RESUMEN
Pulsatile blood flow using incompressible newtonian fluid is investigated numerically in abdominal aortic aneurysm models with the aid of transient Navier-Stokes equations for axisymmetric geometry. The arterial wall is assumed to be rigid. The actual arterial pressure-velocity pulse at the abdominal aorta is used as the inlet boundary condition to the aneurysm. The corresponding velocity at every time-step is assumed to be fully developed parabolic profile at the inlet. Time-dependent formation of vortices and occurrence of stagnation zones are analyzed in this numerical study. It has been found that the distal end of the aneurysm is subjected to maximum shear stress and pressure during the entire cycle. This analysis also confirms that the mechanical forces on the arterial wall, developed by the blood flow which is pulsatile in nature, may play an important role in both development and growth of aneurysms. It has also been found that a quasi-steady state may be used to explain sufficiently the basic flow characteristic within the aneurysm. The wall shear stress in the quasi-steady state at the distal end of the aneurysm during the most adverse condition was approximately the same as in the pulsatile state for a similar situation.
Asunto(s)
Aorta Abdominal/fisiopatología , Aneurisma de la Aorta Abdominal/fisiopatología , Flujo Pulsátil , Fenómenos Biofísicos , Biofisica , Simulación por Computador , Humanos , Modelos CardiovascularesAsunto(s)
Arterias Carótidas/cirugía , Hemodinámica , Modelos Cardiovasculares , Arteria Subclavia/cirugía , Síndrome del Robo de la Subclavia/fisiopatología , Velocidad del Flujo Sanguíneo , Estudios de Evaluación como Asunto , Humanos , Técnicas In Vitro , Síndrome del Robo de la Subclavia/cirugíaRESUMEN
An elastic model of the arterial system has been used in which a specially designed pumping unit simulated the heart action. Physiological pressures and normal geometry, size, and flow distribution together with the normal cardiac output and use of prosthetic heart valves are the features of the system. Atherosclerosis was simulated by introducing blockages of known cross-section at specific sites of predilection. It has been shown that, for some specific occlusion magnitude in the left or right subclavian, or in the brachycephalic arteries, the stagnant no blood flow condition will appear in the left vertebral, or the right vertebral, or right common carotid, or the right internal carotid arteries. For larger occlusions the blood flow in these arteries reverses its direction, i.e., the "steal syndrome" appears. It is shown that besides the known single steal syndrome there exists also a double steal syndrome, i.e., blood reverses its flow direction simultaneously in two arteries, both on the right side of the arterial system. This blood is taken from the circle of Willis, which at the same time is significantly supplemented by the increased blood flow through the other arteries leading into the circle of Willis.
Asunto(s)
Arteriosclerosis/fisiopatología , Encéfalo/irrigación sanguínea , Modelos Cardiovasculares , Síndrome del Robo de la Subclavia/fisiopatología , Velocidad del Flujo Sanguíneo/fisiología , Volumen Sanguíneo/fisiología , Arteria Carótida Común/fisiopatología , Círculo Arterial Cerebral/fisiopatología , Humanos , Modelos Teóricos , Músculo Liso Vascular/fisiopatología , Flujo Pulsátil/fisiología , Resistencia Vascular/fisiología , Insuficiencia Vertebrobasilar/fisiopatologíaRESUMEN
In consideration of the pulsatile blood flow in a conduit, the constitutive equation for the whole human blood of F. J. Walburn and D. J. Schneck (Biorheology, Vol. 13, 1976, pp. 201-210) is utilized. Governing equations are solved numerically yielding the velocity and the shear stress distributions. These results are discussed and compared with the Newtonian fluid, Casson's fluid, and Bingham fluid applications.
Asunto(s)
Velocidad del Flujo Sanguíneo , Fenómenos Fisiológicos Sanguíneos , Modelos Biológicos , Modelos Cardiovasculares , Flujo Pulsátil , Reología , Estrés MecánicoRESUMEN
It is shown analytically and experimentally that, within the scope of a surgery, the effects of variations in the position of the transplant-aorta contact point (relative to the renal artery natural location), in the transplant departure angle (relative to the aorta), in the transplant length and in the transplant curvature are relatively insignificant regarding mean flow resistance. Hence, it is concluded that, from this point of view, it is not important how the transplant will be situated and that the space convenience should be the surgical determining factor. Nevertheless, it is also shown that the rate of blood flow to the kidney may be significantly curtailed if the selected transplant diameter is too small. However, it is indicated that the above may not constitute the only criterion. Since there exists a theory that the atherosclerotic formations begin and develop within the separation regions, additional research is suggested correlating separation regions with the variables indicated above.
Asunto(s)
Riñón/irrigación sanguínea , Modelos Biológicos , Arteria Renal/trasplante , Fenómenos Biomecánicos , Diseño de Equipo , MatemáticaRESUMEN
The aortic arch has, on average, an angle of twist of 15 degrees. The purpose of the research conducted was to ascertain if this twist angle has any effect on the flow field of the aortic arch and the distribution of the flow amongst the branches. It was found that the blood flow distribution is practically independent of the angle of twist of the aortic arch. However, the destination of a fluid particle located at a specific point in the cross-section at the entrance to the aortic arch does depend on the angle of twist.
Asunto(s)
Aorta Torácica/anatomía & histología , Modelos Cardiovasculares , Aorta Torácica/fisiología , Homeostasis , Humanos , Modelos Anatómicos , Pulso Arterial , Flujo Sanguíneo RegionalRESUMEN
Steady flow within a uniform circular curved tube formed by two 90-deg elbows was studied as a function of psi, the angle between the planes of curvature of the two elbows. Boundary layer separation was found at two locations. The sites of these separation zones were observed to be essentially independent of psi while the Reynolds number at which separation was first detected was found to decrease as psi increased. The relation between separation and the pathogenesis of atherosclerosis is discussed. Secondary flow pattern was found to depend on psi and in some instances on Reynolds number as well.
Asunto(s)
Aorta Torácica/fisiología , Modelos Cardiovasculares , Fenómenos Biomecánicos , Ingeniería Biomédica , Humanos , Flujo Sanguíneo RegionalRESUMEN
This short note presents the results from experiments performed on an artificial heart valve, in particular, the aortic valve located at the exit of the left ventricle of the heart. The valve was tested in a full-scale elastic model of the arterial system, with a cam-piston unit duplicating the pumping action of the heart. The dependence of the arterial flow distribution on the angular orientation of the valve was investigated and it was found that there was no discernible influence of valve orientation on the arterial flow distribution.