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O Barnea

Publications and source records attributed to O Barnea.

7 recordsLinked to original sources
PubMed1992

Optimal controller for intraaortic balloon pumping.

An optimal control algorithm was adapted to identify and track the optimal deflation time of the intraaortic balloon pump (IABP). Routines for handling physiologically imposed constraints were added to the algorithm which was implemented in a computer-controlled system. The system was designed to provide real time optimization for the clinical setting. The controller continuously maximizes a performance index while observing the constraints. The index is composed of clinically available hemodynamic variables which indicate changes in myocardial energy balance. Proper values for the algorithm parameters were determined and the system was tested in animal experiments. The results indicate that controlling deflation time relative to the R wave, which precedes the next ejection phase, reduces the time required for optimization when the heart rate varies.

Algorithms↗
PubMed1991

Optimal control system for the intra-aortic balloon pump.

An optimal control system for the intra-aortic balloon pump (IABP) is presented. Control of the IABP is based on a performance index formulated to reflect a tradeoff between maximising cardiac oxygen supply and minimising cardiac oxygen consumption. In the performance index, mean diastolic pressure (MDP) was used to represent oxygen availability and peak systolic pressure (PSP) was used to represent oxygen consumption. An algorithm, implemented using an 8-bit microcomputer, changes the deflation time of the IABP to maximise this performance index by using an optimisation technique that employs both a search and an approximation. The search produces three equally spaced points which define a region that includes the maximum of the performance index. From these points, the optimum deflation time is estimated by a quadratic approximation. The algorithm has been successfully tested using performance index curves generated by computer simulations.

Algorithms↗
PubMed1990

Computer simulation of the mechanically-assisted failing canine circulation.

A model of the cardiovascular system is presented. The model includes representations of the left and right ventricles, a nonlinear multielement model of the aorta and its main branches, and lumped models of the systemic veins and the pulmonary circulation. A simulation of the intra-aortic balloon pump and representations of physiological compensatory mechanisms are also incorporated in the model. Parameters of the left ventricular model were set to simulate either the normal or failing canine circulation. Pressure and flow waveforms throughout the circulation as well as ventricular pressure and volume were calculated for the normal, failing, and assisted failing circulation. Cardiac oxygen supply and consumption were calculated from the model. They were used as direct indices of cardiac energy supply and utilization to assess the effects of cardiac assistance.

Animals↗
PubMed1990

Cardiac energy considerations during intraaortic balloon pumping.

Cardiac oxygen availability and oxygen consumption were used in a theoretical study as indexes of myocardial energy supply and utilization, respectively. A detailed computer simulation of the closed-loop canine cardiovascular system was utilized to study the dependence of these indexes on timing of the intraaortic balloon pump. Oxygen availability exhibited higher sensitivity to balloon timing than oxygen utilization. While maximum augmentation of oxygen availability was 58 percent, oxygen consumption could be reduced by only 13 percent. Animal experiments were initiated to validate the theoretical results. The results of both the animal experiments and the computer simulation suggested that neither balloon timing which maximizes oxygen availability nor timing which minimizes oxygen consumption correlates with timing which minimizes aortic end diastolic pressure. Thus, end diastolic pressure, presently used as a determinant of proper timing in patients undergoing cardiac assistance, was found to be a poor index of ventricular energy consumption. A performance index comprised of clinically available variables, was formulated to reflect myocardial energy balance. In this performance index, mean diastolic pressure was used to represent energy availability and peak systolic pressure was used as an index of oxygen consumption. Their relationship to oxygen balance and their dependence on timing were studied using the computer simulation of the canine cardiovascular system and animal experiments. Theoretical and experimental results suggest that such an index is capable of representing O2 balance and can be used to control phasing of the device.

Animals↗
PubMedDate not supplied

Coronary autoregulation and optimal myocardial oxygen utilization.

The complex relationship among myocardial contractility, preload, afterload, and coronary autoregulation was studied using both analytical and numerical methods. To study autoregulation and coronary reserve changes in response to changes in cardiac oxygen consumption and in arterial pressure generation, a new variable was introduced: myocardial resistance to oxygen flow (RO2). This variable was defined as the ratio of the coronary driving pressure to left-ventricular oxygen uptake. High values for this variable indicate small consumption relative to the generated aortic pressure. Conditions which produce the highest obtainable value for RO2 are considered as optimal. An expression relating RO2 to ventricular hemodynamic variables was developed and studied using a mathematical model of the cardiovascular system. The model included a mechanism of local autoregulation based on the assumption that, in steady state, the amount of oxygen consumed equals the amount extracted from coronary blood. Heart rate, peripheral resistance, end-diastolic volume, and myocardial contractility were varied while the coronary circulation was adjusted to meet ventricular oxygen consumption at each state. The model predicts that, for each state of the circulation, there is an optimal level of cardiac contractility for which the coronary reserve is maximized.

Animals↗