Improving Trendelenburg position effectiveness by varying cardiopulmonary bypass flow.

INTRODUCTION: Trendelenburg position (TP) is used to transport gaseous emboli away from the cerebral region during cardiac surgery. However, TP effectiveness has not been fully considered when combined with varying the cardiopulmonary bypass (CPB) flow. This study simulated the supine and TP at different pump flows and assessed the trapped emboli and embolic load entering the aortic arch branch arteries (AABA). METHODS: A computational fluid dynamics (CFD) approach used a centrally cannulated adult patient-specific aorta model replicating a CPB circuit. Air emboli of 0.1 mm, 0.5 mm, and 1.0 mm (n = 700 each) were injected into the aorta placed in the supine position (0°) and the TP (-20°) at 2 L/min and 5 L/min. The number of emboli entering the AABA were compared. An aortic phantom flow experiment was performed to validate air bubble behaviour. RESULTS: TP at 5 L/min had the lowest 0.1 mm mean (±SD) embolic load compared to the supine 2 L/min (55.3 ± 30.8 vs 64.3 ± 35.4). For both the supine and TP, the lower flow of 2 L/min had the highest number of simulated trapped emboli in higher elevated regions than at 5 L/min (541 ± 185 and 548 ± 191 vs 520 ± 159 and 512 ± 174), respectively. The flow experiment demonstrated that 2 L/min promoted bubble coalescence and high amounts of trapped emboli and 5 L/min transported air emboli away from the AABA. CONCLUSIONS: TP effectiveness was improved by using CPB flow to manage air emboli. These results provide insights for predicting emboli behaviour and improving emboli de-airing procedures.

Effect of aortic cannulation depth on air emboli transport during cardiopulmonary bypass: A computational study.

INTRODUCTION: Varying the insertion depth of the aortic cannula during cardiopulmonary bypass (CPB) has been investigated as a strategy to mitigate cerebral emboli, yet its effectiveness associated with CPB flow is not fully understood. We compared different arterial cannula insertion depths and pump flow influencing air microemboli entering the aortic arch branch arteries (AABA). METHODS: A computational approach used a patient-specific aorta model to evaluate four cannula locations at (1) proximal arch, (2) mid arch, (3) distal arch, and (4) descending aorta. We injected 0.1 mm microemboli (N=720) at 2 and 5 L/min and assessed the embolic load and the particle averaged transit times ( entering the AABA. RESULTS: Location 4 had the lowest embolic load (2 L/min: N= 63) and (5 L/min: N= 54) compared to locations 1 to 3 in the range of (N= 118 to 116 at 2 L/min:) and (N= 92 to 146 at 5 L/min). There was no significant difference between 2 L/min and 5 L/min (p = 0.31), despite 5 L/min attaining a lower mean (±standard deviation) than 2 L/min (38.0±23.4 vs 44.5±21.1), respectively. Progressing from location 1 to 4, increased 3.11s -7.40 s at 2 L/min and 1.81s -4.18s at 5 L/min. CONCLUSION: It was demonstrated that the elongated cannula insertion length resulted in lower embolic loads, particularly at a higher flow rate. The numerical results suggest that CPB management could combine active flow variation with improving cannula performance and provide a foundation for a future experimental and clinical investigation to reduce surgical cerebral air microemboli.

A mock circulation loop to evaluate differential hypoxemia during peripheral venoarterial extracorporeal membrane oxygenation.

INTRODUCTION: Peripheral veno-arterial extracorporeal membrane oxygenation (VA ECMO) creates a retrograde flow along the aorta competing with the left ventricle (LV) in the so-called 'mixing zone' (MZ). Detecting it is essential to understand which of the LV or the ECMO flow perfuses the upper body - particularly the brain and the coronary arteries - in case of differential hypoxemia (DH). METHODS: We described a mock circulation loop (MCL) that enabled experimental research on DH. We recreated the three clinical situations relevant to clinicians: where the brain is either totally perfused by the ECMO or the LV or both. In a second step, we used this model to investigate two scenarios to diagnose DH: (i) pulse pressure and (ii) thermodilution via injection of cold saline in the ECMO circuit. RESULTS: The presented MCL was able to reproduce the three relevant mixing zones within the aortic arch, thus allowing to study DH. Pulse pressure was unable to detect location of the MZ. However, the thermodilution method was able to detect whether the brain was totally perfused by the ECMO or not. CONCLUSION: We validated an in-vitro differential hypoxemia model of cardiogenic shock supported by VA ECMO. This MCL could be used as an alternative to animal studies for research scenarios.

Assessing potential for aortoiliac vascular injury from venoarterial extracorporeal membrane oxygenation cannulae: An in vitro particle image velocimetry study.

Limb ischemia is a major complication associated with peripheral venoarterial extracorporeal membrane oxygenation (VA-ECMO). The high velocity jet from arterial cannulae can cause "sandblasting" injuries to the arterial endothelium, with the potential risk of distal embolization and end organ damage. The aim of this study was to identify, for a range of clinically relevant VA-ECMO cannulae and flow rates, any regions of peak flow velocity on the aortic wall which may predispose to vascular injury, and any regions of low-velocity flow which may predispose to thrombus formation. A silicone model of the aortic and iliac vessels was sourced and the right external iliac artery was cannulated. Cannulae ranged from 15 to 21 Fr in size. Simulated steady state ECMO flow rates were instituted using a magnetically levitated pump (CentriMag pump). Adaptive particle image velocimetry was performed for each cannula at 3, 3.5, 4, and 4.5 L/min. For all cannulae, in both horizontal and vertical side hole orientations, the peak velocity on the aortic wall ranged from 0.3 to 0.45 m/s, and the regions of lowest velocity flow were 0.05 m/s. The magnitude of peak velocity flow on the aortic wall was not different between a single pair versus multiple pairs of side holes. Maximum velocity flow on the aortic wall occurred earlier at a lower pump flow rate in the vertical orientation of distal side holes compared to a horizontal position. The presence of multiple paired side holes was associated with fewer low-velocity flow regions, and some retrograde flow, in the distal abdominal aorta compared to cannulae with a single pair of side holes. From this in vitro visualization study, the selection of a cannula design with multiple versus single pairs of side holes did not change the magnitude of peak velocity flow delivered to the vessel wall. Cannulae with multiple side holes were associated with fewer regions of low-velocity flow in the distal abdominal aorta. Further in vivo studies, and ideally clinical data would be required to assess any correlation of peak velocity flows with incidence of vascular injury, and any low-velocity flow regions with incidence of thrombosis.

Ex vivo assessment of erythrocyte tolerance to the HeartWare ventricular assist device operated in three discrete configurations.

Despite technological advances in ventricular assist devices (VADs) to treat end-stage heart failure, hemocompatibility remains a constant concern, with supraphysiological shear stresses an unavoidable reality with clinical use. Given that impeller rotational speed is related to the instantaneous shear within the pump housing, it is plausible that the modulation of pump speed may regulate peak mechanical shear stresses and thus ameliorate blood damage. The present study investigated the hemocompatibility of the HeartWare HVAD in three configurations typical of clinical applications: standard systemic support left VAD (LVAD), pediatric support LVAD, and pulmonary support right VAD (RVAD) conditions. Two ex vivo mock circulation blood loops were constructed using explanted HVADs, in which pump speed and external loop resistance were manipulated to reflect the flow rates and differential pressures reported in configurations for standard adult LVAD (at 3150 rev⸱min-1 ), pediatric LVAD (at 2400 rev⸱min-1 ), and adult RVAD (at 1900 rev⸱min-1 ). Using bovine blood, the mock circulation blood loops were tested at 37°C over a period of 6 hours (consistent with ASTM F1841-97) and compared with static control. Hemocompatibility assessments were conducted for each test condition, examining hematology, hemolysis (absolute and normalized index), osmotic fragility, and blood viscosity. Regardless of configuration, continuous exposure of blood to the VAD over the 6-hour period significantly altered hematological and rheological blood parameters, and induced increased hemolysis when compared with a static control sample. Comparison of the three operational VAD configurations identified that the adult LVAD condition-associated with the highest pump speed, flow rate, and differential pressure across the pump-resulted in increased normalized hemolysis index (NIH; 0.07) when compared with the lower pump speed "off-label" counterparts (NIH of 0.04 in pediatric LVAD and 0.01 in adult RVAD configurations). After normalizing blood residence times between configurations, pump speed was identified as the primary determinant of accumulated blood damage; plausibly, blood damage could be limited by restricting pump speed to the minimum required to support matched cardiac output, but not beyond.

An advanced mock circulation loop for in vitro cardiovascular device evaluation.

Controlled and repeatable in vitro evaluation of cardiovascular devices using a mock circulation loop (MCL) is essential prior to in vivo or clinical trials. MCLs often consist of only a systemic circulation with no autoregulatory responses and limited validation. This study aimed to develop, and validate against human data, an advanced MCL with systemic, pulmonary, cerebral, and coronary circulations with autoregulatory responses. The biventricular MCL was constructed with pneumatically controlled hydraulic circulations with Starling responsive ventricles and autoregulatory cerebral and coronary circulations. Hemodynamic repeatability was assessed and complemented by validation using impedance cardiography data from 50 healthy humans. The MCL successfully simulated patient scenarios including rest, exercise, and left heart failure with and without cardiovascular device support. End-systolic pressure-volume relationships for respective healthy and heart failure conditions had slopes of 1.27 and 0.54 mm Hg mL-1 (left ventricle), and 0.18 and 0.10 mm Hg mL-1 (right ventricle), aligning with the literature. Coronary and cerebral autoregulation showed a strong correlation (R2 : .99) between theoretical and experimentally derived circuit flow. MCL repeatability was demonstrated with correlation coefficients being statistically significant (P < .05) for all simulated conditions while MCL hemodynamics aligned well with human data. This advanced MCL is a valuable tool for inexpensive and controlled evaluation of cardiovascular devices.

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.

Aortic cannula orientation and flow impacts embolic trajectories: computational cardiopulmonary bypass.

INTRODUCTION: Emboli events are associated with the aortic cannula insertion and final position in the ascending aorta. However, the impact of subtle changes in aortic cannula movement and flow influencing embolic transport throughout the aortic arch is not well understood. The present study evaluated the aortic cannula's outflow and orientation effect on emboli entering the aortic branch arteries. METHODS: A simplified aortic computational model was anteriorly cannulated in the distal ascending aorta with a 21-French straight aortic cannula, and two orientations were analysed by injecting gaseous and solid emboli at pump flows 2, 3 and 5 L/minute. The first aortic cannula orientation (forward flow cannula) was directed towards the lesser curvature. The second aortic cannula orientation (rear flow cannula) was tilted slightly backwards by 15°, providing flow in the retrograde direction. RESULTS: Forward flow cannula produced a primary arch flow, whereas rear flow cannula produced a secondary arch flow resulting in four times longer emboli arch resident times than forward flow cannula. The rear flow cannula had the highest percentage of gaseous emboli entering the brachiocephalic artery of 8%, 12% and 36% (at 2, 3 and 5 L/minute, respectively). Rear flow cannula provided a positive aortic branch arterial flow at all pump flows, whereas at forward flow cannula, the brachiocephalic artery experienced retrograde flows of -1.0% (3 L/minute) and -4.0% (5 L/minute), with the left common carotid -0.23% (5 L/minute). No significant number of solid emboli entered the aortic branch arteries. CONCLUSION: This numerical study illustrated distinct trajectory behaviours between gaseous and solid emboli where slight changes in aortic cannula orientation influenced idealised emboli direction with higher pump flows magnifying the effects.

Evaluation of an intraventricular balloon pump for short-term support of patients with heart failure.

The high cost of ventricular assist devices results in poor cost-effectiveness when used as a short-term bridging solution, thus a low-cost alternative is desirable. The present study aimed to develop an intraventricular balloon pump (IVBP) for short-term circulatory support, and to evaluate the effect of balloon actuation timing on the degree of cardiac support provided to a simulated in vitro severe heart failure (SHF) patient. A silicone IVBP was designed to avoid contact with internal left ventricular (LV) features (ie, papillary muscles, chordae, aortic, and mitral valves) based on LV computed tomography data of 10 SHF patients with dilated cardiomyopathy. The hemodynamic effects of varying balloon inflation and deflation timing parameters (inflation duty [D] and end-inflation point [σ]) were evaluated in a purpose-built systemic mock circulatory loop. Three IVBP actuation timing categories were defined: co-, transitional, and counterpulsation. Compared to the SHF baseline, co-pulsation increased aortic flow from 3.5 to 5.2 L/min, mean arterial pressure from 72.1 to 94.8 mmHg and ejection fraction from 14.4% to 21.5%, while mean left atrial pressure decreased from 14.6 to 10 mmHg. Transitional and counterpulsation resulted in a double ventricular pulse and extended the duration of increased ventricular pressure, potentially impeding diastolic filling and coronary perfusion. This in vitro study showed the IVBP could restore the hemodynamic balance of a simulated SHF patient with dilated cardiomyopathy to healthy levels.

Pulmonary Valve Opening With Two Rotary Left Ventricular Assist Devices for Biventricular Support.

Right ventricular failure is a common complication associated with rotary left ventricular assist device (LVAD) support. Currently, there is no clinically approved long-term rotary right ventricular assist device (RVAD). Instead, clinicians have implanted a second rotary LVAD as RVAD in biventricular support. To prevent pulmonary hypertension, the RVAD must be operated by either reducing pump speed or banding the outflow graft. These modes differ in hydraulic performance, which may affect the pulmonary valve opening (PVO) and subsequently cause fusion, valvular insufficiency, and thrombus formation. This study aimed to compare PVO with the RVAD operated at reduced speed or with a banded outflow graft. Baseline conditions of systemic normal, hypo, and hypertension with severe biventricular failure were simulated in a mock circulation loop. Biventricular support was provided with two rotary VentrAssist LVADs with cardiac output restored to 5 L/min in banded outflow and reduced speed conditions, and systemic and pulmonary vascular resistances (PVR) were manipulated to determine the range of conditions that allowed PVO without causing left ventricular suction. Finally, RVAD sine wave speed modulation (±550 rpm) strategies (co- and counter-pulsation) were implemented to observe the effect on PVO. For each condition, outflow banding had higher PVR (97 ± 20 dyne/s/cm5 higher) for when the pulmonary valve closed compared to reduced speed. In addition, counter-pulsation demonstrated greater PVO than co-pulsation and constant speed. For the purpose of reducing the risks of pulmonary valve insufficiency, fusion, and thrombotic event, this study recommends a RVAD with a steeper H-Q gradient by banding and further exploration of RVAD speed modulation.

Speed Modulation of the HeartWare HVAD to Assess In Vitro Hemocompatibility of Pulsatile and Continuous Flow Regimes in a Rotary Blood Pump.

Although rotary blood pumps (RBPs) sustain life, blood exposure to continuous supra-physiological shear stress induces adverse effects (e.g., thromboembolism); thus, pulsatile flow in RBPs represents a potential solution. The present study introduced pulsatile flow to the HeartWare HVAD using a custom-built controller and compared hemocompatibility biomarkers (i.e., platelet aggregation, concentrations for ADAMTS13, von Willebrand factor (vWf), and free-hemoglobin in plasma (pfHb), red blood cell (RBC) deformability, and RBC-nitric oxide synthase (NOS) activity) between continuous and pulsatile flow in a blood circulation loop over 5 h. The HeartWare HVAD was operated using a custom-built controller, at continuous speed (3282 rev/min) or in a pulsatile mode (mean speed = 3273 rev/min, amplitude = 430 rev/min, frequency = 1 Hz) to generate a blood flow rate of 5.0 L/min, HVAD differential pressure of 90 mm Hg for continuous flow and 92 mm Hg for pulsatile flow, and systolic and diastolic pressures of 121/80 mm Hg. For both flow regimes, the current study found; (i) ADP- and collagen-induced platelet aggregation, and ADAMTS13 concentration significantly decreased after 5 h (P < 0.01; P < 0.05), (ii) ristocetin-induced platelet aggregation significantly increased after 45 min (P < 0.05), (iii) vWf concentration did not significantly differ at any time point, (iv) pfHb significantly increased after 5 h (P < 0.01), (v) RBC deformability improved during the continuous flow regime (P < 0.05) but not during pulsatile flow, and (vi) RBC-NOS activity significantly increased during continuous flow (15 min), and pulsatile flow (5 h; P < 0.05). The current study demonstrated: (i) speed modulation does not improve hemocompatibility of the HeartWare HVAD based on no observable differences being detected for routine biomarkers, and (ii) the time-course for increased RBC-NOS activity observed during continuous flow may have improved RBC deformability.

Time Course Response of the Heart and Circulatory System to Active Postural Changes.

Rotary blood pumps (RBPs) used for mechanical circulatory support of heart failure patients cannot passively change pump flow sufficiently in response to frequent variations in preload induced by active postural changes. A physiological control system that mimics the response of the healthy heart is needed to adjust pump flow according to patient demand. Thus, baseline data are required on how the healthy heart and circulatory system (i.e., heart rate (HR) and cardiac output (CO)) respond. This study investigated the response times of the healthy heart during active postural changes (supine-standing-supine) in 50 healthy subjects (27 male/23 female). Early response times (te) and settling times (ts) were calculated for HR and CO from data continuously collected with impedance cardiography. The initial circulatory response of HR and CO resulted in te of 9.0-11.7 s when standing up and te of 4.7-5.7 s when lying back down. Heart rate and CO settled in ts of 50.0-53.6 s and 46.3-58.2 s when standing up and lying down, respectively. In conclusion, when compared to active stand up, HR and CO responded significant faster initially when subjects were lying down (p < 0.05); there were no significant differences in response times between male and female subjects. These data will be used during evaluation of physiological control systems for RBPs, which may improve patient outcomes for end-stage heart failure patients.

The Effect of Compliant Inflow Cannulae on the Hemocompatibility of Rotary Blood Pump Circuits in an In Vitro Model.

Rotary blood pumps (RBPs) are used for mechanical circulatory support in heart failure patients but exhibit a reduced response to preload changes, which can lead to ventricular suction events. A passive control system, in the form of a compliant inflow cannula (IC), has been developed to mitigate suction, although this device may cause significant hemolysis. This study compared the incidence of mechanically induced hemolysis of two compliant IC designs (strutted and nonstrutted) with a rigid IC (control) in a blood circulation loop over 90 min. The nonstrutted compliant IC introduced high frequency and high amplitude oscillations in RBP inlet pressure and RBP IC resistance. These oscillations were correlated with a significant increase in plasma-free hemoglobin (pfHb) and hemolysis: pfHb increased to 2.005 ± 0.665 g/L, while normalized index of hemolysis (NIH) and modified index of hemolysis (MIH) increased to 0.04945 ± 0.01276 g/100 L and 4.0505 ± 0.6589 after 90 min (P < 0.05). In contrast, the strutted compliant IC performed similar to the clinically utilized rigid IC and did not increase pfHb (0.300 ± 0.090 and 0.320 ± 0.171 g/L, respectively) and rate of hemolysis (NIH 0.00435 ± 0.00155 and 0.00543 ± 0.00371 g/100 L; MIH 0.3896 ± 0.1749 and 0.4261 ± 0.2792, respectively) within the RBP circuit. These data indicated that strutted, compliant ICs meet the hemocompatibility of clinically used rigid ICs while also offering a potential solution to prevent ventricular suction events.

In Vivo Evaluation of Active and Passive Physiological Control Systems for Rotary Left and Right Ventricular Assist Devices.

Preventing ventricular suction and venous congestion through balancing flow rates and circulatory volumes with dual rotary ventricular assist devices (VADs) configured for biventricular support is clinically challenging due to their low preload and high afterload sensitivities relative to the natural heart. This study presents the in vivo evaluation of several physiological control systems, which aim to prevent ventricular suction and venous congestion. The control systems included a sensor-based, master/slave (MS) controller that altered left and right VAD speed based on pressure and flow; a sensor-less compliant inflow cannula (IC), which altered inlet resistance and, therefore, pump flow based on preload; a sensor-less compliant outflow cannula (OC) on the right VAD, which altered outlet resistance and thus pump flow based on afterload; and a combined controller, which incorporated the MS controller, compliant IC, and compliant OC. Each control system was evaluated in vivo under step increases in systemic (SVR ∼1400-2400 dyne/s/cm(5) ) and pulmonary (PVR ∼200-1000 dyne/s/cm(5) ) vascular resistances in four sheep supported by dual rotary VADs in a biventricular assist configuration. Constant speed support was also evaluated for comparison and resulted in suction events during all resistance increases and pulmonary congestion during SVR increases. The MS controller reduced suction events and prevented congestion through an initial sharp reduction in pump flow followed by a gradual return to baseline (5.0 L/min). The compliant IC prevented suction events; however, reduced pump flows and pulmonary congestion were noted during the SVR increase. The compliant OC maintained pump flow close to baseline (5.0 L/min) and prevented suction and congestion during PVR increases. The combined controller responded similarly to the MS controller to prevent suction and congestion events in all cases while providing a backup system in the event of single controller failure.

A compliant, banded outflow cannula for decreased afterload sensitivity of rotary right ventricular assist devices.

Biventricular support with dual rotary ventricular assist devices (VADs) has been implemented clinically with restriction of the right VAD (RVAD) outflow cannula to artificially increase afterload and, therefore, operate within recommended design speed ranges. However, the low preload and high afterload sensitivity of these devices increase the susceptibility of suction events. Active control systems are prone to sensor drift or inaccurate inferred (sensor-less) data, therefore an alternative solution may be of benefit. This study presents the in vitro evaluation of a compliant outflow cannula designed to passively decrease the afterload sensitivity of rotary RVADs and minimize left-sided suction events. A one-way fluid-structure interaction model was initially used to produce a design with suitable flow dynamics and radial deformation. The resultant geometry was cast with different initial cross-sectional restrictions and concentrations of a softening diluent before evaluation in a mock circulation loop. Pulmonary vascular resistance (PVR) was increased from 50 dyne s/cm(5) until left-sided suction events occurred with each compliant cannula and a rigid, 4.5 mm diameter outflow cannula for comparison. Early suction events (PVR ∼ 300 dyne s/cm(5) ) were observed with the rigid outflow cannula. Addition of the compliant section with an initial 3 mm diameter restriction and 10% diluent expanded the outflow restriction as PVR increased, thus increasing RVAD flow rate and preventing left-sided suction events at PVR levels beyond 1000 dyne s/cm(5) . Therefore, the compliant, restricted outflow cannula provided a passive control system to assist in the prevention of suction events with rotary biventricular support while maintaining pump speeds within normal ranges of operation.

In vitro and in vivo characterization of three different modes of pump operation when using a left ventricular assist device as a right ventricular assist device.

Dual rotary left ventricular assist devices (LVADs) have been used clinically to support patients with biventricular failure. However, due to the lower vascular resistance in the pulmonary circulation compared with its systemic counterpart, excessively high pulmonary flow rates are expected if the right ventricular assist device (RVAD) is operated at its design LVAD speed. Three possible approaches are available to match the LVAD to the pulmonary circulation: operating the RVAD at a lower speed than the LVAD (mode 1), operating both pumps at their design speeds (mode 2) while relying on the cardiovascular system to adapt, and operating both pumps at their design speeds while restricting the diameter of the RVAD outflow graft (mode 3). In this study, each mode was characterized using in vitro and in vivo models of biventricular heart failure supported with two VentrAssist LVADs. The effect of each mode on arterial and atrial pressures and flow rates for low, medium, and high vascular resistances and three different contractility levels were evaluated. The amount of speed/diameter adjustment required to accommodate elevated pulmonary vascular resistance (PVR) during support with mode 3 was then investigated. Mode 1 required relatively low systemic vascular resistance to achieve arterial pressures less than 100 mm Hg in vitro, resulting in flow rates greater than 6 L/min. Mode 2 resulted in left atrial pressures above 25 mm Hg, unless left heart contractility was near-normal. In vitro, mode 3 resulted in expected arterial pressures and flow rates with an RVAD outflow diameter of 6.5 mm. In contrast, all modes were achievable in vivo, primarily due to higher RVAD outflow graft resistance (more than 500 dyn·s/cm(5)), caused by longer cannula. Flow rates could be maintained during instances of elevated PVR by increasing the RVAD speed or expanding the outflow graft diameter using an externally applied variable graft occlusion device. In conclusion, suitable hemodynamics could be produced by either restricting or not restricting the right outflow graft diameter; however, the latter required an operation of the RVAD at lower than design speed. Adjustments in outflow restriction and/or RVAD speed are recommended to accommodate varying PVR.

Ventricular Flow Dynamics With an Intra-Ventricular Balloon Pump: An In Vitro Analysis.

Due to the high treatment costs associated with durable ventricular assist devices, an intra-ventricular balloon pump (IVBP) was developed to provide low-cost, short-term support for patients suffering from severe heart failure. It is imperative that intraventricular flow dynamics are evaluated with an IVBP to ensure stagnation points, and potential regions for thrombus formation, are avoided. This study used particle image velocimetry to evaluate flow patterns within the left ventricle of a simulated severe heart failure patient with IVBP support to assess left ventricle pulsatility as an indicator of the likelihood of flow stasis. Two inflation timings were evaluated against the baseline severe heart failure condition: IVBP co-pulsation and IVBP counter-pulsation with respect to ventricular systole. IVBP co-pulsation was found to have a reduced velocity range compared to the severe heart failure condition (0.44 m/s compared to 0.54 m/s). IVBP co-pulsation demonstrated an increase in peak velocities (0.25 m/s directed toward the aortic valve during systole, as opposed to 0.2 m/s in severe heart failure), indicating constructive energy in systole and cardiac output (1.7 L/min increase with respect to severe heart failure baseline - 3.5 L/min) throughout the cardiac cycle. IVBP counter-pulsation, while exhibiting the greatest peak systolic velocity directed to the aortic valve (0.4 m/s) was found to counterasct the natural vortex flow pattern during ventricular filling, as well as inducing a secondary ventricular pulse during diastole and a 23% increase in left ventricle end-diastolic volume (indicative of dilation). Ideal IVBP actuation timing did not result in reduced intraventricular pulsatility, indicating promising blood washout.

Diamond-like carbon films prepared by a low temperature periodic process for application in ventricular assist devices.

Due to the poor tribological properties of titanium (Ti) and its alloy Ti6Al4V (commonly used for ventricular assist devices manufacturing), diamond-like carbon (DLC) films with excellent anti-wear properties are pursued to improve the wear resistance of Ti and its alloys. Considering the effect of temperature on magnets inside pump impellers and workpiece deformation, DLC films are preferred to be prepared under low temperature. In this study, DLC films were prepared on Ti6Al4V alloys by periodic and continuous processes, and the corresponding maximum deposition temperature was 85 and 154°C, respectively. The periodic DLC films exhibited the feature of columnar structure, and the surface hillocks were less uniform than that of continuous DLC films. The periodic DLC films possessed more sp3 -bonded structures, and the accessorial sp3 -bonding mainly existed in the form of CH. Compared to continuous DLC films, the periodic DLC films had lower residual stress and better adhesion with Ti6Al4V substrates. Both DLC films could effectively reduce the friction coefficient and wear rate of Ti6Al4V alloys both in air and fetal bovine serum (FBS), and the periodic DLC films exhibited superior anti-wear properties to that of continuous DLC films in FBS. Haemocompatibility evaluation revealed that both DLC films presented similar levels of more human platelet adhesion and activation as compared with that of bare Ti6Al4V. However, both DLC films significantly prolonged plasma clotting time in comparison to bare Ti6Al4V. This study demonstrates the potential of low-temperature DLC films as wear-resistant surface modification for VADs.

Surface Coatings for Rotary Ventricular Assist Devices: A Systematic Review.

Rotary ventricular assist devices (VADs) are frequently used to provide mechanical circulatory support to patients suffering from end-stage heart failure. Therefore, these devices and especially their pump impeller and housing components have stringent requirements on wear resistance and hemocompatibility. Various surface coatings have been investigated to improve the wear resistance or hemocompatibility of these devices. The aim of the present systematic review was to build a comprehensive understanding of these coatings and provide potential future research directions. A Boolean search for peer-reviewed studies was conducted in online databases (Web of Science, Scopus, PubMed, and ScienceDirect), and a preferred reporting items for systematic reviews and meta-analyses (PRISMA) process was followed for selecting relevant papers for analysis. A total of 45 of 527 publications were included for analysis. Eighteen coatings were reported to improve wear resistance or hemocompatibility of rotary VADs with the most common coatings being diamond-like carbon (DLC), 2-methacryloyloxyethyl phosphorylcholine (MPC), and heparin. Ninety-three percent of studies focused on hemocompatibility, whereas only 4% of studies focused on wear properties. Thirteen percent of studies investigated durability. This review provides readers with a systematic catalogue and critical review of surface coatings for rotary VADs. The review has identified that more comprehensive studies especially investigations on wear properties and durability are needed in future work.