Circulatory Assist Project

The Circulatory Assist project is a collaboration between the Clinic for Cardiovascular Surgery (University Hospital Zurich), the Clinic for Cardiovascular Surgery (University Hospital Bern), and the Institute for Dynamic Systems and Control (ETH Zurich). This project aims at improving the control strategies for Ventricular Assist Devices (VADs).

Overview

The main purpose of VADs is to provide a sufficient blood perfusion to the body. In most cases, this is achieved by parallel operation of the heart and the VAD, i.e the inflow graft of the VAD is connected to the left ventricle and the outflow graft is connected to the aorta.
Two different types of VADs are in clinical use nowadays, namely pulsatile and continuous flow VADs. The former use pressurized air to inflate and deflate a blood sac for pumping. The latter use electric motors to drive centrifugal or axial turbines.

Therapy Concepts

VADs are used in three different therapy concepts: Bridge-to-transplant (BTT), destination therapy (DT), and bridge-to-recovery (BTR). Originally, VADs were developed for BTT, i.e. if the heart of a patient on a transplantation list is too weak to sufficiently supply the body with blood, the circulation of the patient is supported by a VAD until a donor heart is available. Because BTT has made the shortage of donor hearts only more pronounced, the other therapy concepts have soon been developed. DT stands for implantation of a VAD for the rest of the patient’s life. BTR aims at recovery of the patient’s own heart, such that the VAD can be explanted after a certain time. Each of the three concepts imposes its own requirements on the VAD such that ideally different VAD systems are developed specifically for the therapy they will be used for.

Goals of the Project

The focus of this project is on systems for BTR. The following steps are necessary for improving the performance of VADs with respect to recovery:
(1) Analysis of the human physiology, the VAD and their interaction using mathematical models
(2) Identification of parameters that can be used as measures for cardiac recovery
(3) Definition of suitable control strategies that facilitate recovery
(4) Development of advanced monitoring and parameter estimation methods that enable implementation of the derived control strategies.
(5) Determination of possible mechanical improvements compared to existing VADs that meet the defined requirements
The first step is to analyze and solve the challenges in silico, i.e. in computer simulation. The derived solutions are then tested in vitro, i.e. on a highly dynamic blood pump test bench.