A Starling‐like total work controller for rotary blood pumps: An in vitro evaluation

Abstract

Due to improved durability and survival rates, rotary blood pumps (RBPs) are the preferred left ventricular assist device when compared to volume displacement pumps. However, when operated at constant speed, RBPs lack a volume balancing mechanism which may result in left ventricular suction and suboptimal ventricular unloading. Starling‐like controllers have previously been developed to balance circulatory volumes; however, they do not consider ventricular workload as a feedback and may have limited sensitivity to adjust RBP workload when ventricular function deteriorates or improves. To address this, we aimed to develop a Starling‐like total work controller (SL‐TWC) that matched the energy output of a healthy heart by adjusting RBP hydraulic work based on measured left ventricular stroke work and ventricular preload. In a mock circulatory loop, the SL‐TWC was evaluated using a HeartWare HVAD in a range of simulated patient conditions. These conditions included changes in systemic hypertension and hypotension, pulmonary hypertension, blood circulatory volume, exercise, and improvement and deterioration of ventricular function by increasing and decreasing ventricular contractility. The SL‐TWC was compared to constant speed control where RBP speed was set to restore cardiac output to 5.0 L/min at rest. Left ventricular suction occurred with constant speed control during pulmonary hypertension but was prevented with the SL‐TWC. During simulated exercise, the SL‐TWC demonstrated reduced LVSW (0.51 J) and greater RBP flow (9.2 L/min) compared to constant speed control (LVSW: 0.74 J and RBP flow: 6.4 L/min). In instances of increased ventricular contractility, the SL‐TWC reduced RBP hydraulic work while maintaining cardiac output similar to the rest condition. In comparison, constant speed overworked and increased cardiac output. The SL‐TWC balanced circulatory volumes by mimicking the Starling mechanism, while also considering changes in ventricular workload. Compared to constant speed control, the SL‐TWC may reduce complications associated with volume imbalances, adapt to changes in ventricular function and improve patient quality of life.

In Vivo Evaluation of a Physiologic Control System for Rotary Blood Pumps Based on the Left Ventricular Pressure-Volume Loop

“…Physiologic control algorithms for rotary blood pumps that emulate the Frank–Starling mechanism have been proposed based on preload measurements of end-diastolic volume, 18,19 end-diastolic pressure, 15,20–22 and flow pulsatility. 23 Ochsner et al 21 demonstrated in vivo improved preload response using Starling-like control algorithms as compared to fixed speed control.…”

“…While these algorithms have demonstrated physiologic preload sensitivity, proper control will require tuning the control function to fit patient physiology and adapting the control function to periods of rest or exercise. 15,24 Our control strategy differs from these Starling-like control algorithms in that it does not aim to replicate the Frank-Starling mechanism directly. Instead, our control algorithm aims to maintain a fixed level of ventricular unloading, and therefore, a pre-determined preload function is not required as the control system will adjust pump support in response to right ventricular output.…”

“…The feedback loop responded by increasing pump speed in response to an increase in PGA and decreasing pump speed in response to a decrease in PGA, mimicking the Frank–Starling mechanism. Wu et al 15 proposed a similar control scheme to maintain a target work level based on a function of preload. Their control algorithm has the unique advantage of separating work by the native ventricle (P-V stroke work) with pump work, and therefore, the ratio of pump work to cardiac work could be adapted to weaning conditions as LV contractility improved.…”

Control Strategy Design of a Microblood Pump Based on Heart-Rate Feedback

“…According to the Frank Starling mechanism, some developed pump-flow adaptive controllers adjust pump flow in accordance with changes in left ventricular preload [ 22 , 23 , 24 , 25 ]. Although these kinds of controllers have better performance than constant-speed operation in vivo tests [ 26 , 27 ], pump speed remains constant in the local range when preload remains stable in a certain period of time. Petrou et al [ 28 ] developed a multi-objective physiological control system that was dependent on pump inlet pressure (PIP) and implemented signal processing algorithms to extract features from PIP that can meet various objectives; however, the control method relied on the development of a blood-pressure sensor with good blood compatibility.…”

Improved estimation of left ventricular volume from electric field modeling

“…The advanced monitoring of pressures and flows in the circulation would allow to adapt LVAD therapy to individual needs and reduce adverse events [ 4 , 5 ]. In the past, various control strategies of an LVAD that adapt to the loading conditions of the heart measured by different sensor modalities were studied by several groups [ 6 , 7 , 8 , 9 , 10 , 11 ] without being clinical routine. In general, reliable monitoring of hemodynamics has been shown to reduce rehospitalization [ 12 ].…”