Biomedical Sensors
Dr. James A. Smith
What’s Important?
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Accuracy
Operational Range
Response Time
Sensitivity
Resolution
Reproducibility
Classification
• Breakdown into general categories
– Physical
• Goniometer
– Electrical
• EMG (electromyographic)
– Chemical
• Blood oxygen
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
Electrolyte / Metal Electrodes
• Charge distribution
at interface
• Different metals
have different
potentials
Physical Measurements:
Displacement
• Linear Variable Diff. Transformer
• Goniometer
– Knee & Elbow
• Strain
– Wire length & width
– Chest contraction
– Force Plates
• Ultrasonics
QuickTime™ and a
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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
Oxygen Measurement
• Plasma O2: 2% of total oxygen
– Clarke Electrode
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Chem. Reaction with Platinum
Electrode Current is prop. To oxygen content
Transcutaneous
Heat releases oxygen through skin
• Hemoglobin
– Optical oximeter
– Light absorption by blood
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
CO2
• CO2 in solution:
– Weak acid
– Carbonic Acid (H2CO3)
• Use electrodes like in pH system
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
Microbial Sensors
• Assimilation of organic compounds by
microorganisms
• Look for secretions by micros
– H2, CO2, etc.
• Need immobilized microbes
• Examples
– Ammonia & Nitrogen Dioxide
EKG / ECG
• Electrocardiogram (ECG)
• Electrokardiogram (EKG)
• Electrode
– Polymer & carbon / metal filler
– Silver Chloride contact
– Electrolytic foam
– Motion artifacts!
EMG / EEG
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Electromyogram (EMG)
Nerve & Muscle
Surface are like EKG
Direct
– Needle
– Bipolar electrode
• EEG
– Brain
– Cups (gel)
– Subdermal (10mm, 0.5mm)
EMG & Muscles
QuickTime™ and a
decompressor
are needed to see this picture.
Source: http://www.eorthopod.com/images/ContentImages/elbow/elbow_anatomy/elbow_anatomy07c.jpg
EMG: locate muscles
Figure 1
Source: Vernier Inc.
Electrode Placement
Source: Vernier Inc.
Electrical Patterns
Source: http://www.unmc.edu/physiology/Mann/pix_14/emg.gif
EMG Video
QuickTime™ and a
YUV420 codec decompressor
are needed to see this picture.
• http://www.youtube.com/watch?v=k0uSpYd_Ics