Distribution pattern of sudanophilic plaques in the descending thoracic and proximal abdominal human aorta

Haemodynamic Wall Shear Stress, Endothelial Permeability and Atherosclerosis-A Triad of Controversy

A striking feature of atherosclerosis is its patchy distribution within the vascular system; certain arteries and certain locations within each artery are preferentially affected. Identifying the local risk factors underlying this phenomenon may lead to new therapeutic strategies. The large variation in lesion prevalence in areas of curvature and branching has motivated a search for haemodynamic triggers, particular those related to wall shear stress (WSS). The fact that lesions are rich in blood-derived lipids has motivated studies of local endothelial permeability. However, the location of lesions, the underlying haemodynamic triggers, the role of permeability, the routes by which lipids cross the endothelium, and the mechanisms by which WSS affects permeability have all been areas of controversy. This review presents evidence for and against the current consensus that lesions are triggered by low and/or oscillatory WSS and that this type of shear profile leads to elevated entry of low density lipoprotein (LDL) into the wall via widened intercellular junctions; it also evaluates more recent evidence that lesion location changes with age, that multidirectional shear stress plays a key role, that LDL dominantly crosses the endothelium by transcytosis, and that the link between flow and permeability results from hitherto unrecognised shear-sensitive mediators.

Hemodynamic Abnormalities in the Aorta of Turner Syndrome Girls

Congenital abnormalities in girls and women with Turner syndrome (TS), alongside an underlying predisposition to obesity and hypertension, contribute to an increased risk of cardiovascular disease and ultimately reduced life expectancy. We observe that children with TS present a greater variance in aortic arch morphology than their healthy counterparts, and hypothesize that their hemodynamics is also different. In this study, computational fluid dynamic (CFD) simulations were performed for four TS girls, and three age-matched healthy girls, using patient-specific inlet boundary conditions, obtained from phase-contrast MRI data. The visualization of multidirectional blood flow revealed an increase in vortical flow in the arch, supra-aortic vessels, and descending aorta, and a correlation between the presence of aortic abnormalities and disturbed flow. Compared to the relatively homogeneous pattern of time-averaged wall shear stress (TAWSS) on the healthy aortae, a highly heterogeneous distribution with elevated TAWSS values was observed in the TS geometries. Visualization of further shear stress parameters, such as oscillatory shear index (OSI), normalized relative residence time (RRTn), and transverse WSS (transWSS), revealed dissimilar heterogeneity in the oscillatory and multidirectional nature of the aortic flow. Taking into account the young age of our TS cohort (average age 13 ± 2 years) and their obesity level (75% were obese or overweight), which is believed to accelerate the initiation and progression of endothelial dysfunction, these findings may be an indication of atherosclerotic disease manifesting earlier in life in TS patients. Age, obesity and aortic morphology may, therefore, play a key role in assessing cardiovascular risk in TS children.

Distribution of atherosclerotic lesions in various arteries of WHHLMI rabbits, an animal model of familial hypercholesterolemia

In WHHLMI rabbits, arterial lesions develop spontaneously in various arteries even with standard chow. Here, we examined the development of arterial lesions in various arteries to demonstrate standard characteristics of arterial lesions in WHHLMI rabbits. For WHHLMI rabbits at 6, 12, 20, and 30 months of age, lesion areas and areas of arterial lumen surfaces were measured using image analysis software. Histopathological sections of arterial lesions were stained with elastic van Gieson staining. Arterial lesions developed around bifurcations and expanded with aging. In the aorta, atheromatous lesions were severe in the thoracic aorta but were mild in the distal part of the abdominal aorta. Carotid artery lesions progressed in the proximal region and at bifurcations, and the histopathological features were similar to those of coronary lesions. Pulmonary artery lesions contained many foam cells. Fibrous lesions were observed in the proximal and distal areas of the renal arteries, at the bifurcation of the iliac-femoral artery and mesenteric artery, and around the anastomosis of vertebral arteries. Lesions in the celiac artery contained foam cells and/or lipid droplets within fibrous lesions. In a pair of right and left arteries, the arterial lesions tended to progress more in the right artery. Gender did not affect analysis of arterial lesions. In conclusion, the arterial lesions expanded from bifurcations, and the morphological features of the arterial lesions varied depending on the type of artery. These results serve as reference data for arterial lesions in studies using WHHLMI rabbits.

Microscopic findings associated with blood pressure indices in postmortem human aorta samples from young people (ages 15-34)

Standardized postmortem samples of thoracic and abdominal aortas from traumatic death victims (aged 15-34 inclusive) were selected according to renal indices of estimated blood pressure. Half of the males had renal small-artery evidence of elevated blood pressure, and half did not. The group consisted of an approximately equal number of black and white males. All of the individuals were nonsmokers and had similar age, cholesterol, and HDL distribution. Lipid deposition in the thoracic and abdominal aorta sections was determined quantitatively by means of computer micromorphometry in sections stained with Oil Red O. Results showed that there is a marked increase in extracellular lipid deposition in the intima for those arteries studied with elevated renal indices of hypertension. In addition, there is significantly more extracellular lipid in the abdominal aortas in black males than in white males. Also notable was the finding that the thoracic aorta samples exhibited significantly thicker intimas and larger intimal areas in the high blood pressure index groups than in the low blood pressure index groups. These results suggest that the development of atherosclerotic lesions may be due to an increased deposition of extracellular lipid in the matrix of the arterial intima.

Effect of aortic taper on patterns of blood flow and wall shear stress in rabbits: association with age

OBJECTIVE

The distribution of atherosclerotic lesions changes with age in human and rabbit aortas. We investigated if this can be explained by changes in patterns of blood flow and wall shear stress.

METHODS

The luminal geometry of thoracic aortas from immature and mature rabbits was obtained by micro-CT of vascular corrosion casts. Blood flow was computed and average maps of wall shear stress were derived.

RESULTS

The branch anatomy of the aortic arch varied widely between animals. Wall shear was increased downstream and to a lesser extent upstream of intercostal branch ostia, and a stripe of high shear was located on the dorsal descending aortic wall. The stripe was associated with two vortices generated by aortic arch curvature; their persistence into the descending aorta depended on aortic taper and was more pronounced in mature geometries. These results were not sensitive to the modelling assumptions.

CONCLUSIONS

Blood flow characteristics in the rabbit aorta were affected by the degree of taper, which tends to increase with age in the aortic arch and strengthens secondary flows into the descending aorta. Previously-observed lesion distributions correlated better with high than low shear, and age-related changes around branch ostia were not explained by the flow patterns.

Atheroprotective effects of dietary L-arginine increase with age in cholesterol-fed rabbits

NO has several putative atheroprotective properties but its precursor, L-arginine, and inhibitors of its synthesis have had inconsistent effects on the extent of experimental atherosclerosis in rabbits. The location and character of experimental atherosclerosis differ between immature and mature rabbits; both phenomena have been attributed to changes with age in the NO pathway. We investigated whether the influence of dietary L-arginine on experimental atherosclerosis is also age-related. The frequency of lesions was mapped in the descending thoracic and upper abdominal aorta of immature and mature rabbits fed 1 % cholesterol, with or without supplementary L-arginine, for 8 weeks. Consistent with earlier data, the distribution of lesions around the branch points changed with age in control rabbits. The mean frequency of lesions was essentially the same at both ages. L-Arginine supplements had no effect on the distribution of lesions at either age. They significantly reduced the mean frequency of lesions in mature animals but not in immature animals. Thus, the atheroprotective effect of dietary L-arginine in cholesterol-fed rabbits increases with age.

Mass transport in arteries and the localization of atherosclerosis

Atherosclerosis is a disease of the large arteries that involves a characteristic accumulation of high-molecular-weight lipoprotein in the arterial wall. This review focuses on the mass transport processes that mediate the focal accumulation of lipid in arteries and places particular emphasis on the role of fluid mechanical forces in modulating mass transport phenomena. In the final analysis, four mass transport mechanisms emerge that may be important in the localization of atherosclerosis: blood phase controlled hypoxia, leaky endothelial junctions, transient intercellular junction remodeling, and convective clearance of the subendothelial intima and media. Further study of these mechanisms may contribute to the development of therapeutic strategies for atherosclerotic diseases.

Evidence for a reversal with age in the pattern of near-wall blood flow around aortic branches

The changes that occur with age in the distribution of atherosclerotic lesions around arterial branch points challenge accepted theories relating disease to haemodynamic stresses. We investigated whether flow near branch points changes with age in a way that can account for the different lesion distributions. Flow around 20 branches from immature and mature aortas was investigated by examining the length:width ratio and orientation of endothelial nuclei; these properties depend on the magnitude and direction of near-wall flows, respectively. There were significant changes in the pattern of nuclear shape with age, consistent with a reversal in the pattern of shear around branches. In control regions away from branches, there were no such changes. The role of haemodynamic stresses in atherogenesis may require re-evaluation in the light of these results.

Effect of time of day and rabbit strain on patterns of aortic wall permeability

Lipid deposits occur more frequently downstream of branch points than upstream in immature rabbit and human aortas but the opposite pattern is seen in mature vessels. These distributions correlate spatially with age-related patterns of aortic permeability, observed in rabbits, and may be determined by them. The mature but not the immature pattern of permeability is dependent on endogenous nitric oxide synthesis. Although the transport patterns have hitherto seemed robust, recent studies have given the upstream pattern in some mature rabbits but the downstream pattern in others. Here we show that transport in mature rabbits is significantly skewed to the downstream pattern in the afternoon compared with the morning (P < 0.05), and switches from a downstream to an upstream pattern at around 21 months in rabbits of the Murex strain, but at twice this age in Highgate rabbits (P < 0.001). The effect of time of day was not explained by changes in nitric oxide production, assessed from plasma levels of nitrate and nitrate, nor did it correlate with conduit artery tone, assessed from the shape of the peripheral pulse wave. The effect of strain could not be explained by variation in nitric oxide production nor by differences in wall structure. The effects of time of day and rabbit strain on permeability patterns explain recent discrepancies, provide a useful tool for investigating underlying mechanisms and may have implications for human disease.

Two-dimensional maps of short-term albumin uptake by the immature and mature rabbit aortic wall around branch points

In children, aortic lipid deposition develops in triangular regions of the wall downstream of branch points, whilst in adults these regions are particularly free of disease. Comparable age-related patterns occur in rabbit aortas. They may be explained by patterns of wall permeability to circulating macromolecules: along the longitudinal midline through branches, permeability is greater downstream than upstream in immature rabbits, but is greater upstream at later ages. Here we have mapped permeability in detail around such branches, not just along the midline. Short-term uptake of rhodamine-labeled albumin, measured using digital imaging fluorescence microscopy of serial sections, was greatest in an approximately triangular region downstream of immature branches, but in mature animals it was greater upstream, particularly away from the midline, and in streaks to the side of branches. Hence the maps are consistent with earlier permeability data and closely resemble the patterns of disease.

In vitro investigation of calcium distribution and tissue thickness in the human thoracic aorta

Atherosclerosis represents a significant cause of morbidity and mortality in the western world. Manifestations of atherosclerotic disease among the elderly include the development of raised lesions that often include calcified regions with material properties similar to bone. There is little information available about the amount and distribution of these calcified plaques within the human aorta, partly due to the difficulty in obtaining this information during in vivo studies. We report the results of a cadaveric investigation of thoracic aortic wall thickness, diameter and calcium content. A non-destructive x-ray imaging technique was used to obtain two-dimensional maps of total thickness and mineral content in excised thoracic aortic specimens. In a study of 39 individuals (23 male and 16 female, aged 20-92 years) we report a significant non-linear correlation between calcium burden and age, with calcium deposition most commonly occurring proximal to the ostia of major branching vessels. We also found a significant linear correlation between age and both total aortic wall thickness and aortic diameter. An improved understanding of the pathological changes in the ageing thoracic aorta may be useful in the development of strategies to reduce the undesirable vessel calcification associated with atherosclerosis.

Pathologic and histologic results of electrical impulses in a rabbit model of atherosclerosis: 24-hour versus 8-hour regimen

OBJECTIVE

Low frequency electrical impulses (EIs) reduce new atherosclerotic plaque formation in previously diseased arteries and may reverse the extent of previous pathologic damage in these structures.

METHODS

A pacemaker was implanted on the left side of rabbit abdominal aortas, and an electrode was placed close to the other side of the aorta in the psoas major muscle. For the induction of atherosclerosis, the rabbits were placed on a high cholesterol diet (HCD) for 11 weeks. No EIs were applied to the control series I. In the experimental series, the rabbits were fed an HCD for 3 weeks, after which EIs were applied simultaneously with an HCD for 8 additional weeks (3V, 30 contractions per minute). Experimental series II had 24-hour/day EIs, and series III had 8-hour/day EIs.

RESULTS

The closer to the area where the EIs were applied, the more local severity increased (atherosclerosis level and surface area). In the control series, the severity of atherosclerosis in the lower aorta assessed with an arbitrary grading system was 1.75 +/- 0.5 (versus 1.5 +/- 0.57 with 8-hour/day EIs and 0.5 +/- 0.3 with 24-hour/day EIs). The involved surface area was 32.5% +/- 9.5% (versus 1.0% +/- 0.8% with 8-hour/day EIs and 0.75% +/- 0.95% with 24-hour/day EIs).

CONCLUSION

Both 24-hour/day and 8-hour/day EIs applied close to the abdominal aorta decreased the severity of atherosclerosis in rabbits placed on a HCD, but 24-hour/day EIs decreased the severity more extensively.

Strain-dependent differences in the pattern of aortic lipid deposition in cholesterol-fed rabbits

Spontaneous lesions develop downstream of branch points in immature human and rabbit aortas, but occur more frequently at the sides and upstream of these sites in mature vessels. Cholesterol-induced lesions in mature rabbits, however, have shown the downstream distribution in one trial and the more upstream distribution in another. We tested the hypothesis that this discrepancy reflected a difference in the degree of impairment of the nitric oxide pathway. Mature rabbits were fed cholesterol-enhanced versions of the two base diets used in the previous trials, and some were given additional vitamin E or l-arginine to protect the NO pathway or L-NAME to inhibit it. Unexpectedly, the rabbits developed a lesion pattern intermediate between the two previously described, and this distribution was unaffected by the base diet or supplements. Consequently, an exploratory study was conducted to investigate possible effects of other differences between the two earlier trials. These were the precise age of the mature rabbits and the feeding protocol employed; both base diets again were used. Two different lesion patterns were observed in this trial, but there was no systematic effect of any of the controlled variables. Instead, there appeared to be an influence of the supplier from which the rabbits had been obtained. A multivariate analysis of all four trials confirmed that the pattern of disease was associated with rabbit strain, and not with base diet, cholesterol level, or precise age.

Effect of altered flow on the pattern of permeability around rabbit aortic branches

Uptake of circulating macromolecules by the aortic wall is greater downstream than upstream of branch sites in immature rabbits, but the opposite pattern is seen at later ages. The mature pattern is nitric oxide dependent; we tested whether it is also flow dependent. Intercostal arteries of anesthetized rabbits were occluded, sham operated, or left alone. Uptake of rhodamine-labeled albumin was assessed by quantitative fluorescence microscopy of the sections through the aorta. In mature animals, uptake was higher upstream than downstream of the control and sham-operated branches, but the pattern was reversed at occluded branches. In young animals, uptake was not significantly different between regions upstream and downstream of control, sham-operated, or occluded branches. The absence of the normal immature pattern may reflect an influence of anesthesia and will assist in the elucidation of mechanisms underlying this pattern. The data for mature animals provide the first direct evidence that flow determines permeability near arterial branches and may account for the inverse spatial correlation between shear stress and disease prevalence at branches of adult human arteries.

Distribution of lipid deposits around aortic branches of mice lacking LDL receptors and apolipoprotein E

Mice with inactivated genes are increasingly used as models of human atherosclerosis. The aim of the present study was to determine whether the characteristic age-related distributions of lipid deposition seen around human arterial branches are replicated in such mice. Lesions occur downstream of branch ostia in immature human aortas, but these regions are spared in adult vessels, with lesions occurring more frequently at the sides or upstream of the branches. We determined the pattern of lipid staining around 102 intercostal branch ostia from apolipoprotein E/low density lipoprotein receptor double-knockout mice aged 9 to 20 weeks by using en face microscopy and a frequency-mapping technique. Lesion prevalence was high in the ostium and the region immediately surrounding it. Frequencies were 2.12+/-0.30 (mean+/-SEM, n=11) times higher upstream than downstream (P<0.01), but the pattern did not resemble the adult human pattern: there were no peaks in frequency at the sides or upstream of the branch, and there was no sparing downstream. Furthermore, a patch of sparing upstream of the branch was seen, which has not been reported for human vessels, and there was no trend toward a more upstream pattern with age. We conclude that knockout mice may not be a suitable model in which to investigate localizing factors.

Distribution of disease around the aortocoeliac branch of white carneau pigeons at different ages

The distribution of atherosclerotic lesions in the human aorta changes with age. Lipid deposition tends to occur downstream of branch sites in immature vessels but upstream of them at later ages. Comparable age-related distributions of spontaneous and induced lesions have been demonstrated in rabbit aortas. Spontaneous disease is known to develop upstream of the aortocoeliac branch in mature White Carneau pigeons. Using a frequency mapping technique, we investigated whether the same pattern or a downstream one occurs in immature pigeons. Lesions in hatchlings occurred upstream of the branch, to the left of the midline. By 5 months, these lesions had expanded, and a second upstream area, to the right of the midline, was also affected. At later ages, disease frequencies increased in both of these regions but not elsewhere. Thus, contrary to findings in rabbit and human aortas, there was no evidence for a switch from a downstream to an upstream distribution with age. The two rabbit distributions have been attributed to the similar age-related patterns seen in the permeability of the arterial wall; the mature but not the immature pattern of permeability is NO-dependent. The absence of the juvenile disease pattern in pigeons suggests that they might show the NO-dependent pattern of permeability at all ages.

Two patterns of lipid deposition in the cholesterol-fed rabbit

A central feature of arterial lipid deposition is its nonuniform and variable distribution. In immature human and rabbit aortas, spontaneous lesions occur most frequently downstream of branch points, but they tend to occur upstream of the same branches at later ages. In cholesterol-fed rabbits, the juvenile pattern has been seen regardless of age. These distributions may be determined by transport properties of the arterial wall, because uptake of plasma macromolecules is elevated downstream of aortic branches in immature rabbits and upstream in mature ones, except during cholesterol feeding, when the juvenile pattern is seen in adult vessels. The effect of cholesterol could reflect its inhibitory influence on the nitric oxide (NO) pathway because the adult transport pattern is NO dependent. Using protocols expected to preserve NO function and the mature pattern of transport during hypercholesterolemia, we made 2 attempts to induce upstream disease in rabbits. In trial I, plasma concentrations of cholesterol were kept within the normal human range for 15 weeks by using dietary levels of 0.05% to 0.2%. Although disease patterns reverse with age in human vessels exposed to these concentrations, lesions in both immature and mature rabbits occurred downstream of intercostal branch ostia. Trial II used older rabbits, a different base diet containing more vitamin E (96 mg/kg rather than 57 mg/kg), and higher levels of cholesterol (1%, administered for 8 weeks). For some animals, extra vitamin E (2000 mg/kg) was added to the diet. The mature pattern of lipid deposition was apparent around intercostal branches in the first group and was accentuated by the additional vitamin E, a change that was associated with a significant increase in the plasma concentration of NO metabolites. Spontaneous lesions, assessed on the base diet, were too rare to have influenced these distributions. This is the first report of upstream disease in the cholesterol-fed rabbit. The results support but do not prove the view that NO and transport are important in atherogenesis.

Contrasting patterns of spontaneous aortic disease in young and old rabbits

The pattern of spontaneous lipid deposition around aortic branch ostia was mapped in New Zealand White rabbits aged 1 month or 2 to 6 years. The young rabbits were studied within 1 day of weaning, and the older rabbits had been maintained on a low-protein, low-fat diet. Plasma concentrations of total cholesterol for the two groups averaged 75 and 18 mg/dL, respectively. Aortas were fixed in situ at a pressure of 90 to 100 cm H2O, stained with oil red O, and photographed en face under an epifluorescence microscope. Areas of staining contrasted in color with the fixative-stimulated autofluorescence of nondiseased tissue and were mapped by placing grids over the photomicrographs. Disease around intercostal ostia was rare, but two distributions were established by combining data from many branches. In weanlings, staining was seen within a triangular area downstream of the branch. In old animals, this area had the lowest frequency of disease; lesions tended to occur downstream of the spared region, along axes lying to either side of it, and at the lateral and upstream margins of the ostium. Disease was less rare at celiac branches. It occurred mainly downstream of the ostium in weanlings, whereas upstream sites were most affected in old animals, although significant disease remained at the juvenile locations. Earlier reports have described similar age-related distributions of disease in human aortas, consistent with a common underlying mechanism. The distributions also correlate with the spatial variations in arterial transport properties established in previous studies, and may be determined by them.

Changes with age in the influence of endogenous nitric oxide on transport properties of the rabbit aortic wall near branches

Uptake of circulating albumin by the aortic wall is greater downstream than upstream of branches in immature rabbits, but the opposite pattern occurs in mature animals. We investigated the role of NO in determining these variations. Descending thoracic aortas of rabbits were cannulated using techniques that avoid depressurization, overstretching, and excessive fluid dynamic stresses at the endothelial surface. They were perfused in situ at a constant pressure and flow rate with oxygenated, protein-containing physiological buffer, with or without N omega-monomethyl-L-arginine, an inhibitor of NO synthesis. Aortas were fixed 7 to 8 minutes after the addition of rhodamine-labeled albumin to this perfusate, and uptake of the tracer near intercostal ostia was measured by digital imaging fluorescence microscopy of sections through the wall. Despite the absence of pulsatile flow, blood cells, and many plasma components, patterns of transport in control experiments were the same as those occurring in vivo; uptake was greatest downstream of ostia in immature vessels and upstream in mature ones, although mean uptake was higher than previously reported. In the presence of the inhibitor, mean uptake in immature arteries was elevated threefold and the maximum tracer concentration occurred deeper in the wall, but there was no change in the fractional difference between regions. Conversely, the reverse of the control pattern of transport was observed in mature arteries exposed to the inhibitor, but there was no change in mean uptake. The reversal was almost entirely prevented by adding excess L-arginine to the perfusate and was largely stereospecific. Endogenous NO thus appears to determine the mature pattern of transport near branches and helps to maintain the barrier function of the immature wall.

Effect of age on the pattern of short-term albumin uptake by the rabbit aortic wall near intercostal branch ostia

Lipid deposition occurs more frequently downstream than upstream of branches in immature human aorta but the opposite pattern is seen in mature vessels. These distributions may reflect variation in the uptake of plasma macromolecules by the aortic wall. We have recently shown that the quasi-steady state uptake of albumin is greater downstream than upstream of branches in immature rabbit aortas and that the opposite pattern occurs in mature animals. Additionally, there is a sharp drop in the mean uptake shortly after weaning. In the present study, the mechanisms underlying these phenomena were investigated by examining the short-term uptake of albumin and its distribution across the wall. Albumin was labeled with a fluorescent dye and introduced into the circulation of conscious New Zealand White rabbits. Thoracic aortas were fixed in situ 10 minutes later and were sectioned through the center of intercostal ostia. Fluorescence from sections was measured by using digital imaging fluorescence microscopy and was converted to tracer concentrations after appropriate autofluorescence levels had been subtracted. In animals aged 45 days, more tracer was detected in the wall downstream than upstream of branches; the difference between regions was > 100% of the mean value. This percentage halved and the mean uptake decreased almost threefold by 75 days. In mature animals, the mean value remained at the 75-day level but the converse distribution was seen; 22% more tracer was detected upstream than downstream. These trends were insensitive to the depth of the intimal-medial layer examined. In each region, the maximum tracer concentration occurred close to the luminal surface but not always within the first 2.9-microns-thick layer of the wall. Maxima were similar in magnitude to those observed at quasi-steady state, but the fall with increasing distance into the wall was much sharper. In many cases concentrations remained constant over most of the media, and rises toward the adventitial boundary were rarely seen. Uptake after 10 minutes predominantly reflects the rate at which tracer enters the wall. The concentration profiles were consistent with most of the tracer having entered from the luminal surface and with the involvement of convective transport. The trends observed with age closely paralleled those occurring at quasi-steady state. Consequently, the latter are also likely to be determined by changes in the resistance of the wall to macromolecule influx.

Flow patterns in dog aortic arch under a steady flow condition simulating mid-systole

To elucidate the possible connection between blood flow and localized pathogenesis and the development of atherosclerosis in humans, we studied the flow patterns and the distribution of fluid axial velocity and wall shear stress in the aortic arch in detail. This was done by means of flow visualization and high-speed cinemicrographic techniques, using transparent aortic trees prepared from the dog. Under a steady flow condition at inflow Reynolds numbers of 700-1600, which simulated physiologic conditions at early- to mid-systole, slow, spiral secondary, and recirculation flows formed along the left anterior wall of the aortic arch and at the entrance of each side branch adjacent to the vessel wall opposite the flow divider, respectively. The flow in the aortic arch consisted of three major components, namely, an undisturbed parallel flow located close to the common median plane of the arched aorta and its side branches, a clockwise rotational flow formed along the left ventral wall, and the main flow to the side branches, located along the right dorsal wall of the ascending aorta. Thus, looking down the aorta from its origin, the flow in the aortic arch appeared as a single helical flow revolving in a clockwise direction. Regions of low wall shear stress were located along the leading edge of each side branch opposite the flow divider where slow recirculation flows formed, and along the left ventral wall where slow spiral secondary flows formed. If we assume that the flow patterns in the human aortic arch well resemble those observed in the dog, then it is likely that atherosclerotic lesions develop preferentially at these sites of low wall shear stress in the same manner as in human coronary and cerebral arteries.

Age-related variations in transport properties of the rabbit arterial wall near branches

Lipid accumulation in the human aorta occurs predominantly downstream of branches in foetuses, neonates and infants but upstream at later ages. The lipid in these deposits may derive from plasma lipoproteins. We have examined uptake of plasma proteins by the rabbit aortic wall near branches as a function of age. Albumin was labelled with a fluorescent dye and introduced into the circulation of animals fed a normal diet. The aorta was fixed in situ 3 h later and the distribution of tracer in sections through the wall was measured by using digital imaging fluorescence microscopy. Net uptake by the intima-media was higher downstream of intercostal ostia than upstream in young animals but this difference decreased and then reversed with age. Furthermore, the average of uptake by both regions was higher shortly after weaning than at later ages. These age-related variations in transport properties may explain discrepancies between previous studies of uptake, resolve apparent inconsistencies between the properties of rabbit and human arteries and, if applicable to man, might account for the non-uniform and changing pattern of lipid accumulation around arterial branches.

Distribution of lipid and raised lesions in aortas of young people of different geographic origins (WHO-ISFC PBDAY Study). World Health Organization-International Society and Federation of Cardiology. Pathobiological Determinants of Atherosclerosis in Youth

At the Morphometric Reference Center of the World Health Organization-International Society and Federation of Cardiology PBDAY (Pathobiological Determinants of Atherosclerosis in Youth) project, we studied left hemiaortas of 5- through 34-year-old male and female healthy subjects who died of traumatic injury. The subjects were either of European, American, Asian, or African origin. Three hundred fifty-five thoracic and 343 abdominal left hemiaortas, stained and photographed at the Malmö, Sweden, World Health Organization Reference Center, were studied. Lipid and raised lesion extent was evaluated by using computerized techniques. Probability-of-occurrence maps of lipid and raised lesion distribution were obtained by image processing. Our data have shown that the distributions of atherosclerotic lesions in the aortic intimal surface, which were similar in the different ethnic groups, also prevailed in branching regions, where low-blood flow shear stress and turbulence occur. The areas involved by raised lesions and by lipid lesions only partially overlapped. Lipid lesion extent, which was different among the ethnic groups, continuously increased with age in males but not in females, in whom the increase ceased at an age range from 15 through 24 years. This suggests that ethnic and dietary factors influence the extent but not the distribution of atherosclerotic lesions in the human aorta. Probability-of-occurrence maps also provided evidence that not every fatty streak will develop into a raised lesion, or will not develop quickly.

Black-white differences in aortic fatty streaks in adolescence and early adulthood: the Bogalusa Heart Study

Although white adults have more extensive aortic surface involvement with fibrous plaques than do blacks, adolescent blacks have more aortic fatty streaks (FS) than do whites of similar ages. Possible determinants of these racial differences in aortic surface involvement with FS were therefore examined in 44 decedents who had previously been examined as part of the Bogalusa Heart Study. Ages at death ranged from 6 to 27 years (mean, 18 years); the median interval between the last risk factor examination and death was 3.5 years. More extensive aortic surface involvement with FS was observed in blacks (n = 11) as compared with whites (n = 33; 37% vs 16%, p = .0003). This racial difference was independent of age at death, and was seen in both male and female subjects. Black-white differences in several of the previously measured risk factors (serum lipids and lipoproteins, blood pressure, and obesity) were also observed, and in both races, aortic FS were related to several of these characteristics. (For example, the correlation between levels of low-density lipoprotein cholesterol and aortic FS was 0.49 in whites and 0.73 in blacks.) However, even after controlling for antemortem levels of risk factors, blacks had an additional 16% surface involvement with aortic FS as compared with whites (p less than .001). These findings suggest that the more extensive surface involvement of the aorta with FS in young blacks is not due to differences in clinical risk factors. Because more extensive raised lesions are found in white adults, the transition of FS to advanced atherosclerotic lesions may differ in whites and blacks.

Protection against atherogenesis with the polymer drag-reducing agent Separan AP-30

The inhibitory effect of Separan AP-30, an anionic polyacrylamide, on atherosclerotic plaque formation in aortas of rabbits on a high (2%) cholesterol diet was tested over a period extending from 37 to 170 days. Atherogenesis was quantified morphometrically by application of a computer-assisted image analysis of histologic cross sections of the aorta. The area of vessel wall-atheroma interface, fraction of lumen occluded, and other indexes of atherogenesis were measured in each of 26 segments of aorta excised from the animals, half of which were administered injections (intravenous) of Separan three times a week. Regression analysis of the morphometric data indicates that the polyelectrolyte exerts a powerful antiatherogenic effect in all regions of the aorta, inhibiting the formation of plaque mass to less than half in the aortic arch and about one-fifth in the descending aorta as compared with the aortic plaque masses in untreated rabbits. Results are compatible with the suggestion that a novel hemodynamic principle in vivo, polymer drag reduction, might be effectively applied against atherosclerosis.