ABSTRACT
In previous works, a non-linear equation describing variable area (VA) flowmeters in transient was presented. The use of a full nonlinear equation, despite giving accurate results, can be difficult and time-consuming and it requires having specific software and knowledge at one's disposal. The goal of this paper was to simplify the existing model so that it could be used in applications where ease of use and ease of implementation are more important than accuracy. The existing model was linearized and simple formulae describing natural frequency and damping coefficients were derived. With these parameters, it is possible to assess the dynamic properties of a variable area flowmeter. The step response form can be identified and natural frequency and settling time can be estimated. The linearized model and the experiment were in reasonable agreement. The step response type was captured correctly for each of the six VA meter types. The error in the undamped natural frequency was not larger than 15%, which means that the VA meter sensor's dynamic properties can be predicted at the design stage with sufficient precision.
Subject(s)
Flowmeters , SoftwareABSTRACT
OBJECTIVE: The aim of this work was to model the blood flow rate of the POLVAD-MEV pulsatile ventricular assist device (VAD). An adequate flow rate is crucial to restore physiological cardiac output. Unfortunately, during clinical heart support, neither blood flows nor pressures can be measured within the device. In general, the flow rate depends on the control parameters and patient conditions. However, the patient's hemodynamic parameters are not constantly monitored. Therefore, blood flow must be evaluated based on the standard measurements from the device control unit. METHODS: The model identification data were taken from a research stand consisting of a VAD connected to a hybrid cardiovascular simulator. The studies were conducted under different work and control conditions. A compound model of a ventricular assist device was proposed. First, the driving pressure waveform for an idle run of the supply unit is modeled. Next, the blood flow is estimated based on the difference between the measured value of driving pressure and the modeled value for an idle run. RESULTS: The quality of the developed model is good (R=0.92) and similar for all tested cases, confirming the high versatility of the proposed solution. CONCLUSION: The blood flow rate is estimated based on standard signals from the device control unit; therefore, no additional measurements are necessary. SIGNIFICANCE: The developed model application in the VAD control unit will aid the selection of control parameters and might be useful for development of adaptive control system. A preliminary version of this work was reported at the [1].
