Supercomputers listen to the heart

New supercomputer models have come closer than ever to capturing the behavior of normal human heart valves and their replacements, according to recent studies by groups including scientists at the Institute for Computational Engineering and Sciences (ICES) at The University of Texas at Austin and the Department of Mechanical Engineering at Iowa State University.

The studies focused on how heart valve tissue responds to realistic blood flow. The new models can help doctors make more durable repair and replacement of heart valves.

"At the core of what we do is the development of new material models that are much more structurally and biologically informed and can actually integrate mechanisms of failure and remodeling, growth, and adaptation to altered forces that go on," study co-author Michael Sacks said. Sacks is the W.A. Moncrief Endowment Simulation-Based Engineering Science Chair at ICES, and professor of Biomedical Engineering, UT Austin.

ICES has a long history with TACC. Since 2003, ICES has used supercomputers at the Texas Advanced Computing Center (TACC) to study turbulent flow. These recent studies that model the leaflet tissue-blood flow interactions through replacement human heart valves have used millions of CPU hours on the Stampede, Lonestar, and Maverick supercomputers at TACC.

"One of the big advantages to being here at ICES is that we have direct access to TACC facilities," Sacks said. "These jobs run multiple processors over a whole wide range to try and get it working over the cardiac cycle. It's very computationally intensive. The TACC resources are absolutely essential to these models. TACC facilities also allow us to concentrate on the technical and scientific problems at hand, rather than developing and maintaining hardware."

Two studies out in May 2015 centered on the leaflet cells of the mitral valve, the largest of the four heart valves. After a heart attack, the weakened heart wall will often cause the mitral valve to regulate, so that the normal one-way flow of oxygen-rich blood from the lungs between the left atrium into the left ventricle, where it is pumped out to the rest of the body.

On average, the heart beats about 2.5 billion times in a human life. Each pulse puts wear and tear on the constituent cells of the mitral valve leaflet. What's more, the valve tissue remodels itself in response to the strain of its gatekeeping.

A May 2015 study funded by the National Institutes of Health (NIH) and published in the Journal of Theoretical Biology simulated deformations at the cellular level within the anterior leaflet tissue of mitral valve. The science team combined experimental work with computation, stretching heart tissues under a microscope to provide critical data to model the mitral valve leaflet.

Heart valve tissues are built like a four-layer cake of fibrous proteins and cells. One of the main findings showed that each layer of the mitral valve tissue causes the cells within the layer to stretch differently to the relentless pumping of blood. Since the cells are the "maintenance workers" of the valve and respond to the working demands on the valve by being stretched in differing ways, this finding can help us model changes in the self-maintenance of the heart valve that lead to valve failure.