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Biomedical subjects

M R Roach

Publications and source records attributed to M R Roach.

At least 19 recordsLinked to original sources
PubMed1999

Local changes in collagen content in rabbit aortic atherosclerotic lesions with time.

A video-microdensitometry method was used to quantify collagen on a pixel by pixel basis at specific locations within atherosclerotic lesions, induced by feeding New Zealand White rabbits a declining cholesterol diet. Probability mapping (done previously) showed the lesions occurred in predictable locations so the age of any one area of a lesion could be estimated. The oldest part of the lesion was on the lateral lip of the flow divider as lesions always developed there first. Serial sections through three lesions showed the distribution of collagen within the plaque. The measurement of all the lesions showed that early lesions had low collagen levels: 3-6% for the intercostals and 8-11% for the renals. Collagen increased consistently with time on the diet to 11-15%, for the intercostal and approximately 17% for the renal. The aorto-renal lesions were more severe; thicker and with a higher percentage of collagen. The greatest collagen content was on the lateral lip of the flow dividers, where controls had intimal thickening. No fibrous caps were seen. This study shows conclusively that collagen is not evenly distributed in lesions, but develops progressively in specific locations of fatty plaques with the duration of cholesterol feeding. Intimal thickening predisposes to early collagen development.

Animals↗
PubMed1999

The role of radial elastic properties in the development of aortic dissections.

PURPOSE: The response of the upper and lower thoracic aorta to radial tensile stresses was compared with the response to circumferential and longitudinal stresses to understand the role of tensile stress in the tearing phase of an aortic dissection. METHODS: Square tissue samples (1.6 by 1.6 cm) were cut from the upper and lower segments of six porcine thoracic aortas and were elongated in the radial direction with a tensile testing machine. The radial extensibility of the thoracic aorta was compared with adjacent tissue samples that were tested in tension in the circumferential and longitudinal directions based on Young's modulus (ie, the ratio of tensile stress to strain). RESULTS: The elastic properties of the thoracic aorta in the radial direction were markedly different from both the circumferential and longitudinal properties. The average Young's modulus (calculated immediately before failing) was significantly lower in the radial direction for both the upper and lower thoracic segments (61.4 +/- 4.3 kPa, SEM) than the Young's modulus of corresponding segments in the circumferential and longitudinal directions that were not tested to failure (151.1 +/- 8.6 kPa and 112.7 +/- 9.2 kPa, respectively; P <. 05). Sections 7 micrometer thick were collected from four samples obtained from one upper thoracic aorta that were strained at 0, 1.0, 2.5, and 4.0 and then stained either with Movat's pentachrome or with hematoxylin and eosin. Histological analysis of the samples stressed in the radial direction revealed that smooth muscle cells were torn loose from their attachments to each other and to adjacent elastin. CONCLUSION: Although the aorta normally functions under radial compressive stresses associated with lumen blood pressure, these results show that the aorta tears radially at a much lower value of stress than would have been predicted from previous studies that have reported longitudinal and circumferential Young's modulus. This could explain why dissections propagate readily once the initial tear occurs.

Aortic Dissection↗
PubMed1999

Tear propagation in isolated, pressurized porcine thoracic aortas.

OBJECTIVE: To determine the pressure required for the initial medial tear, and for propagtion of dissections, within the media of isolated pressurized porcine thoracic aorta, and to determine whether these vary with tear depth. DESIGN: India ink-stained saline was injected into the media of 48 fresh porcine descending thoracic aorta that were distended with 130 mmHg pressure. The fluid was infused into the media through a 25 gauge needle connected to a constant infusion pump, and the pressure at the entrance to the needle was monitored with a Cobe pressure transducer. The two lumens were not connected. Blebs were made at different depths and measured at the end of the experiment with a Starrett gauge. Seven casts were made in pressurized aortas and nine in nonpressurized ones to determine the shape of the blebs by injecting different volumes of mercox casting material into the media by hand. RESULTS: Mean tearing pressure, expressed as the transmural pressure between the bleb and the true lumen (which was at 130 mmHg) was 547 mmHg (range 208 to 995). Mean propagation pressure was 54 mmHg (range 25 to 93). The ratio of the two pressures was 10.1 (range 5.2 to 21.7). None of these pressures was correlated with tear depth. Casts showed that the leading edge was sharp in all directions. Small blebs were roughly spherical, and large ones were cylindrical with roughly hemispherical ends between the cylinder and the sharp leading edge. CONCLUSIONS: Dissections can propagate at pressures that could be reached under physiological and certainly pathological conditions. The initial tear requires pressures that are too high to create biologically except with trauma. The leading edge of the dissection appears to be very sharp and likely explains why the dissection propagates at relatively low pressures. Tear depth does not affect the results.

Animals↗
PubMed1998

Thickness, taper, and ellipticity in the aortoiliac bifurcation of patients aged 1 day to 76 years.

Lumen area, ellipticity, and wall thickness were measured in the aortoiliac bifurcations obtained at autopsy from 14 patients aged between 1 day and 76 years. The method involved freezing pressure-fixed, stained bifurcations on the stage of a refrigerated microtome and then looking at the block face while sections were removed. Area change was normalized over segment length to produce a value of either taper (narrowing, in mm2/mm), or flare (expansion). The aortoiliac bifurcations were divided into three regions based on the area changes: an apical region corresponding to the bifurcation apex (taper = 2.96 +/- 0.80 mm2/mm), a preapical region (flare = 3.58 +/- 0.87 mm2/mm), and the postapical region (flare = 0.82 +/- 0.80 mm2/mm). Preapical lumen ellipticity showed that the anterio-posterior diameter was always less than the lateral diameter, while the degree of ellipticity increased with age. Average circumferential wall thickness, assessed in polar coordinates, decreased between 0 degree (right lateral) and 120 degrees, while a significant increase in wall thickness was present between 120 degrees and 200 degrees. The most striking difference was found in the 1-day-old, which was very thin posteriorly. This detailed geometric analysis of the aortoiliac bifurcation suggests that taper, flare, and variations in both circumferential and longitudinal wall thickness need to be considered when trying to correlate physical factors in the aorta with the precise location of atherosclerotic lesions and wall remodeling.

Adolescent↗
PubMed1998

The role of taper on the distribution of atherosclerosis in the human infra-renal aorta.

The role of vessel taper on the distribution of atherosclerotic lesions was examined in 11 photographs of human infra-renal aortas, aged 42-76. The aortas, opened anteriorly and pinned flat with the luminal surface facing up, were analysed using Mocha Imaging software. The circumference was measured at intervals of 10 mm and fitted with a third order polynomial function. Taper was calculated for three segments within each aorta as the angle produced by the slope of the decrease in circumference with length. The percent surface area covered by fatty streaks correlated strongly to the coefficients of the polynomial function, while the raised lesions showed a significant increase with an increase in taper angles in the different segments. The results suggest taper plays a role in the distribution of both fatty streaks and raised lesions, however, the nature of the cause and effect remains to be determined.

Adult↗
PubMed1998

The effect of tear depth on the propagation of aortic dissections in isolated porcine thoracic aorta.

An in vitro model was used to determine the influence of tear depth on the propagation pressure of aortic dissections. Saline was injected into the media of segments of 20 porcine thoracic aortas to create blebs. A circumferential slit was made on the intimal side of each bleb, connecting the true lumen to the false lumen. Each aorta was then pressurized under no-flow conditions until propagation in either the anterograde or retrograde direction occurred. Histological sections of each principal propagating edge were used to determine depth of tear, measured as the ratio of elastin layers in the intimal flap to the elastin layers in the intact wall. Propagation occurred for tear depths ranging from 0.44 to 0.89, with dissections closest to the adventitia (with tear depths near 1) requiring the lowest pressures. Propagation pressure (P) depends on the number of elastin layers (L) in the outer wall of a dissection, P = 0.44 L + 25(kPa), r2 = 0.465, p = 0.003 and also on tear depth (d): P = -58 d + 81(kPa), r2 = 0.547, p < 0.001. Various in vivo factors are discussed which may affect these experimentally determined relationships.

Algorithms↗
PubMed1998

Elastic response of human iliac arteries in-vitro to balloon angioplasty using high-resolution CT.

Previous angioplasty studies have used angiography and intravascular ultrasound to obtain vascular dimensions. These imaging methods do not always provide reliable measurements due to limitations in image orientation and resolution. In this study, high-resolution (0.1 x 0.1 x 0.5 mm) transverse CT slices were obtained from human common-iliac arteries in vitro to study their elastic response pre- and post-angioplasty. Seven iliacs from five patients were imaged over the physiological pressure range both pre- and post-angioplasty. Contrast was obtained with humidified air surrounding the artery. Angioplasty was done with 10 or 12 mm diameter Medi-Tech balloon catheters with a balloon pressure of 300 kPa held for 30 s. Lumen circumference, c, measured from the images, was plotted against pressure, P, and curve fitting showed c = A(1 - e(-KP)) + B where A, K, and B are fitting parameters. Six lesions appeared soft and were compressed, while one was calcified and partially lifted off the wall. Normalized changes in parameters B and K were much higher post-angioplasty in the calcified lesion, and were over 3 standard deviations from the means of the normalized changes in the six compressed lesions. Balloon/stenosed lumen diameter ratios greater than 1.2 produced a lumen area increase of 38.6 +/- 4.1%(S.D.)(n = 3); ratios less than 1.2 produced an increase of 4.4 +/- 5.1%(S.D.)(n = 4). There was no correlation between area increase and balloon/normal lumen diameter ratio (the value used clinically). Arteries with lesions containing stiffer plaques that tear from the artery wall during angioplasty appear more distensible over the physiological pressure range post-angioplasty.

Aged↗
PubMed1998

The effect of storage time and repeated measurements on the elastic properties of isolated porcine aortas using high resolution x-ray CT.

A Laboratory CT scanner with a resolution of (0.1 mm)3 was used to determine if storage up to 7 days in saline at 4 degrees C and (or) repeated measurements would alter the compliance, C, and incremental elastic modulus, Einc, of isolated porcine aortas. All specimens were obtained fresh, made pressure-tight, and then mounted in the scanner, with humidified air used to produce adequate x-ray contrast. The specimens were imaged at pressures of 4, 8, 12, 16, 20, and 24 kPa, and vessel measurements were then obtained with a computerized technique and analyzed. Seven thoracic aortas were studied on days 0, 3, 5, and 7, with a significant change (p < 0.05) in compliance first occurring after three imaging studies (i.e., day 5). Compliance of the fresh thoracic aortas (mean +/- SD) was 0.90 +/- 0.28 mm/kPa at 14.4 kPa and 0.85 +/- 0.31 mm/kPa at 22.5 kPa. Six thoracic aortas were studied only on days 0 and 6 with no intermediate measurements. They showed no change in either compliance (0.88 +/- 0.07 mm/kPa at 14.4 kPa and 0.64 +/- 0.09 mm/kPa at 22.5 kPa) or Einc (0.46 +/- 0.05 MPa at 14.4 kPa and 0.88 +/- 0.15 MPa at 22.5 kPa) from day 0 to day 6. Thus, number of measurements rather than time appears to be the important factor. Six abdominal aortas were studied similarly but on days 0, 3, and 6. No significant change occurred in compliance (0.15 +/- 0.06 mm/kPa at 14.4 kPa and 0.032 +/- 0.026 mm/kPa at 22.5 kPa) but Einc showed a change, possibly due to their viscoelastic properties. We conclude that this nondestructive CT measurement method is suitable for repeated studies on porcine thoracic aortas, but not abdominal aortas, if the measurement involves two consecutive imaging sessions separated by no more than 6 days.

Animals↗
PubMed1998

Surface features of human aortic atherosclerosis as seen with scanning electron microscopy.

Using SEM, we have observed surface structures of atherosclerotic lesions of human aortas obtained from autopsies ranging from 59 to 84 years of age (5 males and 4 females). We have found four major interesting features on the lumenal surface of the aortas: 1) blood cells including leukocytes adhering to the endothelial surface, 2) a de-endothelialized surface showing both elastogenesis and elastolysis, 3) abundant cholesterol-ester crystals in extracellular spaces, and 4) cave-like structures possibly suggesting new capillarization in the thrombotic atherosclerotic plaques. We concluded that SEM has a great value in revealing more interesting surface structures if morphological studies are previously done in detail so that the characteristic shapes can be identified, and perhaps then meaningful interpretations can be made on the mechanism of human atherogenesis.

Aged↗
PubMed1996

Collagen quantitation by video-microdensitometry in rabbit atherosclerosis.

A video-microdensitometry method was developed to measure the mass fraction of collagen in portions of tissue sections. A frame grabber and computer are used to capture micrographs and calculate the collagen fraction at each pixel. The method is based on the stoichiometric staining of collagen by picrosirius red stain, and was calibrated for glutaraldehyde fixed tissue; a detailed map of collagen distribution throughout a six-month rabbit atherosclerotic lesion was made. The method is reliable, fast and easily reproduced, since it uses readily available equipment.

Animals↗
PubMed1995

A new probability mapping method to describe the development of atherosclerotic lesions in cholesterol-fed rabbits.

A new probability mapping method was developed to quantify the size and location of lesions near aortic orifices. The precise location of any part of the lesion could be compared between rabbits. Colour photographs of lesions were projected onto a digitizing tablet, and coded as lesion or non-lesion. Next the orifices were warped onto a standard orifice, and then the lesion mapped to maintain the original length and angular location of the lesion from the edge of the orifice. This method, unlike the previously used polar mapping method, excludes neither absent lesions nor ones which surround more than one orifice. In contrast to other probability mapping methods it warps the orifice rather than the artery wall containing the lesion, and so is easier to use for correlation with histological studies. The eventual aim is to use the probability maps as a tool to estimate the age of various positions of the lesion and to identify areas for histological sampling. The method was used to describe the distribution of lesions in 21 rabbits fed a diet with cholesterol levels declining from 0.5% during the first week, to 0.25% during the next two weeks, to 0.125% for weeks 3-10, to 0.1% for weeks 11-24. This feeding protocol produces fatty lesions which are transformed into fibro-fatty and fibrous lesions with time.

Algorithms↗
PubMed1994

The composition and mechanical properties of abdominal aortic aneurysms.

PURPOSE: The composition and mechanical properties of abdominal aortic aneurysms (AAAs) were studied. METHODS: Stereologic study was used to measure volume fractions of the components of the aortic wall. Histochemical methods with picrosirus red and safranin O were developed to differentiate collagen from ground substance because they are difficult to distinguish from each other on histologic sections. Uniaxial tensile stress tests were carried out on a tensile-testing machine, and a stress-strain curve was plotted for each sample to study the mechanical properties of AAAs. The curves were fitted exponentially so sigma = aeb epsilon, where sigma is stress, epsilon is strain, and a and b are parameters. RESULTS: In aneurysms (n = 8) the volume fraction of elastin was decreased from 22.7% +/- 5.7% to 2.4% +/- 2.2%, and the volume fraction of smooth muscle cells was decreased from 22.6% +/- 5.5% to 2.2% +/- 2.0%, whereas the volume fraction of collagen and ground substance combined was increased from 54.8% +/- 4.5% to 95.6% +/- 2.5% compared with nonaneurysmal aortas (n = 8). There was no significant difference (p > 0.05) in the ratio of collagen to ground substance (2.1 +/- 0.5 vs 2.0 +/- 0.4) between AAAs and nonaneurysmal aortas. The elastic diagrams showed that AAAs (n = 7) are less distensible and stiffer than nonaneurysmal aortas (n = 5). Parameter a was unchanged (p > 0.5), but parameter b was significantly greater (p < 0.002) for aneurysmal aortas. CONCLUSIONS: Both the composition and mechanical properties of AAAs are different from those of nonaneurysmal aortas. The aneurysms were stiffer, and the volume fractions of collagen and ground substance were increased, whereas the volume fractions of elastin and muscle were decreased in aneurysms.

Aged↗
PubMed1994

Calcium mass in human aortas from autopsy.

We used a single-energy x-ray method and an image processing system to measure the amount of calcium salts deposited in 60 human aortas (41 male and 19 female) of ages 15-88 y. The aortas were removed at autopsy, slit lengthwise and preserved in formalin. The aortas were x-rayed while flat, together with a calibration block containing known amounts of CaHPO4. We determined the amount of calcium salt, referenced to CaHPO4, from the x-ray film with a personal computer using a frame-grabbing board. There was less calcium in the thoracic than the abdominal aorta both in males and females and those of ages less than 50 y. The coefficient of correlation for abdominal aortic calcium mass versus age in 19 females was 0.557 and in 41 males was 0.321. The higher correlation of mass with age for females may be related to differences in calcium metabolism between sexes.

Adolescent↗
PubMed1994

Variations in strength of the porcine aorta as a function of location.

Dissecting aneurysms split the wall of the aorta and other large arteries to create a false lumen in parallel with the true lumen. Experiments were designed to determine the pressure required to tear the media and the work required per unit area to propagate the dissection once it started. India ink was injected into the media of 17 opened porcine aortas through a needle inserted parallel to the lumen of opened aortas placed in a saline bath. The ink was infused at 0.9 ml/min with a constant infusion pump as the pressure was monitored with a pressure transducer. The size of the bleb formed by the ink in the media was recorded with a video camera mounted perpendicular to the lumenal surface. All data were recorded on a computer. The pressure-volume curve was used to obtain the distensibility of the media (the upslope), the peak pressure, the tearing pressure, and the work of dissection (the area under the P-V curve once tearing occurred). The projected area of the bleb was calculated from the video images, and the work/area was calculated. The peak pressures were always extremely high, and ranged from 634 +/- 204 (SD) mmHg for the lower abdominal aorta to 816 +/- 145 mmHg for the lower thoracic aorta. The work/area ranged from 1.88 +/- 0.89 mJ/cm2 for the upper abdominal aorta to 11.34 +/- 4.05 mJ/cm2 for the lower abdominal aorta. An ANOVA showed that the lower abdominal aorta tore at lower pressures initially, but required much more energy to propagate the dissection. We believe that this is because of structural differences in the elastin pattern in the abdominal aorta.

Animals↗
PubMed1993

The distribution of fibro-fatty atherosclerotic lesions in the aortae of casein- and cholesterol-fed rabbits.

Atherosclerotic lesions were induced in the aortas of 50 rabbits by feeding a semi-purified cholesterol-free casein diet or normal rabbit chow with a low level of added cholesterol for 6 or 10 months. Following perfusion fixation, the aortae from these animals were opened along their length, stained with oil red O and photographed en face. Orifice associated lesions were mapped by measuring radial lesion length at 10 degrees intervals circumferentially around ostia. Histology of these lesions revealed abundant smooth muscle cells surrounded by collagen and elastin in the extracellular matrix, typical of fibrous plaques, as well as oil red O staining lipid and some macrophage derived foam cells. These fibro-fatty lesions were found distal and lateral to ostia, at the same locations as fatty streaks seen in rabbits fed a 2% cholesterol diet for 1 week to 2 months in previous studies. The results of this study show that in moderately hypercholesterolemic rabbits fed an atherogenic diet for 6 to 10 months, advanced atherosclerotic plaques develop in the same location as the fatty streaks seen in short term experiments.

Animals↗
PubMed1993

Elasticity and geometry measurements of vascular specimens using a high-resolution laboratory CT scanner.

Vascular diseases are frequently associated with changes in the mechanical properties of the arterial wall. Existing techniques for studying arterial geometry and mechanical properties in vitro are often destructive, since they involve sectioning of the specimen into strips, or provide average measurements of the mechanical properties over the volume of intact specimens. We developed a high-resolution computed tomography (CT) scanner for in vitro studies of arterial geometry and static elastic properties. The x-ray image intensifier based system can acquire single transverse images, or a volume image, with 2 mm-1 resolution. Images were obtained through an intact abdominal aortic aneurysm at five pressures. The incremental circumferential Young's modulus E(inc) was calculated from the internal and external circumferences, and at physiological pressures E(inc) of the aneurysm was found to be 275 times greater than that of the normal aorta proximal to it. A volume image of the specimen provided landmarks that allowed histological sections to be obtained at locations coincident with those where the elasticity was measured. The histological analysis revealed a sixfold decrease in elastin content in the aneurysm, compared to the normal aorta. We have demonstrated that the static mechanical properties and geometry of vascular specimens can be quantified in vitro with the new high-resolution CT scanner and can be compared subsequently with histological analysis to provide further insight into the understanding of atherogenesis.

Aged↗
PubMed1993

Factors in the initiation and propagation of aortic dissections in human autopsy aortas.

Our goal was to evaluate physical factors in the initiation and propagation of dissections in human aortas. Aortic dissection was simulated in 21 open unpressurized human autopsy aortas by infusing dyed isotonic saline into the media at constant flow. Pressure during growth of the fluid filled cavity was monitored and correlated with volume to give pressure-volume curves, from which distensibility, peak pressure, and work data were calculated. Dissections in specimens occurred at a very high nonphysiological mean pressure of 79 +/- 29 (SD) kPa (596 +/- 214 mmHg). Age and tear depth had no significant effect on medial strength of human aortas but sex, location and atherosclerotic plaque formation did (p < 0.05). The mean pressure value for the female abdominal fibrous/calcified group (92 +/- 30 kPa, 691 +/- 222 mmHg) differed from that of the male abdominal fibrous/calcified group (69 +/- 36 kPa, 508 +/- 269 mmHg). We also observed a significant difference between the male thoracic fibrous calcified (80 +/- 31 kPa, 601 +/- 230 mmHg) and male abdominal fibrous/calcified (68 +/- 36 kPa, 508 +/- 269 mmHg) groups. Significant differences were observed between the female fatty/normal (75 +/- 25 kPa, 562 +/- 187 mmHg) and fibrous/calcified (91 +/- 23 kPa, 685 +/- 176 mmHg) groups of the thoracic aorta and between the male fatty/normal (86 +/- 23 kPa, 650 +/- 169 mmHg) and fibrous/calcified (68 +/- 36 kPa, 508 +/- 269 mmHg) groups of the abdominal aorta. Distensibility data showed no trends. It is probable that dissection does not occur spontaneously in the absence of a connective tissue disorder and/or surgical procedure.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗