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Biomedical subjects

R G Kratky

Publications and source records attributed to R G Kratky.

16 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

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↗
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↗
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↗
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↗
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

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

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

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↗
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

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↗
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↗