When the heart weakens and medication no longer helps, many patients require a donor heart. To reduce lengthy waiting times, artificial heart pumps are used, which are powered via an external cable – which is a gateway for infection. Researchers at the University of Stuttgart's Institute of Electrical Energy Conversion (IEW) want to use inductive energy transmission to improve patient safety and quality of life.
When Professor Nejila Parspour earned her doctorate at the Technical University of Berlin over 20 years ago, artificial heart pumps were usually non-implantable machines that did not leave the patients much freedom of movement. Back then, in collaboration with the German Heart Center, the expert for energy conversion developed a drive system for a highly efficient implantable cardiac support system about the size of a fist, which was used successfully. Such systems are significantly smaller, more efficient and easier to use today. However, the problem of the cable, which connects the implanted pump with the external control system and batteries via an artificial exit point in the abdominal wall, continued to play on Parspours’ mind.“This exit point is a gateway for life-threatening infections and limits the mobility of the sufferers”, explains the current Head of the IEW at the University of Stuttgart. According to figures published by the German Society for Thoracic and Cardiovascular Surgery (DGTHG), some 1000 cardiac support systems were implanted in Germany in 2016 – almost three times as many as in 2005. In most cases, these were left ventricular support systems, i.e., pumps connected to the left ventricle and the aorta and pump blood around the body with a continuous flow and ensure that it gets sufficient oxygen.
Safety and quality of life
Patients always carry the external electronics around with them. Following their release from hospital, they have to keep the exit point scrupulously clean to prevent germs reaching the heart, which makes routine daily tasks, such as showering, problematic. “If we manage to transmit the energy wirelessly”, IEW scientist Alexander Enssle explains, “we’ll increase patient safety and make their lives easier”. With his research, Parspour's doctoral student is taking technologies and developments from the field of inductive energy transmission that have so far gone into wireless charging systems for electric vehicles among other things, and transferring them to the life sciences. Cell phones, laptops, cars and now hearts too: “we're conducting fundamental research for applications that will enable improved mobility”, Parspour explains. The physical phenomenon behind has been known for a long time. An electric current passing through a coil generates a magnetic field, which induces a voltage in a second coil. If one connects an electrical appliance to the second coil, current starts to flow. “Transferring this to a medical device inside the human body will take several years of research effort”, Enssle emphasizes.
“This exit point is a gateway for life-threatening infections and limits the mobility of the sufferers”, explains the current Head of the IEW at the University of Stuttgart. According to figures published by the German Society for Thoracic and Cardiovascular Surgery (DGTHG), some 1000 cardiac support systems were implanted in Germany in 2016 – almost three times as many as in 2005. In most cases, these were left ventricular support systems, i.e., pumps connected to the left ventricle and the aorta and pump blood around the body with a continuous flow and ensure that it gets sufficient oxygen.
A complex contact free system
The prototype, which the scientist developed in collaboration with cardiac surgery experts from the Hannover Medical School, is based on flat coils with a diameter of about eight centimeters. The first is outside the patient's body, and can be sewn into an item of clothing – for example in the chest region – and is connected to the external electronics. The second coil is implanted under the skin either in the stomach or chest region along with the control electronics, batteries and connection to the mechanical pump. The magnetic field generated by Coil 1 outside the body can transmit energy to Coil 2 without breaking the skin.
However, what appears to be simple at first sight still requires some complex fine tuning, to which end Enssle matches all implanted electronic elements to ensure that they function in miniaturized form, safely and as efficiently as possible. To achieve this, he uses magnet field calculations to design both coils such that he can optimize the magnetic coupling between the two but still leave a certain tolerance with respect to their positioning inside and outside of the body. Because heat is given off wherever energy is converted, the transmission system is also designed in a way that ensures that the thermal losses primarily take place outside of the body.
The patients can remove the external energy supply thus regaining their freedom of movement – currently for a maximum of one hour – and a bit more independence. In about three years the system, which has already undergone successful laboratory testing, and which should be useable with every type of cardiac support system, should enter the preclinical trial phase.