Oct. 27, 2008 -- No pulse? No problem, say Texas scientists who are developing an artificial heart that would leave patients pulse-less.
Constant flow pumps, as they are called, are based on ancient technology. The ancient Greek mathematician, Archimedes, first used an elongated screw encased in a tube to raise water from one level to another.
Since 2003 over 1,600 patients have had a screw-shaped pump implanted that operates continuously to help their ventricles pump blood to the rest of their body (formally called a ventricular assist device). They still have a natural heart beat, but put two fingers to their neck or wrist and you won't detect a pulse.
Now doctors at the Texas Heart Institute are teaming up with scientists from the University of Houston, in a effort to completely replace the beating human heart with a humming constant flow pump. MicroMed Cardiovascular, Inc. produces the device. It may not perfectly match a natural heart's activity, but as E.O. Frazier with the Texas Heart Institute, points out, it would perform the same function.
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"For years mankind tried to imitate the way birds fly," said Frazier, a doctor at the Texas Heart Institute who developed the original constant flow ventricular assist device. "We still can't fly like the birds, but we get around pretty well."
Total artificial replacement hearts, such as the pulsed Jarvik-7 or AbioCor artificial hearts, already exist and have been implanted into patients. The mechanical hearts pump blood, similar to natural hearts, but often fail after one to two years because of mechanical failures related to the pumping actions.
Because of this, the artificial hearts are meant to buy patients time until a natural heart becomes available for transplant.
Today's artificial hearts are also large; women, children and many men aren't eligible for the hearts.
"I'm about 6'1'' and about 200 pounds," said Steve Parnis, another Texas Heart Institute doctor. "And I don't think one would fit into me."
A constant flow pump is much smaller, about the size of a C cell battery. The small size of the pumps means they could be placed in a much wider variety of people, even some children. A constant flow pump should also be more resistant to mechanical failures, meaning a pump could last a couple of decades, instead of a couple years.
At first scientists will use two pumps working together to produce blood to the rest of the body. Eventually one screw-shaped pump could replace both valves, says Frazier.
But before any constant flow pump replaces the human heart, years of studies are required to test its efficacy, says Timothy Baldwin of the National Institutes of Health.
"I see the potential for constant flow device as a total artificial heart replacement," said Baldwin. "The research going on right now is just the first step...but 50,000 to 100,000 people could benefit from good circulatory support if we had a device with no safety concerns."
Permanently eliminating one of the most fundamental signs of being alive is a big deal. Scientists aren't sure what the long-term effects of constant blood pressure might be. Both Baldwin and Frazier speculate that the heart's natural pulsing action might help inhibit arterial plaques or blood clots from forming, but aren't sure.
Patients who have had ventricular assist devices for years have done well, one reason why doctors are confident that completely replacing the entire heart will work well.
Removing a person's pulse is a serious matter, but some people are blase enough to find humor in the situation. "Some teens play tricks on their friends with them," said Frazier, explaining a common gag among those with ventricular assist devices is to have a friend try and find their pulse.
A pulse-less patient will also require some changes to medicine, says Matthew Franchek, a biomechanical engineer at the University of Houston who is helping to design the device as a complete heart replacement.
"We used to say that the patient is alive and has a pulse," said Franchek, "Now we'll have to say that they are alive and have flow."
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