scholarly journals High-frequency operation of a pulsatile VAD – a simulation study

2017 ◽  
Vol 62 (2) ◽  
Author(s):  
Mathias Rebholz ◽  
Raffael Amacher ◽  
Anastasios Petrou ◽  
Mirko Meboldt ◽  
Marianne Schmid Daners
Keyword(s):  
Stroke Volume ◽  
High Frequency ◽  
Severe Heart Failure ◽  
Ventricular Assist Devices ◽  
Stroke Work ◽  
Ventricular Assist ◽  
Blood Pumps ◽  
Human Cardiovascular System ◽  
Pulsatile Vad ◽  
Major Reduction

AbstractVentricular assist devices (VADs) are mechanical blood pumps that are clinically used to treat severe heart failure. Pulsatile VADs (pVADs) were initially used, but are today in most cases replaced by turbodynamic VADs (tVADs). The major concern with the pVADs is their size, which prohibits full pump body implantation for a majority of patients. A reduction of the necessary stroke volume can be achieved by increasing the stroke frequency, while maintaining the same level of support capability. This reduction in stroke volume in turn offers the possibility to reduce the pump’s overall dimensions. We simulated a human cardiovascular system (CVS) supported by a pVAD with three different stroke rates that were equal, two- or threefold the heart rate (HR). The pVAD was additionally synchronized to the HR for better control over the hemodynamics and the ventricular unloading. The simulation results with a HR of 90 bpm showed that a pVAD stroke volume can be reduced by 71%, while maintaining an aortic pulse pressure (PP) of 30 mm Hg, avoiding suction events, reducing the ventricular stroke work (SW) and allowing the aortic valve to open. A reduction by 67% offers the additional possibility to tune the interaction between the pVAD and the CVS. These findings allow a major reduction of the pVAD’s body size, while allowing the physician to tune the pVAD according to the patient’s needs.

High-frequency operation of pulsatile ventricular assist devices: A computational study on circular and elliptically shaped pumps

2019 ◽  
Vol 42 (12) ◽  
pp. 725-734 ◽  
Author(s):  
Christian Loosli ◽  
Stephan Rupp ◽  
Bente Thamsen ◽  
Mathias Rebholz ◽  
Gerald Kress ◽  
...  
Keyword(s):  
High Frequency ◽  
Flow Patterns ◽  
Ventricular Assist Devices ◽  
Shear Stresses ◽  
Residence Times ◽  
Pump Frequency ◽  
Ventricular Assist ◽  
Assist Devices ◽  
High Frequency Operation ◽  
Wall Shear

Pulsatile positive displacement pumps as ventricular assist devices were gradually replaced by rotary devices due to their large volume and high adverse event rates. Nevertheless, pulsatile ventricular assist devices might be beneficial with regard to gastrointestinal bleeding and cardiac recovery. Therefore, aim of this study was to investigate the flow field in new pulsatile ventricular assist devices concepts with an increased pump frequency, which would allow lower stroke volumes to reduce the pump size. We developed a novel elliptically shaped pulsatile ventricular assist devices, which we compared to a design based on a circular shape. The pump size was adjusted to deliver similar flow rates at pump frequencies of 80, 160, and 240 bpm. Through a computational fluid dynamics study, we investigated flow patterns, residence times, and wall shear stresses for different frequencies and pump sizes. A pump size reduction by almost 50% is possible when using a threefold pump frequency. We show that flow patterns inside the circular pump are frequency dependent, while they remain similar for the elliptic pump. With slightly increased wall shear stresses for higher frequencies, maximum wall shear stresses on the pump housing are higher for the circular design (42.2 Pa vs 18.4 Pa). The calculated blood residence times within the pump decrease significantly with increasing pump rates. A smaller pump size leads to a slight increase of wall shear stresses and a significant improvement of residence times. Hence, high-frequency operation of pulsatile ventricular assist devices, especially in combination with an elliptical shape, might be a feasible mean to reduce the size, without any expectable disadvantages in terms of hemocompatibility.

Temporary Ventricular Assist Devices in the Intensive Care Unit as a Bridge to Decision

2012 ◽  
Vol 23 (1) ◽  
pp. 55-68 ◽  
Author(s):  
Timothy J. Myers
Keyword(s):  
Anticoagulation Therapy ◽  
Severe Heart Failure ◽  
Ventricular Assist Devices ◽  
Prevention Measures ◽  
Ventricular Assist ◽  
Septic Complications ◽  
Assist Devices ◽  
Arterial Blood ◽  
Definitive Therapy ◽  
Bridge To Decision

Morbidity and mortality in patients with cardiogenic shock remain high despite the recent advances in therapy. New temporary ventricular assist devices (VADs) that are rapidly applied to normalize cardiac output in patients with severe heart failure are being used more frequently. Bridge to decision describes the temporary use of a VAD to stabilize critically ill patients until complete diagnostic tests are performed and decisions about more definitive therapy are made. The CentriMag, Tandem-Heart, and Impella VADs offer versatility for use in many patients and in multiple hospital settings. These VADs provide continuous blood flow, altering the usual assessment of arterial blood pressure. Patients are usually immobilized during support to prevent dislodgement of cannulas. Anticoagulation therapy is commonly required, and bleeding is a frequent complication. Infection prevention measures must be used to avoid septic complications. In the past 10 years, clinical experience with these devices has expanded, but they remain underused.

Associations between hemodynamic parameters at rest and exercise capacity in patients with implantable left ventricular assist devices

2020 ◽  
pp. 039139882094988 ◽  
Author(s):  
Toru Kondo ◽  
Takahiro Okumura ◽  
Hideo Oishi ◽  
Yoshihito Arao ◽  
Hiroo Kato ◽  
...  
Keyword(s):  
Exercise Capacity ◽  
Left Ventricular ◽  
Hemoglobin Level ◽  
Ventricular Assist Devices ◽  
Right Atrial ◽  
Stroke Work ◽  
Hemodynamic Parameters ◽  
Left Ventricular Assist Devices ◽  
Ventricular Assist ◽  
Left Ventricular Assist

Background: Hemodynamic parameters at rest are known to correlate poorly with peak oxygen uptake (VO2) in heart failure. However, we hypothesized that hemodynamic parameters at rest could predict exercise capacity in patients with left ventricular assist device (LVAD), because LVAD pump rotational speed does not respond during exercise. Therefore, we investigated the relationships between hemodynamic parameters at rest (measured with right heart catheterization) and exercise capacity (measured with cardiopulmonary exercise testing) in patients with implantable LVAD. Methods: We performed a retrospective medical record review of patients who received implantable LVAD at our institution from November 2013 to December 2017. Results: A total of 20 patients were enrolled in this study (15 males; mean age, 45.8 years; median duration of LVAD support, 356 days). The mean peak VO2 and cardiac index (CI) were 13.5 mL/kg/min and 2.6 L/min/m2, respectively. CI and hemoglobin level were significantly associated with peak VO2 (CI: r = 0.632, p = 0.003; hemoglobin: r = 0.520, p = 0.019). In addition, pulmonary capillary wedge pressure, right atrial pressure, and right ventricular stroke work index were also significantly associated with peak VO2. In multiple linear regression analysis, CI and hemoglobin level remained independent predictors of peak VO2 (CI: β = 0.559, p = 0.006; hemoglobin: β = 0.414, p = 0.049). Conclusions: CI at rest and hemoglobin level are associated with poor exercise capacity in patients with LVAD.

scholarly journals Haemolysis induced by mechanical circulatory support devices: unsolved problems

Perfusion ◽  
2020 ◽  
Vol 35 (6) ◽  
pp. 474-483
Author(s):  
Inge Köhne
Keyword(s):  
Shear Stress ◽  
Continuous Flow ◽  
Mechanical Circulatory Support ◽  
Ventricular Assist Devices ◽  
Circulatory Support ◽  
Ventricular Assist ◽  
Theoretical Approaches ◽  
Blood Pumps ◽  
Mechanical Circulatory Support Devices ◽  
Support Devices

Since the use of continuous flow blood pumps as ventricular assist devices is standard, the problems with haemolysis have increased. It is mainly induced by shear stress affecting the erythrocyte membrane. There are many investigations about haemolysis in laminar and turbulent blood flow. The results defined as threshold levels for the damage of erythrocytes depend on the exposure time of the shear stress, but they are very different, depending on the used experimental methods or the calculation strategy. Here, the results are resumed and shown in curves. Different models for the calculation of the strengths of erythrocytes are discussed. There are few results reported about tests of haemolysis in blood pumps, but some theoretical approaches for the design of continuous flow blood pumps according to low haemolysis have been investigated within the last years.

Thrombogenicity Comparison of Axial Ventricular Assist Devices by DTE Methodology: MicroMed HeartAssist 5 and Thoratec Heartmate II

2012 ◽  
Author(s):  
Wei-Che Chiu ◽  
Michalis Xenos ◽  
Yared Alemu ◽  
Gaurav Girdhar ◽  
Bryan Lynch ◽  
...  
Keyword(s):  
Severe Heart Failure ◽  
Ventricular Assist Devices ◽  
Heartmate Ii ◽  
Ventricular Assist ◽  
Assist Devices ◽  
Life Saving ◽  
High Incidence ◽  
Organ Donations ◽  
Hemodynamic Performance ◽  
Compact Design

Mechanical circulatory devices, such as ventricular assist devices (VADs), have become the life-saving alternative for the patients who suffered from severe heart failure (1). These devices were utilized as the bridge-transplant devices; however, due to the fast growing population of cardiovascular diseases and the eligible organ donations are very limited, these devices have been considered for the application of life-long implantation. The continuous-flow VADs offer better hemodynamic performance than the first generations pulsatile flow VADs, its compact design offers surgical advantage; however, due to the non-physiological blood flow past constricted geometrics where platelets are exposed to elevated wall shear stress (2), VADs are burdened with high incidence of thromboembolic events, mandating anticoagulation therapies for its recipients (3).

A two-phase flow approach for modeling blood stasis and estimating the thrombosis potential of a ventricular assist device

2020 ◽  
pp. 039139882097540
Author(s):  
Wei-Feng Dai ◽  
Peng Wu ◽  
Guang-Mao Liu
Keyword(s):  
Two Phase Flow ◽  
Blood Stasis ◽  
Economic Benefits ◽  
Experimental Results ◽  
Ventricular Assist Devices ◽  
Phase Flow ◽  
Two Phase ◽  
Ventricular Assist ◽  
Relative Residence Time ◽  
Blood Pumps

Thrombosis and its related events have become a major concern during the development and optimization of ventricular assist devices (VADs, also called blood pumps), and limit their clinical use and economic benefits. Attempts have been made to model the thrombosis formation, considering hemodynamic and biochemical processes. However, the complexities and computational expenses are prohibitive. Blood stasis is one of the key factors which may lead to the formation of thrombosis and excessive thromboembolic risks for patients. This study proposed a novel approach for modeling blood stasis, based on a two-phase flow principle. The locations of blood residual can be tracked over time, so that regions of blood stasis can be identified. The blood stasis in an axial blood pump is simulated under various working conditions, the results agree well with the experimental results. In contrast, conventional hemodynamic metrics such as velocity, time-averaged wall shear stress (TAWSS), and relative residence time (RRT), were contradictory in judging risk of blood stasis and thrombosis, and inconsistent with experimental results. We also found that the pump operating at the designed rotational speed is less prone to blood stasis. The model provides an efficient and fast alternative for evaluating blood stasis and thrombosis potential in blood pumps, and will be a valuable addition to the tools to support the design and improvement of VADs.

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