Stephan Weber

Lerner Research Institute, Cleveland, Ohio, United States

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Publications (21)39.24 Total impact

  • Fernando Casas · Stephan Weber · Ryan Klatte · Vikash Goel · William A Smith ·
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    ABSTRACT: MagScrew total artificial heart (TAH) external battery pack (EBP) cycle bench testing continued over a period of 18 months using two fresh Wilson Greatbatch lithium ion EBPs during continuous charge and discharge cycles under a simulated TAH system current requirement. The same electronic load developed for our initial testing was used to simulate the MagScrew current waveforms typically observed during nominal operation. The current load profiles for this test were modified from the ones previously described and applied to the EBP under test during a voltage-defined discharge cycle. The test ended when EBP#2 reached end of life at 1450 cycles. At that point, EBP#1 remained healthy with a capacity of 175 min until full discharge. Performance of EBP#2 was still within expected ranges. Performance of EBP#1 exceeded expectations. These differences are probably caused by slight manufacturing changes. More tests will provide additional data to define a statistical distribution to better characterize EBP performance. In conclusion, endurance performance of the EBP remained satisfactory.
    Artificial Organs 02/2011; 35(2):188-91. DOI:10.1111/j.1525-1594.2010.01057.x · 2.05 Impact Factor
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    ABSTRACT: The need for pulsatility in the circulation during long-term mechanical support has been a subject of debate. We compared histologic changes in calf renal arteries subjected to various degrees of pulsatile circulation in vivo. We addressed the hypothesis that the local renin-angiotensin system may be implicated in these histologic changes. Sixteen calves were implanted with devices giving differing degrees of pulsatile circulation: 6 had a continuous flow left ventricular assist device (LVAD); 6 had a continuous flow right ventricular assist device (RVAD); and 4 had a pulsatile total artificial heart (TAH). Six other calves were histologic and immunohistochemical controls. In the LVAD group, the pulsatility index was significantly lower (0.28 +/- 0.07 LVAD vs 0.56 +/- 0.08 RVAD, vs 0.53 +/- 0.10 TAH; P < 0.01), and we observed severe periarteritis in all cases in the LVAD group. The number of angiotensin II type 1 receptor-positive cells and angiotensin converting enzyme-positive cells in periarterial areas was significantly higher in the LVAD group (angiotensin II type 1 receptor: 350 +/- 139 LVAD vs 8 +/- 6 RVAD, vs 3 +/- 2 TAH, vs 3 +/- 2 control; P < .001; angiotensin-converting enzyme: 325 +/- 59 LVAD vs 6 +/- 4 RVAD, vs 6 +/- 5 TAH, vs 3 +/- 1 control; P < .001). The reduced pulsatility produced by a continuous flow LVAD implantation induced severe periarteritis in the kidneys. The local renin-angiotensin system was up-regulated in the inflammatory cells only in the continuous flow LVAD group.
    The Journal of thoracic and cardiovascular surgery 07/2008; 136(1):150-8. DOI:10.1016/j.jtcvs.2007.12.023 · 4.17 Impact Factor
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    ABSTRACT: Incompetent inflow valves have been reported with clinical pulsatile left ventricular assist devices that use bioprosthetic valves. Suspected as the cause of premature valve failure within these devices, absolute pressures and instantaneous pressure changes were evaluated in the MagScrew total artificial heart (TAH). The MagScrew TAH is a passively filling pulsatile pump which uses a reciprocating magnetic actuating mechanism under various control modes to propel blood into circulation. Both right and left ejection speeds were modulated and optimized at the onset of hydraulic eject. These various speed profiles were evaluated in vitro at 220 beats per minute (bpm), 100% pump fill, mean aortic pressure of 100 mm Hg and mean pulmonary artery pressure of 20 mm Hg. The pressure inside the left and right pump chambers was measured with Millar Mikro-Tip catheter and captured using Power Lab at a rate of 40 kHz. The pump chamber peak pressure, operating with unmodified eject speeds, measured on average 183 mm Hg for the left and 133 mm Hg for the right. Eject speed profiling for both pumps reduced the peak pressure by 10% and 28% for the left and right pump, respectively. Future studies will assess software controlled optimization of the eject speed profiles under any operating condition and how effective it is in vivo.
    ASAIO journal (American Society for Artificial Internal Organs: 1992) 01/2008; 54(1):58-63. DOI:10.1097/MAT.0b013e31815c8964 · 1.52 Impact Factor
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    ABSTRACT: The fitting of implantable ventricular assist devices (VADs) is a particular challenge for pediatric patients and patients with small body surface area. The purpose of this study was to determine optimal placement of the PediPump, a pediatric VAD currently under development at the Cleveland Clinic, using virtual three-dimensional (3D) on-screen models. Digital models were created from computed tomographic datasets of pediatric hearts using commercially available 3D image processing software. Pixels representing the myocardium, great vessels, sternum, and rib cage were selected and rendered as on-screen models (n = 13) from pediatric patients with or without congenital heart disease (median age 42 months; range 2 days to 13 years 11 months). Using 3D model manipulation software, virtual models of the PediPump (70 x 10 mm) were combined on-screen with the anatomic models. A variety of virtual fitting options were created, which allowed easy detection of device interference with surrounding tissues. Generation of 3D on-screen models of cardiac structures in relation to PediPump placement has provided useful preliminary fitting information, which is being used to guide further development of this device.
    ASAIO journal (American Society for Artificial Internal Organs: 1992) 01/2008; 54(1):133-7. DOI:10.1097/MAT.0b013e31815b4495 · 1.52 Impact Factor
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    ABSTRACT: The PediPump is a small ventricular assist device (VAD) with a hydraulic output range designed to support children from newborns to adolescents. The present report describes our initial evaluation of the PediPump as a left VAD in an acute sheep model. The PediPump was implanted in two sheep (50.8 and 62.7 kg). Pump speed was adjusted to achieve a flow of 2 L/min with the naturally occurring preload and afterload conditions to evaluate pump performance under a steady hemodynamic state for 4 hours. Upon completion, pump performance was evaluated under various blood pressure and heart rate conditions. During steady-state evaluations, the ascending aortic flow and pump speed varied slightly depending on systemic arterial pressure variations. During the hemodynamic manipulation studies, flows ranged between 0.5 and 3.2 L/min with pump speeds of 5,200-16,200 rpm and motor current of 0.06-0.75 A. The PediPump demonstrated good initial hemodynamic performance for use as an implantable left VAD. However, some depositions were detected at the time of explanation, mainly at the rear of the pump. We are continuing with further acute studies to evaluate pump performance in anticipation of beginning chronic studies to evaluate long-term biocompatibility.
    ASAIO journal (American Society for Artificial Internal Organs: 1992) 11/2007; 53(6):766-70. DOI:10.1097/MAT.0b013e3181569c1a · 1.52 Impact Factor
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    ABSTRACT: The PediPump is a passive magnetic bearing, mixed flow, rotary ventricular assist device designed to provide support for the entire range of patient sizes encountered in pediatrics. Blood enters axially at the inlet and is accelerated and turned in the impeller to exit the pump at an intermediate angle. The size of the PediPump facilitates standard cannulation strategies with substantially downsized components. The program pursues three specific objectives: 1) System engineering: Progress within the last year has focused on the assembly and testing of PediPump prototypes. Initial in vitro hydraulic performance and hemolysis testing were judged satisfactory. 2) Anatomic fitting studies: As part of the PediPump program, three-dimensional modeling techniques based on routine, clinically obtained computerized tomography (CT) scans have been developed. During 2006, the same techniques developed for clinical scans were applied to CT scans obtained from sheep to guide the presurgical planning. 3) Animal studies: Animal implantation of PediPump prototypes commenced in July 2006. A total of four 6 hour acute studies were performed throughout the remainder of the year. In vivo performance was satisfactory and compared well with the in vitro results. Hemolysis levels were low.
    ASAIO journal (American Society for Artificial Internal Organs: 1992) 11/2007; 53(6):730-3. DOI:10.1097/MAT.0b013e318159822c · 1.52 Impact Factor
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    ABSTRACT: To evaluate the effects of downsizing of the total artificial heart (TAH), we compared the anaerobic threshold (AT) values in calves with two different types of TAH (Cleveland Clinic-Nimbus TAH and the downsized MagScrew TAH). Exercise studies were performed using a treadmill in 12 calves. During the exercise, parameters to obtain the AT were measured. To evaluate the determinants of the AT, a linear regression analysis was performed between AT and potential variables. AT values from 29 studies revealed no significant differences between the two different TAHs, with no significant differences in hemodynamic or oxygen metabolic parameters. AT values correlated well with pump flow/body weight (Q) multiplied by the hemoglobin level, regardless of the TAH used. In conclusion, downsizing of the original TAH design did not reduce AT without any significant differences in hemodynamic or oxygen metabolic parameters during exercise in calves.
    Artificial Organs 10/2007; 31(9):667-76. DOI:10.1111/j.1525-1594.2007.00445.x · 2.05 Impact Factor
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    ABSTRACT: MagScrew total artificial heart (TAH) external battery pack (EBP) cycle bench testing was conducted on two Wilson Greatbatch (Clarence, NY, USA) lithium ion EBPs over a period of 22 months during continuous charge and discharge cycles under a simulated TAH system current requirement. A custom electronic load was developed to simulate the MagScrew current waveforms typically observed during nominal operation. These current load profiles were applied to the EBP under test during a voltage-defined discharge cycle. EBP endurance indicated a 240-min discharge cycle on a new battery diminishing linearly to 175 min after 800 cycles. A second linear trend started at this knee with 150 min of discharge time at 850 cycles until 10 min at 1600 cycles. Even at 1300 cycles, the EBP could still provide enough power for 60 min of nominal operation. In conclusion, the endurance performance of this EBP was satisfactory while exhibiting a predictable wear-out trend.
    Artificial Organs 10/2007; 31(9):698-702. DOI:10.1111/j.1525-1594.2007.00444.x · 2.05 Impact Factor
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    ABSTRACT: The MagScrew total artificial heart (TAH) is under development. Despite its anticipated durability and reliability, the possibility of a bioprosthetic valve malfunction exists. As a result, the potential for valve replacement surgery, instead of device replacement, would be desirable after a TAH implant. In two of our 90-day animal experiments, we successfully replaced the left-side valves through a left thoracotomy opposite to the right-sided incision site for the initial TAH implant. The results of these cases suggest that the left-side valves could also be replaced through a left thoracotomy approach in humans. To confirm the ability to access the left-side valves in humans, four human cadaver studies were performed with the use of a mock pump designed for human application. This report describes the operative techniques for left-side valve replacement in animals and discusses the advantages of a left thoracotomy in clinical situations, based on results from the human cadaver studies.
    ASAIO Journal 07/2006; 52(4):368-72. DOI:10.1097/01.mat.0000227731.46835.1e · 1.52 Impact Factor
  • Soren Schenk · Stephan Weber · William A Smith · Kiyotaka Fukamachi ·

    The Annals of thoracic surgery 07/2006; 81(6):2338-9. DOI:10.1016/j.athoracsur.2005.10.023 · 3.85 Impact Factor

  • ASAIO Journal 03/2006; 52(2). DOI:10.1097/00002480-200603000-00150 · 1.52 Impact Factor

  • ASAIO Journal 03/2006; 52(2):45A. DOI:10.1097/00002480-200603000-00194 · 1.52 Impact Factor
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    ABSTRACT: The MagScrew Total Artificial Heart (TAH) system is the result of a close collaboration among the Cleveland Clinic Foundation, Foster Miller Technologies, Wilson Greatbatch Ltd, and Whalen Biomedical Inc. The system components are the thoracic blood pumping unit with attached compliance chamber and refill port, implantable electronic control unit, implantable battery pack, transcutaneous energy transmission system, external battery pack, and a telemetry system for communication with the electronic control unit. System in vitro tests are underway for system characterization and durability demonstration, whereas in vivo tests were conducted to evaluate system performance and biocompatibility under physiologic conditions. The passively filling pump uses a left master alternate left and right ejection control mode and has a Starling law-like response to venous pressure. The in vitro tests documented excellent hydraulic pump performance with high device output of over 9 l/min at left atrial pressures below 12 mm Hg. Atrial balance was well maintained under all test conditions. The in vivo tests demonstrated good biocompatibility without use of anticoagulant therapy. Experimental durations have ranged between 0 and 92 days. Postexplant evaluation of tissue samples did not reveal any sign of thromboembolic events or tissue damage due to device operation.
    ASAIO Journal 11/2005; 51(6):xxxvi-xlvi. DOI:10.1097/00002480-200503000-00132 · 1.52 Impact Factor
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    ABSTRACT: The Cleveland Clinic Foundation CPB/ECMO Initiative Forward Casualty Management System is an economical, compact, transportable, disposable system designed to permit a rapid expansion of trauma management services requiring cardiopulmonary bypass (CPB) or extracorporeal membrane oxygenation (ECMO) pulmonary support. The system, composed of a rotary blood pump, a pump motor driver, and an electronic control console as the blood pumping subsystem, also includes commonly used compatible commercial oxygenators, venous reservoirs, and cannulae. In vitro durability testing accumulated over 100 hours without failure. In vivo reliability was tested in 10 calves under general anesthesia during 6 hours of CPB and ECMO under full heparinization at nominal operating conditions of 4-5 l/min and 2-4 l/min blood flow respectively, and mean arterial pressures between 65 and 100 mm Hg. A mean time to failure of 57 hours was reached during the animal series. Results of these test series demonstrated that this system has the capability to reliably operate during a 6-hour conventional CPB or ECMO procedure, while providing flexibility and ease of use for the operator.
    ASAIO Journal 10/2005; 51(6):681-5. DOI:10.1097/01.mat.0000182472.63808.b9 · 1.52 Impact Factor
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    ABSTRACT: Downsizing pulsatile devices requires an increase of beat rate if flow capacity is to be maintained. We applied this concept to the preclinical MagScrew total artificial heart (TAH). The device fills passively with a stroke volume of 45 ml and beat rates up to 250 beats per minute (bpm). Stable hemodynamics were observed during a 30-day bovine implant with a flow of 8.7 +/- 1.2 L/min at beat rates of 204 +/- 18 bpm. Device filling was exceptional up to 250 bpm generating flow of greater than 12 L/min. Beat rate adapted to preload in a way similar to a Frank-Starling response. Left and right atrial pressures were balanced. The aortic pulse pressure was 49-70 mm Hg, which translates to a pulsatility index of 0.49-0.77. Organ functions were preserved and blood damage did not occur. Increasing the beat rate while downsizing the MagScrew TAH was successful with strong flow generation by passive filling. Pulsatility was maintained at high beat rates. This innovative approach may be used to develop small pulsatile pumps.
    The Annals of thoracic surgery 05/2005; 79(4):1378-83; discussion 1383. DOI:10.1016/j.athoracsur.2004.03.064 · 3.85 Impact Factor

  • ASAIO Journal 03/2005; 51(2). DOI:10.1097/00002480-200503000-00143 · 1.52 Impact Factor
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    ABSTRACT: Currently available ventricular assist devices (VADs) have limitations in long-term durability and blood compatibility. We evaluated a prototype of a pulsatile MagScrew VAD for in vivo hemodynamic performance and biocompatibility. The device is composed of an actuator, blood pump housing, diaphragm, pusher plate, and bioprosthetic valves. its protein-coated ("biolized") blood-contacting surface inhibits clot formation. Forces between moving parts of the actuator are transmitted magnetically, eliminating a primary source of friction and wear. The pump fills passively and is highly preload sensitive. The device was implanted into three calves for 90, 10, and 57 days, respectively. No anticoagulants were given postoperatively. The device functioned without technical problems during the entire course of each experiment, with mean device flow ranging between 5.4 and 9.0 L/min. Autopsy of the first two calves revealed no sign of embolization and clean blood-contacting surfaces of the devices. The third experiment was complicated by a prosthetic valve endocarditis with infectious embolization, and a few small depositions were found in the pump. In conclusion, the MagScrew VAD has demonstrated a high level of performance and biocompatibility in three calves studied for 10-90 days. Vigorous development is in progress to bring this device to preclinical readiness and thus provide surgeons with the VAD of choice for permanent implantation.
    ASAIO Journal 08/2003; 49(5):594-598. DOI:10.1097/01.MAT.0000084107.46300.21 · 1.52 Impact Factor
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    ABSTRACT: The purpose of this study was to evaluate the in vitro responses to preload and afterload of our total artificial heart (TAH), the MagScrew TAH. The TAH consists of two blood pumps and a control logic, developed at the Cleveland Clinic, OH, and the MagScrew actuator and its electronic control system, developed by Foster-Miller Technologies, Inc., Albany, NY. Tests were performed on a mock circulatory loop, using water as a test fluid. Preload sensitivity of the Mag-Screw TAH demonstrated a Frank-Starling response to preload in automatic mode. A peak flow of 10 L/min was obtained, with a left atrial pressure of 13 mm Hg. The relationship between right atrial pressure and left atrial pressure was well balanced when tested with a left bronchial shunt flow of 5% and a range of pulmonary artery and aortic pressures. With respect to afterload response, the left pump showed a relatively low sensitivity, which allowed the pump to maintain perfusion over a wide range of aortic pressures. The right pump, on the other hand, was much more sensitive to pulmonary artery pressure, which provided a measure of protection against pulmonary congestion. The very effective physiologic response of the MagScrew TAH is believed to result from employment of a left master, alternating ejection control logic, high inherent sensitivity of the blood pumps to atrial pressure, a lower effective stroke volume for the right pump, and a scaling of right side motor ejection voltage to 80% of that used for the left side ejection.
    ASAIO Journal 11/2002; 48(6):606-11. DOI:10.1097/00002480-200211000-00006 · 1.52 Impact Factor
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    ABSTRACT: The purpose of this study was to evaluate the in vivo pump performance of our total artificial heart (TAH), the "MagScrew TAH." The TAH consists of a blood pump and control logic developed at the Cleveland Clinic and the MagScrew actuator and electronic control system developed by Foster-Miller Technologies, Inc. (Albany, NY). MagScrew TAH implantation was performed in two calves. Study durations were 50 and 5 days. The causes of termination were prosthetic valve endocarditis in one case and cable failure in the other. Mean left pump flow ranged from 8.0 to 9.7 L/min, with left atrial pressure of 3.0 to 16.0 mm Hg. Preload sensitivity of the MagScrew TAH demonstrated a Frank-Starling response to preload in automatic mode. The relationship between right and left atrial pressure was well balanced. Mean arterial pressure and mean pulmonary artery pressure were maintained within physiologic ranges over study duration. There were no signs of bleeding, hemolysis, or organ failure. The MagScrew TAH showed physiologic pump performance, and hemodynamics were well maintained without any organ failure. Further development testing will bring the MagScrew TAH to the point of preclinical readiness testing.
    ASAIO Journal 05/2002; 48(3):222-5. DOI:10.1097/00002480-200205000-00004 · 1.52 Impact Factor
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    ABSTRACT: Cardiopulmonary bypass (CPB), the shunting of blood around the heart and lungs, is a well-established technique that permits difficult surgical procedures on the heart and its adjacent main blood vessels. Extracorporeal membrane oxygenation (ECMO) uses similar equipment, with the primary goal of temporary pulmonary support by increasing the oxygen content and decreasing the carbon dioxide content of the blood, without the intent of performing open chest surgery. It, too, is a well-developed clinical modality, often used in patients with acute respiratory failure. This project is developing a system of disposable, low cost CPB/ECMO components to treat front lines emergency trauma casualties. By cooling the patient to a low temperature of about 10°C and inducing a state of "suspended animation", a severe trauma victim could be preserved and transported to a medical unit capable of performing the required surgical treatment. The system prototype has completed major milestones including heat transfer requirements, CPB/ECMO commercial components selection, low cost disposable CPB pump, command/control console, and driver design fabrication, and extensive in-vitro testing. It is currently undergoing in-vivo testing in two animal models.