Pulse Oximeters

Friday Activity (March 28th, 2025)

ES2 - Spring 2025

A sociotechnical examination of a medical device: the pulse-oximeter

What is a pulse oximeter?

A medical device which measures the oxygen saturation in your blood (O₂-sat or SpO2).

What fraction of the blood in your arteries is oxygenated after going through your lungs?

Healthy individuals are > 98%, below ~95% is concerning, below ~90% should be on supplemental oxygen.

Blood (hemoglobin) “color” depends on oxygenation

RED

YELLOW

BLUE

infrared

GREEN

More light absorbed

NIR “Near infrared”

Oxygenated

Deoxygenated

How does a pulse oximeter work?

How does a pulse oximeter work?

Trick #1: use two different wavelengths

of light (typically two LEDs)

Measurement 1

Measurement 2

Red

IR

Red

IR

Red

IR

Measurement 3

Red

IR

However, this device has racial implications:

Obviously this is biased because of melanin…

Tanghetti, Emil & Jennings, John. (2017). A comparative study with a 755 nm picosecond Alexandrite laser with a diffractive lens array and a 532 nm/1064 nm Nd:YAG with a holographic optic: THREE FRACTIONAL PICOSECOND WAVELENGTHS. Lasers in Surgery and Medicine. 50. 10.1002/lsm.22752.

​

Not so fast!

Lots of tissues have varying spectra, and anatomy varies somewhat, so the pulse oximeter clearly has to account for that.

Trick #2: use the fact that you have a pulse.

Pulse oximetry

https://www.analog.com/en/resources/technical-articles/how-to-design-a-better-pulse-oximeter.html

How much does a pulse oximeter cost?

Let’s go look it up!

How do you test / validate a pulse oximeter?

• Arterial gas measurements — take the blood out of a person and measure it!
• And you have to do this for low SpO2…

(30 mins) Prepare for an end-of-class trial:

Who should fix this?

Each group will take a persona:

1. Patients using and being affected by pulse-oximeters
2. Engineers and scientists creating and validating pulse-oximeters
3. FDA approving and regulating pulse-oximeters
4. Nurses, Doctors, and other health care professionals using pulse-oximeters
5. Insurance companies / Medicare / Medicaid

Questions to prepare responses to:

• Who are you? (Pick a specific case/context).
• What is your role in creating/using/being affected by pulse oximeters?
• What ought to change about how pulse oximeters are made/sold/used?
• How much responsibility do you think belongs to each group?

GROUP ASSIGNMENTS

Persona 1: Patients using and being affected by pulse-oximeters (Groups 1+5). Persona 2: Engineers and scientists creating and validating pulse-oximeters(Groups 2+6). Persona 3: FDA approving and regulating pulse-oximeters (Groups 3+7). Persona 4: Nurses, Doctors, and other health care professionals using pulse-oximeters (Groups 4+8)

Resources to get started:

• Patients using and being affected by pulse-oximeters
1. More health inequality: Black people are 3 times more likely to experience pulse oximeter errors
2. When it comes to darker skin, pulse oximeters fall short
• Engineers and scientists creating and validating pulse-oximeters
• How to design a better pulse oximeter
• FDA approving and regulating pulse-oximeters
• Pulse Oximeters - Premarket Notification Submissions [510(k)s]: ALSO Summary with notes
• Pulse Oximeters: Technology, Accuracy Limitations, and Regulation (start 00:55:13 - 01:21:00) https://www.youtube.com/live/oQoF0XS9QNc?feature=share&t=2833 (skim through slides)
• How does the FDA regulate medical devices? https://www.fda.gov/medical-devices/home-use-devices/fdas-role-regulating-medical-devices
• Recent January 2025 - Pulse Oximeters for Medical Purposes - Non-Clinical and Clinical Performance Testing, Labeling, and Premarket Submission Recommendations | FDA
• Nurses, Doctors, and other health care professionals using pulse-oximeters
• Eliminating racial bias in medicine is an obligation we all share | American Medical Association
• https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10416034/

Trial: What should change, and who should be responsible?

Start with 2-minute (timed) statements in this order:

(1) Patients team

(2) Engineers and scientists

(3) FDA team

(4) Nurses, Doctors team

2-minute responses by teams 5-8 representing same groups (Same order).

• Responses can challenge what has been said and offer more insights.
• Remember to emphasize the role of data in the development/approval/use of the pulse-ox and and conclude by addressing responsibility

Post-Lab Reading and Video:

Black engineers work to fix long-ignored bias in pulse oximeters - STAT

Optional: Tufts ECE Professor Valencia Koomson, MLK Scholar 2021: Research and Reflections