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A new approach is presented for studying the vascular response to hemodynamic stress. A laser doppler anemometer is used to make velocity measurements very near the walls of human arterial casts; these measurements are then correlated with the histology of the artery from which the cast was made. Several illustrative results are given which suggest that the velocity profiles along the outer walls of aortic bifurcations may be significantly determined by the longitudinal variation of cross-sectional area. The shapes of these profiles were qualitatively different for each cast studied. In one specimen, the location of initial lipid deposits appeared to correlate with flow acceleration.

Steady and pulsatile flows were passed through casts of human aortic bifurcations and, by means of a laser Doppler anemometer, fluid velocities were measured at selected sites near the ventral and dorsal walls. At these sites, in the vicinity of the bifurcation, the influence of secondary flow is significant and therefore an appreciation of the phasic variation of secondary flow patterns is important. Results are presented comparing the flow direction in both steady and pulsatile flow at sites in three casts. The common features of the flow at these sites were the persistence of the flow direction during the accelerating and decelerating phases of the pulsatile cycle, and the consistently smaller angle (measured from the inlet centerline) of the pulsatile flow direction as compared to the angle of the flow direction in steady flow.

This experiment was conducted to determine if the pulsatile flow through the proximal portion of the left coronary artery system in man exhibits quasi-steady characteristics. Steady and pulsatile flows were passed through an idealized model whose dimensions were based on a vascular cast. The mean Reynolds number was 180 and the unsteadiness number was 2.7. Velocity profiles were measured by laser Doppler anemometry at several locations along diameters in the parent and both daughter channels in the neighborhood of the “left main” bifurcation. Analysis of the results along one diameter in the “left main” channel shows that unsteady flow in the larger coronary arteries may not be simulated by a series of steady flow experiments.

Velocity measurements are reported for steady and unsteady flow in a rectangular cross-section Y-branch of high aspect ratio. Good agreement is found between the experimental results and two-dimensional calculations. Emphasis is placed on flow velocities near and parallel to the outer wall inasmuch as their gradients are proportional to wall shearing stress which may be of influence in atherogenesis. Large variation in flow velocities and hence shearing stress are found in the immediate vicinity of the corner. The results in this region could support theories which propose either high or low shearing stress as an important consideration in the etiology of arteriosclerosis.

Initial measurements of the time-varying wall shear rate at two sites in a compliant cast of a human aortic bifurcation are presented. The shear rates were derived from flow velocities measured by laser Doppler velocimetry (LDV) near the moving walls of the cast. To derive these shear rate values, the distance from the velocimeter sampling volume to the cast wall must be known. The time variation of this distance was obtained from LDV measurements of the velocity of the wall itself.

Samples having the nominal composition Bi0.7Pb0.3SrCaCu1.8Oy, were prepared by a solid-state reaction and characterized by energy-dispersive x-ray microanalysis, resistivity measurements, and magnetically modulated microwave absorption (MAMMA). Longer annealing times resulted in more homogeneous samples having a single superconducting transition to zero resistance at 108 and 105 K at 0.1 and 1 mA, respectively. The MAMMA measurements clearly show differences in sample homogeneity with different annealing times.

A realistic pulsatile flow was passed through a cast of the aortic bifurcation of a 63-yr-old male with mild atherosclerosis, and a laser Doppler anemometer was used to measure fluid velocities in the cast at 15 selected sites near the lateral and medial walls. Intimal, medial and adventitial thicknesses were measured and sudanophilia was scored at corresponding sites in the vessel from which the cast had been made. A negative correlation was found between intimal thickness (IT) and wall shear rate. The strongest negative correlation (p<0.005) was between IT and “pulse shear rate” (PSR), defined by analogy with pulse pressure. Sudanophilia also correlated negatively with PSR (p<0.01). Medial thickness correlated positively with shear rate, and most strongly with the mean (i.e., time-average) rate (p<0.005). From an analysis of the fluid mechanical data, it appears possible to separate the effects of bifurcation geometry and the shape of the arterial cross section on inter facial shear.