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Hypertension, or high blood pressure, is often described as a 'silent killer', because many people who suffer from it do not show any symptoms. Yet hardening of the arteries can decrease the flow of blood and oxygen to the heart, brain and/or kidneys, causing serious and sometimes fatal damage.
The World Health Organisation (WHO) estimates that 1.28 billion adults aged 30-79 worldwide have hypertension, two-thirds of whom live in low- and middle-income countries. Less than half (42%) of sufferers are diagnosed and treated, and only around a fifth (21%) have the condition under control.
Blood pressure is often measured by health professionals when patients visit medical facilities for check-ups, but consumers can also monitor their blood pressure more regularly at home using commercially available cuff devices, either on the upper arm or the wrist. However, neither arrangement gives physicians what they really need – an accurate and regular supply of blood pressure data that they can use to make diagnoses and manage treatments.
There's a lot of interest in developing a convenient wearable device, either standalone or incorporated into a smartwatch, that can monitor blood pressure continuously and accurately. The first to market, in January 2021, was Aktiia, whose bracelet/smartphone app solution is currently available in the UK for £199.99 and France, Switzerland, Germany/Austria and Italy for €209.99 (~$271).
Aktiia's roots go back to 2005, when its co-founders began 13 years of research on sensor and algorithm development at the Swiss Center for Electronics and Microtechnology (CSEM). This led to a working prototype in 2017, the spin-off of Aktiia in 2018, and further product development, clinical validation and regulatory approval prior to the January 2021 launch.
Aktiia's Optical Blood Pressure Monitoring (OBPM) technology uses standard optical sensors to gather photoplethysmographic (PPG) signals from the arteries in the wrist as they pulsate. The shape of the PPG waveform contains information about blood pressure, and the OBPM algorithm strips the noise from these signals to deliver accurate systolic (pressure when the heart beats) and diastolic (pressure when the heart rests between beats) readings, along with resting heart rate.
Aktiia's wrist-based measurements must be initialised by synchronising them with readings from a traditional upper arm cuff, which is also supplied. The bracelet then needs to be recalibrated on a monthly basis.
The accuracy of blood pressure monitors is validated under the ISO 81060-2 standard, which stipulates that a product must be tested against a trusted reference device: examples include an (invasive) arterial line, an arm cuff and a stethoscope, and a volume clamp on the finger, which allows for measurement in different body positions.
Aktiia's pivotal clinical trial showed that its solution performed within the ISO accuracy standards for systolic and diastolic measurements, and for measurements taken in multiple body positions. This led to it receiving a CE Mark as a Class IIa medical device in December 2020.
"To get physicians to trust this you need to provide them with an overwhelming amount of information," Aktiia's CEO Mike Kisch told ZDNet. "We have nine clinical studies going on right now across the world; we're transparent with our clinical studies and outcomes, and have been published in 22 peer-reviewed publications," he added.
The Aktiia bracelet is a lightweight and unobtrusive wristband device comprising a black silicone strap and a small hardware pod containing the optical sensors, chipset, memory and battery. There's a small charging station into which the bracelet slots, where it's held -- not particularly firmly -- by magnets; the dock connects to a charger (not supplied) via a Micro-USB to USB-A cable. According to Aktiia, battery life is 'up to' nine days, with a full charge taking 90 minutes. When it's charging the bracelet the dock's red LED blinks red, changing to a steady glow when the device is fully charged.
Aktiia bracelet specifications
14-21cm (5.5-8.25 inches)
Polished ceramic casing, hypoallergenic silicone band, durable stainless steel hardware
Up to 9 days; full charge in 90 minutes
Bluetooth 4.2 or later
iOS (11 or later), Android (8 or later)
IP rating (dust/water resistance)
Device: 16mm x 34mm x 8.5mm • Strap: 14mm x 231.5mm x 0.75mm
The initialisation/calibration unit comprises an inflatable upper arm cuff to which is attached a chunky 271g device, much of which is taken up by its 1000mAh battery.
Aktiia cuff specifications
22–42cm (8.75-16.5 inches)
IP rating (dust/water resistance)
74.3mm x 28.2mm x 133mm
Aktiia's smartphone app is available for iOS and Android devices. Once you've created an account and a profile, paired the bracelet and initialised it using the cuff, you're good to go. The app presents colour-coded SYS/DIA readings for two-hour intervals through the day, with week and month views also available. The home page also shows average measurements for the past 24 hours and for night versus day, plus the percentage of time your blood pressure and resting heart rate were in the healthy/normal range over the past 24 hours. One thing you can't currently do is get a spot reading of your blood pressure via the bracelet: for now, you'll have to use the (less convenient) cuff for that.
The app's Devices page lets you make Bluetooth connections to the bracelet and cuff, shows the remaining battery capacity for both devices, and reminds you when the next cuff initialisation is due.
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The Profile page holds information on your gender, height and weight, your sleeping schedule, and any medications you're on. It also lets you download a weekly PDF report – including, if required, all the individual readings. The PDF report is designed to be suitable for presentation to your doctor.
This is a key focus for Aktiia. "To fundamentally change the way blood pressure is monitored certainly involves consumers buying the product and liking it. But equally -- and maybe more importantly -- physicians have to trust the product and be willing to rely upon the data," CEO Mike Kisch told ZDNet. "The great frustration for consumers, certainly with anything worn on the wrist, is that it may gather data, but typically when they take it to the physician, they'll say 'I can't do anything with this' -- and that's not a good experience for either. What we try to do is build a product that the consumer really likes, that they can wear consistently, but they also know that when they bring it to a physician, the physician will be able to go 'Oh, it's Aktiia, I'm familiar with this'."
The out-of-box experience with the Aktiia solution is reasonably straightforward, although there's no quick-start guide and the two printed manuals – for bracelet and cuff – use rather small fonts.
Initialisation using the upper arm cuff took a while to get right, both first time and, as a test, after a couple of weeks using the bracelet. Several adjustments, both of the bracelet and the cuff, were required before the app pronounced that a good-quality signal had been acquired. This included being told to rub the skin on my wrist for 10 seconds, and to 'relax' in a seated position while the cuff inflated and deflated a couple of times.
Obviously it would be preferable, both from a user experience and cost perspective, if Aktiia could dispense with cuff calibration while maintaining measurement accuracy.
"From a consumer perspective, you want to create this easy-to-use product, and this is the one part of the experience where, if you got rid of it, you'd be in a great spot," CEO Mike Kisch told ZDNet. "But when you're a regulated medical device you're always trying to find that balance between consumer experience and building trust and confidence to get people comfortable". However, Kisch forecast that it should be possible to measure blood pressure accurately without cuff calibration "a few years down the line".
In everyday use, the Aktiia solution works well. The app's information displays are clear, and because the optical signals from the bracelet are checked on the phone before being processed and returned by Aktiia's cloud-based algorithms, you only see trusted, validated data. If you check the app regularly it takes just a few seconds for the data to sync and the graphs to update, so long as your phone has an internet connection. If you don't sync regularly, the bracelet has enough memory to store 30 days of sensor data.
We are impressed with the Aktiia 24/7 blood pressure monitor, which delivers a reliable data stream for consumers and, via the downloadable PDF reports, for physicians. 'White coat syndrome', where nervous or stressed patients generate inflated blood pressure measurements when measured using traditional equipment at clinics, should be largely eliminated with technology like this.
Once the system is set up and initialised, the bracelet is comfortable and unobtrusive, and the smartphone app delivers its information quickly and efficiently. Monthly cuff calibration is a bit of a hassle, but this may be phased out in due course, which would be a welcome move. Aktiia does not yet have regulatory approval in the US, but CEO Mike Kisch told ZDNet that this is expected in the next 12 months.
People who already use their smartwatch and smartphone to monitor metrics like heart rhythm and electrical activity (ECG), and oxygen saturation (SpO2), will be very keen to add blood pressure monitoring into the mix. Unfortunately Aktiia doesn't currently integrate with other health apps, making it something of an island. However, given that Aktiia's bracelet uses standard optical sensors and the information they gather is processed by cloud-based algorithms, it's not hard to foresee the company's technology being incorporated into consumer smartwatches and offered as an add-on subscription at some point in the future. That's likely to happen if, or when, cuff calibration can be dispensed with. In the meantime, if you're serious about your health, this device is well worth a look.
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