Physiological control of an LVAD to control aortic valve motion in the human cardiovascular system

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Physiological control of an LVAD to control aortic valve motion

in the human cardiovascular system

Citation for published version (APA):

Bozkurt, S., Pennings, K. A. M. A., Schampaert, S., Vosse, van de, F. N., & Rutten, M. C. M. (2011).

Physiological control of an LVAD to control aortic valve motion in the human cardiovascular system. 682-682.

Poster session presented at conference; XXXVIII Annual ESAO & IV Biennial IFAO Congress; 2011-10-09;

2011-10-12. https://doi.org/10.5301/IJAO.2011.8702

DOI:

10.5301/IJAO.2011.8702

Document status and date:

Published: 01/01/2011

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34(8 ):682

682 Posters: XXXVIII Annual ESAO & IV Biennial IFAO Congress, 9-12 October 2011, Porto, Portugal

P137 (EI0065)

OUTCOMES FOR CONTINUOUS-FLOW LEFT VENTRICULAR ASSIST DEVICE PATIENTS STRATIFIED BY SEVERITY OF CLINICAL STATUS

J. Garbade, M. Barten, H. Bittner, E.M. Langenstroth, A. Rastan, M. Borger, F.W. Mohr

Cardiac Surgery, Heart Center, University of Leipzig, Germany

Objectives: The use of continuous-flow left ventricular assist devices (LVAD) is an accepted therapy for patients with advanced heart failure. New generation of these devices may have an impact on improved survival rates and quality of life (QoL). Here we report about our single-center experience with the new generation of LVADs.

Methods: Between 2006 and 2010, 41 transplantable and 8 non-trans-plantable patients were selected for LVAD-therapy at our institution due to refractory severe heart failure. All patients were INTERMACS Level 1 to 3 (Level 1: n=23; Level 2: n=18 and Level 3: n=8). The cohort included 44 men and 5 women with a mean age of 53±12 (range 20-75 years). The pa-tients were supported either by Heart Mate II (n=39) or HVAD (n=10) LVAD. In-hospital (30-day) and long-term survival, freedom form re-operation and neurological complication, and rate of drive-line infection were examined. Additionally, the QoL was assessed.

Results: Mean support time was 138±53 days (range 1-867 days). In-hos-pital (30-day) mortality was 27% (n=11) due to severe cardiogenic shock with multiple organ failure and sepsis. The follow-up survival for all was 32 of 49 patients (65%). Bleeding requiring reoperation occurred in 13 pa-tients (n=27%). Neurological problems were identified in 12 papa-tients. There were 6 drive-line infections. 63% of all patients were discharged at home. Overall, 3 patients underwent transplantation, 23 patients awaiting a donor organ, 1 patient was successfully weaned and finally, 5 patients are on destination therapy with good QoL.

Conclusions: Treatment of severe heart failure with new continuous-flow LVAD can significantly improve the acute and long-term survival with low device associated complication and improved QoL.

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NGINEERING

P138 (EI0425)

NOVEL 3D MULTILAYERED CO-CULTURE SYSTEM FOR INVESTIGATING STEM CELL DIFFERENTIATION

C.A. Millan1_{, D. Studer}1,2_{, J. Voeroes}1_{, K. Maniura}2_{, M. Zenobi-Wong}1

1_{Laboratory for Biosensors and Bioelectronics, ETH Zurich, Zurich, Switzerland} 2_{EMPA St. Gallen Laboratory for Materials Science and Engineering, St. Gallen,}

Switzerland

Objectives: To develop an ideal co-culture system for mesenchymal stem cells and articular chondrocytes. A number of recent studies show synergistic ef-fects for chondrogenesis when the two cell types are cultured together, but there is still some ambiguity as to the specifics of these interactions. The critical paracrine signals and/or cell-cell adhesion modules involved must be identi-fied. Via tailoring of the chemical and physical environment exposed to the cells in co-culture, ideal conditions will be identified for promoting the synthesis of cartilagenous tissue.

Methods: We intend to explore a novel technique for depositing layer-by-layer nanofilms of ECM molecules on individual cell surfaces to permit cell contacts analgous to native ECM interactions. QCM-D using adhered extensive work on polyelectrolyte multilayers and hydrogel encapsulation of cells are routinely car-ried out in our lab and will be incorporated into a “3D” co-culture system for the cells. Differentiation will be assessed with qRT-PCR, histology, and novel molecular reporters associated with up-regulation of chondro-specific genes. Cell types will be distinguished in situ via cell tracker molecules and/or other fluorescent labels.

Results: An effective, 3D co-culture system will be established for hMSCs and chondrocytes that will permit elucidation of the communication system between the two cell types. We expect to show that cartilage-specific genes are upregu-lated in constructs versus control groups.

Conclusions: A recent trend in literature concerning co-cultures involving adult stem cells is that, instead of promoting lineage specific differentiation, the stem cells rather provide support to improve the relevant function of the adult cells. This work will shed light on which soluble factors and/or cell-cell adhesions are involved in these processes and inform further tissue engineering strategies. Conclusions: Circadian rhythm of motor current could be observed in fixed

ro-tation speed centrifugal-continuous flow LVAD support. The cause and effect of this variation are still unclear although it is speculated to be correlated to physi-ological changes of some hemodynamic-related parameters of patients.

P135 (EI0012)

CAN WE GENERATE SYSTEMIC ARTERIAL HYPERTENSION BY PULSA-TILE LVAD IN OUR PATIENTS?

D. Macku, F. Jezek, P. Hunka

Department of Cybernetics, FEE, Czech Technical University, Prague, Czech Republic

Objectives: On the basis of our personal experience of studying co-temporary scientific articles and the modelling of flow and pressure patterns in systemic vascular beds, we are encouraged to claim, that extremely small patients can experience systemic arterial hypertension generated by pulsatile LVAD. Methods: Our aim is to present our research about “iatrogenic systemic arterial hypertension produced by a left ventricular assist device”. We want to show ar-ticles in medical journals supporting these facts and demonstrate our software application for the modelling of flow and pressure patterns for the confirmation of our thesis. We are able to prove the first author’s hypothesis that different sized vascular beds are adjusted for the appropriate stroke volume of the native heart and so blood circulation in different sized vascular beds must be sup-ported by the pump with an appropriate stroke volume. Thoratec VAD uses only one pump chamber size for all patients with different vascular bed sizes (65mL). After implantation, all patients have the same stroke volume - 65mL, and the same average flow during the ejection period, i.e. 65mL for 300ms (13 L/min!). The average blood flow during the ejection period is higher in non-physiological terms for extremely small patients and may cause iatrogenic systemic arterial hypertension.

Conclusions: A safe and reliable ventricular assist device is a dream for many of us. Let’s consider our work as a contribution for the better understanding of relationships between the human body and the mechanical device (VAD). We anticipate that the new generation of pulsatile VADs will come with adjustable stroke volumes and others parameters. The stroke volume expelled into the aorta must always be adjusted to the patient’s size and actual requirements of the patient’s body.

P136 (EI0194)

PHYSIOLOGICAL CONTROL OF AN LVAD TO CONTROL AORTIC VALVE MOTION IN THE HUMAN CARDIOVASCULAR SYSTEM

S. Bozkurt, K.A.M.A. Pennings, S. Schampaert, F.N. van de Vosse, M.C.M. Rutten

Department of Biomedical Engineering, Eindhoven University of Technology, The Netherlands

Objectives: Continuous Flow Left Ventricular Assist Devices (CF-LVADs) generally operate at a constant speed in the patient. In this mode, they change the systemic blood flow waveform significantly. If the left ventricu-lar pressure is continuously less than the aortic pressure the aortic valve (AV) remains closed over the cardiac cycle. Blood flows through the CF-LVAD from the left ventricle (LV) into the aorta and pulsatility of the blood flow decreases. In this study, blood flow through the AV is controlled by applying a feedback control to the CF-LVAD to generate intermittent flow through the AV.

Methods: PI control was applied to the flow rate through the LVAD in simu-lations. Minimum pump flow (Q_p) was set to 20 mL/s. Three flow ratios were simulated. Qp being equal to 1/3 of AV flow (Qao), Qp equal to Qao and Qp

equal to 3Q_ao. The ventricle was beating at 80 bpm with 45% / 55% systole / diastole ratio.

Results: In the simulations the aortic valve duty cycle (topen/tcardiac cycle) did

not change. However Q_ao changed significantly. The Q_p was controlled as desired by making the CF-LVAD operating speed variable over a cardiac cycle. The cardiac output value was 3.30 for all simulation protocols. Conclusions: Simulation results show that the AV duty cycle does not change for the same cardiac output values. However, change in the amount of the flow rate through the aortic valve indicates that AV valve motion changes. In other words, without compromising total systemic perfusion the AV motion can be controlled by applying variable pump speed control. However, Q_aohas to be estimated because it cannot be measured directly in a patient. Experimental validation will be carried out as a next step.