13-09-2012, 05:08 PM
Body temperature and ECG monitoring using an SMS based telemedicine system
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INTRODUCTION
Cardiovascular disease kills almost seventeen million people around the globe each year [1], with
around twenty million people at a risk of sudden heart failure.Therefore, patients who are at risk
require that their cardiac health to be monitored frequently whether they are indoors or outdoors
so that emergency treatment can be given if problems arise.Telemedicine is currently being used by
doctors, hospitals, and other healthcare providers around the world.Moreover, newer cellular access
technologies, such as GPRS, EDGE, 3G, and WiMAX provide for much higher data transmission
speeds (rates) than the basic 2G GSM cellular system oering future telemedicine solutions endless
choices for high-end designs.
In this paper, we describe a telemedicine system based on mobile messaging services, namely,
Short Messaging Service (SMS), which is an integral part of the original 2G GSM cellular system and
subsequent generations, and Multimedia Messaging Service (MMS), which became available as part
of the 2.5G cellular technologies and onward. This system transfers a patients Electrocardiogram
(ECG) signal and body temperature and can also be expanded to include other vital signs. Our
motivation to use mobile messaging services is that not only does it provide an alternative means
of transmission in a cellular communication system but it is a more versatile and convenient option
since all new phones are SMS and MMS capable.
SYSTEM CONCEPTS
The proposed mobile telemedicine system is shown in Figure. The patient (client) and the health-
care professional can be located anywhere in the globe where there is 2G or 2.5G cellular network
coverage. The patients ECG, body temperature, and other vital-signs if desired, can be acquired
by the patient himself under follow-up scenario, for example. Alternatively, the patient can be
assisted by a family member or a health-care professional in more serious cases depending on
particular patients case. The primary purpose is to monitor patients cardiac activity if there is
a chance that patient has cardiac problems such as an irregular heartbeat or arrhythmia that
require close monitoring or that occur intermittently. The signal acquisition process is performed
by attaching the ECG electrodes (three in the present setup) to the patients body at designated
places as is normally done in a typical single-lead ECG setup, and the Infrared temperature sensor
is pointed to the forehead. The ECG signal and temperature acquisition unit acts as a temporary
storage for the acquired ECG signal and temperature readings; then it communicates with the
smart mobile phone via a Bluetooth connection, which can be established through a Bluetooth
transceiver. The mobile phone in-turn is tasked with plotting the ECG signal before it is captured
and saved as an image, and then sent as an MMS if desired.
Body Temperature Sensor
We used a special rapid response, low-cost, integrated, noncontact, Infrared (IR) temperature sen-
sor IC, the MLX90614, that delivers medical accuracy over a wide operating range in our reference
design. This particular temperature IC delivers 0.1C measurement accuracy in the object tem-
perature range of 36C39C and the wide ambient temperature range. It has on-chip amplication,
signal processing, and conditioning circuit. We interfaced the temperature sensor to the PIC16F877
microcontroller using the I2C port on the microcontroller, which supports SMBus voltage levels.
The Micro controller
The PIC 16F877 is an 8-bit microcontroller, which has an on-chip eight-channel 10-bit Analog-
to-Digital Converter (ADC). The amplied and conditioned ECG signal is fed to channel-0 of the
microcontroller. Also, upon command, the microcontroller reads the temperature sample stored
in the RAM of the MLX90614 through the I2C port and then converts and stores it in its RAM
as two 8-bit unsigned integers (0255). The microcontroller also continuously samples the ECG
signal on channel-0 with a sampling interval of 4 milliseconds (250Hz), which is sucient to resolve
a maximum frequency component of about 125Hz in the frequency content of the ECG signal
according to the sampling theorem. We oversample to get a smoother plot of the ECG signal,
but it is a modest oversampling because we do not want to overburden the microprocessor of the
smart-phone while continuously plotting and refreshing the screen.Samples are written directly to
the serial port in asynchronous mode using the built-in UART of the PIC16F877.