In Vitro Evaluation of an Immediate Response Starling-Like Controller for Dual Rotary Blood Pumps

Estimation of Left Ventricular Stroke Work for Rotary Left Ventricular Assist Devices

Continuous monitoring of left ventricular stroke work (LVSW) may improve the medical management of patients with rotary left ventricular assist devices (LVAD). However, implantable pressure-volume sensors are limited by measurement drift and hemocompatibility. Instead, estimator algorithms derived from rotary LVAD signals may be a suitable alternative. An LVSW estimator algorithm was developed and evaluated in a range of in vitro and ex vivo cardiovascular conditions during full assist (closed aortic valve [AoV]) and partial assist (opening AoV) mode. For full assist, the LVSW estimator algorithm was based on LVAD flow, speed, and pump pressure head, whereas for partial assist, the LVSW estimator combined the full assist algorithm with an estimate of AoV flow. During full assist, the LVSW estimator demonstrated a good fit in vitro and ex vivo (R 2 : 0.97 and 0.86, respectively) with errors of ± 0.07 J. However, LVSW estimator performance was reduced during partial assist, with in vitro : R 2 : 0.88 and an error of ± 0.16 J and ex vivo : R 2 : 0.48 with errors of ± 0.11 J. Further investigations are required to improve the LVSW estimate with partial assist; however, this study demonstrated promising results for a continuous estimate of LVSW for rotary LVADs.

Mock circulatory loop applications for testing cardiovascular assist devices and in vitro studies

The mock circulatory loop (MCL) is an in vitro experimental system that can provide continuous pulsatile flows and simulate different physiological or pathological parameters of the human circulation system. It is of great significance for testing cardiovascular assist device (CAD), which is a type of clinical instrument used to treat cardiovascular disease and alleviate the dilemma of insufficient donor hearts. The MCL installed with different types of CADs can simulate specific conditions of clinical surgery for evaluating the effectiveness and reliability of those CADs under the repeated performance tests and reliability tests. Also, patient-specific cardiovascular models can be employed in the circulation of MCL for targeted pathological study associated with hemodynamics. Therefore, The MCL system has various combinations of different functional units according to its richful applications, which are comprehensively reviewed in the current work. Four types of CADs including prosthetic heart valve (PHV), ventricular assist device (VAD), total artificial heart (TAH) and intra-aortic balloon pump (IABP) applied in MCL experiments are documented and compared in detail. Moreover, MCLs with more complicated structures for achieving advanced functions are further introduced, such as MCL for the pediatric application, MCL with anatomical phantoms and MCL synchronizing multiple circulation systems. By reviewing the constructions and functions of available MCLs, the features of MCLs for different applications are summarized, and directions of developing the MCLs are suggested.

Physiological principles of Starling-like control of rotary ventricular assist devices

Introduction: This review explores the Starling-like physiological control method (SLC) for rotary ventricular assist devices (VADs) for severe heart failure. The SLC, based on mathematical models of the circulation, has two functions modeling each ventricle. The first function controls the output of the VAD to the arterial pool according to Starling's law, while the second function accounts for how the blood returns to the heart from the veins. The article aims to expose clinicians to SLC in an accessible and clinically relevant discussion. Areas Covered: The article explores the physiology underlying the controller, its development and how that physiology can be adapted to SLC. Examples of controller performance are demonstrated and discussed using a benchtop model of the cardiovascular system. A discussion of the limitations and criticisms of SLC is presented, followed by a future outlook on the clinical adoption of SLC. Expert Opinion: Due to its simplicity and emulation of the natural cardiac autoregulation, SLC is the superior physiological control method for rotary VADs. However, current technical and regulatory challenges prevent the clinical translation of SLC of VADs. Further technical and regulatory development will enable the clinical translation of SLCs of VADs in the coming years.

A Starling-like total work controller for rotary blood pumps: An in vitro evaluation

Due to improved durability and survival rates, rotary blood pumps (RBPs) are the preferred left ventricular assist device when compared to volume displacement pumps. However, when operated at constant speed, RBPs lack a volume balancing mechanism which may result in left ventricular suction and suboptimal ventricular unloading. Starling-like controllers have previously been developed to balance circulatory volumes; however, they do not consider ventricular workload as a feedback and may have limited sensitivity to adjust RBP workload when ventricular function deteriorates or improves. To address this, we aimed to develop a Starling-like total work controller (SL-TWC) that matched the energy output of a healthy heart by adjusting RBP hydraulic work based on measured left ventricular stroke work and ventricular preload. In a mock circulatory loop, the SL-TWC was evaluated using a HeartWare HVAD in a range of simulated patient conditions. These conditions included changes in systemic hypertension and hypotension, pulmonary hypertension, blood circulatory volume, exercise, and improvement and deterioration of ventricular function by increasing and decreasing ventricular contractility. The SL-TWC was compared to constant speed control where RBP speed was set to restore cardiac output to 5.0 L/min at rest. Left ventricular suction occurred with constant speed control during pulmonary hypertension but was prevented with the SL-TWC. During simulated exercise, the SL-TWC demonstrated reduced LVSW (0.51 J) and greater RBP flow (9.2 L/min) compared to constant speed control (LVSW: 0.74 J and RBP flow: 6.4 L/min). In instances of increased ventricular contractility, the SL-TWC reduced RBP hydraulic work while maintaining cardiac output similar to the rest condition. In comparison, constant speed overworked and increased cardiac output. The SL-TWC balanced circulatory volumes by mimicking the Starling mechanism, while also considering changes in ventricular workload. Compared to constant speed control, the SL-TWC may reduce complications associated with volume imbalances, adapt to changes in ventricular function and improve patient quality of life.

Mock circulatory test rigs for the in vitro testing of artificial cardiovascular organs

In vitro study plays an important role in the experimental study of cardiovascular dynamics. An essential hardware facility that mimics the blood flow changes and provides the required test conditions, a mock circulatory test rig (MCTR), is imperative for the execution of in vitro study. This paper examines the current MCTRs in use for the testing of artificial cardiovascular organs. Various aspects of the MCTRs are surveyed, including the necessity of in vitro study, the building of MCTRs, relevant standards, general system structure (e.g., the motion and driving, fluid, measurement subsystems), classification, motion driving mechanism of MCTRs, and the considerations for the modelling of the physiological impedance of MCTRs. Examples of the steady and pulsatile flow types of the MCTRs are introduced. Recent developments in MCTRs are inspected and possible future design improvements suggested. This study will help researchers in the design, construction, analysis, and selection of MCTRs for cardiovascular research.

In vitro evaluation of an adaptive Starling-like controller for dual rotary ventricular assist devices

Rotary ventricular assist devices (VADs) operated clinically under constant speed control (CSC) cannot respond adequately to changes in patient cardiac demand, resulting in sub-optimal VAD flow regulation. Starling-like control (SLC) of VADs mimics the healthy ventricular flow regulation and automatically adjusts VAD speed to meet varying patient cardiac demand. The use of a fixed control line (CL - the relationship between ventricular preload and VAD flow) limits the flow regulating capability of the controller, especially in the case of exercise. Adaptive SLC (ASLC) overcomes this limitation by allowing the controller to adapt the CL to meet a diverse range of circulatory conditions. This study evaluated ASLC, SLC and CSC in a biventricular supported mock circulation loop under the simulated conditions of exercise, sleep, fluid loading and systemic hypertension. Each controller was evaluated on its ability to remain within predefined limits of VAD flow, preload, and afterload. The ASLC produced superior cardiac output (CO) during exercise (10.1 L/min) compared to SLC (7.3 L/min) and CSC (6.3 L/min). The ASLC produced favourable haemodynamics during sleep, fluid loading and systemic hypertension and could remain within a predefined haemodynamic range in three out of four simulations, suggesting improved haemodynamic performance over SLC and CSC.

Structure and motion design of a mock circulatory test rig

Mock circulatory test rig (MCTR) is the essential and indispensable facility in the cardiovascular in vitro studies. The system configuration and the motion profile of the MCTR design directly influence the validity, precision, and accuracy of the experimental data collected. Previous studies gave the schematic but never describe the structure and motion design details of the MCTRs used, which makes comparison of the experimental data reported by different research groups plausible but not fully convincing. This article presents the detailed structure and motion design of a sophisticated MCTR system, and examines the important issues such as the determination of the ventricular motion waveform, modelling of the physiological impedance, etc., in the MCTR designing. The study demonstrates the overall design procedures from the system conception, cardiac model devising, motion planning, to the motor and accessories selection. This can be used as a reference to aid researchers in the design and construction of their own in-house MCTRs for cardiovascular studies.

The Importance of Venous Return in Starling-Like Control of Rotary Ventricular Assist Devices

Rotary ventricular assist devices (VADs) are less sensitive to preload than the healthy heart, resulting in inadequate flow regulation in response to changes in patient cardiac demand. Starling-like physiological controllers (SLCs) have been developed to automatically regulate VAD flow based on ventricular preload. An SLC consists of a cardiac response curve (CRC) which imposes a nonlinear relationship between VAD flow and ventricular preload, and a venous return line (VRL) which determines the return path of the controller. This study investigates the importance of a physiological VRL in SLC of dual rotary blood pumps for biventricular support. Two experiments were conducted on a physical mock circulation loop (MCL); the first compared an SLC with an angled physiological VRL (SLC-P) against an SLC with a vertical VRL (SLC-V). The second experiment quantified the benefit of a dynamic VRL, represented by a series of specific VRLs, which could adapt to different circulatory states including changes in pulmonary (PVR) and systemic (SVR) vascular resistance versus a fixed physiological VRL which was calculated at rest. In both sets of experiments, the transient controller responses were evaluated through reductions in preload caused by the removal of fluid from the MCL. The SLC-P produced no overshoot or oscillations following step changes in preload, whereas SLC-V produced 0.4 L/min (12.5%) overshoot for both left and right VADs. Additionally, the SLC-V had increased settling time and reduced controller stability as evidenced by transient controller oscillations. The transient results comparing the specific and standard VRLs demonstrated that specific VRL rise times were improved by between 1.2 and 4.7 s ( x ¯ = 3.05 s), while specific VRL settling times were improved by between 2.8 and 16.1 seconds ( x ¯ = 8.38 s) over the standard VRL. This suggests only a minor improvement in controller response time from a dynamic VRL compared to the fixed VRL. These results indicate that the use of a fixed physiologically representative VRL is adequate over a wide variety of physiological conditions.

Artificial Organs 2017: A Year in Review

In this Editor's Review, articles published in 2017 are organized by category and summarized. We provide a brief reflection of the research and progress in artificial organs intended to advance and better human life while providing insight for continued application of these technologies and methods. Artificial Organs continues in the original mission of its founders "to foster communications in the field of artificial organs on an international level." Artificial Organs continues to publish developments and clinical applications of artificial organ technologies in this broad and expanding field of organ Replacement, Recovery, and Regeneration from all over the world. Peer-reviewed Special Issues this year included contributions from the 12th International Conference on Pediatric Mechanical Circulatory Support Systems and Pediatric Cardiopulmonary Perfusion edited by Dr. Akif Undar, Artificial Oxygen Carriers edited by Drs. Akira Kawaguchi and Jan Simoni, the 24th Congress of the International Society for Mechanical Circulatory Support edited by Dr. Toru Masuzawa, Challenges in the Field of Biomedical Devices: A Multidisciplinary Perspective edited by Dr. Vincenzo Piemonte and colleagues and Functional Electrical Stimulation edited by Dr. Winfried Mayr and colleagues. We take this time also to express our gratitude to our authors for offering their work to this journal. We offer our very special thanks to our reviewers who give so generously of time and expertise to review, critique, and especially provide meaningful suggestions to the author's work whether eventually accepted or rejected. Without these excellent and dedicated reviewers the quality expected from such a journal could not be possible. We also express our special thanks to our Publisher, John Wiley & Sons for their expert attention and support in the production and marketing of Artificial Organs. We look forward to reporting further advances in the coming years.