When Is Bluetooth LE Useful in Medical Devices?

Bluetooth's latest iteration Bluetooth Low Energy is providing plenty of opportunity for medical device designers, but the technology also has its downsides.

Chris Newmarker

Bluetooth LE (which stands for "low energy") is a popular protocol for medical device communications and for good reason: In addition to its low energy consumption implied in its name, it is also relatively inexpensive and offers connectivity with most smartphones.

"If you take a look at the medical device and drug delivery market, the big trends there are smaller and smarter. ... Devices that were mechanical only are having more electronics integrated in them. That's the perfect place for Bluetooth Low Energy to provide an additional value add that you're not going to get from a mechanical device," says Bill Welch, chief technology officer at medical device contract manufacturer Phillips-Medisize (Hudson, WI).

But that doesn't mean BLE is a solution for everything.

Here are four important factors to consider:

1. The Amount of Information and Latency Are Important

Traditional Bluetooth was designed to be good at streaming data like audio, while Bluetooth LE saves energy by normally sending small data packages at infrequent intervals, says Chris Conger, Phillips-Medisize's director of technology development. Bluetooth LE's ability to stream data is very limited and not good enough to support high quality audio streaming. 

"In the medical space, that means that there's a lot of applications where it's very good. If you have a heart rate monitor and you have to send just a few bytes of data every second, that's a very low amount of data compared with streaming of audio, where you are sending maybe 200,000 bits of data every second," Conger says. (See Welch and Conger discuss Bluetooth LE at MD&M East, June 9-11, 2015 in New York City.) 

Streaming audio would also be problematic because it requires low latency. "You have to send it with very little time delay if the audio has to be synchronized with visual cues, as in video or live hearing assistance applications," Conger says.

It would also be tough to use BLE for clinical and hospital-quality ECG, Conger says. "The max data rate for BLE is not good enough to transmit this type of data, and be reliable enough for this environment. ... Research-quality ECG is probably not possible."

But Bluetooth LE is a great option when it comes to body-area networks for medical testing in a clinic or home.  During a sleep apnea study, for example, a patient wears a collection of sensors during a night of sleep, covering everything including heart rate, blood oximetry, breathing, snoring, chest expansion, and 1 or 2 channel low resolution ECG. Bluetooth LE would be optimal for the sensors because it would allow the sensors to be really small.

2. There Is Wiggle Room, But It Could Come at a Price

When it comes to latency, it is possible to program BLE's connection interval anywhere from a fraction of a second to a few seconds.

"If you had a remote control for a medical device, and chose a connection interval for 2 seconds, what that means is that if you press a button on a control, you would have to wait up to 2 seconds for the resulting action to happen. ... Would it be annoying for the users?" Conger says.

3. BLE Works on Most Smartphones

The Bluetooth LE standard came out in 2010, so essentially all smartphones now have the technology, Conger says. "If you put it into your medical device, it's likely to be compatible with any smartphone in the market, because smartphones turn over quickly. There are very few smartphones out there that were in use before 2011."

If you want a smartphone app for your medical device, Bluetooth LE can be a great option--a huge connectivity advantage in the realm of fitness devices and unregulated consumer medical products.

In the regulated space, it's much more complicated because the FDA would be resistant when it comes to an app for multiple smartphones controlling a critical medical device. There are too many phone models and operating systems that would need to be tested, according to Conger.

"Someone might have an app that allows them to see how their medical device is performing, but it doesn't do the opposite. It doesn't allow them to control their medical device," Conger says.

For example, BLE would be useful when it came to diabetes injection pens transmitting dose recommendations synthesized off data including meals, blood glucose meter readings, time of day, and exercise. "The app would recommend the dose, and the patient would accept and administer the dose directly on the pen."

Automated drug inhalers could use Bluetooth Low Energy to send dose history from the inhaler and provide an improved user experience through a smartphone app, according to Conger. They could even provide links to YouTube videos when various user errors occur.

4. Bluetooth LE Doesn't Work Well in Implantable Devices

Both Bluetooth and Bluetooth Low Energy have limited implantable medical device applications because they use 2.4GHz radio frequency, and cannot penetrate well into human tissue. 

"This obviates its use in implantable applications," Conger says. "Even in hearing aid applications, the body proximity causes degraded performance.  You can demonstrate this easily by cupping your hand around a BLE device to cause the wireless link to drop out."

Chris Newmarker is senior editor of Qmed and MPMN. Follow him on Twitter at @newmarker.

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