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At least 55 records · Page 3Linked to original sources
PubMed2000

Estimation of in situ elastic properties of biphasic cartilage based on a transversely isotropic hypo-elastic model.

Articular cartilage is known to behave nonlinearly for large deformations. Mechanical properties derived from small strain experiments yield excessively large deformations in finite element models used in the study of severe blunt impact to joints. In this manuscript, a method is presented to determine the nonlinear elastic properties of biphasic cartilage based on a transversely isotropic hypo-elastic model. The elastic properties were estimated by fitting two force-displacement curves (in rapid loading and at equilibrium) obtained from large deformation indentation relaxation tests on cartilage using a nonporous spherical indentor. The solid skeleton of the cartilage was modeled as a transversely isotropic hypo-elastic material and a commercial finite element program was employed to solve the problem of a layer indented by a rigid sphere. Components of the hypo-elasticity tensor were made dependent on deformation according to the variations defined by a transversely isotropic hyperelastic formulation given earlier by others. Material incompressibility was assumed during the initial stage of rapid loading. The analysis was utilized for the determination of in situ properties of rabbit retropatellar cartilage at large deformations. The model was able to fit the material response to rapid loading and equilibrium indentation test data to approximately 50 percent strain. This material model suggested even higher percentage of stress supported by the fluid phase of cartilage than given earlier by small deformation theories of biphasic cartilage.

Animals↗
PubMed2005

Vitamin A deficiency alters the pulmonary parenchymal elastic modulus and elastic fiber concentration in rats.

BACKGROUND: Bronchial hyperreactivity is influenced by properties of the conducting airways and the surrounding pulmonary parenchyma, which is tethered to the conducting airways. Vitamin A deficiency (VAD) is associated with an increase in airway hyperreactivity in rats and a decrease in the volume density of alveoli and alveolar ducts. To better define the effects of VAD on the mechanical properties of the pulmonary parenchyma, we have studied the elastic modulus, elastic fibers and elastin gene-expression in rats with VAD, which were supplemented with retinoic acid (RA) or remained unsupplemented. METHODS: Parenchymal mechanics were assessed before and after the administration of carbamylcholine (CCh) by determining the bulk and shear moduli of lungs that that had been removed from rats which were vitamin A deficient or received a control diet. Elastin mRNA and insoluble elastin were quantified and elastic fibers were enumerated using morphometric methods. Additional morphometric studies were performed to assess airway contraction and alveolar distortion. RESULTS: VAD produced an approximately 2-fold augmentation in the CCh-mediated increase of the bulk modulus and a significant dampening of the increase in shear modulus after CCh, compared to vitamin A sufficient (VAS) rats. RA-supplementation for up to 21 days did not reverse the effects of VAD on the elastic modulus. VAD was also associated with a decrease in the concentration of parenchymal elastic fibers, which was restored and was accompanied by an increase in tropoelastin mRNA after 12 days of RA-treatment. Lung elastin, which was resistant to 0.1 N NaOH at 98 degrees, decreased in VAD and was not restored after 21 days of RA-treatment. CONCLUSION: Alterations in parenchymal mechanics and structure contribute to bronchial hyperreactivity in VAD but they are not reversed by RA-treatment, in contrast to the VAD-related alterations in the airways.

Adaptation, Physiological↗
PubMed1990

Electron microscopic study on the elastic and elastic related fibres in the human fascia transversalis at different ages.

An electron microscopic study of the elastic fibre and elastic related fibres of the fascia transversalis of the human inguinal triangle was performed in 20 male patients aged 13 to 81 a with right indirect inguinal hernia submitted to surgical repair. The 3 fibre types comprising the elastic system (oxytalan, elaunin, and elastic fibres) tend to be ordered in a precise manner and sequence among the fibrils, fibres, and collagen fibre bundles, respectively. The present findings show that with aging, there is a decrease in the oxytalan fibres and an increase in the amorphous substance of the elastic fibres. The authors concluded that the decrease in oxytalan fibres as a function of age may be responsible for alteration in the resistance of the transversalis fascia.

Actin Cytoskeleton↗
PubMed1993

Effects of physical exercise on the elasticity and elastic components of the rat aorta.

To evaluate the effects of exercise on aortic wall elasticity and elastic components, young male rats underwent various exercise regimes for 16 weeks. In the exercised rats, the aortic incremental elastic modulus decreased significantly when under physiological strain. The aortic content of elastin increased significantly and the calcium content of elastin decreased significantly in the exercised group. The accumulated data from the exercised and sedentary groups revealed that the elastin calcium content was related positively to the incremental elastic modulus. We concluded that physical exercise from an early age decreases the calcium deposit in aortic wall elastin and that this effect probably produced in the exercised rats a distensible aorta.

Animals↗
PubMed2005

The tissue distribution of murine Abcc6 (Mrp6) during embryogenesis indicates that the presence of Abcc6 in elastic tissues is not required for elastic fiber assembly.

Mutations in the gene coding for the ABC transporter, ABCC6, in humans cause Pseudoxanthoma elasticum, which is characterized by the deposition of aberrant elastic fibers. To investigate whether the presence of ABCC6 in tissues synthesizing elastin is required for elastin deposition and elastic fiber assembly, we have compared the steady-state levels and tissue distribution of Abcc6 and tropoelastin mRNAs during mouse embryogenesis. Whereas tropoelastin mRNA levels rose during embryogenesis and were the highest in neonatal mice, Abcc6 mRNA levels remained constantly low throughout embryogenesis. In some tissues, both Abcc6 and tropoelastin mRNA were detected. However, Abcc6 mRNA and protein were not detected in neonatal aorta and arteries, which produce large amounts of elastin indicating that the presence of Abcc6 in elastic tissues is not required for elastic fiber assembly.

ATP-Binding Cassette Transporters↗
PubMed1976

Enzymatic destruction of the elastic lamella at the mouth of cerebral berry aneurysm? An ultrastructural study with special regard to the elastic tissue.

Destruction of the elastic tissue is probably an acquired lesion and is decisive for the appearance of cerebral arterial aneurysms at the sites of congenital media defects. The elastic component in the mouths of aneurysms has therefore been studied by electron microscopy, using two new staining methods, i.e. ruthenium-red staining and prolonged osmium-tetroxide treatment. The hypertrophic, duplicated, elastic lamellae showed a disintegration of their luminal portions not earlier described. In close connection with the disintegrated portions, extracellular lysosome-like granules were observed. It is hypothesized that discharged leucocyte grannules containing elastase help to destroy the elastic lamellae.

Adult↗
PubMed1984

Volume elasticity, modulus of elasticity and compliance of normal and arteriosclerotic human aorta.

In order to measure the flow-dynamical effect of arteriosclerotic changes of the vessel wall we determined volume elasticity E' and modulus of elasticity of 53 human aortae in a static p-V-test as other authors did, too. The p-V-curves are normalized to the aortic basic volume Vo, so that we could determine the haemodynamic effect of arteriosclerosis immediately from E' and. Diameter, length, and, accordingly, the basic volume of the aorta without prestressing increase significantly in aortae with severe arteriosclerosis in comparison to those without sclerosis. The volume elasticity E' as a function of the static aortic pressure has a minimum within physiological pressure range and changes into a linear function when arteriosclerosis increases. The modulus of elasticity of a normal aorta remains constant within a pressure range of 20 to 100 mm Hg and it shows a linear increase at higher pressure. The differences between Vo, E' and of aortae with and without severe arteriosclerosis, however, are highly significant.

Adult↗
PubMed1980

Elastic tissue and smooth muscle volume in elastic and muscular type arteries in the dog.

1. Relative elastic tissue and smooth muscle volumes were determined by a stereological point-counting method in arteries with a progressively diminishing diameter, from the aorta towards the periphery. 2. The volume relationship between the smooth muscle cell and its nucleus was determined by the same method. Mean nuclear volume amounted to 6.9% of total smooth muscle cell volume. 3. Relative elastic tissue volume fell from the aorta towards the peripheral arteries, from 22.6% in the ascending aorta to 4--6% in the smallest arteries examined. 4. Relative smooth muscle volume was practically the same and differences between the individual values in the vast majority of arteries examined were non-significant. Total smooth muscle volume, calculated from the volume of the smooth muscle cell nuclei, varied mostly from 45 to 55%. 5. It can be concluded from these results that the ability of small and medium muscular type arteries to change their diameter actively by muscular contraction (as against elastic type arteries, in which this ability is less expressed) is facilitated not only by the organization of the structural components of the arterial wall, but also by the lower elastic tissue volume, which is compensated by the volume of the other passive components of the vascular wall, while relative smooth muscle volume remains the same.

Animals↗
PubMed1994

Elastic moduli and visco-elastic relaxation.

The elastic moduli of dental biomaterials are discussed in relation to the various intrinsic and extrinsic factors that can influence the magnitude of these parameters and hence the extent of modulus-matching with oral tissues. The time-dependent visco-elastic response is shown to be an important feature of both natural and many synthetic biomaterials. This modifies the stress magnitudes sustained in the restored unit, especially when polymeric chains or networks are a major constituent of the overall structure. An understanding of both moduli and visco-elasticity is valuable in the appraisal of clinical performance of biomaterials.

Acrylic Resins↗
PubMed2002

Pulsatile flow inside moderately elastic arteries, its modelling and effects of elasticity.

Pulsatile flow inside a moderately elastic circular conduit with a smooth expansion is studied as a model to understand the influence of wall elasticity in artery flow. The solution of the simultaneous fluid-wall evolution is evaluated by a perturbative method, where the zeroth order solution is represented by the flow in a rigid vessel; the first order correction gives the wall motion and induced flow modification without the need to solve the difficult coupled problem. Such an approach essentially assumes a locally infinite celerity, therefore it represent a good approximation for the fluid-wall interaction in sites of limited extent (branches, stenosis, aneurism, etc.), which include typical situations associated with vascular diseases. The problem is solved numerically in the axisymmetric approximation; the influence of wall elasticity on the flow and on the unsteady wall shear stress is studied in correspondence of parameters taken from realistic artery flow. Attention is posed to the role of phase difference between the incoming pressure and flow pulses.

Arteries↗
PubMed2000

Single-beat estimation of ventricular end-systolic elastance-effective arterial elastance as an index of ventricular mechanoenergetic performance.

BACKGROUND: The ratio of ventricular end-systolic elastance (Ees) to effective arterial elastance (Ea) is known to reflect not only ventricular mechanical performance but also energetic performance. Despite these useful features, technical difficulties associated with estimating Ees make the clinical application of Ees/Ea impractical. We developed a framework to estimate Ees/Ea without measuring ventricular volume or altering the loading condition. METHODS: To achieve this goal, we approximated the ventricular time-varying elastance curve with two straight lines, one for the isovolumic phase and the other for the ejection phase, and characterized the curve with the slope ratio, k, of these two straight lines. Using the concept of the pressure-volume relationship, Ees/Ea is algebraically expressed as Ees/Ea = Pad/Pes (1 + k. ET/PEP) - 1, where Pes is end-systolic pressure, Pad is aortic diastolic pressure, ET is ejection time, and PEP is pre-ejection period. In 11 anesthetized dogs, we recorded arterial and ventricular pressures and ventricular volume and estimated Ees and Ea under various contractile states and loading conditions. RESULTS: An empirical relation between k and Ees/Ea was found as k = 0.53 (Ees/Ea)0.51. Simultaneous solution of these two equations yielded Ees/Ea as a function of Pad/Pes and ET/PEP. The estimated Ees/Ea values correlated well with the measured Ees/Ea values ([Measured Ees/Ea] = 0.96 [Estimated Ees/Ea] + 0.098, r = 0.925, SEE = 0.051). CONCLUSIONS: The proposed framework is capable of estimating Ees/Ea from ventricular and aortic pressure.

Animals↗
PubMed2000

Single-beat estimation of end-systolic elastance using bilinearly approximated time-varying elastance curve.

BACKGROUND: Although left ventricular end-systolic elastance (E(es)) has often been used as an index of contractility, technical difficulties in measuring volume and in changing loading conditions have made its clinical application somewhat limited. By approximating the time-varying elastance curve by 2 linear functions (isovolumic contraction phase and ejection phase) and estimating the slope ratio of these, we developed a method to estimate E(es) on a single-beat basis from pressure values, systolic time intervals, and stroke volume. METHODS AND RESULTS: In 11 anesthetized dogs, we compared single-beat E(es) with that obtained with caval occlusion. Although the decrease (but not the increase) in contractility (5.3 to 11.4 mm Hg/mL) and the change in loading conditions (3.7 to 34.0 mm Hg/mL) over wide ranges significantly altered the slope ratio, the estimation of E(es) was reasonably accurate (y=0.97 x 0.46, r=0. 929, SEE=2.1 mm Hg/mL). CONCLUSIONS: E(es) can be estimated on a single-beat basis from easily obtainable variables by approximating the time-varying elastance curve by a bilinear function.

Animals↗
PubMed2000

Series of exon-skipping events in the elastic spring region of titin as the structural basis for myofibrillar elastic diversity.

Titins are megadalton-sized filamentous polypeptides of vertebrate striated muscle. The I-band region of titin underlies the myofibrillar passive tension response to stretch. Here, we show how titins with highly diverse I-band structures and elastic properties are expressed from a single gene. The differentially expressed tandem-Ig, PEVK, and N2B spring elements of titin are coded by 158 exons, which are contained within a 106-kb genomic segment and are all subject to tissue-specific skipping events. In ventricular heart muscle, exons 101 kb apart are joined, leading to the exclusion of 155 exons and the expression of a 2.97-MDa cardiac titin N2B isoform. The atria of mammalian hearts also express larger titins by the exclusion of 90 to 100 exons (cardiac N2BA titin with 3.3 MDa). In the soleus and psoas skeletal muscles, different exon-skipping pathways produce titin transcripts that code for 3.7- and 3.35-MDa titin isoforms, respectively. Mechanical and structural studies indicate that the exon-skipping pathways modulate the fractional extensions of the tandem Ig and PEVK segments, thereby influencing myofibrillar elasticity. Within the mammalian heart, expression of different levels of N2B and N2BA titins likely contributes to the elastic diversity of atrial and ventricular myofibrils.

Amino Acid Sequence↗
PubMed1976

Iron gallein elastic method---a substitute for Verhoeff's elastic tissue stain.

A method for staining elastic fibers in formalin fixed, paraffin embedded sections is described. After deparaffinizing and dehydration, sections are stained for 30 minutes in a solution prepared by mixing equal parts of 1% gallein dissolved in ethylene glycol and absolute alcohol (1:4), and 1.16% aqueous ferric chloride in 1% hydrochloric acid. The sections are washed in water and then differentiated in 2% ferric chloride for 2 minutes. After washing in water, the sections are counterstained with a variant of Van Gieson's picric acid-acid fuchsin for 1 minute. The results are similar to Verhoeff's elastic stain with elastic fibers staining black. An advantage to this staining procedure is that visually controlled differentiation is not necessary.

Aorta↗
PubMed1985

[Non-invasive measurement of the elastic properties of the abdominal aorta and the analysis of aging change--changes of elasticity of the aorta by aging].

For the purpose of the non-invasive measurement of the elastic properties of human abdominal aorta, we developed high sensitive measurement system of small displacement of tissue. This system consists of phase locked echo tracking loop combined with conventional B-mode imaging. The sensitivity to displacement in the model experiment was in the order of micro meter. Pressure strain elastic modulus (Ep) and stiffness parameter (beta) of abdominal aorta were calculated by our equipment in 61 persons, which were subdivided into 3 age groups, the young group (20 persons less than 35 yrs.), the middle aged group (21 persons between 35 yrs. and 60 yrs.), and the old group (20 persons more than 60 yrs.). Ep in the young group was 0.99 +/- 0.34 X 10(6) dynes/cm2, the middle aged group 1.55 +/- 0.68 X 10(6) dynes/cm2, the old group 3.80 +/- 2.05 X 10(6) dynes/cm2. Beta in the young group was 9.3 +/- 3.3, the middle aged group 12.0 +/- 4.5, the old group 27.6 +/- 14.0. The values of Ep and beta in the old group were significantly different from those in the young group and the middle group. Moreover large deviation of the both values was showed within the old group. The influence of aging on the elastic properties of abdominal aorta was found with large individual variation in relation to the progression of the sclerotic change.

Adult↗
PubMed1980

Elastic system fibers (oxytalan, elaunin and elastic fibers) in the skin of a freshwater teleost : optical and electron microscopy study.

The oxytalan, elaunin and elastic fibers which represent a system of connective tissue fibers -- the elastic system (ESP) -- were studied in the dermis of a teleost by optical and electron microscopy. The oxytalan fibers were identified at the dermo-epidermal junction. They are bound, by one of their extremities to the basal lamina, and by the other are in continuity with elaunin fibers. The elaunin fibers cross the entire stratum compactum perpendicularly and in the deeper zone are interconnected to other elaunin fibers. Thick elastic fibers, forming an apparent continuous layer were observed between the stratum compactum and the stratum spongiosum. The ultrastructural characteristics and functional properties of the ESF are discussed.

Animals↗
PubMed1977

Pre-elastic (oxytalan) fibres in the developing elastic cartilage of the external ear of the rat.

During chondrogenesis in the external ear of the rat oxytalan fibres precede the appearance of mature elastic fibres by 6-7 days. The spatial distribution of oxytalan fibres in fetal and neonatal pre-cartilage corresponds to that of the elastic fibres in mature cartilage. These findings support the hypothesis that oxytalan fibres in the pre-cartilage of the external ear of the rat are pre-elastic in nature.

Age Factors↗