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Experimental Device for Determining the Feasibility of Non-Invasive Blood Viscosity Measurement

Experimental Device for Determining the Feasibility of Non-Invasive Blood Viscosity Measurement. by Fredrick South and Sayan Chaki. Presentation Overview. Experimental Theory Project Design Testing and Verification Results Future Work. Pulse Oximeter  Probe *.

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Experimental Device for Determining the Feasibility of Non-Invasive Blood Viscosity Measurement

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  1. Experimental Device for Determining the Feasibility of Non-Invasive Blood Viscosity Measurement by Fredrick South and Sayan Chaki

  2. Presentation Overview • Experimental Theory • Project Design • Testing and Verification • Results • Future Work

  3. Pulse Oximeter  Probe * Hemoglobin Absorption Spectrum ** *image from diytrade.com ** image from [1]

  4. No Magnetic Field-- Random Orientation Electromagnet Electromagnet Magnetic Field— Disc Plane Parallel to Field

  5. Features • Portable, stand-alone system • User control of magnetic field • Simple keypad/LCD interface • Autocorrelation to wait for a stable pulse

  6. Features • FFT processing to capture differences between magnetized and non-magnetized pulses • Save several tests worth of data to an SD card • Emergency shutdown of magnets if needed

  7. Oximeter/Magnet System Microchip PIC16F877A (40 Pin) TI TMS320D6713 Floating-Point DSP Lumex S01602 16x2 Character LCD Rogue Robotics uMMC-100-a3 Data Module ACT 4x4 Switching Keypad

  8. Masimo SET Rad-9 Pulse Oximeter 220# Hold 12VDC Electromagnet 220# Hold 12VDC Electromagnet Pulse Oximeter Finger Probe 12V / 4A Kepco 25-4M Power Supply Gnd

  9. 1.95 Gauss 10cm 214.884 Gauss Electromagnet Electromagnet 402.334 Gauss

  10. Effects of Magnetic Field on Pulse Oximeter • Pulse oximeter routinely used in MRI (>1.5T) • Only danger is induced currents from RF (MHz) pulses • Faraday's Law:    EMF = -dΦB/dt • Our maximum frequency limited by heart rate ~= 3Hz • Induced EMF 6 orders of magnitude less • Magnetic field 0.04T, 37.5 times smaller

  11. Power on Peak Detection Choose Magnetic Period Alternate Magnetic Field / Acquire Data Valid Period? No Pulses >=20 No Begin Autocorrelation Shut down magnet No Clean waveform? Write out data

  12. Controls

  13. Peak Detection Algorithm* *image found in [2]

  14. Spectrum Digital 6713 Digital Starter Kit (DSK) Board

  15. DSP Design • The waveform was obtained using a 6-pin DIN analog output from the pulse oximeter to the MIC IN input of the 6713 DSK board • The pulse oximeter updates the signal every 30 ms, or at 33 Hz • In software, the input was downsampled to 50 Hz, as the 6713 DSK can natively only sample from 8 kHz to 48 kHz

  16. DSP Design • Needed to be able to collect data and process it in real-time • Movement from the subject can cause artifacts to appear in the pulse oximeter signal • Chose an autocorrelation function to decide the quality of the pulse oximeter signal • The offsets for the autocorrelation were half of the buffer size, 128 samples

  17. DSP Design • The pulse oximeter signals should have differing characteristics depending on the applied magnetic field  • Applied an FFT to the input to distinguish these characteristics • Used a 256-point Discrete Fourier Transform, with rectangular window • Used an FFT to capture high frequency content in the falling region of the waveform

  18. DSP Testing: 40 Hz Audio Tone Amplitude Time (s)

  19. DSP Testing: 40 Hz Audio Tone, FFT output Amplitude Frequency (Hz)

  20. DSP Pulse Oximeter Input

  21. Expected FFT Output

  22. Actual FFT Output Amplitude Frequency (Hz)

  23. Data Module • RS232 not native to DSP board • Attempted to work around this using PIC

  24. Future Work • Use of better suited DSP • More powerful magnets • Correlate with blood viscosity • Additional signal processing functions

  25. References: [1] S. B. Duun, R. G. Haahr, et. al., "A Ring-Shaped Photodiode Designed for Use in a Reflectance Pulse Oximetry Sensor in Wireless Health Monitoring Applications," Sensors Journal, IEEE, vol. 10, no. 2, pp. 261-268, Feb. 2010. [ 2 ] H. S. Shin, C. Lee, et al. "Adaptive Threshold Method for the Peak Detection of Photoplethysmographic waveform," Computers in Biology and Medicine, vol. 39, pp. 1145-1152, Aug. 2009. M. Iino, "Effects of a homogeneous magnetic field on erythrocyte sedimentation and aggregation," Bioelectromagnetics, vol. 18, pp. 215-222, 1997. Yousef Haik, Vinay Pai, and Ching-Jen Chen, "Apparent viscosity of human blood in a high static magnetic field," Journal of Magnetism and Magnetic Materials, vol. 225, pp. 180-186, 2001. T. Yamamoto, Y. Nagayama, and M. Tamura, "A blood-oxygen-dependent increase in blood viscosity due to a static magnetic field," Phys. Med. Biol., vol. 49, 2004.

  26. References: D. M. Blakely, et al., "MRI Compatible Pulse Oximetry System," U.S. Patent 5 323776, Jun. 28, 1994. J. Webster, Design of Pulse Oximeters. New York: Taylor & Francis Group, 1997, p. 194.

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