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Biomedical Sensors

Biomedical Sensors. Dr. James A. Smith. What’s Important?. Accuracy Operational Range Response Time Sensitivity Resolution Reproducibility. Classification. Breakdown into general categories Physical Goniometer Electrical EMG (electromyographic) Chemical Blood oxygen.

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Biomedical Sensors

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  1. Biomedical Sensors Dr. James A. Smith

  2. What’s Important? • Accuracy • Operational Range • Response Time • Sensitivity • Resolution • Reproducibility

  3. Classification • Breakdown into general categories • Physical • Goniometer • Electrical • EMG (electromyographic) • Chemical • Blood oxygen

  4. Sensor Packaging • “In vivo” • Inside the organism! • Risky! • Biocompatibility • Host can affect the sensor & vice versa • Protein absorption / cell. Deposits • Permeability affected • Inflamation of tissue (latex!) • Sterilization • Steam, ethylene oxide, gamma radiation

  5. Electrolyte / Metal Electrodes • Charge distribution at interface • Different metals have different potentials

  6. Physical Measurements: Displacement • Linear Variable Diff. Transformer • Goniometer • Knee & Elbow • Strain • Wire length & width • Chest contraction • Force Plates • Ultrasonics

  7. Temperature • Tightly controlled body variable • 37.0 +/- 0.5 C at core • Too high: disease or infection • Too low: trauma / shock • Thermistor • Change resistance with temperature • Cavity or closed area

  8. Oxygen Measurement • Plasma O2: 2% of total oxygen • Clarke Electrode • Chem. Reaction with Platinum • Electrode Current is prop. To oxygen content • Transcutaneous • Heat releases oxygen through skin • Hemoglobin • Optical oximeter • Light absorption by blood

  9. pH Electrodes • Acid: excess hydrogen ions • Base: excess hydroxl ions • Normal blood pH: 7.4 (basic) • CO2 removal by lungs • Kidneys acid-base regulation • Organic dye strips • Electrodes in solution • a battery consisting of two electrodes, • each immersed in its respective solution • joined by a salt bridge • Glass electrodes • Glass membrane can wear out

  10. CO2 • CO2 in solution: • Weak acid • Carbonic Acid (H2CO3) • Use electrodes like in pH system

  11. Enzyme Biosensors • Biological specific mediators • Reagents for reaction or catalyzing • Enzymes • 2000 proteins w/ biocatalytic properties • Accelerate reactions in cells • Embed in neutral matrix • Glucose sensor • Enzyme glucose oxidase • Useful for diabetics • Measure gluconic acid or hydrogen peroxide

  12. Microbial Sensors • Assimilation of organic compounds by microorganisms • Look for secretions by micros • H2, CO2, etc. • Need immobilized microbes • Examples • Ammonia & Nitrogen Dioxide

  13. EKG / ECG • Electrocardiogram (ECG) • Electrokardiogram (EKG) • Electrode • Polymer & carbon / metal filler • Silver Chloride contact • Electrolytic foam • Motion artifacts!

  14. EMG / EEG • Electromyogram (EMG) • Nerve & Muscle • Surface are like EKG • Direct • Needle • Bipolar electrode • EEG • Brain • Cups (gel) • Subdermal (10mm, 0.5mm)

  15. EMG & Muscles Source: http://www.eorthopod.com/images/ContentImages/elbow/elbow_anatomy/elbow_anatomy07c.jpg

  16. Figure 1 EMG: locate muscles Source: Vernier Inc.

  17. Electrode Placement Source: Vernier Inc.

  18. Electrical Patterns Source: http://www.unmc.edu/physiology/Mann/pix_14/emg.gif

  19. EMG Video • http://www.youtube.com/watch?v=k0uSpYd_Ics

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