Author: Sukky Nd-Ezuma

Recently, during the COVID-19 pandemic, there was a high count of Blacks dying from this virus compared to Whites. Apparently, when Blacks visit the hospital to check their oxygen level using the pulse oximeter it gives data that says they are healthy, and in fact, they are not. The Food and Drug Administration(FDA) discovered this high death toll in the Black and investigated. They came down to the conclusion that 1 in 10 pulse oximeters gives wrong readings for people of color.

A research carried out by the University of Michigan Hospital did research on acute hypoxemia with a large cohort of 10,000 patients of both Black and White races. They tested for occult hypoxemia, arterial oxygen saturation of <88% despite an oxygen saturation of 92 to 96% on pulse oximetry. In this research a pulse oximeter and arterial oxygen saturation in arterial blood; this is basically the ultimate test where the blood sample is taken from the patient and tested in the lab for its oxygen level. Black patients had nearly three times the frequency of occult hypoxemia that was not detected by pulse oximetry as White patients.

HOW DOES THIS DEVICE WORK?

A commercial pulse oximeter is made up of a light sensor and two lights; the red light at 660 nanometers and the Infrared at 940 nanometers in the visible spectrum.

The above picture shows why only red and infrared lights are used because those lights can penetrate past the tissues and reach your arterial veins where blood flows from the heart.

Deoxyhemoglobin is a form of hemoglobin (blood) without oxygen and is represented as Hb. Oxyhemoglobin is a form of hemoglobin with oxygen and is represented as HbO2. The graph below shows the absorption level to the wavelength of the red and infrared light. From the below graph, you see that deoxyhemoglobin absorbs more red light while oxyhemoglobin absorbs more infrared light.

A group of doctors from Jerusalem College Technology(JCT) had a project for building a pulse oximeter and came up with the following data and formulas. This graph gives you the heartbeat of the patient. And it is measured from trough to peak. This uses light to measure blood flow.

AC is the trough to peak amplitude and DC is the mean value of the pulse basically the average and should not be mistaken for distance. The bigger the AC the more accurate your result tends to be.

The extinction coefficient is the absorbance divided by the concentration and path length basically how transmissive light can be. This formula has been labeled questionable because these values cannot be found from the data collected.

This explains the theory behind scattered and direct light when passed through something. Ideally when light passes through the finger of a person, the output or absorption level is dependent on how thick that finger is. That is if your finger is really thick the absorption level would be small due to the fact that lights do scatter and vice versa.

This basically is the combination of both the extinction coefficient and path length formula. This is assumed to be a more accurate formula for calculating the peripheral capillary oxygen saturation, an estimate of the amount of oxygen in the blood.

This is an empirical formula. K1 to K4 are not derived numbers they don’t look them up in the literature they literally took people’s heart ratio and SPO2 and took enough of those until they could fit those numbers. There is no fundamental science behind this formula this is just getting numbers that work.

Apparently, every formula that was derived before this empirical formula was thrown away and they ended up with this empirical formula. This raises a lot of questions. We do not know the extinction coefficient and path length which seems to be important in building a pulse oximeter.

The above graph is a piece of information I would like you to hold on to for further explanation and it shows us that red light is absorbed by melanin and infrared is barely absorbed by melanin. So basically red light is affected by how much melanin a person has and infrared is not.

DESIGN OF PULSE OXIMETER

My intention was to build a pulse oximeter similar to the ones used commercially using a 3D printer. This turned out to be a failure specifically because of the hinges that connect the led holder and sensor holder together. I spent a lot of time trying to perfect this design but I couldn’t. As Prof Eric Remy would say ” We are too focused sometimes on one particular goal we forget that there is more to do and achieve.”

My failures using a 3D printer to build the commonly used commercial pulse oximeter.

So I moved on from this design and made an All-in-One pulse oximeter that contains the light sensor and led lights. Below are my designs using the Tinkercad software and 3D prints.

Tinkercad design of All-in-One pulse oximeter

Tinkercad design of All-in-One pulse oximeter

DATA COLLECTION

Two types of data were collected the visible light(red) data and infrared light data. Like I stated earlier the bigger the distance from the trough to peak the more accurate it tends to be.

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This data shows that the Black male’s graph for visible light(red) is difficult to read and you can barely get any information from it and this is due to the fact that melanin affects reds light just like we pointed out in the melanin absorption graph and that is why the graph seems unstable and the AC(trough to peak) is really low or sound to signal ratio is low. In the infrared light, we suddenly see that the Black male’s graph has a better sound to signal ratio and this proves the point from the melanin absorption graph that melanin barely affects infrared light.

CONCLUSION

The commercial pulse oximeters do not measure two major factors and this could result in the misleading of data analysis. This is especially for People of Color. These factors may include;

The thickness of one’s finger and

The percentage of melanin present in a person’s skin.

Therefore, I do not believe these devices can be trusted because of their inaccuracy. I would advise that people who try to check their oxygen level especially now that it is used at a high rate due to covid-19 should visit the hospital and opt to take the ultimate test that involves extracting the patient’s blood and taken to a lab for analysis and accurate results.

APPRECIATION

I thank God for the completion of this research project and appreciate my DTSF supervisors, fellow interns, and family. I wouldn’t have been able to accomplish this much without the love and care I got from everyone thank you! Thank you Gettysburg College. It has been an honor to be a part of this family.

REFERENCE

Sjoding, Michael W., et al. “Racial Bias in Pulse Oximetry Measurement.” New England Journal of Medicine, vol. 383, no. 25, Dec. 2020, pp. 2477–78. Taylor and Francis+NEJM, doi:10.1056/NEJMc2029240.

Yossef Hay, Ohad, et al. “Pulse Oximetry with Two Infrared Wavelengths without Calibration in Extracted Arterial Blood.” Sensors (Basel, Switzerland), vol. 18, no. 10, Oct. 2018, p. 3457. PubMed Central, doi:10.3390/s18103457.

Zonios, George, et al. “Melanin Absorption Spectroscopy: New Method for Noninvasive Skin Investigation and Melanoma Detection.” Journal of Biomedical Optics, vol. 13, no. 1, International Society for Optics and Photonics, Jan. 2008, p. 014017. www.spiedigitallibrary.org, doi:10.1117/1.2844710.

This week was centered on analyzing the data I collected and referring to the papers I found from week six. I analyzed different races and gender. The papers had some interesting and scientific questionable findings. But first, after analyzing some data I noticed a big discrepancy with the Black male compared to the White male and Hispanic female. It was hard to get reasonable data from the black male because there was no significant distance from the trough to peak. And in one of the papers by Yossef Hay, Ohad, et al. To have an accurate result there must be a significant distance from trough to peak and this was represented by AC in the ratio of blood flow formula. So, this raises a lot of questions like what factors could make the result of a person of dark skin have a less accurate result. My hypothesis was that melanin plays a major role in this data collection.

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I researched more on my project and acquired a lot of data to compare and deduce something. In my study, I studied research where a group of doctors from Jerusalem College of Technology (JCT) was building a pulse oximeter for babies, and it had several formulas.

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First, was the ratio of blood flow formula which is basically the distance of the trough to peak divided by the average PPG or lux. Extinction coefficient formula basically involved the Eo of Deoxyhemoglobin and Oxyhemoglobin which I would say had some doubts, path length formula that explained scattered and direct light, a correctional formula that had both and the extinction coefficient and path length merged. The empirical formula had fixed constants from their samples. These formulas were used to design a pulse oximeter. And these are questionable because these commercial pulse oximeters’ do not calculate two very major factors that could affect the readings of how much oxygen is in the hemoglobin. These factors include.

• Melanin affects the how much light is absorbed based on the Melanin Absorption Spectroscopy.

• Thickness of finger because everyone has different sizes of fingers and when light passes through the finger it scatters differently depending on how thick that finger is and this affects the light output.

Now with these factors is there a pulse oximeter that has been invented that measures these important factors before giving out data to its users? I don’t think so! This medical device is scientifically questionable.

I collected up to 20 samples of different races and gender. While reading these data they were some unpleasant results, and this was due to some factors.

Firstly, we noticed that the red led overheats over time and tends to give inaccurate readings and the infrared light didn’t overheat so we added a breadboard with a 440 ohms resistor to avoid overheating and stabilized the reading. Secondly, after some research on the commercial pulse oximeter, we noticed the pulse oximeter goes through a cycle of red on and infrared off, red off and infrared on, red off, and infrared off under one second. This was a challenge for us because our sensor (TSL2591) could not read that fast and we considered increasing the integration time and gain but the consequence of doing this was that the accuracy of the reading would reduce. So, we wrote a code that gives reads 5 times per second but what we wanted was 10 times per second.

Towards the middle of the week, I moved my attention to researching written articles and journals on Pulse Oximeter. Below are some cited articles and journals that I studied.

Sjoding, Michael W., et al. “Racial Bias in Pulse Oximetry Measurement.” New England Journal of Medicine, vol. 383, no. 25, Dec. 2020, pp. 2477–78. Taylor and Francis+NEJM, doi:10.1056/NEJMc2029240.

Yossef Hay, Ohad, et al. “Pulse Oximetry with Two Infrared Wavelengths without Calibration in Extracted Arterial Blood.” Sensors (Basel, Switzerland), vol. 18, no. 10, Oct. 2018, p. 3457. PubMed Central, doi:10.3390/s18103457.

Zonios, George, et al. “Melanin Absorption Spectroscopy: New Method for Noninvasive Skin Investigation and Melanoma Detection.” Journal of Biomedical Optics, vol. 13, no. 1, International Society for Optics and Photonics, Jan. 2008, p. 014017. www.spiedigitallibrary.org, doi:10.1117/1.2844710.

DESIGNING AND DATA COLLECTION

I came up with a design that suited my environment more. I call it an all-in-one P.O design. It is cylindrical in shape and has an LED and light sensor attached to it. With this design getting a more accurate reading would be little or no problem because it has stability, and the light sensor and LEDs are tightly fitted with zero percent movement. Also, to ensure perfect stability, I used siliconized acrylic latex sealant to make sure there was not any LED movement while taking readings. Below are the diagrams of the pulse oximeter.

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Data collection started immediately after my device was all set up. And currently, a lot of observations have been made and they are as follows:

• No movement of the device or its components while taking readings for an accurate result.
• The tip of the LED must be directly facing the light sensor.
• The position of the finger is important and should not be too deep into the device.
• The IR values from the data has a saturation of 65535 and for the visible 0.
• I constructed a graph that shows the plot of the IR values and Visible values, and it was observed that they both had similar visualization but different values i.e. they moved at the same rate.

• After taking readings on myself, overtime the light ray’s data reduces due to the LED being ON for a long time. But are they ratio significantly close because if they are it does not matter?

So, the ratio between the values in the IR was calculated to see the difference and it turned out they have significant ratios. GOOD NEWS! Then the ratio of the IR and Visible was calculated and they also gave me similar ratios. This is what we wanted so it did not matter if the light ray’s data reduced over time.

• Two samples were acquired next. Sample A was a male and a person of color with very dark skin tone and Sample B was a male Caucasian. The reading was taken from their middle finger on the right hand, and we made some interesting observations. The average of the ratio of IR and Visible light passing through the finger for the person of color and that of the male Caucasian had a large difference. Could this be because of the thickness of the skin or the clear color difference of the skin?

Next week we would be assessing a larger sample class with different skin colors and using both the index and middle finger on the right hand and on the left hand, we would be using the already manufactured pulse oximeter to see the difference. So basically, taking readings at the same time and seeing the difference between what we built and what’s in the market selling. By doing this we would be able to answer some questions that are arising.

Tinkercad is a user-friendly app for 3D design, electronics, and coding. I also used an Ultimaker Cura to slice my design from Tinkercad. I got acquainted with these softwares and used them for my designs to be able to contain both the LED(RED and IR) and the light sensor.

These designs are designed to hold my light sensor and LED lights. I faced a lot of failure from the product of my print. I had to consider how much the curve would be for the finger to rest on. I also had to ensure there was no movement from the sensor, LED’s and inserted finger to ensure an accurate result. Also we don’t want the pulse oximeter to be too bogus we want simplicity but also very effective. I came up with several designs but failed in some way. It was either the holes for the LED’s and sensor were too small or too big. In some cases where the finger was meant to rest wasn’t curved well enough. It was also important that the LED was facing directly on the light sensor(the middle) which was also a discovery I made from the other prints produced. Below are pictures of the 3D prints I made that had one or more of the above explained errors.

I have been working on trying to perfect my design before a final print. It gets frustrating but the hunger to get it right is more than the frustration and I know I will get it to work. Professor Eric Remy would say ” We are too focused sometimes on one particular goal we forget that there is more to do and achieve” So I plan on moving forward with my project like working on smoothing my data output and also trying to figure out the right design, maybe it doesn’t have to be what we commonly see in the market and that is two rectangles that hold the LED and light sensor. It would be nice to think outside the box and design something more conducive and suited to my environment. Hopefully by next week I hope to have something better than my above designs.

Pulse Width Modulation(PWM) is a method of reducing the average power delivered by an electrical signal, by effectively chopping it up into discrete parts. That way you could dim a light. I also discovered that when dimming light it basically just goes off and on at a particle ratio and cycle. Isn’t that cool?! Yes, it is!!! Light is awesome! I built a PWM to see how it works using an Arduino board, jump wire, breadboard, potentiometer, 220 ohms resistor. The potentiometer is a component that controls electric flow for different light intensities. I used this device to dim and brighten the LED at different ratios. It is also possible to do this experiment without a potentiometer and instead write a code in Arduino to control the dimness and brightness. One of the problems I faced was finding the right ratio that way the on and off won’t be visible to human eyes. It requires several test runs. This also applied to an IR light but won’t be visible to the human eyes to see the different levels of emission.

I included a TSL2591 sensor to read the different levels of light emitted while using a potentiometer. I also observed that the sensor gets saturated at some point.

Another interesting observation was that the sensor has to be facing directly on top of the RED/IR light to get an accurate reading. The next step for me is to design a case on the 3D printer that takes the sensor and the LED/IR light.

Hi everyone,

A LED is a light-emitting diode that emits light when current flows through it. The infrared red (IR) light is a type of radiant energy that can not be seen by the human eyes but can be seen by a sensor and we can feel as heat. It also is located right next to red light on the electromagnetic spectrum at 800nm to 1m. Red light is a type of radiant energy that can be seen by human eyes, seen by a sensor, and can feel as heat. It has a wavelength of 630nm-700nm.

This week I learned and understood how to turn on an LED and IR light using a breadboard, Arduino UNO board, jump wires, LED, IR, and a 220 ohms resistor. The picture below shows my connections. The LED is inserted into the breadboard. A jump wire connects the GND(ground) to the negative row of the LED(shorter leg) on the breadboard. A 220 ohms is connected on the same row as the positive row of the LED(longer leg). A different Jump wire connects the digital output 13 on the Arduino board and shares the same row as the other end of the resistor. When this is done a code is run on the Arduino to emit light.

The picture below shows my connections. The LED is inserted into the breadboard. A jump wire connects the GND(ground) to the negative row of the LED(shorter leg) on the breadboard. A 220 ohms is connected on the same row as the positive row of the LED(longer leg). A different Jump wire connects the 5V on the Arduino board and shares the same row as the other end of the resistor. When this is done light is emitted.

A photoresistor also known as a light dependent resistor is a components that decreases its resistance when there is high level of light. It is mostly used by devices to detect the presence of light. An IR receiver is a device used to receive an infrared signal and interprets the signal.

I used the photoresistor to read the light in the room and the red LED. I also observed the data output. I also noticed that the photoresistor could not read an IR light. Below is a picture of my connections. The photoresistor has three pins and is connected to the breadboard. From the left, is the signal(S) and a jump wire is connected from the S pin on the breadboard to the digital output 13 on the Arduino board and the middle pin on the breadboard is connected to the 5V on the Arduino board using a jump wire. To the far right, a jump wire connects the negative pin on the breadboard to the GND on the Arduino board. Now, these connections are in place in order to receive data you would need the photoresistor library on Arduino and run the code given.

Hi everyone,

My name is Sukky Nd-Ezuma and I am a rising junior and a Computer Science major and Data Science minor in Gettysburg college. My project is on a medical device known as a pulse oximeter. A pulse oximeter is a device used to check the oxygen level in the blood. This device uses two lights the RED and Infrared Light(IR Light) and a sensor that measures the amount of light passing through the blood. Recently, it was discovered by FDA during the covid-19 pandemic that a lot of wrong data was gotten from this device when used on a Person of Color compared to Caucasians. My hypothesis is that these lights are absorbed by the skin color before reaching the blood for data collection which results in giving inaccurate data. I intend on rebuilding the pulse oximeter and deduce a way to make the data more accurate for everyone.

In my first week, I was opportune to be in Nigeria where I collected data using a pulse oximeter purchased from the same country and one purchased from the United States of America. This data comprised of the following information; age, sex, device used( Nigeria or USA), %SPO2(oxygen level in blood), and bpm (heartbeat per minute). Returning to the USA a similar procedure was carried out. This data would be compared to visualize its differences and would also be compared to the pulse oximeter I plan on building.