A photo of an Eko Health Core digital stethoscope on a patient's chest.

Eko Health’s Core 5000 digital stethoscope has a rechargeable lithium-ion battery that lasts up to 300 minutes of continuous use, or up to 60 hours of regular clinical use. The stethoscope uses Bluetooth 4.2 low-energy
and offers a wireless listening option. [Photo courtesy of Eko Health]

Eko Health has learned a bit about batteries and Bluetooth while developing AI-powered medical devices to help physicians detect cardiovascular disease.

Eko Health’s devices include hardware — in the form of its Duo and Core digital stethoscopes — and algorithms that analyze the acoustic and electrocardiogram (ECG) signals collected by those handheld devices. Together, their hardware and software is cleared by the FDA to detect heart murmurs, atrial fibrillation (AFib) and signs of low left ventricular ejection fraction.

Related: How Eko Health’s AI-powered stethoscope detects early signs of heart failure

In an interview with Medical Design & Outsourcing, Eko Health co-founder and CEO Connor Landgraf said Bluetooth and battery advances deserve some of the credit for making the device developer’s products possible. He shared some of Eko Health’s lessons with those technologies — including considerations when choosing between Apple’s iOS and Android platforms — as well as general advice for medical device designers and engineers.

Bluetooth design tips

A physician uses an Eko Health Duo digital stethoscope to collect acoustic and ECG data from a patient.

Eko Health’s algorithms use acoustic and ECG data collected by digital stethoscopes (pictured is Eko’s Duo stethoscope). [Photo courtesy of Eko Health]

“Surprisingly, we’ve actually been able to work pretty well with inside the bounds of Bluetooth,” he said. “Part of that was writing a custom protocol and going down to very low level in terms of the actual design of the control of the Bluetooth protocol and firmware, and being able to do a lot of work around data compression in a lossless fashion signal processing above that to ensure that we are really honed in on the frequency that we cared about, and then optimizing for error checking and the appropriate assessment to make sure that there was no data loss or data corruption in transit.”

“We basically wrote a protocol specifically for the data type that we were trying to transfer, and as a result, we have been really happy with the durability and reliability of these connections,” he continued. “We’re not talking 30,40 feet here, we’re talking 5 feet in the exam room. It’s worked quite well for us and we’re really happy with it.”

He had words of caution for device designers and engineers tempted to start from scratch.

A portrait of Eko Health co-founder and CEO Connor Landgraf.

Eko Health co-founder and CEO Connor Landgraf [Photo courtesy of Eko Health]

“At least in our situation, we’ve definitely seen plenty of other companies choosing to rewrite stuff from the ground up and choosing their own customized protocol and not relying on Bluetooth, but using some modified version of a different 2.4 GHz protocol or something like that,” he said. “Operating inside the constraints of a very well accepted and well tested platform like Bluetooth but then doing a lot of customization to get the exact type of data and the exact type of packet structure and the appropriate checksums and such worked really well for us. We got all the structure and stability of a really well tested code base like Bluetooth that was supported by a lot of different vendors and different chipsets, and got the customizability that we wanted to be able to make it work on our specific structure.”

Apple iOS vs. Android

One of the biggest considerations when working with Bluetooth is the variable quality of receivers, which might influence a device developer’s choice on whether to support Apple’s iOS versus Android platforms.

“In the Android ecosystem you have a huge number of Bluetooth chipsets from a huge number of manufacturers with highly variable quality between them. That creates a testing challenge as well as a never-ending list of possible handsets or tablets that customers might be using. You’d have to kind of narrow it down to the ones you’re going to support and the rest are not necessarily going to be officially supported,” he said. “A constrained set of compute environments that you’re going to support on the mobile side for us was pretty important. We ran into problems otherwise. In our situation, we found the iOS support for Bluetooth and just the quality of the chipset is quite a bit better and it’s a much smaller set of vendors and chipsets to deal with, therefore a more constrained problem to solve.”

“The big chip guys, the big vendors in Android are great,” he continued. “The ones that make up 80% of the market are fantastic. But that last 20%, it’s just absolutely staggering how many vendors you’ve never heard of that are making different random phones. The quality of the hardware falls off pretty fast and it’s just not solvable in those situations.”

Battery tips for handheld medical devices

On the portable power side, Landgraf said there’s “nothing particularly revolutionary” about the rechargable batteries Eko uses, but he offered some general tips for mobile device developers.

“We ended up choosing pretty standardized battery structure and battery chemistry — off-the-shelf lithium ion for the most part — with a lot of rigorous validation of the batteries to ensure that they’re high quality,” he said. “With any sort of med device battery, there’s a good bit of variability in the quality of vendors on the battery side, so pick a vendor that has the certifications that you want on the cells and has the appropriate rigor and just overall quality to be able to support consistency and and save batteries. That’s a big priority.”

“Many times with small batteries, you run into problems when you try to squeeze very high volumes or very high capacities into a small space,” he continued. “If you can relax those constraints and use a slightly less dense battery, not trying to optimize capacity quite as much, you just find that durability and reliability in the batteries improves a lot. But when you try to cram in large number of cells or larger capacity into a very small face, it creates more problems for many of those battery manufacturers who are trying to squeeze the narrowest area between connectors and stuff like that.”

Read more from our interview with Eko Health co-founder and CEO Connor Landgraf here.