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 in all 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, but it surely's enough to delay necessary 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 heartbeat oximeter to offer accurate readings in patients of all skin tones. Researchers on the University of California San Diego are investigating a way 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 predominant innovation is that it replaces red light with green light.
Red light, green light
Conventional oximetry devices, which are often 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 otherwise than oxygen-poor hemoglobin, so oxygen saturation may 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 quite than absorption – that's, how much light is reflected. As with conventional oximetry, the green light method uses two wavelengths. Each has a distinct shade of green, and the 2 types of hemoglobin reflect them otherwise.
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 quite 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.
A drawback
The green light approach may very well 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 may be obtained from the arterial pulse.
Changes within the arterial pulse, often called waveforms, “can tell us a couple of patient’s hydration status. [for instance]”, said Chander. “In a mechanically ventilated patient, this variation within the respiratory cycle may give us insight into how well the patient responds to fluid therapy when their blood pressure is just too low.”
Taking these considerations under 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.