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Project Artificial Heart: ”An absolutely reliable function has to be guaranteed over a long period of time“
Professor Ulrich Steinseifer; © RWTH Aachen
It is the dream of those who are on the waiting list for a donor heart: an artificial heart that can be immediately implanted as needed and thus saves lives. ReinHeart is the name of the artificial heart system that is currently being developed at the Institute for Applied Medical Technology at RWTH Aachen University (AME).
MEDICA.de spoke with Professor Ulrich Steinseifer on how far the project is now and what patients may hope for.
MEDICA.de: Donor hearts, as the name already implies, come from human donors. Professor Steinseifer, you want to develop an artificial heart that is able to replace the function of the human heart. What are the technical characteristics that you are faced with?
Ulrich Steinseifer: You have to pay attention to several things when you develop an artificial heart. For one, an absolutely reliable function has to be guaranteed over a long period of time. Our natural heart beats about 40 million times each year at rest. We build our artificial heart in a way to where it beats for at least five years, that is to say, it has to be able to safely and guaranteed complete about 200 million cycles. Technically speaking, we talk about fatigue strength.
The second requirement is the so-called biocompatibility. The artificial heart in every way has to get along with the body. Above all, this pertains to our blood, because blood has several characteristics – if it stagnates, it agglutinates (clumps) and coagulates (clots) very quickly for example. This causes a thrombus, which could be washed away, and for instance cause a stroke or something similar – this must not happen. However, if you pump the blood too hard so it continuously flows, you destroy the red blood cells. In this case, we talk about hemolysis. The red blood cells are being destroyed and the patient develops anemia, whereby oxygen transport is no longer ensured.
Therefore, it is important that optimum flow velocity is always achieved. Biocompatibility however also includes the surfaces, because blood does not like foreign surfaces. If blood touches a foreign surface, it clots. That is to say, we have to use biocompatible materials or apply them on the surfaces. There are different options. In our case, we use very specific biocompatible polyurethane that is very blood compatible. In conjunction with anticoagulants, which the patients have to take, and blood flow optimization, we are able to prevent blood clotting.
ReinHeart Pumpunit. Reiner Körfer, a supporter of the project, gave his name for the artificial heart; © RWTH Aachen
MEDICA.de: How does the artificial heart react to different body conditions? Are patients for instance allowed to do light exercises?
Steinseifer: That is a difficult question. A healthy heart can run different frequencies. The average citizen has 70 beats per minute at rest –it is more, if we exert ourselves. The average citizen also pumps approximately five liters of blood per minute through his/her body; extreme athletes like cyclists can pump up to 40 liters per minute. With artificial heart patients, we act on the assumption that they will no longer run any marathons. That is why we have designed the heart to where it is able to pump about six to seven liters. Then the heart frequency is of course a little higher.
However, the organic heart knows that it has to achieve more when we run. The artificial heart does not know this – it is oftentimes software-controlled and only knows that it should run at 70 beats per minute. To adapt to this, is actually the most difficult point. We are working on this. We have corresponding test facilities where we can reenact such situations. Corresponding sensors are being integrated that notice that there is a higher demand. We measure the blood pressure for example and if it drops, we know that not enough is being pumped here: the vessels have dilated, because the patient is doing something at the moment. For the pressure to remain stable, the artificial heart has to accelerate. It is very difficult to automatically control this. That is why so far the frequency for artificial hearts is manually adjusted at the push of a button.
MEDICA.de: How do you regulate the power supply for the artificial heart?
Steinseifer: Our artificial heart is powered by an electric motor that is powered with electricity. That is to say, we have to be able to conduct electricity into the body. With other systems, you can oftentimes still do this via normal conductors, which means a passage through the skin however. This in turn means danger of infection. This is why we work on a TET system, which stands for transcutaneous energy transmission. We use two coils through which we inductively transfer energy. One coil is implanted and connected with the artificial heart, while the other is placed onto the skin on the outside and sends energy. However, the coils have to consistently sit on top. The effectiveness of the energy charge depends on how precisely the coils are aligned. Due to the movement of our body, this is sometimes not so easy. Needless to say, we build in a buffer battery for safety, because it would be fatal if the coil slips even briefly. Then the artificial heart would turn off because the battery is missing. That is why the buffer battery can take over the energy supply for the artificial heart for a half or almost an entire hour. The external coil itself is connected to rechargeable batteries that the patient wears in a fanny pack or vest pocket.
Artificial Heart: 1.Pumpunit, 2.Compliance System, 3.Transcutaneous Energy System, 4.Internal Controller & Buffer Battery, 5. External Controller, 6.External power supply; © RWTH Aachen
MEDICA.de: Why can you not charge the artificial heart directly for up to 24 hours?
Steinseifer: This depends on the size of the buffer battery and unfortunately, we are clearly limited due to the size of the human ribcage. We have to find an optimum between that which we still think the body can handle and which technology we can pack into this size. However, it would of course be wonderful if battery technology would develop to a point where it becomes even smaller and more efficient. Maybe in a few years, we can then develop a system that runs all on its own for several hours.
MEDICA.de: What is the status of your project currently?
Steinseifer: We are presently in the developmental stage. If all goes well, the first human implant will occur at the end of 2014, beginning of 2015. So far, we are in the animal experimental stage. We have performed seven acute animal experiments with calves. Acute means that we only run the artificial heart for a few hours in the animal’s body. We try for example to re-enact specific circulation conditions to see how the artificial heart reacts to them. The next step will be chronic experiments. This way we hope to have developed an artificial heart in a few years that can compensate for the lack of natural donor hearts.
The interview was conducted by Simone Ernst and translated by Elena O'Meara.