Campus engineering professor research determines particles most likely to cause stroke

While some mechanical engineers use their supercomputers to build airplanes and vehicles, Shawn Shadden uses his to map the inner workings of the human heart. Shadden, an assistant professor in the campus department of mechanical engineering, is examining the bodily mechanisms that allow small particles from the heart to enter the bloodstream and travel into the brain, causing a stroke. He works with Robert Schwartz, a researcher for the Minneapolis Heart Institute Foundation. “Whether you are left-handed or right-handed, about 80 to 90 percent of your speech center is in the left brain,” Schwartz said. “Depending on the way your arteries are aligned, it’s sometimes a straight shot for a particle to head right up and hit the speech center, which is a catastrophe.” Together, the two researchers are working to create computer models that replicate the direction and movement of problematic, stroke-causing particles. They focus on strokes that can take place during a medical procedure called transcatheter aortic valve replacement, also known as TAVR, which replaces a person’s poorly functioning heart valve. According to the researchers, this procedure has a higher incidence of stroke than similar methods. During this procedure, bodily particles such as blood clots or calcified tissue are displaced by the artificial heart valve being installed, the researchers explained. Depending on their size, these particles then travel down into the person’s legs, where the body can safely deal with them, or up the neck into the person’s brain. “Not much is known about this, because it happens rarely, and it also happens very serendipitously,” Schwartz said. He went on to explain that in other procedures, large particles may break off and enter the bloodstream and cause minimal complications. But in the case of TAVR, very small particles are able to permeate the brain and “cause larger problems.” By mapping the directions that particles of different sizes would likely move in patients’ bodies, Shadden determined that the most dangerous particle size is 1 millimeter, which is considered medium-sized. Such particles showed an extremely high incidence of making their way to the brain and, in turn, causing a stroke. In order to prevent the strokes caused by the procedure, Keystone Heart, a medical technology company, is developing a screen that will cover the arteries leading to the brain to block particles from entering. The company has modified its design to block the medium-sized particles Shadden pinpointed and is currently working with him to model and compute whether the screen will be effective in practice. “Engineering has always played a huge role in revolutionizing medicine, whether it’s how we diagnose cardiovascular problems or how we perform the procedures themselves,” Shadden said. “We’re really just trying to build on that.”