A real-time technique that uses light and color to measure oxygen delivery to individual red blood cells could enable researchers to study the process in relation to diseases and their treatments. Red blood cells deliver oxygen through arteries, capillaries and veins to the body’s cells and tissues. Pulse oximeters, devices that clamp onto the index finger, are the current standard for measuring the amount of oxygen in the blood, but these devices measure oxygen levels in the arteries only, providing a limited picture of oxygen metabolism. The new technology, called photoacoustic flowoxigraphy, developed by Dr. Lihong Wang of Washington University in St. Louis, uses light in a novel way to watch blood cells flowing through tiny capillaries, the smallest of the body’s blood vessels at about the width of one red blood cell. “By firing two laser pulses of different colors at a red blood cell 20 microseconds apart — nearly simultaneously — we hit the same red blood cell at almost the same location, so we get signals back at both colors,” said Wang, the Gene K. Beare Distinguished Professor of Biomedical Engineering. “That allows us to figure out the color of the red blood cell at any given moment. By watching the color change, we can determine how much oxygen is delivered from each red blood cell per unit of time or distance. From there, we can determine the average oxygen delivery per unit length of capillary segment.” Wang and colleagues observed the red blood cells as they chose which direction to travel when encountering a “fork” in the capillary, called a bifurcation. The cells travel in bunches to where oxygen is most needed in the body at that time, he said. Although the cells travel very quickly, the speed of the device — 200 Hz, or 20 3-D frames per second — allows the researchers to see the cells in real time. In comparison, a film at a movie theater moves at 30 Hz, fast enough that the eye cannot see the individual frames. “Photoacoustic flowoxigraphy is considered an engineering feat, enabling oximetry at the most fundamental level, namely, the single-cell level,” Wang says. The technique has applications for further biological studies as well as in the clinical setting, he said. “There are many biomedical questions that this technology could answer: How would cancer or diabetes change oxygen metabolism? How would cancer therapy or chemotherapy affect oxygen level?” We’d like to see if we could use this technique to monitor or predict therapeutic efficacy.” Getting the technique into the hands of researchers is the next step, Wang says. The investigators would like to license the technique to a company that would move it forward to make it available to biologists and physicians for applications. The research, funded by the National Institutes of Health, was published in PNAS Online Early Edition. Wang recently received a National Science Foundation grant for related work measuring oxygen consumption rates of individual cells. See: Wang to Study Cellular Oxygen Consumption Under NSF Grant). For more information, visit: www.wustl.edu