Publications by authors named "Christine R Flick"

11 Publications

  • Page 1 of 1

Left Atrial Circulatory Assistance in Simulated Diastolic Heart Failure Model: First in Vitro and in Vivo.

J Card Fail 2022 Jan 10. Epub 2022 Jan 10.

Department of Biomedical Engineering, Lerner Research Institute, Cleveland Clinic, Cleveland, Ohio.

Background: We are developing a left atrial assist device (LAAD) that is implanted at the mitral position to treat diastolic heart failure (DHF) represented by heart failure with preserved ejection fraction.

Methods: The LAAD was tested at 3 pump speeds on a pulsatile mock loop with a pneumatic pump that simulated DHF conditions by adjusting the diastolic drive. The LAAD was implanted in 6 calves, and the hemodynamics were assessed. In 3 cases, DHF conditions were induced by using a balloon inserted into the left ventricle, and in 2 cases, mitral valve replacement was also performed after the second aortic cross-clamp.

Results: DHF conditions were successfully induced in the in vitro study. With LAAD support, cardiac output, aortic pressure and left atrial pressure recovered to normal values, whereas pulsatility was maintained for both in vivo and in vitro studies. Echocardiography showed no left ventricular outflow tract obstruction, and the LAAD was successfully replaced by a mechanical prosthetic valve.

Conclusions: These initial in vitro and in vivo results support our hypothesis that use of the LAAD increases cardiac output and aortic pressure and decreases left atrial pressure, while maintaining arterial pulsatility.
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http://dx.doi.org/10.1016/j.cardfail.2021.11.024DOI Listing
January 2022

Characterization and Development of Universal Ventricular Assist Device: Computational Fluid Dynamics Analysis of Advanced Design.

ASAIO J 2021 Nov 10. Epub 2021 Nov 10.

SimuTech Group, Hudson, Ohio SimuTech Group, Huntsville, Alabama R1 Engineering LLC, Euclid Department of Biomedical Engineering, Lerner Research Institute, Cleveland Clinic, Cleveland Cleveland Clinic Lerner College of Medicine of Case Western Reserve University, Cleveland, Ohio, USA.

We are developing a universal, advanced ventricular assist device (AVAD) with automatic pressure regulation suitable for both left and right ventricular support. The primary goal of this computational fluid dynamics (CFD) study was to analyze the biventricular performance of the AVAD across its wide range of operating conditions. An AVAD CFD model was created and validated using in vitro hydraulic performance measurements taken over conditions spanning both left ventricular assist device (LVAD) and right ventricular assist device (RVAD) operation. Static pressure taps, placed throughout the pump, were used to validate the CFD results. The CFD model was then used to assess the change in hydraulic performance with varying rotor axial positions and identify potential design improvements. The hydraulic performance was simulated and measured at rotor speeds from 2,300 to 3,600 revolutions/min and flow rates from 2.0 to 8.0 L/min. The CFD-predicted hydraulic pressure rise agreed well with the in vitro measured data, within 6.5% at 2300 rpm and within 3.5% for the higher rotor speeds. The CFD successfully predicted wall static pressures, matching experimental values within 7%. High degree of similarity and circumferential uniformity in the pump's flow fields were observed over the pump operation as an LVAD and an RVAD. A secondary impeller axial clearance reduction resulted in a 10% decrease in peak flow residence time and lower static pressures on the secondary impeller. These lower static pressures suggest a reduction in the upwards rotor forces from the secondary impeller and a desired increase in the pressure sensitivity of the pump. The CFD analyses supported the feasibility of the proposed AVAD's use as an LVAD or an RVAD, over a wide range of operating conditions. The CFD results demonstrated the operability of the pump in providing the desired circumferential flow similarity over the intended range of flow/speed conditions and the intended functionality of the AVAD's automated pressure regulation.
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http://dx.doi.org/10.1097/MAT.0000000000001607DOI Listing
November 2021

Computational Fluid Dynamics Model of Continuous-Flow Total Artificial Heart: Right Pump Impeller Design Changes to Improve Biocompatibility.

ASAIO J 2021 Sep 20. Epub 2021 Sep 20.

From the SimuTech Group, Hudson, Ohio R1 Engineering LLC, Euclid, Ohio Department of Biomedical Engineering, Lerner Research Institute, Cleveland Clinic, Cleveland, Ohio Cleveland Clinic Lerner College of Medicine of Case Western Reserve University, Cleveland Clinic, Cleveland, Ohio.

Cleveland Clinic is developing a continuous-flow total artificial heart (CFTAH). This novel design operates without valves and is suspended both axially and radially through the balancing of the magnetic and hydrodynamic forces. A series of long-term animal studies with no anticoagulation demonstrated good biocompatibility, without any thromboemboli or infarctions in the organs. However, we observed varying degrees of thrombus attached to the right impeller blades following device explant. No thrombus was found attached to the left impeller blades. The goals for this study were: (1) to use computational fluid dynamics (CFD) to gain insight into the differences in the flow fields surrounding both impellers, and (2) to leverage that knowledge in identifying an improved next-generation right impeller design that could reduce the potential for thrombus formation. Transient CFD simulations of the CFTAH at a blood flow rate and impeller rotational speed mimicking in vivo conditions revealed significant blade tip-induced flow separation and clustered regions of low wall shear stress near the right impeller that were not present for the left impeller. Numerous right impeller design variations were modeled, including changes to the impeller cone angle, number of blades, blade pattern, blade shape, and inlet housing design. The preferred, next-generation right impeller design incorporated a steeper cone angle, a primary/splitter blade design similar to the left impeller, and an increased blade curvature to better align the incoming flow with the impeller blade tips. The next-generation impeller design reduced both the extent of low shear regions near the right impeller surface and flow separation from the blade leading edges, while maintaining the desired hydraulic performance of the original CFTAH design.
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http://dx.doi.org/10.1097/MAT.0000000000001581DOI Listing
September 2021

Left atrial assist device for heart failure with preserved ejection fraction: initial results with torque control mode in diastolic heart failure model.

Heart Fail Rev 2021 May 1. Epub 2021 May 1.

Department of Biomedical Engineering, Lerner Research Institute, Cleveland Clinic, Cleveland, OH, USA.

A novel pump, the left atrial assist device (LAAD), is a device specifically for the treatment of heart failure with preserved ejection fraction (HFpEF). The LAAD is a mixed-flow pump that is implanted in the mitral position and delivers blood from the left atrium to the left ventricle. During the development process, we aimed to explore whether device activation in torque control (TC) mode would improve the function of the LAAD. The TC mode causes adjustment of the pump speed automatically during each cardiac cycle in order to maintain a specified torque. In this study, we tested four different TC settings (TC modes 0.9, 1.0, 1.25, and 1.5) using an in vitro mock circulatory loop. Mild, moderate, and severe diastolic heart failure (DHF) conditions, as well as normal heart condition, were simulated with the four TC modes. Also, we evaluated the LAAD in vivo with three calves. The LAAD was implanted at the mitral position with four TC settings (TC modes 0.9, 1.0, 1.1, 1.2). With LAAD support, the in vitro cardiac output and aortic pressure recovered to normal heart levels at TC 1.25 and 1.5 even under severe DHF conditions with little pump regurgitation. The TC mode tested in vivo with three calves, and it also showed favorable result without elevating the left ventricular end-diastolic pressure. These initial in vitro and in vivo results suggest that the TC mode could be potentially effective, and the LAAD could be a treatment option for HFpEF patients.
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http://dx.doi.org/10.1007/s10741-021-10117-6DOI Listing
May 2021

Short-term in vivo performance of the Cleveland clinic PediPump left ventricular assist device.

Artif Organs 2014 May 1;38(5):374-82. Epub 2013 Oct 1.

Department of Biomedical Engineering, Lerner Research Institute.

The PediPump was implanted in six healthy lambs (mean 25.6 ± 1.4 kg) between the left ventricular apex and the descending aorta to evaluate in vivo performance for up to 30 days. Anticoagulation was achieved by continuous heparin infusion. Three animals were euthanized prematurely, two because of respiratory dysfunction and one because of deteriorating pump performance resulting from thrombus formation inside the pump. Three lambs were electively sacrificed 30 days after implantation; all had stable hemodynamics and minimal hemolysis, as indicated by low plasma free hemoglobin (2.5 ± 3.1 mg/dL). Mean 30-day pump flow was 1.8 ± 0.1 L/min at a pump speed of 12 200 ± 400 rpm. Neither activated clotting time nor activated partial thromboplastin time followed the changes in heparin dose. At necropsy, depositions were observed at the front (n = 1) and rear rotor axial positioning stops (n = 4); improved polishing techniques on the stationary stop surfaces and the addition of a hard-carbon, thin-film coating on the rotating stop of the pumps used for the last two experiments addressed the deposition seen earlier. In conclusion, the PediPump showed excellent hydraulic performance and minimal hemolysis during support for up to 30 days. Depositions observed at the axial positioning stops in earlier experiments were addressed by design and material refinements. We continue to focus on developing effective anticoagulation management in the lamb model as well as on further evaluating and demonstrating pump biocompatibility.
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http://dx.doi.org/10.1111/aor.12179DOI Listing
May 2014

The PediPump: a versatile, implantable pediatric ventricular assist device--update IV.

Artif Organs 2009 Nov;33(11):1005-8

The Department of Biomedical Engineering, Lerner Research Institute, Cleveland Clinic, Cleveland, OH, USA.

Cleveland Clinic's PediPump (Cleveland, OH, USA) is a ventricular assist device designed for the support of pediatric patients. The PediPump is a mixed-flow ventricular assist device with a magnetically suspended impeller measuring 10.5 mm in diameter by 64.5 mm in length. Progress and achievements for the PediPump program are considered according to the development project's three primary objectives: Basic engineering: along with size reductions, substantial design improvements have been incorporated in each design iteration including the motor, magnetic bearings, axial touch points, and heat transfer path; Anatomic modeling and device fitting studies: Techniques based on computed tomography and magnetic resonance imaging have been developed to create three-dimensional anatomic-modeling and device-fitting tools to facilitate device implantation and to assist in preoperative planning. For in vivo testing, to date, six acute (6-h duration) and nine chronic (30-day target duration) implantations have been performed in sheep; the implantation of the PediPump appears to be relatively easy with excellent hemodynamic performance and minimal hemolysis during support. Cleveland Clinic's PediPump program supported by the National Heart, Lung and Blood Institute's Pediatric Circulatory Support Program has led to the development of a pediatric ventricular assist device that has satisfactory performance in preclinical evaluation and appears to be ready to support a program of clinical testing.
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http://dx.doi.org/10.1111/j.1525-1594.2009.00946.xDOI Listing
November 2009

Pressures generated within the chambers of the MagScrew TAH: an in vitro study.

ASAIO J 2008 Jan-Feb;54(1):58-63

Department of Biomedical Engineering, Lerner Research Institute, Cleveland Clinic, Cleveland, Ohio 44195, USA.

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.
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http://dx.doi.org/10.1097/MAT.0b013e31815c8964DOI Listing
June 2008

Hemodynamic and metabolic changes during exercise in calves with total artificial hearts of different sizes yet similar output.

Artif Organs 2007 Sep;31(9):667-76

Department of Biomedical Engineering, Lerner Research Institute, Cleveland Clinic, Cleveland, OH, USA.

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.
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http://dx.doi.org/10.1111/j.1525-1594.2007.00445.xDOI Listing
September 2007

Replacement of the left-side valves of an implanted total artificial heart.

ASAIO J 2006 Jul-Aug;52(4):368-72

Department of Biomedical Engineering, Lerner Research Institute, Cleveland Clinic, Cleveland, Ohio, USA.

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.
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http://dx.doi.org/10.1097/01.mat.0000227731.46835.1eDOI Listing
September 2006

MagScrew total artificial heart in vivo performance above 200 beats per minute.

Ann Thorac Surg 2005 Apr;79(4):1378-83; discussion 1383

Department of Biomedical Engineering, The Cleveland Clinic Foundation, Cleveland, Ohio 44195, USA.

Purpose: 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).

Description: The device fills passively with a stroke volume of 45 ml and beat rates up to 250 beats per minute (bpm).

Evaluation: 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.

Conclusions: 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.
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http://dx.doi.org/10.1016/j.athoracsur.2004.03.064DOI Listing
April 2005

In vivo performance and biocompatibility of the MagScrew ventricular assist device.

ASAIO J 2003 Sep-Oct;49(5):594-8

Department of Biomedical Engineering, Lerner Research Institute, The Cleveland Clinic Foundation, 9500 Euclid Avenue, Cleveland, OH 44195, USA.

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.
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http://dx.doi.org/10.1097/01.mat.0000084107.46300.21DOI Listing
May 2004
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