Mock Loop Research Articles

The design modification of advanced ventricular assist device to enhance pulse augmentation and regurgitant flow shut-off.

The new Advanced ventricular assist device (Advanced VAD) has many features such as improving pulsatility and preventing regurgitant flow during pump stoppage. The purpose of this study was to evaluate the effects of design modifications of the Advanced VAD on these features in vitro. Bench testing of four versions of the Advanced VAD was performed on a static or pulsatile mock loop with a pneumatic device. After pump performance was evaluated, each pump was run at 3000 rpm to evaluate pulse augmentation, then was stopped to assess regurgitant flow through the pump. There was no significant difference in pump performance between the pump models. The average pulse pressure in the pulsatile mock loop was 23.0, 34.0, 39.3, 33.8, and 37.3 mm Hg without pump, with AV010, AV020 3S, AV020 6S, and AV020 RC, respectively. The pulse augmentation factor was 48%, 71%, 47%, and 62% with AV010, AV020 3S, AV020 6S, and AV020 RC, respectively. In the pump stop test, regurgitant flow was -0.60±0.70, -0.13±0.57, -0.14±0.09, and -0.18±0.06 L/min in AV010, AV020 3S, AV020 6S, and AV020 RC, respectively. In conclusion, by modifying the design of the Advanced VAD, we successfully showed the improved pulsatility augmentation and regurgitant flow shut-off features.

Getting Past the Spin: The CorWave LVAD, a Membrane Wave Pump Providing Physiologic Pulsatility without High Shear

Purpose A new LVAD is under development which employs a completely novel pumping technology. Magnetically driven oscillation of a polymer membrane creates a wave motion, gently pushing the blood through the pump. By changing the oscillation frequency and magnitude, pressure generation and blood flow rates can be dynamically adjusted over timescales as short as 30 msec. This approach offers a less damaging method for efficiently pumping blood while generating physiologic pulsatility. We evaluated pump actuation parameters and control algorithms in mock circulation loops and an acute animal study to evaluate and optimize pulse generation. Methods The LVAD was evaluated on a physiologic mock-loop to determine the optimal performance parameters. Pulsatility is created by switching rapidly between levels of pump output. A period of high output was generated following detection of systole to augment native cardiac output. Pump flow was reduced during diastole to avoid suck-down of the ventricle and limit back flow. The initial target was pump generated aortic dP/dt of >400 mmHg/sec under heart failure conditions with pump flow of 3-6 LPM. In parallel, hemolysis was measured using porcine blood. The pulsatility algorithm was evaluated with the pump implanted in an ovine model to validate the systole detection method. Results Evaluation on the mock circulatory loop achieved a high degree of pulsatility, defined as delta AoP=40mmHg, dP/dt=410mmHg/s, AoF=4.7 lpm, MAP=83mmHg vs. heart failure model of delta AoP=28mmHg, dP/dt=430mmHg/s, AoF=3.7lpm, MAP= 67mmHg. Generation of free hemoglobin at both high and low operating points are in a clinically acceptable range and well controlled transition between the two points does not significantly increase hemolysis. The acute animal study, the pulsatility algorithm correctly detected systole in >90% of beats. Conclusion Bench testing indicated that the pump provided augmented pulsatility to the failing heart, while achieving targeted levels of aortic flow and pressure without increased hemoglobin release. Augmented pulsatility offers a new mechanism to reduce bleeding and renal complications of VAD therapy with the intriguing possibly to increase cardiac recovery. Studies are underway to further evaluate the pulsatile operating mode algorithms and related hemoglobin release in an ovine heart failure model.

Aortic Insufficiency during LVAD Support: A Mock Loop Study

Purpose Aortic valve (AoV) insufficiency (AI) is a serious complication in more than 20% of Left Ventricle Assist Device (LVAD) patients within 12 months of LVAD implantation. Normal AoV have developed AI following long-term LVAD support,which has been associated with a significant reduction in LVAD patient survival. During LVAD support, the AoV pressure difference is increased, which reduces systolic opening and worsens regurgitant flow through an incompetent valve. The goal of this study was to measure the effect of LVAD support on intraventricular flow during AI. Methods The velocity field was measured in the midplane of a dilated silicone LV model attached to a rotary LVAD (Abbott Labs, Chicago IL) in a mock circulatory loop. A Pre-LVAD without AI condition (BL) of 20% ejection fraction was established, followed by testing at three LVAD speeds. AI was created with a small 3-D printed stent which was nonobstructive to forward flow but prevented the leaflets from fully closing. LV and aortic pressure, and LVAD and distal aortic flow, were recorded. Results At the Pre-LVAD BL condition, the mean aortic pressure was 63 mmHg and the cardiac output was 2.3 L/min; AI maintained a similar pressure but reduced flow to 1.8 L/min producing a 32% regurgitant fraction (mild-moderate AI). At an LVAD speed of 6400rpm, total systemic flow was 4.3 L/min and 3.1 L/min for BL and AI, respectively, and LVAD flow was 4.2 and 3.6 L/min, producing a 45% regurgitant fraction (moderate-severe AI). The reduction of systemic flow was accompanied by higher LVAD flow, confirming that a regurgitant loop was present. Net forward flow through AoV during BL decreased progressively by 23%, 12% and 0.5% for 4800, 5400, and 6400rpm respectively. AI reduced forward flow and increased backward flow, such that net forward flow was 0.5%, -14%, and -17% at 4800, 5400 and 6400rpm. The AI vena contracta width increased from 2.3 to 3.4 mm as LVAD speed increased. Conclusion Overall, the results showed that an initially mild level of AI worsened with LVAD support prior to any remodeling, simply due to the altered biomechanics of the AoV. These findings provide a foundation for new strategies that can restore AoV biomechanics and reduce the impact of AI on patients with LVAD support.

Hemodynamic Improvement with Application of Mechanical Circulatory Support in Heart Failure with Preserved Ejection Fraction in a Mock Circulation Loop

Purpose Mechanical circulatory support (MCS) is a non-obvious therapy for heart failure with preserved ejection fraction (HFpEF) because ventricular systolic function is not reduced. We hypothesize MCS of the left ventricle (LV) or left atrium (LA) can improve the hemodynamics in HFpEF including when pulmonary arterial hypertension (PH) is present. Methods Hemodynamic conditions of HFpEF ± PH were recreated on a mock circulation loop (MCL) with a tunable resistance, arterial compliance, peripheral resistance, inertance, venous compliance, and replication of the Frank-Starling mechanism. Hemodynamic parameters were recorded, including atrial and ventricular pressures, ventricular volumes, ejection fraction, and cardiac output. A HeartWare HVAD™ (Medtronic, MN) was used in two different support configurations: 1) LV to aorta (Ao) and 2) LA to Ao. The pump speed was titrated to achieve systemic flow (Qs) of 4.0 L/min and 4.5 L/min. Results Conditions typically seen in patients with HFpEF ± PH were created in the MCL with complete hemodynamic profiles including HVAD support seen in Table1. In both configurations and regardless of PH status, further Qs augmentation was associated with a reduction in LV end-diastolic pressure, LA pressure and mean pulmonary artery pressure. In the LV to Ao configuration, LV volumes decreased, and ejection fraction improved. In the LA to Ao configuration, LV volumes increased. In the LV to Ao configuration, pressure-volume loop (PVL) data show a reduction in pressure-volume area including a decrease in both stroke work and potential energy. In LA to Ao configuration, PVL data show a decrease in stroke work but an increase in potential energy. This study was not designed to evaluate for suction events. Conclusion In HFpEF ± PH, MCS can increase Qs and reduce LA pressure. As compared to LV decompression, LA decompression does not volume unload the LV. This study shows potential for MCS as a therapeutic alternative for HFpEF.

Development of Continuous-Flow Total Artificial Heart for Use in Infants

Purpose Heart transplantation in infants and children is an accepted therapy for congenital heart disease, but donor organ availability remains unstable. Mechanical circulatory support is another standard option, but there is a lack of implantable devices due to size and functional range. The purpose of this study was to evaluate in vivo performance of the initial prototype of an infant continuous-flow total artificial heart (I-CFTAH) with one motor and one rotating assembly supported by a hydrodynamic bearing. Methods The I-CFTAH was designed to cover a range of 3 kg infant to 9 kg child (flange diameter - 26.9 mm; length - 44 mm), with nominal design point was matched to a 6 kg child, requiring 1.0 L/min of flow. I-CFTAH was tested using in silico virtual simulation mock loop (VML; MATLAB; MathWorks®) and simulated the hemodynamics as they surge through the system implanted with blood pump (run at 0.5 L/min for 3 kg infant). Lumped-parameter model including systemic/pulmonary circulation, values for impedance, beat rate, and blood volume was used. Results The in silico experiments showed intended performance of scaled down pump (left and right pump flows - 0.5 L/min at 4380 RPM). The difference between the left and right atrial pressures was maintained within ± 5-15 mm Hg. Simulation of I-CFTAH was successfully performed and allowed creating arterial pulsation with this device. Conclusion The present simulation-based approach showed feasibility of I-CFTAH design. The I-CFTAH met the proposed requirements for self-regulation, performance and pulse modulation. Further in vitro validation and in vivo implantation will be necessary to explore this technology in more detail.

Mechanical Circulatory Support for Biventricular Heart Failure Using Continuous-Flow Total Artificial Heart

Purpose Biventricular assist device (BVAD) implantation is the treatment of choice in patients with severe biventricular heart failure (BHF) and cardiogenic shock . We previously developed a miniaturized continuous flow double-ended centrifugal pump intended for total artificial heart implant (CFTAH). The purpose of this initial in vitro study was to prove that scaled down CFTAH can be suitable for biventricular support. Methods The CFTAH was tested in BVAD configuration at 2 pump speeds (4500 and 6000 rpm) on a pulsatile mock loop with two pneumatic ventricles that simulated normal and heart failure conditions (moderate and severe) by adjusting the systolic and diastolic drive pressures to simulate hemodynamics of the failing biventricular function. Results The BVAD performance was maintained very well for both atrial and ventricular cannulation within the 4500 - 6000 rpm range. A stable hemodynamics were maintained, and the pump's self-regulating performance was confirmed with the most of atrial pressure difference (LAP-RAP) falling within ±5-15 mm Hg in (Mod.) and severe (Sev.) right (RHF) and left HF (LHF) conditions. Left and right pump flows (LPF and RPF) and total flow (TF) increased as the BVAD speed was increased (Figure). The TF was higher than LPF and RPF due to output from the native ventricles, and the LPF was higher than RPF with pump speed of 6,000 rpm, but the TF appeared balanced due to larger native right ventricular output vs. native left ventricle with given condition. Conclusion These initial in vitro study demonstrated that use of the CFTAH as BVAD supports cardiac output and arterial pressure in BHF conditions. In vivo evaluation of this technology is currently pending.

Evaluation of New Left Ventricular Assist Device for Transapical Insertion Using Virtual Mock Loop Model

Purpose The aim of this study was to assess a new pump's performance and function by using a virtual mock loop (VML) system for device characterization and mapping. Methods We are developing a novel miniaturized left ventricle assist device (LVAD) configured for transapical insertion (Perfusions Solutions Inc., South Euclid, OH). The results of pump testing in the laboratory, such as pressure-flow performance curves, were used for the analysis of its function as an LVAD. The VML system was programmed to mimic various types of heart failure and provide hemodynamic pressure values before and after activation of LVAD. The circulatory conditions of the VML system were systolic heart failure (SHF), diastolic HF (DHF), and both systolic and diastolic HF (BHF). Results Before and after pump activation with SHF condition and with a pump speed of 14000 RPM, aortic pressure (AoP) increased from 71/50 to 99/97 mm Hg, pulmonary artery pressure (PAP) changed from 44/36 to 44/33 mm Hg, mean left atrium pressure (mLAP) decreased from 25 to 18 mm Hg, mean right atrium pressure (mRAP) increased from 7 to 10 mm Hg; with DHF, AoP changed from 116/81 to 129/113 mm Hg, PAP was 45/34 to 45/31 mm Hg, mLAP was 18 to 15 mm Hg, mRAP was 10 to 12 mm Hg; with BHF, AoP was 65/46 to 98/96 mm Hg, PAP was 44/36 to 45/33 mm Hg, mLAP was 26 to 19 mm Hg, mRAP was 7 to 10 mm Hg. (Figure A; pressure-volume curve with BHF, B; pressure curve with BHF without LVAD, 14000 RPM and 16000 RPM of the pump speed) Conclusion Due to the test results from the VML system, the new LVAD for transapical insertion could have the ability enough to ease symptoms of the patients with various types of heart failure based on results from VML system.

A Novel Rotary Blood Pump for HFpEF

Purpose Heart Failure with preserved ejection fraction (HFpEF) currently has no treatment options for improving symptoms or survival. We have developed a long-term novel pulsed assist device for treatment of patients with HFpEF. Methods We have developed a small diagonal centrifugal rotary blood pump which utilizes hydrodynamic suspension for magnetically elevated support of a four-blade impeller with partial unloading from the left atrium (LA) to the descending aorta. The pump is adaptive: the physiological needs of the patient are adjusted by both ECG and sensor feedback algorithms. Pulsed power and speed (rpm) maintain pulse pressure at a normal level. The device is designed for minimally invasive Implantation through a 9 × 3 cm thoracotomy. Repeated animal testing (sheeps) is performed. Results Animal studies testing a spectrum of unloading with simultanous hemodynamic and echocardiographic monitoring, have demonstrated adequate pulsed pump unloading between 1.5-3.0 l/min. ECG gated rpm increase in systole avoids LA suction, interference with mitral valve opening and ventricular filling. Blood pressure was maintained at 95-70 mmHg, central venous pressure (CVP) at 10 mmHg and native cardiac output of 3 l/m. Repeated studies with human whole blood without added anticoagulation in a mock loop for 8 hours have demonstrated no hemolysis, no increase in energy consumption or heat, and no clotting inside the pump. Long-term animal studies are planned. Conclusion Partial systolic pulsed unloading of the LA using a novel rotary blood pump demonstrated adequate hemodynamics and maintained normal pulse pressure. This novel pump may become the first possible treatment for patients with HFpEF.

Corwave LVAD Development Update

Purpose The Corwave Neptune LVAD is being developed to employ gentle oscillation of a membrane to propel blood, based on the wave motion of swimming fish. The pump output can be readily tuned by adjusting membrane oscillation frequency and magnitude. The purpose of this project was increase the hydraulic efficiency, implement a physiologic pulsatility control algorithm, and confirm performance in animal implants. Methods The fluid path of the pump was simulated by Fluid-Structure-Interaction (FSI) computational fluid dynamic analysis in COMSOL. Membrane size, oscillation frequency, oscillation magnitude, and the blood flow path were modeled and refined to improve hydraulic performance and eliminate areas of flow stagnation. Pumps were then tested in blood analogs and blood in mock circulation loops and in vitro hemolysis testing. Non-hermetic pumps were implanted in a total of 25 sheep for acute and chronic implants. Results Design simulations and individual component testing resulted in a pump which can generate 6+ LPM of blood flow against physiologic pressures with maximum shear rates orders of magnitude lower that those of rotary blood pumps. Mock loop testing demonstrated the pumps have “flat” HQ (pressure vs. flow) curves. Three control methods were developed: fixed, asynchronous pulsatile, and synchronous pulsatile. Pulsatile modes generated dP/dt>400 mmHg/sec using sensorless detection of native ventricle systole. Animal implants demonstrated low hemolysis and an absence of renal infarcts, but were limited to about a week in duration due to the non-hermetic sealing of the pumps. Conclusion Application of robust computational simulation and bench top testing have produced a unique new kind of VAD, offering the flow capacity and reliability of rotary pumps, but adding physiologically relevant pulsatility without excessive shear rates. Future efforts will implement full hermeticity to extend animal study durations and confirm von Willebrand Factor compatibility. The Corwave Neptune LVAD is being developed to employ gentle oscillation of a membrane to propel blood, based on the wave motion of swimming fish. The pump output can be readily tuned by adjusting membrane oscillation frequency and magnitude. The purpose of this project was increase the hydraulic efficiency, implement a physiologic pulsatility control algorithm, and confirm performance in animal implants. The fluid path of the pump was simulated by Fluid-Structure-Interaction (FSI) computational fluid dynamic analysis in COMSOL. Membrane size, oscillation frequency, oscillation magnitude, and the blood flow path were modeled and refined to improve hydraulic performance and eliminate areas of flow stagnation. Pumps were then tested in blood analogs and blood in mock circulation loops and in vitro hemolysis testing. Non-hermetic pumps were implanted in a total of 25 sheep for acute and chronic implants. Design simulations and individual component testing resulted in a pump which can generate 6+ LPM of blood flow against physiologic pressures with maximum shear rates orders of magnitude lower that those of rotary blood pumps. Mock loop testing demonstrated the pumps have “flat” HQ (pressure vs. flow) curves. Three control methods were developed: fixed, asynchronous pulsatile, and synchronous pulsatile. Pulsatile modes generated dP/dt>400 mmHg/sec using sensorless detection of native ventricle systole. Animal implants demonstrated low hemolysis and an absence of renal infarcts, but were limited to about a week in duration due to the non-hermetic sealing of the pumps. Application of robust computational simulation and bench top testing have produced a unique new kind of VAD, offering the flow capacity and reliability of rotary pumps, but adding physiologically relevant pulsatility without excessive shear rates. Future efforts will implement full hermeticity to extend animal study durations and confirm von Willebrand Factor compatibility.

A novel adaptor system enables endovascular access through extracorporeal life support circuits

ObjectiveExtracorporeal life support has traditionally been used as a supportive platform for patients with cardiopulmonary failure. Many of these patients require endovascular access for the performance of diagnostic or therapeutic procedures, and obtaining vascular access in these patients can be problematic. We sought to develop a novel system that allows the extracorporeal life support circuit to serve as an access point to the cardiovascular system. MethodsBy using computer-aided design, modeling, and 3-dimensional printing, a novel adaptor that can be easily inserted and removed from an extracorporeal life support circuit was developed. A mock loop was used to measure flow and pressure at various pump speeds with insertion of guidewires and catheters through the adaptor. The ability of the system to enable performance of endovascular procedures in vivo was then tested in a porcine extracorporeal life support model. ResultsBy using a small arterial cannula (15F) at 3500 RPM and 3.2 LPM, 15% and 24% decrements in circuit flow were observed when a 0.035” guidewire and 5F angiography catheter, respectively, were passed through the adaptor (P < .001). However, when using a larger arterial cannula (23F) at 3500 RPM and 4.7 LPM, only 3% and 5% decrements in flow were observed (P < .001), respectively, with intermediate changes when using 17F to 21F cannulas. In vivo testing confirmed that this system enables the performance of a variety of endovascular procedures, including left ventriculography, aortic root and coronary angiography, and descending aortography. ConclusionsThis novel system successfully enables endovascular access through an extracorporeal life support circuit. This technology may transform extracorporeal life support from a purely supportive strategy to a platform for endovascular intervention.

A Novel Sensorized Heart Valve Prosthesis: Preliminary In Vitro Evaluation.

Background: Recent studies have shown that subclinical valve thrombosis in heart valve prosthesis (HVP) can be responsible for reduced leaflet motion detectable only by advanced imaging diagnostics. We conceived a novel sensorized HVP able to detect earlier any thrombus formation that may alter the leaflets motion using an electric impedance measurement, IntraValvular Impedance (IVI). Methods: For IVI measurement, dedicated electrodes are embedded in the structure of the HVP to generate a local electric field that is altered by the moving valve leaflets during their cyclic opening/closing. We present preliminary in vitro results using a first prototype of sensorized mechanical heart valve connected to an external impedance measurement system. The prototype was tested on a circulatory mock loop system and the IVI signals were recorded during both normal dynamics and experimentally induced altered working of the leaflets. Results: Recordings showed a very repetitive and stable IVI signal during the normal cyclic opening/closing of the HVP. The induced alterations in leaflet motion were reflected in the IVI signal. Conclusions: The novel sensorized HVP has great potential to give early warning of possible subclinical valve thrombosis altering the valve leaflet motion, and to help in tailoring the anticoagulation therapy.

Use of a Mechanical Circulatory Support Simulation to Study Pump Interactions With the Variable Hemodynamic Environment.

The Virtual Mock Loop, a versatile virtual mock circulation loop, was developed using a lumped-parameter model of the mechanically assisted human circulatory system. Inputs allow specification of a variety of continuous-flow pumps (left, right, or biventricular assist devices) and a total artificial heart that can self-regulate between left and right pump outputs. Hemodynamic inputs were simplified using a disease-based input panel, allowing selection of a combination of cardiovascular disease states, including systolic and diastolic heart failure, stenosis, and/or regurgitation in each of the four valves, and high to low systemic and pulmonary vascular resistance values. The menu-driven output includes a summary of hemodynamic parameters and graphical output of selected flows, pressures, and volumes in the heart's four chambers as well as in the pulmonary artery and aorta. New tools to augment experimental research on implantable heart-assist devices and to increase our understanding of patient-specific pump interactions are in high demand. The purpose of this ongoing study is to demonstrate the use of a system analysis computer simulation to explore and better comprehend the interactions of mechanical circulatory support pumps with a more extensive combination of patient-specific or simulation conditions than can be established by practical experimentation. Usability is an important factor in constructing computer models for research purposes, and among our primary objectives in creating this simulation model were to make it as portable and useful as possible outside the lab environment, by people not involved in the creation of its operational software.

Mock loop for bubble generation in a centrifugal blood pump for fault simulation

Abstract In extracorporeal blood circulation intensive care treatments, the occurrence of gas within the circulation is one known major hazard. This gas volume can cause severe harm to the patient like infarctions. Consequently, within risk assessment for these treatments gas bubbles are usually addressed by either constructive or signal based approaches. All signal-based approaches do have in common that they need a sufficient amount of data to be parameterized. These data can only be acquired in animal trials or laboratory experiments, as they could result in harm to patients. Hence, we designed a mock loop, which is automatically able to create annotated data of gas bubbles injected into an extracorporeal circulation. We were able to run this setup with a periodicity of 15 seconds, which results in 240 annotated measurements per hour. For the evaluation, we created 1095 bubbles of varying sizes (0.3 to 0.5 ml). The elaborated setup enables us to produce a great amount of annotated data, which is shown to be comparable to manually generated data in a convenient and fully automated manner.

In-Vitro Evaluation of Cardiac Energetics and Coronary Flow with Volume Displacement and Rotary Blood Pumps.

Bridge to recovery with left ventricular assist device (LVAD) support has been more prominent with volume displacement pumps (VDPs) than with rotary blood pumps (RBPs), which may be due to VDPs providing greater ventricular unloading and coronary artery flow. To compare ventricular unloading and coronary flow of VDPs and RBPs in a repeatable environment, a physiologic coronary circulation was added to a pre-existing mock circulatory loop. In this study, a physiologic coronary circulation, mimicking a healthy or diseased auto-regulatory response was implemented in a mock circulatory loop. Using the mock circulation loop, a VDP with original (Björk-Shiley) and then replacement (jellyfish) valves was operated in clinically recommended modes and compared to full and partial assist RBP operating at constant speed and rapid speed modulated modes. The Björk-Shiley VDP resulted in increased pressure-volume area, which resulted in greater coronary artery flow when compared to the improved jellyfish valves. Full assist RBP support reduced left ventricular stroke work, pressure-volume area and coronary flow compared to partial assist, whilst the effect of speed modulation modes was not as significant. Of all LVAD operating modes, the counter-pulsed VDP with jellyfish valves demonstrated the greatest reduction in pressure-volume area and improved coronary flow. This study provides a basis for further investigation into RBP speed modulation profiles to match the improved haemodynamic performance of VDPs.

Correction: Changes in aortic pulse wave velocity of four thoracic aortic stent grafts in an ex vivo porcine model.

[This corrects the article DOI: 10.1371/journal.pone.0186080.].

Characterizing the HeartMate II Left Ventricular Assist Device Outflow Using Particle Image Velocimetry.

Ventricular assist devices (VADs) are implanted in patients with a diseased ventricle to maintain peripheral perfusion as a bridge-to-transplant or as destination therapy. However, some patients with continuous flow VADs (e.g., HeartMate II (HMII)) have experienced gastrointestinal (GI) bleeding, in part caused by the proteolytic cleavage or mechanical destruction of von Willebrand factor (vWF), a clotting glycoprotein. in vitro studies were performed to measure the flow located within the HMII outlet cannula under both steady and physiological conditions using particle image velocimetry (PIV). Under steady flow, a mock flow loop was used with the HMII producing a flow rate of 3.2 L/min. The physiological experiment included a pulsatile pump operated at 105 BPM with a ventricle filling volume of 50 mL and in conjunction with the HMII producing a total flow rate of 5.0 L/min. Velocity fields, Reynolds normal stresses (RNSs), and Reynolds shear stresses (RSSs) were analyzed to quantify the outlet flow's potential contribution to vWF degradation. Under both flow conditions, the HMII generated principal Reynolds stresses that are, at times, orders of magnitude higher than those needed to unfurl vWF, potentially impacting its physiological function. Under steady flow, principal RNSs were calculated to be approximately 500 Pa in the outlet cannula. Elevated Reynolds stresses were observed throughout every phase of the cardiac cycle under physiological flow with principal RNSs approaching 1500 Pa during peak systole. Prolonged exposure to these conditions may lead to acquired von Willebrand syndrome (AvWS), which is accompanied by uncontrollable bleeding episodes.

Sound analysis of a left ventricular assist device: A technical evaluation of iOS devices.

The use of left ventricular assist device (LVAD) has grown rapidly. Adverse events do continue to occur. In recent years, analysis of LVAD sound recordings emerged as a means to monitor pump function and detect pump thrombosis. The aim of this study was to characterize the sounds from HeartMate II and to evaluate the use of handheld iOS devices for sound recordings. Signal analysis of LVAD sound recordings, with dedicated recording equipment and iOS devices, was performed. Two LVADs running in mock loop circuits were compared to an implanted LVAD. Spectral analysis and parametric signal models were explored to quantify the sound and potentially detect changes in it. The sound recordings of two LVADs in individual mock loop circuits and a third one implanted in a patient appeared to be similar. Qualitatively, sound characteristics were preserved following changes in pump speed. Recordings using dedicated equipment showed that HeartMate II sound comprises low-frequency components corresponding to pump impeller rotation, as well as high-frequency components due to a pulse width modulation of the electric power to the pump. These different signal components interact and result in a complicated frequency spectrum. The iPhone and iPod recordings could not reproduce the sounds as well as the dedicated equipment. In particular, lower frequencies were affected by outside disturbances. This article outlines a systematic approach to LVAD sound analysis using signal processing methods to quantify and potentially detect changes, and describes some of the challenges, for example, with the use of inexpensive recording devices.

Long-Term Durability Test for the Left Ventricular Assist System EVAHEART under the Physiologic Pulsatile Load.

The EVAHEART Left Ventricular Assist System (LVAS) was designed for the long-term support of a patient with severe heart failure. It has an original water lubrication system for seal and bearing and wear on these parts was considered one of its critical failure modes. A durability test focusing on wear was designed herein. We developed a mock loop, which generates a physiologic pulsatile flow and is sufficiently durable for a long-term test. The pulsatile load and the low fluid viscosity enable the creation of a severe condition for the mechanical seal. A total of 18 EVAHEART blood pumps completed 2 years of operation under the pulsatile condition without any failure. It indicated the EVAHEART blood pump had a greater than 90% reliability with a 88% confidence level. The test was continued with six blood pumps and achieved an average of 8.6 years, which was longer than the longest clinical use in Japan. The test result showed that no catastrophic, critical, marginal, or minor failures of the blood pump or their symptoms were observed. The seal performance was maintained after the test. Moreover, the surface roughness did not change, which showed any burn or abnormal wear occurred. The original water lubrication system equipped in EVAHEART LVAS prevent severe wear on the seal and the bearing, and it can be used in the bridge to transplant and destination therapy.

Initial in vitro testing of a paediatric continuous-flow total artificial heart.

Mechanical circulatory support has become standard therapy for adult patients with end-stage heart failure; however, in paediatric patients with congenital heart disease, the options for chronic mechanical circulatory support are limited to paracorporeal devices or off-label use of devices intended for implantation in adults. Congenital heart disease and cardiomyopathy often involve both the left and right ventricles; in such cases, heart transplantation, a biventricular assist device or a total artificial heart is needed to adequately sustain both pulmonary and systemic circulations. We aimed to evaluate the in vitro performance of the initial prototype of our paediatric continuous-flow total artificial heart. The paediatric continuous-flow total artificial heart pump was downsized from the adult continuous-flow total artificial heart configuration by a scale factor of 0.70 (1/3 of total volume) to enable implantation in infants. System performance of this prototype was evaluated using the continuous-flow total artificial heart mock loop set to mimic paediatric circulation. We generated maps of pump performance and atrial pressure differences over a wide range of systemic vascular resistance/pulmonary vascular resistance and pump speeds. Performance data indicated left pump flow range of 0.4-4.7 l/min at 100 mmHg delta pressure. The left/right atrial pressure difference was maintained within ±5 mmHg with systemic vascular resistance/pulmonary vascular resistance ratios between 1.4 and 35, with/without pump speed modulation, verifying expected passive self-regulation of atrial pressure balance. The paediatric continuous-flow total artificial heart prototype met design requirements for self-regulation and performance; in vivo pump performance studies are ongoing.

A Human Paired Sample Mock Loop for In Vitro Blood Pump Testing

A Human Paired Sample Mock Loop for In Vitro Blood Pump Testing