Weaning of rotary blood pump recipients after myocardial recovery: A computer study of changes in cardiac energetics

Brain Research Institute, University of Vienna, Wien, Vienna, Austria
Journal of Thoracic and Cardiovascular Surgery (Impact Factor: 4.17). 07/2004; 127(6):1743-50. DOI: 10.1016/j.jtcvs.2003.09.029
Source: PubMed


Weaning of patients from mechanical cardiac support after myocardial recovery has always involved multiple, interacting factors, particularly the training of the myocardium during reduction of pump flow. Rotary pumps offer training advantages when support flow is reduced, even to nearly zero. We report a computer analysis that evaluates the work required of the heart during partial unloading and removal of rotary pumps.
A computer model of the assisted circulation, previously implemented in MATLAB (The MathWorks Inc, Natick, Mass), has been augmented with a model of the MicroMed DeBakey ventricular assist device (MicroMed Technology, Inc, Houston, Tex). Flow, pressure patterns, and external work (pressure-volume area, calculated as the area of the ventricular pressure-volume loop [external work] plus potential energy) were calculated for nonassisted and various continuously assisted patients. Under low-flow conditions, the heart imposes an oscillating forward-backward flow through the non-occlusive rotary pump, causing an increase in ventricular work. Thus, an assist flow of 1 to 1.5 L/min requires work equivalent to that of the unsupported heart. At 60% contractility, the nonassisted pressure-volume area is 1.10 Ws/beat, and the potential energy is 0.38 Ws/beat. At a Qpump of 1 L/min, the pressure-volume area is 1.21 Ws/beat, and the potential energy is 0.37 Ws/beat. At a Qpump of 3 L/min, the pressure-volume area is 0.93 Ws/beat, and the potential energy is 0.29 Ws/beat. These conditions cannot be achieved with pulsatile systems.
During weaning and retraining, an implanted rotary pump can provide a workload to the heart like that in the nonassisted situation, thus increasing the predictability of weaning and reducing the risk of reiterating heart failure.

Download full-text


Available from: Georg Wieselthaler, Mar 24, 2014

  • Wiener klinische Wochenschrift 08/2008; 120:15-20. DOI:10.1007/s00508-008-1043-0 · 0.84 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Nowadays, a rotary blood pump can be used as not only for a bridge to transplantation (BTT) but also for a bridge to recovery (BTR) and a destination therapy (DT). In such cases, evaluation of the recovery level of the native heart provides useful information to improve the clinical strategy and decide adequate timing for removing of the RBP. In contrast, the indices for cardiac function have been studied. However, most of them do not consider the assistance with the RBP. In this study, we aimed at evaluating whether Emax, which is an index for cardiac function based on the pressure-volume relationships, is still valid during assistance with the RBP from an animal experiment. In the acute animal experiment with an adult goat, we measured pressure-volume (P-V) loops while cardiac function was normal, augmented or diminished. The experimental results revealed that there were typical differences in the shapes of P-V loops when the cardiac function was altered, and Emax can still be used as an index for the cardiac function even if the assistance with the RBP is ongoing.
    Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 02/2006; 1:5378-81. DOI:10.1109/IEMBS.2006.260079
  • [Show abstract] [Hide abstract]
    ABSTRACT: Aim of this work is to study the impact of left ventricular rotary blood pump assistance, on energetic variables, when mechanical ventilation (MV) of the lungs is applied. Computer simulation was used to perform this study. Lumped parameter models reproduce the circulatory system. Variable elastance models reproduce the Starling's law of the heart for each ventricle. After the reproduction of ischemic heart disease left ventricular assistance was applied using a model of rotary blood pump. The pump speed was changed in steps and was assumed to be constant during each step. The influence of mechanical ventilation was introduced by different values of positive mean thoracic pressure. The increase of the rotational speed has a significant influence on some ventricular energetic variables. In fact it decreased left ventricular external work, left and right ventricular pressure-volume area and the left ventricular efficiency. Finally, it increased the right ventricular efficiency but had no influence on the right ventricular external work. The increase of thoracic pressure from -2 to +5 mmHg caused a significant decrease of external work, pressure-volume area (right ventricular pressure-volume area dropped up to 50%) and an increase of right ventricular efficiency (by 40%) while left ventricular efficiency remained almost stable. Numerical simulation is a very suitable tool to predict changes of not easily measurable parameters such as energetic ventricular variables when mechanical assistance of heart and/or lungs is applied independently or simultaneously.
    Methods of Information in Medicine 02/2006; 45(5):574-83. · 2.25 Impact Factor
Show more