Intra-aorta Pump Research Articles

The Hemodynamic Effect of Phase Differences Between the BJUT‐II Ventricular Assist Device and Native Heart on the Cardiovascular System

The BJUT-II VAD (which was previously called the intra-aorta pump) is a novel left ventricular assist device (LVAD) with a special structure and connection with the native heart. The hemodynamic effect of the phase difference of this pump on the cardiovascular system is still unclear. In this work, seven speed waveforms, whose phase differences vary from 0° to 180°, are used to evaluate the hemodynamic effect of change in phase difference on the cardiovascular system. The external work (EW), equivalent afterload (EAL), pulsatile ratio (PR), and mean aortic pressure during diastolic period (MAPD) are chosen to evaluate the hemodynamic state of the circulatory system. Mathematical study results show that the support levels generated by the BJUT-II VAD under various phase differences are comparable. In contrast, EW, EAL, PR, and MAPD are significantly affected by change in phase difference. It is found that EW reaches its maximum value when the phase difference equals 30°. Similarly, EAL declines with increasing phase difference. PR reaches its maximum value when the phase difference is at 60°. In addition, MAPD decreases with increasing phase difference and then achieves its maximum value at 30°. To obtain comprehensive evaluation of the hemodynamic effects of phase difference on the cardiovascular system, a weight detection algorithm (WDA) whose output indicates the hemodynamic state of the circulatory system is also designed, with EW, PR, and MAPD chosen as the inputs. The minimum value of the output of the WDA indicates the optimal hemodynamic state and optimal phase difference for the BJUT-II VAD. According to the output of the WDA, 30° is considered to be the optimal phase difference for the BJUT-II VAD.

The Hemodynamic Effect of the Support Mode for the Intra‐Aorta Pump on the Cardiovascular System

Intra-aorta pump is a novel rotary ventricular assist device. Because of the special structure and connection with the native heart, the hemodynamic effect of support mode of this pump on the cardiovascular system is not clear. In this work, three support modes, including "constant speed" mode, "co-pulse" mode, and "counter-pulse" mode, have been designed for the intra-aorta pump to evaluate the hemodynamic effect of different support modes on the cardiovascular system. Simulation results demonstrate that that both "co-pulse" mode and "counter-pulse" mode can achieve better unloading performance than "constant speed" mode. The intra-aorta pump controlled by "co-pulse" mode is beneficial for improving coronary flow. Moreover, the external work, which is defined as the product of left ventricular pressure and cardiac output, under "co-pulse" mode is the minimum of the three support modes (0.783 w vs. 0.615 w vs. 0.702 w). The pulsatility ratio, defined as the ratio of the peak-to-peak value of arterial pressure (AP) to the mean arterial pressure value, under "co-pulse" mode is the maximum of the three modes (24% vs. 32.8% vs. 23.7%). The equivalent afterload value, which is the ratio of pulsatile pressure at the pump inflow and pulsatile pump flow, is larger than other support modes (0.596 mm Hg.s/mL vs. 0.9704 mm Hg.s/mL vs. 0.55 mm Hg.s/mL). In brief, the intra-aorta pump under "co-pulse" mode support is beneficial for improving myocardial perfusion and restoring pulsatility of AP, while "counter-pulse" mode is beneficial to the perfusion of vital organs.

Effect of Continuous Arterial Blood Flow of Intra-Aorta Pump on the Aorta - A Computational Study

In this study, a computational fluid dynamics (CFD) study based on a finite element method (FEM) was performed for the human aorta with four different flow time patterns (healthy to full intra-aorta pump support). Fully coupled fluid-solid interaction (FSI) simulation was used to investigate the flow profiles in the aortic arch and its branches where the maximum disturbed and non-uniform flow patterns, and the wall shear stress profiles on the same areas. The blood flow was assumed as a homogeneous, incompressible, and Newtonian fluid flow. Flow across four inlets of aortas was derived from a lumped parameter model (LPM). The inlet flow rate waveforms were divided by different blood assist index (BAI), and were calculated with the physiological information of a heart failure patient.

Physiological Controller of an Intra-Aorta Pump Based on Baroreflex Sensitivity

Left ventricular assist devices are increasingly used for long-term support in heart failure patients. It is important to find an optimum operating point for the pump that is appropriate for the existing function of the heart and the state of the circulatory system. Therefore, baroreflex sensitivity (BRS), as an indicator of heart function, is chosen as the control variable. In order to find an optimum point automatically, an extremum search algorithm (ESA) is designed to find an optimal mean arterial pressure (MAP), for which the BRS is maximum. Then, a MAP controller based on model-free adaptive control is designed to ensure that the measured MAP tracks the desired one. In order to test the feasibility of the control strategy, numerical simulations and simplified in vitro experiments were conducted. A mathematic model of the cardiovascular system simulating left ventricular failure, physical activity, and recovery of cardiac function is used in the simulation. The numerical simulations show that the maximum value of BRS can be found automatically by using ESA. The rotational speed of the pump is automatically increased (from 6500 rpm to 7000 rpm), and peripheral resistance is decreased to simulate slight physical activity. When E(max) is increased from 0.6 mm Hg/mL to 1.8 mm Hg/mL to mimic heart recovery, the speed is decreased from 7000 rpm to 6300 rpm in response. The optimum operating point for the pump can be detected by the proposed control strategy without the need to set a reference value for the control variable by operators.

Hemodynamic Simulation Study of a Novel Intra-Aorta Left Ventricular Assist Device

The intra-aorta pump proposed here is a novel left ventricular assist device (LVAD). The mathematic model and the in vitro experiment demonstrate that the pump can satisfy the demand of human blood perfusion. However, the implantation of LVAD will change the fluid distribution or even generate a far-reaching influence on the aorta. At present, the characteristics of endaortic hemodynamics under the support of intra-aorta pump are still unclear. In this article, a computational fluid dynamics study based on a finite-element method was performed for the aorta under the support of intra-aorta pump. To explore the hemodynamic influence of intra-aorta pump on aorta, fully coupled fluid-solid interaction simulation was used in this study. From the flow profiles, we observed that the maximum disturbed flow and nonuniform flow existed within the aortic arch and the branches of the aortic arch. Flow waveforms at the inlets of aortas were derived from the lumped parameter model that we proposed in our previous study. The results demonstrated that the intra-aorta pump increased the blood flow in the aorta to normal physiologic conditions, but decreased the pulsatility of the flow and pressure. The pulsatility index changed from 2,540 to 1,370. The pressure gradient (PG) for heart failure conditions was 18.88 mm Hg/m vs. 25.51 mm Hg/m for normal physiologic conditions; for intra-aorta pump assist conditions, normal PG value could not be regained. Furthermore, our experimental results showed that the wall shear stress (WSS) of aorta under heart failure and normal physiologic conditions were 1.5 and 6.3 dynes/cm, respectively. The intra-aorta pump increased the WSS value from 1.5 to 4.1 dynes/cm.

Computational Analysis of the Effect of the Control Model of Intraaorta Pump on Ventricular Unloading and Vessel Response

The intraaorta pump is a novel left ventricular assist device (LVAD) whose hemodynamic effects on the circulatory system is unknown. This article aims to evaluate the different effects on the circulatory system supported by the intraaorta pump. In this article, the pump is controlled by three control strategies, including the continuous flow method, the constant rotational speed, and the constant pressure head. A cardiovascular pump system, which includes cardiovascular circulation, intraaorta pump, and regulating mechanisms of systemic circulation, has been proposed. Left ventricle pressure (LVP), end-diastolic volume (EDV), and left ventricular external work (LVEW) were used to evaluate the degree of ventricular unloading. The pulsatile index (PI), which is defined as a ratio of pulse pressure and mean arterial pressure (MAP), was used to evaluate the effect of the vessel response by three control strategies. The comparison results showed that LVP and EDV were lower than those measured before the intraaorta pump was implanted. For LVEW, the constant pressure head strategy provided a superior ventricular unloading compared with other strategies. Support of the pump led to the lower pulsatility by the three models. However, the PI of the constant pressure head was the most at 0.37. In conclusion, these results indicate that the intraaorta pump controlled by constant pressure head strategy provides superior ventricular unloading and pulsatility of the vessel.

A Pulsatile Control Algorithm of Continuous-Flow Pump for Heart Recovery

The intra-aorta pump is a novel continuous flow (CF) left ventricular (LV) device. According to literatures, the pulsatile flow LV device can provide superior LV unloading and circulatory support compared with CF LV assist devices at the same level of ventricular assist device flow. Therefore, a pulsatile control algorithm for the intra-aorta pump is designed. It can regulate the pump to generate pulsatile arterial pressure (AP) and blood flow. A mathematic model of the cardiovascular-pump system is used to verify the feasibility of the control strategy in the presence of LV failure. The surplus hemodynamic energy (SHE), pulsatile ratio (PR), and pulsatile attenuation index (PAI) are used to evaluate the pulsatility of AP and blood flow. The SHE is 8,012.0 ergs/cm(3) by using the pulsatile control strategy (PCS) compared with 5,630.0 ergs/cm(3) by failing heart without support. The PR is 0.302 in the PCS vs. 0.315 in failing heart without support. Meanwhile, the PAI is 85.9% in the PCS compared with 69.7% in failing heart without support. The results demonstrate that the presented control strategy can maintain the pulsatility of AP and blood flow. Moreover, the pulsatile controller provides notably LV unloading. To test the response of the controller to the change of blood demand of patients, another simulation is conducted. In this simulation, the peripheral resistance is reduced to mimic the status of a slight physical active; the Emax is increased to simulate the ventricular contractility recovery. The simulation results demonstrate that the proposed control strategy can automatically regulate the pump in response to the change of the parameters of the circulatory system. To test the dynamic character of the intra-aorta pump, an in vitro experiment is conducted on an in vitro experiment rig. The experimental results demonstrate that the intra-aorta pump can achieve the pulsatile pump speed calculated by the pulsatile controller. The PCS is feasible for the intra-aorta pump. As a key feature, the proposed control strategy provides adequate perfusion in response to the change of blood demands of patients, while restoring the pulsatility of AP and blood flow.

Physiological Control of Intraaorta Pump Based on Heart Rate

Because of the special structures of intraaorta pump, the pressure and blood flow sensors cannot be implanted in the blood pump. Moreover, the cardiovascular pump is a very complex system that has no accurate model but much uncertainty and disturbance. Hence, the conventional control algorithm cannot achieve good performance. To overcome this problem, on one hand, a cardiovascular pump model is established. The heart rate in this model is chosen as a controlled variable that is a nonlinear function of the mean arterial pressure. On the other hand, a fuzzy logic feedback control algorithm, which maintains the actual heart rate tracking the desired heart rate, is designed. Computer simulations are performed to verify the robustness and dynamic characters of the controller. The simulation results demonstrate that the controller can maintain the actual heart rate tracking the desired one without static error. When the desired heart rate changed from 100 to 80 bpm, the settling time is <10 seconds. When the peripheral resistance increases from 1.0 to 0.7 mm Hg/ml, the settling time is <10 seconds.

Modeling and Identification of an Intra-Aorta Pump

The intra-aorta pump is a novel left ventricular assist device (LVAD) that assists the heart without the need for percutaneous wires and conduits. It is implanted between the radix aortae and the aortic arch to avoid damage to the aortic valve. To predict the mean pressure head and blood flow, a nonlinear lumped parameter model, which does not need the parameters of the circulatory system, is established. The model includes a speed-controlled current source, an internal resistor, and an inductance for simulating the pressure-flow rate relationship. The speed-controlled current source is used to represent the blood flow caused by the kinetic energy from the impeller, the internal resistor is used to stimulate the resistance character of the radial clearance of the intra-aorta pump, and the inductance is used to model the inertia of the blood that passes through the radial clearance. Each part of the model has clear physical significance, which is helpful for extending the model to other blood pumps. It can generate all status of the pump from suction to pulmonary congestion. The model is summarized as a function of the pressure head, the blood flow, and rotational speed of which the values of parameters in the model are determined by experiment. The model and prediction method are tested experimentally on an in vitro mock loop. A comparison of the predicted pressure head obtained from our model with experimental data shows that our model can predict the differential pressure accurately with error <5% for all experimental conditions over the entire range of intended use of the intra-aorta pump.

A Global Sliding Mode Controller Design for an Intra-Aorta Pump

Both the intra-aorta pump system and the circulation system are nonlinear systems with external perturbation and internal uncertainty. Classical control methods are suggested for linear systems. Therefore, a global sliding mode controller (GSMC) is reported in this article. A dynamic disturbance compensator was used to estimate the uncertainty of the controlled intra-aorta pump system for eliminating chattering effect. Simulations were performed to verify the robustness and dynamic characters of the controller. Simulation results demonstrate that the chattering effect of the controller output is eliminated. The settling time of step response of flow rate (5 L/min) is 0.08 seconds without overshot or steady-state error. When the load torque step disturbance increases to 0.4 Nm, the settling time of the controlled system is 0.025 seconds. When the desired flow rate is pulsatile flow, the dynamic response time is 0.08 seconds, and the maximum flow rate error is 0.03 L/min. To verify the dynamic character of the GSMC, an experiment was conducted. Because the feedback frequencies of rotational speed and flow rate in the experiment were slower than the ones in the simulation, the performance of the controller deteriorates. The experiment results illustrate that the settling time of step response of flow rate (5 L/min) is 0.26 seconds, and the flow rate error is 0.1 L/min.