Engineering at Nebraska, Spring 2009
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On the Pulse of Progress

Soft TissueFrom top:
Kamenskiy calibrates load cells before a test.

Kamenskiy explains his work to Dr. William Chang, director of the Beijing office of the U.S. National Science Foundation and Dr. Namas Chandra, UNL College of Engineering's associate dean for Research and Graduate Studies.

High values (measured in Pascals) represent zones prone to restenosis in this diagram on the distribution of the effective stress on the exterior of the carotid artery wall, after endarterectomy and patching with Accuseal PTFE patch. From the Finite Element Model of the Patched Human Carotid, a 2009 reference for vascular and endovascular surgery.

Using real patients' CAT scans, Kamenskiy prepares advanced modeling that reconstructs the arteries' threedimensional structures, with all their complexities.

By putting two fingers on a pulse-point along the side of the neck, we feel the beat of the carotid artery, the main artery that supplies the brain with blood. But as people age they may develop atherosclerosis, which blocks blood vessels; strokes can occur when blood no longer reaches the brain.

For Alexey Kamenskiy, a graduate student in Engineering Mechanics at UNL, keeping this pulse drives his work to potentially benefit stroke victims.

"My research is a compound of engineering and medicine, focused on the biomechanics of the human carotid artery," said Kamenskiy.

Current treatment for this kind of arterial disease is a surgical procedure to either remove the occluding plaque from the blood vessel (a procedure called endarterectomy), place a patch and close the incision, or widen the narrowed artery by dilating it (angioplasty) and inserting a stent.

"The choice made by the surgeon is almost purely intuitive," Kamenskiy said. More knowledge is needed about treatment materials, including their properties and individual responses-as well as the mechanical properties of the carotid artery itself-to combat repetitive plaque formation and minimize other complications observed during patients' follow-up.

Seeking further information, Kamenskiy initiated two protocols with the University of Nebraska Medical Center and the Nebraska-Western Iowa Veterans Affairs Clinic in Omaha. He works with Dr. Iraklis I. Pipinos, M.D., associate professor of surgery at UNMC and the VA Clinic. Pipinos is a principal investigator with his own related projects and those in collaboration with Kamenskiy.

"These protocols allow me to closely interact with surgeons and perform studies of blood flow hemodynamics and wall mechanics in real patients," said Kamenskiy, who added that this exclusive type of data is extremely valuable for mechanical modeling.

"Precise models allow performing of virtual patient-specific operations prior to real surgery," Kamenskiy explained. "Specifically, my research includes soft-tissue biaxial testing, real in vivo measurements of blood velocity profiles and pressure waveforms, threedimensional artery geometry reconstruction, and advanced modeling."

Kamenskiy described challenges in the testing and modeling work from soft tissue's anisotropic nature, having different properties in different directions, as well as its nonlinear characteristics, with no constant proportion between the applied load and the amount the material has stretched under it.

He cited a benefit from working with UNL Engineering Mechanics. "Our department has a custom-built soft-tissue device that is able to stretch the tissue sample in two different directions and record the accurate deformation response. With only a few such devices at top U.S. universities, we are lucky to have one here. I'm using this device to test carotids, veins and patching materials used for carotid surgery."

Another challenge is that knowledge of blood flow in the carotid artery is very limited.

"Skewing the velocity profiles in the arterial branches has significant effect on the shear stresses in the blood flow, which in turn has significant effect on atherosclerosis," said Kamenskiy. "Understanding how much the profile is actually skewed and how its shape changes during the cardiac cycle is essential for understanding carotid artery hemodynamics."

Kamenskiy said, "I believe the complexity of an artery's geometry has significant effect on the blood flow in it and therefore it must be accounted for in the model." He uses real patients' CAT (computed axial tomography) scans to reconstruct the three-dimensional body of the artery-with all its kinks, narrowings, widenings, turns, and branches-and then applies that to his advanced modeling.

Evaluating different materials and approaches helps to better determine the treatment method for optimized results and