Technology and Health Care - Volume 3, issue 3

Authors: Perktold, Karl | Rappitsch, Gerhard

Article Type: Research Article

Abstract: The importance of arterial flow phenomena with regard to atherosclerosis motivates detailed studies of local cardiovascular flow dynamics. The quantitative analysis of flow characteristics can contribute to the understanding of fluid dynamic induced and favored mechanisms in atherogenesis. Numerical methods are very useful in supporting experimental methods and often enable the determination of flow variables which are difficult to obtain in experiments. Due to the development of improved numerical procedures for the blood specific flow equations and due to the application of modern computer technology, the calculations can be carried out under conditions describing the physiological situation in a realistic …manner including essential effects. Here various aspects of arterial flow simulation are presented and discussed. The possibilities and difficulties of numerical simulation of arterial flow using finite element approximations are illustrated with the aid of the human carotid artery bifurcation and a distal end-to-side anastomosis model. Further convective-diffusive mass transport in a curved tube model is considered. Show more

Keywords: Arterial blood flow, Atherosclerosis, Mathematical mode ling, Computer simulation

DOI: 10.3233/THC-1995-3301

Citation: Technology and Health Care, vol. 3, no. 3, pp. 139-151, 1995

Authors: Kaluzynski, K. | Liepsch, D.

Article Type: Research Article

Abstract: The purpose of this work was to find out whether a rough surface in the sinus of a carotid model affects the flow velocity distribution and the properties of the corresponding ultrasonic Doppler spectrum, in view of potential application to the evaluation of risk of cerebral embolism. True-to-scale elastic models of carotid artery were used in the experiments. Experiments were performed in three models with varying severity of roughness and a normal (physiologically healthy) model. The different degrees of roughness in the three models were created by melting graded holes in the wax cast used to make the model. Velocity …data were collected using 4 Mhz pulsed ultrasonic and single component laser Doppler velocimeters. The roughness resulted in modified velocity distribution, affecting to various extent ultrasonic Doppler spectral parameters, in particular the measure of symmetry of spectral distribution. Show more

Keywords: Carotid sinus, (bifurcation), Laser doppler, Ultrasound doppler, Cerebral embolism

DOI: 10.3233/THC-1995-3302

Citation: Technology and Health Care, vol. 3, no. 3, pp. 153-159, 1995

Authors: Bertram, C.D. | She, J.

Article Type: Research Article

Abstract: Published measurements of canine arterial propagation coefficients show large disparities in pulse wave attenuation and considerable variation with frequency, suggesting both random and systematic error. Here we devise methods of assessing the likely magnitude of each measurement error source, and calculate the individual and cumulative effects on the propagation coefficients derived using three different schemes to compensate for reflections: the three-point method (3PT), the total occlusion method (OCC) and the general iterative method applied to Cox's arrangement of four transducers (GEN). Results from measurements using impulse excitation in a latex tube show that each method accumulates error in a characteristic …frequency pattern. The predicted error bands for OCC are very small except at the fundamental, and clearly exclude a significant further error component. The predicted 3PT error is large at low and at high frequency, and the error bands are better predictors of actual error than in the OCC case. Transducer position error is less than anyone of the three pressure measurement errors. The predicted GEN error increases with frequency and when averaged across frequency is of magnitude intermediate between those for OCC and 3PT. Results for the OCC and GEN methods from the canine aorta in vivo generally confirm these trends, but the concentration of natural pulse wave energy at low frequencies acts to reduce low-frequency error and increase high-frequency error. Show more

Keywords: Aorta, canine, Measurement error, Propagation coefficient

DOI: 10.3233/THC-1995-3303

Citation: Technology and Health Care, vol. 3, no. 3, pp. 161-184, 1995

Authors: Liepsch, Dieter W. | Zimmer, R.

Article Type: Research Article

Abstract: Deposits and blockages are often found in the carotid, coronary, renal and femoral arteries. This paper deals with laser-Doppler velocity measurements in models of bifurcations of the human femoral arteries. Several models were prepared for the studies: a simplified 35° glass model, two elastic-silicone-rubber models with a wall thickness of 1 mm and 2 mm, and true-to-scale rigid and elastic models. These measurements give a clearer picture of how hemodynamics influences the formation of atherosclerotic plaques where there is a hardening of the arterial walls and a loss of elasticity. In addition to the effects of elasticity, the influence of …the flow's pulsatility were studied. The measurements were done in steady and pulsatile flow. From the velocity measurements the shear stresses were calculated. Show more

Keywords: Pulsatile flow, Dynamics, Artery, Model artery

DOI: 10.3233/THC-1995-3304

Citation: Technology and Health Care, vol. 3, no. 3, pp. 185-199, 1995

Authors: Pythoud, F. | Stergiopulos, N. | Meister, J.-J.

Article Type: Research Article

Abstract: A nonlinear method has been developed to separate arterial pressure and flow waves into their forward and backward running components. It takes into account nonlinearities arising from the area-pressure relationship as well as convective acceleration. The method is based on the treatment of the Riemann invariants and requires measurements of pressure, flow and diameter at one arterial location. The method has been successfully tested by means of a simulation experiment in which the forward and backward waves were known a priori. It was shown that the new method is significantly more accurate in the predictions of the forward and backward …waves when compared to the classical linear method. The new wave separation method was then applied to simulated aortic waves for a) a healthy subject and b) a subject with decreased compliance. Comparison with the classical linear method showed that neglecting nonlinearities leads to an overestimation of the forward and backward pressure wave amplitudes of the order of 5 to 10%. Show more

Keywords: Arterial pressure wave, Riemann invariants, Forward pressure, backward pressure

DOI: 10.3233/THC-1995-3305

Citation: Technology and Health Care, vol. 3, no. 3, pp. 201-207, 1995

Authors: Schmid, P. | Stuber, M. | Boesiger, P. | Hess, O.M. | Niederer, P.

Article Type: Research Article

Abstract: The determination of characteristic cardiac parameters, such as displacement, stress and strain distribution are essential for an understanding of the mechanics of the heart. The calculation of these parameters has been limited until recently by the use of idealised mathematical representations of biventricular geometries and by applying simple material laws. On the basis of 20 short axis heart slices and in consideration of linear and nonlinear material behaviour we have developed a FE model with about 100 000 degrees of freedom. Marching Cubes and Phong' s incremental shading technique were used to visualise the three dimensional geometry. In a quasistatic …FE analysis continuous distribution of regional stress and strain corresponding to the endsystolic state were calculated. Substantial regional variation of the Von Mises stress and the total strain energy were observed at all levels of the heart model. The results of both the linear clastic model and the model with a nonlinear material description (Mooney-Rivlin) were compared. While the stress distribution and peak stress values were found to be comparable, the displacement vectors obtained with the nonlinear model were generally higher in comparison with the linear elastic case indicating the need to include nonlinear effects. Show more

Keywords: Heart, human, mechanics, FE analysis, Distribution of stress

DOI: 10.3233/THC-1995-3306

Citation: Technology and Health Care, vol. 3, no. 3, pp. 209-214, 1995