Computer and physical modeling of blood circulation pump support for a new field of application in palliative surgery.

OBJECTIVES: One of the most popular palliative procedures performed to increase pulmonary blood flow in children with congenital heart defects is a shunt operation (Blalock-Taussig graft or Glenn procedure), which creates the new blood channel to the pulmonary artery. The main problem with this kind of surgery is poor shunt effectiveness and the lack of possibility to regulate the flow. The aim of this work is to use advanced computer simulation methods to study the effectiveness of a new idea to introduce a small axial blood pump into a Blalock-Taussig (B-T) or Glenn shunt in order to control the blood flow and prevent any increase in the graft stenosis. METHODS: Physical and computer 3-D simulation based on a finite element mesh (FEM) model was applied. Studies for optimization of the shunt and hybrid shunt with pump were performed for different stages of the disease. RESULTS AND CONCLUSION: The graft with the axial pump creates good conditions for the vascular system and pulmonary artery blood flow as well as regulating blood pressure under variable conditions caused by palliative procedures. Its use permits the afterload of the left heart ventricle to be decreased. A palliative procedure is only a temporary solution. When a child grows, while the graft size is fixed, the blood flow through this graft may be not sufficient under changing hemodynamic conditions. The use of an axial pump for regulating the blood flow volume, during palliative procedures, allows to obtain the optimal flow conditions in pulmonary artery and safely wait on the final cardiac surgery correction later. However, the use of a pump mounted inside the graft increased hemodynamic resistance, which caused the flow to decrease up to 70% in the graft when the axial pump was not working.

Physical and computer modelling of blood flow in a systemic-to-pulmonary shunt.

UNLABELLED: The aim of this work was the application of computer and physical in vitro simulation methods for estimating surgery procedure hemodynamics. The modified Blalock-Taussig (mB-T) palliative surgical procedure is performed to increase the pulmonary blood flow in children with congenital heart defects. Such a systemic-to-pulmonary shunt yields substantial modification in the blood flow within the large blood vessels. The objective of the present study was to investigate basic characteristics of the flow, flow pattern and pressure-flow efficiency, before and after opening of the mB-T graft. METHODS: The model was based on the vessel geometry obtained from the Visible Human Project and included the arch of aorta, the three arteries branching from the arch, the pulmonary trunck, and the left and right pulmonary arteries. The graft was added between the left subclavian artery and the left pulmonary artery. The glass model of the vessels was produced and investigated in a physical model of the cardiovascular system with an artificial ventricular device as the blood pump. Flow rate and hydrostatic pressure were measured at the inlet to and outlets from the glass model and in a few points within the system. Laser flow visualization was also performed. Computer simulations were done using the boundary conditions from the physical model. RESULTS: The opening of the mB-T graft changed flow distribution in all branches (including inflow). A complex flow pattern with large eddies and channelling of the flow in the vicinity of the graft and within it was observed in flow visualization and in computer simulations. Because of that complexity the local measurements of hydrostatic pressure at the vessel wall could not predict the average flow rate. The reversed flow in the graft was observed during the systole. CONCLUSIONS: The complex flow pattern developed in the physical model of the mB-T graft. The channelling of the flow and the formation of large eddies may yield high shear stress and modify blood properties. The rigid wall model can describe only some flow characteristics observed in vivo. Computer simulation is a very fast and accurate method which permits earlier qualification of cardiac surgeons on how to change cardiac vascular blood flow after operations.

Robin Heart 2003--present state of the Polish telemanipulator project for cardiac surgery assistance.

The Polish telemanipulator (Robin Heart), for use in cardiac surgery, has been realized by the Foundation of Cardiac Surgery Development in Zabrze, Poland, in cooperation with specialists from the Technical University of Lodz and Warsaw University of Technology. The brief history of robotic surgery and fundamental advantages of employing robots in this field--safe, reliable and repeatable operative results with less patient pain, trauma and recovery time--follow the assumptions of the Polish Cardio-Robot project. The cardiac surgery robot, Robin Heart, is an original construction with a segment type structure which allows the various combination of its parts for different types of surgery. The telemanipulator for cardiac surgery will consist of two arms equipped with tools and one arm holding the camera. Several models suitable for surgeon contact systems, using the experience of centers designing the artificial hand and haptic systems have been worked out. The detailed mechanical analysis and original construction of main parts of the robot and development of the surgical planning system are presented in further sections.

The analysis of driving mode influence on energy dissipation in pneumatic artificial heart chambers.

The energy dissipated in blood or on a total artificial heart (TAH) chamber's elements directly or indirectly decreases the biological or technical safety of the TAH's work. The energetic analysis of the Polish total artificial heart (POLTAH) external work with the objective of estimating the valve and membrane roles in energy dissipation has been performed. The simulation of left and right artificial heart chamber work under physiological conditions using a self-constructed physical model of the circulatory system has been performed for the full systole percent and frequency range and for different valves. The total energy dissipated on valves equals 15-30% of the chambers' work value. Energy losses on valves are influenced by the driving mode. The usage of inappropriate systolic and diastolic times increases the value of the energy dissipated on the membrane and on valves in the overall energy balance. The absolute value of the energy dissipated on the valves increases with the increase of the cycle time and depends on the valve type. The energy dissipated on the outlet valve decreases with the frequency (if the remaining driving parameters are kept constant) and for 150 bpm is nearly 3 times lower than that for 30 bpm. The energy dissipated on the membrane equals 10-50% of the TAH's work during systole, depending on the driving parameters. The filling process is assisted by the pressure from the atrium, and a great amount of energy during the diastolic period is consumed by the start of the membrane movement. We have also estimated the influence of the driving parameters on the valves' functions, measuring the acoustic wave intensity. The conclusions drawn are of a general character; they are applicable to all membrane, pneumatically powered blood pumps.