An Indirect Monitoring System for Controlling Rotor Blood Pumps

Abstract

IntroductionRotor blood pumps (RBP) have been extensively used in clinics during the last decade for mechanical sup port of heart activity. This is due to the reduction of RBP size and weight, increased service life, and decreased RBP cost as compared to pulsation pumps.RBP control is mediated solely by pump rotor rota tion rate. The RBP used in clinics provides a stabilization scheme of rotor rotation rate.The parameters of RBP are: head, run off, and con sumed power. These parameters are determined by rotor rotation rate (according to counter EMF signals) and blood viscosity. Pump power is determined as a product of pump current multiplied by power source voltage. Pump head is monitored using pressure sensors installed on input and output hoses. Run off rate is monitored using special liquid flow rate sensors.Pressure sensors should not contact blood as this contact decreases sensor sensitivity because of protein deposits on the sensor membrane. Such contact also increases probability of thrombosis. The use of run off rate sensors is also counterproductive as it increases sys tem weight and size and decreases system reliability. Thus, information about pump parameters should be obtained directly from the pump. There are various meth ods of determination of hemodynamic parameters: pres sure drop monitoring and run off rate measurement.Pump parameters, such as rotor rotation rate, consumed power, motor current and power source voltage, can be used for this purpose.The goal of this work was to develop biotechnical indirect monitoring system (BTS) for controlling rotor blood pumps (RBP) providing adequate pump operation under physiological conditions. BTS Structure for RBP ControlDuring the development of RBP control systems the mode of pump operation was adapted not only to changes in the patient's physical activity, but also to the necessity to limit its operation under extreme conditions (upper and lower productivity limits).The basic requirements to RBP control system are: -determining minimal allowable rate of rotor rota tion. Blood flow is reversed at lower rate;-determining maximal allowable rate of rotor rota tion. Left ventricle develops rarefaction and cardiac chambers are collapsed at rotation rate above this level; -maintaining RBP rotation rate at optimal level according to physiological needs.The BTS structure for RBP control is shown in Fig. 1. In Fig. 1 elements of the microcontroller are shown as a dashed line; MCMS stands for elements of the microcontroller measuring system; MCCU stands for microcontroller control unit; n c and n r stand for current and required values of rotor rotation rate, respectively.The measuring system monitors pump current and rotor rotation rate. The MCMS data is transmitted to the control system for rotation rate correction. RBP sensors Control of rotor blood pumps by rotor rotation rate should be adapted to the requirements of the patient's body. Physiological control of rotor blood pumps is based on information about the blood circulation system. The sen sors should no...

Bench Tests of an Implantable Axial Blood Pump

“…Pump voltage U P , V, and pump current I P , A, of set rotation rate N 3 , rpm, and actual rotation rate N A , rpm, were monitored using an extracorporeal control unit [4,5]. U P and I P measuring error was ±3%; N A , ±3 rpm.…”