UNC-CH mathematician studies how little hearts develop

knordstrom@newsobserver.comSeptember 16, 2012 

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Laura Miller a professor of mathematics at UNC Chapel Hill who studies the flow of fluids in (or around) living creatures.

DAN SEARS — UNC Chapel Hill

Laura Miller’s work could one day save lives.

But Miller is not developing a new medicine or vaccine. She’s a professor of mathematics at UNC Chapel Hill who studies the flow of fluids in (or around) living creatures. One of Miller’s projects looks at the blood flow in the embryonic heart and lays the groundwork for people to surgically correct heart defects, possibly in utero.

The importance of fluid flow in our bodies can’t be understated. Our body tissues get nutrients and oxygen from blood. Flow problems, such as blood clots, can be fatal. The force of a fluid can even trigger chemical reactions and turn genes on and off.

A human embryo’s heart starts as a tube, the size of a hair. An adult’s heart is the size of a fist. The blood through the adult heart flows easily, like sucking water through a straw. In the embryonic tube, it’s more like sucking honey. In the embryo, blood seeps surely and steadily. In the adult heart, the blood flows in one direction on average, but it also swirls a bit.

Blood is pumped through the embryonic heart tube. But evidence suggests this early pumping isn’t for the purpose of nutrient delivery: Nutrients will spread out on their own, like cream in coffee.

Rather, the blood flow creates pressure and stresses on the cells that make up the tube. This can trigger additional cell division, expanding the tube. While growing, the embryonic heart tube twists and bends, like a balloon animal. Certain parts swell, and eventually form the heart chambers.

The blood flow is also thought to trigger some tube cells to transform into “cushion” cells on the tube walls. The cushions eventually become the heart valves.

“These cardiac cushions grow between chambers and the outflow tract, and the growth coincides with a number of changes in the fluid dynamics,” Miller said.

The mathematical equations that govern fluid flow at this scale are, well, complicated. Solving them for real-world situations requires powerful computers. Until now, it was impossible to have a solid understanding of the flow.

But it’s a good thing to study. “It is also thought that many congenital heart diseases may begin to appear at this critical stage, including problems with the formation of the valves,” said Miller.

In her lab’s simulations, they can easily tweak different conditions and see what effect it has on the flow rate and pattern. They can verify their simulations by looking at experimental systems – not actual hearts, but Plexiglas models that capture the same physics.

The effects of minor tweaking can be surprising. “If the chambers are a little smaller or the blood a little less viscous, there can be a big difference (in flow pattern),” said Miller.

“If you can get an (3-D) image of a particular patient’s heart (with MRI), then you can use these simulations to see how you might correct things with surgery,” Miller said.

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