A blood assist index control by intraaorta pump: a control strategy for ventricular recovery

A Scalable Approach to Determine Intracardiac Pressure From Mechanical Circulatory Support Device Signals

OBJECTIVE

Effective mechanical circulatory support (MCS) relies on cardiac function measures to guide titration. Left ventricular end diastolic pressure (LVEDP) is a useful measure that is indirectly estimated using pulmonary artery catheters (PACs). PACs require additional intervention and provide intermittent and unreliable estimations. MCS device signals can estimate LVEDP but are prone to inter-device variability and require rigorous specialized characterization. We present a scalable and implementable approach to calculate LVEDP continuously using device signals.

METHODS

LVEDP was calculated from MCS device measured aortic pressure and motor current, which approximates the pressure head between the aorta and left ventricle. This motor current-pressure head relationship is device-specific but approximated using existing flow calibration and assumed physiologic relationships. Performance was evaluated with comparison from direct measurement of LVEDP in a series of acute animal models.

RESULTS

LVEDP measures (n = 178,279) from 18 animals had good correlation (r = 0.84) and calibration (Bland-Altman limits of agreement -7.77 to 7.63 mmHg; mean bias -0.07 ± 0.02 mmHg). The total mean error prediction interval was -3.42 to 3.32 mmHg and RMS error was 3.85 mmHg.

CONCLUSION

LVEDP can be continuously calculated using device signals without specialized characterization. Calculated LVEDP values improved upon PAC estimations and were found using a scalable and manufacturer-accessible method.

SIGNIFICANCE

This method improves upon existing LVEDP measures without the need for rigorous characterization, external calibration, or additional intervention; this allows widescale deployment of continuous LVEDP measurement for patients on MCS and demonstrates key considerations necessary to translate research-grade technologies.

Computational analysis of the hemodynamic characteristics under interaction influence of β-blocker and LVAD

Background

Hemodynamic characteristics of the interaction influence among support level and model of LVAD, and coupling β-blocker has not been reported.

Methods

In this study, the effect of support level and model of LVAD on cardiovascular hemodynamic characteristics is investigated. In addition, the effect of β-blocker on unloading with LVAD is analyzed to elucidate the mechanism of LVAD coupling β-blocker. A multi-scale model from cell level to system level is proposed. Moreover, LVAD coupling β-blocker has been researching to explain the hemodynamics of cardiovascular system.

Results

Myocardial force was decreased along with the increase of support level of LVAD, and co-pulse mode was the lowest among the three support modes. Additionally, the β-blocker combined with LVAD significantly reduced the left ventricular volume compared with LVAD support without β-blocker. However, the left ventricular pressure under both cases has no significant difference. External work of right ventricular was increased along with the growth of support level of only LVAD. The LVAD under co-pulse mode achieved the lowest right-ventricular EW among the three support modes.

Conclusions

Co-pulse mode with β-blocker could be an optimal strategy for promoting cardiac structure and function recovery.

Hemodynamic effects of perfusion level of peripheral ECMO on cardiovascular system

Background

Peripheral ECMO is an effective cardiopulmonary support in clinical. The perfusion level could directly influence the performances and complications. However, there are few studies on the effects of the perfusion level on hemodynamics of peripheral ECMO.

Methods

The geometric model of cardiovascular system with peripheral ECMO was established. The blood assist index was used to classify the perfusion level of the ECMO. The flow pattern from the aorta to the femoral artery and their branches, blood flow rate from aorta to brain and limbs, flow interface, harmonic index of blood flow, wall shear stress and oscillatory shear index were chosen to evaluate the hemodynamic effects of peripheral ECMO.

Results

The results demonstrated that the flow rate of aorta outlets increased and perfusion condition had been improved. And the average flow to the upper limbs and brain has a positive correlation with BAI (r = 0.037, p < 0.05), while there is a negative correlation with lower limbs (r = − 0.054, p < 0.05). The HI has negative correlation with BAI (p < 0.05, r < 0). The blood interface is further from the heart with the BAI decrease. And the average WSS has negative correlation with BAI (p < 0.05, r = − 0.983) at the bifurcation of femoral aorta and has positive correlation with BAI (p < 0.05, r = 0.99) at the inner aorta. The OSI under different BAI is higher (reaching 0.4) at the inner wall of the aortic arch, the descending aorta and the femoral access.

Conclusions

The pathogenesis of peripheral ECMO with different perfusion levels varies; its further research will be thorough and extensive.

Computational Analysis of Intra-Ventricular Flow Pattern Under Partial and Full Support of BJUT-II VAD

Background

Partial support, as a novel support mode, has been widely applied in clinical practice and widely studied. However, the precise mechanism of partial support of LVAD in the intra-ventricular flow pattern is unclear.

Material/Methods

In this study, a patient-specific left ventricular geometric model was reconstructed based on CT data. The intra-ventricular flow pattern under 3 simulated conditions – “heart failure”, “partial support”, and “full support” – were simulated by using fluid-structure interaction (FSI). The blood flow pattern, wall shear stress (WSS), time-average wall shear stress (TAWSS), oscillatory shear index (OSI), and relative residence time (RRT) were calculated to evaluate the hemodynamic effects.

Results

The results demonstrate that the intra-ventricular flow pattern is significantly changed by the support level of BJUT-II VAD. The intra-ventricular vortex was enhanced under partial support and was eliminated under full support, and the high OSI and RRT regions changed from the septum wall to the cardiac apex.

Conclusions

In brief, the support level of the BJUT-II VAD has significant effects on the intra-ventricular flow pattern. The partial support mode of BJUT-II VAD can enhance the intra-ventricular vortex, while the distribution of high OSI and RRT moved from the septum wall to the cardiac apex. Hence, the partial support mode of BJUT-II VAD can provide more benefit for intra-ventricular flow pattern.

The study on hemodynamic effect of series type LVAD on aortic blood flow pattern: a primary numerical study

Background

Left ventricular assist device (LVAD) has become an alternative treatment for end-stage heart failure patients. Series type of LVAD, as a novel LVAD, has attracted more and more attention. The hemodynamic effects of series type LVAD on aortic blood pattern are considered as its important characteristics; however, the precise mechanism of it is still unclear.

Methods

To clarify the hemodynamic effects of series type LVAD on aortic blood flow pattern, a comparative study on the aortic blood flow pattern and hemodynamic states were carried out numerically for two cases, including series type LVAD support and normal condition. The steady-state computational fluid dynamic (CFD) approach was employed. The blood flow streamline, blood velocity vector and distribution of wall shear stress (WSS) were calculated to evaluate the differences of hemodynamic effects between both conditions.

Results

The results demonstrated that the aortic flow pattern under series type LVAD showed significant different from that of normal condition. The strength of aortic swirling flow was significantly enhanced by the series type LVAD support. Meanwhile, the rotating direction of swirling flow under LVAD support was also dominated by the rotating direction of series type LVAD. Moreover, the blood velocity and WSS under LVAD support were also significantly enhanced, compared with that under normal condition.

Conclusion

The hemodynamic states, including the aortic swirling flow characteristic, was significantly dominated by LVAD support. Present investigation could provide not only a useful information on the vascular complications caused by LVAD support, but also provide a useful guide for optimal the structure of the series type LVAD.

The effect of captopril on the performance of the control strategies of BJUT-II VAD

Background

With the development of left ventricular assist device (LVAD), the long-term support has been paid more attention by various researchers. According to previous researches, the combination of LVAD and pharmacological therapy can significantly improve the heart rate recovery and survival rate of patient. However, the effect of pharmacological therapy on the cardiovascular hemodynamic states with LVAD support is still unclear.

Methods

In this study, pharmacokinetic model of captopril is established to describe the relationship between plasma–drug concentration and time. Then, combination model, consisting of pharmacokinetic model of captopril and lumped parameter model of cardiovascular system with BJUT-II VAD support, is established to mimic the effect of pharmacological therapy on cardiovascular hemodynamics. BAI control strategy and HR control strategy for BJUT-II VAD are chosen to evaluate their performance by the combination model.

Results

The simulation results demonstrate that the concentration of captopril could affect the pressure and heart rate by changing the peripheral resistance, and then affect the performance of BJUT-II VAD in a short duration. Under the regulation of control strategies of BJUT-II VAD, the hemodynamic states of cardiovascular system returned to the standard value in 10 s.

Conclusion

This study could provide useful information about how to design coupled strategy of LVAD support and pharmacological therapy.

Effect of Different Rotational Directions of BJUT-II VAD on Aortic Swirling Flow Characteristics: A Primary Computational Fluid Dynamics Study

Background

The BJUT-II VAD is a novel left ventricular assist device (LVAD), which is thought to have significant effects on the characteristics of aortic swirling flow. However, the precise mechanism of the rotational direction of BJTU-II VAD in the aortic swirling flow is unclear.

Material/Methods

A patient-specific aortic geometric model was reconstructed based on the CT data. Three pump’s output flow profiles with varied rotational direction, termed “counterclockwise”, “flat profile”, and “clockwise”, were used as the boundary conditions. The helicity density, area-weighted average of helicity density (Ha), localized normalized helicity (LNH), wall shear stress (WSS), and WSS spatial gradient (WSSG) were calculated to evaluate the swirling flow characteristics in the aorta.

Results

The results demonstrated that the swirling flow characteristics in the aorta and 3 branches are directly affected by the output blood flow of BJUT-II VAD. In the aortic arch, the helicity density, supported by the clockwise case, achieved the highest value. In the 3 branches, the flat profile case achieved the highest helicity density, whereas the maximum WSS and WSSG generated by clockwise case were lower than in other cases.

Conclusions

The outflow of the BJUT-II VAD has significant effects on the aortic hemodynamics and swirling flow characteristics. The helical blood profiles can enhance the strength of aortic swirling flow, and reduce the areas of low WSS and WSSG regions. The clockwise case may have a benefit for preventing development of atherosclerosis in the aorta.

Hemodynamic Differences Between Central ECMO and Peripheral ECMO: A Primary CFD Study

Background

Veno-arterial extracorporeal membrane oxygenation (VAECMO), including central ECMO (cECMO) and peripheral ECMO (pECMO), is widely used in cardiopulmonary surgery. The outcomes and complications of both types of ECMO are quite different from each other. The hemodynamic differences among them are hypothesized as a key factor. Hence, a numerical study was conducted to test this hypothesis.

Material/Methods

Ideal cardiovascular models with pECMO and cECMO were established. The aortic pressure and flow rate were chosen as boundary conditions. The flow pattern, blood flow distributions, flow junction, harmonic index (HI) of blood flow, wall shear stress (WSS), and the oscillatory shear index (OSI) were calculated to evaluate the hemodynamic states.

Results

pECMO could achieve better upper limb and brain perfusion (0.05458 vs. 0.05062 kg/s), and worse lower limb perfusion (0.03067 vs. 0.03401 kg/s). There exist low WSS (<0.4 pa) regions at the inner and posterior wall of the aorta, and high WSS (>2 pa) region at the access of the femoral artery. These regions also have relatively high OSI value (reaching 0.45). In contrast, for cECMO, there exist high WSS at the posterior wall of the aortic arch.

Conclusions

The hemodynamic performances of various types of ECMO are different from each other, which maybe the key reasons for the differences in the outcomes and complications. Therefore, for pEMCO, the lower-extremity ischemia is a complication that must be considered. The type, support level, and duration of ECMO should also be carefully regulated according to the patients’ condition, as they are the important factors related to vascular complications.

The study on hemodynamic effect of varied support models of BJUT-II VAD on coronary artery: a primary CFD study

BJUT-II VAD (Beijing University of Technology ventricular assist device II) is a novel left ventricular assist device. Because of the special connection between the pump and native heart, the hemodynamic effects of BJUT-II VAD on coronary artery are still unclear. Hence, numerical simulations have been conducted to clarify changes in hemodynamic effects of different support modes. A patient-specific left coronary arterial geometric model is reconstructed based on the computed tomography (CT) data. Three support modes, "constant speed mode," "co-pulse mode," and "counter pulse mode," are used in this study. The wall shear stress (WSS), wall shear stress gradient (WSSG), cycle-averaged wall shear stress (avWSS), oscillatory shear index (OSI), and the flow pattern are calculated to evaluate the hemodynamic states of coronary artery. The computational results demonstrate that the hemodynamic states of coronary artery are directly affected by the support modes. The co-pulse modes could achieve the highest blood perfusion (constant speed: 153 ml/min vs. co-pulse: 775 ml/min vs. counter pulse: 140 ml/min) and the highest avWSS (constant speed: 18.1 Pa vs. co-pulse: 42.6 Pa vs. counter pulse: 22.6 Pa). In addition, both the WSS and WSSG at the time of peak blood velocity under the constant speed mode are lower than those under other two support modes. In contrast, the counter pulse mode generates the highest OSI value (constant speed: 0.365 vs. co-pulse: 0.379 vs. counter pulse: 0.426). BJUT-II VAD under co-pulse mode may have benefits for improving coronary perfusion and preventing the development of atherosclerosis; however, the constant speed mode may have benefit for preventing the development of plaque vulnerability.

Hemodynamic effects of various support modes of continuous flow LVADs on the cardiovascular system: a numerical study

Background

The aim of this study was to determine the hemodynamic effects of various support modes of continuous flow left ventricular assist devices (CF-LVADs) on the cardiovascular system using a numerical cardiovascular system model.

Material/Methods

Three support modes were selected for controlling the CF-LVAD: constant flow mode, constant speed mode, and constant pressure head mode of CF-LVAD. The CF-LVAD is established between the left ventricular apex and the ascending aorta, and was incorporated into the numerical model. Various parameters were evaluated, including the blood assist index (BAI), the left ventricular external work (LVEW), the energy of blood flow (EBF), pulsatility index (PI), and surplus hemodynamic energy (SHE).

Results

The results show that the constant flow mode, when compared to the constant speed mode and the constant pressure head mode, increases LVEW by 31% and 14%, and EBF by 21% and 15%, respectively, indicating that this mode achieved the best ventricular unloading among the 3 support modes. As BAI is increased, PI and SHE are gradually decreased, whereas PI of the constant pressure head reaches the maximum value.

Conclusions

The study demonstrates that the continuous flow control mode of the CF-LVAD may achieve the highest ventricular unloading. In contrast, the constant rotational speed mode permits the optimal blood perfusion. Finally, the constant pressure head strategy, permitting optimal pulsatility, should optimize the vascular function.

Development of ventricular assist devices in China: present status, opportunities and challenges

The growing number of heart failure patients and the scarcity of organ donors account for the huge need for the development of mechanical circulatory systems, including ventricular assist devices (VADs) and artificial hearts, in China. Several research programmes on blood pumps have been under way for the last three decades. However, unlike in other countries, the development of VADs has been extremely slow, and no system is currently approved and available for clinical application. There are many reasons for this situation. This article provides an overview of the present development of experimental and clinical research on VADs in China. In addition, the challenges for the clinical development of mechanical circulatory support in China are discussed.

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.

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.