PULSE OXIMETRY
Medical equipment
This report has been submitted to university of Duhok
collage of engineering
biomedical department
Prepared by: Mohammed Nozad
Lecturer: Mr.Ali Abdulrahman
Table of Contents
Introduction: ................................................................................................................................................. 2
Physiological aspects: ................................................................................................................................... 3
Why Would I Need This Test? ....................................................................................................................... 4
Purpose and uses: ......................................................................................................................................... 4
How does the pulse oximeter work? ............................................................................................................ 5
Principles of pulse oximeter: ........................................................................................................................ 6
Measurement technique: ............................................................................................................................. 7
Troubleshooting Factors: .............................................................................................................................. 8
1- user factors ....................................................................................................................................... 8
A) Nail varnish or pigment on finger ......................................................................................................... 8
B) Patient movement ................................................................................................................................ 9
C) Insufficient Blood Flow ....................................................................................................................... 10
D) Health Conditions: .............................................................................................................................. 10
E) Body Temperature .............................................................................................................................. 10
2- Device Factors ................................................................................................................................ 11
A) Due to improper care ......................................................................................................................... 11
B) fault in manufacturing ........................................................................................................................ 12
Preventative maintenance: ......................................................................................................................... 12
Ways to improve the oximeter: .................................................................................................................. 13
1- an oximeter with built-in data base and additional sensors: ............................................................. 13
2-taking measurement from more than one point (by adding more LEDs & photo detection diodes). 14
Summary: .................................................................................................................................................... 15
Bibliography ................................................................................................................................................ 16
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Introduction:
Dr. Takuo Aoyagi a Japanese Bioengineer, whose pioneering work in 1974 led to the invention of
modern first commercially available. who invented pulse oximetry to measure the oxygen
saturation in the blood hemoglobin.
A pulse oximeter is a device that is usually placed at your fingertips. A light beam is used to
estimate blood oxygen saturation and pulse rate. Oxygen saturation provides information about the
amount of oxygen transported in the blood. The pulse oximeter can estimate the amount of oxygen
in the blood without taking a blood sample.
Most pulse oximeters display two or three numbers. The most important number, oxygen
saturation, is usually abbreviated as SpO2 and is expressed as a percentage. Pulse rate (similar to
heart rate) is abbreviated as PR, and there may be a third number of signal strengths. Oxygen
saturation is between 95% and 100% in most healthy people, but can be low in people with lung
problems. Oxygen saturation is also generally slightly lower for people living at higher altitudes.
One of most common question that are asked by users is, how many categories of this device are
available?
There are mainly two categories which are prescription use and over the counter (OTC).
•
Prescription oximeters are reviewed by the FDA, receive 510(k) clearance, and are
available only with a prescription. The FDA requires that these pulse oximeters undergo
clinical testing to confirm their accuracy. They are most often used in hospitals and
doctors’ offices, although they may sometimes be prescribed for home use.
•
Over-the-counter (OTC) oximeters are sold directly to consumers in stores or online and
include smart phone apps developed for the purpose of estimating oxygen saturation. Use
of OTC oximeters has increased as a result of the COVID-19 pandemic. These products
are sold as either general wellness or sporting/aviation products that are not intended for
medical purposes, so they do not undergo FDA review. [1]
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Figure (1) an example of pulse oximeter (OTC) is illustrated.
Physiological aspects:
One definition of oxygen intake in the frame is the made from the arterial-venous oxygen
saturation variations and blood flow. The frame consumes oxygen in part thru cardio metabolism.
In this method, oxygen is used to transform glucose to pyruvate, freeing molecules of adenosine
triphosphate (ATP).
An essential issue of this method is the oxygen-hemoglobin dissociation curve. In the blood,
hemoglobin binds loose oxygen hastily to shape oxyhemoglobin leaving most effective a small
percent of loose oxygen dissolved with inside the plasma. The oxygen-hemoglobin dissociation
curve is a plot of percentage saturation of hemoglobin as a feature of the partial stress of oxygen
(PO2).
At a PO2 of one hundred mmHg, hemoglobin can be one hundred% saturated with oxygen, that
means all 4 heme organizations are bound. Each gram of hemoglobin is able to sporting 1.34 mL
of oxygen. The solubility coefficient of oxygen in plasma is 0.003. This coefficient represents the
quantity of oxygen in mL a good way to dissolve in 100mL of plasma for every 1 mmHg increment
with inside the PO2.
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A system then calculates the oxygen content material, in order that Oxygen Content = (0.003 ×
PO2) + (1.34 × Hemoglobin × Oxygen Saturation). This system demonstrates that dissolved
oxygen is a small enough fraction of general oxygen with inside the blood; therefore, the oxygen
content material of blood may be taken into consideration same to the oxyhemoglobin levels. [2]
Why Would I Need This Test?
It can:
•
Diagnose symptoms like shortness of breath.
•
Track your blood oxygen level during surgery.
•
Manage a heart or lung condition that could affect your blood oxygen levels, like heart
failure, COPD, asthma, or pneumonia.
•
Show if you need extra oxygen when you exercise.
•
Show whether your breathing stops while you sleep, a condition called sleep apnea.
Purpose and uses:
The purpose of pulse oximetry is to check how well your heart is pumping oxygen through your
body so it can measure the amount of oxygen in your blood.
It may be used to monitor the health of individuals with any type of condition that can affect blood
oxygen levels, especially while they’re in the hospital. These conditions include:
•
chronic obstructive pulmonary disease (COPD)
•
asthma
•
pneumonia
•
lung cancer
•
anemia
•
heart attack or heart failure
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•
congenital heart defects
There are a number of different common use cases for pulse oximetry, including:
•
to assess how well a new lung medication is working.
•
to evaluate whether someone needs help breathing.
•
to evaluate how helpful a ventilator is.
•
to monitor oxygen levels during or after surgical procedures that require sedation.
•
to determine how effective supplemental oxygen therapy is, especially when treatment is
new.
•
to assess someone’s ability to tolerate increased physical activity.
•
to evaluate whether someone momentarily stops breathing while sleeping — like in cases
of sleep apnea — during a sleep study.
How does the pulse oximeter work?
Pulsed oximeters measure the absorption of specific wavelengths of light in oxidized hemoglobin
relative to the reduction of hemoglobin. Oxygenated arterial blood is red due to the quality of
oxyhemoglobin it contains, which causes it to absorb light of a certain wavelength. The oximeter
has two light-emitting diodes (LEDs), one red and one infrared, located on one side of the probe.
The transducer is placed on an appropriate part of the body, usually a fingertip or an earlobe, and
LEDs transmit light wavelengths through pulsed arterial blood to an optical sensor on the other
side of the transducer. Infrared light is absorbed by oxyhemoglobin; red light due to decreased
hemoglobin. Arterial blood pulsation during systole causes an influx of oxyhemoglobin into the
tissues, absorbing more infrared light and allowing less light to reach the photodetector. The
oxygen saturation in the blood determines the degree of light absorption. Results are processed in
a digital oxygen saturation display on the oximeter display, denoted by SpO2. [2]
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Figure (2). Block Diagram of Pulse Oximeter, copied from Chan (2016)
Principles of pulse oximeter:
As in the previously described oximeters the diodes are switched on in sequence with a pause with
both diodes off. This pause allows the photocell and microprocessor to detect and compensate for
any ambient light which may have penetrated round the sensor cover. The diodes are switched on
and off at high frequency, several hundred times a second. Consequently, this does not prevent the
oximeter detecting the cyclical changes in the signal due to arterial blood flow during systole.
A microprocessor is programmed to analyze these changes of light absorption during the arterial
pulsatile flow and ignore the no pulsatile component of the signal due to the tissues and venous
blood. Therefore, pulse oximeter can give positive results about oxygen saturation in the arteries.
[3]
Figure (3) a basic schematic process of principles in oximeter is shown
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Measurement technique:
As we have said before Pulse oximeter measures the peripheral capillary oxygen saturation non-inversely,
referred as 𝑆𝑝𝑂2. It can be used to estimate arterial saturation of oxygen (𝑆𝑎𝑂2), 9 which is the ratio of
oxyhemoglobin divided by the total of arterial hemoglobin available
𝑆𝑎𝑂2 = 𝐻𝑏𝑂2 / (𝐻𝑏 + 𝐻𝑏𝑂2)
As discussed before Simple pulse oximeter measures oxygen saturation (𝑆𝑝𝑂2) with three diodes. Two
LEDs transmit light, where one transmits in the infrared region (940 nm) and the other in the visible light
region (660 nm). Photodetector diode detects the transmitted light from both diodes. [4]
Figure (4) Measurement technique of pulse oximeter from fingertip, copied from Wijshoff (2012)
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As the light travels through tissue, it gets absorbed by various substances by utilizing the Beer-Lambert
law with the knowledge that hemoglobin color varies according to bound oxygen molecules.
Beer-Lambert law enables the use of light as a way to determine how much absorbance has occurred for
a specific medium. It can be presented as an equation:
Troubleshooting Factors:
1- user factors
A) Nail varnish or pigment on finger
The color can absorb light emitted by the oximeter and interfere with the detection of oxygenated
hemoglobin.
It is always best to remove nail varnish from one finger. In emergencies the probe may be turned
sideways. Use another site if possible
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Here are two patients with henna pigmentation on their fingers
The oximeter may detect a pulse but is unable to measure SpO2 due to the pigment blocking the
signal.
Select a toe or ear lobe instead!
B) Patient movement
Patients with conditions that can lead to increased and rapid movement or shivering can have an
inaccurate reading. There are some devices however that can overcome this shortcoming.
pulse waveform can be erratic and not being well detected.
For the same patient but has now while shivering which can result in an abnormal reading and
cause confusion.
To solve this problem, hold the hand steady or wait until the patient has stopped shaking and
recheck.
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C) Insufficient Blood Flow
The sensors in the probes, reach across to the blood to detect the saturation of oxygen. But in
cases of poor perfusion where the blood flow is inadequate, readings will be affected greatly. It is
a must for the blood pressure to be above 80. The low pressure of the blood can be caused by any
of the following:
•
cold, nerve blocker medications and fear
•
Wrong placement of probes and compression
•
Because of cardiac arrest
•
Vascular impingement
•
Tight clothing, pressure cuffs or restraints
D) Health Conditions:
There are certain health conditions of the patient themselves that can lead to inaccurate readings;
for instance, patients with unreliable carboxyhemoglobin readings, methemoglobinemia, sickle
cell anemia, thalassemia and anemia will always have wrong readings.
E) Body Temperature
Heat loss is an almost inevitable consequence of anesthesia. The volatile anesthetics used in
general anesthesia change the set point for thermoregulation. This change results in the patient’s
inability to respond to changes in body temperature. If a response is initiated it may be ineffective
at restoring normal body temperature.
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2- Device Factors
A) Due to improper care
•
Probe cleanliness
When the probe gets dirty clean it gently with a damp cloth or alcohol swab
•
The battery
Keep the battery fully charged
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B) fault in manufacturing
•
Bright light on the probe
Lights can also affect the readings of a pulse oximeter if it is too harsh. It can be tested by covering the light
source and taking the readings again. The presence of any sort of radiated lights like infrared or ultraviolet can
definitely have an impact on the reading.
•
Faulty components
Malfunctioning LEDs, improper blinking frequency, faulty sensor, or any other component of the circuit
board could provide false results or even not provide any all.
Preventative maintenance:
A device as important as pulse oximetry should be checked much often to be said after every use or weakly
or twice or more per week since its being used a lot. The following points are to be done when doing
Preventative maintenance for pulse oximetry:
•
Inspect exterior of equipment for damaged or missing hardware.
•
Inspect the power cord, strain relief and plug/s for any signs of damage.
•
Turn unit off, unplug***, open user accessible covers and inspect unit for damage.
•
Clean unit interior components and exterior with compressed air.
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Inspect interior for signs of corrosion or missing hardware. Repair as required.
•
Inspect electrical components for signs of excessive heat or deterioration.
•
Clean exterior with warm water and liquid soap or mild detergent.
•
Replace probe if disposable.
•
Ensure nothing is blocking LEDs or photodetector on probe. If blocked, clean with isopropyl alcohol
solution or mild detergent, mild chlorine bleach solution, hydrogen peroxide solution, or isopropyl
alcohol. Do not use acetone, butyl alcohol, denatured ethanol, Freon, trichloroethylene or any
petroleum-based solutions. Verify red light is being emitted in probe.
•
Place probe on finger and make sure SpO2 and heart rates (if applicable) appear.
•
Remove probe from finger and verify that alarm is working.
•
Unplug probe and verify that alarm is working.
•
Examine switches and controls for proper function.
•
Confirm lights, indicators, and displays are working.
•
Verify machine can run on line power without battery.
•
Check suggested replacement date for battery to see if date is passed or approaching and replace
battery if necessary. [5]
Ways to improve the oximeter:
No matter how good a device is there is always room for improvement as biomedical
engineering student I believe that if the following statements will make the pulse oximetry
device better and more accurate in measuring SpO2 level in the blood.
1- an oximeter with built-in data base and additional sensors:
Since multiple factors influence the measured signal, we can add a database which would store various factors
obtained and analyzed from previous test result of different patients.
If we take these factors into consideration and include them with the results obtained from the patient, we
could use such information to use as a reference point to get more accurate results even with the presence of
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such factors. Therefore, a built-in database which can be updated regularly and will be helpful in estimating
the true oxygen saturation within the blood.
We know that the patient’s body temperature affects the readings of an oximeter. If the same patient is tested
with different, controlled body temperatures, the difference in results could be analyzed through an algorithm
and be used as a reference for future patients with similar temperature factors.
The more data that is included within the database, the more accurate the result would be. Basically, using
machine learning to predict results where certain factors are present by referencing the stored data. For this to
be done we have to integrate thermal sensor into the oximeter.
The same concept could be used with the factor of skin color. It has been observed that dark skinned patients
had a 10% difference in their readings if their oxygen levels were low, therefore patients with an SpO2 level
of 80% or less should be closely monitored. If a sensor was added to measure the skin pigmentation levels,
then that factor could also be added into the database easily. And in case these factors affect the results
differently depending on the gender, that could also be added manually for more information.
2-taking measurement from more than one point (by adding more LEDs & photo
detection diodes).
We could also add more LEDs and sensors at different locations to provide additional data of different angles.
This might require a different script of code and will need the LEDs to alternate so that they’re not on at the
same time. Therefore, we have to get the average of all the measurement of the process and it will help us to
get a better accuracy in the results. If happen to be on at the same time as the LEDs in another location, they
will interfere with the signal and give false results.
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Summary:
At the end we must know that oximeter is a device that is being used for measuring the saturation of oxygen
in hemoglobin cells in red blood cells. And it works by two (LEDs) and a photo detective diode, which the
red light and infrared light diode produces light that goes through the hemoglobin cells to hit the photo detector
and that photo detector takes those measurements and send it to the microprocessor which is then changed
into digital measurements and displayed onto the screen. However, these measurements could be affected by
factors related to either the patient using the device, or the device itself being manufactured with faults or
being poorly maintained.
There is always room for improvement. Adding a reference database which collects and analyzes information
through machine learning could have the oximeter provide accurate results regardless of certain factors which
would otherwise impact the readings greatly.
More LEDs and sensors could also be added to get more data from different angles, which may avoid any
problems that might be due to faulty components.
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Bibliography
[1] https://www.fda.gov/medical-devices/safety-communications/pulse-oximeter-accuracy-and-limitations-fda-safety-communication. [Online].
[2] https://www.pharmatutor.org/content/pharmapedia/know-about-pulse-oximeter-how-it-work-factors-affecting. [Online].
[3] https://www.sciencedirect.com/topics/engineering/arterial-oxygen. [Online].
[4] https://www.theseus.fi/bitstream/handle/10024/124218/piiroinen_stefan.pdf?sequence=1&isAllowed=y. [Online].
[5] https://bmet.ewh.org/bitstream/handle/20.500.12091/223/Pulse%20Oximeter%20Preventative%20Maintenance.pdf?sequence=1&isAllowed=y.
[Online].
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