Operating point control system for a continuous flow artificial heart: in vitro study

Noninvasive blood-flow meter using a curved cannula with zero compensation for an axial flow blood pump

In order to monitor the condition of a patient using a left ventricular assist system (LVAS), blood flow should be measured. However, the reliable determination of blood-flow rate has not been established. The purpose of the present study is to develop a noninvasive blood-flow meter using a curved cannula with zero compensation for an axial flow blood pump. The flow meter uses the centrifugal force generated by the flow rate in the curved cannula. Two strain gauges served as sensors. The first gauges were attached to the curved area to measure static pressure and centrifugal force, and the second gauges were attached to straight area to measure static pressure. The flow rate was determined by the differences in output from the two gauges. The zero compensation was constructed based on the consideration that the flow rate could be estimated during the initial driving condition and the ventricular suction condition without using the flow meter. A mock circulation loop was constructed in order to evaluate the measurement performance of the developed flow meter with zero compensation. As a result, the zero compensation worked effectively for the initial calibration and the zero-drift of the measured flow rate. We confirmed that the developed flow meter using a curved cannula with zero compensation was able to accurately measure the flow rate continuously and noninvasively.

Physiological control of an in-series connected pulsatile VAD: numerical simulation study

This paper investigates ventricular assist device (VAD)-assisted cardiovascular dynamics under proportion-integration-differentiation (PID) feedback control. Previously, we have studied the cardiovascular responses under the support of an in-series connected reciprocating-valve VAD through numerical simulation, and no feedback control was applied in the VAD. In this research, we explore the contribution of the VAD control on the circulatory dynamics assisted by the reciprocating-valve VAD, in response to the changing physiological conditions. The classical PID control algorithm is implemented to regulate the VAD stroke beat-to-beat, based on the error signal between the expected and the realistic mean aortic pressures. Simulation results show that under the PID VAD control, physiological variables such as left atrial, ventricular and systemic arterial pressures, cardiac output and ventricular volumes are satisfactorily maintained in the physiological ranges. With the online PID feedback control, operation of the reciprocating-valve VAD can be satisfactorily regulated to accommodate metabolic requirements under various physiological conditions including normal resting and exercise situations.

Computational modelling and evaluation of cardiovascular response under pulsatile impeller pump support

This study presents a numerical simulation of cardiovascular response in the heart failure condition under the support of a Berlin Heart INCOR impeller pump-type ventricular assist device (VAD). The model is implemented using the CellML modelling language. To investigate the potential of using the Berlin Heart INCOR impeller pump to produce physiologically meaningful arterial pulse pressure within the various physiological constraints, a series of VAD-assisted cardiovascular cases are studied, in which the pulsation ratio and the phase shift of the VAD motion profile are systematically changed to observe the cardiovascular responses in each of the studied cases. An optimization process is proposed, including the introduction of a cost function to balance the importance of the characteristic cardiovascular variables. Based on this cost function it is found that a pulsation ratio of 0.35 combined with a phase shift of 200° produces the optimal cardiovascular response, giving rise to a maximal arterial pulse pressure of 12.6 mm Hg without inducing regurgitant pump flow while keeping other characteristic cardiovascular variables within appropriate physiological ranges.

Minimal Sensor Count Approach to Fuzzy Logic Rotary Blood Pump Flow Control

A rotary blood pump fuzzy logic flow controller without flow sensors was developed and tested in vitro. The controller, implemented in LabView, was set to maintain a flow set point in the presence of external pressure disturbances. Flow was estimated as a function of measured pump's delta P and speed, using a steady-state, nonlinear approximation. The fuzzy controller used the pump's flow estimate and delta P as feedback variables. The defuzzified control output manipulated the pump speed. Membership functions included flow error, delta P, and pump speed. Experimental runs in a mock loop (water/glycerin 3.5 cPs, 37 degrees C), using the estimated flow, were compared with those using a Transonic flow meter for nine conditions of flow and delta P (4 to 6 L/min, 150 to 350 mm Hg). Pressure disturbances generated by a servo pinch valve ranged from +/-23 to +/-47 mm Hg. Results indicated that the fuzzy controller ably regulated the flow set point to within +/-10% of the baseline even under large swings in pressure. There was no difference in controller performance between the ultrasonic flow measurement and the estimated flow calculation scenarios. These tests demonstrated that the fuzzy controller is capable of rejecting disturbances and regulating flow to acceptable limits while using a flow estimate.

Hemodynamic characteristics of a mixed flow pump prototype: progress report of in vitro and acute animal experiments

A new dual-inlet mixed-flow blood pump was designed and tested in our laboratory. The objective of the present study was to analyze hemodynamic characteristics of the pump prototype in vitro and during acute in vivo experiments. The mixed-flow pump was first tested in vitro and then implanted in 11 pigs and 3 calves. The left ventricular apex was cannulated with the pump and an outflow graft was anastomosed to the descending thoracic aorta. Flow and pressure probes were also implanted. Animals were killed 3 to 12 hours after surgery. In 11 pigs, pump outflow averaged 3.8 +/- 0.4, 4.5 +/- 0.4, 5.2 +/- 0.8, 5.9 +/- 0.3, and 6.5 l/min at 8,000, 9,000, 10,000, 11,000, and 12,000 pump speed in rpm. Differential pressure at the pump averaged 45 +/- 6, 54 +/- 8, 68 +/- 16, 70 +/- 12, and 85 +/- 7 mm Hg at 8,000, 9,000, 10,000, 11,000 and 12,000 rpm. Mean aortic pressure averaged 64 +/- 15 mm Hg throughout the procedures. In 3 calves, mean aortic pressure and left ventricular pressure remained stable during 4, 6, and 9 hours of support at 9,500, 10,000, 10,500, 11,000, and 11,500 rpm. The hemodynamic performance of our mixed-flow pump appears satisfactory during short-term support in animals. It supports similarly to axial-flow blood pumps in clinical trials. Based on these findings, an ameliorated design of this mixed-flow pump running at smaller rotational speed against a similar pressure head is under way.