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At least 757 records · Page 42Linked to original sources
PubMed1998

Experimental hypercholesterolemia induces ultrastructural changes in the elastic laminae of rabbit aortic valve.

Atherosclerosis is the most severe problem in the high-pressure systemic circulation and similar changes also occur in the high-pressure loading valve. This study was designed to test the hypothesis that early atherosclerosis, induced by a high cholesterol diet in rabbits, is characterized by significant ultrastructural change in the elastic laminae of the aortic valve. However, it is not known whether this process is also taking place in the cardiac valve at the early stage of atherosclerosis. Animals were fed either a high cholesterol diet (n = 5) or a control diet (n = 5) for 10-12 weeks. Histologic analysis demonstrated that subendothelial thickening and foam-cell infiltration were evident in the arterialis of aortic valves. Confocal microscopy revealed an altered pattern characterized by fragmentation and disorganization of the arterialis elastic laminae of hypercholesterolemic valves. Computerized digital analysis of the images obtained by confocal scanning microscopy demonstrated that compared to normal valves, the arterialis elastic laminae of hypercholesterolemic valves decreased in percentage of their elastin content (29.03 +/- 1.10% vs. 42.94 +/- 1.35%, p = 0.023). Immunohistochemical staining for matrix metalloproteinase-3 (MMP-3) revealed MMP-3 immunoreactivity was increased in hypercholesterolemic valves, predominantly in the arterialis. This study demonstrated that early atherosclerosis, induced by a high cholesterol diet in rabbits, is characterized by significant ultrastructural change in the elastic laminae of the aortic valve. The arterialis endothelium of the aortic valve may be a more atherosclerosis-prone area compared with the ventricularis. The presence of ultrastructural defect in the elastic laminae may play a role in chronic degenerative change and a resultant valvular dysfunction.

Animals↗
PubMed1991

A mathematical model to describe the nonlinear elastic properties of the gastrocnemius tendon of chickens.

A phenomenological model was developed to describe the nonlinear elastic behavior of the avian gastrocnemius tendon. Quasistatic uniaxial tensile tests were used to apply a deformation and resulting load on the tendon at a deformation rate of 5 mm/min. Plots of deformation versus load indicated a nonlinear loading response. By calculating engineering stress and engineering strain, the experimental data were normalized for tendon shape. The elastic response was determined from stress-strain curves and was found to vary with engineering strain. The response to the applied engineering strain could best be described by a mathematical model that combined a linear function and a nonlinear function. Three parameters in the model were developed to represent the nonlinear elastic behavior of the tendon, thereby allowing analysis of elasticity without prior knowledge of engineering strain. This procedure reduced the amount of data needed for the statistical analysis of nonlinear elasticity.

Analysis of Variance↗
PubMed1992

Super-elasticity and thermal behavior of Ni-Ti alloy orthodontic arch wires.

Bending properties and thermal behavior of twenty commercial Ni-Ti alloy orthodontic arch wires were investigated quantitatively to characterize their suitability for clinical use. There was substantial difference among the load-deflection curves obtained by a three-point bending test. Some wires exhibited super-elasticity; load decreased little with decreasing deflection. Others showed good spring-back properties only; load was nearly proportional to deflection. Thermal behavior due to phase transformation of the alloy was examined by differential scanning calorimetry (DSC). Some of the wires did not have the correct transformation temperatures to exhibit super-elasticity at body temperature. Moreover, thermal behavior was closely related to super-elasticity. There were clear thermal peaks in the DSC curves of the super-elastic wires. However, wires without super-elasticity had no peak in the DSC curves.

Dental Alloys↗
PubMed2004

Determination of elastic modulus of the components at dentin-resin interface using the ultrasonic device.

The purpose of this study was to determine the elastic moduli of the components at resin-dentin interface with the use of an ultrasonic device. Dentin plates were obtained from freshly extracted bovine incisors with a shape in rectangular form. Resin composites and bonding agents were polymerized and trimmed in the same shape as the dentin specimens. The ultrasonic equipment employed in this study was comprised of a Pulser-Receiver, transducers, and an oscilloscope. Each elastic modulus was determined by measuring the longitudinal and shear wave sound velocities. The mean elastic modulus of mineralized dentin was 17.4 GPa, while that of demineralized dentin was 1.4 GPa. When the demineralized dentin was immersed in bonding agents, the elastic modulus changed to 3.7-4.7 GPa, and these values were significantly higher than those of demineralized dentin. A gradient in elastic modulus was detected as the analysis shifted from the dentin side to the resin composite.

Analysis of Variance↗
PubMed1994

[The dermal connective tissue of leprosy patients. Part 1. The elastic fibers and the skin appendages].

Leprosy patients who are keeping long quiescent conditions show some characteristic changes clinically on their skins. The elastic fibers and skin appendages are important factors for the peculiar skin characters. We calculated the collagen and elastic fibers in the limbs and redundant facial skins of leprosy patients by automated computerized image analyser. Histopathological studies of these samples were also done. All cases were over sixty years old and many of them were in quiescent conditions. The control cases were taken from the same parts of age matched normal skins. We found the dermal thickness of lower legs of patients was significantly lower than that of controls. The amount of collagen fibers had tendensy of decrease accompanied with decreased dermal thickness, but the elastic fibers of leprosy patients did not show the same tendensy. In the patients' skin, the elastic fibers arranged irregularly, sometimes fragmented and focally coagressed. Skin appendages were greatly decreased and intraepidermal pores of sweat ducts were almost disappeared, but many sweat glands have survived. Of the facial skins, only 1 case showed a compatible feature with solar elastosis. We concluded that the dermal elastic fibers of leprosy patients had characteristic features. The types of leprosy, duration periods of active condition, destructed dermal structures, all these factors were suspected to have some relations with these phenomena.

Aged↗
PubMed1994

[Studies on silver soldering of super-elastic Ti-Ni alloy wire to Co-Cr alloy wire].

In order to attain joining the super-elastic Ti-Ni alloy wire to the Co-Cr alloy wire and be able to maintain the super-elasticity of the Ti-Ni alloy wire, a new soldering method was devised. The silver solder was first molten on the 0.016 x 0.022 inch Co-Cr alloy wire (Co-Cr) and then flowed onto the 0.016 x 0.022 inch super-elastic Ti-Ni alloy wire (Ti-Ni) to form soldering. The specimens of soldered Ti-Ni to Co-Cr butt joint, TN-CC, were examined for its super-elasticity, torsional strength, tensile strength and the metallographic structure of the soldered joint. The findings were as follows: 1. TN-CC still maintained its super-elasticity. 2. The torsional strength of TN-CC was equal to that of Ti-Ni. The tensile strength of TN-CC was 73% of that of Ti-Ni. 3. The tensile strength of TN-CC immersed in 1%NaCl solution at 37 degrees C for 30 days was considered to be still strong enough for clinical use. 4. During the tensile strength test, the breakage of TN-CC occurred at the area of merger of the solder and Ti-Ni. As the reason for this breakage, it suggested that Ti-Ni was stretched and narrowed at the soldered area and that the Sn-rich phase in the solder was induced along Ti-Ni. 5. This new soldering method was shown to be useful in clinical cases, and the fabrication of new orthodontic appliance using two distinct types of wire, one to independently move teeth and the other to be the anchorage, has already been developed.

Child↗
PubMedDate not supplied

Effects of changes in heel fat pad thickness and elasticity on heel pain.

The heel fat pad has a unique structure that is important for its shock-absorbing function. Loss of elasticity and changes in the thickness of the heel pad have been suggested as causes of heel pain. The present study of a population with heel pain shows the relationship between the thickness and elasticity of the heel fat pad and age, sex, obesity, duration of symptoms, subcalcaneal spurs, and noninvasive conservative treatment. Of 182 patients with heel pain who visited an outpatient clinic during a 3-year period, 50 (67 heels) fulfilling specific criteria were treated with a combination of nonsteroidal anti-inflammatory drugs, contrast baths, stretching exercises, and change of footwear habits. Patients were followed up for 1 year. Delayed healing, increased thickness, and decreased elasticity of the heel fat pad were found in patients who were older than 40 years, who had symptoms for longer than 12 months before treatment, and who had a large subcalcaneal spur. An increase in heel fat pad thickness with aging and increased body weight reduce the elasticity of the heel fat pad. In addition, subcalcaneal spurs diminish the elasticity of the heel fat pad and play a role in the formation of heel pain.

Adipose Tissue↗
PubMed1999

Age-related changes in the elastic fiber network of the human splenic capsule.

The structural arrangement of elastic fibers in the splenic capsule from 16 human cadavers ranging in age from 1 month to 76 years was studied by histologic sections stained with selective methods for elastin. In infants the elastic fibers of the splenic capsule were homogeneously intermingled with collagen fibers, an arrangement that stabilizes the capsule during spleen growth and enlargement. With aging, collagen fibers predominate in the outer capsular surface over elastic fibers with the latter more evident in the deep lamina of the splenic capsule. In elderly individuals, the elastic fibers shorten, fragment, and thicken. The progressive decrease in the amount of elastic fibers in the splenic capsule with aging may restrict splenic distention and contribute to involution of the spleen as one grows older.

Adolescent↗
PubMed1999

Elasticity and fracture strain of whole blood clots.

The measurement of clot elasticity and fracture strain is carried out using a rotational rheometer with a controlled stress system. The elasticity is quantified by a shear elastic modulus and fracture strain by a critical strain (deformation) when the clot begins to break up. The results indicate a decrease of elasticity and increase of fracture strain of the clot with increasing hematocrit. Moreover, the elastic modulus of the clot is not constant but increasing with deformation.

Blood Coagulation↗
PubMedDate not supplied

[Results of measuring the modulus of elasticity of microorganism cell walls].

The elasticity modulus of Escherichia coli cell walls was found to change in the course of growth of the culture. It decreased in the middle of the exponential phase, apparently as a result of intensification of biosynthetic and related to them transport processes at this period. If the cells were treated with EDTA, their elasticity modulus was lower, by an order of magnitude, than that of the control cell walls. If the cells were treated with lysozyme, the elasticity modulus of their walls decreased by three orders of magnitude. The elasticity modulus of cell walls was less in gram-positive rods than in E. coli. The elasticity modulus of spherical cells cannot be determined using this technique.

Bacillus megaterium↗
PubMed2002

Arterial elasticity among normotensive subjects and treated and untreated hypertensive subjects: influence of race.

OBJECTIVES: To determine arterial elasticity in normotensives and in treated and untreated hypertensive Black and White subjects. METHODS: A prospective multicenter, controlled clinical trial evaluated large (C-) and small (C2) artery elasticity indices among 3 groups: 1) normotensive subjects with or without a family history of hypertension; 2) controlled and treated hypertensive subjects; and 3) untreated and uncontrolled hypertensive subjects. Blood pressure was measured using a mercury manometer and arterial compliance or elasticity was determined using a CVProfilor DO-2020 CardioVascular Profiling System (Hypertension Diagnostics, Inc, Eagan, Minn). These parameters were measured in triplicate 3 minutes apart in a random sequence, with the patient in a supine position. Two-way ANOVA was used for statistical evaluation. RESULTS: One hundred seventy eight subjects met stratification and enrollment criteria. The mean age was 46 years. 109 were White and 69 were Black. [table: see text] CONCLUSION: Small and large arterial elasticity indices are reduced as hypertension status worsens. Age and height were important covariates of C1 and C2. Race was not found to be a significant predictor of either C1 or C2. Large and small artery elasticity indices do not differ between White and Black subjects with varying degrees of hypertension after adjusting for covariates. More studies with a larger number of subjects are required.

Adolescent↗
PubMed2002

Reduction of early elastic recoil by cutting balloon angioplasty as compared to conventional balloon angioplasty.

BACKGROUND: Restenosis after successful balloon angioplasty remains problematic. Early elastic response after angioplasty is significant when considering the possible development of restenosis. The purpose of this study was to compare early elastic recoil within 10 minutes after successful percutaneous transluminal coronary angioplasty and early lumen loss at 24 hours after angioplasty in a cutting balloon group and a conventional balloon group. METHODS: Extent of early elastic recoil was quantitatively measured as the difference of mean balloon diameter at maximal inflation pressure and minimal luminal diameter after angioplasty in 82 cutting balloon-treated lesions and 51 conventional balloon-treated lesions. RESULTS: Reference diameter and balloon/artery ratio were similar between the cutting balloon and conventional balloon groups (2.89 0.47 mm vs. 2.88 0.60 mm; 1.19 0.11 vs. 1.19 0.13, respectively). Early elastic recoil after angioplasty was significantly smaller in the cutting balloon than the conventional balloon group (0.96 0.40 mm vs. 1.12 0.37 mm, respectively; p = 0.04). Also, the mean amount of lumen loss from 10 minutes after angioplasty to 24 hours after was significantly smaller in the cutting balloon than the conventional balloon group (0.08 0.28 mm vs. 0.20 0.33 mm, respectively; p = 0.02). CONCLUSION: There is significantly less early elastic recoil in the cutting balloon angioplasty than in the conventional balloon angioplasty group. The efficacy of cutting balloon continues 24 hours after angioplasty.

Aged↗
PubMedDate not supplied

Mechanical analysis of elasticity and flexibility of virgin and polymer-treated hair fiber assemblies.

The elasticity and flexibility of virgin and polymer-treated hair fiber assemblies were investigated by employing straight hair tresses or hair shaped into omega loops. Polymer treatment was accomplished by saturating fibers with polymeric solutions, resulting in a deposition of 10-90 mg of polymer per gram of hair. The mechanical testing procedure consisted of subjecting omega-loop-shaped hair or straight hair tresses to multiple bending deformations at 25% strain in a texture analyzer. A total of ten deformations were typically carried out, and elasticity or flexibility parameters were evaluated from data such as (a). the force at 8% deformation, i.e., within the elastic region of bending deformation for hair shaped into an omega loop, (b). maximum force in the first (F(1)) and tenth (F(10)) deformation cycles, (c). elastic modulus in the first (E(1)) and tenth (E(10)) deformation cycles, and (d). the change in hair sample dimensions between the first (H(1)) and tenth (H(10)) deformation cycles. Parameters such as stiffness ratio (1), F(10)/F(1), E(10)/E(1), and H(10)/H(1) were employed to characterize hair tress rigidity, flexibility or resistance to breakage, and plasticity. Untreated hair was found to be almost perfectly elastic and flexible at 50% RH, evident by the linear dependence of force vs deformation. Flexibility parameters F(10)/F(1), E(10)/E(1), and H(10)/H(1) were in the range of 0.95 to 1.0 at low humidity, while the parameters F(10)/F(1) and E(10)/E(1) and were 10% lower at 90% RH. Examination of polymer-modified hair allowed for classification of treatments into categories termed brittle, quite flexible and nonplastic, flexible and plastic, very flexible and very plastic, and very flexible and nonplastic. Poly(vinyl pyrrolidone) is shown as an example of a quite flexible and nonplastic material, with its flexibility and stiffness dependent upon its molecular weight. The effect of plasticizers on polymer behavior is also discussed.

Animals↗
PubMed2002

[The relationship between the thickness and elasticity of the heel pad and heel pain].

OBJECTIVES: We investigated the factors affecting the thickness and elasticity of the heel pad and sought relationship between the heel pad thickness and elasticity and heel pain. METHODS: Of 182 patients who presented with a complaint of heel pain over a three year period, 50 patients (38 females, 12 males; mean age 46 years; range 23 to 73 years) met specific criteria for the study. A combined treatment modality was conducted throughout a year which consisted of non-steroidal anti-inflammatory drugs, contrast baths, stretching exercises, and changes in footwear design. At the end of a year, the results were assessed according to the criteria proposed by Wolgin et al. Measurements of heel pad thickness were performed according to the technique described by Jorgensen: compressibility index of the heel pad was calculated on anteroposterior and lateral radiographs of the heel, loaded and unloaded by body weight. RESULTS: The results were good in 35 patients (70%), fair in 12 patients (35%), and poor in three patients (6%). Four patients (8%) developed recurrences. Increased heel pad thickness, decreased elasticity, and delayed healing were observed in males, in patients above 40 years of age, in obese patients, in those with a pretreatment symptom duration exceeding 12 months, and in those with a greater subcalcaneal spur. CONCLUSION: The thickness of heel pad increases in relation to age and weight, resulting in decreased elasticity. In addition, subcalcaneal spur may be involved in heel pain induction through decreasing heel pad elasticity.

Adult↗
PubMed2003

Experimental flow studies in an elastic Y-model.

To determine the causes and history of atherosclerosis it is necessary to understand the hemodynamic parameters of blood circulation. Hemodynamic parameters play an important role in the formation of atherosclerotic plaques, especially near bends and bifurcations where the flow separates from the wall. Here the flow is laminar and non-axial with eddies, secondary flow, flow separation and stagnation points. Stenoses are found predominantly in flow separation areas. Therefore, it is important to separately study the following flow parameters: steady and pulsatile flow, wall elasticity and non-Newtonian flow behavior of blood. A simplified silicon elastic y-model simulating the human carotid artery was used for the analysis of these parameters. This model can be used for numerical studies as well. Flow was visualized at steady flow using dyes and at pulsatile flow with a photoelastic apparatus and a birefringent solution. The local axial velocity at steady and pulsatile flow was determined with a one-component Laser-Doppler-Anemometer (LDA). Pulsatile flow was generated by a piston membrane pump. A glycerin-water solution was used to simulate the Newtonian flow behavior of blood. A DMSO-Separan water solution was used to simulate the non-Newtonian flow behavior. Pulsatile flow creates higher and lower shear rates so called oscillating shear rate compare to steady flow depending on the velocity amplitude. The non-Newtonian fluid showed a markedly different flow behavior than the Newtonian fluid especially in areas of flow separation. Shear gradients were calculated from these velocity measurements using a bicubic spline interpolation. Shear stresses were calculated from these velocity shear gradients and the viscosity of the non-Newtonian fluid at these shear gradients. At special areas, high shear stresses > 10 Pa were found. The elasticity of the model wall also influences the flow behavior. The measurements showed that the characteristics of pulsatile flow and the elasticity of the model wall should be observed concomitantly. This paper presents the steady and pulsatile flow with a Newtonian and non-Newtonian fluid in an elastic model.

Arteriosclerosis↗
PubMed2002

Mechanics of elastin: molecular mechanism of biological elasticity and its relationship to contraction.

Description of the mechanics of elastin requires the understanding of two interlinked but distinct physical processes; the development of entropic elastic force and the occurrence of hydrophobic association. Elementary statistical-mechanical analysis of AFM single-chain force-extension data of elastin model molecules identifies damping of internal chain dynamics on extension as a fundamental source of entropic elastic force and eliminates the requirement of random chain networks. For elastin and its models, this simple analysis is substantiated experimentally by the observation of mechanical resonances in the dielectric relaxation and acoustic absorption spectra, and theoretically by the dependence of entropy on frequency of torsion-angle oscillations, and by classical molecular-mechanics and dynamics calculations of relaxed and extended states of the beta-spiral description of the elastin repeat, (GVGVP)n. The role of hydrophobic hydration in the mechanics of elastin becomes apparent under conditions of isometric contraction. During force development at constant length, increase in entropic elastic force resulting from decrease in elastomer entropy occurs under conditions of increase in solvent entropy. This eliminates the solvent entropy change as the entropy change that gives rise to entropic elastic force and couples association of hydrophobic domains to the process. Therefore, association of hydrophobic domains within the elastomer at fixed length stretches interconnecting dynamic chain segments and causes an increase in the entropic elastic force due to the resulting damping of internal chain dynamics. Fundamental to the mechanics of elastin is the inverse temperature transition of hydrophobic association that occurs with development of mechanical resonances within fibrous elastin and polymers of repeat elastin sequences, which, with design of truly minimal changes in sequence, demonstrate energy conversions extant in biology and demonstrate the special capacity of bound phosphates to raise the free energy of hydrophobic association.

Animals↗
PubMed1992

Endothelium and elastic tears in the afferent arteries of experimental arteriovenous fistulae in rabbits.

The endothelium and underlying internal elastic lamina of the arteries from 16 carotid-jugular arteriovenous fistulae in rabbits were examined using the en face technique and scanning electron microscopy respectively. Tears appeared in the internal elastic lamina of the arteries 3 days post-operatively. The overlying endothelium exhibited cytoplasmic pallor, loss of argyrophilia of cell borders, and at times attenuated endothelial cells bridging thrombus covered regions of denudation. Early endothelial lesions repaired rapidly and were found only 3-7 days post-operatively despite progressive increase in frequency and extent of tears and the development of interconnecting longitudinal tears with time. Following repair endothelial cells over the tears were small with hyperchromatic nuclei and oriented mostly parallel to the arterial axis. Endothelial cell density overlying these elastic tissue tears increase to three times that in contralateral arteriotomized common carotid arteries. These endothelial changes were sharply delineated by the margins of the elastic tears. Cell density over the tears reached its maximum 9-11 days post-operatively with mitotic figures both in the floor of the tears and over islands of residual elastic lamina. With time the cell density progressively diminished and endothelial cells assumed a more conventional elongated spindle shape.

Animals↗
PubMed2003

[Effect of elastic stress on expression of corebinding factor a 1 mRNA in human periodontal ligament cells in vitro].

OBJECTIVE: To investigate the osteoblast-like characteristics of human periodontal ligament cells affected by elastic stress in vitro, and the role of corebinding factor a 1 (cbfa1) in alveolar bone formation during orthodontic tooth movement. METHODS: Rat dig-labeled cbfa1 cDNA probe was prepared from SD rat osteoblasts cultured in vitro. Human periodontal ligament cells were cultured on the elastic bottom plate and stimulated by elastic stress using mechanical loading system for cultured cells in vitro. The expression of cbfa1 mRNA was detected by in situ hybridization method. RESULTS: Cbfa1 mRNA express in human periodontal ligament cells stimulated by elastic stress and did not express in normal human periodontal ligament cells. CONCLUSION: It is suggested that elastic stress plays a role in the differentiation process from human periodontal ligament cells to osteoblast-like cells. Cbfa1 is a transcription factor in alveolar bone remodeling during orthodontic tooth movement.

Adolescent↗