How Apple will probably implement their blood pressure technology.
Whenever I go to my annual Doctor’s visit, it's nice to notice certain technological advancements when getting that initial screening by the nurse.
Your height is measured by what I would call an extremely large digital caliper connected to the weighing scale, where they lay the top part of the “caliper” on your head, and instantly know your height.
Your weight is digitally and effortlessly measured. I do miss the old scales where you had to move the weights and find that point where the balance finally starts to budge. It was more dramatic since you could see the nurse constantly sliding the weight past the point where you would hope the scale would balance out, only to realize you put on a few more pounds.
Your pulse is checked with an oversized digital clothespin that they put on your finger instead of the nurse clutching your wrist.
Your temperature is checked execution style as they shoot your forehead with infrared rays instead of sticking a thermometer up your…in your mouth.
Finally your blood pressure (BP) is checked…the old-fashioned way. You still have to remove your bulky jacket and strap that overly “velcrofied” arm cuff on while the nurse uses her stethoscope to check your blood pressure.
It’s the one vital information of your health that still requires old methods to get right. As a matter of fact, one could argue that your blood pressure reading is the most important reading of that visit because high blood pressure, or hypertension, leads to worse outcomes for every other health condition.
It’s the most important, yet it is also the most tedious because your blood pressure constantly changes throughout the day. If you buy any sort of portable blood pressure machine, you will notice a whole list of prerequisites before you take your blood pressure. Here is what the CDC says you should do before taking your blood pressure:
Don't eat or drink anything 30 minutes before you take your blood pressure.
Empty your bladder before your reading.
Sit in a comfortable chair with your back supported for at least 5 minutes before your reading.
Put both feet flat on the ground and keep your legs uncrossed.
Rest your arm with the cuff on a table at chest height.
Make sure the blood pressure cuff is snug but not too tight. The cuff should be against your bare skin, not over clothing.
Do not talk while your blood pressure is being measured.
There are other factors as well, such as “white-coat syndrome,” where a patient is nervous about getting their blood pressure taken, and it becomes falsely elevated.
This is all assuming you’re using an arm cuff, which is the most accurate. Wrist cuffs are more convenient but less accurate, and now you have to factor that into the equation.
There have been advances in how blood pressure is measured leading to more convenient choices in the future, such as photoplethysmography (PPG). This is where your device can be used to shine infrared lights into your skin to detect blood volume changes. It is a graphical representation similar to an ECG, where people who know a heck of a lot more than me can determine what is wrong with a person's heart.
This PPG technology can be used on your finger, your wrist, your foot, and even your ears. (Apple Ring and Apple Toe Ring anyone?)
It’s really inexpensive compared to an ECG, and your Apple Watch uses PPG all the time to get information about your pulse, blood oxygen levels, and your cardio health. If someone had a sensor on their wrist and on their finger for example, you can then calculate the pulse travel time (PTT) between the wrist and their finger, and use that time measurement to estimate blood pressure.
According to a study by Nature, that is still less accurate than using an ECG along with one PPG datapoint, such as your wrist or finger. This is actually better for the end user because you only need to have one device, along with an ECG which your Apple Watch already measures.
So in theory, your Apple Watch measures an ECG which has its own waveform, which can be correlated with a PPG waveform that measures changes in blood volume. You end up with 2 waveforms that can then be studied and analyzed along with machine-learning and anonymous, historical user data to determine blood pressure.
That would be how the Apple Watch can analyze blood pressure without any other complicated cuffs that inflate on your wrist, which would be a disaster since so many things can go wrong with an “Apple Cuff.”
“You’re using it wrong.”
“You’re placing it wrong.”
The Apple Watch by itself naturally sits on the flat part of your wrist, and you don’t have to tell anyone how to wear it.
But it doesn’t end with the Apple Watch.
Apple already has another device that can be just as good, dare I say, even better at determining blood pressure.
According to researchers at the University of Toronto, noise-cancelling earbuds have the potential to measure blood volume changes in your ears, giving more data points to analyze a person’s blood pressure:
Many earbuds have noise-cancelling technology, which relies on having an outer microphone and an in-ear microphone. The outer microphone listens for ambient sound while the in-ear microphone listens to what’s happening inside the ear. It turns out that the in-ear microphone is able to pick up on some very interesting sounds inside the body, including heart sounds. Research has shown that you can use the audio recorded from inside the body to measure heart rate, but you’re really able to get the same sounds you would hear from a stethoscope. We’re hoping that we can analyze these heart sounds using different signal processing techniques to infer someone’s blood pressure.
Furthermore, they are even optimistic of bridging many technologies together to get better results:
One study we’re hoping to do alongside this project, or maybe a little later, would be to compare and contrast all the different technologies being considered for blood pressure monitoring – earbuds, smartwatches, smartphones – to see what works best. Can we get better performance with earbuds versus a smartwatch? Can we combine a smartwatch and earbuds to get an even more accurate measurement?
I found another study where they did use time differences between pulses going into the left and right ear, and they were able to get promising blood pressure results that did not significantly differ from the true blood pressure measured with a proper arm cuff.
They called it “Stereo Blood Pressure,” which just sounds awesome.
Not only that, but their diagram even had a guy wearing AirPods.
These studies still had limitations due to small sample sizes and the candidates all being normal healthy individuals, but it’s still progress.
When will Apple actually implement blood pressure measurements into their devices?
Apple doesn’t want to be first at something, they want to be the best.
They were first with Siri, and look at what that’s done for them.
Whenever Apple releases blood pressure monitoring, I think it will be a feature for both AirPods and the Apple Watch. They will work together to get the best data and eliminate any hurdles.
For example, you can’t wear AirPods when sleeping, but you can wear your Apple Watch to sleep and get data and information when in a more relaxed state.
Another hurdle could be a lack of data points for better accuracy. Each device separately only provides 2 data points each:
Apple Watch - single-lead ECG and PPG on the wrist.
AirPods - PPG on the left and right ear.
It’s not hard for most people to wear an Apple Watch and AirPods, so getting information from 4 data points will be a lot easier and unobtrusive.
When you combine those 4 data sets along with advances in AI, machine learning, and historical data analysis, you get a pretty good recipe for blood pressure monitoring.
Of course it sounds easy on paper, but it makes sense for Apple to take a safer approach like they did with Sleep Apnea. Their blood pressure technology will sense changes in blood pressure and not actually give you a reading like 120/80. It will probably alert you if you have an elevated BP over a sustained amount of time, and it will err on the side of under-diagnosing versus over-diagnosing incorrectly.
They would rather have false negatives and put their disclaimer similar to their sleep apnea disclaimer:
It's important to remember: not all people with sleep apnea will receive a notification. If you believe you have sleep apnea you should talk to a doctor.
When this technology is released and ready, it will be a game changer for the healthcare industry because of how effortless blood pressure monitoring can be. Simply wear your AirPods and your Apple Watch and go about your day.
The icing on the cake?
Not knowing when your blood pressure is being taken is the most accurate way of measuring it.