Green Light Pulse Oximetry: A Potential Solution for Dark-Skinned Patients

Researchers at the University of Texas, Arlington are developing a green light pulse oximetry technology to address the limitations of traditional pulse oximeters in accurately measuring oxygen saturation in patients with darker skin.

A New Dawn in Pulse Oximetry Technology

The team’s promising new device is being heralded as a “first-in-class technology” by bioengineer Dr. Sanjay Gokhale, who leads the research. Phase I studies involving human volunteers have shown encouraging results, demonstrating both sensitivity and accuracy.

This effort is part of a broader initiative to modernize pulse oximetry, a technology that has remained largely unchanged for half a century and was originally based on research conducted on lighter-skinned individuals.

The Challenge with Traditional Pulse Oximetry

Traditional pulse oximeters measure the saturation of oxygen in hemoglobin, a protein found in red blood cells. However, these devices tend to overestimate oxygen saturation by about 2% to 3% in patients with darker skin. While this discrepancy may seem minor, it can lead to significant treatment delays for conditions like COVID-19.

The Impact of False Readings

“Falsely elevated readings from commercial oximeters have delayed treatment of Black COVID-19 patients for hours in some cases,” reports Divya Chander, MD, Ph.D., an anesthesiologist based in Oakland, CA (not involved in the UT Arlington research).

Several institutions including Brown University, Tufts University, and University of California San Diego are conducting independent research to redesign pulse oximeters for accurate readings in patients of all skin tones.

A Fresh Approach: Green Light Pulse Oximetry

The UT Arlington team’s device utilizes an algorithm, but its primary innovation is substituting red light with green light in pulse oximetry. Traditional devices use LEDs to emit light through the skin at two wavelengths, one in the red part of the spectrum and the other in the infrared. The light passes through arterial blood as it pulses. 

The device then calculates oxygen saturation based on how much light of each wavelength is absorbed by hemoglobin in the blood. However, melanin in the skin can interfere with light absorption, affecting the results.

How Green Light Differs

The green light strategy measures reflectance rather than absorption. It uses two different shades of green light, which are reflected differently by the two forms of hemoglobin. An algorithm developed by the researchers allows the device to capture readings in patients of all skin tones, they claim.

Additionally, the device is applied on the wrist, eliminating issues with cold fingers or dark nail polish that can reduce accuracy in traditional oximetry.

Preliminary Research Results

In recent experiments, the researchers tested the technology on synthetic skin samples with varying amounts of melanin, according to Gokhale. The device detected changes in blood oxygen saturation even in samples with high melanin levels. 

In a study published last year, the technology was tested in 16 people against an invasive handheld blood analyzer and a noninvasive commercial pulse oximeter and was found to be comparable to the invasive method.

Limitations of the Green Light Approach

Chander suggests that the green light methodology could bring about a game-changing shift. However, it comes with its limitations.

The penetration depth of green light is not as profound, meaning it only measures the blood oxygen saturation in capillary beds—tiny blood vessels located near the skin surface. In contrast, conventional oximetry assesses the oxygen saturation in a pulsating artery, hence the term pulse oximetry.

There’s a significant value in data obtained from an arterial pulse.

For example, variations in the arterial pulse, referred to as waveforms, can provide insights about a patient’s hydration status, according to Chander. In patients on mechanical ventilation, these fluctuations correlated with their respiratory cycle can offer feedback on how they might respond to fluid resuscitation if their blood pressure falls too low.

Taking these factors into account, Chander points out that the green light method might serve better as a complementary tool, rather than a complete substitute, for standard pulse oximetry.