Effects of lower-body negative pressure on blood flow with applications to the human cardiovascular system.

The paper reports a theoretical investigation into the effects of lower-body negative pressure on blood flow through the human cardiovascular system. The human cardiovascular system is modelled as a closed network of arteries, arterioles, capillaries, venules and veins of different lengths and cross-sections. The pumping action is provided by the contraction of the ventricles. The model has been analysed using the finite-element method. The pertinent equations incorporating the effects of lower-body negative pressure for the pressures and flow velocities have been derived, and the quantitative results have been computed. Percentage changes in flow velocities, pressure drops and conductances under the application of lower-body negative pressure in the various segments and organs of the entire cardiovascular system are obtained. The lower-body negative pressure has no effect on the flow rates in carotid, ulnar and coronary arteries, nor on the supply of blood to the upper extremities, kidneys, spleen and liver. The major effects are found in the lower extremities.

Mathematical modelling of the human cardiovascular system in the presence of stenosis.

This paper reports a theoretical study on the distribution of blood flow in the human cardiovascular system when one or more blood vessels are affected by stenosis. The analysis employs a mathematical model of the entire system based on the finite element method. The arterial-venous network is represented by a large number of interconnected segments in the model. Values for the model parameters are based upon the published data on the physiological and rheological properties of blood. Computational results show how blood flow through various parts of the cardiovascular system is affected by stenosis in different blood vessels. No significant changes in the flow parameters of the cardiovascular system were found to occur when the reduction in the lumen diameter of the stenosed vessels was less than 65%.

The effects of exercise on blood flow with reference to the human cardiovascular system: a finite element study.

This paper reports on a theoretical investigation into the effects of vasomotion on blood through the human cardiovascular system. The finite element method has been used to analyse the model. Vasoconstriction and vasodilation may be effected either through the action of the central nervous system or autoregulation. One of the conditions responsible for vasomotion is exercise. The proposed model has been solved and quantitative results of flows and pressures due to changing the conductances of specific networks of arterioles, capillaries and venules comprising the arms, legs, stomach and their combinations have been obtained.

Mathematical modelling of flow distribution in the human cardiovascular system.

The paper presents a detailed model of the entire human cardiovascular system which aims to study the changes in flow distribution caused by external stimuli, changes in internal parameters, or other factors. The arterial-venous network is represented by 325 interconnected elastic segments. The mathematical description of each segment is based on equations of hydrodynamics and those of stress/strain relationships in elastic materials. Appropriate input functions provide for the pumping of blood by the heart through the system. The analysis employs the finite-element technique which can accommodate any prescribed boundary conditions. Values of model parameters are from available data on physical and rheological properties of blood and blood vessels. As a representative example, simulation results on changes in flow distribution with changes in the elastic properties of blood vessels are discussed. They indicate that the errors in the calculated overall flow rates are not significant even in the extreme case of arteries and veins behaving as rigid tubes.

Simulation of steady cardiovascular flow in the presence of stenosis using a finite element method.

Stenosis could affect one or more segments of the human cardiovascular system. It is a problem capable of causing grave effects. In the present study, the finite element method has been utilised to construct a computer simulation model for the human cardiovascular system in which one or more blood carrying elastic segments are affected by stenosis. Computational effects on the effects of stenosis in aorta arch, carotid, and coronary arteries on parameters of steady flow through the system are presented. It is found that when the total flow rate through the heart is maintained constant, the most notable effect is a very marked increase in pressure drop occurring over the length of the vessel affected with stenosis. Pressure drop in many other segments also increases but by a much smaller extent. On the other hand, when the pressure at the inlet of the ascending aorta and the outlet of the vena cava are maintained constant, the most marked effect is a decrease of flow rate through the stenosed vessel. Stenosis not only causes a pressure drop in the affected segments but it also changes pressures at points distal from the site of stenosis. It also causes a redistribution of flow through the cardiovascular system.

Steady flow of a viscous fluid through a network of tubes with applications to the human arterial system.

The paper presents a finite-element model for the analysis of steady flow of a viscous fluid through a connected system of elastic tubes with the aim of simulating the conditions of blood flow through the human arterial system. The governing equations of the model are non-linear in character and are solved through an iterative computational procedure. This model is capable of incorporating the effects of stenosis on flow and pressure. Typical results are presented and discussed. Quantitative results have been obtained on blood flow through a model of the human arterial system corresponding to the sets of prescribed conditions at the terminations. Also computational results on the effect of stenosis in typical arteries of the system are presented.

Blood flow through the human arterial system in the presence of a steady magnetic field.

The effects of the interaction between a magnetic field and the haemodynamics of the arterial system have been studied. An analysis of a supine subject has been carried out in the presence of an externally applied magnetic field. A finite-element technique has been used to solve the magnetohydrodynamics of the fluid flow problem in a network of rigid tubes. The analysis is carried out by considering arteries as rigid tubes, i.e. the arterial expansion is neglected. In real situations, the arteries are elastic. The method requires the derivation of an expression of the conductance of a single artery in the presence of a transverse magnetic field. Computational results corresponding to two different sets of boundary conditions have been obtained. The quantitative effects of intensity and orientation of the applied magnetic field in the presence and absence of stenosis in the aortic arch are presented and discussed.

Analysis of blood flow through a model of the human arterial system under periodic body acceleration.

The human system may be subjected to a body acceleration deliberated for example by making subjects lie down on vibrating tables or more frequently unintentionally, for example during travel in water and land or in air and space. The present study is concerned with the effects of externally imposed body accelerations on blood flow in a branched system of arteries. A finite-element model of flow in the arterial system subject to periodic body accelerations is presented. Computational results on the flow rates through selected arteries and the corresponding inlet and outlet pressures under different conditions (magnitude, frequency and direction) of applied acceleration are presented.