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EOG for REM Sleep Detection. Robert Slavicek & Andrew Wassef. Description of Problem. Over 12 million people suffer from sleep apnea Americans average 6.22 hours of sleep a night, well below the recommended 7 to 8 hours

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EOG for REM Sleep Detection

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EOG for REM Sleep Detection

Robert Slavicek & Andrew Wassef


Description of Problem

  • Over 12 million people suffer from sleep apnea

  • Americans average 6.22 hours of sleep a night, well below the recommended 7 to 8 hours

  • Currently sleep studies of patients must be done outside of the home and are expensive


Objectives

  • Wanted to create a cheap, portable sleep observation system

  • Taking input signals from temperature and eye movement

  • Be able to identify when patient is in REM sleep


Original Design

Test Subject

(Electrodes)

Signal Filtering

and Amplification

Signal Filtering

and Amplification

Test Subject

(Thermistor)

Summer

Circuit

Data Acquisition

&

Storage

C Program

&

Display


Original Design

  • Obtain clear, useable signal

  • Have system be functional for multiple patients

  • Need to insure patient safety

  • Need to sample at a frequency high enough so that no relevant eye data is lost


Overview of Information Flow


Eye Dipole


Biosignal: Corneal Retinal Potential

  • Natural mV dipole between the cornea and the retina of the eye

  • Front of eye is positively charged, while back is negatively charged

  • Measured by placing electrodes directly lateral to each eye on the canthi and a reference electrode to the forehead


Eye Motion

If you look right: - right electrode reads positive voltage

- left electrode reads negative voltage

- circuit takes difference of electrodes

- net voltage is positive (pos-neg)

If you look left: - exact opposite of looking right

- net voltage is negative (neg-pos)


Circuit


Circuit Diagram


Buffer Circuit: isolates the output from the signal source

Differential Amplifier: Rejects signals common to both electrodes

4th Order Low Pass Filter: attenuates signals from frequencies greater than 35Hz


Variable Amplifier: allows operator to control the gain for each subject

Summer Circuit: allows operator to block DC offset

Inverting Amplifier: increases signal to better differentiate eye movement


Wein Bridge Oscillator

Electronic oscillator used to generate a sine wave so that the temperature sensor is at a different frequency spectrum


Temperature Sensor

Implementing the temperature signal with the eye signal


Data Acquisition


Data Acquisition

  • Used a 16-bit sound card to acquire data

  • Data was collected through a program Audacity

  • Audacity collected the data into a .wav file at 8000KHz sampling

  • Files of a night’s sleep were about 230 MBs of storage.


Data Acquisition

  • From Audacity, we import the .wav file into Matlab

  • Matlab’s “wavread()” command sorts the .wav data into a M by 2 Matrix


Data Acquisition

  • When we sort this data into a matrix, we can perform the FFT (Fast Fourier Transform)

  • We isolate the frequency range of the eye signal from the temperature signal


Data Acquisition

  • Using Matlab’s “sptool” command, we could isolate each signal for analysis

  • Sptool contains FIR bandpass and LS low pass filters that can filter out either signal


Data Acquisition

  • Used LS low pass filter, order of 80 cutoff at 170 Hz


Data Acquisition

  • After filtering the original signal we can send the time domain signal back to matlab in a data array

  • The data array can be exported as a .txt file to be further analyzed.

Filtered


C Program


C Program Analysis of Data

Output file from Matlab


C Program Analysis of Data


C Program Analysis of Data


C Program Analysis of Data

remsun1> eog

Enter input file name: eogin.txt

Enter sampling frequency (Hz): 20

Would you like to average the data (y/n)?: n

The output file 'out.txt' was written successfully!

Would you like to view it (y/n)?: y

Left at 0.4500 s due to -0.2017 V

Right at 1.9500 s due to 0.2179 V

Left at 3.7500 s due to -0.2174 V

Right at 5.5000 s due to 0.2285 V

Left at 7.2500 s due to -0.2547 V

Right at 9.0000 s due to 0.2144 V

Left at 10.7000 s due to -0.2121 V

Right at 12.5000 s due to 0.2120 V

Left at 14.3000 s due to -0.2259 V

Right at 16.0000 s due to 0.2297 V

Left at 18.0500 s due to -0.2486 V

Right at 18.4500 s due to 0.2181 V

Left at 18.8500 s due to -0.2195 V

Right at 19.3500 s due to 0.2295 V

Left at 19.9000 s due to -0.2308 V


Final Output


Final Output File

Left at 0.4500 s due to -0.2017 V

Right at 1.9500 s due to 0.2179 V

Left at 3.7500 s due to -0.2174 V

Right at 5.5000 s due to 0.2285 V

Left at 7.2500 s due to -0.2547 V

Right at 9.0000 s due to 0.2144 V

Left at 10.7000 s due to -0.2121 V

Right at 12.5000 s due to 0.2120 V

Left at 14.3000 s due to -0.2259 V

Right at 16.0000 s due to 0.2297 V

Left at 18.0500 s due to -0.2486 V

Right at 18.4500 s due to 0.2181 V

Left at 18.8500 s due to -0.2195 V

Right at 19.3500 s due to 0.2295 V

Left at 19.9000 s due to -0.2308 V


Functional Tests

Left at 0.0500 s due to -0.2066 V

Right at 0.5500 s due to 0.4051 V

Left at 1.2000 s due to -0.2246 V

Right at 1.9500 s due to 0.4172 V


Functional Tests

Left at 0.0500 s due to -0.4279 V

Right at 0.1500 s due to 0.1525 V

Left at 0.4000 s due to -0.3228 V

Right at 0.6500 s due to 0.1831 V

Left at 0.8500 s due to -0.3472 V

Right at 1.0500 s due to 0.1239 V

Left at 1.3500 s due to -0.3410 V

Right at 1.5500 s due to 0.1944 V

Left at 1.8500 s due to -0.3426 V

Right at 2.1000 s due to 0.2452 V

Left at 2.3000 s due to -0.3210 V

Right at 2.5500 s due to 0.1284 V

Left at 2.8000 s due to -0.3957 V

Left at 3.2500 s due to -0.3876 V

Right at 3.5500 s due to 0.2024 V

Left at 3.7500 s due to -0.3952 V

Right at 4.0500 s due to 0.2044 V

Left at 4.2500 s due to -0.4400 V

Left at 4.7000 s due to -0.3433 V

Right at 4.9500 s due to 0.1645 V

Left at 5.1500 s due to -0.3439 V


Functional Testing


Functional Testing

remsun1> eog

Enter input file name: eogin.txt

Enter sampling frequency (Hz): 20

Would you like to average the data (y/n)?: n

The output file 'out.txt' was written successfully!

Would you like to view it (y/n)?: y

Left at 1.5500 s due to -0.2017 V

Right at 1.9500 s due to 0.2179 V

Left at 2.4500 s due to -0.2174 V

Right at 2.8000 s due to 0.2285 V

Left at 3.2500 s due to -0.2547 V

Right at 3.8000 s due to 0.2144 V

Left at 4.4500 s due to -0.2121 V

Right at 5.1000 s due to 0.2120 V

Right at 6.0500 s due to 0.2297 V

Left at 7.9500 s due to -0.2486 V

Right at 8.4500 s due to 0.2181 V

Left at 8.8500 s due to -0.2195 V

Right at 9.3500 s due to 0.2295 V

Left at 9.9000 s due to -0.2308 V

Right at 11.3500 s due to 0.2295 V

Right at 13.0000 s due to 0.2235 V

Right at 18.4500 s due to 0.2102 V


Successes

  • Effectively captured lateral eye motion and temperature changes in human subjects in a portable device

  • Measured and stored changes in these signals over an entire night of sleep

  • Ensured patient safety

  • Display in a user friendly fashion when a subject displays mannerisms of REM sleep


Challenges

  • Actually recovering a signal from the lateral eye motion

  • Offset of electrodes pushed signal out of viewable range and signals were lost due to saturation

  • Electrodes slipped off during sleep / uneasy sleep

  • Digitally sample the two signals in one sound card

  • Temperature not responsive enough to accurately gauge when REM sleep occurs


Recommendations

  • Could add more functionality by adding EEG, EMG, HR, or BP monitors to help better determine the exact time of REM sleep


Recommendations

  • A feedback loop in the circuit to normalize the retinal-corneal dipole signal from all users rather than having to manually adjust the potentiometer in the circuit and the threshold values in the program

  • A more accurate and sensitive temperature sensor


Questions?


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