Evaluation of Left Ventricular Relaxation in Rotary Blood Pump Recipients Using the Pump Flow Waveform: A Simulation Study
Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, AKH-4L, Waehringer Guertel18–20, 1090 Vienna, Austria.Artificial Organs (Impact Factor: 2.05). 12/2011; 36(5):470-8. DOI: 10.1111/j.1525-1594.2011.01392.x
In heart failure, diastolic dysfunction is responsible for about 50% of the cases, with higher prevalence in women and elderly persons and contributing similarly to mortality as systolic dysfunction. Whereas the cardiac systolic diagnostics in ventricular assist device patients from pump parameters have been investigated by several groups, the diastolic behavior has been barely discussed. This study focuses on the determination of ventricular relaxation during early diastole in rotary blood pump (RBP) recipients. In conventional cardiology, relaxation is usually evaluated by the minimum rate and the time constant of left ventricular pressure decrease, dP/dt(min) and τ(P) . Two new analogous indices derived from the pump flow waveform were investigated in this study: the minimum rate and the time constant of pump flow decrease, dQ/dt(min) and τ(Q) . The correspondence between the indices was investigated in a numerical simulation of the assisted circulation for different ventricular relaxation states (τ(P) ranging from 24 to 68 ms) and two RBP models characterized by linear and nonlinear pressure-flow characteristics. dQ/dt(min) and τ(Q) always correlated with the dP/dt(min) and τ(P) , respectively (r>0.97). These relationships were influenced by the nonlinear pump characteristics during partial support and by the pump speed during full support. To minimize these influences, simulation results suggest the evaluation of dQ/dt(min) and τ(Q) at a pump speed that corresponds to the borderline between partial and full support. In conclusion, at least in simulation, relaxation can be derived from pump data. This noninvasively accessible information could contribute to a continuous estimation of the remaining cardiac function and its eventual recovery.
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ABSTRACT: Mechanical circulatory support (MCS) is increasingly used in the end-stage heart failure patients. The rotary blood pump (RBP) is a novel technology of MCS that currently used in the left ventricular (LV) failure patient. After RBP implanted in LV, some patient immediately need another RBP on the right side of the heart. The effect of LV-RBP or left ventricular assist device (LVAD) on the right ventricle (RV) has been simulated in both normal RV and pathology RV for education proposes. This simulation was regulated the pathology of the heart from normal heart (Maximum Elastance; Emax: 100%) to pathological heart (Emax: 50%) and the level of RBP support in the LV (partial support and full support). The result of this simulation showed the hemodynamics during LV-RBP support. The end-diastolic volume of left ventricle was depended on pump speed. The increasing of right ventricular volume during support was showed in the pathological RV. In contrast, the remaining of right ventricular volume during support was showed in the normal RV. In conclusion, this computer simulation can re-generated the hemodynamics and pressure-volume loop heart failure patient with MCS.
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ABSTRACT: Estimation of instantaneous flow in rotary blood pumps (RBPs) is important for monitoring the interaction between heart and pump and eventually the ventricular function. Our group has reported an algorithm to derive ventricular contractility based on the maximum time derivative (dQ/dt(max) as a substitute for ventricular dP/dt(max) ) and pulsatility of measured flow signals. However, in RBPs used clinically, flow is estimated with a bandwidth too low to determine dQ/dt(max) in the case of improving heart function. The aim of this study was to develop a flow estimator for a centrifugal pump with bandwidth sufficient to provide noninvasive cardiac diagnostics. The new estimator is based on both static and dynamic properties of the brushless DC motor. An in vitro setup was employed to identify the performance of pump and motor up to 20 Hz. The algorithm was validated using physiological ventricular and arterial pressure waveforms in a mock loop which simulated different contractilities (dP/dt(max) 600 to 2300 mm Hg/s), pump speeds (2 to 4 krpm), and fluid viscosities (2 to 4 mPa·s). The mathematically estimated pump flow data were then compared to the datasets measured in the mock loop for different variable combinations (flow ranging from 2.5 to 7 L/min, pulsatility from 3.5 to 6 L/min, dQ/dt(max) from 15 to 60 L/min/s). Transfer function analysis showed that the developed algorithm could estimate the flow waveform with a bandwidth up to 15 Hz (±2 dB). The mean difference between the estimated and measured average flows was +0.06 ± 0.31 L/min and for the flow pulsatilities -0.27 ± 0.2 L/min. Detection of dQ/dt(max) was possible up to a dP/dt(max) level of 2300 mm Hg/s. In conclusion, a flow estimator with sufficient frequency bandwidth and accuracy to allow determination of changes in ventricular contractility even in the case of improving heart function was developed.
Conference Paper: Development of pressure estimation for external rotary blood pump[Show abstract] [Hide abstract]
ABSTRACT: The improvement of heart function are the important consideration for heart failure patient with rotary blood pump (RBP). The capable of function evaluation depend on good monitoring system, which facilitate the physician for diagnosis. In this study, pressure estimation from measured flow rate for the patients with external RBP support is implemented with the non-invasive technique for cardiac function assessment. Measured flow rate from our mock circulation experiment at difference rotational speeds were used to apply with a notable RBP models. Our purpose is to find the optimal parameter values for pressure estimation from our RBP prototype. MUPD-VAD02 that is the external rotary blood pump for pediatric patients was used in this study. The suitable model for our pump prototype is the linear pressure - flow characteristics relationship with speed dependent resistant (Rp), which appeared linear correlations between estimated and measured pressure in a slope of 0.96 (R2 = 0.9603). In conclusion, the parameters and modified RBP model for pressure estimation of MUPD-VAD02 is developed.
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