Measurement for implantable rotary blood pumps

Rotary blood pumps offer a cost-effective way to assist the failing heart. Relative to their pulsatile cousins, they can consist of remarkably few moving parts, with attendant advantages in reliability. These advantages are realized in full only if the entire assist system is kept maximally simple. Control of the pump must therefore be based on a minimum number of measurement devices. This paper reviews the measurements that are made in the wide range of implantable rotary blood pump designs that are in development for ventricular assist. In a number of these, fluid-mechanical variables are estimated indirectly from measurements of motor speed and current or power. The introduction explains the goals of rotary blood pump control by comparison to the innate properties of the natural heart. Then motor and fluid-mechanical variables that may be transduced are discussed. Methods of indirect estimation of pressure drop and flow-rate are dealt with, followed by ways of detecting unusual states such as inflow obstruction. It is found that detection of these alone can be the basis of an adequate control strategy. Some groups have estimated variables pertaining to the heart that is being assisted, and there has also been work on monitoring the ongoing health of the assist system itself. The review concludes with a brief look at the wider measurement context for the intensive-care facility that proposes to use such devices to provide circulatory support.