Rice engineers help design a pulse-less pump for heart replacement

Rice engineers help design a pulse-less pump for heart replacement
Researchers collaborate with Texas Heart Institute, MicroMed Cardiovascular and University of Houston on NIH-funded study

BY B.J. ALMOND
Rice News staff

Rice University engineers are collaborating with researchers at the Texas Heart Institute (THI) at St. Luke’s Episcopal Hospital and others to develop two heart-assist pumps that individually perform the function of the left and right ventricles.

	MATTEO PASQUALI

Rather than mimic the pulse of the natural heart, the devices for this study pump blood continuously. The device for the left ventricle — the heart’s main pumping chamber — circulates blood throughout the body; the one for the right ventricle pumps blood to and from the lungs. The continuous-flow pumps are smaller — about the size of a C battery — and simpler than their complex predecessors that were programmed to pump with a pulse-like rhythm.

Led by THI, the research team received a $2.8 million grant from the National Institutes of Health for this project. In addition to THI and Rice, other members of the team are from MicroMed Cardiovascular Inc. and the University of Houston. Rice’s role is to develop a computer model to analyze blood flow and any damage to the blood cells and platelets that might result as blood travels through the pump. Depending on their analysis, the Rice researchers may then suggest modifications to the design before the pumps are tested in animals.

“Because these pumps will be implanted for the long term, we have to make sure that blood damage is minimal,” said Matteo Pasquali, Rice professor in chemical and biomolecular engineering and in chemistry.

The engineers will monitor the computer models for two main types of blood damage: excessive release of hemoglobin from the red blood cells, which can be toxic to the kidneys and liver, and the platelet activation process that can lead to formation of white thrombi, or clots of white blood cells, which could cause a blockage in the brain or small blood vessels.

“We are trying to understand why and where these thrombi form so we can suggest how to change the shape of the pump,” Pasquali said.

Also of concern to the engineers is how to make the pumps respond to the body’s changing needs for blood, such as during exercise, and how to ensure that the left and right ventricles stay in sync with each other.

“The heart has a built-in self-regulating ability,” Pasquali said. “Since the two pumps constituting the total artificial heart bypass the whole heart, it’s important to build a mechanism for regulation in the devices. Otherwise, you could get an accumulation of blood in the lungs if the left pump is pumping too slow compared to the right pump.”

COURTESY PHOTO
Rather than mimic the pulse of the natural heart, the MicroMed-DeBakey VAD (ventricular assist device) pumps blood continuously.

Researchers at the University of Houston are investigating the control mechanism that will mimic the self-regulating function of the heart.

Pasquali is collaborating with Marek Behr on creating computer simulations for the pumps. Behr is the holder of the chair for Computational Analysis of Technical Systems in the Department of Mechanical Engineering at RWTH Aachen University in Aachen, Germany. Previously a professor at Rice, Behr still maintains a close connection here as an adjunct professor in chemical and biomolecular engineering.

“The ventricular assist device (VAD) design is driven by contradictory demands,” Behr said. “On one hand, the pumps need to be made smaller to ease implantation and use in children. But on the other hand, the pumps need to deliver adequate blood flow and cause minimal damage to the passing blood cells.”

The researchers will apply what they learn from computer simulation to physical models of the pump that are manufactured and tested in laboratories at MicroMed. This Houston-based company makes the MicroMed DeBakey VAD that is being used for this study. The pump, which is already used in human patients in Europe, is named for heart surgeon Michael DeBakey, now chancellor emeritus of Baylor College of Medicine.

DeBakey pioneered the development of heart pumps. In the 1960s, he collaborated with chemical engineering professor Bill Akers, who led the Biomedical Engineering Laboratory at Rice. They produced the first successful left ventricular heart bypass device that was a precursor to the VADs used as the base design in the current research project.

Once the researchers get satisfactory results from the computer simulation and laboratory models, they will test the total artificial heart in calves, which will pave the way for testing in humans.

	DHRUV ARORA
	The engineers will monitor the computer models for two main types of blood damage: excessive release of hemoglobin from the red blood cells, which can be toxic to the kidneys and liver, and activation of the process that causes clots, or thrombi, of white blood cells to form in the pump, from which they can detach and cause a blockage in the brain or small blood vessels.

The engineers will monitor the computer models for two main types of blood damage: excessive release of hemoglobin from the red blood cells, which can be toxic to the kidneys and liver, and activation of the process that causes clots, or thrombi, of white blood cells to form in the pump, from which they can detach and cause a blockage in the brain or small blood vessels.

“We have been working in this field for more than 40 years, and the technical challenges inherent in developing a total artificial heart have, to date, limited its application,” said the study’s principal investigator, Bud Frazier, who is chief of Cardiopulmonary Transplantation and of the Center for Cardiac Support and director of Surgical Research at the Texas Heart Institute.

With heart failure the leading cause of death in the United States, the research on VADs could save lives and money. More than five million people in the U.S. have been diagnosed with heart failure. The American Heart Association estimates the direct and indirect cost of heart failure in the U.S. for 2008 to be nearly $35 billion.

“The availability of an effective, reliable mechanical replacement for the failing human heart would have an enormous impact on health care,” said Denton Cooley, THI president and surgeon-in-chief.

The grant was awarded under the NIH Bioengineering Research Partnership, a special program to encourage collaborations among medical and engineering experts.