Brown Ph.D. student working to correct skin color bias in pulse oximeters

Pulse oximeters often provide inaccurate readings for people with darker skin, a significant health disparity that physics Ph.D. student Rutendo Jakachira is working to eliminate.

PROVIDENCE, R.I. [Brown University] — Pulse oximeters provide a quick, non-invasive way to check someone’s pulmonary health, using light shown through the skin to estimate the amount of oxygen in a person’s blood. But the devices, which usually clip onto a finger, don’t work well for everyone. Research has shown that people with darker skin are at much greater risk for inaccurate readings than those with lighter skin.

Rutendo Jakachira, a second-year Brown University Ph.D. student in physics, is working to change that. She is developing new optical techniques that return accurate oxygen saturation levels results regardless of skin tone. She presented promising preliminary results for her new device last month at a conference hosted by SPIE, an international society for optics and photonics. And another professional society, Optica, awarded Jakachira its Amplify Scholarship to continue her work.

The inaccuracy of pulse oximeters for people of color represents a significant concern in health care delivery, Jakachira says.

“It has been found that there can be up to a 10% difference in oxygen saturation measurements among different pulse oximeters for individuals with darker skin tones,” she said. “It has also been found that people of darker skin tones are three times more likely to have hypoxemia, and it is likely to be missed by pulse oximetry.” 

That’s because pulse oximeters tend to overestimate blood oxygen for people with dark skin. In other words, someone with dangerously low blood oxygen levels could receive a pulse ox reading that appears perfectly normal. The problem became particularly acute during the COVID-19 pandemic, during which doctors relied on pulse oximeter readings taken in clinics and in homes to gauge the severity of a patient’s illness.

The incorrect readings arise because melanin, the dark pigment found in skin and hair, tends to absorb light traveling through the skin. In people with dark skin, that high level of melanin scattering can interfere with oxygen readings. Jakachira, working with Professor of Engineering and Senior Associate Engineering Dean Kimani Toussaint, is looking to reduce the interference caused by the surface of the skin by using radially polarized light — light beams that produce a diversity of electric-field directions that vary depending on the spatial position on the beam.   

Jakachira and Toussaint have demonstrated in experiments what they believe to be the first LED-based light source that can emit radially polarized light. Testing of the device’s ability to detect blood oxygen levels looks good so far, Jakachira says.

“It looks like our device is working,” she said. “We did a preliminary study on about five people, and although it was a small study, the results are promising… We are looking toward doing a study on a larger population group, and the next step would be a clinical trial.”

Toussaint says he’s impressed with the work that Jakachira has done so far.

“Rutendo has approached this project with a combination of dedication, ingenuity and strong interest,” Toussaint said. “This has allowed us to gain a better understanding of the problem in terms of the underlying optical physics, and to creatively think outside of the box in developing a solution.”

This story was adapted from a story by Pete Bilderback, a program manager in the Department of Physics.