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PubMed2002

On the microscopic foundations of elasticity.

The modeling of the elastic properties of disordered or nanoscale solids requires the foundations of the theory of elasticity to be revisited, as one explores scales at which this theory may no longer hold. The only cases for which microscopically based derivations of elasticity are documented are (nearly) uniformly strained lattices. A microscopic approach to elasticity is proposed. As a first step, microscopically exact expressions for the displacement, strain and stress fields are derived. Conditions under which linear elastic constitutive relations hold are studied theoretically and numerically. It turns out that standard continuum elasticity is not self-evident, and applies only above certain spatial scales, which depend on details of the considered system and boundary conditions. Possible relevance to granular materials is briefly discussed.

Journal Article↗
PubMed1996

A new technique for study of impact of arterial elasticity on left ventricular mass in rats.

We investigated possible links between left ventricular mass and central arterial elasticity in the adult spontaneously hypertensive rat (SHR) and in a subgroup of SHR in which blood pressure was normalized by chronic antihypertensive drug treatment; results were compared with those of age-matched normotensive Wistar-Kyoto rats. Two indexes of arterial elasticity, based on the measurement of aortic pressure pulse wave velocity, were used. First, the slope relating carotidofemoral pulse wave velocity to blood pressure in the phenylephrine-infused pithed preparation was used as a pressure-independent index of wall elasticity. Second, to account for hypertension- and treatment-induced aortic remodeling, elastic modulus was determined from the pulse wave velocity recorded when blood pressure reached that measured in awake animals before anesthesia and pithing, together with values for wall thickness and lumen diameter evaluated by histomorphometric analysis after in situ fixation at the same pressure. In control SHR, regression analysis of variance revealed significant correlations between left ventricular mass and both wave velocity/pressure slope and elastic modulus. Chronic antihypertensive treatment normalized all three parameters. In conclusion, this new technique provides experimental evidence of a link between left ventricular mass and central arterial elasticity.

Animals↗
PubMed1983

Elastic characteristics of the lung perivascular interstitial space.

An analysis of the elastic behavior of the lung perivascular interstitial space during interstitial fluid accumulation is presented. Fluid accumulation must deform the lung parenchyma and vascular walls that form the interstitial space boundaries. The deformations of these boundaries are predicted from previously published data on the elastic properties of the boundary materials. The analysis gives the relationships among the elastic properties of the boundaries, the compliance of the interstitium, the lung volume, and the lung elastic recoil pressure. Values of the interstitial compliance are predicted to decrease with increasing lung recoil pressure and are dependent on the lung pressure-volume history. At low recoil pressures over 70% of the interstitial compliance results from deformation of the parenchyma. As the recoil pressure increases, either with increasing lung volume or due to the lung pressure-volume history, the contributions of the parenchymal and vascular wall deformations become similar. The predictions are generally consistent with published data on interstitial compliance obtained from measurements of isolated lung weight gain during vascular fluid transudation. This correlation suggests that the elastic behavior of the interstitial space can be accounted for by the known elastic properties of the boundary materials.

Animals↗
PubMed1994

Effects of detection and classification of resistive and elastic loads on endogenous event-related potentials.

Resistive and elastic loads added to inspiration are readily detected, and detection latencies vary as a function of load magnitude and load type. In the present study, we recorded endogenous event-related potentials (i.e., N2 and P3) to the detection and classification of large (15.0 cmH2O.1-1.s and 70.0 cmH2O/l) and small (1.45 cmH2O.1-1.s and 19.0 cmH2O/l) loads equated for subjective magnitude in 14 men (mean age 21.14 yr). In blocks of trials comprised of either large or small loads, subjects made a button-press response upon detecting a load and then classified the load as resistive or elastic. Loads were presented briefly (for approximately 200 ms) early in inspiration and at the same level of inspiratory pressure. For loads of comparable magnitude, subjects detected equivalent numbers of resistive and elastic loads but could not discriminate reliably between load types. On the other hand, the latency of N2 was shorter to larger than to smaller loads, to resistive than to elastic loads, and to correct than to incorrect load classifications. The latency of P3 was affected similarly by load magnitude and load type. These findings demonstrate that event-related potentials are elicited by brief presentations of resistive and elastic loads and that N2 and P3 latencies vary reliably as a function of load magnitude and load type. Most importantly, event-related potential latencies are sensitive to load type and to classification accuracy even when resistive and elastic loads are not distinguishable subjectively.

Adolescent↗
PubMed1984

Small airway disease is associated with elastic recoil changes in excised human lungs.

We studied 54 excised human lungs, 15 with no emphysema and 39 with varying degrees of emphysema, to examine the relationship of small airway disease and elastic recoil. We found a negative correlation between the total small airway pathology score and the mean internal bronchiolar diameter (r = -0.309, p = less than 0.03), as well as with other measurements of small airway size. The internal bronchiolar diameter correlated well with both the elastic recoil expressed as a percentage of predicted values at 70% of total lung capacity (r = 0.533, p less than 0.001) and elastic recoil expressed as an exponential constant k (r = -0.370, p less than 0.01). Fibrosis of the small airways was associated with a reduced internal bronchiolar diameter (r = 0.460, p less than 0.001), as well as the percentage of predicted elastic recoil at 70% of total lung capacity (r = -0.382, p less than 0.01) and elastic recoil expressed as an exponential constant k (r = 0.348, p less than 0.02). We have concluded that changes in elastic recoil seen in these lungs and fibrosis of small airways may be related by a common inflammatory process.

Bronchi↗
PubMed1991

The alpha 1 chain of type VIII collagen is associated with many but not all microfibrils of elastic fiber system.

The antigen of monoclonal antibodies which had labeled the hexagonal lattice of Descemet's membrane in a specific manner was shown to be the alpha 1 chain of type VIII collagen by immunoblotting followed by amino acid sequence analysis. With this antibody, the localization of alpha 1 (VIII) in various tissues was studied by several immunocytochemical methods. Under light microscopy, the alpha 1 (VIII) was found in a fine fibrillar form in various capsular tissues such as capsules of the liver, kidneys, adrenals, lungs and so on. It was also present in dense connective tissues such as the Achilles tendon, and periodontal and perivertebral ligaments. When some dense connective tissues which had been negative to the label including the intima of aorta, perimysium and Glisson's sheath of the liver, were subjected to pepsin digestion, epitopes were revealed which showed a specific immunofluorescence pattern. In many locations the pattern of localization coincided with that of elastic fiber components, and full or partial colocalization with tropoelastin or costaining with resorcin-fuchsin staining was observed. In immunoelectron microscopy, the antigen (alpha 1 (VIII)) was localized on the surface of, but not inside, elastic fibers. However, some tissues which are rich in elastic fibers or microfibrils remained unlabeled. These included elastic fibers of the aortic media and ligamentum nuchae as well as ciliary zonules. Therefore it is suggested that alpha 1 (VIII) is a collagen associated with microfibrils of some elastic fiber systems, but is not an intrinsic component of either elastic fibers or of microfibrils.

Amino Acid Sequence↗
PubMed2004

Retrieving seawater-backscattering profiles from coupling Raman and elastic lidar data.

We propose a technique for retrieving seawater-backscattering profiles that is based on the joint use of elastic and Raman lidar returns. We suggest using two lidar channels: the Raman channel and the elastic channel with a light frequency equal to a half-sum of initial and Raman-shifted frequencies of the Raman channel. These specific wavelengths provide the same attenuation laws for elastic and Raman signals if absorption and scattering spectra can be approximated by a power law. In particular, seawater supplies such a possibility in the region of 400-500 nm if extremely bioproductive waters are not considered and the chlorophyll absorption peak at 440 nm does not come out of the background of dissolved organic matter absorption. With these specific initial wavelengths, the elastic and Raman lidar returns differ only in the backscattering coefficients. Because the Raman-backscattering coefficient is constant along the profile, the (elastic-to-Raman) ratio of these lidar returns directly produces the profile of the elastic-backscattering coefficient. This technique stays valid even under multiple-scattering conditions, which is of great importance for seawater sounding.

Journal Article↗
PubMed2002

Accelerated calcification represses the expression of elastic fiber components and lysyl oxidase in cultured bovine aortic smooth muscle cells.

Vascular calcification is a common feature of advanced atherosclerosis resulting in reduced elasticity of elastic arteries. However, the relationship between elastic fibers and vascular calcification at the molecular and cellular levels remains unknown. We investigated the expression of major elastic fiber components such as tropoelastin (TE) and fibrillin-1 (FBN1) and elastin-related enzyme, lysyl oxidase (LO), in a calcification model using beta-glycerophosphate (beta-GP) in cultured bovine aortic smooth muscle cells (BASMCs). Ten mM of beta-GP stimulated calcium deposition in a time-dependent manner. As determined by Western blot analysis, 10 mM of beta-GP time-dependently decreased TE and FBN1 protein levels. TE, FBN1, and LO mRNA levels, assessed by reverse transcription-polymerase chain reaction, were also decreased by exposure to 10 mM beta-GP. Furthermore, we investigated whether the processes of calcification in BASMCs directly control these regulations. In experiments using levamisole, an alkaline phosphatase inhibitor, and DMDP, a bisphosphonate, both inhibitors inhibited down-regulation during beta-GP-induced calcification, suggesting that the down-regulation of TE, FBN1, and LO directly relates to calcium deposition. In cases of vascular calcification, the decreased expression of TE, FBN1, and LO may be partially responsible for decreased vascular elasticity and also for the decreased formation of new elastic fibers.

Alkaline Phosphatase↗
PubMed2000

[Placebo controlled efficacy of class 1 elastic stockings in chronic venous insufficiency of the lower limbs].

OBJECTIVE: To compare, in a 4-week clinical trial, the efficacy of class 1 Elastic Compression Stockings (pressure at the ankle 10 to 15 mmHg) to that of Placebo Stockings (pressure at the ankle 3 to 6 mmHg) in women consulting in general practice for mild, symptomatic, chronic venous insufficiency of the lower limbs. PATIENTS AND METHODS: This was a 4-week multicentre, randomised, double-blind, placebo-controlled clinical trial conducted on two parallel groups of patients presenting with mild chronic venous insufficiency grade C(1-3S) E(p) A(S1-5) according to the CEAP classification. Treatment efficacy was assessed by the following criteria: global impairment as assessed at each visit on a visual analogue scale (primary efficacy parameter), Quality of Life measured by the CIVIQ questionnaire, symptoms index (sum of individual scores for pain, limb heaviness, paresthesias, cramps and evening limb oedema), limb volume measured by volumetry, and the evolution of global impairment during the course of the trial as assessed by repeated auto-evaluations on visual analogue scales. Compliance was assessed by the number of days patients wore the stockings for at least ten hours per day. Treatment tolerability was assessed by the record of the possible adverse events. RESULTS: Three hundred and forty one patients were included in total. Statistically significant differences were observed on global score of quality of life in favour of class 1 Elastic Compression Stockings group. In the subgroup of patients with evening limb oedema at inclusion, the decrease of limb volume noted with class 1 Elastic Compression Stockings was all the more marked that evening limb oedema was more pronounced at baseline. A good compliance was observed in 76% to 80% of patients according to the treatment group. Tolerability of class 1 Elastic Compression Stockings was comparable to that of the Placebo Stockings. CONCLUSIONS: After four weeks of treatment, compression with class 1 Elastic Compression Stockings allows a statistically significant improvement of Quality of Life and a decreasing of limb oedema in patients presenting with mild chronic venous insufficiency of the lower limbs. Moreover, the tolerability of class 1 Elastic Compression Stockings was confirmed by the high level of patient compliance.

Bandages↗
PubMed1992

The effect of elastic compression on the venous tone in patients with varicose veins.

The long term effect of elastic compression, with an emphasis on the changes in venous wall elasticity, was studied in 10 limbs with varicose veins. By simultaneously measuring venous volume, using the air plethysmograph (APG), and venous pressure, while the venous outflow was occluded, the pressure/volume (P/V) relationship of the venous system of the leg could be studied and the elastic modulus calculated. These measurements were performed prior to the application of elastic stockings and 6 weeks later, one day after the stockings had been removed. Statistically significant improvements were noted in the APG parameters studied and in the P/V curve derived elastic modulus calculations. The limbs could be divided into two groups based on the response of the P/V curves to elastic stockings and the severity of disease. Those limbs with milder disease tended to shift their P/V curves downward and to the right after compression (giving them a more normal pattern). Limbs with more severe disease showed evidence of a similar pattern of improvement at low but not at high venous pressures.

Bandages↗
PubMed2006

Validity and reliability of measurements of elbow flexion strength obtained from older adults using elastic bands.

PURPOSE: This study determined the validity and reliability of measurements of elbow flexion strength obtained from older adults using elastic bands. METHODS: Forty-eight community-dwelling older adults with documented functional limitations completed 3 assessments of elbow flexion strength: a 30-second test using elastic bands to generate resistance, a similar test using dumbbells, and a test using an isokinetic dynamometer. One week later, subjects repeated the 30-second elbow flexion test using elastic bands. RESULTS: The 30-second elbow flexion test using elastic bands was significantly correlated with both the 30-second elbow flexion test using dumbbells (r = 0.62, P < 0.01 ) and the maximum isokinetic torque of the elbow flexors (r = 0.46, P < 0.01 ). The 30-second elbow flexion test using elastic bands demonstrated a high degree of test-retest reliability (intraclass correlation coefficient = 0.89, P < 0.01 ). CONCLUSION: The validity and reliability elbow flexion strength measured with elastic bands supports its use among functionally limited elders.

Aged↗
PubMed1990

Diabetic microangiopathy treated with elastic compression--a microcirculatory evaluation using laser-Doppler flowmetry, transcutaneous PO2/PCO2 and capillary permeability measurements.

One hundred and forty patients with diabetic microangiopathy were studied by laser-Doppler flowmetry--measuring skin blood flow at rest (RF) and the venoarteriolar response (VAR)--by transcutaneous PO2 and PCO2 measurements and by evaluation of capillary permeability (rate of ankle swelling = RAS). Seventy were treated for 12 months with below-knee, elastic stockings. Seventy patients were left without compression acting as a control group. After 5 and 12 months there were no significant changes in the control group. However there was a significant improvement of microcirculatory parameters in patients treated with elastic compression. RF (increased at the beginning of the study) decreased. The VAR (impaired at the beginning of the study) improved significantly. PO2 (increased after treatment) and PCO2 (decreased) were also positively changed by elastic stockings. The abnormally increased capillary permeability was also improved. Elastic compression seems to be useful in diabetic microangiopathy improving microcirculatory parameters and decreasing capillary permeability and edema. However further studies, treating with elastic compression more patients for longer periods, are needed to confirm the positive effects of elastic stockings in improving diabetic microangiopathy and in slowing down its rate of progression.

Adult↗
PubMedDate not supplied

Elastic and thrombogenic properties for different vascular grafts and its influence on graft patency.

In a sheep model elastic and thrombogenic properties for various vascular graft materials were studied using peroperative compliance measurements and Indium-111-oxine labeled platelets in vivo. It was found that the least thrombogenic arterial vascular substitute was the autologous vein while a significantly higher thrombogenicity was recorded for the polytetrafluoroethylene (PTFE) graft and the Chinese pure silk graft. The two latter grafts did not differ significantly in thrombogenicity except for that the silk graft revealed a significantly higher peak value for deposited platelets onto its surface than the PTFE graft. Compliance measurements at graft implantation revealed that both the silk and the vein grafts were more elastic than the PTFE graft. The two grafts did not differ in elasticity from each other significantly. Elasticity for all grafts increased during the first 10 weeks after implantation. There was a good correlation between elastic properties and graft patency for all tested graft materials. However, the silk graft with favourable elastic characteristics was found to have less favourable thrombogenic properties and is therefore in its present form not the ideal graft for small caliber artery reconstructions.

Animals↗
PubMed1997

An immunological correlation between the anchoring filaments of initial lymph vessels and the neighboring elastic fibers: a unified morphofunctional concept.

Little has been published on the histochemical and cytochemical properties of anchoring filaments of initial lymph vessels. Previous research suggests that the microfibrils of the anchoring filaments have ultrastructural, histochemical and cytochemical characteristics similar to those of the microfibrils associated with elastic fibers. With the aim of further investigating the histological identity of anchoring filaments, we performed an immunohistochemical study with human skin lymphatics, using antibody HB8, specific for elastic fiber microfibrils. The findings suggested strong molecular similarities between elastic fibers and the fibrils of anchoring filaments of the initial lymph vessels. A comparison of these fibrils showed both constitutional homogeneity and structural continuity from the abluminal surface of the initial lymph vessel to the perivascular elastic fibers and to the adjacent elastic network of connective tissue. In conjunction with previous findings, we propose a unified hypothesis that the elastic fiber system composed of anchoring filaments, perilymphatic sheath and adjacent connective tissue acts by alternating stretching and relaxation to propel lymph towards lymph collectors and draining lymph nodes.

Actin Cytoskeleton↗
PubMed1996

The relationship between brain surface elastance and brain reexpansion after evacuation of chronic subdural hematoma.

BACKGROUND: Brain stiffness has been thought to be a factor affecting brain re-expansion after the evacuation of chronic subdural hematoma. METHODS: As an index of brain stiffness, the pressure for compressing the brain using an ophthalmodynamometer was defined as brain-surface elastance. This elastance in 14 patients was measured and analyzed in relation to brain re-expansion. RESULTS: Patients with an enlarged subdural space on computed tomography 1 month after the operation had higher elastance. There was a correlation between high elastance and high age. CONCLUSIONS: Measuring the elastance after evacuation of the hematoma may help predict the persistence of a subdural space.

Aged↗
PubMed1998

An elastin gene mutation producing abnormal tropoelastin and abnormal elastic fibres in a patient with autosomal dominant cutis laxa.

Elastin is the protein responsible for the characteristic elastic properties of many tissues including the skin, lungs and large blood vessels. Loss-of-function mutations in the elastin gene are known to cause the heart defect supravalvular aortic stenosis (SVAS). We and others have identified deletions, nonsense mutations and splice site mutations in SVAS patients that abolish the function of one elastin gene. We have now identified an elastin mutation in a patient with a completely different phenotype, the rare autosomal dominant condition cutis laxa. A frameshift mutation in exon 32 of the elastin gene is predicted to replace 37 amino acids at the C-terminus of elastin by a novel sequence of 62 amino acids. mRNA and immunoprecipitation studies show that the mutant allele is expressed. Electron microscopy of skin sections shows abnormal branching and fragmentation in the amorphous elastin component, and immunocytochemistry shows reduced elastin deposition in the elastic fibres and fewer microfibrils in the dermis. These findings suggest that the mutant tropoelastin protein is synthesized, secreted and incorporated into the elastic matrix, where it alters the architecture of elastic fibres. Interference with cross-linking would reduce elastic recoil in affected tissues and explain the cutis laxa phenotype.

Adult↗
PubMed1995

Elastic modulus of orbicularis oculi muscle in normal humans, humans with Graves' eye disease, and cynomolgus monkeys.

We built an experimental apparatus to investigate the passive elastic characteristics of orbicularis oculi muscle and examined specimens from normal humans, humans with stable Graves' eye disease, and cynomolgus monkeys. Stress-strain curves were determined and found to be exponential. The elastic modulus (Young's modulus), analogous to the stiffness of the material, was calculated as a function of strain. Elastic modulus as a function of instantaneous stress was linear. Monkey elastic modulus values were determined, but did not allow meaningful interspecies comparison because of the small sample size. No significant difference was found between normal humans and humans with Graves' eye disease with respect to elastic modulus values.

Animals↗
PubMed2006

Storage and recovery of elastic potential energy powers ballistic prey capture in toads.

Ballistic tongue projection in toads is a remarkably fast and powerful movement. The goals of this study were to: (1) quantify in vivo power output and activity of the depressor mandibulae muscles that are responsible for ballistic mouth opening, which powers tongue projection; (2) quantify the elastic properties of the depressor mandibulae muscles and their series connective tissues using in situ muscle stimulation and force-lever studies; and (3) develop and test an elastic recoil model, based on the observed elastic properties of the depressor mandibulae muscles and series connective tissues, that accounts for displacement, velocity, acceleration and power output during ballistic mouth opening in toads. The results demonstrate that the depressor mandibulae muscles of toads are active for up to 250 ms prior to mouth opening. During this time, strains of up to 21.4% muscle resting length (ML) develop in the muscles and series connective tissues. At maximum isometric force, series connective tissues develop strains up to 14% ML, and the muscle itself develops strains up to 17.5% ML. When the mouth opens rapidly, the peak instantaneous power output of the depressor mandibulae muscles and series connective tissues can reach 9600 W kg(-1). The results suggest that: (1) elastic recoil of muscle itself can contribute significantly to the power of ballistic movements; (2) strain in series elastic elements of the depressor mandibulae muscle is too large to be borne entirely by the cross bridges and the actin-myosin filament lattice; and (3) central nervous control of ballistic tongue projection in toads likely requires the specification of relatively few parameters.

Animals↗