28-05-2014, 02:32 PM
WIRELESS ECG
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Abstract
The overall objective of this project is to design and implement a prototype ECG
system which replaces wired connections between sensor points and a central
node with wireless links. Successful implementation of the final system would
be of benefit to all involved in the use of electrocardiography as access to, and
movement of, the patient would not be impeded by the physical constraints
imposed by the cables. Most aspects of the design would also be portable to
other sensor applications, making the work relevant to a vast range of systems
where movement of sensors is desirable and constrained by hard-wired links.
The design and implementation of the wireless link and ECG sensor electronics
to produce an ECG signal form the basis of the Wireless ECG Monitors. The
Wireless Sensor Protocol (WSP) was hence produced to handle the wireless
link. Analogue electronics are used to obtain the signal and to filter noise, while
PC based software is used to display the results.
The WSP for the ECG system consists of two Slave nodes and one Master
node. The Slave node prototype consists of an ECG sensor (with associated
electronics), PIC microcontroller and Nordic's nRF401 UHF transceiver, as
'patches' ordinarily placed on the patient. Altera’s Nios Softcore processor (16
bit design) with Nordic's nRF401 UHF transceiver forms the Master (base) node
where data is collected and an ECG signal is calculated for displaying to the
medical staff.
Introduction
Thesis Introduction
Ever since the existence of mankind, the goal of humans has forever been to
make life simpler. The wheel was invented by the Sumerians to help with
transportation. The computer was created to improve and quicken several
tedious tasks. In the last decade though, the greatest scope and emphasis is
being seen in the wireless technology sector. The aim of this technology is to
reduce the number of cables and wires which may be tedious and often even
hazardous. Scientists and Engineers have been exerting, both a lot of time and
money on these technologies, and hence we have the beginning of what many
are calling the Wireless Age.
In today’s day and age, it is common to see the likes of mobile phones, laptops,
computers, personal digital assistants (PDAs) and of late, MP3 players. Such
devise seem useful, but the concept of these devices being able to interact with
each other is what has caught the eye of designers. The thought of being able
to meet an acquaintance and immediately having exchanged personal details
wirelessly, seems far-fetched yet very realistic.
ECG
ECG Theory
Electrocardiogram (ECG/EKG) is a representation of electrical activity of the
heart muscle as recorded from the body surface, which is used in the analysis
of heart disease. It was developed by William Einthoven in 1903 using a crude
galvanometer. This electrical activity is related to the impulse that travels
through the heart which determines its rate and rhythm. For a full ECG
examination of a patient, he/she must be wired up with 12 electrodes. The ECG
signal obtained represents the polarization and the depolarization of the cells
during a heartbeat. Figure 2.1 shows an example of an ideal ECG signal
Need for Wireless ECG
An ECG signal is useful for a doctor to evaluate a patient’s heart condition
relating to:
• Whether a heart attack has occurred
• What parts of the heart is damaged
• Irregular heart beats
• Whether the heart is not receiving enough blood or oxygen
As has been demonstrated, an ECG signal is extremely valuable, making it a
conventional mechanism used in hospitals by both doctors and nurses. The aim
of this thesis is to develop a wireless system to provide a more user-friendly
device. By eliminating the long cables between nodes, the patient is comfortably
able to move around without the hassle of wires, while also being able to place
the electrodes on themselves without being impeded by leads. Similarly it
provides the doctor or nurse with a trouble-free approach to the patient’s ECG
signal. In addition, software could allow ECG signals to be saved and sent
possibly by email to other parts of the world. In fact, for patients in rural and
regional areas an ECG report could be sent via email to a doctor for
examination.
BlueNurse
As has been explained previously, the need for such a device is immense,
hence there are projects’ similar to this that are being conducted throughout the
world. This idea of a Wireless ECG was first introduced to the University of
Queensland Computer Systems and Electrical Engineering department last
year as the thesis project BlueNurse, completed by three colleagues, Daniel
Marr, David Lin, Naveenan Vasudevan. The BlueNurse design involved a point-
to-point communication system with three nodes connected to a single
Bluetooth module and another Bluetooth module used to receive ECG data for
the PC. This project was successfully able to communicate wirelessly with the
two modules, however it lacked in that it did not display an ECG signal on the
PC. [16, 22]
ECG System Design
A design system consisting of a single Master and two Slave network design
was incorporated into this project. The master node comprises of the interface
to the PC which is responsible for communicating directly with each particular
slave as shown in figure 4.1. The two slave nodes which are placed on the
patient’s body to collect ECG data will in turn send data packets through the RF
transceivers to the master which will display the ECG information through a
graphic user interface (GUI).