Biomedical subjects

M R Roach

Publications and source records attributed to M R Roach.

At least 37 records · Page 2Linked to original sources

PubMed1993

The importance of taper proximal and distal to Y-bifurcations in arteries.

Changes in luminal cross-sectional area from human cerebral arteries, porcine renal arteries and human aorto-iliac junctions were found to be both significant and gradual. Proximal to the flow divider, luminal cross-sectional area increased by 10.8 +/- 5.7% for the human aorto-iliac and 94.5 +/- 5.0% for the cerebrals. Distal to the flow divider, the summed luminal area of the two daughter branches decreased by 36.4 +/- 4.0% for the cerebrals and 15.9 +/- 5.2% for the renals. Taper was defined as the ratio of the area change to the vessel length over which the change occurred. Positive taper corresponded to a narrowing in cross-section while negative taper represented an expansion in luminal area. All taper values were significantly different from zero (t-test, P < 0.05). Arterial ellipticity was examined from the ratio of lateral and antero-posterior diameters of cross-sections in the parent trunk from human aorto-iliacs and porcine renal arteries. We have shown that ellipticity begins one parent-tube diameter from the apex of the bifurcation in both samples studied. These large changes in luminal area and taper, which have been overlooked previously, have significant implications for the propagation of flow and pressure waves as well as for flow patterns.

Animals↗

PubMed1992

Taper: an important feature of Y-bifurcations in porcine renal arteries and human cerebral arteries.

The geometry of arterial bifurcations has been shown to alter fluid flow and the propagation of both pressure and flow waves. Here we provide a more complete description of the renal artery bifurcation geometry and show that the geometry of the bifurcation is more complex than was believed previously. The objective of this study was to quantify changes in cross-sectional luminal area in systemic arterial bifurcations using the method developed by Macfarlane [Ph.D. thesis, University of Western Ontario, Ontario (1985)] to study the geometry of human cerebral bifurcations. Porcine renal arterial bifurcations from seven young (6-14 weeks) and six old (greater than 52 weeks) animals were pressure-fixed (P = 140 mmHg) for 3 h with 10% formalin. Bifurcations were embedded in a block of frozen latex paint. Serial sections were cut at 20 microns (+/- 0.01 microns) using a sledge microtome while the block face was scanned with a video camera and the images were stored on a videotape. The luminal area was measured digitally upon playback. Bifurcations from the two age groups changed in cross-sectional area not only at the flow divider but also along the so-called straight regions. Proximal linear increases in cross-sectional area were observed proximal to the apex of the bifurcation in both young and old vessels, while linear luminal area decreases were measured in the daughter branches of both young and old porcine renals. Taper was defined as the change in luminal area per unit length of parent and daughter branches, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1992

Morphological evidence of pulmonary vascular leakage through gaps observed with casting methods and S.E.M.

We have used selective casting methods to separate pulmonary elastin from vascular elastin in the lungs of rabbits, dogs and pigs. The lungs are digested with 0.1 N NaOH at 75 degrees C for 24 approximately 48 hours with frequent turning as the lungs are filled with air to about 80% of the vital capacity prior to the casting which is done at pressure of 20 approximately 50 mmHg. After vascular injections, we saw many small globular bits of casting material well separated from cast vessels and lying in the pulmonary elastin. Surface forces should make the casting material creep along the vessels even if they are not completely filled, so that the spherical shape is the one expected if the case is extruded into the parenchymal space and the air space. We conclude that this suggests that the pulmonary circulation is partially and temporarily 'open' as seen in the spleen and some other organs, rather than a completely 'closed' one as is generally accepted. At least some of these extravasations may be associated with lymphatics, although we have not proved this.

Animals↗

PubMed1991

Quantitative measurement of fixation rate and dimension changes in the aldehyde/pressure-fixed canine carotid artery.

Excised canine carotid arteries held at constant physiologic length were cycled from -13 to +27 kPa with a constant-flow infusion pump, and the pressure-volume curves were recorded. The change in diameter on reducing the pressure from 16 to 0 kPa was determined and the strain of recoil [(diameter16--diameter0)/diameter16] calculated. Diameter recoil was reduced from 51% (fresh tissue) to 5% after 3 h pressure fixation in 4% formaldehyde and to 9% after 15 min in 2% glutaraldehyde with little further change. Lengthwise recoil was reduced from 37 to 10% after 5 min in 2% glutaraldehyde. Photographs were taken to measure outer diameter during pressure fixation. There was no change in diameter in either fixative from the first minute up to 3 days at the constant pressure of 16 kPa.

Aldehydes↗

PubMed1991

Vascular collagen fibril morphology in type IV Ehlers-Danlos syndrome.

Morphometric analysis of transmission electron micrographs of blood vessel, skin and dura mater collagen fibers were performed on postmortem tissues taken from 28-year-old female with Ehlers-Danlos type IV syndrome (EDS IV). Vascular tissue from this patient was compared to 5 age- and sex-matched controls (age range 26-28 years). Our study revealed significant variation in collagen fibril diameter in the walls of almost all the vessels studied. In general, the EDS IV tissue showed a net decrease in average collagen fibril cross sectional area in arterial wall samples. This decrease was significant (p less than .05) across the entire wall of the renal artery, in the media of the carotid artery, and in the media and adventitia of the common iliac artery. Samples from the vena cava show significant increases in collagen fibril cross sectional area across the vessel wall (p less than .005). The only areas studied which did not show significant changes were the intimal and adventitial regions of the common carotid artery. The observed changes may be contributory to the decreased arterial wall strength typical of the syndrome.

Adult↗

PubMed1990

The strength of the aortic media and its role in the propagation of aortic dissection.

The elastic properties of the thoracic aorta are well known, but this is the first study of the inherent strength of the tunica media. The latter is crucial to understand how dissecting aneurysms occur. Pressure-volume (P-V) measurements were recorded as a dilute suspension of India ink was infused into the tunica media using a constant flow pump (0.21 or 0.88 ml min-1) attached to a 20 G needle inserted into the media. Tests done on 31 opened pig upper descending thoracic aortas showed the peak pressure to tear the media averaged 77.2 +/- 1.5 kPa (579 mm Hg). The initial slope of the P-V curve revealed the average distensibility of the media of 3.02 +/- 0.28 (MPa)-1. The work per unit area of tissue required to propagate a tear in the aorta was 15.9 +/- 0.9 mJ cm-2. These values were independent of the tear depth at the 95% confidence interval.

Aortic Dissection↗

PubMed1990

A comparison of the size of fenestrations in the internal elastic lamina of young and old porcine aortas as seen with the scanning electron microscope.

The size of the fenestrations (windows) in the internal elastic lamina (IEL) of arteries may be important in the functioning of the blood vessel wall. The fenestrations are filled with collagen, muscle, and (or) ground substance, which must be removed to make the fenestration visible with the scanning electron microscope. All of the nonelastic components are removed with a hot alkali solution. Our experiments were designed to compare the fenestration size in the IEL of the thoracic aorta of young (6-8 weeks) and old (6-9 months) pigs. A protocol for digestion of young pig tissue was developed and showed that fresh young aortas should be digested in 0.1 M NaOH at 75 degrees C for 2 h and fixed tissue should be digested for 5 h. The average area of the fenestrations for young pig thoracic aortas digested for 2 h was 1.8 +/- 0.29 (SE) microns 2 and for the old pig aortas digested for 2 h was 1.7 +/- 0.11 (SE) microns 2. These values were not significantly different (p greater than 0.05), but the IEL from young pigs appeared rougher than the previously reported smooth IEL of the adult pigs.

Aging↗

PubMed1990

The effects of age, vessel size, and Ehlers-Danlos type IV syndrome on the waviness index of arteries.

Ehlers-Danlos Syndrome is a rare hereditary connective tissue disorder produced by collagen abnormalities. The Type IV variant causes vascular rupture in the second and third decades. Definitive diagnosis at present is based on demonstrating a deficiency of Type III collagen or procollagen chemically or in fibroblast cultures. Both require fresh tissue. We have shown in fixed autopsy tissue that the elastin in two EDS IV patients appears accordion-pleated with a high waviness index (WI) of 1.58 +/- 0.028 (n = 90) compared to 1.35 +/- 0.08 (n = 446) for 21 controls aged 9 to 71. The WI is the ratio of the length of elastin in the internal elastic lamina to the circumference. The group were significantly different statistically (p less than 0.01) with a randomized block design analysis. Vessel size and age did not alter the WI in either controls or patients. There was significant overlap of data points between the two groups so that no conclusions can be drawn on individual vessels. However, if the waviness index is greater than 1.8, the vessels are unlikely to be normal. We did not study patients with other connective tissue diseases. The WI may be a useful qualitative guide of abnormality in a retrospective study if the diagnosis of Ehlers-Danlos Type IV is entertained.

Adolescent↗

PubMed1989

Quantitative measurements of early atherosclerotic lesions on rabbit aortae from vascular casts.

We have measured the size and location of fatty atherosclerotic lesions in the cholesterol fed rabbit by scanning electron microscopic analysis of vascular casts. The aortic periorificial lesions examined in this study have been divided into proximal (upstream), distal (downstream) and lateral (to the sides of the branch). Lateral lesions developed after 1 week on diet, followed by distal lesions at 2 weeks, and occasional proximal lesions at 4 weeks. The area covered by the lesions shows a strong linear relationship (P less than 0.001) to the cross-sectional area of the branch after 2 weeks on the cholesterol diet.

Acrylic Resins↗

PubMed1989

The canine tail artery as a model for cerebral aneurysm studies.

The occluded canine tail artery, which comes off in the same plane as the aortoiliac junction, has been used as a flow model for cerebral aneurysms. These experiments were designed to determine if it is a realistic distensible model of human intracranial aneurysms. Distensibility studies were done on the aorta, and the iliac and tail arteries of four dogs. From these pressure-volume studies, tension-strain curves, elastances, and collagen slack were obtained. The tail artery is stiffer longitudinally and more distensible circumferentially than the other vessels. The iliac arteries and the aorta are not significantly different. The elastance of elastin and collagen is lower in the tail artery, and the collagen is more wavy circumferentially. Longitudinally, the collagen slack is least for the tail artery, and the elastance of elastin is not different in all three vessels. The number of elastin layers in the iliac and tail arteries seen in cross section is not significantly different, but the aorta is different from both these vessels. In another four dogs the aorta proximal to the trifurcation was cannulated and infused with saline to increase pressure. India ink marks were put on the surface to measure changes in length. Photographs were taken at intervals of 10 mmHg(1 mmHg = 133.3 Pa). This was done with the vessels tethered and untethered in the body and then taken out and studied with the same method in vitro. Arteries tethered in the body expanded circumferentially more than longitudinally. The tail artery becomes less distensible if untethered in the body and therefore acts more like an aneurysm.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1989

Effects of age on the anisotropy of the descending human thoracic aorta determined by uniaxial tensile testing and digestion by NaOH under load.

Strips of human thoracic aortic wall taken at autopsy from 23 individuals aged 15-81 years have been tested in two ways: in uniaxial loading and by digestion in 0.1 M NaOH at 75 degrees C under a load of 50 g. The circumferentially oriented strips were more extensible in loading and took a longer time to fail while being digested under load than the longitudinal strips from the same location. The stress versus strain curve was fitted to an exponential equation of the form, stress = A[exp(B strain)]. For circumferentially oriented strips from 19 subjects, parameter A was independent of age. Parameter B increased by a factor of 2.75 from 19 to 81 years. For longitudinally oriented strips for 14 subjects, A was also independent of age and B increased by 2.4 times from 25 to 81. With digestion under load for 11 matched pairs of strips aged from 32 to 75 the circumferential strips failed in 117 +/- 23 min (standard error), while the longitudinal ones failed in 20.3 +/- 3.2 min (standard error) (p less than 0.003). The results have important implications for vessel attachments to the aorta in heart transplantation and in vascular surgery.

Adolescent↗

PubMed1989

The role of hypertension and hypercholesterolemia on aortic sudanophilia and carotid distensibility in rabbits.

These experiments were designed to determine if male New Zealand white rabbits made mildly hypertensive (20-30 mm Hg increase) with bilateral renal artery clips developed more or less sudanophilic lesions than controls, and if the animals responded differently if hypercholesterolemia was produced soon (one week) or late (eight weeks) after the animals were operated on. Both groups received the diet of 2% cholesterol and 6% corn oil for six weeks. We also studied the distensibility of the carotid artery to determine if altered elastic behaviour played a role in lesion development. The experiments showed that the acute hypertensive group developed most lesions (by area), but that the lesions in all groups had the same shape and location. The carotid arteries from the chronic hypertensives were least distensible, and most of the changes appeared to be in the elastance of collagen. The blood pressure actually dropped slightly in the chronic shams after the diet was started. These experiments suggest that, at least, in the rabbit, the duration of the hypertension may determine how the arterial wall responds to hypercholesterolemia. They show that mild hypertension, like hypercholesterolemia, alters the rate at which lesions develop, rather than altering their distribution. The changes do not appear to be related to altered distensibility.

Analysis of Variance↗

PubMed1989

Quantitative measurement from vascular casts.

A review of quantitative measurements show casting materials shrink from 0.2 - 20% and have viscosities ranging from 1.4 - 100,000 centipoise. Blood vessels have highly variable mechanical properties. Some microvessels are very stiff having little change in dimensions with pressure. Larger vessels generally change diameter significantly but show highly variable changes in length with pressure. Perfusion fixation does not fix the dimensions of blood vessels. Dog carotid arteries well fixed with glutaraldehyde at physiologic dimensions retain approximately 20% of their elastic recoil circumferentially and approximately 30% longitudinally. We recommend vascular casting as a method of accurately measuring the vasculature if care is taken to use low shrinkage casting resins and maintain physiologic transmural pressures for the duration of any casting procedure, even if prefixation is used. We measured a approximately 10% error in our method of measuring both the size and location of periorificial atherosclerotic lesions from aortic casts. Little is known about how vascular smooth muscle tone changes during casting.

Animals↗

PubMed1988

Arterial elastin as seen with scanning electron microscopy: a review.

All large arteries contain elastin, collagen, and muscle which can be seen with light microscopy and transmission electron microscopy. Elastin forms an internal elastic lamina (IEL) in all arteries, but also forms multiple fenestrated sheets in the media of the aorta and other large arteries. The fenestrations in the media are larger than those in the IEL. The adventitial elastin is more fibrous and often contains tubular elastin surrounding vasa vasorum when prepared by removing all non-elastin by placing the aorta in 0.1 N NaOH at 70-75 degrees C for five hours. The fenestrations are larger near branches and in an experimentally created poststenotic dilatation. Atherosclerosis appears associated with both new elastin formation in early atherosclerosis and elastolysis in late disease.

Animals↗

PubMed1988

Scanning electron microscopy of early atherosclerosis in rabbits using aortic casts.

Our research involves measuring the size and location of atherosclerotic lesions on the intimal surface of arteries. To this end we have developed a new method in which scanning electron micrographs of vascular casts with impressions of these lesions on their surface are used. This method is compared with light microscopy and scanning electron microscopy of tissue with lesions. All three methods are found to detect lesions equally well. We also examine the cellular elements in the lesion to determine how the images are formed.

Animals↗

PubMed1987

Factors in the propagation of aortic dissections in canine thoracic aortas.

Factors were examined which altered the propagation of aortic dissections in canine aortas. Thoracic aortas were removed from sacrificed dogs from the distal end of the arch to the diaphragm. An intimal tear was created at the proximal end of the aorta. The dissection was propagated using a pulsatile pressure system with no flow. The aorta was perfused with a dilute black paint solution, which allowed both video monitoring of the extension of the dissection and measurement of the dissection rate. The dependence of the dissection rate on the variables peak pressure, (dP/dt)max and intimal tear depth was examined. The dissection rate was found to be dependent on (dP/dt)max (p less than 0.005) and the intimal tear depth, expressed as a percentage of wall thickness (p less than 0.01), but not on the peak pressure or intimal tear length. The equation relating the significant variables was log (dissection rate) = (-0.034) X % tear depth +(1.89 +/- 0.56) X (dP/dt)max -(4.3 +/- 1.8); r = 78. Thus a higher (dP/dt)max was associated with a more rapid dissection rate and a deeper intimal tear was associated with a slower dissection rate.

Aortic Dissection↗

PubMed1987

A biophysical and histological analysis of factors that lead to aortic rupture in normal and lathyritic turkeys.

These experiments were designed to determine if local differences in elastic properties or wall structure contributed to the development of aortic rupture in turkeys. Static elastic properties were measured from pressure-volume curves of cylindrical segments of upper and lower thoracic aorta and innominate artery in two groups of lathyritic birds and two age-matched control groups. The biggest changes were in the young lathyritic group that was on 0.04% beta-aminoproprionitrile at 3 weeks of age and continued for 2, 3, or 4 weeks. Much smaller changes were seen in the older group that started on 0.05% beta-aminoproprionitrile at 6 weeks of age for 10 days and then 0.02% beta-aminoproprionitrile for the next 9-12 weeks. The biggest changes were seen in the abdominal aorta, which ruptured spontaneously in 50% of the young lathyritic group. The birds had a marked decrease in the number of elastin layers per unit wall thickness. Analysis of the elastic diagrams showed that the elastance of both elastin and collagen were altered in the young lathyritic group. Rupture appeared to follow partial dissection of plaques, but true longitudinal dissection did not occur.

Aminopropionitrile↗

PubMed1987

Endothelial cell morphometry near branch junctions of rabbit aortae.

Endothelial cell morphometric data were gathered from corrosion casts of the aorta and its branches of six New Zealand white rabbits weighing 2-3 kg. The endothelial cell outlines were ditigized to provide cell orientation index (COI) from the equation COI = 2Ms/2M1-1, where 2Ms and 2M1 are the second moments of area about short and long axes of the cell. The COI varies from zero to infinity. The former occurs when cells are symmetrical (e.g., circular) since 2Ms = 2M1 and the latter occurs for a straight line. Large values of COI were found distal to intercostals, lumbars, and the aortorenal junction, and probably reflect relatively stable high shear regions. Values close to zero occur on the flow divider where the shear stress approaches zero. Other values were less predictable and we concluded that while the long axis of the cell appears to indicate flow direction, the shape of the cell does not appear to be a reliable indicator of either tensile forces or shear stress acting in it, but probably reflects a combination of the two.

Animals↗