In Vitro Comparison of Active and Passive Physiological Control Systems for Biventricular Assist Devices

Abstract

The low preload and high afterload sensitivities of rotary ventricular assist devices (VADs) may cause ventricular suction events or venous congestion. This is particularly problematic with rotary biventricular support (BiVAD), where the Starling response is diminished in both ventricles. Therefore, VADs may benefit from physiological control systems to prevent adverse events. This study compares active, passive and combined physiological controllers for rotary BiVAD support with constant speed mode. Systemic (SVR) and pulmonary (PVR) vascular resistance changes and exercise were simulated in a mock circulation loop to evaluate the capacity of each controller to prevent suction and congestion and increase exercise capacity. All controllers prevented suction and congestion at high levels of PVR (900 dynes s cm(-5)) and SVR (3000 dynes s cm(-5)), however these events occurred in constant speed mode. The controllers increased preload sensitivity (0.198-0.34 L min(-1) mmHg(-1)) and reduced afterload sensitivity (0.0001-0.008 L min(-1) mmHg(-1)) of the VADs when compared to constant speed mode (0.091 and 0.072 L min(-1) mmHg(-1) respectively). The active controller increased pump speeds (400-800 rpm) and pump flow by 2.8 L min(-1) during exercise, thus increasing exercise capacity. By reducing suction and congestion and by increasing exercise capacity, the control systems presented in this study may help increase quality of life of VAD patients.

In Vivo Evaluation of Active and Passive Physiological Control Systems for Rotary Left and Right Ventricular Assist Devices

“…Additionally, a second-order Butterworth low pass filter with a cut-off frequency of 0.1 Hz was used for smoothing the pressure and flow signals. 25 5 45 −3.5 KP, proportional gain; KI, integral gain; θ, sensitivity of master controller; a, patient-specific offset of master controller; α, sensitivity of the slave controller; c, patient-specific offset of the slave controller.…”

In vitro evaluation of an adaptive Starling‐like controller for dual rotary ventricular assist devices

“…Physiological controllers have been designed to automatically adjust VAD speed and, therefore, flow to meet the varying patient cardiac demand, thereby restoring flow balance and reducing the likelihood of over‐ or under‐pumping. Several review papers outlining and comparing different physiological controllers have demonstrated that Starling‐like control (SLC) of VADs, which uses measured LV end‐diastolic pressure () as a preload indicator, consistently outperforms other physiological control systems . An SLC consists of two components, a control line (CL) which emulates the native cardiac response curve, and a return path, which emulates the native venous return.…”

“…Several review papers outlining and comparing different physiological controllers have demonstrated that Starlinglike control (SLC) of VADs, which uses measured LV enddiastolic pressure (P LVED ) as a preload indicator, consistently outperforms other physiological control systems. [7][8][9][10][11] An SLC consists of two components, a control line (CL) which emulates the native cardiac response curve, and a return path, which emulates the native venous return. When combined, the CL and return path can be used to accurately predict the required VAD flow for a given patient state.…”

The Effect of Compliant Inflow Cannulae on the Hemocompatibility of Rotary Blood Pump Circuits in an In Vitro Model

“…Flow and pressure estimators (sensor‐less approach) may be used to overcome the limitation of sensor‐based controllers; however, changes in RBP circuits, such as the formation of thrombus, may introduce error into estimations and lead to an inaccurate controller . Our group recently developed a novel, passive control strategy to overcome some of the limitations of active control systems in the form of a compliant inflow cannula (IC) . The compliant IC is essentially a flexible section of tubing placed at the RBP inlet which passively restricts the internal diameter as preload decreases, thus increasing RBP inflow resistance and reducing RBP Q and avoiding ventricular suction events.…”

“…The compliant IC is essentially a flexible section of tubing placed at the RBP inlet which passively restricts the internal diameter as preload decreases, thus increasing RBP inflow resistance and reducing RBP Q and avoiding ventricular suction events. In vitro and in vivo studies demonstrated the ability of the compliant IC to increase preload sensitivity of RBPs and mitigate incidences of ventricular suction during variations in systemic and pulmonary vascular resistance, exercise and passive postural changes . Nevertheless, the evaluation of the compliant IC for RBP therapy is incomplete without investigating its ability to minimize the imminent problem associated with shear‐induced hemolysis.…”