Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “ELASTICITY”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 811 records · Page 45Linked to original sources
PubMedDate not supplied

A histomorphological study in age related changes in the elastic fiber system of the basilar artery.

The aim of the study was to quantify the distribution of elastic fibers within the wall of the basilar artery. Three age groups were studied: 1) 0-1 yr.; 2) 20-50 yr. 3) > 50 yr. A histomorphometrical study was undertaken using an estimation of the linear density of the components of the fibrous elastic tissue system: the full length in the proximal and distal segments of the basilar artery was evaluated. Our results showed that: The elastic tissue of the basilar artery is not evenly distributed throughout the tunica media. Compared to the 0 to 1-year age group, mature elastic, elauninic and oxytalan fibers decreased with age. In all age groups the linear density of the mature elastic fibers was more evident in the proximal than in the distal segment of the artery.

Adult↗
PubMed1997

Spatial transformation and registration of brain images using elastically deformable models.

The development of algorithms for the spatial transformation and registration of tomographic brain images is a key issue in several clinical and basic science medical applications, including computer-aided neurosurgery, functional image analysis, and morphometrics. This paper describes a technique for the spatial transformation of brain images, which is based on elastically deformable models. A deformable surface algorithm is used to find a parametric representation of the outer cortical surface and then to define a map between corresponding cortical regions in two brain images. Based on the resulting map, a three-dimensional elastic warping transformation is then determined, which brings two images into register. This transformation models images as inhomogeneous elastic objects which are deformed into registration with each other by external force fields. The elastic properties of the images can vary from one region to the other, allowing more variable brain regions, such as the ventricles, to deform more freely than less variable ones. Finally, the framework of prestrained elasticity is used to model structural irregularities, and in particular the ventricular expansion occurring with aging or diseases, and the growth of tumors. Performance measurements are obtained using magnetic resonance images.

Aging↗
PubMed1999

Dynamic Surface Elasticity of Micellar and Nonmicellar Solutions of Dodecyldimethyl Phosphine Oxide. Longitudinal Wave Study.

Measurements of the dynamic surface properties are used for the first time for the determination of the mean aggregation number of micelles. An approximate expression for the dilational dynamic surface elasticity of micellar solutions in the concentration region near the CMC is obtained on the basis of the more general theory which has been developed several years ago (B. A. Noskov, Izv. Akad. Nauk SSSR. Mekh Zydkasty i gaza N2, 105 (1989)). If the reverse frequency of external perturbations does not exceed the characteristic time of the slow step of the micellization process, the only properties of micelles which determine the dynamic surface elasticity are the mean aggregation number and the mean diffusion coefficient. The method of longitudinal surface waves has been applied to determine the dynamic surface elasticity of solutions of dodecyldimethyl phosphine oxide in the frequency range from 0.2 to 1.8 Hz. Both the real and the imaginary components of the dynamic surface elasticity depend nonmonotonically on the concentration below the CMC. All the experimental data agree reasonably well with the pure diffusional adsorption mechanism. Above the CMC both components of the surface elasticity decrease faster with the surfactant concentration. This fact can be explained by the contribution of micelles to the mass exchange between the surface layer and the bulk phase. Application of the theory of dynamic surface properties of micellar solutions to experimental data allows us to obtain an estimation of the mean aggregation number of micelles of dodecyldimethyl phosphine oxide. Copyright 1999 Academic Press.

Journal Article↗
PubMed1998

A survey of the primary structure and the interspecies conservation of I-band titin's elastic elements in vertebrates.

Titin is a >3000-kDa large filamentous protein of vertebrate-striated muscle, and single titin molecules extend from the Z disc to the M line. In its I-band section, titin behaves extensible and is responsible for myofibrillar passive tension during stretch. However, details of the molecular basis of titin's elasticity are not known. We have compared the motif sequences of titin elastic elements from different vertebrate species and from different regions of the molecule. The I-band titin Ig repeats that are expressed in the stiff cardiac muscle and those that are tissue-specifically expressed in more elastic skeletal muscles represent distinct subgroups. Within the tissue-specifically expressed Ig repeats, a super-repeat structure is found. For the PEVK titin sequences, we surveyed interspecies conservation by hybridization experiments. The sequences of the titin gene which code for the C-terminal region of the PEVK domain are conserved in the genomes of a larger variety of vertebrates, whereas the N-terminal PEVK sequences are more divergent. Future comparisons of titin gene sequences from different vertebrates may improve our understanding of how titin contributes to species diversity of myofibrillar elasticity. Within one species, different classes of Ig repeat families may contribute to elastic diversity of the titin spring in different segments.

Amino Acid Sequence↗
PubMed1999

Serial elastic elements in the damselfly wing: mobile vein joints contain resilin

Two main types of joints occur in the damselfly wing: mobile and immobile. Some longitudinal veins (RP2(-), RP3&4(-), and MP(-)) are elastically joined with cross veins, whereas other longitudinal veins (IR1(+), IR2(+), MA(+), CuA'(+)) are firmly joined with cross veins. In this study we mapped the distribution of serial elastic elements in the wing. The occurrence of resilin, a rubberlike protein, in mobile joints suggests that the automatic twisting mechanism of the leading edge by aerodynamic force works not by flexibility but by the elasticity of these joints. First, it should result in elastic energy storage in the distal areas of the wing. Second, serial elastic elements of wing presumably act as dampers of an aerodynamic force, which are responsible for gradual twisting of the leading edge.

Journal Article↗
PubMed2003

The income elasticity of health care spending. A comparison of parametric and nonparametric approaches.

Parametric and nonparametric estimation techniques are compared in estimating the relationship between income and health expenditures with implications for the reliability of past estimates of health expenditure income elasticity. Relative to a more flexible nonparametric approach, a parametric approach can generate over or underestimates in health expenditure. Three time series cross-section data sets are used: (a) United States state level data from 1980-1997, (b) Canadian province level data from 1965-2000, and (c) national level data for 16 OECD countries from 1960-1997. Relative to ordinary least squares, locally weighted scatterplot smoothing allows for variability in the income elasticity of health spending as income varies. Generally, results of the latter suggest that income elasticities are higher at low-income levels and lower at higher income levels. As well, these results confirm that income elasticity does vary by level of analysis with international income elasticities being generally larger than national or regional studies.

Journal Article↗
PubMed1976

An elastic protein from the cortical layer of the sea-urchin egg.

An elastic protein was isolated from the cortical layer of the fertilized eggs of two species of sea-urchin. Young's modulus of the fiber of the sea-urchin protein was approximately 1-10(7) dyne/cm2. The amino acid compositions of the elastic protein from the two species of sea-urchin eggs were very similar to that of connectin, elastic protein from vertebrate skeletal muscle. The fluorescent antibody against muscle connectin stained the cortical layer of the sea-urchin egg. It appears that the elastic protein is responsible for the elasticity of the egg cortex.

Amino Acids↗
PubMed1989

The low-frequency dependence of respiratory system resistance and elastance in normal dogs.

The resistance (R) and elastance (E) of the respiratory system were determined by fitting the equation: pressure = R x flow + E x volume to data obtained from normal anesthetized/paralyzed dogs during mechanical ventilation at different frequencies (5 to 50 breaths per min) and tidal volumes. R exhibited a 50% decrease with increasing frequency while E showed a less marked but still distinct increase with frequency. Volume-time profiles were also recorded in the same animals during passive expiration, and the frequency dependence of resistance and elastance from 0 to 1 Hz predicted from the bi-exponential curves fitted to the profiles. The way in which resistance and elastance were predicted to vary with frequency was similar to the variations determined from regular ventilation data. There were, however, some systematic differences between the actual values of resistance and elastance obtained by the two methods which may reflect certain nonlinear characteristics of the respiratory system such as static hysteresis. Nonlinearities were also evident in that both the resistances and the elastances at all frequencies showed a slight decrease with increasing tidal volume. We conclude that a large part of the mechanical behaviour of the normal canine respiratory system at low frequencies can be accounted for in terms of a two-compartment model describing a homogeneous alveolar region surrounded by viscoelastic tissue.

Airway Resistance↗
PubMed1992

Analysis of the contraction of series and parallel muscles working against elastic loads.

The purpose of the present study was to analyze the manner in which series and parallel arrangements of respiratory muscles, contracting together, augment the forces and displacements applied to external elastic loads over those produced by a single muscle contracting alone. We first developed a series of mathematical expressions to describe the behavior of various arrangements of muscles contracting against elastic loads. We then compared the predictions of these equations with the results from experiments in which the forces and displacements produced by simple arrangements of muscles were measured. Both theoretical and experimental results indicate that, against high elastic loads, parallel arrangements of muscle strips produce greater forces and greater displacements than do single muscles; parallel arrangements do not, however, significantly increase the displacement or force applied to low elastic loads. Conversely, series arrangements result in greater forces and greater displacement of low loads, but are no better than single muscles when contracting against high loads. Against moderate loads parallel and series arrangements of muscles appear to be equivalent in generating forces and displacements during contraction. This analysis suggests that a major determinant of the effects of contraction of various networks of inspiratory muscles is the magnitude and character of the respiratory impedance against which these muscles must work. The primary difference between series and parallel arrangements of muscles is that muscles arranged in series are most effective against low elastic loads and muscles in parallel act most effectively against high loads.

Animals↗
PubMed1990

Elastic band mobilisation after flexor tendon repair; splint design and risk of flexion contracture.

Elastic band mobilisation of repaired flexor tendons in zone 2 may be complicated by flexion contracture of the P.I.P. joint. The mechanics of three types of elastic band mobilisation were analysed from lateral video-recordings of finger movement and the flexion moment at the P.I.P. joint was derived at every 10 degrees of flexion. The conventional forearm attachment of the elastic band produced a steep rise in P.I.P. joint flexion moment during extension; this effect was greatest when the M.P. joint was at 70 degrees and least at 20 degrees. Flexion moments for attachments around the dorsum of the hand or under a palmar pulley were lower, uniform throughout the range of P.I.P. joint motion and independent of the position of the M.P. joint. The effort needed to extend the P.I.P. joint is strongly influenced by the method of elastic band attachment; consideration should be given to both tension and moment arm in application of elastic band mobilisation.

Bandages↗
PubMed2005

Calcification of elastic fibers in human atherosclerotic plaque.

The present study was undertaken to systematically investigate whether calcification of elastic fibers occurs in human atherosclerotic plaques. Fourteen carotid artery segments obtained by endarterectomy were examined by a combination of electron microscopy and cytochemistry. The analysis demonstrated that calcification of elastic fibers occurred in all 14 specimens. Two distinct types of calcification of elastic fibers were identified. In type I calcification, elastin itself was observed to undergo calcification and no visible structural alterations preceded the calcification. In type II of calcification, structural alteration of elastin preceded calcification of elastic fibers and included vacuolization of elastin accompanied by the accumulation of neutral lipids and unesterified cholesterol within altered elastic fibers. In type II calcification, calcified deposits were found to form in an association with unesterified cholesterol. Type II calcification was widespread throughout the plaque matrix while type I calcification occurred only in the deep portions of plaques.

Aged↗
PubMed2006

The influence of vessel wall elasticity and peripheral resistance on the carotid artery flow wave form: a CFD model compared to in vivo ultrasound measurements.

The Doppler flow wave form and its derived measures such as the pulsatility index provide clinically important tools for the investigation of arterial disease. The typical shape of Doppler flow wave forms is physiologically known to be largely determined by both peripheral resistance and elastic properties of the arterial wall. In the present study we systematically investigate the influence of both vessel wall elasticity and peripheral resistance on the flow wave form obtained from a CFD-simulation of blood flow in the carotid bifurcation. Numerical results are compared to in vivo ultrasound measurements. The in vivo measurement provides a realistic geometry, local elasticities and an input flow wave form for the numerical experiment. Numerical and experimental results are compared at three different sites in the carotid branches. Peripheral resistance has a profoundly decreasing effect on velocities in the external carotid artery. If elasticity is taken into account, the computed peak systolic velocities are considerably lower and a more realistic smoothing of the flow wave form is found. Together, the results indicate that only if both vessel wall elasticity and positive peripheral resistance are taken into account, experimentally obtained Doppler flow wave forms can be reproduced numerically.

Biomechanical Phenomena↗
PubMed2006

Osteoblast response to the elastic strain of metallic support.

It is known that metallic elements of joint endoprostheses undergo elastic strain due to their mechanical function. This is one of the factors which may be responsible for the loosening of endoprostheses. Since mechanisms involved in it remain unclear, it seems valuable to verify if cells responsible for bone regeneration are affected by a strain of the implant. Our experiment examines the influence of elastic strain applied to Ti6Al4V samples on osteoblasts cultured on their surface in vitro. Human bone-derived cells are observed in contact with metallic plates. Titanium alloy was chosen as a support since it is one of the most commonly used materials for stems in joint endoprostheses. Cyclic elastic deformation of 0.1% was applied to the support once daily for 7 days. Two thousand cycles were applied each time. Samples which were not subject to strain served as control. After the observation period XTT assay was performed, alkaline phosphatase activity as well as osteocalcin concentration and nitric oxide secretion were determined and compared with the results obtained in the control group. It was found that the number of viable cells in the mechanically stimulated population was significantly higher than in control, while both alkaline phosphatase activity and osteocalcin concentration were significantly lower in the experimental group. Nitric oxide secretion was found in the culture which was subject to elastic strain, but not in the control. The possible clinical implication is that elastic strain of the metallic endoprostheses may influence osteoblasts which are in contact with the implant in vivo.

Adolescent↗
PubMed2004

Elasticity analysis of density-dependent matrix population models: the invasion exponent and its substitutes.

In density-independent models, the population growth rate lambda measures population performance, and the perturbation analysis of lambda (its sensitivity and elasticity) plays an important role in demography. In density-dependent models, the invasion exponent lambdaI replaces lambda as a measure of population performance. The perturbation analysis of lambdaI reveals the effects of environmental changes and management actions, gives the direction and intensity of density-dependent natural selection on life history traits, and permits calculation of the sampling variance of the invasion exponent. Because density-dependent models require more data than density-independent models, it is tempting to look for substitutes for the invasion exponent, the sensitivity and elasticity of which can be calculated from a density-independent model. Here we examine the accuracy of two such substitutes: the dominant eigenvalue of the projection matrix evaluated at equilibrium (An) and the dominant eigenvalue of the matrix averaged over the attractor (A). Using a two-stage model that represents a wide range of life history types, we find that the elasticities of An or A often agree to within less than 5% error with those of the invasion exponent, even when population dynamics are chaotic. The exceptions are for semelparous life histories, especially when density-dependence affects fertility. This suggests that the elasticity analysis of density-independent models near equilibrium, or averaged over the attractor, provides useful information about the elasticity of the invasion exponent in density-dependent models.

Humans↗
PubMed2003

Overexpression of semicarbazide-sensitive amine oxidase in smooth muscle cells leads to an abnormal structure of the aortic elastic laminas.

Elevated semicarbazide-sensitive amine oxidase (SSAO) activity has been observed in several human conditions, eg, diabetes, and it has been speculated that SSAO contributes to the development of vasculopathies associated with this disease. To investigate in vivo consequences of elevated expression of SSAO in vascular tissues, we have developed a transgenic model for overexpression of human SSAO in mice. A smooth muscle-specific promoter, smooth muscle alpha-actin promoter 8 (SMP8) was used. Transgenic expression of human SSAO in tissues with a high content of smooth muscle cells was confirmed by Northern blot analysis. Enzymatic analysis of homogenates from transgenic tissues showed elevated levels of SSAO activity compared to non-transgenic littermates. Furthermore, when plasma SSAO activity was analyzed, much higher activity was detected compared to plasma from control mice, indicating that plasma SSAO may originate from smooth muscle cells. Histopathological evaluation of aorta and renal artery from transgenic mice revealed an abnormal structure of the elastin tissue. Instead of the regularly folded elastic laminae normally found in tunica media of sacrificed mice, the elastic laminae were straight and unfolded with irregularly arranged elastic fibers, forming tangled webs, between the intercalating elastic laminae. These alterations of the elastin structures suggest that overexpression of SSAO has led to a reduced elasticity of the arteries. Moreover, the mean femoral arterial pressure of the SMP8 SSAO transgenic mice was significantly lower in comparison to non-transgenic littermates. This suggests that the transgenic mice have a defect in their ability to regulate blood pressure.

Amine Oxidase (Copper-Containing)↗
PubMed1999

Relation between urethral elasticity and bladder outlet obstruction and histologic composition of the prostate in patients with benign prostatic hyperplasia.

OBJECTIVES: In benign prostatic hyperplasia (BPH), bladder outlet obstruction is caused by mechanical blockage resulting from an enlarged prostate, and by the increased tone of prostatic smooth muscle. In patients with obstructive BPH, the prostatic urethra urodynamically corresponds to the flow-controlling zone (FCZ). We sought to investigate the relation between the obstruction and elastic properties of the FCZ and the histologic composition of the prostate in symptomatic patients with BPH. METHODS: The grade of infravesical obstruction was classified according to preoperative pressure-flow data from 30 men with symptomatic BPH, and the elastic properties of the FCZ were evaluated as the mean elastance, which was calculated using the three-parameter model. The area densities of smooth muscle, fibrous tissue, epithelium, and lumen were determined by quantitative morphometry, using BPH tissue obtained by transurethral resection. RESULTS: The area density of smooth muscle had a negative correlation with mean elastance (p = -0.50, P <0.01), the linear passive urethral resistance relation (p = -0.43, P <0.05), and the group-specific urethral resistance factor (p = -0.39, P <0.05). No other histologic element was correlated with these variables. CONCLUSIONS: Our results suggest that urethral elasticity and bladder outlet obstruction grade are influenced by the relative content of smooth muscle within the prostate in patients with BPH.

Aged↗
PubMed2002

Effects of fluoride concentration and elastic tensile strain on the corrosion resistance of commercially pure titanium.

The corrosion resistance of commercially pure (CP) titanium in 1% NaCl + 0 approximately 1% NaF solution (pH = 6) under different elastic tensile strains was investigated by using electrochemical impedance spectroscopy (EIS) measurement technique. The polarization resistance (Rp), which is inversely proportional to the corrosion rate, of CP titanium in the test solution was obtained from the EIS data. Different elastic tensile strains, namely 0%, 1%, 2%, and 4%, were applied on the test specimens by using a tensile test machine during the corrosion tests. Corrosion morphology was characterized by using a scanning electron microscope. Surface chemical analyses were performed by using energy dispersive spectroscopy and X-ray photoelectron spectroscopy. The results showed that the NaF concentration and the elastic tensile strain had a statistically significant influence on the Rp (P<0.001). The Rp decreased on increasing the NaF concentration and the elastic tensile strain. When the NaF concentration was lower than 0.10%, the Rp value (> 3.4 x 10(5) omega cm2) was mainly ascribed to the formation of a protective titanium dioxide (TiO2) on the metal surface, regardless of the elastic tensile strain applied. However, when the NaF concentration was higher than 0.1%, the protectiveness of TiO2 was destroyed by fluoride ions, leading to severe corrosion of CP titanium.

Corrosion↗
PubMed2006

[Nevocytic nevi associated elastic fibers hyperplasia: a type of "twin nevus"].

BACKGROUND: In common intradermal or compound nevi, nevocytes may be associated with other kinds of cells, tissues or lesions. In rare cases, they are associated with notable hyperplasia of the elastic fibers. CASE-REPORTS AND RESULTS: In 11 nevi (10 intradermal or compound nevi and 1 blue nevus), we observed striking hyperplasia of the elastic fibers strictly limited to the nevi, with normal aspect of the elastic fibers in the surrounding reticular dermis. These fibers were thicker than normal elastic fibers and showed tight connexions with nevus cells. This hyperplasia was not clinically relevant. It was correlated neither with the age and sex of patients nor with the site of the excised nevi. It was seen in 0.1% of excised nevi. DISCUSSION: Hyperplasia of elastic fibers in some common nevi is a curiosity which may be classified together with other vascular, nervous, epithelial or connective twin lesions occasionally associated with the nevocytic nevi. It has to be added to the list of so-called "twin nevi".

Adolescent↗