Biomedical subjects

M R Roach

Publications and source records attributed to M R Roach.

At least 55 records · Page 3Linked to original sources

PubMed1987

Extensibility changes of calcified soft tissue strips from human aorta.

Some degree of calcification was noted in more than half of the 59 aortas of individuals aged from 15 to 88 we have examined at autopsy. The calcification, which is determined by x-raying the opened and flat aorta, is in patches. We have studied the influence of calcification on stress versus strain, breaking strength, and modulus of elasticity of strips of aorta to determine its importance in vascular disease. Strips of aortic wall 5 x 30 mm were cut with orientation parallel or perpendicular to the vessel axis. Elongation versus load was measured with an Instron tensile testing machine. The true stress and true strain were calculated for both calcified and uncalcified strips from the thoracic and abdominal regions in both orientations. From the stress-strain curve the following values were selected: strain, stress, and slope at 80 mmHg equivalent pressure (1 mmHg = 133.3 Pa); maximum stress, strain, and slope; and breaking stress, strain, and slope if the sample broke. There were statistically significant differences in 13 of the 36 categories between calcified and uncalcified strips. The breaking strength and strain is lower in the calcified strips. The stress-strain curve for the uncalcified strip was mathematically transformed by reducing the amount of elongation so that the curve coincided with that of the calcified strip for eight matched pairs from the same individuals. The calcification appears to immobilize part of the strip, probably causing the boundary of the calcified tissue to be a region of high stress where tissue breakdown can occur.

Adolescent↗

PubMed1987

Hemodynamic method to predict whether hunterian ligation of the basilar artery will lead to thrombosis of basilar bifurcation aneurysms.

In some cases, basilar artery aneurysms cannot be repaired surgically and the basilar artery is occluded near the neck of the aneurysm to stop flow into the aneurysm. After the operation, the aneurysm can fill only by flow through the posterior communicating arteries (PCoAs). Hemodynamically if the flow were the same in both PCoAs and there were no phase lag in the pressures, there would be no pressure gradient for flow to go across the neck of the aneurysm and therefore the aneurysm would thrombose. We have assumed that the diameter of the artery is roughly proportional to the flow that goes through it chronically. We measured the diameters of the PCoAs in 25 patients who had hunterian ligation of the basilar artery. We also measured the maximal width, height, and depth of the aneurysms on angiograms obtained before and after operation. Eleven aneurysms thrombosed completely and had a diameter ratio of greater than 0.6; 10 aneurysms thrombosed partially and had a diameter ratio of 0.46 approximately 1.0; 4 aneurysms did not change and had a diameter ratio of less than 0.45. The ratio of the sizes of the PCoAs pre- and postoperatively was comparable in most cases, so we believe that it is possible to predict reasonably accurately from this simple measurement whether the aneurysm is likely to thrombose if the basilar artery is ligated.

Basilar Artery↗

PubMed1986

The structure and elastic properties of arterial junctions.

Light microscopic studies showed marked differences in the elastin pattern at aorto-branch junctions on the proximal and distal lips of the junctions, both for small elastic branches such as the intercostals, and for the large muscular branches arising from the abdominal aorta. A light-pipe method showed that the internal apical curvature of translucent human cerebral arteries became flatter as the pressure increased. Longitudinal strips of aorto-branch junctions from sheep and dogs were stretched at known strain rates. There appear to be differences in the two species as the flow divider is least distensible in sheep and most distensible in dogs. Scanning electron microscopy of NaOH-digested arteries showed that the internal elastic membrane is a fenestrated sheet, the adventitia has fibrous elastin, and the medial layers are transitional. There are many interlamellar connections.

Animals↗

PubMed1985

Steady flow visualization in a rigid canine aortic cast.

Steady flow studies were conducted in a transparent canine aortic cast. The cast segment stretched from the aortic valve to beyond the renal arteries and included all major branches. Flow was visualized by analysis of dye streaklines. Flow rates for basal and exercising cardiovascular states were simulated. The Reynolds numbers in the ascending aorta for basal and exercising conditions were 900 and 1587 respectively. Aortic core flow was laminar in basal simulations. Disturbed flow commenced in the upper descending aorta with exercising flow rates. Separation zones existed along the inner curvature of the aortic arch and the proximal walls of the brachiocephalic, left subclavian, and coeliac arteries. Such zones may exist over a portion of the cardiac cycle. If either renal artery was occluded, then a vortex formed. This vortex is associated with high shear regions which correlate well with sites where sudanophilic lesions have been reported in cholesterol-fed nephrectomized rabbits.

Animals↗

PubMed1985

Organization of medial elastin at aortic junctions in sheep and lambs.

Aortas from four sheep and three fetal lambs were fixed at physiological pressure in 10% neutral buffered formalin. The regions with branches were serially sectioned in either cross or longitudinal section at 7-micron intervals and stained for elastin with Gomori-aldehyde-fuchsin. A large model of one aortointercostal junction was made from Plexiglas to show that bundles of elastin appeared to be continuous from the aorta into the branch. These bundles were then studied from large photomicrographs of the other junctions. At the intercostals and lumbars, the elastin lamellae ran continuously from the outer third of the media into the branch. There was often an added "pad" of elastin and other acellular material on the flow divider (distal lip). The large muscular branches which arose from the abdominal aorta have much less elastin than the intercostals. In them the aortic elastin appears to merge into a raphe on the proximal and lateral sides of the junction, with a very abrupt transition. A "tongue" of muscle from the branch often penetrated into the media of the aorta distally. Occasionally a small acellular cap was seen on the apex of the flow divider. There were few significant differences between the lambs and the sheep, probably because embryologically the arteries develop very early. The proximal and distal lips of all junctions were easily distinguished from each other, and the small and large branches were also different. We suspect these regions may respond differently to pressure, but we did not test this hypothesis.

Age Factors↗

PubMed1985

The elastic properties of canine abdominal aorta at its branches.

The elastic properties of the abdominal aorta at regions of junctions were studied using strips from 17 dogs. Strips of tissue cut longitudinally and circumferentially at the celiac, mesenteric, and renal branches were used to compare the properties of the proximal and distal junctions, as well as the aorta and artery regions adjoining. The tissues were stored for at least 24 h to ensure that no active component of the smooth muscle remained. The elastic properties measured here are due to elastin and collagen, with a small contribution from dead smooth muscle cells. The tissue strips were tested at 20 degrees C while immersed in saline using an Instron tensile testing machine. Elongation of the three regions was measured from photographs taken as the tissue was stretched. Stress values went to 200 kN/m2 as the strain increased to approximately 0.8. (The physiological range for the dog was calculated as 40-85 kN/m2.) The distal junctional region was found to be the most extensible for both longitudinally and circumferentially oriented strips. These results have important implications for flow models as they imply that the shape of the junctional region probably changes between diastole and systole.

Animals↗

PubMed1985

Scanning electron microscopic studies of the vasa vasorum of thoracic aortas.

Using hot alkaline solution, the elastic laminae were extracted from aortas and observed with scanning electron microscopy. Vascular structures were found in the elastin layers of the tunica media in descending thoracic aortas of sheep, dogs, and pigs, and these tube-like structures were filled with elastomer which was injected through the heart of the animal in vivo. Sub-intimal microvessels were also found to be filled with the elastomer and it is concluded that vasa vasorum can exist close to the internal elastic lamina in these animals.

Animals↗

PubMed1985

A morphological comparison of aortic elastin from five species as seen with the scanning electron microscope.

The elastic laminae were extracted from thoracic aortas of adult animals including sheep, dogs, rabbits, cats and rats by treating them in hot alkaline solution (0.1 N NaOH at 75 degrees C) and observed with a scanning electron microscope. The elastic laminae are comprised of sheet-like internal elastic lamina, fibrous and membraneous elastin in tunica media, interlamellar fibers and hollow spaces which we presume were formerly filled with smooth muscle cells in the tunica media. These structures are the same in all five species except that the number of layers and the total thickness of the wall differs.

Animals↗

PubMed1985

Stenotic and occlusive disease of the venous drainage system of deep brain AVM's.

Angiograms obtained prior to treatment in 53 cases of deep-seated cerebral arteriovenous malformations (AVM's) were retrospectively analyzed with particular attention to the topography of the AVM nidus and the venous drainage. The location of the lesion was determined by a combination of angiography and computerized tomography. Twenty-seven AVM's involved the basal ganglia and thalamus, 12 were located in the corpus callosum, six were intraventricular, and eight involved the mesencephalon and brain stem. Forty-one patients (77.3%) presented with intracranial hemorrhage. Vessel wall irregularities and/or stenosis of the system of the vein of Galen were observed in 14 cases, and occlusion of the deep venous system was present in seven cases. These AVM's showed numerous collateral venous pathways through enlarged medullary and cortical regional veins. There was dominant participation of the basal vein of Rosenthal in all cases. Unique local hemodynamic factors produced by the convergence of the draining veins of the AVM's into the vein of Galen and straight sinus may lead to a higher incidence of stenosis and/or occlusion of the venous drainage. The relatively high incidence of intracranial hemorrhage in these deep-seated AVM's may suggest a relationship between an increased incidence of intracranial bleeding and impaired venous outlets.

Adolescent↗

PubMed1984

Comparison of fenestrations in internal elastic laminae of canine thoracic and abdominal aortas.

All non-elastin tissue was removed from canine aortas by placing them in 0.1 N NaOH at 75 degrees C for varying periods of time. The segments of aorta were weighed in a Mettler Chemical Balance at intervals. In 10 dogs the average weight of the thoracic aorta was 5.01 +/- 0.388 (SE) g while that of the abdominal aorta was 3.08 +/- 0.346 g. After digestion, the thoracic aorta weighed 3.34 +/- 0.0275 g and the abdominal aorta 0.85 +/- 0.085 g. Thus, the elastin makes up 67% of the thoracic aorta but only 28% of the abdominal aorta. These are equivalent to 0.334 g/kg body weight for the thoracic aorta and 0.224 g/kg body weight for the abdominal aorta. The values were always stable between 5 and 7 h and usually between 3 and 12 h. Aortic elastin was obtained from 5 dogs after 5-7 h of digestion and prepared for analysis by scanning electron microscopy. The dimensions of the fenestrations in the internal elastic laminae were quantified as described previously. The lower abdominal aorta had the largest holes (2.227 +/- 0.048 micron), and the upper thoracic aorta the smallest holes (0.954 +/- 0.032 micron). There was no significant difference in the size of the fenestrations along the thoracic aorta, but those in the lower abdominal aorta were larger than those in the upper abdominal aorta. The possible significance of the fenestrations in the genesis of aortic disease is discussed briefly.

Animals↗

PubMed1983

The pattern of elastin in the aorta and large arteries of mammals.

The arteries of mammals contain large amounts of elastin arranged in concentric lamellae known as medial lamellar units (MLU). In adult mammals of a variety of species the number of lamellar units is roughly proportional to the radius of the artery and the tension/MLU ratio is roughly constant in all species, but greater in the abdominal than in the thoracic aorta. Re-analysis of these data shows that the number of MLU of the abdominal aorta is linearly related to the pulse pressure, while the number of MLU in both the thoracic and abdominal aorta increases exponentially with stroke volume. Preliminary data are presented showing the decrease in number of MLU along the thoracic aorta of both fetal lambs and sheep, and evidence is provided that some of this elastin may be involved in the formation of the small arteries, such as the intercostals, which arise from the aorta. Scanning electron microscopy showed that the elastin on the intimal side of the media was in the form of fenestrated sheets while that on the adventitial side was a fibrous network. The size and density of the fenestrations was greater in fetal lambs and may play a role in allowing growth of the artery.

Animals↗

PubMed1983

Rabbit bladder-surface mucin: a thermodynamic mechanism for inhibiting bacterial adhesion.

A possible thermodynamic mechanism for the inhibition of bacterial adhesion to the epithelial bladder surface was investigated in rabbits. Contact angles of aqueous polymeric droplets were measured to assess the relative hydration and surface-free energy, of normal and mucin-free bladder surfaces. We measured an angle of 91.2 +/- 1.2 degrees (SEM), n = 37 for the intact mucin surface and an angle of 120.5 +/- 1.2 degrees, n equal 46 for the epithelium after the mucin was removed with acid. These results indicate that mucin makes the epithelial surface significantly more hydrophilic and so produces a very low free energy interface with the urine environment. Such a low energy surface would inhibit bacterial adhesion because the surface already exists at its free energy minimum.

Adhesiveness↗

PubMed1983

The use of ligament efficiency to model fenestrations in the internal elastic lamina of cerebral arteries. I--modelling scheme.

The spatial geometry of fenestrations (windows) in the internal elastic lamina from human cerebral arteries is being characterized by a single parameter termed 'ligament efficiency', which is a ratio of the solid band of material to the centre-to-centre spacing between two or more holes. As a result, the apparent random distribution of fenestrations with variable diameters may be represented as a uniform array of holes with a single diameter. The actual arrangement of fenestrations from three separate tissue specimens were replicated in thin latex sheets by transposing the image of the fenestrations from photomicrographs obtained with the scanning electron microscope. In a similar manner, the uniform array of holes with an equivalent ligament efficiency are modelled in latex sheets. The tensile (stress-strain) properties of the latex sheets representing the replication and model configurations were comparable for all three specimens, even though their individual ligament efficiencies were different. The close similarity between the elastic characteristics for the two configurations, verifies the application of ligament efficiency to represent the spatial geometry of a perforated material such as the fenestrated internal elastic lamina.

Biomechanical Phenomena↗

PubMed1983

The use of ligament efficiency to model fenestrations in the internal elastic lamina of cerebral arteries. II--analysis of the spatial geometry.

During uniaxial extension of the latex model, the holes (both marked on the sheet and perforated) demonstrated a distinctive change in their shape, from circular to elliptical. Measurements of the axial and transverse diameters of a consistent row of holes, along with the width of the sample at distinct elongations were converted into an area, ligament efficiency (transverse and axial) and shape factor (eccentricity). Values for the expansion ratio of the holes and necking of the latex sheet were also computed. The perforations expanded more rapidly than with the holes only marked on the solid material, which translated into a more rapid increase for the axial diameter, area and eccentricity, while the axial ligament efficiency decreased more rapidly. The transverse diameter and transverse ligament efficiency remained essentially constant. Necking of the latex sheet was consistent for all of the specimens (both solid and perforated). The relative expansion ratios paralleled the relative changes for the standardized stresses presented in Part I.

Biomechanical Phenomena↗

PubMed1983

Are enlarged fenestrations in the internal elastic lamina of the rabbit thoracic aorta associated with poststenotic dilatation?

A stenosis amounting to 45-60% of the luminal diameter was made in the thoracic aorta of six New Zealand White rabbits. The progress of the ensuing poststenotic dilatation (PSD) was followed by daily X-ray analysis after which angiograms were taken for the calculation of luminal diameters. Specimens of the aorta proximal and distal (PSD) to the stenosis were digested to expose the internal elastic lamina (IEL) and viewed using a scanning electron microscope. The dilatations, which ranged between 7 and 30% reached their maximum diameter after only 8-10 days. The average diameter of the fenestrations distal (2.30 +/- 0.53 SEM) to the stenosis were significantly larger (p less than 0.01) than proximal (1.33 +/- 0.16 SEM) and covered a significantly larger (p less than 0.005) percent of the surface area of the IEL. It is suggested that the enlarged fenestrations may result in changes to the mechanical properties of the IEL which would play an important role in the genesis of PSDs.

Animals↗

PubMed1983

Medial elastin in the thoracic and abdominal aorta of sheep and lambs.

Aortas were removed from six mature lambs and four sheep and pressure fixed at 100 and 120 mmHg pressure (1 mmHg = 133.322 Pa), respectively, in 10% buffered formalin. The numbers of elastin layers were counted from cross sections at different distances down the aorta, from the distal arch to the iliac bifurcation, and showed a linear decrease in the thoracic aorta. In the abdominal aorta there was no difference in values from the diaphragm to the aortoiliac bifurcation in the lamb, but a slight decrease in the sheep. If y = mx + b, where y is the number of medial lamellar units (MLU), b the intercept, x the distance from the last brachiocephalic branch in centimetres, and m the slope, we obtained the following equations (with standard deviations): lamb thoracic aorta; y = -6.29 (+/- 0.71)x + 106 (+/- 12); sheep thoracic aorta; y = -3.46 (+/- 0.40)x + 140 (+/- 21.4); lamb abdominal aorta; y = 0.51 (+/- 1.48)x + 37 (+/- 7.7); sheep abdominal aorta; y = -0.85 (+/- 0.28)x + 66 (+/- 5.9). Tension per lamellar unit was calculated and plotted versus distance yielding a linear increase in the entire lamb aorta but an abrupt increase between thoracic and abdominal aortas in the sheep. This causes the pulse wave to move uniformly with increasing speed along the length of the lamb aorta but would cause an abrupt change in the wave at or about the diaphragm in the sheep. Distortions in the pulse wave could produce local stress concentrations in the abdominal aorta which might render it more susceptible to atherosclerosis than the thoracic aorta.

Animals↗

PubMed1983

Static elastic studies of lathyritic rabbit carotid arteries and thoracic aorta.

Sixteen New Zealand White rabbits with an average initial weight of 1.6 kg were used to determine if lathyrism altered the static elastic properties of the aorta and carotid arteries. Eight were given 1% beta-aminopropionitrile in their drinking water for the same period. All were fed regular rabbit chow. Blood pressures and body weights were taken twice weekly. Blood pressure was not significantly different between the two groups but the lathyritic animals did lose weight while the controls gained. The rabbits were sacrificed at the end of 4 weeks with an overdose of sodium pentobarbital (Nembutal) and the carotid arteries and thoracic aorta were removed for pressure--volume experiments. From these experiments tension--strain curves, elasticities, and slack of the collagen were obtained. The longitudinal distensibility curves for the aortas and carotid arteries for both groups were almost identical. The longitudinal elasticities of elastin and collagen, and the slack were not significantly different between the two groups. The circumferential-distensibility curves for the same arteries showed few differences, however, the elasticities of elastin and collagen, and the slack decreased indicating an alteration in the elastin and a decrease in collagen fibres or a defect in the intramolecular cross-links of collagen.

Animals↗

PubMed1983

Mechanical anisotropy of purified elastin from the thoracic aorta of dog and sheep.

Mechanical anisotropy was found in elastin from the wall of the thoracic aorta by testing digested vessels from seven mature dogs and five pregnant ewes. The elastin was purified by removing the muscle and collagen with 0.1 N NaOH at 75 degrees C for 5 h. Strips oriented circumferentially and longitudinally with respect to the vessel axis were cycled at increasing loads until failure. Combining the results for four dogs and three sheep the ultimate tensile strength was 405 X 10(3) +/- 155 X 10(3) SD N/m2 circumferentially and 189 X 10(3) +/- 85 X 10(3) SD N/m2 longitudinally. The difference is significant at p less than 0.01. The ultimate strain was not significantly different, 1.19 +/- 0.29 SD circumferentially and 1.01 +/- 0.26 SD longitudinally. At 0.4 strain, the Young's modulus for four samples from four dogs was 404 X 10(3) +/- 64 X 10(3) SD N/m2 circumferentially; the modulus for five samples from five dogs was 245 X 10(3) +/- 60 X 10(3) SD N/m2 longitudinally. The difference is significant at p less than 0.05. At 0.7 strain, the Young's modulus for four dogs was 486 X 10(3) +/- 82 X 10(3) SD N/m2 circumferentially and 343 X 10(3) +/- 62 X 10(3) SD N/m2 longitudinally. The difference is significant at p less than 0.05. The reasons for the anisotropy in terms of the structure are not obvious from preliminary studies using the scanning electron microscope with stretched samples.

Animals↗