July 26, 2023 – Researchers in Texas are developing a “green light” technology that they hope will solve a critical problem highlighted by the pandemic: the constraints of pulse oximeters in patients with darker skin.
A recent study supports earlier findings that their device works.
“It's a new, first-in-class technology,” said Dr. Sanjay Gokhale, the bioengineer leading the research on the University of Texas at Arlington. “The team has done extensive preclinical work and conducted Phase I trials in human volunteers to demonstrate sensitivity and accuracy.”
It is one among several ongoing projects to modernize pulse oximetry, a technology based on research on light-skinned people and not much has changed in 50 years.
The pulse oximeter measures the oxygen saturation in your hemoglobin (a protein in red blood cells). However, in patients with darker skin, it tends to overestimate oxygen saturation by about 2 to three%. That may not sound like much, nevertheless it's enough to delay essential treatment for respiratory illnesses like COVID-19.
“Falsely elevated readings from commercial oximeters have delayed treatment of black COVID-19 patients in some cases for hours,” said Divya Chander, MD, PhD, an anesthesiologist in Oakland, California, and chair of neuroscience at The Singularity Group. (Chander was not involved within the research at UT Arlington.)
Initial research work was carried out individually at Brown University And Tufts University goals to revamp the heart beat oximeter to offer accurate readings in patients of all skin tones. Researchers on the University of California San Diego are investigating a technique for measuring blood oxygen through the use of sound in combination with light. Other solutions try Skin tone correction with algorithms.
The UT Arlington device also uses an algorithm, but its major innovation is that it replaces red light with green light.
Red light, green light
Conventional oximetry devices, which are frequently attached to the patient's fingertip, use LEDs to shine light through the skin at two wavelengths: one within the red a part of the spectrum, the opposite within the infrared. The light is transmitted from one side of the clip to the opposite, penetrating the arterial blood because it pulsates.
The device calculates a patient's oxygen saturation based on the quantity of sunshine of every wavelength absorbed by hemoglobin within the blood. Oxygen-rich hemoglobin absorbs light in a different way than oxygen-poor hemoglobin, so oxygen saturation could be expressed as a percentage; 100% means all the hemoglobin is fully oxygenated. However, the melanin within the skin can interfere with light absorption and affect the outcomes.
The green light method measures reflection somewhat than absorption – that’s, how much light is reflected. As with conventional oximetry, the green light method uses two wavelengths. Each has a unique shade of green, and the 2 types of hemoglobin reflect them in a different way.
Using an algorithm developed by the researchers, the device can take readings on patients of all skin tones, the researchers say. And because it really works on the wrist somewhat than the finger, the device also eliminates problems with cold fingers and dark nail polish – each of that are known to affect the accuracy of traditional oximetry.
In the latest experimentsThe researchers tested the technology on synthetic skin samples with different amounts of melanin, Gokhale said. The device detected changes in blood oxygen saturation even in samples with high melanin content.
In a study published last yearThe technology was tested on 16 people in comparison with an invasive portable blood analyzer and a noninvasive business pulse oximeter and was found to be comparable to the invasive method.
An obstacle
The green light approach might be “game-changing,” Chander said. But it also has a downside.
Because green light doesn’t penetrate as deeply, this approach measures blood oxygen saturation in capillary beds (small blood vessels very near the skin's surface). In contrast, traditional oximetry measures oxygen saturation in a pulsating artery—hence the name pulse oximetry.
Valuable information could be obtained from the arterial pulse.
Changes within the arterial pulse, referred to as waveforms, “can tell us a few patient’s hydration status. [for instance]”, said Chander. “In a mechanically ventilated patient, this variation within the respiratory cycle can provide us insight into how well the patient responds to fluid therapy when their blood pressure is simply too low.”
Taking these considerations into consideration, the Greenlight method could also be useful as a complement, but not as a whole alternative for a traditional pulse oximeter measurement, noted Chander.