Bluetooth connectivity enable remote patient monitoring

How do we use technology and available infrastructure to minimize doctor-patient visits? The answer: telemedicine. Give a person the ability to test and monitor oneself, and submit the data to a qualified medical professional for evaluation without having to visit the hospital. By providing remote healthcare, unnecessary hospital visits can be minimized or eliminated.

So, how do we accomplish telemedicine? In the past years, telemedicine used to operate by sending information over traditional telephone lines. However, this method can be inconvenient because telephone lines may not be available in undeveloped rural areas. Thankfully nowadays almost everyone owns a mobile phone. Many developing countries opt for wireless infrastructure rather than “wired infrastructure”.As we already know, mobile phones are not only for making and receiving phone calls, they are for sending and receiving data as well. The mobile phone has become indispensable and is considered the “gateway” from personal area network (PAN) to wide area network (WAN). Also, with the advent of Bluetooth wireless technologies, mobile phones can communicate with other devices such as headsets and computers.

With medical devices such as glucose meter, blood pressure meter, pulse oxymeter, ECG and EEG, which can now be kept by patients in their homes, remote healthcare will soon become a common practice. The information that can be collected from a patient will be channeled to the proper diagnostic or medical data center through the use of mobile phones.

Commercially available technologies such as sensors, micro-electro-mechanical sensors (MEMS), analog-to-digital conversion, microcontrollers (MCUs), and short-range wireless communication transceivers combine to create the medical device node. The medical device node can easily transfer various physiological parameters from a remote medical device to a mobile phone, a PC, or any Bluetooth-enabled device.

BLUETOOTH-ENABLED ARCHITECTURE

The architecture to be discussed in this article was built with ease of implementation and simplicity in mind. The idea was to develop a modular solution that would allow for a single microcontroller to do the tasks of the application and the baseband processor of the Bluetooth.

The Bluetooth RF transceiver contains the lower level stack up to the host control interface (HCI), and the upper level stack resides on the single MCU in the system. The Bluetooth upper level stack supports the following profiles: serial-port-profile (SPP), human interface device (HID), and emulation of dial-up-networking (DUN). Again, these profiles are implemented in the MCU.

The upper level stack is incorporated into a real-time operating system (RTOS) and allows for easy task management between application code and Bluetooth functions. The complete Bluetooth circuit needs only a few external components such as a discrete band-pass filter with integrated impedance matching, an antenna, clock oscillators, and a few capacitors.

Figure 1 shows the block diagram of the architecture, which includes ST’s STM32 Flash MCU based on ARM’s latest 32-bit processor core, the CortexM3, as well as ST’s Bluetooth v2.1 baseband-radio chip.

PERSONAL MEDICAL DEVICES

A typical application of a Bluetooth-enabled medical device is described in Figure 2. A Bluetooth-enabled medical device – such as a glucose meter, a blood pressure meter, or an oxymeter – is in charge of taking measurements of physiological parameters, and collecting and storing these data in its internal memory, The device then transfers the records to a mobile phone, handheld PDA, or laptop via Bluetooth.

Then mobile phone transmits the records to a medical data center through SMS or GPRS/UMTS connection. In return, the medical data center sends the results (medical interpretations of the data) to the patient – for example, if the result is good or not; if the patient must re-take the test; or if the patient should visit the doctor.

Thanks to Bluetooth protocol, a medical device can directly contact the medical data center by a simple dial-up networking (DUN) connection that will use the mobile phone as a GPRS/UMTS gateway. In this case, the DUN profile of the Bluetooth is used. All the patient has to do is to initiate the dial-up on the medical device by (for example) simply pressing a button. This will enable various types of Web-based services allowing remote patient monitoring.

In order for STMicroelectronics to configure its platform to this kind of medical use cases, it studied different use cases of a periodic glucose meter and a continuous glucose meter. A periodic glucose meter corresponds to the use case where the patient needs to send measurements over Bluetooth a few times day after each measurement, or the meter waits until the end of the day and sends all daily measurements at once. The Bluetooth link is then activated to send the data and is switched off after the tasks have been completed.

The number of times the Bluetooth link has to be enabled in a day is less than 10 times. This function is governed by the fact that the period of Bluetooth activity is very small compared to the period of inactivity. In this case, the MCU can command the Bluetooth chip to complete power down, thus consuming very small amount of current.

The period of Bluetooth activity is usually less than few seconds. Over a full day, Bluetooth current consumption remains very low – just enough to support the requirements of a battery-powered glucose meter, for example.

On the other hand, a continuous glucose meter corresponds to a device that needs to keep the Bluetooth link active all the time because remote monitoring is done continuously. In this case, Bluetooth cannot be switched ON/OFF, and it is better from the point of view of current consumption to use the sniff subrating feature that is a key feature introduced in the latest Bluetooth standard release, BT 2.1 Lisbon. This feature is automatically enabled when the Bluetooth chip detects no activity after a certain time, which can be completely done in an asynchronous way and does not require microcontroller intervention.

FUTURE EVOLUTION

One technology trend for these kinds of applications is to evolve toward the ultra low power (ULP) Bluetooth standard. Indeed, the new standard will implement new hardware features and protocol enhancements that will be perfectly optimized for these kinds of applications requiring transfer of low data rates at very low power consumption.

In this context, the roadmap will also be driven here by the mobile phone roadmap which requires the implementation of the ULP Bluetooth standard. This will allow all market segments to get quick access to inexpensive chipsets, offering better economy of scale than using proprietary RF transceiver technologies.

In addition, Bluetooth SIG (the industry consortium driving Bluetooth standardization) is currently developing a new Bluetooth profile for medical applications. All this combined will offer new possibilities in the medical device industry.

CONCLUSION

The healthcare device market is growing. Through leveraging established technologies developed for consumer and mobile phone industries, engineers can easily and confidently implement Bluetooth connectivity and optimize solutions for the medical device space.

As Bluetooth technology becomes more and more pervasive (Bluetooth is incorporated in more than 60 percent of mobile phones sold in 2008), healthcare and medical markets can benefit from the development of the technology for portable medical devices to enable new applications and services.

Click here for the illustrations:

Figure 1, Figure 2