Physiological control of a rotary blood pump with selectable therapeutic options: control of pulsatility gradient

A control strategy for rotary blood pumps meeting different user-selectable control objectives is proposed: maximum support with the highest feasible flow rate versus medium support with maximum ventricular washout and controlled opening of the aortic valve (AoV). A pulsatility index (PI) is calculated from the pressure difference, which is deduced from the axial thrust measured by the magnetic bearing of the pump. The gradient of PI with respect to pump speed (GPI) is estimated via online system identification. The outer loop of a cascaded controller regulates GPI to a reference value satisfying the selected control objective. The inner loop controls the PI to a reference value set by the outer loop. Adverse pumping states such as suction and regurgitation can be detected on the basis of the GPI estimates and corrected by the controller. A lumped-parameter computer model of the assisted circulation was used to simulate variations of ventricular contractility, pulmonary venous pressure, and aortic pressure. The performance of the outer control loop was demonstrated by transitions between the two control modes. Fast reaction of the inner loop was tested by stepwise reduction of venous return. For maximum support, a low PI was maintained without inducing ventricular collapse. For maximum washout, the pump worked at a high PI in the transition region between the opening and the permanently closed AoV. The cascaded control of GPI and PI is able to meet different control objectives and is worth testing in vitro and in vivo.     

Hemodynamic controller for left ventricular assist device based on pulsatility ratio

Hemodynamic control of left ventricular assist devices (LVADs) is generally a complicated problem due to diverse operating environments and the variability of the patients: both the changes in the circulatory and metabolic parameters as well as disturbances that require adjustment to the operating point. This challenge is especially acute with control of turbodynamic blood pumps. This article presents a pulsatility ratio controller for LVAD that provides a proper perfusion according to the physiological demands of the patient, while avoiding adverse conditions. It utilizes the pulsatility ratio of the flow through the pump and pressure difference across the pump as a control index and adjusts the pump speed according to the reference pulsatility ratio under the different operating conditions. The simulation studies were performed to evaluate the controller in consideration of the sensitivity to afterload and preload, influence of the contractility, and effect of suction sensitivity. The controller successfully adjusts the pump speed according to the reference pulsatility ratio, and supports the natural heart under diverse pump operating conditions. The resulting safe pump operations demonstrate the solid performance of the controller in terms of sensitivity to afterload and preload, influence of the contractility, and effect of suction sensitivity.     

Safety-enhanced optimal control of turbodynamic blood pumps

A safety-enhanced optimal (SEO) control algorithm for turbodynamic blood pump is proposed. Analysis of in vivo animal experimental data reveals that two new control indices-the gradient of pulsatility of pump pressure head with respect to pump speed and the gradient of minimum pump flow-have their peak within a proximity to the suction point but not at the exact suction point. They were also verified to satisfy the requirement of cost function for the extremum seeking control (ESC). New cost functions were tested for ESC to find and track the new operating point--SEO operating point--where sufficient cardiac perfusion and safety margin to suction is guaranteed. By computer simulation, it is confirmed that the SEO operating point was successfully found and tracked in both fixed and varying hemodynamic load scenarios using proposed control indices without resorting to a slope seeking control algorithm where the reference slope must be supplied.     

Theoretical Foundations of a Starling-Like Controller for Rotary Blood Pumps

A clinically intuitive physiologic controller is desired to improve the interaction between implantable rotary blood pumps and the cardiovascular system. This controller should restore the Starling mechanism of the heart, thus preventing overpumping and underpumping scenarios plaguing their implementation. A linear Starling‐like controller for pump flow which emulated the response of the natural left ventricle (LV) to changes in preload was then derived using pump flow pulsatility as the feedback variable. The controller could also adapt the control line gradient to accommodate longer‐term changes in cardiovascular parameters, most importantly LV contractility which caused flow pulsatility to move outside predefined limits. To justify the choice of flow pulsatility, four different pulsatility measures (pump flow, speed, current, and pump head pressure) were investigated as possible surrogates for LV stroke work. Simulations using a validated numerical model were used to examine the relationships between LV stroke work and these measures. All were approximately linear (r² (mean ± SD) = 0.989 ± 0.013, n = 30) between the limits of ventricular suction and opening of the aortic valve. After aortic valve opening, the four measures differed greatly in sensitivity to further increases in LV stroke work. Pump flow pulsatility showed more correspondence with changes in LV stroke work before and after opening of the aortic valve and was least affected by changes in the LV and right ventricular (RV) contractility, blood volume, peripheral vascular resistance, and heart rate. The system (flow pulsatility) response to primary changes in pump flow was then demonstrated to be appropriate for stable control of the circulation. As medical practitioners have an instinctive understanding of the Starling curve, which is central to the synchronization of LV and RV outputs, the intuitiveness of the proposed Starling‐like controller will promote acceptance and enable rational integration into patterns of hemodynamic management.     

Motor Feedback Physiological Control for a Continuous Flow Ventricular Assist Device

The response of a continuous flow magnetic bearing supported ventricular assist device, the CFVAD3 (CF3) to human physiologic pressure and flow needs is varied by adjustment of the motor speed. This paper discusses a model of the automatic feedback controller designed to develop the required pump performance. The major human circulatory, mechanical, and electrical systems were evaluated using experimental data from the CF3 and linearized models developed. An open-loop model of the human circulatory system was constructed with a human heart and a VAD included. A feedback loop was then closed to maintain a desired reference differential pressure across the system. A proportional-integral (PI) controller was developed to adjust the motor speed and maintain the system reference differential pressure when changes occur in the natural heart. The effects of natural heart pulsatility on the control system show that the reference blood differential pressure is maintained without requiring CF3 motor pulsatility.     

Effect of parameter variations on the hemodynamic response under rotary blood pump assistance

Numerical models, able to simulate the response of the human cardiovascular system (CVS) in the presence of an implantable rotary blood pump (IRBP), have been widely used as a predictive tool to investigate the interaction between the CVS and the IRBP under various operating conditions. The present study investigates the effect of alterations in the model parameter values, that is, cardiac contractility, systemic vascular resistance, and total blood volume on the efficiency of rotary pump assistance, using an optimized dynamic heart-pump interaction model previously developed in our laboratory based on animal experimental measurements obtained from five canines. The effect of mean pump speed and the circulatory perturbations on left and right ventricular pressure volume loops, mean aortic pressure, mean cardiac output, pump assistance ratio, and pump flow pulsatility from both the greyhound experiments and model simulations are demonstrated. Furthermore, the applicability of some of the previously proposed control parameters, that is, pulsatility index (PI), gradient of PI with respect to pump speed, pump differential pressure, and aortic pressure are discussed based on our observations from experimental and simulation results. It was found that previously proposed control strategies were not able to perform well under highly varying circulatory conditions. Among these, control algorithms which rely on the left ventricular filling pressure appear to be the most robust as they emulate the Frank-Starling mechanism of the heart.     

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/cm⁵) and pulmonary (PVR ～200–1000 dyne/s/cm⁵) 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.     

Physiological Control of Dual Rotary Pumps as a Biventricular Assist Device Using a Master/Slave Approach

Dual rotary left ventricular assist devices (LVADs) can provide biventricular mechanical support during heart failure. Coordination of left and right pump speeds is critical not only to avoid ventricular suction and to match cardiac output with demand, but also to ensure balanced systemic and pulmonary circulatory volumes. Physiological control systems for dual LVADs must meet these objectives across a variety of clinical scenarios by automatically adjusting left and right pump speeds to avoid catastrophic physiological consequences. In this study we evaluate a novel master/slave physiological control system for dual LVADs. The master controller is a Starling‐like controller, which sets flow rate as a function of end‐diastolic ventricular pressure (EDP). The slave controller then maintains a linear relationship between right and left EDPs. Both left/right and right/left master/slave combinations were evaluated by subjecting them to four clinical scenarios (rest, postural change, Valsalva maneuver, and exercise) simulated in a mock circulation loop. The controller's performance was compared to constant‐rotational‐speed control and two other dual LVAD control systems: dual constant inlet pressure and dual Frank–Starling control. The results showed that the master/slave physiological control system produced fewer suction events than constant‐speed control (6 vs. 62 over a 7‐min period). Left/right master/slave control had lower risk of pulmonary congestion than the other control systems, as indicated by lower maximum EDPs (15.1 vs. 25.2–28.4 mm Hg). During exercise, master/slave control increased total flow from 5.2 to 10.1 L/min, primarily due to an increase of left and right pump speed. Use of the left pump as the master resulted in fewer suction events and lower EDPs than when the right pump was master. Based on these results, master/slave control using the left pump as the master automatically adjusts pump speed to avoid suction and increases pump flow during exercise without causing pulmonary venous congestion.     

Hemodynamic Response to Exercise and Head‐Up Tilt of Patients Implanted With a Rotary Blood Pump: A Computational Modeling Study

The present study investigates the response of implantable rotary blood pump (IRBP)‐assisted patients to exercise and head‐up tilt (HUT), as well as the effect of alterations in the model parameter values on this response, using validated numerical models. Furthermore, we comparatively evaluate the performance of a number of previously proposed physiologically responsive controllers, including constant speed, constant flow pulsatility index (PI), constant average pressure difference between the aorta and the left atrium, constant average differential pump pressure, constant ratio between mean pump flow and pump flow pulsatility (ratio_PI or linear Starling‐like control), as well as constant left atrial pressure control, with regard to their ability to increase cardiac output during exercise while maintaining circulatory stability upon HUT. Although native cardiac output increases automatically during exercise, increasing pump speed was able to further improve total cardiac output and reduce elevated filling pressures. At the same time, reduced venous return associated with upright posture was not shown to induce left ventricular (LV) suction. Although control outperformed other control modes in its ability to increase cardiac output during exercise, it caused a fall in the mean arterial pressure upon HUT, which may cause postural hypotension or patient discomfort. To the contrary, maintaining constant average pressure difference between the aorta and the left atrium demonstrated superior performance in both exercise and HUT scenarios. Due to their strong dependence on the pump operating point, PI and ratio_PI control performed poorly during exercise and HUT. Our simulation results also highlighted the importance of the baroreflex mechanism in determining the response of the IRBP‐assisted patients to exercise and postural changes, where desensitized reflex response attenuated the percentage increase in cardiac output during exercise and substantially reduced the arterial pressure upon HUT.     

Use of a Novel Diagonal Pump in an In Vitro Neonatal Pulsatile Extracorporeal Life Support Circuit

One approach with the potential to improve morbidity and mortality rates following extracorporeal life support (ECLS) is the use of pulsatile perfusion. Currently, no ECLS pumps used in the United States can produce pulsatile flow. The objective of this experiment is to evaluate a novel diagonal pump used in Europe to determine whether it provides physiological pulsatility in a neonatal model. The ECLS circuit consisted of a Medos Deltastream DP3 diagonal pump, a Hilite 800LT polymethylpentene diffusion membrane oxygenator, and arterial/venous tubing. A 300‐mL pseudopatient was connected to the circuit using an 8Fr arterial cannula and a 10Fr venous cannula. A clamp maintained constant pressure entering the pseudopatient. Trials (64 total) were conducted in nonpulsatile and pulsatile modes at flow rates of 200 mL/min to 800 mL/min. Flow and pressure data were collected using a custom‐based data acquisition system. The Deltastream DP3 pump was capable of producing an adequate quality of pulsatility. Pulsatile flow produced increased mean arterial pressure, energy equivalent pressure (EEP), and surplus hemodynamic energy (SHE) at all flow rates compared to nonpulsatile flow. Pressure drop across the cannula accounted for the majority of pressure loss in the circuit. The greatest loss of SHE and total hemodynamic energy occurred across the arterial cannula due to its small diameter. The Deltastream DP3 pump produced physiological pulsatile flow without backflow while providing EEP and SHE to our neonatal pseudopatient. Further experiments are necessary to determine the impact of this pulsatile pump in an in vivo model prior to clinical use.     

In Vitro Performance Analysis of a Novel Pulsatile Diagonal Pump in a Simulated Pediatric Mechanical Circulatory Support System

The objective of this study was to evaluate the pump performance of the third‐generation Medos diagonal pump, the Deltastream DP3, on hemodynamic profile and pulsatility in a simulated pediatric mechanical circulatory support (MCS) system. The experimental circuit consisted of a Medos Deltastream DP3 pump head and console (MEDOS Medizintechnik AG, Stolberg, Germany), a 14‐Fr Terumo TenderFlow Pediatric arterial cannula and a 20‐Fr Terumo TenderFlow Pediatric venous return cannula (Terumo Corporation, Tokyo, Japan), and 3 ft of tubing with an internal diameter of in. for both arterial and venous lines. Trials were conducted at flow rates ranging from 250 mL/min to 1000 mL/min (250‐mL/min increments) and rotational speeds ranging from 1000 to 4000 rpm (1000‐rpm increments) using human blood (hematocrit 40%). The postcannula pressure was maintained at 60 mm Hg by a Hoffman clamp. Real‐time pressure and flow data were recorded using a Labview‐based acquisition system. The pump provided adequate nonpulsatile and pulsatile flow, created more hemodynamic energy under pulsatile mode, and generated higher positive and negative pressures when the inlet and outlet of the pump head, respectively, were clamped. After the conversion from nonpulsatile to pulsatile mode, the flow rates and the rotational speeds increased. In conclusion, the novel Medos Deltastream DP3 diagonal pump is able to supply the required flow rate for pediatric MCS, generate adequate quality of pulsatility, and provide surplus hemodynamic energy output in a simulated pediatric MCS system.     

Effect of Pressure-Flow Relationship of Centrifugal Pump on In Vivo Hemodynamics: A Consideration for Design

Abstract We have been developing centrifugal pumps for an implantable left ventricular assist device. We manufactured 2 prototype centrifugal pumps (PI, PII). These two have similar designs except for the PII having a volute casing and a large output port. To determine the differences in the hydraulic characteristics between the PI and PII, we carried out in vitro and in vivo experiments. In vitro study showed that the PII had a shallower H-Q curve than that of the PI, and the PII required a pump speed faster than the PI for the same flow rate and pressure head. On the other hand, in vivo study showed that the PII demonstrated a flow pulsatility greater than that of the PI at 1,900 rpm and 8 L/min although no significant change was observed at low pump speeds (≤1,500 rpm). This greater pulsatility consisted of a large discharge according to the small differential pressure during the systolic phase and a small discharge according to the large differential pressure during the diastolic phase. In contrast, the PI, having the steeper H-Q curve, showed a small discharge in the systolic phase and a large discharge in the diastolic phase. These results showed that pulsatility synchronized with the native heart beating depended on the slope of the H-Q curve. As a result, the slope of the H-Q curve is important to determine the component of pulsatility synchronized with native cardiac output. Regarding the slope of the H-Q curve, a pump having a volute casing and a large outlet port demonstrates a shallow slope in the H-Q curve. In conclusion, we suggest that a centrifugal pump for use in left ventricular aortic bypass should be designed considering the effect on the native heart pulsatility.     

In Vitro Hydrodynamic Analysis of Pin and Cone Bearing Designs of the Jarvik 2000 Adult Ventricular Assist Device

The Jarvik 2000 adult ventricular assist device (VAD) is a second‐generation blood pump with mechanical contact bearings. The original configuration of the pump employed a pin bearing and a more recent configuration uses a cone bearing. We compare the hydrodynamic performance of the two designs under steady‐state and pulsatile flow conditions in vitro. Furthermore, we employ the Intermittent Low Speed (ILS) Flowmaker Controller to demonstrate the effect on pulsatility index (PI) performance of both device configurations. We use an open‐loop flow system in both steady‐state and pulsatile arrangements, complete with pressure transducers and flow probes. Working fluid was a 3.6 cP blood‐analog, glycerin‐water solution. Steady‐state flow tests were carried out to determine pressure‐flow (H‐Q) performance curves. Pulsatile tests under normotensive, hypertensive, and hypotensive conditions were executed with controller speed 3 (10 710 ± 250 rpm) at 100 beats per minute. Steady‐state tests show greater capacity for pressure and flow with the cone bearing, compared with pin bearing, with best efficiency point (BEP) 68% greater for cone bearing. Pulsatile tests show the cone bearing design to yield a 20% increase in Q_avg, a 17% decrease in pulsatility index (PI_Q), and a qualitative increase in pressure responsivity. The ILS mode (for both bearing designs) decreases Q_avg by 68% and likewise increases PI_Q by 360% and pulsatility ratio (R_pul) by 200%. The ILS controller regularly reduces the flow, increasing pulsatility index during device operation. The Jarvik 2000 continuous‐flow VAD can sustain pulsatile flow under pulsating pressure conditions. The new cone bearing design yields increased flow rates over the earlier pin bearing design.     

An anti-suction control for an intra-aorta pump using blood assistant index: a numerical simulation

With the extensive use of the left ventricular assist device (LVAD) as a treatment of heart failure, suction detection has become a key issue that directly affects the treatment. To detect the phenomenon of suction, a blood assistant index (BAI) is defined, which reflects the unloading level of the pump. The BAI is a ratio of the external work of LVAD and the input power of cardiovascular system. Using the theory of model‐free adaptive control algorithm, an anti‐suction controller, which chooses the heart rate and BAI as control variables, is designed. As a key feature, the proposed control algorithm adjusts the pump speed according to not only the blood demand of circulatory system but also the function of the native heart. Subsequently, the performance and robustness of the controller are evaluated using a numerical simulation of the assisted circulation and an in vitro experiment. The simulation and experimental results demonstrate that the BAI detects the suction occur accurately, and the controller can maintain the heart rate and BAI tracking the reference values with a response time of less than 6 s.     

Electrocardiogram-synchronized rotational speed change mode in rotary pumps could improve pulsatility

Continuous-flow left ventricular assist devices (LVADs) have greatly improved the prognosis of patients with end-stage heart failure, even if continuous flow is different from physiological flow in that it has less pulsatility. A novel pump controller of continuous-flow LVADs has been developed, which can change its rotational speed (RS) in synchronization with the native cardiac cycle, and we speculated that pulsatile mode, which increases RS just in the systolic phase, can create more pulsatility than the current system with constant RS does. The purpose of the present study is to evaluate the effect of this pulsatile mode of continuous-flow LVADs on pulsatility in in vivo settings. Experiments were performed on eight adult goats (61.7 ± 7.5 kg). A centrifugal pump, EVAHEART (Sun Medical Technology Research Corporation, Nagano, Japan), was installed by the apex drainage and the descending aortic perfusion. A pacing lead for the detection of ventricular electrocardiogram was sutured on the anterior wall of the right ventricle. In the present study, we compared pulse pressure or other parameters in the following three conditions, including Circuit-Clamp (i.e., no pump support), Continuous mode (constant RS), and Pulsatile mode (increase RS in systole). Assist rate was calculated by dividing pump flow (PF) by the sum of PF and ascending aortic flow (AoF). In continuous and pulsatile modes, these assist rates were adjusted around 80-90%. The following three parameters were used to evaluate pulsatility, including pulse pressure, dp/dt of aortic pressure (AoP), and energy equivalent pulse pressure (EEP = (∫PF*AoP dt)/(∫PF dt), mm Hg). The percent difference between EEP and mean AoP is used as an indicator of pulsatility, and normally it is around 10% of mean AoP in physiological pulse. Both pulse pressure and mean dp/dt max were decreased in continuous mode compared with clamp condition, while those were regained by pulsatile mode nearly to clamp condition (pulse pressure, clamp/continuous/pulsatile, 25.0 ± 7.6/11.7 ± 6.4/22.6 ± 9.8 mm Hg, mean dp/dt max, 481.9 ± 207.6/75.6 ± 36.2/351.1 ± 137.8 mm Hg/s, respectively). In clamp condition, %EEP was 10% higher than mean AoP (P = 0.0078), while in continuous mode, %EEP was nearly equivalent to mean AoP (N.S.). In pulsatile mode, %EEP was 9% higher than mean AoP (P = 0.038). Our newly developed pulsatile mode of continuous-flow LVADs can produce pulsatility comparable to physiological pulsatile flow. Further investigation on the effect of this novel drive mode on organ perfusion is currently ongoing.     

Exercise Studies in Patients With Rotary Blood Pumps: Cause,Effects, and Implications for Starling‐Like Control of Changes in Pump Flow

This multicenter study examines in detail the spontaneous increase in pump flow at fixed speed that occurs in exercise. Eight patients implanted with the VentrAssist rotary blood pump were subjected to maximal and submaximal cycle ergometry studies, the latter being completed with patients supine and monitored with right heart catheter and echocardiography. Maximal exercise studies conducted in each patient at three different pump speeds on separate days established initially the magnitude and consistency of increases in pump flow that correlated well with changes in heart rate. However, there was considerable variation, coefficients of variation for mean heart rate and pump flow being 47.9 and 49.3%, respectively. Secondly, these studies indicated that increasing pump flows caused significant improvements in maximal exercise capacity. An increase of 2.1 L/min (35%) in maximum blood flow caused 12 W (16%) further increase in achievable work, 1.26 (9.3%) mL/kg/min in maximal oxygen uptake, and 2.3 (23%) mL/kg/min in anaerobic threshold. Mean increases in lactate were 0.85 mm (24%), but mean B‐type natiuretic peptide fell by 126 mm , (?78%). From submaximal supine exercise studies, multiple linear regression of pump flow on factors thought to underlie the spontaneous increase in pump flow indicated that it was associated with increases in heart rate (P = 0.039), pressure gradient across the left ventricle (P = 0.032), and right atrial pressure (P = 0.003). These changes have implications for the recently reported Starling‐like controller for pump flow based on pump pulsatility values, which emulates the Starling curve relating pump output to left ventricular preload. Unmodified, the controller would not permit the full benefits of this effect to be afforded to patients implanted with rotary blood pumps. A modification to the pump control algorithm is proposed to eliminate this problem     

Numerical Simulation of Nonpulsatile Left Ventricular Bypass

Abstract: A computer simulation was carried out to investigate the influence of nonpulsatile left ventricular assistance on hemodynamics. A simulation circuit was constructed to represent the circulatory system. A source of current was added to denote the nonpulsatile blood pump. The left and right ventricles were replaced by variable compliances. Left heart failure was simulated by decreasing the amount of compliance change of the left ventricle. We introduced a pulsatility indicator (PI) to clarify the pulsatility characteristics in the hemodynamics; this PI was defined as the ratio of the pulse pressure (PP) to the mean aortic pressure (AoP). When nonpulsatile bypass flow increased, the mean AoP, tension time index (TTI), and diastolic pressure time index (DPTI) increased, and cardiac output, PP, and PI decreased. When assisted flow increased with the constant total flow rate, the mean AoP and DPTI changed little; the PP, TTI, and PI decreased, and the endocardial viability rate increased. The PI would be helpful in evaluating the effect of pulsatility.     

Evaluation of Conventional Nonpulsatile and Novel Pulsatile Extracorporeal Life Support Systems in a Simulated Pediatric Extracorporeal Life Support Model

The objective of this study is to evaluate two extracorporeal life support (ECLS) circuits and determine the effect of pulsatile flow on pressure drop, flow/pressure waveforms, and hemodynamic energy levels in a pediatric pseudopatient. One ECLS circuit consisted of a Medos Deltastream DP3 diagonal pump and Hilite 2400 LT oxygenator with arterial/venous tubing. The second circuit consisted of a Maquet RotaFlow centrifugal pump and Quadrox‐iD Pediatric oxygenator with arterial/venous tubing. A 14Fr Medtronic Bio‐Medicus one‐piece pediatric arterial cannula was used for both circuits. All trials were conducted at flow rates ranging from 500 to 2800 mL/min using pulsatile or nonpulsatile flow. The post‐cannula pressure was maintained at 50 mm Hg. Blood temperature was maintained at 36°C. Real‐time pressure and flow data were recorded using a custom‐based data acquisition system. The results showed that the Deltastream DP3 circuit produced surplus hemodynamic energy (SHE) in pulsatile mode at all flow rates, with greater SHE delivery at lower flow rates. Neither circuit produced SHE in nonpulsatile mode. The Deltastream DP3 pump also demonstrated consistently higher total hemodynamic energy at the pre‐oxygenator site in pulsatile mode and a lesser pressure drop across the oxygenator. The Deltastream DP3 pump generated physiological pulsatility without backflow and provided increased hemodynamic energy. This novel ECLS circuit demonstrates suitable in vitro performance and adaptability to a wide range of pediatric patients.     

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.     

Left and Right Pump Output Control in One-Piece Electromechanical Total Artificial Heart

Abstract: Left master alternate (LMA) ejection control based on the left pump fill method was implemented for a one-piece electromechanical total artificial heart (TAH). The TAH consists of left and right pusher-plate-type blood pumps sandwiching a compact electromechanical actuator comprising a direct current (DC) brushless motor and a planetary roller screw. The motor rotation is controlled on the basis of the roller-screw position as detected by a Hall effect sensor and a commutation pulse-counting method. Since the pusher-plate shaft and roller screw are decoupled during filling, both pumps fill passively with the right and left atrial pressure. To obtain response to the right atrial pressure change in the LMA mode, the left fill trigger level as detected by a Hall effect position sensor is adjusted to operate the pump at a higher rate and to drive the right pump at 85–90% of the full stroke level. The invitro evaluation demonstrated that this method can respond to right atrial pressure changes provided that the right pump is operated at less than the full stroke level. When the preload is high and the right pump goes into full stroke operation, the left eject level can be decreased to run the pump at a higher rate and to transfer more blood from the right to the left. In the in vivo evaluation, which lasted 1 week in a 95 kg calf, the left and right atrial pressures were kept within physiological ranges. The LMA mode triggered by the left pump fill can protect the lungs and can also respond to venous return change and therefore is a reliable control method for a one-piece to-tally implantable TAH system.