Short Wave - Meet One Engineer Fixing A Racially Biased Medical Device

Episode Date: February 13, 2023

During the COVID-19 pandemic, one measurement became more important than almost any other: blood oxygen saturation. It was the one concrete number that doctors could use to judge how severe a case of COVID-19 was and know whether to admit people into the hospital and provide them with supplemental oxygen. But pulse oximeters, the device most commonly used to measure blood oxygen levels, don't work as well for patients of color. Kimani Toussaint, a physicist at Brown University, is leading a group trying to make a better, more equitable alternative a reality.See pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences.NPR Privacy Policy

You're listening to Shortwave from NPR. It was 2020 at the height of the COVID-19 pandemic when Kimani Toussaint first heard about the problems with pulse oxymeters. We're all watching the news and finding out what was going on and this is before any vaccines. Sick patients were showing up at the hospital with dangerously low blood oxygen saturation levels. And health care workers were relying more and more on a device called a pulse oxymeter. to monitor their condition and to determine how much extra oxygen to give them. But doctors at the University of Michigan Hospital noticed something was wrong.

The device, which uses light to shine through a fingertip, wasn't recognizing low oxygen levels in patients with darker skin tones. The Michigan doctors published their study in the New England Journal of Medicine in December 2020, and it sent shockwaves through the medical world. And Kimani, who is a professor in the School of Engineering at Brown University, heard about it from his wife, Diana Grigsby-Toussaint, an epidemiologist at Brown. She actually knew before the Michigan study

about the concerns with pulse oxymeters. I said to him, you know, it's highly relevant. You're an engineer, and this is something you should go and look into in terms of why this is the case. What was fascinating and surprising and disturbing was that this problem had been documented much earlier than the pandemic, the COVID pandemic, But even myself, being in optics, I just wasn't aware of it, even though I was familiar with the technology.

So he listened to me. So I was like, you see, this is what happens when you listen to your spouse. Meanwhile, the Michigan study was getting a lot of attention. Study got a lot of pushback, and the device manufacturer said this couldn't be true. Our devices, you know, work really well. The controversy caught the eye of Ushali McFarlane, a national science correspondent for stat. And then it was followed by, I won't say an hour. Avalanche, but a series of many stories that said, yes, this is happening in ICU's.

This is delaying COVID treatment for patients who have darker skin. This is happening in veterans' hospitals. It's even happening on general surgical floors where patients aren't that sick. So it really became clear it was a huge issue affecting probably millions of Americans in their health. But some people did know. Studies showing that pulse oxymeters give racially disparate results date back two decades. But as Usha points out, they were published in smaller journals, never got attention from bigger journals, never made their way into textbooks to be read by doctors in training. This totally shocked Dr. Noha Albulata and her colleagues.

She kept thinking about the implications, how undoubtedly black and brown patients struggling to breathe have been sent home without oxygen because their pulse oxymetry seemed fine. There was a lot of sort of somber moments and conversations being. had and just a lot of, I would say, anger that this was something that we should have been taught about in school. This had been known for quite some time. And it is a problem that the FDA has finally started to pay attention to, dedicating a 10-hour meeting to pulse oxymeters last November amid growing concerns. As for NOHA, she wants something better, a next-generation pulse oxymeter accurate for all skin tones. Some of her, something that only an engineer can build.

As part of our Black History Month programming today on the show, how Kimani Toussaint is reimagining a better health tool for all. I'm Emily Kwong and this is Shortwave, the Daily Science Podcast from NPR. Before we get into this, I just want to be clear. There is more than one way to measure blood oxygen levels. In fact, the gold standard in medicine is something called an arterial blood gas test, or ABG. Blood gets drawn from the artery in a patient's wrist and has to be put on ice for immediate sampling in a lab. But a test this invasive isn't always possible in a fast-paced emergency room or outpatient clinic,

which is why more and more doctors, especially during the pandemic, came to rely on pulse oxymeters. They're simply clipped to a patient's finger or earlobe or the foot of an infant for instant reading, no needles, no blood. These devices have become ubiquitous in medicine, and there was a boom in home sales of them during the pandemic. In some clinics, the number on the pulse oxymeter is treated as a vital sign, as important as your pulse or your blood pressure. Kimani Toussaint explained how they work. When the blood leaves the heart, it travels along the arteries, and this hemoglobin molecule carries oxygen. So we call it oxyhemoglobin. And once it's delivered all of that, then now we have blood that circulates back to the heart via the veins without oxygen.

And that molecule is called deoxyhemoglobin. And the pulse oxymeter is designed to measure both deoxyhemoglobin and oxyhemoglobin swimming in our blood vessels at the tip of our finger. And it does this through light. When you shine light on these protein molecules, the hemoglobin with oxygen and hemoglobin without oxygen, where how much light is absorbed, it becomes very waveless specific. Now, most pulse oxymeters shine two wavelengths of light. One is infrared, the other is red. And how it works when it's clipped on your finger is that one side of the pulse

oxymeter shines light through your finger and the other side measures how much was absorbed. And then we look at the relative absorptions and take the ratio metric measure of how much one gets more absorbed than the other and use that. to estimate the amount of oxygen that saturated in our blood. And that reading appears on a little screen. Doctors call it your oxygen saturation, or sometimes your periphery oxygen saturation. The lingo doesn't really matter.

The point is that that number can dictate your care. A reading between 95 and 100% is healthy, but once you get below 89%, doctors start to worry. At 88%, a patient qualifies for home oxygen under the Medicare system. meaning they can use supplemental oxygen to keep them healthy. The problem is that these pulse oxymeters aren't always right. Multiple factors can knock them off by two or three degrees, from poor circulation and tobacco use to jewelry and nail polish.

But by far, the factor with the biggest implications for human health is skin pigmentation. Black and brown skin contains more melanin, which absorbs light at different wavelengths. melanin in skin can block the light absorption properties of the device, meaning a pulse oxymeter might not register low oxygen saturation in patients with darker skin tones. Teasin out or separating out the contribution of melanin, which would overlap with the contributions of oxy and deoxyhemoglobin, that is the challenge. It's an engineering problem, but it is also a health equity problem. If you don't have people in the room that are representative of,

the population of people that you are trying to address with this technology, you are automatically creating blind spots. And the imprecision in these medical devices was there from the beginning. Ushali McFarling has been following the story for Stad. You know, I don't think there's a better example of the invisible systemic racism within medicine than this tiny device that's nevertheless so important. These devices to measure, you know, low oxygen were made for mountaineers and jet pilots. who are in very extreme conditions. And in the 50s and 60s, these are generally very white, you know,

populations. And then the device we use today, its basic setup was invented in Japan. And that's a very homogenous and also pretty light-skinned population. And then when they went to be approved in the United States, they were tested in the 80s in a time when there was so little diversity in our clinical trials and testing. So we basically tested on a white population. Now, there was once a better oxymeter on the market. Amy Moran Thomas wrote an article for Wired about it. Hewlett Packer created something in the 1970s that was the size of a record player. It used eight wavelengths and was clipped on the person's ears. And because their oxymeter was tested on black and white patients, its accuracy was more equitable. The light could actually

be calibrated for different skin tones. But in the 1980s, HP shifted away from selling medical devices to focus on computers. And that pulse oxymeter developed in Japan took off. During the pandemic, pulse oxymeter readings were used as cutoffs in overwhelmed emergency rooms. People were sent home if their readings were above a certain number. And if you think about it, a reading that was inaccurate by a few percentage points because of melanin blocking some of the light wouldn't be known by doctors. Here's Noha Abolata again. CEO of the Roots Community Health Center in Oakland. So I think that there's no doubt in my mind that this has led to people not getting care,

not getting timely care, or even being sent home or staying home to die, specifically from COVID-19. Some recent studies do back this up. And in September, NOHA and fellow doctors in Northern California published their findings. They reported that pulse oxymetry, systematically overestimated blood oxygenation by about 1% in non-Hispanic, black, African-American patients compared with non-Hispanic white patients. Noha says that thinking about all of her past patients and these tiny percentage points that

might have made a huge difference has been the hardest part. I could remember a patient where the Pulseox just did not look like what I was seeing in front of me and this is someone who had emphysema and I was trying to get. qualified for home oxygen and just could not get them qualified with the Pulse Sox. And so I decided to send them in for that arterial blood gas test. And sure enough, they qualified. And at that time, it felt great. You know, oh, okay, good. I, you know, I pursued this and this person got their home oxygen. But now looking back on it, it makes me angry. Noha now has workarounds. She tells patients to watch for

large swings in the pulse oxymeter readings and not put as much stock in the numbers themselves. It's a shaky compromise that leaves many doctors anxious for a new and better device. And one of them is underway at Brown University. Kimani Toussaint has developed a prototype with his doctoral student, Retendo Jokashira. Our technology is still pulse-oximetry in a sense that it's a light-based techniques based on similar elements. where we differ is we are trying to exploit the polarization or electric field properties of light. So rather than two sources of light, the theory is to build an oxymeter that uses a single light source with unique polarization properties that allow the detected signal to be measured independent of the effect of melanin.

It's complicated, but similar to the technology used for sunglasses, all dependent on polarization. And they're working with a local hospital in Rhode Island, the Miriam Hospital and collaborator Jane Carter, to test this prototype on patients. It's a lot bigger, the size of a shoebox with lasers and mirrors inside. And in some ways, it's kind of like the model built by Hewlett Packard in the 1970s, bigger, clunkier, but more customizable for different skin tones. As word gets out about his work,

Kimani says he's been getting emails from people all over the country. I've had emails from people who just has seen one of these stories and they, you know, the common everyday person who's like, can you tell me kind of where you are with this, you know, is this something that can be solved, right? So it's one of those things where it's really hit me just how much impact that this work could have if it's successful. And that to me is exciting, but I do also appreciate that significant responsibility associated with that. He told me, this is about so much more than pulse oxymetry. If you have a health equity story you want us to talk about, send us an email at shorthwave at npr.org. Today's episode was co-reported with Anil Oza, who also checked the facts. It was produced by Thomas Liu and edited it.

by Gabriel Spitzer. The audio engineer was Neil Tewald. Rebecca Ramirez is our supervising producer. Brendan Crump is our podcast coordinator. Our senior director of programming is Beth Donovan. And the senior vice president of programming is Anya Grundman. I'm Emily Kwong. Thanks for listening to Shorewave.

Daily Science Podcast from NPR.