Cardiovascular disease is the number one cause of death in the world. About 1.2 million Americans suffer from heart attacks every year. Approximately 2,000 Americans get heart transplants each year, but transplant hearts are in short supply, and many thousands of other advanced heart failure patients are left on the waiting list.
The ventricular assist device, or VAD, was designed to serve as a “bridge-to-transplant” device to keep a patient alive until a donor heart is available for transplant. In some cases, it may be intended as a “destination therapy” — long-term support for patients who are ineligible for transplant due to age or other circumstances.
Like many other medical technologies, the evolution of the VAD has benefited from NASA. In the 1990s, a collaboration between renowned heart surgeon Dr. Michael DeBakey and NASA resulted in the design of a better solution than what was already on the market. By applying their experience with simulating fluid flow through rocket engines, NASA engineers worked with doctors to analyze blood flow through the batterypowered heart pump. They suggested design improvements that led to the development of a miniaturized, highly efficient blood pump.
Approximately 3 inches long, 1 inch in diameter, and weighing less than 4 ounces, the pump was designed to be lower-cost, smaller, and less invasive than other commercially available ventricular assist devices. NASA patented the invention and licensed it to MicroMed Technology (Houston, TX) in 1996. MicroMed went on to refine the technology, which is now in its fifth generation: the HeartAssist 5™ VAD. The company recently partnered with Numerex Corp. to make this technology wireless, allowing for continual remote monitoring of data to clinicians, doctors, and technicians. MicroMed also makes the only FDAapproved pediatric VAD in the U.S., and was awarded a grant from NIH to develop a “pulse-less” total artificial heart using two MicroMed VADs — one to circulate blood throughout the body, and the other to circulate blood to and from the lungs.
Cardiovascular technology continues to make progress every day. Doctors in Italy achieved a new milestone in April 2012, when the world's smallest artificial heart was implanted in a 16- month-old boy. The device, a tiny titanium pump that weighed only 11 grams and could handle a blood flow of 1.5 liters a minute, successfully kept the infant alive for 13 days until a donor was found for a transplant.
Just as in the case of the DeBakey pump, collaboration between physicians and engineers in other industries may be key to improving heart pumps of the future. Doctors at the Texas Heart Institute are working with engineers from Cameron Manufacturing and Engineering (Houston, TX) to improve heart pumps and artificial heart technology. The engineers have created a mock prototype of the device (Fig. 1), and are still a long way from trials, but the hope is that the engineers can use their expertise in flow technologies and other applications in the energy field to help the physicians improve heart pumps in new, innovative ways.
This article will highlight a few other ongoing research advancements in the continually changing field of cardiovascular technology.
In yet another example of how cardiovascular technology is reaping the benefits of interdisciplinary collaboration, a heartpowered pacemaker is now being developed by aerospace engineers at the University of Michigan. Pacemakers are minimachines that send electrical signals to the heart to keep it beating in a healthy rhythm. However, their batteries last only five to 10 years, creating the need for inconvenient battery replacement surgeries. Using research that originates from efforts to harvest energy from wing vibrations in light unmanned airplanes, the engineers are now trying to figure out how to harvest energy from the reverberation of heartbeats through the chest, and convert it to electricity to run a pacemaker or an implanted defibrillator.
“The idea is to use ambient vibrations that are typically wasted and convert them to electrical energy,” said Amin Karami, a research fellow in the U-M Department of Aerospace Engineering. “If you put your hand on top of your heart, you can feel these vibrations all over your torso.”
The researchers haven't created a prototype yet, but they have designed and run simulations demonstrating the viability of this concept. A hundredth-of-aninch thin slice of a special piezoelectric ceramic material would essentially catch heartbeat vibrations and briefly expand in response. Piezoelectric materials can convert mechanical stress (which causes them to expand) into an electric voltage. Karami and his colleague Daniel Inman, chair of Aerospace Engineering at U-M, have engineered the ceramic layer to a shape that is optimal for harvesting vibrations across a broad range of frequencies. They also incorporated magnets, whose additional force field can drastically boost the electrical signal that results from the vibrations.
Researchers anticipate that the new device could generate 10 microwatts of power — about eight times the amount of power a pacemaker requires to operate. It also performs at heart rates from 7 to 700 beats per minute — well below and above the normal range.
Wireless VAD Charger
A wireless transcutaneous energy-transfer (TET) unit could help more people benefit from VADs, without fear of the risk of infection from an invasive surgery. A team of seniors at Rice University engineered a TET unit to power a minimally invasive ventricular assist device (VAD). The TET unit is a complementary device that sits a centimeter under the skin and feeds power to the VAD without wires (Fig. 2). Since the portal through the skin to a power supply can normally become infected, the fact that this device is wireless reduces this risk.
The prototype consists of a small coil and a battery that would be inserted one centimeter under the skin at the patient's waist and wired to the VAD. The patient would also wear a beltmounted external battery and coil to generate alternating magnetic fields and induce alternating current in the subcutaneous coil; the coils charge the battery, which can operate the pump for more than three hours. The device is still in the prototype stage, but students are working with Houston-based Procyrion, a developer of a VAD, to prepare the device for large animal testing as part of the path to FDA approval.
“Now that we're able to take the risk (of passing a wire through the skin) out of the equation, we're starting to talk about bringing VADs to people who aren't that sick and can just use a little bit of support,” said Rice alum Michael Cuchiara, director of research and development at Procyrion.
The University of Pittsburgh is developing a cell-free, biodegradable artery graft that could greatly improve the results of coronary artery bypass surgery. In the study, 90 days after surgery, the regenerated artery left no trace of synthetic graft materials in the body.
After examining graft porosity and selecting parameters that allowed immediate cell infiltration, researchers chose a graft material — an elastic polymer called PGS — that is resorbed quickly by the body. They used a procedure developed by another team of Pitt researchers to wrap the vascular graft with a fibrous sheath to trap the cells. They also added a coating called heparin, which would reduce blood clotting and bind many growth factors. The team made grafts as small as 1 mm in diameter and monitored the graft's transformation in vivo for three months. Because the graft was highly porous, cells were able to easily penetrate the graft wall, and mononuclear cells occupied many of the pores within three days.
At 90 days, most inflammatory cells were gone, which correlated with the disappearance of the graft materials. The artery was regenerated in situ and pulsed in sync with the host; the composition and properties of the new arteries are nearly the same as native arteries. The newly developed graft is made in a few days, stores in a dry pouch at ambient temperature, and is readily available off the shelf.
Skin Patches Replace ECGs
People may one day place “electronic skin” patches onto their arms in order to wirelessly diagnose health problems or deliver treatments. This development, reported at the American Chemical Society, indicates that patches have the potential to replace unwieldy monitoring equipment in a doctor's office or hospital room. Moreover, they would offer the benefit of delivering important information about the status of brain, heart, and muscle activity while patients are carrying out everyday activities, rather than just in a medical setting.
The electronic skin patches, developed at the University of Illinois at Urbana- Champaign, are about the thickness of a human hair, but can pack full-scale electronic circuits needed to monitor health status; the data could one day be transmitted to patients' cell phones or doctors' offices. The patches are transferred to the skin just like a temporary tattoo, with water and a backing that peels off. A spray-on was developed to protect the circuit from water and normal wear and tear, to keep it on the skin for up to a week. John Rogers, Ph.D., one of the developers of the device, co-founded a company called mc10 that plans to put the patches on medical instruments that go inside the body, such as catheters. The electronic skin patch would be placed on the outside surface of the catheter. When the catheter expands in the heart, the patch expands with it and touches the inside of the heart, taking measurements used to guide surgery.