Sensorless estimation of inlet pressure in implantable rotary blood pump for heart failure patients

Abstract

A dynamical model for mean inlet pressure estimation in an implantable rotary blood pump is proposed. Noninvasive measurements of pump motor power (P), pulse width modulation, and impeller rotational speed (v) were used as inputs to the model. Linear regression analysis between estimated and measured inlet pressures obtained from in vivo greyhound data (N ¼ 3) resulted in a highly significant correlation (R 2 ¼ 0.957) and a mean absolute error (e) of 2.292 mmHg. Furthermore, the proposed model was stable which allowed accurate study and estimation of the transient response and the dynamics of the pump inlet pressure (P in ).Introduction: The shortage of donor organs for heart transplantation has led to a variety of treatment options for heart failure patients. Implantable rotary blood pumps (IRBPs) are emerging not only as a bridge to the transplant option but also as a means of long-term support.Noninvasive estimation of hemodynamic parameters of an IRBP plays a crucial role in designing an automatic, robust and responsive noninvasive control system that effectively copes with the body's physiological demands and perturbations. The implantation of additional sensors is not a preferred option as they result in thrombus formation and require regular calibration owing to measurement drifts. A stable dynamical model for noninvasive estimation of pulsatile flow and differential pressure in an IRBP was proposed and verified in [1]. The proposed model was also used to design a control algorithm for continuous and pulsatile flow [2]. A parameter-optimised model for the cardiovascular system assisted by an IRBP was verified in [3].The problem of noninvasive estimation of inlet pressure (P in ) in an IRBP has not been frequently studied, possibly because of its highly variable nature especially during abnormal pumping states such as ventricular collapse where, for example, the inlet pressure (P in ) during the diastolic period in VentrAssist TM (Ventracor Limited, Sydney, Australia) left ventricular assist device (LVAD) may be as low as 2160 mmHg, and varies between +10 mmHg during normal pump operation. During diastole, inlet pressure (P in ) and left ventricular (LV) end diastolic pressure, i.e. preload to the LV, are closely related. In normal humans, the operation of the heart satisfies the FrankStarling mechanism, i.e. the stroke volume depends on LV end diastolic volume. Therefore, one design requirement of IRBPs is to simulate the Frank-Starling law. On the other hand, in heart failure patients with an LV assisted by an IRBP, when the volume in the LV is low, inlet pressure (P in ) will automatically decrease and this may cause suction if the same target speed were to be maintained. To ensure patient safety, a control system that effectively detects and thus avoids such undesired pumping states is needed. This shows one example that makes the noninvasive estimation of inlet pressure of utmost importance for a pump control strategy. For instance, the proposed model could provide a definitive input for a controller t...

Developments in control systems for rotary left ventricular assist devices for heart failure patients: a review

“…Suction would be avoided with both these strategies. For the first time, in our laboratory, we used non-invasive measurements of ω, P, together with the pulse-width modulation signal (PWM) as inputs to a novel dynamical ARX model to estimate average inlet pressure during the diastolic period (AlOmari et al 2010(AlOmari et al , 2011a.The resulting model is stable and simple, thus offering a tractable control design solution. The average diastolic inlet pressure estimation model was validated using in vivo animal data obtained from acute implantation of a VentrAssist TM LVAD in greyhound dogs (N = 3) under wide ranges of speed ramp studies performed under different operating conditions which includes healthy, variations in heart contractility by administration of a beta blocker (metoprolol), systemic vascular resistance by administration of metaraminol or sodium nitroprusside, and by varying the total blood volume.…”

Optimal control of permanent-magnet motor for pulsatile axial blood pump applications

“…For the assistant artificial heart, the requirement of flow is 4-6 L/min and requirement of pressure is 40-80 mmHg [11]. Fig.1 shows the experimental axial blood pump, in which the permanent-magnet motor is adopted in order to achieve high power density and high efficiency.…”