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At least 919 records · Page 51Linked to original sources
PubMed1999

Application of dynamic computed tomography for measurements of local aortic elastic modulus.

A novel computed tomographic (CT) technique used for the instantaneous measurement of the dynamic elastic modulus of intact excised porcine aortic vessels subjected to physiological pressure waveforms is described. This system was comprised of a high resolution X-ray image intensifier based computed tomographic system with limiting spatial resolution of 3.2 mm-1 (for a 40 mm field of view) and a computer-controlled flow simulator. Utilising cardiac gating and computer control, a time-resolved sequence of 1 mm thick axial tomographic slices was obtained for porcine aortic specimens during one simulated cardiac cycle. With an image acquisition sampling interval of 16.5 ms, the time sequences of CT slices were able to quantify the expansion and contraction of the aortic wall during each phase of the cardiac cycle. Through superficial tagging of the adventitial surface of the specimens with wire markers, measurement of wall strain in specific circumferential sectors and subsequent calculations of localised dynamic elastic modulus were possible. The precision of circumferential measurements made from the CT images utilising a cluster-growing segmentation technique was approximately +/- 0.25 mm and allowed determination of the dynamic elastic modulus E(dyn) with a precision of +/- 8 kPa. Dynamic elastic modulus was resolved as a function of the harmonics of the physiological pressure waveform and as a function of the angular position around the vessel circumference. Application of this dynamic CT (DCT) technique to seven porcine thoracic aortic specimens produced a circumferential average (over all frequency components) E(dyn) of 373 +/- 29 kPa. This value was not statistically different (p < 0.05) from the values of 430 +/- 77 and 390 +/- 47 kPa obtained by uniaxial tensile testing and volumetric measurements respectively.

Animals↗
PubMed1998

Cell contraction caused by microtubule disruption is accompanied by shape changes and an increased elasticity measured by scanning acoustic microscopy.

The state of crosslinking of microfilaments and the state of myosin-driven contraction are the main determinants of the mechanical properties of the cell cortex underneath the membrane, which is significant for the mechanism of shaping cells. Therefore, any change in the contractile state of the actomyosin network would alter the mechanical properties and finally result in shape changes. The relationship of microtubules to the mechanical properties of cells is still obscure. The main problem arises because disruption of microtubules enhances acto-myosin-driven contraction. This reaction and its impact on cell shape and elasticity have been investigated in single XTH-2 cells. Microtubule disruption was induced by colcemid, a polymerization inhibitor. The reaction was biphasic: a change in cell shape from a fried egg shape to a convex surface topography was accompanied by an increase in elastic stiffness of the cytoplasm, measured as longitudinal sound velocity revealed by scanning acoustic microscope. Elasticity increases in the cell periphery and reaches its peak after 30 min. Subsequently while the cytoplasm retracts from the periphery, longitudinal sound velocity (elasticity) decreases. Simultaneously, a two- to threefold increase of F-actin and alignment of stress fibers from the cell center to cell-cell junctions in dense cultures are induced, supposedly a consequence of the increased tension.

Actins↗
PubMedDate not supplied

Effect of a growth hormone treatment on bone orthotropic elasticity in dwarf rats.

A refinement of the current ultrasonic elasticity technique was used to measure the orthotropic elastic properties of rat cortical bone as well as to quantify changes in elastic properties, density, and porosity of the dwarf rat cortex after a treatment with recombinant human growth hormone (rhGH). The ultrasonic elasticity technique was refined via optimized signal management of high-frequency wave propagation through cubic cortical specimens. Twenty dwarf rats (37 days old) were randomly assigned to two groups (10 rats each). The dwarf rat model (5-10% of normal GH) was given subcutaneous injections of either rhGH or saline over a 14-day treatment period. Density was measured using Archimedes technique. Porosity and other microstructural characteristics were also explored via scanning electron microscopy and image analysis. Statistical tests verified significant decreases in cortical orthotropic Young's (-26.7%) and shear (-16.7%) moduli and density (-2.42%) concomitant with an increase in porosity (+125%) after rhGH treatments to the dwarf model (p < 0.05). A change in material symmetry from orthotropy toward planar isotropy within the radial-circumferential plane after GH treatments was also noted. These results demonstrate some alteration in bone properties at this time interval. Structural implications of these changes throughout physiological loading regimens should be explored.

Animals↗
PubMed2005

Direct measurement of single-molecule visco-elasticity in atomic force microscope force-extension experiments.

Measuring the visco-elastic properties of biological macromolecules constitutes an important step towards the understanding of dynamic biological processes, such as cell adhesion, muscle function, or plant cell wall stability. Force spectroscopy techniques based on the atomic force microscope (AFM) are increasingly used to study the complex visco-elastic response of (bio-)molecules on a single-molecule level. These experiments either require that the AFM cantilever is actively oscillated or that the molecule is clamped at constant force to monitor thermal cantilever motion. Here we demonstrate that the visco-elasticity of single bio-molecules can readily be extracted from the Brownian cantilever motion during conventional force-extension measurements. It is shown that the characteristics of the cantilever determine the signal-to-noise (S/N) ratio and time resolution. Using a small cantilever, the visco-elastic properties of single dextran molecules were resolved with a time resolution of 8.3 ms. The presented approach can be directly applied to probe the dynamic response of complex bio-molecular systems or proteins in force-extension experiments.

Data Interpretation, Statistical↗
PubMed2006

Aortic elastic properties in young pregnant women.

This study aimed to investigate the aortic elastic properties of young pregnant women by comparing them with those of age-matched healthy females. The study group consisted of 21 pregnant women at a mean age of 26 +/- 1 years; 22 healthy women at a mean age of 25 +/- 1 years constituted the control group. Doppler-color echocardiographic variables and serum estradiol (E2) levels were measured from both groups. The blood samples were obtained from the control group in the first week after menstrual bleeding. Diastolic and systolic blood pressure (DBP and SBP, respectively) were measured with a sphygmomanometer. Systolic and diastolic aortic diameters (AOS and AOD, respectively) were measured 3 cm proximal to the aortic valves. Aortic elastic properties were assessed according to the following formulas: 1, Aortic strain = (AOS - AOD)/AOD; 2, Aortic distensibility = 2 x (AOS - AOD)/(PP x AOD); 3, Aortic diameter change = AOS - AOD; 4, Aortic stiffness index = ln(SBP/DBP)/(AOS - AOD)/AOD. The results were expressed as mean +/- standard deviation and compared by t-test between groups. P < 0.05 was considered as statistically significant. All women in the study group were in their first pregnancy and second trimester. The height and weight were 160 +/- 5 vs 164 +/- 6 cm and 60 +/- 9 vs 54 +/- 3 kg in the study vs control groups, respectively (P < 0.05). The AOD was 26 +/- 3 vs 26 +/- 4 mm and AOS 29 +/- 3 vs 28 +/- 4 mm. Pulse pressure was 43 +/- 3 vs 45 +/- 8 mmHg in the study vs control groups, respectively (P > 0.05). The serum E2 level was significantly higher in pregnant women (21 300 +/- 2 300 pg/ml). Derived aortic elastic properties in pregnant women were also increased significantly (P < 0.0005). The indexes of aortic elastic properties are altered and aortic stiffness is decreased among young pregnant women. This may be due to the adaptation mechanisms including high estradiol levels detected in pregnancy.

Adult↗
PubMed2005

Disulphide reaction staining for the identification of integumental elastic fibres.

Based on specific methods (Sippel-APM-chromotropic acid technique; IC3-PE-maleimide fluorescence reaction) and skin samples of four domesticated mammals (dog, cattle, horse, pig), disulphide groups were demonstrated in the elastic component of the basement membrane of the epidermis, the elastic fibre system of the dermis, the elastic components of the connective tissue sheath of hair follicles, apocrine tubular glands, and sebaceous glands, and of the connective tissue surrounding the cutaneous muscle. The results are discussed regarding the relation of this reaction staining to the presence of microfibrils (fibrillin) in the elastic fibres.

Animals↗
PubMed2000

Elastic properties of muscle-tendon complex in long-distance runners.

The purpose of this study was to investigate the elastic properties of muscle-tendon complex (MTC) in knee extensor muscles and the capacity for elastic energy utilization in long-distance runners (LDR) by comparing with data obtained from untrained individuals (CON). The elongation (L) of the tendon and aponeurosis of vastus lateralis muscle during isometric knee extension was determined by real-time brightness mode ultrasonography, while the subjects developed a gradually increasing torque from 0 (relaxed) to maximal effort (MVC) within 7 s. In addition, performances in two kinds of maximal vertical jumps, i.e. squatting (SJ) and counter-movement jumps (CMJ), were measured. The relationship between L muscle and force (F) was curvilinear and consisted of an initial region (toe region), characterized by a large increase in L with increasing F, immediately followed by a linear region. The slope of the regression equation for the L-F relationship in the range 50%-100% of MVC was defined as an index of MTC compliance, where the rate of the changes in L to that in muscle F at every 10% of MVC became almost constant. The maximal L (Lmax) and MTC compliance were significantly lower in LDR than in CON: 29.9 (SD 3.9) mm in LDR compared to 33.3 (SD 5.5) mm in CON for Lmax and 1.55 (SD 0.25) x 10(-2) mm.N-1 in LDR compared to 1.88 (SD 0.82) x 10(-2) mm.N-1 in CON for MTC compliance. Also, LDR showed significantly less elastic energy absorption (Ee) than CON, defined as the area below the L-F relationship curve from 0 to 100% of MVC. Not only jump heights but also the differences between the heights in SJ and CMJ, expressed as the percentage of the height in SJ, were significantly lower in LDR than in CON. The augmentation with counter-movement was significantly correlated to either MTC compliance (r = 0.554, P < 0.05) or Ee (r = 0.563, P < 0.05). Thus, the present results would indicate that MTC of vastus lateralis muscle is less compliant and its potential for energy storage during MTS lengthening is lower in LDR than untrained individuals. These elastic profiles of vastus lateralis muscle in LDR may be associated with their lower performances during CMJ.

Adult↗
PubMed2001

Biochemical analysis of elastic and rigid cuticles of Cirsium horridulum.

The cuticle is a complex structure of soluble lipids, lipid polymers and polysaccharides. In addition to its functions to reduce water loss and provide a protective barrier, its mechanical properties may be significant to plant growth and development. We investigated the cuticle of Cirsium horridulum Michx. because of its involvement in the thigmonastic contraction of staminal filaments. The staminal filaments and portions of the style are surrounded by a highly elastic cuticle in contrast to the rigid cuticle of the corolla and leaves. Our aim was to determine if the biochemical composition affected the elasticity of the cuticle. We discovered that the ratio of carbohydrates to lipids is 1:7 in floral parts but 2:1 in leaf cuticle. Esterified cutin components represented about 80% of the cuticle and di-hydroxyhexadecanoic acids were the major monomers of cutin, regardless of origin. The cutin of elastic tissues is characterized by a higher content of tri-hydroxy monomers than the cutin of rigid tissues. The data suggest that hydroxyl groups enhance the hydrophilic character of the cuticle and contribute to cuticular elasticity.

Asteraceae↗
PubMed1999

Increase of segments of elastic-type blood vessel walls in fetal placental stem villi during pre-eclampsia at term.

In recent studies we described the presence of elastic-type blood vessels within trunci and rami chorii of human placental stem villi. For systemic and pulmonary hypertension it is known that elastic fibres are enhanced in arteries. The aim of our study was, therefore, to examine whether pre-eclampsia may lead to an increase of elastic tissue fibres in blood vessel walls of placental stem villi and whether there are differences in the thickness of blood vessel walls within these villi when compared to normotensive pregnant women. Twenty-six women with uncomplicated pregnancies and 25 patients with pre-eclampsia were investigated. Unfixed cryostat serial sections were processed for conventional orcein staining and for the demonstration of alpha-actin-immunoreactivity. The intensity of orcein staining of stem villus blood vessel walls was evaluated by a semiquantitative score method. Significant higher intensities of orcein staining (P<0.00001) were calculated for blood vessel walls of placentae with pre-eclampsia. The amount of thick stem villus vessels (>41 microm) increased during pre-eclampsia from 39 gestational weeks onwards. Our study demonstrates that segments of thick blood vessel walls and elastic-type vessel walls are increased in placental stem villi of patients with pre-eclampsia. This reaction may protect the fetal placental vessels and avert an increase of the fetal hypertension.

Chorionic Villi↗
PubMed2000

Pre-eclampsia associated alterations of the elastic fibre system in umbilical cord vessels.

Although pre-eclampsia (PE) is often associated with fetal hypoxia, hypertension and/or disturbed function of the fetal circulation, the effect of these altered hemodynamic parameters on the structure and composition of umbilical vessels has not been systematically investigated before. Therefore, this study focuses on PE-associated changes of the elastic fibre system in umbilical cord vessels investigated by light and electron microscopy, immunocytochemistry and biochemistry. In umbilical cord veins, no changes in thickness of the vessel wall or of any sublayer were observed. However, the internal elastic lamina of the veins was split in 80% of the PE-group in contrast to 20% in uncomplicated pregnancies. This effect was significant (alpha <0.01) from 36 weeks of gestation onwards. In umbilical cord arteries, the entire arterial vessel wall was found to be 15% thicker in PE than in uncomplicated pregnancies. The enlargement was caused by an increase of both the tunica intima and tunica media. The thickening of the tunica intima was attributed to a migration of smooth muscle cells towards the endothelium, accompanied by a splitting of the internal elastic lamina. Compared to uncomplicated pregnancies, smooth muscle cells of arteries and veins in PE showed a metabolic activation demonstrated by highly dilated endoplasmic reticulum. A semiquantitative score method as well as a quantitative dot blot assay indicated a PE-associated reduction of elastin expression in the arterial vessel walls. In summary, PE obviously induces a decrease of the elastin content accompanied by a thickening of the vessel wall in umbilical cord arteries. This remodeling of the elastic fibre system, together with an increased migration of smooth muscle cells, might represent part of the functional adaptation system of the umbilical cord arteries on the altered hemodynamic conditions in PE.

Adult↗
PubMed2004

Intima-media thickness and arterial elasticity in hypertensive children: controlled study.

The objective of this cross-sectional controlled study was to evaluate the intima-media thickness (IMT) of the common carotid artery (cIMT) and superficial femoral artery (fIMT), as well as the elastic properties of the common carotid artery, in children with essential arterial hypertension. The study included 49 children with newly detected essential hypertension [mean age 14.5 (range 6-20) years] and 61 healthy normotensive children [mean age 13.5 (range 6-20) years]. The cIMT and fIMT were evaluated by ultrasonography. The elastic properties of the carotid artery were calculated from actual blood pressure values, arterial dimensions, and carotid wall thickness. Hypertensive children had greater values of both cIMT (0.45+/-0.05 mm) ( P=0.0001) and fIMT (0.37+/-0.05 mm) ( P=0.005) than controls (0.41+/-0.04 and 0.33+/-0.06 mm, respectively). The internal systolic and diastolic diameters of the common carotid artery were also significantly greater in hypertensive patients. The distensibility and elasticity of the common carotid artery were significantly decreased in hypertensive patients, while arterial compliance was significantly greater than in controls. cIMT and fIMT correlated with systolic and pulse pressure values, body mass index (BMI), homocysteine, low high-density lipoprotein, and apolipoprotein AI. After subdividing the control group and patients according to BMI below or above the 95th percentile for age and sex, there were differences only between normal-weight normotensive children and the two groups of hypertensive children. The stepwise regression analysis showed that the predictive factor for cIMT was pulse pressure and for fIMT body mass and homocysteine. Hence, in newly diagnosed children with essential hypertension, functional and anatomical changes in elastic and muscular arteries are observed. Pulse pressure and biochemical risk factors for cardiovascular damage were predictors of vessel wall injury, even if it remained within the normal range. BMI is an important factor influencing IMT values.

Adolescent↗
PubMed1992

Comparison of acute elastic recoil after directional coronary atherectomy versus standard balloon angioplasty.

We evaluated intraprocedural "elastic recoil" in 25 patients (22 men and 3 women) undergoing directional coronary atherectomy (DCA) of left anterior descending stenoses, and compared these with 25 temporally-matched (14 men and 11 women) patients having balloon angioplasties (PTCA). Quantitative arteriography was performed using the Coronary Measurement System (Leiden, The Netherlands), with "elastic recoil" defined as the difference in maximum device or balloon size minus residual minimum diameter. In addition, we determined the effects of relative device size, specific anatomic location (proximal/mid artery), lesion length, eccentricity (symmetry index), and dystrophic calcification on acute "recoil" severity after both procedures. Although initial coronary stenoses were similar (minimum stenotic diameter, DCA = 0.59 +/- 0.20 mm versus PTCA = 0.55 +/- 0.23 mm, p = NS), less "elastic recoil" was observed after atherectomy (DCA = 0.83 +/- 0.57 mm versus PTCA = 1.26 +/- 0.56 mm, p < 0.01), and this was confirmed by absolute recoil/maximum device size ratios (DCA = 23.5 +/- 16.0% versus PTCA = 41.6 +/- 13.8%, p < 0.01). Acute "elastic recoil" was also influenced by maximum device size/"normal" coronary artery ratios [(ratio < 0.9, DCA = 0.26 +/- 0.10 mm versus PTCA = 0.84 +/- 0.13 mm, p < 0.01); (ratio 0.9 to 1.1, DCA = 0.69 +/- 0.41 mm versus PTCA 0.75 +/- 0.32 mm, p = NS); (ratio > 1.1, DCA = 1.09 +/- 0.64 mm versus PTCA = 1.59 +/- 0.48 mm, p < 0.05)].(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1984

Elastic property ratios of a triple-stranded stainless steel arch wire.

The general elastic property ratio equations for nth-stranded wires are derived and then specified for the case of a triple-stranded arch wire. Several parameters are defined, including the modulus of elasticity (E) and the helical spring (kappa) and bending plane (lambda) shape factors. Thereafter, the elastic property ratios of a wide range of compositional/configurational combinations are determined, using a representative triple-stranded 0.0175 inch (3 X 0.008 inch) stainless steel wire as the base line. These results show that the particular 3 X 0.008 inch wire studied possesses the stiffness of an 0.010 inch stainless steel wire but has at least 20% more strength and range. Furthermore, the stiffness of the 3 X 0.008 inch multistranded wire is similar to an 0.016 inch nickel-titanium wire but only 40% that of an 0.016 inch beta titanium wire. When these elastic property ratios are compared with the previous results reported by Thurow, Burstone, and Kusy, differences are noted which can be explained on the basis of the mechanical property values and/or the geometric modeling assumed.

Elasticity↗
PubMed1990

Morphological and biochemical evidence for elastic fibres in the Syrian hamster temporomandibular joint disc.

Elastic fibres are considered to be important for the normal biomechanical functions of the TMJ. The objective here was to correlate morphological evidence for the presence of elastic fibres in discal tissues with biochemical evidence for elastin. For light microscopy, the joints were removed en bloc, processed for paraffin embedding, sectioned and stained with resorcin-fuchsin. For biochemical study, a radioimmunoassay for desmosine was used to estimate the amount of elastin in excised articular discs. The histological preparations showed that numerous elastic fibres were present in various areas of the disc and in some of the discal attachments to surrounding bone. Radioimmunoassay also indicated that elastin was present in these tissues. Therefore, the biochemical findings support the morphological in suggesting that elastic fibres are present in the articular disc of the hamster TMJ.

Animals↗
PubMed1981

The microfibrillar components of porcine lung elastic fiber.

Lung elastic fiber was isolated from anatomically defined porcine parenchymal tissue. Constituent microfibrillar acidic structural glycoproteins (external and meso) were obtained by mild dissociative quantitative procedures, leaving the elastin-rich fraction as the insoluble residue. The presumptive cross-link lysylnorleucine was identified in both of the highly aggregated acidic structural glycoprotein fractions. The external-acidic structural glycoproteins require dithiothreitol but not sodium dodecyl sulfate for solubility. Both sodium dodecyl sulfate and dithiothreitol at 55 degrees C are required to release meso-acidic structural glycoproteins from the elastic fiber. On the basis of physical characteristics, I propose a new fraction from elastic fiber, the meso-acidic structural glycoprotein. The meso-acidic structural glycoproteins may have been in longest and closest contact with the elastin core of the elastic fiber. Alkali-soluble peptides from the elastin-rich fraction contained desmosine and high concentrations of hydroxyproline, polar amino acids and lysylnorleucine. The cross-link, lysylnorleucine, may be evidence of covalent bonding of glycoprotein to elastin, explaining my inability to obtain the biopolymer elastin with the composition of tropoelastin corrected for the desmosine-lysine content.

Amino Acids↗
PubMed1985

Three-dimensional architecture of elastic tissue in early atherosclerotic lesions of the rat aorta.

The overall three-dimensional architecture of elastic tissue in early atherosclerotic lesions of the rat aorta was studied using scanning electron microscopy (SEM) after hot-formic acid extraction followed by a freeze-drying method. These lesions were induced by feeding the rats a diet containing 2% cholesterol, 0.5% cholic acid and 0.2% methylthiouracil. SEM revealed two types of alterations in the elastic tissue; one was an increase in the dome-like elastic lamina with few fenestrations that might be due to the reduplication of the internal elastic lamina (IEL), and the other was an increase in fibrous elastin, generally oriented longitudinally in the intima. The former was discussed with respect to its barrier function to such macromolecules as fibrinogen and low density lipoprotein (LDL), and was assumed to be a structure related to prevention of early atherosclerotic lesions.

Animals↗
PubMed1984

A continuous wave technique for the measurement of the elastic properties of cortical bone.

A continuous wave technique is described for measuring the nine independent orthotropic elastic coefficients from a single cubic specimen. The side dimensions of this cubic specimen are on the order of 5 mm. Because of the small size of the specimen, the spatial resolution of material inhomogeneity using this technique is quite good. Although it is possible to apply this technique to any elastic material such as woods or metals, the elastic properties of human and canine cortical femora are presented here. The orthotropic elastic coefficients and the variation of these coefficients are presented as a function of anatomical position.

Animals↗
PubMed1985

The bone tissue of the canine mandible is elastically isotropic.

This paper reports experimental measurements which show that canine mandibular bone tissue is elastically isotropic. Earlier work has established that human, canine and bovine cortical bone tissue of the femur, tibia and skull are elastically anisotropic and therefore the reported isotropy of mandibular tissue was unexpected. The isotropic elastic moduli of the canine mandible are represented by a Young's modulus of 7.5 GPa and a Poisson's ratio of 0.4. Earlier work gave the three orthotropic Young's moduli of the cortical one of the canine femur as 12.8 GPa, 15.6 GPa and 20.1 GPa. The experimental technique employed is elastic wave propagation at ultrasonic frequencies.

Animals↗