Senior Capstone Design Project RealTime Electrocardiogram Spectral Analyzer

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Senior Capstone Design Project Real-Time
Electrocardiogram Spectral Analyzer

• Ryan Carnathan, Keith Berry,
• Mark Stadick, Greg Michaelson
• Electrical Computer Engineering

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Presentation Overview

• Introduction
• Hardware
• QRS Detector
• Spectral Analysis
• User Interface
• Summary and Conclusion
• Demonstration

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Requirements

• Apply knowledge
• Solve Real World Problems
• Work in Multidisciplinary Teams
• To become actively involved in a company or
  community organization.

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Purpose

• Used in conjunction with the HP Merlin bedside
  monitor
• Real-time spectral analysis of the beat-to-beat
  variability
• Assess the potential for
• Improved bedside clinical monitoring
• Diagnostic and predictive information

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Function

• Graphical interface for the display and analysis
  of
• ECG Waveforms
• QRS Complex Detection
• Heart Rate Variability (HRV) Spectrogram
• These functions are performed and displayed in
  real-time.

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Implementation

• Hardware
• QRS Detection
• Spectral Analysis
• Integration and User Interface

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Definition of terms

• Electrocardiogram (ECG)
• Heart Rate Variability (HRV)
• QRS Complex
• RR v.s. NN
• The ECG Waveform
• The QRS Complex

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Presentation Overview

• Introduction
• Hardware
• QRS Detector
• Spectral Analysis
• User Interface
• Summary and Conclusion
• Demonstration

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Hardware

• Data Acquisition Card (DAQ)
• Laptop Computer
• Accessories

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Data Acquisition Card

• Capabilities
• Sample Rate
• 500 kS/s
• Number of Channels
• 8 Differential
• 16 Single Ended
• Gains
• 0.5, 1, 2, 5, 10, 20, 50, 100
• Voltage Levels
• 10 V - 50 mV

• Configuration
• Sample Rate
• 1 kS/s
• Number of Channels
• 1 Differential
• Gain Setting
• 1
• Voltage Levels
• 5 V

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Laptop Computer

• CPU
• Intel 600 MHz Pentium
• 256 k Level 2 Cache
• Storage
• 20 GB Hard Drive
• 3 ½ inch Floppy Drive
• Memory
• 512 MB of Ram

• Peripherals
• Infrared Transfer
• 10/100 Network Card
• 56k Modem
• (2) PCMCIA Slots
• 1 Taken by DAQ
• Operating System
• Windows 2000 SP 1

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Laptop Configuration

• CPU
• 600 MHz
• 500 MHz (Battery)
• Hard Drive
• 15.4 GB Free
• Ram Used
• 128 MB (System)
• 384 MB Available

• DAQ Input
• 1 Differential Channel
• 1 kHz Sample Rate
• BNC Connection

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Accessory Box

• Component Box
• Connector Block
• BNC Connection
• Ribbon Cable
• Strain Relief Device

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Connections

• Merlin To DAQ
• 6.35 mm Audio Cable To BNC
• DAQ to Laptop
• 68 Pin Ribbon Cable (0.2 M)

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Software Integration

• Program Functions
• Initialize DAQ
• Start Acquisition
• Check Buffer
• Transfer Buffer
• Stop Acquisition

• Software
• LabWindows CVI
• MatLab 6.0

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Acquisition Sample
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Battery Efficiency

• CPU
• Voltage 1.35V (Full Power)
• Average Power lt 2.0 Watts
• Voltage 1.1V (Battery)
• Average Power lt 1.0 Watts
• Battery Life
• 315 per Battery
• 2 Batteries Possible

• DAQ Requirements
• 5 VDC (5)
• 280 mA typ
• 400 mA max
• 70 mA unused

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Presentation Overview

• Introduction
• Hardware
• QRS Detector
• Spectral Analysis
• User Interface
• Summary and Conclusion
• Demonstration

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QRS Detection Overview

• QRS detection algorithm
• Current Status
• Future work
• Summary

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QRS Detector Algorithm

• Block Diagram

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QRS Detector Algorithm cont.

• ECG Input Data
• Remove Offset
• Filter
• Clip
• QRS Peak Detection
• Output QRS N-N Interval

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QRS Detector Sample Output
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Current Status

• Operational
• Remove d.c. offset
• Clip below amplitude threshold
• Detect QRS complexes (clean signals only)
• Pending
• Integration with graphical user interface
• Digital Filter
• QRS Accept/Reject function

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Future Work

• 1st Priority
• Integration with graphical user interface
• Digital Filter
• QRS Accept/Reject function
• Final report outline
• Testing and debugging

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Future Work Continued

• 2nd Priority
• Adaptive amplitude threshold function
• Final report draft
• Speed and performance improvements
• 3rd Priority
• Final report
• Final presentation

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Presentation Overview

• Introduction
• Hardware
• QRS Detector
• Spectral Analysis
• User Interface
• Summary and Conclusion
• Demonstration

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Spectral Analysis

• Heart Rate Variability (HRV)
• Inter Beat Intervals (IBI)
• variation in the time intervals between beats
• assumes irregular beats have been removed
• normal to normal (NN) beats
• Instantaneous Heart Rate (IHR)
• variation in consecutive instantaneous heart
  rates
• inverse of IBI

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Spectral Analysis

• Power Spectral Density (PSD)
• Distribution of Variance Over Frequency
• Three Operations
• Resample
• Filter
• Generate Spectrogram
• Fast Fourier Transform (FFT)
• Transforms Time Signal to Frequency

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Block Diagram
Resample
QRS Detector
Filter
FFT
GUI Plot
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QRS Output

• Elapsed Time vs Number of Heart Beats

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NN Intervals

• Re-Interpreted Data From QRS Detector
• NN Intervals
• Indexed by Heart Beats

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Resampling Overview

• Interpolate
• Generate Continuous Curve
• Passes Through Existing Points
• Sample New Series
• Constant Time Period
• Required for Fast Fourier Transform (FFT)
• NN Intervals vs Time

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Resampling

• Input Signal from QRS Detector
• Resampled Signal

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Filtering

• Spikes in Signal
• Missed Beats by QRS Detector
• Distort Valid Data
• Filter
• Flattens Large Excursions
• Modifies Only Large Outlying Data Points

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Filtering

• Resampled Signal
• Filtered Signal

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Spectrogram Algorithm

• Estimating Spectral Power
• Remove Mean Value
• Perform FFT
• Power Calculation - FFT2

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Spectrogram Example

• PSD vs Time

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Presentation Overview

• Introduction
• Hardware
• QRS Detector
• Spectral Analysis
• User Interface
• Summary and Conclusion
• Demonstration

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Features

• Implemented
• Plots
• ECG
• User Controls
• Start/Stop
• Window Size
• Scrolling
• Modes
• Historical
• Real Time

• Planned
• Plots
• Beat to Beat
• Spectrogram
• Scaleogram
• User Controls
• Graph Selection
• Notes

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Process Budget

• Limits
• Data Acquisition
• 10-15 of CPU
• Little Memory
• Beat Detection
• 5-10 of CPU
• Lots of Memory
• Spectrogram Calculation
• 30 of CPU

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Presentation Overview

• Introduction
• Hardware
• QRS Detector
• Spectral Analysis
• User Interface
• Summary and Conclusion
• Demonstration

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Completed

• Hardware
• Specified Needs
• Purchased / Acquired
• Built
• Software Completed
• Tested on Merlin
• GUI
• 2 Plots
• Scrolling
• Integration of Hardware
• Real-time ECG Display
• Historical Mode

• QRS Detector
• Literature Review
• Scaling
• Clipping
• Beat Detection
• Spectrogram
• Resampling
• Median Filter
• Spectral Estimation

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Remaining Tasks

• GUI
• Spectrogram Integration
• QRS Detector Integration
• User Notepad

• QRS Detector
• Filtering
• Ectopic Beat Rejection
• Spectral Analysis
• Filter Refinement
• Higher Resolution Spectrogram Plot

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Presentation Overview

• Introduction
• Hardware
• QRS Detector
• Spectral Analysis
• User Interface
• Summary and Conclusion
• Demonstration