CONTROL FOR MYOCARDIUM CONTACTING PERICARDIAC ASSIST DEVICES

Abstract

A pericardiac assist device requires control over the level of force applied to the heart and the six ot the assist device around the heart. Variable assistance is also desirable, for example, increasing the level of assistance when the level of exercise increases. Also required is a stable operation and smooth transitions between contact and non-contacting phases. An impedance controller was developed, utilising a force and position control strategy. The applied force to the heart is monitored, if the stiffness parameter within the impedance controller is high then the desired trajectory is followed closely and thus the heart is assisted. If the stiffness parameter is small, the desired trajectory will be adjusted such that the heart is not assisted. It is through constant updating of the stiffness coefficient that variable assistance can be provided, beat by beat. By assessing the expected amount of work required and the stiffness coefficient for the next cycle, the level of assistance is obtained. Control performance is evaluated through the assist device acting upon pneumatic sacks of varying compliance. Heart rates between 60 to 120b/min were used and peak pressure varied from 90–1 70mmHg. Outflow and pressure were recorded allowing the level of assistance to be evaluated. Three conditions were simulated, a failing heart, a weak heart during rest and a weak heart during exercise. A contractile band was able to provide approximately 10% assistance whilst meeting main criteria, hence impedance controller is suitable.