Kidney patients who suffer low blood pressure during hemodialysis can take hope from an optical technology being developed by researchers in Lehigh’s Complex Fluids and Soft Materials Laboratory.
Led by Daniel Ou-Yang, professor of physics and director of the lab, the researchers are using optical fibers to help doctors more quickly and efficiently determine the cause of the hypotension and the best way of treating it.
The Lehigh group is collaborating with researchers at the University of Virginia Biomedical Engineering Department and Medical School.
During the three or four hours required to remove, clean and restore the blood of a dialysis patient, says Ou-Yang, hypotension often results from low blood volume or from dilation (enlargement) of the blood vessels.
Either a transfusion or a saline injection can raise the blood pressure, but before doctors and nurses can decide which method is superior, they must determine the cause of hypotension from the ratio of red blood cells to blood protein, and from the portion of red blood cells in the body’s capillaries versus the portion in its larger arteries and veins. The two portions are different because red blood cells deform and take on a different shape when they squeeze through capillary openings.
The conventional method of obtaining this ratio is with an ultrasound transducer, which measures the speed of sound waves through blood. Precise measurements are needed, because this speed varies only slightly according to the contents of the blood, particularly the quantity of red blood cells.
Because of the size and bulkiness of the transducer, says Ou-Yang, the conventional method requires a patient’s blood to be analyzed with a relatively large (8-millimeter-wide) catheter while the blood is circulating through dialysis tubes outside the body.
Ou-Yang hopes to achieve more precise measurements – and to do so inside the body – by using optical fibers. By coupling the transducer with a fiber-optic ultrasound sensor, his group hopes to generate and detect the sound signal optically, and to improve by two orders of magnitude the signal-to-noise ratio over the conventional pulse-and-echo method of the speed-of-sound measurements in complex fluids.
With the application of the optical technology, Ou-Yang anticipates that medical technicians will one day be able to determine the ratio of red blood cells to blood protein within seconds and with minimum invasiveness, by inserting a 1-millimeter-wide fiber-optic catheter into a vein.
Meanwhile, Ou-Yang’s improvement in sound speed measurements by the phase-lock-in method is being used with hemodialysis patients at UVA’s medical school.
Ou-Yang’s Lehigh partners are Olga Lysenko, a visiting scientist from Belarus; Volkmar Dierolf, associate professor of physics; Larry Hough, a Ph.D. candidate in physics, and several undergraduate students. These include Jim Cybulski ‘02, who will go to graduate school at the Massachusetts Institute of Technology to study mechanical engineering this fall.