Pulse Oximetry
Wikipedia, Pulse Oximeter [photograph]. Retrieved from https://en.wikipedia.org/wiki/Pulse_oximetry
Summary
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Clinical Use
History
Specifications
Principles of Operation
Block Diagram
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Commercial Examples
Preventive Maintenance
Common Problems
Test Procedures
Oxygen Transport in the Body
Ratznium (2010), Oxyhaemoglobin dissociation curve [image]. Retrieved from https://commons.wikimedia.org/wiki/File:Oxyhaemoglobin_dissociation_curve.png
Oxygen Transport in the Body
• O2 delivered = (cardiac output) x (O2 concentration)
• Body consumes 1023 molecules of oxygen per
second
• 99% of the O2 in arterial blood
is hemoglobin-bound O2
• During exercise
• Cardiac output to 20 L/min (normally 5 L/min)
• Venous saturation to 40% (normally 60 – 80 %)
Hypoxia
Results:
• Decrease work capacity of muscles
• Depressed mental activity
• Cell death
History
1930 oxygen saturation devices
incapable of distinguishing between
arterial and venous blood (coloured
light)
1970’s, the Hewlett−Packard –
measures the transmission of light
across the earlobe at more than two
wavelengths.
Clinical Use
• Measures the oxygen saturation of the
hemoglobin in the blood
• Indicator of the oxygen carrying capacity of the
blood
• In order to verify the gas exchange process one
needs to measure the venous CO2 concentration
as well
Specifications
• Input:
– Visible light (655 nm-660 nm)
– Infrared light and (805 nm - 940 nm)
• Output Electronically (display)
– Heart rate, bpm
– SpO2 – oxygen saturation
Electromagnetic Spectrum
Zedh (2007), Electromagnetic Spectrum [image]. Retrieved from https://commons.wikimedia.org/wiki/File:EM_spectrum.svg
Principles of Operation
• Optical measurement
Developing World Healthcare Technology Laboratory. “Pulse Oximeters.” From the Publication: “Biomedical Technicians Training Program, Session 3 v2, Special
Topics: Cardiac Equipment.” Engineering World Health, March 1, 2011, p. 1-161.
Principles of Operation
Beer’s Law
By Adilia James and Sarah Coutlee [Public domain], via Wikimedia Commons. Retrieved from https://commons.wikimedia.org/wiki/File:Beer%27s_Law_Plot.jpg
Principles of Operation
Optical Measurement: Photoplethysmogram
Spl4 (2006), Photoplethysmograph [photograph]. Retrieved from https://en.wikipedia.org/wiki/File:NiprideEffectOnPPG-large.png
Arterial versus Venous Blood
Kelvinsong (Own work) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons. Retrieved from
https://commons.wikimedia.org/wiki/File:Blood_vessels-en.svg
Red Light
Source 660 nm
Infrared Light
Source 940 nm
SO2
[ HbO2 ]

x100%
Hbtotal
Analysis
Target
AnalysisTarget
Hemoglobin
in Vitro Measurement
Photodetector
SO2
A(1 )
 c1  c2
A(2 )
Engineering World Health (no date), Hemoglobin In Vitro [image]. Original image.
Hemoglobin
in Vivo Measurement
Absorption
How to measure ONLY arterial blood concentration?
Pulse
added arterial
continuous
blood
venous
tissue
Time
Engineering World Health (no date), Hemoglobin In Vivoo [image]. Adapted from original image (unknown)
Extinction vs Wavelength
Oxygenated hemoglobin
(HbO2) and reduced
hemoglobin (Hb) exhibit
markedly different
absorption (extinction)
characteristics to red light
@ 660 nm and infrared
light @ 940 nm.
Developing World Healthcare Technology Laboratory. “Pulse Oximeters.” From the Publication: “Biomedical Technicians Training Program, Session 3 v2, Special
Topics: Cardiac Equipment.” Engineering World Health, March 1, 2011, p. 1-161.
Sensors
Quinn Dombrowsky (2011), Pulse Oximeter Sensor [image]. Retrieved from https://commons.wikimedia.org/wiki/File:Pulse_oximeter_sensor.jpg
UusiAjaja (2011), Wrist Oximeter [image]. Retrieved from https://commons.wikimedia.org/wiki/File:Wrist-oximeter.jpg
Characteristics
Advantages
• Easy to use
• Calibration unnecessary
Limitations
• Limited to tissues that can transmit light
• Highly sensitive to motion
Addressing Hypoxia
Developing World
Healthcare
Technology
Laboratory.
“Pulse
Oximeters.” From
the Publication:
“Biomedical
Technicians
Training Program,
Session 3 v2,
Special Topics:
Cardiac
Equipment.”
Engineering
World Health,
March 1, 2011, p.
1-161.
Commercial Examples
Wikipedia “Pulse Oximeter.” Wikipedia 1-4
https://en.wikipedia.org/wiki/Pulse_oximetry
Commercial Examples
Wikipedia “Pulse Oximeter.” Wikipedia 1-4
https://en.wikipedia.org/wiki/Pulse_oximetry
Controls
Developing World Healthcare Technology Laboratory. “Pulse Oximeters.” From the Publication: “Biomedical Technicians Training Program, Session 3 v2, Special
Topics: Cardiac Equipment.” Engineering World Health, March 1, 2011, p. 1-161
Patient’s Safety
• Invasive
– Thrombosis
– Infection
– Bleeding
• Non-invasive
– Long exposure can result in skin burn, specially in
premature infants
Preventive Maintenance
• No calibration required
• Probe:
– Tape glue can sometimes build up on the LEDs and
photodetector
– Alcohol will soften the dirty and make removal easy
Common Problems
• Probe:
– Lead breakage
– Missing probe
– Different manufacturers
• Power supply
Malkin (2006), Medical Instrumentation in the Developing World [image]. Retrieved from library.ewh.org
Common Problems
• User error
– Sensor placement
– Avoid ambient light
– Nail polish an block light
– If the patient is cold the blood vessels
may constrict making detection of blood
flow difficult
Test Procedures
• Test on yourself: Heart Rate
• Check alarms
• Check battery (if present) charging circuit
Questions