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D Liepsch

Publications and source records attributed to D Liepsch.

43 records · Page 3Linked to original sources
PubMedDate not supplied

Correlation of endothelial cell shape and wall shear stress in a stenosed dog aorta.

The pattern of endothelial geometry at various locations along stenosed dog aortas was examined. This was done to test the hypotheses that the shape of an endothelial cell is related to the local wall shear stress associated with the flowing blood and that alterations in hemodynamics, produced by vascular geometrical changes, influence endothelial cell geometry. Aortic stenosis with a reduction of 71% of the cross-sectional area was produced. The animals were sacrificed 12 weeks later, and the endothelial cell geometry and orientation were studied using the vascular casting technique and a computerized analysis to determine cell area and shape index. The regions of the stenosis examined were those known to experience different hemodynamic conditions. The value of the shape index was found to fall rapidly in the convergent region of the stenosis and to increase suddenly in the divergent region, eventually returning to the prestenotic value at a more distal site. Using a model of a stenosis made from a vascular cast, laser Doppler anemometry was applied to measure velocity profiles and to estimate the local wall shear stress in a stenosed aorta. It is shown that the shape index distribution along these stenosed vessels may be correlated with the level of wall shear stress, with more elongated cells occurring in regions of higher shear stress.

Animals↗
PubMedDate not supplied

Experimental analysis of the influence of stenotic geometry on steady flow.

We studied the flow behavior under steady flow conditions in four models of cylindrical stenoses at Reynolds numbers from 150 to 920. The flow upstream of the constrictions was always fully developed. The constriction ratios of the rigid tubes (D) to the stenoses (d) were d/D = 0.273; 0.505; 0.548; 0.786. The pressure drop at various locations in the stenotic models was measured with water manometers. The flow was visualized with a photoelasticity apparatus using an aqueous birefringent solution. We also studied the flow behavior at pulsatile flow in a dog aorta with a constriction of 71%. The flow through stenotic geometries depends on the Reynolds number of the flow generated in the tube and the constriction ratio d/D. At low d/D ratios, (with the increased constriction), the flow separation zones (recirculation zones, so-called reattachment length) and flow disturbances increased with larger Reynolds numbers. At lower values, eddies were generated. At high Re, eddies were observed in the pre-stenotic regions. The pressure drop is a function of the length and internal diameter of the stenosis, respective ratio of stenosis to the main vessel and the Reynolds numbers. At low Re-numbers and low d/D, distinct recirculation zones were found close to the stenosis. The flow is laminar in the distal areas. Further experiments under steady and unsteady flow conditions in a dog aorta model with a constriction of 71% showed similar effects. High velocity fluctuations downstream of the stenosis were found in the dog aorta. A videotape demonstrates these results.

Animals↗
PubMedDate not supplied

Some flow visualization and laser-Doppler-velocity measurements in a true-to-scale elastic model of a human aortic arch--a new model technique.

Flow studies were done in an elastic true-to-scale silicone rubber model of an aortic arch to study further hemodynamic influences on atherosclerosis. The model was prepared from a cast of a young woman. A revised model technique was used. The model had a compliance similar to that of the human aortic arch. Velocity measurements were done in the model with a two component laser-Doppler-anemometer in steady and pulsatile flow using a calcium chloride solution with a viscosity of eta = 3.18 mPas and density of rho = 1.28 kg/m3 at 20 degrees C. The time average Reynolds numbers over a whole cycle in the ascending aorta was Re = 1350. The Womersley parameter for pulsatile flow was a = 20. The pulse wave velocity in the ascending aorta was about c = 5.4 m/sec. The secondary flow behavior was discussed for steady and pulsatile flow. Reverse flows were found, especially along the inner radius of the aortic arch in the descending aorta in steady and pulsatile flow and also in small areas of the ascending aorta and at the branches of the aortic arch. The formation of atherosclerotic plaques at preferred local flow regions is discussed.

Aorta, Thoracic↗
PubMedDate not supplied

Color-flow Doppler sonography in the identification of ulcerative plaques in patients with high-grade carotid artery stenosis.

PURPOSE: To assess the ability of color-flow Doppler sonography (CFDS) to detect plaque ulcerations in patients who had high-grade to thread-like carotid artery stenosis and who underwent carotid endarterectomy. METHODS: CFDS is a noninvasive diagnostic technique that allows, in addition to spatial visualization of blood flow, the identification of abnormal blood flow patterns such as vortex formation. There is evidence that pathologic anatomic changes in the vascular wall (such as ulcerations) may result in characteristic hemodynamic alterations. Therefore, solely hemodynamic criteria (detection of vortices) were used to diagnose ulceration. The results of preoperative examinations were compared to the intraoperative findings in 89 patients in a prospective and blinded way. RESULTS: CFDS proved highly sensitive (95.3%), specific (93.5%), and accurate (94.0%) for demonstrating ulcerative plaques. CONCLUSION: CFDS may be of significant advantage for examining plaque morphology in patients who have high-grade internal carotid artery stenosis, and in whom accurate, noninvasive diagnosis of plaque ulceration was previously difficult, if not impossible.

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