Heart of the Matter
Heart failure is the leading cause of death in the United States, and the American Heart Association estimates the direct and indirect cost of heart failure in the United States for 2008 at nearly $35 billion. It’s a major predicament whose only solution seems to be the creation of a simple and reliable artificial heart.
In fact, Denton Cooley, president and surgeon-in-chief of the Texas Heart Institute (THI), said, “The availability of an effective, reliable mechanical replacement for the failing human heart would have an enormous impact on health care.” He should know. In 1969, Cooley became the first surgeon to implant a complete artificial heart in a human.
Since then, several implantable artificial hearts have been developed, all of which were designed to mimic the pulse of the natural heart. As a consequence, they are somewhat bulky and mechanically complex, which leads to issues of reliability. To solve the problem, the National Institutes of Health has funded a project to design smaller and more reliable heart pumps under the Bioengineering Research Partnership, a special program to encourage collaborations among medical and engineering experts. Led by THI, the project includes engineers from Rice University, St. Luke’s Episcopal Hospital, MicroMed Cardiovascular Inc. and the University of Houston.
The researchers are developing two heart-assist pumps that individually perform the function of the left and right ventricles.
Rather than trying to mimic the pulses of the natural heart, the devices pump blood continuously. The one 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, rhythmic predecessors. Their small size will ease implantation and use in children as well as adults.
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.
“Because these pumps will be implanted for the long term, we have to make sure that blood damage is minimal,” said Matteo Pasquali, Rice associate professor in chemical and biomolecular engineering and in chemistry.
Pasquali and his colleagues 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 leads 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.
Researchers at the University of Houston are investigating the control mechanism that will mimic the self-regulating function of the heart in an effort to ensure that the left and right ventricles stay in sync with each other and to make the pumps respond to the body’s changing needs for blood, such as during exercise.
“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.”
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 ventricular assist device (VAD) that is being used for this study. The pump, which already is used in human patients in Europe, is named for the late heart surgeon Michael DeBakey, who pioneered the development of heart pumps. In the 1960s, he collaborated with chemical engineering professor Bill Akers, who led Rice’s Biomedical Engineering Laboratory, to produce the first successful left ventricular heart bypass device — a precursor to the VADs used as the base design in the current research project.Learn more:
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