Abstract
A driving unit for artificial hearts has been produced. This unit uses sodium solution for the transmission of force between the power source and the artificial ventricle instead of the commonly used compressed air and thus avoids the danger of an air embolism. The power source of the hydraulic driving unit is an electromagnet; its armature drives a rolling membrane pump (safety chamber) which moves the transmission fluid (sodium solution) to the artificial ventricle (ellipsoid heart). The incompressible connection between the safety chamber and the ellipsoid heart allows direct control of the membrane motion in the ellipsoid heart and of the volume of pumped blood by measuring the armature stroke. The stroke is measured continuously with an optical position sensor; preprogrammable positions determine the systole end and diastole end respectively, so that the membrane need not strike the housing and is not exposed to additional stress. This volume-controlled mode is characterized by automatic selfregulation according to Starling's law. The microcomputer is programmed in a two-level technique. In the interrupt level the solenoid current is calculated according to the operating mode and armature position every 10 ms which is sufficient to simulate continuous operation. In the main-program level every operational parameter (maximum force, systole end, diastole end; systole duration and beat frequency for the frequency-fixing mode) is displayed on the CRT and can be changed via keyboard entry without any interruption in pumping. The durations of systole and diastole, respectively, are determined by the pumping force, the friction in the hydraulic transmission system and the preload and afterload respectively. The preload and afterload can be calculated from a time-force relation without invasive measurements. The driving unit has shown its haemodynamic efficiency in several in vivo experiments and has been running for 8 months in an in vitro durability test.
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