Track 11. Artificial Organs

7824 We, 14:45-15:00 (P34) Flow visualisation studies with different dialysis catheters in a model o f the vena cava superior and the right atrium in variant pos i t ions M. Stock 1 , D. Liepsch 1, L. Topakli Levent 2, L. Coli 3. 1University of Appiled Sciences, Munich, Germany, 2Technical University Munich, Germany, 3 poilcilnico S.Orsola Malpighi, Bologna, Italy

Patients with chronic kidney disease (CKD) have often only the final ability to a catheter placed in the vena cava superior for blood exchange. An important factor for the efficiency of blood exchange and the thromboembolism is the shape and the position of the catheter. We investigated the flow field in a silicone rubber model of the vena cava superior and the right atrium. First of all we visualized the flow field under normal conditions. In a second step we appliquated different types of catheters with an averaged blood flow in the cannula of the catheter of 300 ml/min and a position of the tip direct in the right atrium. In a third step we placed the catheter in the vena cava superior and under the same circulatory conditions we visualized the flow field. The visualisation was made by photoelasticity and a birifringent solution (vanadium-pentoxide) was used. When diluted, this material behaves like a Newtonian fluid. This method gives a complete picture of the entire flow field. Zones of flow seperation and disturbed flow can be seen and the location and size of disturbed areas observed. Unseparated flow regions downstream from disturbed zones can properly visualized and the method can be used for pulsatile flow as well as steady flow. The study demonstrates the flow behavior in different regions where the arterial and venous blood of the catheter recirculates and where hemodynamic effects have been suggested to participate in artherogenesis. The positioning of the tip of the dialysis catheter is an important factor in dial- ysis for the percentage of recirculation with more accurate risk of thrombosis. Primary studies will be presented.

7825 We, 15:00-15:15 (P34) Dialysis equipment: safety and usability - Actual situation and progress in the relevant standards C. Mueller. Fresenius Medical Care, Schweinfurt, Germany

The use of dialysis equipment has changed considerably with regard to innovative functional features in recent years. The aim of these changes has been improving treatment quality and patient survival. But how is the situation with regard to safety when applying these features in the clinical setting? On basis of the relevant standards 60601-1 (basic safety), 60601-1-6 (usability) and 60601-2-16/39 (dialysis equipment) the state of the art in safety issues and usability engineering will be discussed. In this context the definitions of 'single fault condition', 'user error' and 'predictable misuse' will be explained. Safety and usability issues in daily life are features which determine possible safety and usability issues in the field of hemodialysis and treatment of uremic patients. Examples of device recalls, where usability issues have been the basis of complaints, will be described. Actual technical solutions on how to avoid user errors and how to increase patient safety will complement the talk.

11.2. Cardiac Assist Devices

11.2.1. Devices

6564 Tu, 14:00-14:15 (P22) Risk of cardiac assist devices and their peripherals H. Schima 1,2,3, P. Zrunek 2, Z. Deckert 2, L. Huber 2,3, M. Vollkron 3, W. R6thy 2, D. Zimpfer 2, G. Wieselthaler 2,3 . 1 Center of Biomed Engineering and Physics, 2Dept. of Cardiothoracic Surgery and 3 LBI for Cardiosurg. Research, Med. Univ. Vienna, Austria

Background: Ventricular assist devices have become an increasingly used therapy for end stage heart failure until transplantation and recently also as destination therapy. Especially in patients without ventricular recovery their uninterrupted reliable function is crucial for patient survival and quality of life. Whereas the pump and basic controller functions have been studied in extensive risk analysis, the risks correlated to peripherals are rarely discussed. Therefore the experiences with external system components in our center was retrospectively investigated. Methods: The records of 110 patients with 5 different ventricular assist systems were retrospectively analyzed in respect to complications correlated with peripheral equipment. Results: Connectors, batteries, handling problems due to limited physical ability or confusion, and cable entangling were the most frequently observed incidences, which exceeded by far the number of device related problems. Further, a staged alarm system with clear, unambiguous messages appeared to be difficult to obtain. Training with real pumps on mock circulations improved the reaction of patients and caregivers.

11.2. Cardiac Assist Devices - Devices $249

Conclusions: Beside the safety of the pump itself, the safety of peripherals, their handling and acceptance is crucial for the success of VAD application. For a mature therapeutic approach, a perfect design of these components is inevitable.

5691 Tu, 14:15-14:30 (P22) VERSUS (VEntricular Recovery SUpport System) status update August 2006 P.B. Kwant 1 , T. Finocchiaro 1 , U. Steinseifer 1 , M. Verkroost 2, R. Brouwer 2, G. Rakhorst 3, T. Schmitz-Rode 1 . 1Helmholtz Institute Aachen, RWTH, Aachen, Germany, 2University Medical Centre Nijmegen, The Netherlands, 3University of Groningen, The Netherlands

Chronic heart disease is the leading cause of death in industrialised countries. Heart transplantation and cardiac support are the only long-term therapies for patients with chronic heart failure. Cardiac support can be used as a bridge to transplant, as a bridge to recovery of the natural heart or as destination therapy. The only two FDA approved implantable pulsatile Ventricular Assist Devices (VAD) are Novacor and Heartmate. Both are large systems and implantation in the abdomen is required. Development of most current ventricular assist devices has shifted towards rotary blood pumps, being smaller and less complex. Still, a new and smaller generation of displacement pumps, such as Novacor II, DLR-Heart and VERSUS is being developed. One of their primary design goals is to be implanted into the hemi thorax. The VERSUS consists of an extremely flat energy converter encapsulated into a titanium housing and a PUR pump chamber. Its main mechanism is the KafSr gear system, which converts the rotational movement of the brushless DC Motor into a translational movement of the pusher plate. The VERSUS is canulated to the left atrium and the aorta descendens. VERSUS delivers an output of 1.5 to 4.01it/min at pump rates between 60 and 150 BPM. Power consumption averages 3.3W. From 2002 to 2005, twelve chronic animal experiments were performed with a maximum duration of over one month. Blood values of the calf normalized one to three days after the operation and then remained within physiological ranges. At the end of the experiment the gear mechanism still functioned perfectly and the pump was completely covered by newly grown native tissue. Currently the VERSUS system is subjected to wear tests in newly design mock loops. Also further animal experiments (n =6, duration: 6 weeks) are being performed in order to finalize the proof of concept.

7184 Tu, 14:30-14:45 (P22) The PediPump®: a versatile, implantable pediatric ventricular assist device B.W. Duncan 1,2, M.W. Kopcak 2, D.T. Dudzinski 2, A.M. Noecker 2, K. Fukamachi 2, W.A. Smith 2. 1Pediatric and Congenital Heart Surgery, Children's Hospital, Cleveland Clinic, USA, 2The Department of Biomedical Engineering, The Lemer Research Institute, Cleveland Clinic, USA

The PediPump is a new ventricular assist device designed specifically for pediatric applications. The design is based on a rotary dynamic pump; an important aspect of the design is the absence of a seal with suspension of the rotor on magnetic bearings. The pump rotating assembly consists of an impeller in the front, front and rear radial magnetic bearings and a motor magnet in its center. The pump measures approximately 7mm 75mm with a priming volume of 0.6ml which imparts less than 10% of the physical displacement of currently available axial flow pumps while retaining good flow capacity. The device provides pressure and flows capable of supporting adults, far exceeding the requirements for support of children in the 2 to 25 kg weight range. This basic pump design may be suitable for right ventricular, left ventricular or biventricular support; the pump may also be used in acute or chronic clinical settings. The current development program for the PediPump includes three specific aims: 1. Determination of the basic engineering requirements for hardware and

control logic including design analysis for system sizing, evaluation of control concepts and bench testing of prototypes.

2. Performance of pre-clinical anatomic fitting studies using CT-based 3D modeling.

3. Evaluation with animal studies to provide characterization and reliability testing of the device.

At the completion of studies in this proposal the following will have been achieved: • Development and testing of a small pediatric VAD including the acquisition

of initial multi-year durability data. • Determination of deployment methods for the wide range of sizes and

anatomic variation encountered in children with heart disease using 3D modeling techniques based on CT imaging.

$250 Journal o f Biomechanics 2006, Vol. 39 (Suppl 1)

• Documentation of the responsiveness and reliability of the pump in the implant environment and determination of the host response to the presence of the pump from animal implantations.

7021 Tu, 14:45-15:00 (P22) Initial in vitro and in vitro performance results for the pediatric cardiopulmonary assist system (pCAS)

G. Pantalos 1 , C. Ionan 1 , J. Colyer 1 , S. Koenig 1 , M. Mitchell 1 , E. Austin III 1 , J. Speakman 2, C. Lucci 2, G. Johnson 2, M. Gartner 2. 1University of Louisville, Louisville, Kentucky, USA, 2Ension Inc., Pittsburgh, Pennsylvania, USA

The ability of the 4", 3", and 2" versions of the pCAS pumps to restore acceptable hemodynamics while providing left ventricular assistance (LVA), cardiopulmonary support (CPS), and veno-venous ECMO (VVE) was eval- uated using an instrumented infant mock circulation that creates clincally relevant normal ventricular function (NVF) and left or right ventricular failure (LVF, RVF). The left atrium was cannulated with a 20 Fr. Edwards Lifesciences pediatric cannula (LVA), and the right atrium with an 8 Fr. Medtronic Biomedicus uptake cannula (CPS) and a 14 Fr. OriGen double lumen cannula (WE). Aortic return was via an 18 Fr. cannula. Data were collected while providing (1) LVA during LVF, (2) CPS during RVF and NVF, and (3) VVE during NVF with the pCAS operating in continuous and pulsatile modes using water (1 cP viscosity) and 40% glycerin/water (3.5 cp) as test fluids. Equivalent pCAS performance resulted using 40% glycerin/water. Initial 3" pCAS performance for LVA had a similar performance trajectory as the 4" pCAS, but required an additional 250 RPM to achieve the same flow rate as the 4" pCAS. In vivo performance of the 4" and 3" pCAS pumps was evaluated in a infant animal model (10Kg p ig le t )o f ischemic left ventricular dysfunction (LVD). Following the creation of a stable model of LVD, LVA (left atrium, 20 Fr. Edwards Lifesciences, to aorta, 16 Fr. Edwards Lifesciences) was evaluated with the pCAS pumps operating in continuous flow mode and in pulsatile flow mode at rates of 100 and 140 beats/minute. Both the 4" and 3" pCAS pumps were able to deliver blood in excess of 1 liter/minute flow (100/ml/min/Kg) while rectifying the abnormal hemodynamics associated with LVD. These data demonstrate early acceptable pumping performance of the pCAS for infant circulatory support. NHLBI Contract No. HHSN268200449189C.

7609 Tu, 15:00-15:15 (P22) Optimization of ventricle-shaped chambers for the implantable DLR assist device T. Schmid 1 , W. Schiller 3, K. Spiegel 4, M. Stock 1 , D. Liepsch 2, B. Laschka 2, G. Hirzinger 1 , H. Oertel 4, A. Welz 3. 1Institute ef Robotic Systems, DLR, Wessling, Germany, 2 Chair of Fluid Mechanics, Technical University Munich, Germany, 3Heart Surgery Clinic, University of Bonn, Germany, 4Institute of Fluid Mechanics, University of Karlsruhe, Germany

In order to minimize the risk of thrombo-embolism, ventricle-shaped pump chambers are to be developed. The chambers should provide a velocity distribution similar to the human left ventricle and improve the total efficiency of the assist device. To verify the quality of the chambers, flow visualization with a birefringent fluid and flow measurements with Particle Image Velocimetry and a bloodlike non- Newtonian model fluid were carried out. The chambers were compressed with a rigid pusher plate and, in a second experiment, with a hydraulic fluid. 3D- shear stress, vorticity and 3D-pathlines were calculated (Resolution: 1.3 mm). Numerical flow simulation with moving boundaries was used to modify the chamber's geometry. Acute animal studies (pigs, n=3) were carried out to verify the results. A nearly physiological flow field could be generated in the new chambers. During the filling phase, two recirculation zones, similar to those found in the human left ventricle, were observed. Due to the new chambers, the pump flow could be increased from 6.6 I/min to 8.2 I/min, the total efficiency of the VAD from 38% to 45%. Increased shear rates up to 1500 1/s were observed downstream from the inflow at the front of the pusher plate during the filling phase. Particles were washed out within two cycles, at the most. Flow disturbances created by the rigid pusher plate are significant. They lead to less intensive vortex formation and low shear rates at the bottom of the chamber. Due to modifications of the inflow angle, of the chambers' geometry in the vicinity of the valves and the chambers' total volume, the dissipation could be reduced significantly. On the basis of these experiments, the characteristic number 'degree of circulation' was defined to characterize the efficiency of artificial pump chambers.

Oral Presentations

7661 Tu, 15:15-15:30 (P22) PID vs fuzzy logic control for the new adaptive transcutaneous energy transfer system (TET) for implantable devices B. Vodermayer 1 , R. Gruber 1, T. Schmid 1 , W. Schiller 2, G. Hirzinger 1 , D. Liepsch 3, A. Welz 2. 1Institute of Robotic Systems, German Aerospace Center (DLR), Munich, Germany, 2Heart Surgery Clinic, University of Bonn, Germany, 3Institute for Biotechnic, Munich, Germany

Aim: The wireless transfer of energy into the body is a major requirement for future implants. The flexible adaptation of transmitted energy to the actual demand of the implant will reduce exposure to electromagnetic radiation and enhance the longevity of the electronic components. Methods: An inductive TET with two coils, an external control unit, external accumulator and an implantable electronic (IE) with back-packed accumula- tors was developed. The implantable, coreless coil is a flexible ring made of braided copper (diameter 150mm, thickness 8mm, weight 70g). The integrated electronics' microcontrollers in TET and VAD handle infrared (Ir) data-communication (115 kBit/s), charging of the onboard accumulators, data- acquisition and the adaptation of the transferred energy. For IR-transmission, a robust protocol was developed. The inverter frequency (121-130kHz) is adjusted automatically for optimization purposes. Energy-control was realized with a PID controller and with a fuzzy logic controller working on multi variable control (MVC). Results: The system was able to transmit up to approx. 50W at 50mm distance between the coils. The PID-control algorithm for power adaptation was able to balance all major and minor electrical disturbances during in vivo tests. The maximum efficiency of the system was approx. 78% at 5 mm distance between the coils and 61% at 10mm. A horizontal and/or vertical displacement of the coils of 20 mm led to a decrease in efficiency of approx. 5%. Higher distances (>25 mm) reduced the efficiency to approx. 50% and led to increased temperature of the external converter. The newly introduced fuzzy logic controller (FLC) showed to be a reliable substitute for the PID by optimizing energy-transfer. Conclusion: The TET showed reliable transmission even at high horizontal and vertical displacements. Transmitted energy was automatically adapted to the demand, high power requirements were effectively compensated. Both controllers showed good results while the FLC could optimize control efficiency. Animal studies showed no impact to the tissue near the coils.

11.2.2. Modelling

7266 Th, 08:15-08:30 (P38) Current and emerging blood pumping systems: opportunities for modeling techniques G. Pantalos. Cardiovascular Innovation Institute, University of Louisville, Louisville, Kentucky, USA

Ventricular assist devices (VAD) and total artificial hearts (TAH) have been in clinical use for nealy four decades. During this period of time, success in post-cardiotomy cardiogenic shock, bridge-to-transplant, and destination therapy applications of these devices have been demonstrated as feasible options for heart failure patients with good outcomes. As confidence in the performance of these devices increases, so does the desire to enhance device features and extend the duration of use. The development of VADs for infants and children adds additional design and performance challenges. Although standard testing techniques, such as mock circulation experiments and animal implantation experiments, are useful evaluation tools for developing devices, there are some situations that these techniques cannot address or address in a complete and timely manner. Modeling techniques can provide a useful adjunct if not only approach to assess certain aspects of blood pump function to guide design development. Computational fluid dynamics (CFD) can be very useful to assess the quality of the flow field through a blood pump especially when the geometry may not lend itself to flow field visualization experiments. Mass transport considerations can be incorporated to a CFD analysis for pumping systems that are also involved with gas exchange. The use of 3-dimensional image construction techniques from serial CT or MRI scans are useful in guiding the optimization of pump placement in the thorax or abdomen and cannulae or connection design to the native anatomy. Reliability modeling techniques based on established component performance and physiologic loading can be a valuable predictive tool prior to committing to real-time reliability testing of a blood pump system. The current clinical experience with blood pump systems and the use of various modeling techniques will be reviewed.

4455 Th, 08:30-08:45 (P38) Frequently asked questions on evaluation of blood trauma M.V. Kameneva. University of Pittsburgh, Pittsburgh, USA

Survival and quality of life of patients supported with mechanical circulatory assist devices depend on reliability and biocompatibility of these devices.