Wireless Medical and Fitness System Design Guidelines Leverage Low-power Communications Protocols

By Dave Bursky

Contributed By Electronic Products

Medical instruments are getting more portable and cutting the cord when it comes to sending data back to a host system. In a system well-designed for improving health, people with heart disease or diabetes can transmit their vital signs, blood pressure, heart rate, oxygen saturation, glucose levels, temperature, weight, and respiration, seamlessly from home to their health professional, and get real-time feedback on their condition. A busy professional is able to receive a daily electronic check-up on the health status of an aging parent who lives alone, suffers from a series of chronic conditions, and is on multiple medications. Similarly, fitness devices that measure pulse rate, temperature, breathing, and other factors have also gone wireless so a traveling businessperson can have a real-time discussion about the workout they just completed with a trainer who is hundreds or thousands of miles away. Also gaining in popularity are smart watches that pack wireless interfaces and sensors. These devices can also be used to link to medical equipment, providing readouts of data collected from body sensors.

Whether the devices are in a hospital, a doctor's office, or in a consumer's home, Wi-Fi and Bluetooth wireless interfaces are the links that connect the medical systems or fitness products to each other and to a host system, either locally or remotely via the Internet.

Wireless standards

To help ensure that all of the varied devices can talk to each other, the Continua Health Alliance (henceforth referred to as Continua), a non-profit, open-industry organization of healthcare and technology companies with over 200 members worldwide is dedicated to establishing a system of interoperable, personal, connected-health solutions that will foster independence and empower individuals while providing the opportunity for truly personalized health and wellness management.

One Continua goal is to establish systems of interoperable telehealth devices and services in three major categories: chronic disease management, independent aging, and health and physical fitness. Design guidelines published by Continua are based on proven connectivity technical standards and include Bluetooth for wireless and USB for wired device connections. Version 1 of the guidelines was released to the public in June 2009, and an updated set of guidelines, Version 2, will soon be released.

Continua selected Bluetooth low energy and ZigBee wireless protocols as the wireless standards for its Version 2 Design Guidelines.¹ Bluetooth low energy will be used for low-power mobile devices, while ZigBee will be used for networked low-power sensors such as those enabling independent living. The Alliance is establishing a product certification program that will provide consumers with increased assurance of interoperability between devices, enabling them to more easily share information with caregivers and service providers. The guidelines help technology developers build end-to-end, plug-and-play systems more efficiently and cost effectively.

The Continua Health Alliance's Design Guidelines contains references to the standards and specifications that Continua selected for ensuring interoperability of devices. It also contains additional Design Guidelines for interoperability that further clarify these standards and specifications by reducing options in the underlying standard or specification or by adding a feature missing in the underlying standard or specification.

For the interfaces, the Continua Alliance has selected the IEEE 11073-20601 Personal Health Device Communication protocol for the optimized exchange of information. This international standard provides an interoperable messaging protocol and has definitions and structures in place to convert from an abstract data format into a transmission format. Therefore, a consistent Continua data exchange layer is enabled across the interfaces. The IEEE 11073-20601 protocol acts as a bridge between device-specific information defined in individual so-called device specializations and the underlying transports to provide a framework for optimized exchange of interoperable data units. The selected device specialization standards specify the data model and nomenclature terms to be used for individual devices.

The Alliance has also defined a touch area network (TAN) interface that permits a Continua device to communicate with a Continua Application Hosting Device (AHD), with a short touch using near-field communications (NFC). A user brings the two devices into close proximity for a short period of time – touching. While the devices are touching, data may be exchanged bidirectionally. In a typical use case, a user would transfer blood pressure readings from their blood pressure meter (Continua device) into a mobile phone (Continua AHD) by simply touching the two devices together.

In a personal area network application, the protocols selected permit the device to transfer data in the following three communication styles:
  • Transaction communication style: When it is required that the transport between the device and the AHD communicates a single data point immediately.
  • Streaming communication style: When it is required that the transport between the device and the AHD communicates several data points continuously.
  • Batch communication style: When it is required that the transport between the device and the AHD communicates previously collected data points at a later time.
As part of the PAN, the Bluetooth low energy specification has been selected as the low-power wireless technology for the alliance. The specifications relating to Bluetooth low energy are in version 4.0 of the core Bluetooth specifications. Any related profile specifications are detailed in separate documents. Bluetooth devices that support Bluetooth low energy can be either a dual-mode device, which is a device that supports both standard BR/EDR Bluetooth and Bluetooth low energy, or a single-mode device, which is a device that supports Bluetooth low energy only. It is envisioned that service components supporting Bluetooth low energy will mostly be single-mode devices.

Google Glass and more

Smartphones and tablets with their embedded Bluetooth and Wi-Fi interfaces have become an indispensable companion to the medical and sporting products. Running an application on the phone or tablet turns those devices into data collection and data analysis tools that help evaluate the person’s condition or performance. Even the forthcoming Google Glass wearable computer headset is finding a home in medical applications such as surgery, anesthesia, and telemedicine (Figure 1). At the heart of the Google Glass headset is an OMAP4430 processor from Texas Instruments running at 1 GHz with 400 MHz DDR2 memory, 16 Gbytes of Flash memory from SanDisk, a MEMS microphone, a lithium-ion battery, a projection display and camera, a bone-conduction speaker, and a custom touchpad controller.

Google Glass headset

Figure 1: The Google Glass headset with its camera and projection display can be used by surgeons to stream video to a remote expert during an operation to get guidance, or sent to a classroom to teach students.

Two other Google Glass components are worthy of special note:
  • A nine-axis (Gyro + Accelerometer + Compass) module from CSR, designated SiRFstarIV GSD4e, is a complete navigation processor built on a low-power RF CMOS single die. Incorporating the baseband, integrated navigation solution, software, ARM7 processor, and RF functions that form a complete internal ROM-based standalone or aided-GPS engine, the part’s SiRFaware technology allows it to both avoid maintaining full power to achieve maximum performance and not having to turn the GPS receiver completely off to save power. It requires only 50 to 500 µA to maintain hot-start capability.
  • InvenSense's MPU-9150 MEMS inertial sensor is an integrated nine-axis device that combines a three-axis MEMS gyroscope, a three-axis MEMS accelerometer, a three-axis MEMS magnetometer, and a Digital Motion Processor hardware accelerator engine. The MPU-9150 incorporates InvenSense’s MotionFusion and run-time calibration firmware that enables manufacturers to eliminate the costly and complex selection, qualification, and system-level integration of discrete devices in motion-enabled products, and guarantees that sensor fusion algorithms and calibration procedures deliver optimal performance for consumers. InvenSense also offers a dev/eval board for MPU-9150 designated MPU-9150EVB.
One of the latest applications for the Google Glass comes from Pristine, a company based in Austin, Texas. They have developed a HIPAA-compliant application called EyeSight that delivers secure first-person video streaming to and from the Google Glass headset. Surgeons in an operating room can use the EyeSight application to stream the operation viewed by the Google Glass camera to a remote expert to help guide the operation and receive real-time feedback (both audio and video). Additionally, the video could be streamed to a classroom to teach doctors or students.

Among the newest data collection tools available to consumers or medical practitioners is the smart watch or smart bracelet. There are already over a dozen smart watch vendors from which to choose, and more are expected to join the fray. However, what exactly is a smart watch? The answer actually takes two paths: the first path is a more cellphone-targeted device that helps with phone calls, text messaging, email, and other smartphone-related wireless functions. The second path is more sports/health related in which the watch or bracelet monitors blood flow, movement, skin temperature, and other body vitals. Let’s examine what goes into one of these.

One of the latest entries is the Basis watch from MyBasis.com. The watch contains multiple sensors: an optical blood-flow sensor, a three-axis accelerometer, a perspiration monitor, and sensors for both skin-temperature and ambient temperature (Figure 2, left and right). The sensors on the back of the watch contact the skin or, in the case of the blood flow sensor, send out a beam of green light and measure the reflection. Able to continuously capture heart-rate patterns, motion, perspiration, and skin temperature throughout the day and night, the Basis watch runs via an internal lithium-ion polymer battery that can last up to four days without recharging. Data collected by the watch can be sent via a Bluetooth 2.1 link to an Android or iOS smartphone or tablet and a companion application running on the phone or tablet lets the user analyze the data.

The Basis smart watch

Figure 2: The Basis smart watch contains multiple sensors to measure blood flow, motion, perspiration, skin temperature and other parameters (left). To measure the blood flow, the green LED on the back side of the watch shines its light into the skin and the reflected light is detected by an optical sensor (right).

There are many other medical-, health-, and sports-related solutions. The examples mentioned here are just the proverbial tips of the iceberg of what can be designed and implemented. For more information on the parts discussed in this article, use the links provided to access product information pages on the Digi-Key website.

  1. Continua Health Alliance Design Guidelines

Disclaimer: The opinions, beliefs, and viewpoints expressed by the various authors and/or forum participants on this website do not necessarily reflect the opinions, beliefs, and viewpoints of Digi-Key Electronics or official policies of Digi-Key Electronics.

About this author

Dave Bursky

About this publisher

Electronic Products

Electronic Products magazine and ElectronicProducts.com serves engineers and engineering managers responsible for designing electronic equipment and systems.