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.     

人工心脏泵辅助对左心室血流动力学影响的数值研究

目的采用数值模拟方法研究人工心脏辅助装置植入对左心室内血流动力学的影响。方法首先利用心血管集中参数模型获取了健康状态、心衰状态以及人工心脏泵辅助状态下收缩末期左心室三维几何模型,其中选取超弹性材料Ogden为心肌材料,以左心房压力,主动脉压力以及通过左心室容积计算获取的左心室壁面位移作为边界条件,利用CFD方法对上述三种情况进行左心室的数值模拟。同时对比了健康时的模拟结果和生理状态下的左心室压力,以及心衰和人工心脏泵辅助两种状态下的血流动力学指标的差别。通过左心室压力和流速等评价灌注和负荷的情况,通过壁面切应力和涡流,评价人工心脏泵辅助后的左心室血流动力学变化规律。结果健康状态下模拟的左心室压力与生理指标相符合。在心衰和人工心脏泵辅助状态下,收缩期内左心室压力与健康状态比分别降低了1718 Pa和8455 Pa,辅助后左心室最大压力下降速度高于心衰时。人工心脏泵辅助后,舒张期壁面切应力峰值由4.3 Pa降低至3.8 Pa,收缩期壁面切应力峰值由4.1 Pa降低至1.3 Pa,射血速度峰值由1.61 m/s降低至0.68 m/s,主动脉瓣开放时间由0.25 s增加至0.65 s,左室射血分数由43.6%增加至52.7%,心室底端漩涡持续时间由0.35 s增加至0.51 s,顶端漩涡出现血流分离。结论左心室压力对比表明本研究方法可以用来模拟左心室的行为。人工心脏泵辅助能够快速降低心室内压力和心室负荷,增加灌注时间,提高器官灌注,降低左心室壁面切应力以及提高左心室内血液流场的涡流强度,延长涡流持续时间。     

In vitro evaluation of the PUCA II intra-arterial LVAD

The "pulsatile catheter" (PUCA) pump is a minimally invasive intra-arterial left ventricular assist device intended for acute support of critically ill heart failure patients. To assess the hydrodynamic performance of the PUCA II, driven by an Arrow AutoCat IABP driver, we used a (static) mock circulatory system in which the PUCA II was tested at different loading conditions. The PUCA II was subsequently introduced in a (dynamic) cardiovascular simulator (CVS) to mimic actual in vivo operating conditions, with different heart rates and 2 levels of left ventricular (LV) contractility. Mock circulation data shows that PUCA II pump performance is sensitive to afterload, pump rate and preload. CVS data demonstrate that PUCA II provides effective LV unloading and augments diastolic aortic pressure. The contribution of PUCA II to total flow is inversely related to LV contractility and is higher at high heart rates. We conclude that, with the current IABP driver, the PUCA II is most effective in 1:1 mode in left ventricles with low contractility.     

Continuous Left Ventricular Ejection Fraction Monitoring by Aortic Pressure Waveform Analysis

We developed a technique to monitor left ventricular ejection fraction (EF) by model-based analysis of the aortic pressure waveform. First, the aortic pressure waveform is represented with a lumped parameter circulatory model. Then, the model is fitted to each beat of the waveform to estimate its lumped parameters to within a constant scale factor equal to the arterial compliance (C _a). Finally, the proportional parameter estimates are utilized to compute beat-to-beat absolute EF by cancelation of the C _a scale factor. In this way, in contrast to conventional imaging, EF may be continuously monitored without any ventricular geometry assumptions. Moreover, with the proportional parameter estimates, relative changes in beat-to-beat left ventricular end-diastolic volume (EDV), cardiac output (CO), and maximum left ventricular elastance (E _max) may also be monitored. To evaluate the technique, we measured aortic pressure waveforms, reference EF and EDV via standard echocardiography, and other cardiovascular variables from six dogs during various pharmacological influences and total intravascular volume changes. Our results showed overall EF and calibrated EDV root-mean-squared-errors of 5.6% and 4.1 mL, and reliable estimation of relative E _max and beat-to-beat CO changes. These results demonstrate, perhaps for the first time, the feasibility of estimating EF from only a blood pressure waveform.     

老年大鼠模型视网膜血管改变及视网膜中央动脉血流变化的高分辨率超声图像检测

背景：视网膜对缺血非常敏感,所以眼部血流动力学的改变可直接影响眼的功能,目前评估眼部血液循环可借助多种仪器设备。 目的：应用高分辨率小动物超声影像系统检测视网膜中央动脉的血流动力学变化,结合视网膜血管消化铺片技术检测视网膜血管结构变化,以明确老年大鼠视网膜中央动脉血流动力学的变化规律。 方法：使用高分辨率小动物超声影像系统测量老年大鼠和青年大鼠及视网膜中央动脉的血流参数,包括收缩期峰值血流速度、舒张末期血流速度,计算搏动指数、阻力指数和收缩期舒张期血流速度比值。同时使用视网膜血管消化铺片技术检测视网膜血管形态学改变。 结果与结论：与青年大鼠组相比,老年组大鼠视网膜血管内皮细胞增生,排列紊乱,管径增粗,血管壁不光滑;视网膜中央动脉血流速度、舒张末期血流速度均降低(P < 0.01),计算搏动指数、阻力指数及收缩期峰值与舒张末期血流速度比值则升高(P < 0.01)。说明使用高分辨率小动物超声影像系统检测视网膜中央动脉收缩期和舒张期峰值速度及阻力指数能较敏感地反映血管的老化过程。     

Arterial pulsatility improvement in a feedback-controlled continuous flow left ventricular assist device: An ex-vivo experimental study

Continuous flow left ventricular assist devices (CF-LVADs) reduce arterial pulsatility, which may cause long-term complications in the cardiovascular system. The aim of this study is to improve the pulsatility by driving a CF-LVAD at a varying speed, synchronous with the cardiac cycle in an ex-vivo experiment. A Micromed DeBakey pump was used as CF-LVAD. The heart was paced at 140 bpm to obtain a constant cardiac cycle for each heartbeat. First, the CF-LVAD was operated at a constant speed. At varying-speed CF-LVAD assistance, the pump was driven such that the same mean pump output was generated. For synchronization purposes, an algorithm was developed to trigger the CF-LVAD each heartbeat. The pump flow rate was selected as the control variable and a reference model was used for regulating the CF-LVAD speed. Continuous and varying-speed CF-LVAD assistance provided the same mean arterial pressure and flow rate, while the index of pulsatility doubled in both arterial pressure and pump flow rate signals under pulsatile pump speed support. This study shows the possibility of improving the pulsatility in CF-LVAD support by regulating pump speed over a cardiac cycle without compromising the overall level of support.     

Hemodynamic modes of ventricular assist with a rotary blood pump: continuous, pulsatile, and failure

Pulsatile operation of rotary blood pumps (RBPs) has received interest due to potential concern with nonphysiological hemodynamics. This study aimed to gain insight to the effects of various RBP modes on the heart-device interaction. A Deltastream diagonal pump (Medos Medizintechnik GmbH) was inserted in a cardiovascular simulator with apical-to-ascending aorta cannulation. The pump was run in continuous mode with incrementally increasing rotating speed (0-5000 rpm). This was repeated for three heart rates (50-100-150 bpm) and three levels of left ventricular (LV) contractility. Subsequently, the Deltastream was run in pulsatile mode to elucidate the effect of (de)synchronization between heart and pump. LV volume and pressure, arterial pressure, flows, and energetic parameters were used to evaluate the interaction. Pump failure (0 rpm) resulted in aortic pressure drops (17-46 mm Hg) from baseline. In continuous mode, pump flow compensated by diminished aortic flow, thus yielding constant total flow. High continuous rotating speed resulted in acute hypertension (mean aortic pressure up to 178 mm Hg). In pulsatile mode, unmatched heart and pulsatile pump rates yielded unphysiologic pressure and flow patterns and LV unloading was found to be highly dependent on synchronization phase. Optimal unloading was achieved when the minimum rotating speed occurred at end-systole. We conclude that, in continuous mode, a perfusion benefit can only be achieved if the continuous pump flow exceeds the preimplant (baseline) cardiac output. Pulsatile mode of support results in complex pressure and volume variations and requires accurate triggering to achieve optimal unloading.     

In vitro evaluation of left ventricular assistance by cannulation of both femoral arteries

The possibility of achieving effective mechanical ventricular assistance without the need for thoracotomy provides great clinical advantages. Two in vitro systems were used to assess left ventricular unloading by means of a small-diameter cannula inserted retrograde into the left ventricle by cannulation of the femoral artery. This cannula is connected to the inlet of a centrifugal blood pump (CP) that delivers the blood into the contralateral femoral artery. Steady-flow test circulation was used to pump fluid in a closed loop from a reservoir through the test cannula back into the reservoir. Pressure drops over cannulae with inner diameters of 4, 5, 6, 7, and 8 mm at flows of 2, 2.5, 3 L/min, against a pressure of 60, 80, 100, and 120 mmHg were calculated. A stationary pressure drop of 120 mmHg was measured at a flow of 3 L/min through a 100 cm cannula with an inner diameter of 6 mm. The second system was a pulsatile mock circulation composed of an atrial and an arterial reservoir linked by a pneumatic prosthetic ventricle. This system was coupled with a 100 cm cannula, 6.1 mm inner diameter, which was passed across the outflow valve of the pulsatile prosthetic ventricle and connected to a CP. Fluid was withdrawn from the ventricle and pumped back into the arterial reservoir. Pulsatile pressure drop over the cannula was measured at different CP flows for increasing systolic ventricular pressure; heart unloading was quantified as a function of CP flow under baseline and failing conditions of the prosthetic left ventricle model. At a constant CP flow the pressure drop over the cannula increased with the pulsatility inside the ventricle. The work of the prosthetic ventricle was reduced by more than 50% when the CP pump was set to 3 L/min; at the same flow setting, when the situation of a failing left ventricle was simulated, the CP was able to take over all the work of the prosthetic ventricle, establishing a stationary flow and a 25% higher mean aortic pressure. This approach to left ventricular assistance may have significant clinical relevance.     

In vitro evaluation of an axial flow pump: mock-pump interaction and an approach to control

Continuous flow pump support has emerged as an alternative therapy in patients with congestive heart failure. For long-term applications, it is important to have a control system that changes the pump function according to the physiological conditions of the patient, thereby preventing risk situations. In the early stages of development, the evaluation of control algorithms for artificial blood pumps can be done in vitro using cardiovascular mock systems. A systemic cardiovascular mock loop was constructed and an axial flow pump was connected to it. The level of pump assistance was estimated using a pulsatility index (IPAo) obtained from the aortic pressure wave. An IPAo proportional-integral control system was implemented and its responses to peripheral resistance and systemic compliance changes were evaluated. IPAo is an indicator of the assistance level of a continuous flow pump operated at constant speed. The IPAo control algorithm responds by increasing the pump speed when peripheral resistance or systemic compliance is reduced. Control system operation around an IPAo fixed value provides a safety point for pump operation by maintaining aortic pressure pulsatility and avoiding ventricular suction. In vitro experimental results show that the IPAo can be taken into consideration in multiobjective control algorithm designs.     

In vitro evaluation of the performance of Korean pulsatile ECLS (T-PLS) using precise quantification of pressure-flow waveforms

The Twin-Pulse Life Support System (T-PLS) is a novel pulsatile extracorporeal life support system developed in Korea. It has been reported that the T-PLS achieves higher levels of tissue perfusion of the kidney during short-term extracorporeal circulation and provides more blood flow to coronary artery than nonpulsatile blood pumps. However, these results lack pulsatility quantifications and thus make it hard to analyze the effects of pulsatility upon hemodynamic performance. We have adopted the concepts of hemodynamic energy, energy equivalent pressure (EEP), and surplus hemodynamic energy (SHE) to evaluate pulsatility performance in the different circuit configurations of the T-PLS and a membrane oxygenator (MO) in vitro. In a mock system, three different circuits were constructed depending on the location of an MO: pump-MO-pump (serial), MO-pumps (parallel A), and pumps-MO (parallel B). In parallel A, a low-resistance MO was used to preserve the pulsatility from the pump. All circuits showed good pulsatility in terms of EEP (serial: 13.2% +/- 3.2%, parallel A: 10.0% +/- 1.6%, parallel B: 7.00% +/- 1.1%; change from aortic pressure to EEP; p < 0.003). The SHE levels were 17,404 +/- 3750 ergs/cm3, 13,170 +/- 1486 ergs/cm3, and 9192 +/- 1122 ergs/cm3 in each circuit setup (p < 0.001). Although EEP levels were somewhat lower, both parallel types provided higher pump output compared with the serial type (serial: 1.87 +/- 0.29 l/min, parallel A: 3.09 +/- 0.74 l/min, parallel B: 3.06 +/- 0.56 l/min; p < 0.003 except parallel A vs. parallel B, p = 0.90). Conclusively, the precise quantifications of pressure flow waveforms, EEP, and SHE are valuable tools for evaluating pulsatility of the mechanical circulatory devices, and are expected to be used as additional performance indexes of a blood pump. The pulsatility performances are different according to circuit setups. However, the parallel A circuit could achieve higher pump output and generate adequate pulsatility level. Thus, the parallel A circuit is suggested as the optimal configuration in T-PLS applications.     

The enabler cannula pump: a novel circulatory support system.

BACKGROUND: The enabler circulatory support system is a catheter pump which expels blood from the left or right ventricular cavity and provides pulsatile flow in the ascending aorta or pulmonary artery. It is driven by a bedside installed pulsatile driving console. The device can easily be implanted by a minimal invasive approach, similar to the Hemopump. PURPOSE: To demonstrate the hemodynamic performance of this new intracardiac support system. METHODS: In a series of 9 sheep, hemodynamic evolutions were recorded in various conditions of myocardial contractility (the non-failing, the moderately failing and the severely failing heart). Heart failure was induced by injection of microspheres in the coronary arteries. RESULTS: Introduction of the cannula through the aortic valve was feasible in all cases. Pump flow by the enabler was gradually increased to a maximum of 3.5 L/min. Diastolic (and mean) aortic blood pressure is significantly increased in the non-failing and moderately failing condition (counterpulsation mode). In heart failure, cardiac output is significantly increased by the pump (p < 0.0001). A drop in left atrial pressure (indicating unloading) is achieved in all conditions but reaches significant levels only during heart failure (p=0.0068). CONCLUSIONS: This new circulatory support system contributes to stabilization of the circulation in the presence of cardiac unloading. In heart failure it actually supports the circulation by increasing cardiac output and perfusion pressure.     

Circulatory depression and ventricular arrhythmias induced by compound 48/80 in anaesthetized rats

The effects of graded doses of compound 48/80 on various cardiovascular and respiratory parameters were studied in pentobarbitone-anaesthetized rats. Following intravenous injections, this compound significantly depressed the mean blood pressure (MBP), left ventricular pressure (LVP) and d_LVP/dt_max, and caused ventricular tachycardia (VT) or fibrillation (VF) and death. Heart rate (HR) response were variable, and there were no marked changes in airway resistance or blood gases. Pretreatment of the animals with either cimetidine or diphenhydramine significantly prolonged the time of onset of VT/VF but failed to alter the changes in other circulatory variables. A combination of cimetidine and diphenhydramine significantly alleviated the decreases in MBP and LVP and prevented the occurrence of VT/VF. It is suggested that the circulatory depression and the occurrence of ventricular arrhythmias following the administration of compound 48/80 result from activation of H₁- and H₂-receptors by elevated blood histamine levels due to release of the amine from tissues.     

A computer model of the pediatric circulatory system for testing pediatric assist devices

Lumped parameter computer models of the pediatric circulatory systems for 1- and 4-year-olds were developed to predict hemodynamic responses to mechanical circulatory support devices. Model parameters, including resistance, compliance and volume, were adjusted to match hemodynamic pressure and flow waveforms, pressure-volume loops, percent systole, and heart rate of pediatric patients (n = 6) with normal ventricles. Left ventricular failure was modeled by adjusting the time-varying compliance curve of the left heart to produce aortic pressures and cardiac outputs consistent with those observed clinically. Models of pediatric continuous flow (CF) and pulsatile flow (PF) ventricular assist devices (VAD) and intraaortic balloon pump (IABP) were developed and integrated into the heart failure pediatric circulatory system models. Computer simulations were conducted to predict acute hemodynamic responses to PF and CF VAD operating at 50%, 75% and 100% support and 2.5 and 5 ml IABP operating at 1:1 and 1:2 support modes. The computer model of the pediatric circulation matched the human pediatric hemodynamic waveform morphology to within 90% and cardiac function parameters with 95% accuracy. The computer model predicted PF VAD and IABP restore aortic pressure pulsatility and variation in end-systolic and end-diastolic volume, but diminish with increasing CF VAD support.     

Endothelium-dependent vasodilation and structural and functional changes in the cardiovascular system are dependent on age in healthy subjects.

The aim of this study was to evaluate possible associations between endothelium-dependent vasodilatation (EDV) and cardiovascular structure and function. EDV could influence peripheral resistance and be affected by atherosclerosis and might thereby influence indices of cardiovascular structure and function. In a group of 31 apparently healthy men and 25 women (age range 20-69 years), EDV was evaluated by infusion of metacholine (4 micrograms min-1), and endothelium-independent vasodilatation (EIDV) was assessed by nitroprusside infusion (SNP, 10 micrograms min-1) in the brachial artery. Forearm blood flow (FBF) was measured by venous occlusion plethysmography. Left ventricular (LV) geometry and function and the intima-media thickness in the carotid artery were assessed by ultrasonography. The stroke index to pulse pressure ratio was used to evaluate arterial compliance. Several indices of cardiovascular structure and function were found to be related to an index of endothelial function, the EDV to EIDV ratio. Furthermore, left ventricular mass (LVM), the atrio-ventricular plane displacement, E/A ratio, IVRT, the intima-media thickness of the carotid artery and arterial compliance were all significantly related to both EDV and EIDV in women. However, most indices of cardiovascular structure and function, as well as endothelial function, change with age and only the relation between LV diastolic function and endothelial function in men remained significant (P < 0.05) after including age in multiple regression analysis. Age was related to both cardiovascular structure and function, as well as to endothelial function. Multiple regression analysis showed that ageing generally affects cardiovascular characteristics and endothelial function in parallel in these healthy subjects.     

Development and evaluation of endurance test system for ventricular assist devices

We developed a novel endurance test system that can arbitrarily set various circulatory conditions and has durability and stability for long-term continuous evaluation of ventricular assist devices (VADs), and we evaluated its fundamental performance and prolonged durability and stability. The circulation circuit of the present endurance test system consisted of a pulsatile pump with a small closed chamber (SCC), a closed chamber, a reservoir and an electromagnetic proportional valve. Two duckbill valves were mounted in the inlet and outlet of the pulsatile pump. The features of the circulation circuit are as follows: (1) the components of the circulation circuit consist of optimized industrial devices, giving durability; (2) the pulsatile pump can change the heart rate and stroke length (SL), as well as its compliance using the SCC. Therefore, the endurance test system can quantitatively reproduce various circulatory conditions. The range of reproducible circulatory conditions in the endurance test circuit was examined in terms of fundamental performance. Additionally, continuous operation for 6 months was performed in order to evaluate the durability and stability. The circulation circuit was able to set up a wide range of pressure and total flow conditions using the SCC and adjusting the pulsatile pump SL. The long-term continuous operation test demonstrated that stable, continuous operation for 6 months was possible without leakage or industrial device failure. The newly developed endurance test system demonstrated a wide range of reproducible circulatory conditions, durability and stability, and is a promising approach for evaluating the basic characteristics of VADs.     

各种辅助泵对心室功能恢复的影响

应用自制隔膜泵、非捕动流叶轮泵和捕动流叶轮泵,以及临床应用的美国Ｓａｒｎｓ转子泵分别在迷你猪和小公牛身上做左心室或双心室辅助试验。结果显示搏动流泵在自然心脏衰竭时能维持动物主动脉压的搏动特性,从而降低周身而增加血流循环流量,而叶轮泵及转子泵因没有瓣膜返流能提高动物主动脉舒张压,增加自 脏冠状动脉灌注,因此搏动流叶轮泵对于衰竭心脏功能的恢复,最为有利。     

模拟心血管系统装置的研制及其在血液动力学测试中的应用

为研究心血管系统血液动力学特性和评测人工心脏,本文根据弹性腔模型建立了一套能反映血液动力学特性的体外血液循环模拟实验装置,测试血液动力学参量与心室后负荷(即外周阻力R和动脉顺应性C)以及每搏心输出量Vs,心动周期T,心室收缩时间间隔Ts和前负荷等六个参量之间的相互关系,通过改变六个参量的某一个参量而固定其余参量,测试这个参量对动脉血压及流量的影响情况.实验结果与生理情况和数学模型分析相符合,整个模拟装置能够反映血液动力学特性.     

Analysis of the relationship between left ventricular pressure and motor current for evaluation of native cardiac function during left ventricular support with a centrifugal blood pump

Control of the ventricular assist device (VAD) for native heart preservation should be attempted, and the VAD could be one strategy for dealing with the shortage of donors in the future. In the application of nonpulsatile blood pumps for ventricular assistance from the ventricular apex to the aorta, bypass flow and hence the motor current of the pumps change in response to the ventricular pressure change. Utilizing these intrinsic characteristics of the continuous-flow pumps, in this study we investigated whether motor current could be used as an index for continuous monitoring of native cardiac function. In study 1, a centrifugal blood pump (CFP) VAD was installed between the apex and descending aorta of a mock circulatory loop. In this model, a baseline with a preload of 10 mmHg, afterload of 40 mmHg, and LV systolic pressure of 40 mmHg was used. The pump speed was fixed at 1300, 1500, and 1700 rpm, and LV systolic pressure was increased up to 140 mmHg by steps of 20 mmHg while the changes in LV pressure, motor current, pump flow, and aortic pressure were observed. In study 2, an in vivo experiment was performed using three sheep. A left heart bypass model was created using a centrifugal pump from the ventricular apex to the descending aorta. The LVP was varied through administration of dopamine while the changes in LV pressure, pump flow, and motor current at 1500 and 1700 rpm were observed. An excellent correlation was observed in both in vitro and in vivo studies in the relationship between motor current and LV pressure. In study 1, the correlation coefficients were 0.77, 0.92, and 0.99 for 1300, 1500, and 1700 rpm, respectively. In study 2, they were 0.88 (animal no. 1), 0.83 (animal no. 2), and 0.88 (animal no. 3) for 1500 rpm, and 0.95 (animal no. 2) and 0.93 (animal no. 3) for 1700 rpm. These results suggest that motor current amplitude monitoring could be useful as an index for the control of VAD for native heart preservation.     

体外模拟心血管系统血液动力学性能分析

为研究人工心脏和心血管系统之间的血液动力学作用机制．根据弹性腔模型建立了一套能反映血液动力学特性的体外血液循环模拟实验装置，测试血液动力学参量与心室后负荷（即外周力R和动脉顺应性C）以及每搏心输出量Vs，心动周期T和心室收缩时间间隔Ts，前负荷等六个参量之间的相互关系．通过改变六个参量中的某一个参量而固定其余参量，测试这个参量对动脉血压及流量的影响情况。实验结果与生理情况和数学模型分析相符合。压力和流量波呈脉动性，与真实生理波形相似。整个模拟装置能够反映血液动力学特性。     

Physiologic control of rotary blood pumps: an in vitro study

Rotary blood pumps (RBPs) are currently being used as a bridge to transplantation as well as for myocardial recovery and destination therapy for patients with heart failure. Physiologic control systems for RBPs that can automatically and autonomously adjust the pump flow to match the physiologic requirement of the patient are needed to reduce human intervention and error, while improving the quality of life. Physiologic control systems for RBPs should ensure adequate perfusion while avoiding inflow occlusion via left ventricular (LV) suction for varying clinical and physical activity conditions. For RBPs used as left ventricular assist devices (LVADs), we hypothesize that maintaining a constant average pressure difference between the pulmonary vein and the aorta (deltaPa) would give rise to a physiologically adequate perfusion while avoiding LV suction. Using a mock circulatory system, we tested the performance of the control strategy of maintaining a constant average deltaPa and compared it with the results obtained when a constant average pump pressure head (deltaP) and constant rpm are maintained. The comparison was made for normal, failing, and asystolic left heart during rest and at light exercise. The deltaPa was maintained at 95 +/- 1 mm Hg for all the scenarios. The results indicate that the deltaPa control strategy maintained or restored the total flow rate to that of the physiologically normal heart during rest (3.8 L/m) and light exercise (5.4 L/m) conditions. The deltaPa approach adapted to changing exercise and clinical conditions better than the constant rpm and constant deltaP control strategies. The deltaPa control strategy requires the implantation of two pressure sensors, which may not be clinically feasible. Sensorless RBP control using the deltaPa algorithm, which can eliminate the failure prone pressure sensors, is being currently investigated.