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Biomedical subjects

M R Roach

Publications and source records attributed to M R Roach.

At least 73 records · Page 4Linked to original sources
PubMed1983

Comparison of longitudinal elastic properties of proximal and distal strips of aorta-branch junctions from the abdominal aorta of sheep.

Narrow longitudinal continuous strips were cut from the abdominal aorta and its major branches so that each strip contained the same width of aorta, bifurcation, and branch although the lengths of the three segments were different. A grid was marked on each region, and photographs made at a variety of strains as the whole strip was stretched at a strain rate of 2 cm/min with an Instron tensile testing machine. Measurements from the grids gave the strains for each region, and stress-strain curves were calculated. The proximal bifurcation zone was much more extensible than any of the other regions, owing mainly to changes in the "slack" of the collagen fibers (p less than 0.01). This would imply that the shape and cross-sectional area of the bifurcation region are apt to change between diastole and systole, and implies that model studies which assume the shape of the bifurcation region is constant may not be accurate.

Animals↗
PubMed1983

Quantitative changes in the size of fenestrations of the elastic laminae of sheep thoracic aorta studied with SEM1.

The elastic laminae were extracted from thoracic aortas of 6 adult sheep by treating them in 0.1 N NaOH at 75 degrees C, and the surface of internal elastic lamina (IEL) was observed for windows by scanning electron microscopy. The fenestration analysis on IEL showed that mean diameters of the holes ranged from 0.46 microns (+/- 0.013 SEM) to 1.35 microns (+/- 1.019 SEM), which is smaller than those of human cerebral arteries (7.0 +/- 0.34 at the apex of the bifurcation and 2.1 +/- 0.13 SEM microns in the straight sections; [3]), and mean densities ranged from 6,513 to 31,544/mm2. Both size and density of windows are found to increase when the digestion time in the hot alkaline solution is increased form 1 to 3 h. It is concluded that the IEL of the sheep thoracic aorta has smaller windows than human cerebral arteries and because of the wall thickness the thoracic aorta requires longer digestion times than human cerebral arteries.

Animals↗
PubMed1983

Computer-based video analysis of cerebral arterial geometry using the natural fluorescence of the arterial wall and contrast enhancement techniques.

The walls of mammalian arteries fluoresce with ultraviolet excitation in the wavelength range of 350-400 nm. We are using this property of natural fluorescence in conjunction with episcopic fluorescence microscopy, frozen section techniques, selective contrast enhancement, and a semi-automatic computer-based video analysis system to obtain dimensional data and 3-D coordinate maps of cerebral bifurcation geometry. The computer-video analysis system, comprised of commercially available video components, a Cromemco Z2D Computer, and electronic components built in our lab has a resolution of +/- 1/256 mm at full-screen magnification. Our technique is based upon measurement of the video image of the block face during frozen sectioning of cerebral bifurcations. This technique allows us to obtain axially symmetric coordinate maps of cerebral bifurcation geometry without the use of block markers. In addition to mapping lumenal and adventitial surfaces the system can be used to map atheromatous lesions and the outline of the internal elastic lamina. Our initial geometrical data suggest a linear increase of 50-60% in cross-sectional area in the apical region and widening of the apical region in the plane of the daughter branches.

Aged↗
PubMed1983

Rabbit arterial endothelium and subendothelium. A change in interfacial free energy that may promote initial platelet adhesion.

Endothelial damage and exposure of the subendothelium is accompanied by platelet adhesion and aggregation. Thermodynamically, adhesion will occur if this process decreases the total free energy of the system. In this investigation, we have developed a contact angle technique to measure relative changes in the surface free energy of the arterial wall, before and after the endothelium has been removed. Sections of descending thoracic aorta from seven rabbits were tested with an equilibrium two-phase system of 4% polyethylene glycol (mol wt: 20,000)/4% dextran (mol wt: 2,000,000) in Hepes-buffered physiological saline. The tissue was split longitudinally, immersed in the polyethylene glycol phase, and test droplets of the denser dextran phase were placed on its surface. Advancing contact angles of the drop were measured from photomicrographs taken with polarizing optics. After testing, the endothelium was removed with a saline jet, which we had calibrated previously with scanning electron microscopy, and the tissue was retested. We measured angles of 86.0 +/- 1.1 degree (SEM), n = 64 for the intact endothelium and 20.0 +/- 0.8 degree (SEM), n = 61 on the subendothelial surface. Since the physical behavior of blood is probably similar to our polyethylene glycol bathing medium the subendothelium may also represent a surface of high interfacial free energy in vivo. Assuming that the surface energy of platelets is low, platelet adhesion to the subendothelium could reduce the total free energy of the system, by covering this high interfacial free energy surface.

Adsorption↗
PubMed1983

Relationship between aortic endothelial cell morphology and atherosclerosis in rabbits.

Previous studies on cholesterol-induced sudanophilic lesions in rabbit aortas showed that the earliest lesions were periorificial with the greatest involvement distal to branch sites. In order to determine if there is a relationship between endothelial cell morphology and the regional differences in susceptibility to atherosclerosis we compared cell morphology distal to several aortic ostia and away from ostia. We examined the en face morphology of the intimal surface. Vascular casts were made of silver stained normal aortae. The surface was micrographed by SEM. Cell outlines were entered into a computer to calculate three parameters: the cell orientation index which indicates the cell shape, the en face cell area, and the distance between centers index which gives the position of the center of area with respect to the center of a longitudinal axis drawn through the cell. Differences were found between the region distal to branch sites and the region away from branch sites. Differences were also found between the regions distal to different branch sites. The complex variation of morphology led to no conclusive relationship between endothelial cell morphology and atherogenesis in the non-cholesterol-fed rabbit.

Animals↗
PubMed1980

A quantitative study of the preparation of rabbit aortic endothelial cells for scanning electron microscopy.

Quantitative studies were done with the scanning electron microscope (SEM) on aortic endothelial cells from ten rabbits. Of these, five were plastic casts and five were dehydrated with three different, but standard, techniques. The results indicated that all forms of dehydration caused significant shrinkage artefacts and that these were different in different directions in both the thoracic and abdominal aorta. The greatest shrinkage was found with the critical point drying technique, 45% in the abdominal aorta and 31% in the thoracic aorta. In the abdominal aorta this shrinkage was mainly due to a shrinkage in length (36%) rather than a shrinkage in width (15%). In comparison, in the thoracic aorta critical point drying resulted in a 15% shrinkage in length and a 19% shrinkage in width. Air drying and alcohol dehydration caused considerable shrinkage (29% and 18% respectively in the thoracic aorta, 29% nad 36% respectively in the abdominal aorta). Directional differences were also found with these techniques, for instance alcohol dehydration in the thoracic aorta resulted in 0% shrinkage in length and 18% shrinkage in width.

Animals↗
PubMed1980

Elasticity of ligated carotid arteries of rabbits with and without a cholesterol-rich diet.

Elasticity of carotid arterial segments of rabbits proximal and distal to an induced ligation was examined. In the presence of both ligation and hypercholesterolemia, longitudinal distensibility was decreased while circumferential distensibility increased. The decrease in longitudinal distensibility was attributed to a decrease in the slack of collagen while the increase in circumferential distensibility was attributed to an increase in the slack of collagen as well as a decrease in the elastances of elastin and collagen. Cholesterol alone was found not to affect the elasticity, while ligation acting alone slightly decreased the circumferential distensibility while leaving the longitudinal distensibility unchanged. High serum cholesterol was also found to accelerate intimal proliferation in regions near the ligature. Some intimal proliferation was seen near the ligature, but this could not be quantitated as the sections were too short for pressure fixation. If intimal proliferation is a precursor of atherosclerotic lesions, then formation of these lesions might be accelerated near occluded regions and maybe also in regions of disturbed blood flow when high serum cholesterol is present.

Animals↗
PubMed1980

Flow studies in glass models of aortic aneurysms.

A photodensitometer was used to make a quantitative analysis of flow into and out of glass models of three types of aortic aneurysm (small and large fusiform and small saccular). The "aneurysms" were perfused with steady flow and injected with Evans' blue dye. The aneurysms tended to fill linearly with time, but emptied exponentially. Flow out of both large and small fusiform aneurysms did not alter as a function of the Reynolds number (a nondimensional measurement used to compare flows in tubes of the same shape but of different sizes), while flow from the saccular aneurysm did. The results suggest that the flow in fusiform aneurysms is very sluggish. This may increase the risk of thrombosis and could also lead to a false arteriographic analysis of size, particularly in large aneurysms. Emptying of saccular aneurysms is much more dependent on the Reynolds number and hence on location and blood viscosity.

Aortic Aneurysm↗
PubMed1980

The effect of daily injections of cadmium on the systolic pressure of conscious rats.

The systolic blood pressure of nine conscious male Wistar rats of initial weight 170-200 gm was measured daily with a tail cuff. Once the blood pressure was stable, and the rats were used to being handled, six of them received intraperitoneal injections of 0.6 mg/kg of CdCl2 on five days of each week. The other three received comparable volumes of saline on five days of each week. The injections were carried out over a six-week period. During this period, none of the rats developed any significant change in systolic pressure as measured before the daily injections. By contrast, if the pressure was measured immediately after the injection, the pressure was measured immediately after the injection, the pressure rose abruptly, and remained elevated for several hours. Hypertonic saline had the same effect on one control rat and we speculated that transient hypertension could be due to mesenteric irritation rather than to some metabolic effect of the cadmium.

Animals↗
PubMed1978

A quantitative study of the development of sudanophilic lesions in the aorta of rabbits fed a low-cholesterol diet for up to six months.

Eighteen New Zealand white rabbits were placed on a diet containing 0.25% cholesterol and 6% corn oil for periods of up to 6 months. The animals were divided into 4 gours and sacrificed after 2, 3, 4, and 6 months. The aortae were removed, stained with Sudan III, and analyzed with the polar coordinate technique. While the periorificial lesions developed more slowly on this diet than on the diet with 2% cholesterol and 6% corn oil we had used previously, there was no differences in either the location or the shape of the lesions. In the descending thoracic aorta, lesions developed initially distal to orifices; however, significant lateral and proximal components were observed as atherogenesis progressed. The coronary lesions completely surrounded the ostia in all stages of development. The total area of the lesions was more related to time (r = 0.74, P less than 0.01), than to serum cholesterol (r - 0.51, P less than 0.05) or to cholesterol-time product (r = 0.69, P less than 0.01).

Animals↗
PubMed1978

Artefacts of localization of atherosclerosis in pinned aortas.

Detailed studies of aortas from 8 rabbits showed that serious artefacts occur if the aortas are pinned at their in vivo dimensions, rather than fixed at physiological pressure. In the pinned aortas, the proximal parts of the branches were pulled up onto the aortic wall. This was more pronounced for the large branches of the abdominal aorta than for the smaller intercostal branches. This artefact caused atherosclerotic lesions, which had developed at the origin of the branch, to appear as if they were entirely on the aortic wall. We found that a marked change in the elastin pattern was present at the origin of the branch; this can be used to mark the true origin of the branch. With the pressure technique we found that lesions had different shapes and locations at different branch points.

Animals↗