By Pamela J. Waterman

Fluent has been involved in pharmaceutical delivery, medical devices, and physiological studies for eight or nine years, reports Ahmad Haidari, global industry director for Fluent’s healthcare division. He says that the company’s earliest medical work involved heart valve and blood pump design, but that the field has widened a great deal.

   

This is a study of air velocity as it travels through the nasal cavity using Fluent; the nostrils are at the lower left.

“For example,” notes Haidari, “laser eye surgery raises heat-transfer questions. Should the laser pulse be long and not have too many repetitions, or short and more frequent for the safest results? And now people are using CFD for electrophoresis and labs on a chip, where fluids are moved in micro-channels under electromechanical charges.”

Haidari finds that one of the most intriguing areas for CFD use is the study of human physiology in conjunction with medical imaging. “The graphical resolution of medical imaging has become excellent, and one can now see physiological flow and the interaction of medicine and devices on the body.” When the physician understands the extent of a problem such as an aneurism by viewing a medical image, he can choose whether to correct it with a stent, where to put it, and how to install it.

   

3D surfaces reconstruction from CT scans and modeled using Fluent by Dr. Daniel Kurtz, State University of New York Upstate Medical University produces a computional grid of a problematic nasal passageways.

The same principles apply to respiratory system studies, Haidari says. Understanding what happens to airflow in the back of the mouth, for instance, aids inhaler design for drug delivery. But the fastest growth he has seen is in medical imaging. “If they have an MRI or CAT scan, users can save the image as an STL file, create an analysis domain from that, grid, and solve.”

Chris Reid, vice president and general manager of the fluids business unit for ANSYS, reports growing use of CFX for heart, circulatory, and respiratory system product development –such items as stents, blood pumps, and inhalers. “Blood flow itself is a multiphase flow problem,” Reid says. “Modeling this has become easier with today’s software. We can model multiphase, nonlinear behavior in arterial walls with software for fluid-structural interaction (FSI). An important application area for FSI is medicine delivery in the respiratory tract. Designs for asthmatics require modeling the whole respiratory system.”

   

Here, ANSYS CFX simulates the progress of helium in nitrogen in the tracheo-bronchial tree to predict drug concentration in the lungs.

Reid says that CFD offers ways to model the behavior of a variety of medicine delivery methods. “For example, CFD can track particles to study respiratory drugs in the air flow,” he says. “Users can work with different velocities, first in steady state, and then see what happens in the first few critical seconds after activating an asthma inhaler. It’s a complicated problem, but extensive tools now exist to simulate such problems.”

Materials present challenges in the medical arena, says Dennis Nagy, vice president of marketing and business development for CD-adapco. “Medical equipment by itself is similar in terms of analysis to other equipment. The physiological issues, however, are more challenging. A blood pump is still a pump, but the material properties of blood are different from most fluids, and the application is more critical.”
   

Engineers at the Lerner Research Institute of The Cleveland Clinic Foundation used ANSYS CFX to improve the design of cardiac pumps by minimizing sheer stress levels and the creation of vortices.

Haidari of Fluent agrees. “It’s important to obtain accurate information about sheer fields in blood flow, for example, where high-velocity flow causes a flow gradient in a product such as stent, or detects parts of the stent where blood flow may stop, such as going around a bend. CFD shows which regions are being sheered and at what rate, and how that affects circulation.”

The material properties for tissue, Nagy says, are challenging, and CD-adapco has seen the use of software and consulting grow in that area. “Consulting –that is, running simulations for customers– accounts for about 21 percent of our total business. Many such projects are in the medical world, because typically medical equipment is developed by smaller companies, or by small departments with small engineering teams, in larger companies.”

He points out that CFD is being used extensively for research. “One researcher with whom we work is studying smoke deposited in the lungs of smokers –to find out what the effects are on lung tissue, how particles are dispersed or deposited, and what gets out of the lungs.”

Hengchu Cao is the manager of CAE for heart valves at Edwards Lifesciences, a medical equipment company in Irvine, CA, and a user of STAR-CD. He says, “CFD has really taken off with the availability of high-performance computing –especially for problems with 3D complexity and needing 3D mesh. It helps as well to have advanced solvers that can model viscous flow of fluids like blood.”

   

The EU-funded BloodSim project demonstrated a coupled fluid-structure interaction in the popular St. Jude heart valve using CFX.

He sees CFD in use by engineers dealing with ventometers, heart valves, catheters, a variety of diagnostic tools, as well as drug delivery and diffusion in the cardiovascular system. “It is possible to study these products with experimental methods such as ultrasound. However, the resolution of the instrumentation is limited, though improving. The real problem is that physical testing doesn’t enable what-if studies, where the performance of devices can be simulated in normal and abnormal physiology. With simulation, we can modify the physiology and study many phenomena that may occur in use. It enables true design optimization.”

Dr. Rupak Banerjee, associate professor of biomedical engineering at the University of Cincinnati, uses Fluent. He has performed studies of the cardiovascular system, drug delivery –with an emphasis on thermal and ultrasound, ablation, ocular, and spinal applications. “A major benefit of CFD simulation in biomedical studies is that it makes it possible to reduce the number of animal experiments.”

He finds that it also assists in making treatments safer and more precise. “Such simulations help us to customize devices and make them patient-specific. If a device needs to be implanted in a patient, its size and placement can be worked out carefully in advance of operating.” In addition, CFD studies also make it possible to work out therapies on a patient-specific basis. “If a physician wants to deliver medication to a tumor, for example, he can target the delivery differently from patient to patient,” says Banerjee.
   

CD-adapco’s STAR-CD was used to study how blood flows through a healthy aortic arch.

Dan White is a senior CFD application engineer working for HeartWare Inc. of Miramar, FL, and is a user of ANSYS CFX. He finds a very real advantage of CFD simulation in reduction of design time. “Prototypes and physical testing can be cut down to just a few iterations. And unlike physical testing, CFD lets engineers see every part of the machine –including inside, which we can’t do with physical testing.”

He adds that he finds CFD invaluable in any problem that requires looking at flow. “In complex products with flow, CFD offers the best return on investment.”

Reid of ANSYS points out, “Anywhere you have high-performance equipment and health issues, you can run into heat-transfer issues. The applications for CFD in medicine are limitless.”

Contributing Editor Louise Elliott is a freelance writer based in California. Offer Louise your feedback on this article by clicking here. Please reference “CFD & Biomed, February 2006” in your message.

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Product Information

ANSYS
Canonsburg, PA

CD-adapco
Mellville, NY

Fluent
Lebanon, NH