Continuous-flow Total Artificial Heart Research Articles

Implantable continuous-flow total artificial heart for newborns and small pediatric patients: First report of working model

ObjectiveThe need for safe and reliable mechanical circulatory support (MCS) for smaller children with severe heart failure (HF) is well defined. More specifically, in pediatric patients with advanced congenital HF, there is no implantable total artificial heart (TAH) device available for small patients. Herein, we report the development of the infant continuous-flow total artificial heart (I-CFTAH), a fully implantable in infants and newborns. MethodsAfter extensive engineering analysis, we performed an unprecedented effort: reducing the I-CFTAH's displacement volume to be 14% of the adult CFTAH pump while simultaneously decreasing pump diameter (6.2 cm to 2.6 cm) and axial length (9.8 cm to 4.8 cm). Facilitated by these proportional reductions, for the first time, a durable total artificial heart device was successfully fit in the chest of infants and newborns (height of ≥50 cm). ResultsThe functional I-CFTAH prototype demonstrated capability to support stable hemodynamics and desired device performance. The pump flow range (0.5-1.5 L/min) was confirmed in a mock circulatory testing loop. Within the tested flow range, the I-CFTAH can support small patients that could benefit from the intended cardiac output. ConclusionsThis successful effort demonstrated the feasibility of the miniature continuous-flow total artificial heart, intended for very small patient populations. I-CFTAH showed stable hemodynamics and could, therefore, become one of the few therapeutic options as a bridge to transplantation, aiming to enhance both the quality and duration of life for pediatric patients with advanced HF.

Pediatric continuous-flow total artificial heart with rotor axial position tracking technology: First report of in vivo assessment

BackgroundThe pediatric continuous-flow total artificial heart (P-CFTAH) is a novel double-ended centrifugal pump designed with the intent to provide circulatory support for pediatric heart failure. ObjectivesTo enable continuous monitoring of pump hemodynamics, Hall effect sensors (HES) were embedded inside the P-CFTAH design to track both axial movement and position of the pump rotor post-implantation. Herein, we report an early in vivo evaluation of the P-CFTAH with HES, implanted in small-sized ovine models. MethodsFive healthy lambs were used for the P-CFTAH implantation via a full median sternotomy and cardiopulmonary bypass support. Successful evaluation of the P-CFTAH was achieved in four out of five (n = 4, 20.9 ± 1.3 kg). The hemodynamics and operating conditions were continuously recorded with varying pump speeds (2,800-5,000 rpm), systemic/pulmonary vascular resistance ratio, and high- and low-volume conditions. Among the four cases, P-CFTAH with HES embedded in the rotor was used in two cases. ResultsAll surgical procedures were uneventful, and the optimal anatomical fit of the pump was shown in the chest. Differences between the left and right atrial pressures were mostly maintained within the intended limit of ± 10 mm Hg throughout the design range of systemic and pulmonary vascular resistance. The HES accurately traced the rotor position, showing a positive correlation with atrial pressure differences. ConclusionsThe findings suggest that the P-CFTAH has the potential to provide self-balancing circulatory support for pediatric heart failure patients. The study contributes to the development of a pediatric-sized total artificial heart with improved monitoring.

Cleveland Clinic Continuous-Flow Total Artificial Heart: Progress Report and Technology Update.

Cleveland Clinic's continuous-flow total artificial heart (CFTAH) is being developed at our institution and has demonstrated system reliability and optimal performance. Based on the results from recent chronic in vivo experiments, CFTAH has been revised, especially to improve biocompatibility. The purpose of this article is to report our progress in developing CFTAH. To improve biocompatibility, the right impeller, the pump housing, and the motor were reviewed for design revision. Updated design features were based on computational fluid dynamics analysis and observations from in vitro and in vivo studies. A new version of CFTAH was created, manufactured, and tested. All hemodynamic and pump-related parameters were observed and found to be within the intended ranges, and the new CFTAH yielded acceptable biocompatibility. Cleveland Clinic's continuous-flow total artificial heart has demonstrated reliable performance, and has shown satisfactory progress in its development.

Human fitting of pediatric and infant continuous-flow total artificial heart: visual and virtual assessment.

This study aimed to determine the fit of two small-sized (pediatric and infant) continuous-flow total artificial heart pumps (CFTAHs) in congenital heart surgery patients. This study was approved by Cleveland Clinic Institutional Review Board. Pediatric cardiac surgery patients (n = 40) were evaluated for anatomical and virtual device fitting (3D-printed models of pediatric [P-CFTAH] and infant [I-CFTAH] models). The virtual sub-study consisted of analysis of preoperative thoracic radiographs and computed tomography (n = 3; 4.2, 5.3, and 10.2 kg) imaging data. P-CFTAH pump fit in 21 out of 40 patients (fit group, 52.5%) but did not fit in 19 patients (non-fit group, 47.5%). I-CFTAH pump fit all of the 33 patients evaluated. There were critical differences due to dimensional variation (p < 0.0001) for the P-CFTAH, such as body weight (BW), height (Ht), and body surface area (BSA). The cutoff values were: BW: 5.71 kg, Ht: 59.0 cm, BSA: 0.31 m2. These cutoff values were additionally confirmed to be optimal by CT imaging. This study demonstrated the range of proper fit for the P-CFTAH and I-CFTAH in congenital heart disease patients. These data suggest the feasibility of both devices for fit in the small-patient population.

Artificial Deep Neural Network for Sensorless Pump Flow and Hemodynamics Estimation During Continuous-Flow Mechanical Circulatory Support.

The objective of this study was to compare the estimates of pump flow and systemic vascular resistance (SVR) derived from a mathematical regression model to those from an artificial deep neural network (ADNN). Hemodynamic and pump-related data were generated using both the Cleveland Clinic continuous-flow total artificial heart (CFTAH) and pediatric CFTAH on a mock circulatory loop. An ADNN was trained with generated data, and a mathematical regression model was also generated using the same data. Finally, the absolute error for the actual measured data and each set of estimated data were compared. A strong correlation was observed between the measured flow and the estimated flow using either method (mathematical, R = 0.97, p < 0.01; ADNN, R = 0.99, p < 0.01). The absolute error was smaller in the ADNN estimation (mathematical, 0.3 L/min; ADNN 0.12 L/min; p < 0.01). Furthermore, strong correlation was observed between measured and estimated SVR (mathematical, R = 0.97, p < 0.01; ADNN, R = 0.99, p < 0.01). The absolute error for ADNN estimation was also smaller than that of the mathematical estimation (mathematical, 463 dynes·sec·cm -5 ; ADNN, 123 dynes·sec·cm -5 , p < 0.01). Therefore, in this study, ADNN estimation was more accurate than mathematical regression estimation. http://links.lww.com/ASAIO/A991.

(388) Early in vivo Acute Experience with Pediatric Continuous-Flow Total Artificial Heart with Rotor Axial Position Tracking

(388) Early in vivo Acute Experience with Pediatric Continuous-Flow Total Artificial Heart with Rotor Axial Position Tracking

Biventricular circulatory support using single-device and dual-device configurations: Initial pump characterization in simulated heart failure model.

Severe biventricular heart failure (BHF) can be remedied using a biventricular assist device (BVAD). Two devices are currently in development: a universal ventricular assist device (UVAD), which will be able to assist either the left, right, or both ventricles, and a continuous-flow total artificial heart (CFTAH), which replaces the entire heart. In this study, the in vitro hemodynamic performances of two UVADs are compared to a CFTAH acting as a BVAD. For this experiment, a biventricular mock circulatory loop utilizes two pneumatic pumps (Abiomed AB5000™, Danvers, MA, USA), in conjunction with a dual-output driver, to create heart failure (HF) conditions (left, LHF; right, RHF; biventricular, BHF). Systolic BHF for four different situations were replicated. In each situation, CFTAH and UVAD devices were installed and operated at two distinct speeds, and cannulations for ventricular and atrial connections were evaluated. Both CFTAH and UVAD setups achieved our recommended hemodynamic criteria. The dual-UVAD arrangement yielded a better atrial balance to alleviate LHF and RHF. For moderate and severe BHF scenarios, CFTAH and dual UVADs both created excellent atrial pressure balance. Conversely, when CFTAH was atrial cannulated for LHF and RHF, the needed atrial pressure balance was not met. Comprehensive in vitro testing of two different BVAD setups exhibited self-regulation and exceptional pump performance for both (single- and dual-device) BHF support scenarios. For treating moderate and severe BHF, UVAD and CFTAH both functioned well with respect to atrial pressure regulation and cardiac output. Though, the dual-UVAD setup yielded a better atrial pressure balance in all BHF testing scenarios.

Novel hybrid total artificial heart with integrated oxygenator.

There continues to be an unmet therapeutic need for an alternative treatment strategy for respiratory distress and lung disease. We are developing a portable cardiopulmonary support system that integrates an implantable oxygenator with a hybrid, dual-support, continuous-flow total artificial heart (TAH). The TAH has a centrifugal flow pump that is rotating about an axial flow pump. By attaching the hollow fiber bundle of the oxygenator to the base of the TAH, we establish a new cardiopulmonary support technology that permits a patient to be ambulatory during usage. In this study, we investigated the design and improvement of the blood flow pathway from the inflow-to-outflow of four oxygenators using a mathematical model and computational fluid dynamics (CFD). Pressure loss and gas transport through diffusion were examined to assess oxygenator design. The oxygenator designs led to a resistance-driven pressure loss range of less than 35 mmHg for flow rates of 1-7 L/min. All of the designs met requirements. The configuration having an outside-to-inside blood flow direction was found to have higher oxygen transport. Based on this advantageous flow direction, two designs (Model 1 and 3) were then integrated with the axial-flow impeller of the TAH for simulation. Flow rates of 1-7 L/min and speeds of 10,000-16,000 RPM were analyzed. Blood damage studies were performed, and Model 1 demonstrated the lowest potential for hemolysis. Future work will focus on developing and testing a physical prototype for integration into the new cardiopulmonary assist system.

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

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.

P7: Design and Development of Pediatric Continuous-Flow Total Artificial Heart

P7: Design and Development of Pediatric Continuous-Flow Total Artificial Heart

BIO9: Fitting Studies of an Infant Continuous-Flow Total Artificial Heart in Pediatric Population: Surgical and

BIO9: Fitting Studies of an Infant Continuous-Flow Total Artificial Heart in Pediatric Population: Surgical and

BIO25: Pediatric Continuous-Flow Total Artificial Heart Performance: Current Development Update

Background: The pediatric continuous-flow total artificial heart (P-CFTAH) is a novel mechanical circulatory support system intended for pediatric population with end-stage heart failure. P-CFTAH has been evaluated in animal models and additional design modifications or adjustments from multiple perspectives are ongoing. Herein, we report a thorough summary and update on the P-CFTAH development. Methods: A working prototype of the P-CFTAH was fabricated at the scale of 0.70 of adult CFTAH, and human intraoperative fitting study was performed to determine the range of appropriate anatomical fit for this device. In vivo studies (n=2) with healthy lambs (20.5 and 22.4 kg) were performed through a full median sternotomy. As a parallel effort, computational fluid dynamics (CFD) analyses were performed to guide and evaluate the pump’s flow path design. Results: From the fitting study, we analyzed and concluded that the P-CFTAH could be implanted in children over 5.7 kg of body weight and 0.31 m2 of body surface area. In vivo animal experiments, the anatomical and surgical fit of the P-CFTAH was optimal. All implantations were uncomplicated, and the P-CFTAH ran as expected during the experiment over a wide range of ratios of systemic/pulmonary vascular resistance (0.1 to 37.4). The CFD results were used to select the nominal bearing radial clearance, visualize the flow field throughout the pump, and identify potential flow-related improvements for a next generation design. Conclusion: The P-CFTAH has demonstrated optimal anatomical fitting in small-size models and reasonable selfregulation in various test configurations.

Pulsatility hemodynamics during speed modulation of continuous-flow total artificial heart in a chronic in vivo model.

BackgroundThe evaluation of pulsatile flow created by the new Cleveland Clinic continuous‐flow total artificial heart (CFTAH100), which has a re‐designed right impeller and motor, had not been tested in vivo. The purpose of this study was to evaluate the feasibility of pulsatility with the CFTAH100 during the application of pump speed modulation protocols in a chronic animal model.MethodsA 30‐day chronic animal experiment was conducted with a calf. Five pulsatile studies were performed on the alert animal. The mean pump speed was set at 2800 rpm, and modulated sinusoidally within a range of 0 to ± 35% of mean speed, in increments of 5% at 80 beats per minute (bpm). The pressures and pump flow were collected and a pulsatility index (PI) was calculated.ResultsThe calf was supported with the CFTAH100 without any major complications. The maximum and minimum pump flows changed significantly from baseline in all conditions, while the mean pump flow did not change. All flow pulsatility (FP) readings in all conditions significantly increased from baseline, and the percent modulation (%S) and FP had a strong positive correlation (r = 0.99, p < 0.01). The PI also increased significantly in all conditions (maximum at %S of 35%, 2.2 ± 0.05, p < 0.01), and a positive correlation between %S and PI (r = 0.99, p < 0.01) was observed.ConclusionThe CFTAH100 showed the feasibility of creating pulsatile circulation with sinusoidal pump speed modulation.

Total Artificial Heart Computational Fluid Dynamics: Modeling of Stator Bore Design Effects on Journal-Bearing Performance.

Cleveland Clinic's continuous-flow total artificial heart (CFTAH) is a double-ended centrifugal blood pump that has a single rotating assembly with an embedded magnet, which is axially and radially suspended by a balance of magnetic and hydrodynamic forces. The key to the radial suspension is a radial offset between the stator bearing bore and the magnet's steel laminations. This offset applies a radial magnetic force, which is balanced by a hydrodynamic force as the rotating assembly moves to a "force-balanced" radial position. The journal-bearing blood passage is a narrow flow path between the left and right impellers. The intent of this study was to determine the impact of the stator-bearing bore radius on the journal-bearing hydraulic performance while satisfying the geometric design constraints imposed by the pump and motor configuration. Electromagnetic forces on the journal bearing were calculated using the ANSYS EMAG program, Version 18 (ANSYS, Canonsburg, PA). ANSYS CFX Version 19.2 was then used to model the journal-bearing flow paths of the most recent design of the CFTAH. A transient, moving mesh approach was used to locate the steady state, force-balanced position of the rotating assembly. The blood was modeled as a non-Newtonian fluid. The computational fluid dynamics simulations showed that by increasing stator bore radius, rotor power, stator wall average shear stress, and blood residence time in journal-bearing decrease, while blood net flow rate through the bearing increases. The results were used to select a new bearing design that provides an improved performance compared with the baseline design. The performance of the new CFTAH-bearing design will be confirmed through upcoming in vitro and in vivo testing.

Initial Fitting Study of a Pediatric Continuous-Flow Total Artificial Heart

<h3>Purpose</h3> End-stage heart failure is frequently encountered in complex congenital heart disease. Currently, we are developing a pediatric continuous flow total artificial heart (P-CFTAH). Due to the variations in congenital heart anomalies, the device should be suitable for multiple inflow and outflow structures. The purpose of this study is to evaluate the fitness of a replica of the prototype of P-CFTAH in different ages, weights and morphologies. <h3>Methods</h3> The P-CFTAH pump was derived from the adult CFTAH configuration by downsizing it with a scale factor of 0.70 (1/3 of total volume, Fig. 1a). The 3D-printed models of the pump were evaluated for anatomical fit during open-heart surgery for a variety of congenital heart anatomies. A total of 23 patients were enrolled so far (3.2-30 kg) and divided into 2 groups after the fitting study: fit or non-fit group. The pre-op thoracic size (mm), heart size (mm), cardio thoracic ratio (CTR) were measured using their pre-op chest X-rays and the differences between the 2 groups were statistically analyzed. <h3>Results</h3> Among the 23 patients, 13 patients were assigned to the fit group, and 10 patients assigned to the non-fit group after the intraoperative visual assessment. There were significant differences (p < 0.0001) between fit/non-fit groups for body weight (BW), height (Ht), body surface area (BSA), thoracic and heart size (A, B, C, D in Fig. 1b). The cutoff values of each are, BW: 5.71 kg, Ht: 66.5 cm, BSA: 0.31 m², A: 148.0 mm, B: 84.0 mm, C: 57.0 mm, D: 76.0 mm, and the area under curve of all of the parameters were >0.94. The CTR (B/A in Fig.1b) showed no significant differences among groups. <h3>Conclusion</h3> This study revealed suitability of the P-CFTAH for wide range of pediatric patients, and the range of proper fit was evident. Further studies including the evaluation of the pump performance <i>in vivo</i> and the development of even smaller pumps for the patients below the cutoff line.

Modeling of Virtual Mechanical Circulatory Hemodynamics for Biventricular Heart Failure Support.

In this study, a mechanical circulatory support simulation tool was used to investigate the application of a unique device with two centrifugal pumps and one motor for the biventricular assist device (BVAD) support application. Several conditions-including a range of combined left and right systolic heart failure severities, aortic and pulmonary valve regurgitation, and combinations of high and low systemic and pulmonary vascular resistances-were considered in the simulation matrix. Relative advantages and limitations of using the device in BVAD applications are discussed. The simulated BVAD pump was based on the Cleveland Clinic pediatric continuous-flow total artificial heart (P-CFTAH), which is currently under development. Different combined disease states (n = 10) were evaluated to model the interaction with the BVAD, considering combinations of normal heart, moderate failure and severe systolic failure of the left and right ventricles, regurgitation of the aortic and pulmonary valves and combinations of vascular resistance. The virtual mock loop simulation tool (MATLAB; MathWorks®, Natick, MA) simulates the hemodynamics at the pump ports using a lumped-parameter model for systemic/pulmonary circulation characteristic inputs (values for impedance, systolic and diastolic ventricular compliance, beat rate, and blood volume), and characteristics of the cardiac chambers and valves. Simulation results showed that this single-pump BVAD can provide regulated support of up to 5 L/min over a range of combined heart failure states and is suitable for smaller adult and pediatric support. However, good self-regulation of the atrial pressure difference was not maintained with the introduction of aortic valve regurgitation or high systemic vascular resistance when combined with low pulmonary vascular resistance. This initial in silico study demonstrated that use of the P-CFTAH as a BVAD supports cardiac output and arterial pressure in biventricular heart failure conditions. A similar but larger device would be required for a large adult patient who needs more than 5 L/min of support.

Continuous-flow total artificial heart port-to-port connection technique using dedicated de-airing sleeve.

Preventing the introduction of air while a mechanical circulatory support device is being implanted is critical for successful outcomes. A substantial amount of air may be introduced into the circulation during the pump-to-outflow and/or pump-to-inflow port connection, which can be detrimental to optimal pump function and long-term survival. We have developed a novel connecting sleeve that enables an airless connection of the continuous-flow total artificial heart to the conduits. Herein, we describe the device design and surgical techniques evaluated in vivo.

Total Artificial Heart Incorporating Novel Stacked Motor; First In Vivo Results

The latest version of the continuous flow total artificial heart (CFTAH), which incorporates a novel stacked motor to improve passive self-regulation of pressure difference between the left and right atria, and reduce pump rotor over-excursion, was tested in vivo in a calf model to assess operational performance. The CFTAH was implanted in a calf and run at various pump operating conditions including mean pump speeds from 2400 to 3600 RPM, sinusoidal speed modulations from 0 to 25%, and speed modulation rates from 80 to 120 B.M. It was also tested under various combinations of simulated high and low systemic vascular resistance and pulmonary vascular resistance via outlet graft clamping and administration of a Nitroprusside respectively. The CFTAH responded to all control inputs and ran as expected during the experiment. The head curves of the right and left pumps generated from measured pressures, measured right flow and calculated left flow, were consistent with in vitro data on this pump. The passive atrial pressure regulation performed well in the normal operating range, and there were no signs of excessive rotor axial displacement during extreme pressure excursions as had been seen in the previous versions of the pump. The left atrial pressure was unusually low throughout most of the experiment and we believe that this may have been due to partial blockage of the of the left inflow cuff proximal to the pressure line tap. This led to several left inlet suction conditions and extreme pressure conditions. The replacement of the standard, single stack stator motor with the new dual stator stack motor resulted in better passive regulation of the pressure difference between the left and right atria. Also, the extreme pressure conditions resulting from left inlet suction events did not cause the pump's rotor to rub against the volute housing as had been seen in previous versions of the pump. Even though the self-regulation was acceptable, shifting of the regulation characteristic to increase the nominal LAP-RAP value will improve the regulation further, and this modification will be implemented prior to the next in vivo experiment.

Optimization of Device Deairing and Airless Connection Techniques for Cleveland Clinic Continuous-Flow Artificial Heart

Prevention of air introduction during mechanical circulatory support device implant is critical for a successful outcome. A substantial amount of air may be introduced into the circulation during pump to outflow port connection, which may become detrimental for optimal pump function and long-term survival. In this study, we evaluated techniques of seamless, airless connection of double-ended centrifugal pump (continuous-flow total artificial heart [CFTAH]) in vivo. The airless CFTAH connection techniques were evaluated in acute in vivo (n=2) CFTAH implants (Jersey calves, weight: 77.8 and 80.8 kg). Techniques consisted of pump priming with normal saline (Fig. 1 A) and application of specifically designed connection sleeve (Fig 1B). The silicone sleeve (0.3-0.5 mm thick) was prototyped using multilayer dip-coating technique over a 3D-printed mandrel. A suture line was added along the long axis, to enable easy removal. Deairing sleeve was pre-placed on each outflow port (conduit) and proximal port (port) ends (Fig.1 C). The present air was evacuated upward from an open line. The conduit and pump ports were connected within the sleeve (Fig.1 D), with air being fully excluded from circuit. The CFTAH was started at the minimum speed (2,200 rpm) after connection. The CFTAH pump were successfully primed with saline prior to implant to remove entrapped air. The completely seamless pump connection and exclusion of air from pump and outflow grafts has been found feasible. There were no clinical signs of air embolism in the pulmonary or systemic circulation observed during the experiment. The seamless connection of CFTAH to outflow grafts using specifically designed connection sleeve and its easy removal was demonstrated to be feasible. Device development is ongoing and will aim to address optimal geometry, size and material selection.

Investigation of the inherent left-right flow balancing of rotary total artificial hearts by means of a resistance box.

With the incidence of end-stage heart failure steadily increasing, the need for a practical total artificial heart (TAH) has never been greater. Continuous flow TAHs (CFTAH) are being developed using rotary blood pumps (RBPs), leveraging their small size, mechanical simplicity, and excellent durability. To completely replace the heart with currently available RBPs, two are required; one for providing pulmonary flow and one for providing systemic flow. To prevent hazardous states, it is essential to maintain balance between the pulmonary and systemic circulation at a wide variety of physiologic states. In this study, we investigated factors determining a CFTAH's inherent ability to balance systemic and pulmonary flow passively, without active management of pump rotational speed. Four different RBPs (ReliantHeart HA5, Thoratec HMII, HeartWare HVAD, and Ventracor VentrAssist) were used in various combinations to construct CFTAHs. Each CFTAH's ability to autonomously maintain pressures and flows within defined ranges was evaluated in a hybrid mock loop as systemic and pulmonary vascular resistance (PVR) were changed. The resistance box, a method to quantify the range of vascular resistances that can be safely supported by a CFTAH, was used to compare different CFTAH configurations in an efficient and predictive way. To reduce the need for future in vitro tests and to aid in their analysis, a novel analytical evaluation to predict the resistance box of various CFTAH configurations was also performed. None of the investigated CFTAH configurations fully satisfied the predefined benchmarks for inherent flow balancing, with the VentrAssist (left) and HeartAssist 5 (right) offering the best combination. The extent to which each CFTAH was able to autonomously maintain balance was determined by the pressure sensitivity of each RPB: the sensitivity of outflow to changes in the pressure head. The analytical model showed that by matching left and right pressure sensitivity the inherent balancing performance can be improved. These findings may ultimately lead to a reduced need for manual speed changes or active control systems.