. You could even use a measurement of pulse timing to isolate the bioimpedance changes of interest to specific sampling times. It is also possible to measure bioimpedance across a range of frequencies, which may help increase signal to noise. There is a commercial IC (AD5933) which measures bioimpedance though it would probably be too slow to use in this application. Here’s a paper about a bioimpedance application of the IC which might be interesting: https://www.cs.dartmouth.edu/~kotz/research/cornelius-wearable/cornelius-wearable.pdf There are other papers online about the many potential applications of bioimpedance.
As a physician , this might sound good but you need more than 10 patients to validate it. Even automatic cuffs are not as accurate as the manual ones. I guess time will tell.
Hum, might be reading it wrong (in the paper itself), but they trained a ML model for each person using the ring, and as far as I can tell, the reported results were from the same data the models were trained on… So they basically are just reporting the difference from their trained model to the results of the BP readings from conventional sensors, using the same data.
I’m reasonably sure they can get some results from this on a second run, but seeing as they even used ultrasound to position the rings over the artery, I’d be very suspicious that this can be used in the field with any usable readings.
It surely cannot be used in the field today, but it’s a start. It proves it’s possible. If it’s economical is another question, that would not need to be answered if they could not prove it’s possible.
IIRC Finger blood pressure monitoring has never been shown to be accurate ‘enough’. Not under ideal conditions, much less built into a ring. IIRC it’s just biology. Bad circulation, bad data.
Weather ‘enough’ is a legal or medical term is up to debate.
Solution: Wrap this tech around test subject’s necks. Then, perhaps, arm blood pressure monitors won’t be accurate ‘enough’.
It always seems prudent, whether or not a prototype or idea becomes mainstream, it’s likely important to establish prior art in the event some medical equipment manufacturer tries to rip off your idea. More power to the folks with ideas.
I can’t imagine anyone preferring to wear a ring with wires instead of something on the arm or wrist. At least if they actually do anything during the day.
Slight tangent, but I always thought it must be pretty easy to measure blood pressure with an implant (a tiny sealed capsule with a strain gauge, in contact with the bloodstream). You could power it through an RFID interface, and the temporal resolution should be good enough to measure your pulse as well.
That’s what I was also thinking so ….. +1.
I’ve been wishing for a long time for a subcutaneous sensor that records various body parameters. You can then just go to your doctor and get him to read it out and help with the diagnosis of a pain, lack of sleep or whatever. If enough data is collected, the cause of most of diseases can be solved in a short period of time. The biggest hurdle will be addressing the privacy of this data.
No, that’s not pretty easy. You’d have to insert it in an artery, which means it will have to be locked into place, so it does not get swept away and causes an embolism downstream. Which also means you have to open up an artery, an invasive procedure. The material will need to not cause immune reactions, but also not to cause clots to form in it. All relatively easy with implants in tissue, harder in the bloodstream.
It would be a real surgical procedure, yes, but the reason I always think about this for blood pressure in particular is that the entire thing can be encased in glass or silicone, as it doesn’t need to (and shouldn’t) interact with the blood chemically.
It also doesn’t necessarily need to be inside an artery, any more than a BP cuff does – all the squishy stuff is pressurised. Though if it was inside an artery, it could potentially also have some kind of spectrometer, to monitor dissolved gases, blood sugar and stuff like that, while still being sealed in glass.
As @elmesito says, with something like this you could show your doctor exactly what happened when you blacked out at the mall. In terms of medical semiotics, it’d be like going from police sketches to CCTV.
That’s not how coagulation works. Any disruption to laminar blood flow will cause clots. Look up and oldie but goodie- the Virchow triad How “inert” the material is barely matters. Mechanical heart valves, for instance, require life long anticoagulation.
The engineering part is “easy,”… If you can solve the clot issue you would have a major Nobel level discovery on your hands with huge and far reaching applications.
pig and cow valves are also used as an alternative to mechanical valves and don’t require anticoagulants; could similar sterile biological material be used to encase the device?
I’ll put another towards not having it in the artery itself. There’s no reason it couldn’t go around an artery and sense the pressure changes still.
Sp02 is already able to be detected with light so there’s no reason it still couldn’t have a super low power light sensor to do the same thing.
Combine it with something like RFID like you mentioned and you can have it link with a special smart watch or ring or whatever that powers it and gets it’s data continuously.