1. Wireless Enabled Holter Monitor and ECG Analysis System Final Year Project 4 th Electronic and Computing Engineering Brendan Maguire 03633721

2. Traditional Holter Monitor Systems Portable device for continuously monitoring the electrical activity of a heart (ECG waveforms) Records electrical signals from the heart via series of electrodes attached to the patients chest Sampling frequency usually between 250Hz and 500Hz Records ECG signal for extended periods of time (24 - 48 hours) Extended recording period is useful for observing occasional abnormal heart rhythms Allows the patient to be monitored in their home

3. Disadvantages of Traditional Systems Current Holter Monitors record the patient’s heartbeat for a period of time on a tape or a flash drive The physical drive is then brought to the cardiology department for analysis This results in a long turnaround time between the first results been recorded and the technician making their analysis Inconvenient for patients to have to travel to the department No support for real time monitoring of the patient

4. Aims of this Project This project involved designing a wireless enabled Holter Monitoring System which:  Allows speedier access to the ECG signal by using a home wireless network or WLAN hotspots to send the data over the internet to be stored in a database  Facilitates faster turnaround times  Incorporates the use of GPS technology so that high risk patients can be located quicker on the detection of a serious cardiac event  Allows the technician to view the recorded data through a web based interface using any Java enabled web browser  Allows the technician to view the signal in real time through the web based interface

5. Schematic of the System

6. Holter Monitor Platform The gumstix platform was chosen to implement the Holter Monitor System on for a number of reasons:  Small in size  Runs a full Linux operating system  Cheaper than other similar platforms  Supports wireless communications and GPS functionality through the use of expansion boards  Easy to expand functionality at a later date by swapping expansion boards

7. Analogue to Digital Converter No suitable ADC incorporated into the gumstix or expansion boards Used an external ADC and interfaced it with the gumstix through the GPIO pins on the GPSstix Decided to use the AD7862 from Analog Devices  12 bit A/D converter  2 input channels  Capable of 250,000 samples per second

8. Sampling Rate of 500Hz – Problem Originally attempted to sample ADC from within a process running in user space on the gumstix Used memory mapping technique to access the registers controlling the GPIO pins Continuously sampled ADC within a loop with sleep induced delay of 2 milliseconds on each iteration Problem occurred as Linux scheduler on the gumstix could only switch between tasks at a rate of 100Hz

9. Sampling Rate of 500Hz – Solution Decided to use a timer interrupt on the gumstix which triggered every 2 milliseconds 4 match registers present on the PXA255, of which 3 were unused Access to the relevant registers and the registration of the interrupt service routine for the timer interrupt had to be performed from within a kernel module Modules are loaded into the kernel at run time to extend functionality of the kernel to support hardware devices

10. global buffer1[1000], buffer2[1000], read_count = 0, write_count = 0, flag_buffer_access = 0, queue; interrupt_service_routine { if ( flag_buffer_access == 1 ) { buffer2[write_count] = get_voltage_values(); } else { buffer1[write_count] = get_voltage_values(); } write_count = (++write_count) % 1000; wake_up(queue); } read (user_space_buffer) {......... } Kernel Module Pseudo Code If the read function is using buffer1 then write to buffer2 instead Wake up all process in the queue

11. Kernel Module Pseudo Code read (user_space_buffer) { if ( write_count == read_count) { wait_on_queue(queue); } flag_buffer_access = 1; user_space_buffer = buffer1[read_count]; buffer1[read_count] = EMPTY; flag_buffer_access = 0; if ( user_space_buffer == EMPTY ) { user_space_buffer = buffer2[read_count]; } read_count = (++read_count) % 1000; } Wait for data to become available Set the buffer access flag, read from buffer1 and then clear the flag to indicate the read is finished If buffer1 was empty then the result is actually stored in buffer2

12. Access to Kernel Module Functions A new device node file, located at /dev/adc, is created to allow the process running in user space access to the functions in the module The module enables the generation of the timer interrupt upon the open function been called, and disables it when the close function is called The user space process continuously reads using the device node file If data is not available when the read function is invoked then it goes into an interruptible sleep until new data is available

13. Database MySQL database used to store sampled signals Advantages of using MySQL:  Fast  Free  Reliable  Runs on a wide variety of platforms  Widely used and supported

14. Database Storage Format 03_20_200703_15_2007 03_22_2007 h16 h17h18 h19h20 Decimal(4,3) IntTime Voltage2Voltage1MillisecondsTimestamp

15. GPS Use of active GPS antenna in conjunction with the GPSstix expansion pack GPS module outputs data at a rate of 1Hz On receipt of a request from the remote client, the current location of the antenna is determined and transmitted Google Map is used to illustrate the current position of the patient

16. GPS

17. Data Transfer Data transfer over a network Data transfer within a system

18. Web Based GUI Allows access to both the stored signal samples in the database and real time data from the monitor device Request the current location of the gumstix and invoke Google Map on receipt of this information Written in Java for portability between platforms Applet format to allow viewing from within a web browser

19. Web Based GUI Has multiple features such as:  Automatic scanning of database entries to provide list of dates and times for which data is available  Allow the user to specify gumstix and database IP addresses  Variable signal replay rate  Save and Load configuration settings from local file  Password protection

20. Web Based GUI

21. Future Enhancements Support for monitoring of multiple patients simultaneously Remote control of the monitor unit through the web based interface Formatting of recorded data to comply with professional medical standards Increased sampling rate for patient's with pacemakers

22. Any Questions??