Simulations give insight to bedsore problems

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Kara Gray  / CEI
Mark Carlson /  MSC Software

Each year, an estimated one million people suffer from painful bedsores in U.S. hospitals. These sores, the result of long-term confinement to a bed or wheelchair, often become seriously infected or develop gangrene. Bedsores are painful and sometimes deadly. They are linked to a four-fold increase in death, with a hospital mortality rate of 23 to 37%. Compounding the problem, patients who develop bedsores also experience a five-time longer hospital stay, putting them at much greater risk of developing other ailments. Of course, there are financial implications: Conservative estimates peg the cost of bedsores in U.S. hospitals at $55 billion per year. (All sources: http:// leedergroup.com/bulletins/bed-sores).

Finding a way to prevent bedsores is a high priority for hospitals, nursing homes and long-term care facilities, as well as bed manufacturers. Conventional means of studying possible solutions typically involve long prototyping processes and the use of human test subjects, who are asked to lie in a bed for an extended period to see if they develop a bedsore.

MSC two panel bedsore picsInstead, MSC Software’s Senior Engineer Mark Carlson and his team have developed a simulation test bed—both literally and figuratively—for assessing in a matter of hours instead of months, the impact of potential bed designs on bedsore formation and with absolutely no risk to human health. The simulation combines the non-linear finite element solution capabilities in MSC Marc with the multi-body dynamics analysis of MSC Adams, and the 3D post-processing visualization provided by EnSight from CEI.

The analysis has been able to uncover critical, previously unattainable insights into the problem of bedsores. This helps equipment manufacturers build better beds that can help prevent bedsores from forming in the first place.

More than skin deep
A critical challenge in studying bedsore development is understanding how, where, and why they develop. Carlson and his team knew that the buttocks and heels are the primary locations for bedsore formation. Bed manufacturers have been experimenting for years with different types of bed surfaces, foam materials, positioning and angling, and other parameters to help better distribute the stresses caused by pressure and gravity across the body.

Conventional testing, however, typically involves two methods, both with limitations. First, manufacturers ask human test subjects to lie on a pressure sensitive pad, which indicates how the contact patches manifest externally on the surface of the skin. Researchers have long theorized that bedsores are more than just a surface problem—they actually manifest under skin, deep in the tissues of the flesh, muscles, and even bone interfaces.

Close up of the calf contact stressSecond, lab tests using body parts give insight into molds in a compression-test machine can study the forces applied by those parts onto the bed, but only for those specific, individual parts—just the heel or the torso, for example. This kind of test makes no consideration for the changes, sometimes significant, which could occur when entire human bodies of varying sizes and anthropometric characteristics are positioned across an entire bed.

Co-simulation reveals hidden insights

To study the problem more holistically, Carlson and team developed an advanced co-simulation solution that let researchers study the problem more thoroughly and faster, and accelerate material and equipment design, testing, and market delivery.
Carlson began with Adams to simulate the rigid component geometry of the human body, using the Life Mod plugin (http://www. lifemodeler.com/products/lifemod/) from Life Modeler of San Clemente, Calif., to model the anthropometric data for various parts, sizes and characteristics of the human body from the pre-loaded Life Modeler geometry database. Adams software was able to simulate the effects of bed settling due to gravity across 15 different body segments, accounting for accurate range of motion calculations, as well as the other complex dynamics and kinematics present in the various human joints.
Gravity settling, however, is only part of the equation. The next step is to understand the contact patches and associated stresses caused by loading conditions in relationship to the bed. With MSC’s nonlinear finite element solver, Marc, the team was able to develop a mathematical model of the bed, including simulation of a wide array of foam materials, foam layering configurations, and other properties. In addition, the team created its own simulated foam materials and configurations for scenario testing.

The co-simulations ran the two solvers (Marc and Adams) simultaneously to include the complex physical contact interactions along with accurate representation of the human motion. This was critical to understanding the complete picture of the conditions under which bedsores develop, even beneath the skin’s surface. More importantly, the team was able to better understand and quantify the sensitivities of attribute combinations, and evaluate how even small changes in bed design, positioning, foam material and other parameters could have significant effect on contact stresses, even into the deep tissue layers below the surface.

With the time synchronous, co-simulation solution, the team was able to test in short order hundreds of combinations that included varying anthropometric characteristics, bed geometries, and complex foam materials.

A clearer picture with EnSight
While Marc and Adams have their own built-in post processors, they still generate separate data sets. To merge the two, Carlson and his team used CEI’s EnSight 3D visualization software from Computational Engineering International (CEI Inc.) of Apex, NC to concurrently view the data sets. “Looking at Adams only, you’d see the human body sinking into nothingness, and with Marc you’d see the finite elemental deformations in the bed—the contact points—but no body. Once we time-sync the two and import the results into EnSight, you get a clear picture of the combination of both data sets at once,” Carlson said.

“EnSight is so flexible and easy to use, that we can also plot data at the same time as we visualize, look at each data set separately, or combine them into a single, immersive 3D view.”

In addition to EnSight, the team used CEI’s EnLiten file viewer to share the 3D simulations with others who may not have EnSight. Carlson says the ability to demonstrate the research and results in a visually compelling way that everyone can access makes a tremendous impact in understanding and humanizing the results. “The enhanced communication we achieved with EnSight and EnLiten is huge,” he said. “Not only in presentations that I put together, but also in the fact that I can send someone a full 3D EnLiten model, which they can study on their own, interact with, manipulate views and angles, turn parts and plots off. It’s free and they can use it independently of the simulation and visualization software.”

A positive prognosis
With the research enabled through the Marc/ Adams co-simulation, hospital bed and other equipment manufacturers can gain greater visibility into what’s going on internally with the body in relationship to external forces and how to solve related challenges.

“This capability is like installing sensors inside the body and on the surface the body rests on to get a picture of how the two interact. That just wasn’t possible before,” Carlson said. “And, it’s so much faster and less expensive than building prototypes, bringing in real people for testing, and exposing them to the risk of complications, and then having to go back to the drawing board for every variable change. With Marc, Adams and EnSight working together, we can set up several variations to run simultaneously and have results the same day, versus waiting weeks or months for physical test or clinical trial results.”

Originally developed as a customized solution, the Marc/Adams co-simulation tool is now available as a pre-packaged general purpose product. EnSight and it’s free 3D viewer, EnLiten, are compatible with MSC’s entire suite of solvers including Marc, Adams, Dytran, and Nastran for stunning and compelling 3D visualization and communication. For more, visit www.mscsoftware.com and www.ensight10.com.

Editor’s note: Interested researchers can purchase this solution. It is a combination of MSC Adams multibody dynamics software with Nonlinear FEA software (for modeling the materials like foam) called Marc, plus partner technology called CEI EnSight 3D, the  visualization software. It merges the results from Marc and Adams.  The company has another product called MSC One Start Edition. It’s a pool of tokens that lets a company get access to both Adams and Marc – as well as other MSC products for under $15,000.  When they buy tokens, the use those tokens to access the suite of software. For more: http://www.mscsoftware.com/product/msc-one

CEI, however, is a separate product and not in the MCS Software token system.

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