Effect of calcification on the mechanical stability of plaque based on a three-dimensional carotid bifurcation model

Background

This study characterizes the distribution and components of plaque structure by presenting a three-dimensional blood-vessel modelling with the aim of determining mechanical properties due to the effect of lipid core and calcification within a plaque. Numerical simulation has been used to answer how cap thickness and calcium distribution in lipids influence the biomechanical stress on the plaque.

Method

Modelling atherosclerotic plaque based on structural analysis confirms the rationale for plaque mechanical examination and the feasibility of our simulation model. Meaningful validation of predictions from modelled atherosclerotic plaque model typically requires examination of bona fide atherosclerotic lesions. To analyze a more accurate plaque rupture, fluid-structure interaction is applied to three-dimensional blood-vessel carotid bifurcation modelling. A patient-specific pressure variation is applied onto the plaque to influence its vulnerability.

Results

Modelling of the human atherosclerotic artery with varying degrees of lipid core elasticity, fibrous cap thickness and calcification gap, which is defined as the distance between the fibrous cap and calcification agglomerate, form the basis of our rupture analysis. Finite element analysis shows that the calcification gap should be conservatively smaller than its threshold to maintain plaque stability. The results add new mechanistic insights and methodologically sound data to investigate plaque rupture mechanics.

Conclusion

Structural analysis using a three-dimensional calcified model represents a more realistic simulation of late-stage atherosclerotic plaque. We also demonstrate that increases of calcium content that is coupled with a decrease in lipid core volume can stabilize plaque structurally.     

Metamorphic changes in the intestine of three species of lampreys

Measurements have been made of those changes which lead to increases in the surface area of the intestine during the metamorphosis of three species of lampreys. Although the intestine of the Southern Hemisphere lamprey, Geotria australis, increases in length by 1.13 times and in diameter by 1.12 times, the main factor influencing the 5.71 times increase in surface area is the development of longitudinal folds. The contribution of the typhlosole to the internal perimeter of the intestine is less in most life cycle stages of G. australis than in Lampetra spp. The changes in the various intestinal measurements of the nonparasitic species L. planeri parallel those of the presumed ancestral parasitic species, L. fluviatilis, during the first six stages of metamorphosis. However, the longitudinal folds, but not the typhlosole, subsequently start regressing in L. planeri just after the time when the rate of gonadal development increases markedly. An account is also given of the pattern of fold formation and the development of the typhlosolar vein in G. australis.     

Effect of coitus on serum levels of testosterone and LH in male and female rabbits.

Levels of testosterone (T) and LH in the peripheral serum of male and female rabbits were measured and compared following coitus. Blood was collected by heart puncture from restrained, unanesthetized animals of both sexes. In male rabbits, basal serum T levels were highly variable, ranging from 131 to 12,149 pg/ml, and if low preceding coitus they tended to rise; whereas, if high, they usually dropped as they did in nonmated males subjected to repeated heart punctures. In contrast, basal serum LH levels in males were quite constant (mean +/- SE, 1993 +/- 152 pg/ml) and were not significantly altered after coitus unless blood T levels had been drastically lowered by two priming doses of estradiol benzoate. In intact does, on the other hand, copulation which resulted in ovulation induced an approximately 20-fold increase in serum LH concentration which was sustained for about 4 hr. Postcoital elevations in serum LH also occurred in estrogen-primed intact and estrogen-primed ovariectomized does. Under the conditions of our experiments, the parallel elevations in serum LH and T observed postcoitally in the female rabbit could not be demonstrated in the male.     

Programmed Instruction: New Bottle for Rediscovered Wine

Programmed instruction is attracting attention at all educational levels. While this approach is new, the educational principles it incorporates are well established: instructional goals are defined in advance, the content is meticulously organized, active student participation is demanded, immediate feedback is provided to students, and each instructional unit is subjected to testing and revision. With its established effectiveness as a vehicle for introducing new topics, and for providing remedial and supplementary instruction, it can free the medical teacher to devote his time to matters which are more deserving of his attention, such as identifying and responding to individual student needs, exploring complex concepts, and working directly with students to provide a model and critical supervision. A more important potential contribution of programming may be that it has reminded us of sound educational precepts which deserve our attention in all forms of instruction.