Cuffless Blood Pressure Monitors: Approved but Unproven

Jagmeet P. Singh, MD, PhD; Ramakrishna Mukkamala, PhD; George S. Stergiou, MD


April 12, 2023

Recorded on March 24, 2023. This transcript has been edited for clarity.

Jagmeet P. Singh, MD, PhD: Hi. I'm Jag Singh from Medscape Cardiology. I'm delighted to be here with two esteemed panelists. We have with us George Stergiou, who's a professor of medicine and hypertension from the University of Athens in Greece, and we have Rama Mukkamala, from the University of Pittsburgh, who's a senior engineer.

It's going to be a phenomenal discussion on the arena of cuffless blood pressure monitoring — where it's going in the future and how we need to keep on top of it.

Let me start with you, George. Hypertension is a big issue. Monitoring is a big issue. Why are people having so many problems with cuff-based strategies that we're now thinking about cuffless strategies?

George S. Stergiou, MD: First, I have to say that cuff-based measurement has been the basis for the whole chapter of clinical hypertension. This is how we managed to identify the condition, to diagnose, to manage, and to follow. This has been a great success for efficiently treating people with high blood pressure and preventing disease. It has been a success story.

On the other hand, cuff measurement causes several issues when it is used in the office, when it is used by people at home, and also for ambulatory monitoring. First, it takes very little information on the blood pressure behavior. Blood pressure is a continuous phenomenon for 24 hours, beat to beat. By taking two or three measurements in the office, or morning and evening at home, or even every 20 minutes for one 24-hour period every few months, we get too little information on the burden that the vasculature in the heart and the brain sees from high blood pressure.

Current Cuffless Strategies

Singh: Let me move to Rama. Rama, what are the different cuffless strategies that are available right now, and how do you differentiate among them?

Ramakrishna Mukkamala, PhD: There are a number of cuffless blood pressure measurement methods, and several devices now have regulatory clearance in at least one country. Off the top of my head, I can think of seven. These seven, at least — and perhaps all the devices that have regulatory clearance — operate based on pulse wave analysis and pulse arrival time. Pulse wave analysis involves measuring a peripheral arterial waveform, usually using an optical sensor or a force sensor, and then extracting features from the waveform using machine learning and calibrating the features to blood pressure values.

Pulse arrival time methods work in conjunction with pulse wave analysis methods. Pulse arrival time methods also record the electrocardiogram. They will also extract features from that signal and the arterial waveform.

Then those features are likewise calibrated to blood pressure values. The calibration is aided by periodic cuff blood pressure measurements, so you need to take a cuff blood pressure measurement, say, every month, and that's used in the calibration process. That's the most typical way to do the calibration. There are some devices that will now do the calibration just based on the demographic information of the user.

Singh: I understand that there are — and again, correct me if I'm wrong — reproducibility issues with them and that there are several demographic variables that can confound the measurements.

I'd love to get your thoughts, George. With all that exists right now, what is the stance of the European Society of Hypertension on cuffless monitoring?

Stergiou: We, as clinicians, care about accuracy, but also usefulness. We see the potential of these technologies for providing to us a complete picture of the blood pressure profile and behavior of an individual. We expect these devices to be more useful to establish the risk associated with the blood pressure behavior in an individual.

On the other hand, we realize that, on top of what Rama said about different technologies —it was an engineering presentation you had — for me as a clinician, these are tools. There are different tools — not only different technologies but different tools. It's different if it's a wearable device, a smartwatch, or a portable device; it is on your smartphone, or it is a device that needs calibration, so it becomes an individual device.

We believe in the potential of these technologies. In fact, I personally believe that if we get it right, we can take the whole chapter of measurement and get rid of what we have. We need to prove the accuracy and you need to prove the usefulness on top of what we already have. We are happy with complexity, but it has to prove its added value.

Aurora Project: Current Tech Doesn't Work

Singh: Rama, can you tell us a little bit about the Aurora Project?

Mukkamala: Yes. George and I wrote an editorial on the Microsoft Research Aurora Project. Let me give you the gist. Microsoft Research, as we all know, is one of the most prestigious companies in the world, and they put huge resources into investigating cuffless blood pressure measurement.

They basically studied the same tech as the regulatory-cleared devices. They found that the devices didn't work. It's not that they didn't work well, it's that they offer zero value. They gave their data away from their study, and based on everything in the public domain, they apparently quit cuffless blood pressure measurement.

Singh: Wow. I don't know how to interpret that, but it's certainly a setback. It helps us understand what we need to do for the future. On that note, George, what needs to change and how do we use this information to guide the future?

Stergiou: First, it's not only this project, which is a mega-project, but other, smaller projects. It's important because they come from different directions, from independent study, and show to the same direction — that we don't have it for the moment.

As a clinician, I understand that it's more difficult than I thought. I'm not going to invent something like that. Rama and other engineers will do that. We realize that although it would be superb to have it and investigate how to use it, it doesn't seem that we are going to get it soon.

For the moment, we are quite skeptical on how to inform people, our colleagues and our patients, because everybody is very excited with cuffless technologies. Everybody likes to wear something, have your blood pressure read, and they don't care too much for the details.

I'd also like to add that the paper by Microsoft Aurora Project was too complex for me to understand. This is why we wrote this editorial, to try to explain to our colleagues the message behind a mega-project on cuffless measurements, which means we don't have it yet for clinical medicine.

Clinicians Are From Venus, Engineers Are From Mars

Singh: You told me right at the outset, George, that clinicians are from Venus. So you're from Venus and Rama is from Mars, as he's an engineer.

Rama, what do you think needs to happen from the engineering side, or is it the clinician perspective that is what is creating issues out here? How would you approach this?

Mukkamala: I think there are two things. The first thing is more on George's expertise, but to have a standard to validate cuffless devices would be important, so that the regulatory bodies could adopt it and that's how they could clear devices. It would prevent inadequate devices from being used for clinical purposes.

On the technology side, the general approach is to make measurements that are easy, and then let's throw it in a neural net and see if we can get blood pressure. So far, that hasn't worked. It's not that machine learning doesn't work; machine learning works great. It's just that the measurements that are being made don't have blood pressure information in them.

I think we need to look at different approaches, so technological breakthroughs on completely different methods. Maybe taking inspiration from how automatic cuffs work. Maybe targeting the aorta. Most of these devices target small vessels, they have smooth muscle, and that causes many technical problems. The aorta is more elastic and it's hard to get convenient measurements from it. I didn't mean to get too technical.

Singh: No, I think that's perfectly on point.

George, I find the whole concept daunting. Our entire literature has been based on cuff-based monitoring, and how we practice medicine is based on cuff-based monitoring. Do you think that the advent of cuffless, whenever it comes down the pike, is going to mean that we have to redo all those studies again? What are your thoughts on that?

Stergiou: Any new technology has to take into account the huge amount of clinical data that we have, and it has to serve the science that we have developed, which has been very efficient — but can improve.

There is no question that these devices have to be able to inform based on the thresholds we have, which are based on millimeters of mercury. We can't change that. It's so difficult to replicate all this work. It has to continue the clinical science we have developed for decades. They have to report millimeters of mercury.

Singh: For sure. That makes sense. Changing the units is going to totally change our mindset and really impact the way we treat our patients. That can become a huge challenge.

Stergiou: We have done that already by adopting electronic devices. Today, we recommend devices for office, home, and ambulatory. They are also cuff devices, but they are different. They have nothing to do with mercury and millimeters of mercury. They use another principle, but they transform the measurements to millimeters of mercury. It's so difficult to change all humans...

Singh: Absolutely.

Stergiou: …patients, doctors, and primary care to a different kind of measurement.

Singh: Absolutely. That's a great point. Before we close out, I'm going to give both of you a quick opportunity to share any wrap-up comments. Rama, let me start with you. Any takeaway comments for clinicians and engineers that you'd like to leave us with?

Mukkamala: I think there are many studies in the literature, and many of them on the same tack — this pulse wave analysis and pulse arrival time. Many of them will report that those methods work well. In most instances, they're actually misleading. I would say, don't take these papers at face value. We have to look at them critically and then conclude whether we think that the data show these devices work well or not.

Singh: Good to know. Any parting pearls from you, George?

Stergiou: Jag, I said at the beginning that you invited here my friend from Mars, and I'm from Venus. On Venus, we don't care how the devices work. We don't care because we cannot understand. We don't have the background. At the end of the day, we will take the devices and try to see if they work in our patients in the way we use them. We have standards to evaluate them and we don't care how they work — provided that they do.

For 30 years, the Americans had a different protocol, the Europeans another one, the British their own protocol, and the Germans their own protocol. A few years ago, we decided to have a universal standard, and then we were happy and relaxed. What's the problem? The problem is that this universal standard provides almost zero information for testing cuffless devices. If you see cuffless devices tested using this universal standard that we love, it's not enough.

The second is that we need another standard. And we don't need another one; we need several, because this is not one technology. Rama has taught me that they work differently. They are different in their background technology, in the kind of devices, in the intended use, and whether they are wearable. We need to end up with a standard that works for every kind of cuffless device. We'll probably need some time to come up with something useful. When we have it, it can really make a change to us and our patients.

Singh: I couldn't agree with you more. Whether you're from Venus or Mars, whether you love patients or technology, the ultimate goal out here is to provide better patient care and make the outcomes much better than where they are today. I want to thank you both for taking the time to be here.

This was a fascinating discussion on cuffless strategies, and I cannot wait to get you back again to see where this has further advanced, because this is certainly an area to watch.

Thank you, once again, and thank you to all those who are listening.

This is Jag Singh from Medscape Cardiology.

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