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At least 775 records · Page 43Linked to original sources
PubMed2004

Model-based reconstructive elasticity imaging of deep venous thrombosis.

Deep venous thrombosis (DVT) and its sequela, pulmonary embolism, is a significant clinical problem. Once detected, DVT treatment is based on the age of the clot. There are no good noninvasive methods, however, to determine clot age. Previously, we demonstrated that imaging internal mechanical strains can identify and possibly age thrombus in a deep vein. In this study the deformation geometry for DVT elasticity imaging and its effect on Young's modulus estimates is addressed. A model-based reconstruction method is presented to estimate elasticity in which the clot-containing vessel is modeled as a layered cylinder. Compared to an unconstrained approach in reconstructive elasticity imaging, the proposed model-based approach has several advantages: only one component of the strain tensor is used; the minimization procedure is very fast; the method is highly efficient because an analytic solution of the forward elastic problem is used; and the method is not very sensitive to the details of the external load pattern--a characteristic that is important for free-hand, external, surface-applied deformation. The approach was tested theoretically using a numerical model, and experimentally on both tissue-like phantoms and an animal model of DVT. Results suggest that elasticity reconstruction may prove to be a practical adjunct to triplex scanning to detect, diagnose, and stage DVT.

Aging↗
PubMedDate not supplied

Increased dermal elastic fibers in the tight skin mouse.

OBJECTIVE: The tight skin (Tsk-1) mouse has been proposed as a model for systemic sclerosis on the basis of increased accumulation of collagen and glycosaminoglycans in the skin, and by the presence of serum autoantibodies. The genetic basis of the mutation has been identified as a genomic duplication within the fibrillin-1 (Fbn-1) gene that results in a larger than normal Fbn-1 transcript, but the mechanism that leads to dermal fibrosis is unclear Fibrillin molecules associate into a polymer that is coated with elastin molecules to form elastic fibers. To further evaluate the Tsk-1 mouse model of scleroderma, we have studied elastic fibers in the skin of these mice. METHODS: Skin sections obtained from C57BL/6-TSK+ (Tsk-1) and C57BL6-pa/+ (control) mice were stained with Masson's trichrome for evaluation of collagen and Gomori's aldehyde fuchsin stain for elastic tissue. Computer assisted image analysis was performed to quantify differences in histologic sections. RESULTS: Tsk-1 mice had a highly significant increase in the percentage of elastic fibers (19.6%) in the dermis compared to control mice (7.9%) [p < 0.001]. This correlates with the findings in the skin of systemic sclerosis patients where increased elastic fibers have been observed. In addition, an increased level of dermal collagen staining was also observed in the Tsk-1 dermis (82.9%) compared with the level in normal sections (73.7%) [p < 0.01]. CONCLUSION: These data support the use of the Tsk-1 mouse as a model for the connective tissue abnormalities of human scleroderma.

Animals↗
PubMed2005

[Regional differences in viscosity, elasticity and wall buffering function in systemic arteries: pulse wave analysis of the arterial pressure-diameter relationship].

INTRODUCTION AND OBJECTIVES: Regional variations in the incidence of vascular diseases have been related to regional differences in arterial viscoelasticity. The aim of this study was to characterize the differences in the elastic and viscous modulus and in wall buffering function between central and peripheral systemic arteries, through a time-series analysis of the pressure-diameter relationship. MATERIAL AND METHOD: Pressure and diameter were measured in seven arterial segments (carotid, brachiocephalic trunk, ascending aorta, proximal, middle and distal descending thoracic aorta, and femoral artery) from six sheep. Each segment was mounted on an in vitro mock circulatory system and perfused with Tyrode solution, with a pulse frequency of 1.8 Hz and systemic pressure levels. We used the Kelvin-Voigt model to calculate the pressure-diameter elastic (Epd, mmHg/mm) and viscous (Vpd, mmHg.s/mm) modulus, and to quantify the local wall buffering function (Vpd/Epd). We also calculated the incremental Young's and pressure-strain elastic modulus and pulse wave velocity for each segment. RESULTS: The elastic and viscous modulus increased from proximal to distal segments. The wall buffering function did not differ significantly between arteries. The lower rigidity of the central arteries compared to the distal ones may indicate that the systolic arterial compliance function is concentrated in the central arterial segments. On the other hand, the greater viscosity in the distal segments may indicate that viscous energy loss is concentrated in these segments. CONCLUSIONS: Arterial elasticity and viscosity can be interpreted as properties that are dependent on the region of the vessel, whereas wall buffering function can be considered region-independent.

Animals↗
PubMed2004

Non-linear mechanical behavior of visco-elastic biological structures--measurements and models.

Mechanical properties of biological structures affect functional ability of organism. Current knowledge is prevailingly concentrated on static characteristics. The present work analyzed dynamic mechanical responses of various biological materials. Following biological structures were measured: samples of aorta walls of human origin and from model organisms, human body surface, and samples of bones of various types and origin. Linear approximation leads in case of aortas and bones to simple Voight's model. Modules of elasticity (in tensile loading) of aortas were from 10(2) kPa to 10(3) kPa. Module of elasticity of bones were from 10(6) Pa to 10(10) Pa. Viscous coefficients of aortas were from 102 Pa.s to 10(3) Pa.s. Viscous coefficients of bones were from 10(0) Pa.s to 10(2) Pa.s. Nonlinearities: We found that following types of nonlinearities are significant: strain-stress relationship, time-dependent changes in elastic as well as viscose bodies. Strain and stress is well approximated by quadratic function sigma = a epsilon2 + b epsilon + c with parameters a = 1833, b = 135, c = 20.0 (porcine aorta). Time-dependence in elastic coefficient: At the beginning of responses the elastic coefficient was of 42% lower then at 0.02 s of duration of the response (porcine aortas). Analogical results follow also from experiments on other structures (skin, bones).

Adult↗
PubMed1992

[The mechanism of age-related change in lung elastic recoil pressure].

To investigate the mechanism of age-related change in lung elastic recoil, golden syrian hamsters were divided into three age groups (11-wk group, n = 20; 24-wk group, n = 25; 60-wk group, n = 15). Pressure-volume curves in isolated lungs, length-tension properties of alveolar wall, surface tensions by modified Wilhelmy balance, and collagen and elastin concentrations in the lung tissue were measured. Light and electron micrographs and morphometry were studied. Age-related change was not observed in lung elastic recoil in hamsters. However, old hamsters significantly increased a mean linear intercept and the elasticity constant of alveolar wall. On one hand, a surface tension was increased in old hamsters, associating with the decrease in the number of lamellar body of alveolar type 2 cells. These findings suggested that the reduction in lung elastic recoil which should be caused by both the increase in air space and the decrease in extensibility of alveolar wall would be compensated by the increase in surface tension in old hamsters, which may account for the no age-related change in elastic recoil in hamster lungs.

Aging↗
PubMedDate not supplied

A morphometric study of age-related changes in the elastic systems of the common carotid artery and internal carotid artery in humans.

The present study aims to quantify the distribution of the elastic fiber system in the walls of the common carotid artery and the internal carotid artery in humans. In order to identify specific fibers, segments of carotid arteries were stained using the Verhoeff (for elastic fibers), Weigert (for elastic and elauninic fibers) and Weigert-oxone (for elauninic and oxytalanic fibers) methods. A histomorphometric study was undertaken in order to estimate the linear density (LV) of the fibrous components present in the elastic system and determine the total length of these components in each segment. Microscopic fields were sampled using a test system in which the colors and bands defined in the current study were superimposed on the histological preparations. Data were analyzed through linear regression using first-order rate equations and computer software. The internal carotid artery can be loosely defined as muscular in nature. In order to classify common carotid arteries, it is necessary to consider subject age. From 0 to 30 years of age, the LV of mature elastic fibers does not change significantly in either (left or right) common carotid artery, although a significant reduction in the LV of this type of fiber occurs in the right internal carotid artery. The most marked reduction in oxytalanic and elauninic fibers occurs between 0 and 10 years of age, becoming less intense between the ages of 10 and 30.

Adult↗
PubMed2005

[Changes of elastic properties of magistral arteries in patients with ischemic heart disease during treatment with atorvastatin and simvastatin].

AIM: To elucidate effect of atorvastatin and simvastatin on elastic properties and reactivity of large arteries in patients with ischemic heart disease. MATERIAL: Patients (n=38) with ischemic heart disease receiving atorvastatin (10 mg/day, n=20) and simvastatin (20 mg/day, n=18). METHODS: Elasticity of arteries was assessed by pulse wave propagation velocity measured by Coloson computer system. Test with reactive hyperemia was used for assessment of large muscular type vessels reactivity in response to blood flow augmentation was assessed by. RESULTS: Treatment with statins for 6 months was associated with positive changes of elasticity of arteries of elastic type (-10.05% and -4.66% in atorvastatin and simvastatin treated patients, respectively) and endothelium dependent reactivity of arteries of muscular type (-16.01%, p<0.001 and -11.1% p<0.001 compared with initial values in atorvastatin and simvastatin treated patients, respectively). CONCLUSION: Therapy with statins positively affects parameters of elasticity and reactivity of large arteries.

Anticholesteremic Agents↗
PubMed2005

Effects of various periodontal ligament elastic moduli on the stress distribution of a central incisor and surrounding alveolar bone.

BACKGROUND AND PURPOSE: Previous studies investigating the effects of core or post on the fracture strength of teeth often omitted the periodontal ligament (PDL) because its physical properties are difficult to reliably quantify. This study investigated the effects of various PDL elastic moduli on the stress distribution around a central incisor and surrounding alveolar bone using 3-dimensional finite element stress analyses. METHODS: Four 3-dimensional finite element models of an upper central incisor and the dento-alveolar complex were established. Five models were constructed, including: no PDL, as well as a PDL with elastic moduli of 6.9 MPa, 68.9 MPa, and 1750 MPa. Two loading conditions were simulated, one with protrusive force and one with intrusive force. Protrusive loading was generated using a point force of 200 N at 45 degrees inclination to the longitudinal axis of the incisor applied on the lingual side. Intrusive loading was generated using a point force of 200 N applied perpendicular to the incisal edge. RESULTS: The absence of a PDL had detrimental effects on the surrounding bone, because the applied stress remained concentrated at the bone crest and cervical third of the root. A PDL with a lower elastic modulus, on the other hand, helped to alleviate the magnitude of stress throughout the surrounding bone and the bone crest, in particular, by distributing the stress deeper towards the apical region. The stress distribution at the crown was unaffected by variations in the PDL elastic modulus. CONCLUSIONS: PDL with a lower elastic modulus can help protect the alveolar bone crest from stress concentration.

Alveolar Process↗
PubMed1991

A morphometric quantitation of developmental changes in elastic fibers in rat lung parenchyma: variability with lung region and postnatal age.

Elastin has long been thought to play a pivotal role in alveolar septal development by providing the structural framework around which new alveoli develop in the immature lung. This theory was derived from observations that the dramatic increase in lung elastin and alveolar septal development occurred during the same time period, days 4 to 13 in the rat. Using stereologic techniques, we evaluated volume density of respiratory tissue in parenchyma and total length of parenchymal elastic fibers in the lungs of neonatal rats ranging in age from 4 to 26 days. Lung tissue was obtained from each of the four right lung lobes and from the upper, middle, and lower regions of the left lung. When changes in these two parameters in the lung as a whole were considered by averaging values for each of the seven regions, a continuous increase was observed in both the volume of parenchymal tissue in parenchyma and the total length of elastic fibers from days 4 to 22. A significant correlation was found between the volume of respiratory tissue in parenchyma and the length of parenchymal elastic fibers from days 4 to 26, supporting the existing theory that a causal relationship exists between these two parameters. A comparison of the ratios of elastic fiber length to volume density of respiratory tissue in parenchyma (Lv/Vrp) from each of the seven lung regions sampled indicated a significant variability in Lv/Vrp within different regions of the same lung. In addition, the effects of postnatal age and lung region on Lv/Vrp were interdependent; the lung regions that differed with respect to the length density of elastic fibers varied with postnatal age.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1991

[Effects of enflurane on the elastic properties of frog skinned skeletal muscle fiber under relaxed and rigor conditions].

We studied the effects of enflurane on the elastic property of the mechanical skinned fiber prepared from M. Semitendinosus of bullfrog. Longitudinal and lateral elastic properties of the skinned fibers were measured under relaxed and rigor conditions to clarify the effects of enflurane on actomyosin complex. Under the rigor condition, enflurane did not change the lateral elasticity of the fibers, but enflurane decreased the longitudinal elasticity. On the other hand, under the relaxed condition, enflurane did not change the elasticity. The results suggest that enflurane probably decreases the force of binding of cross-bridges to actin, which is one of the factors to reduce the maximal force.

Animals↗
PubMed1990

[Electron microscopic study of the choroidal melanocytes and elastic fibers].

The relationship between choroidal melanocytes and elastic fibers as well as collagen fibers was studied by electron microscopy. In pigmented rabbits (Dutch rabbits), the choroidal melanocytes were distributed mainly at the suprachoroidea and formed layers alternating with fibroblasts. The elastic fibers and oxytaran fibers were in close proximity to the melanocytes and their cytoplasmic processes aligned along the long axis of the elastic fibers. Furthermore, the bundles of the collagen fibers were engulfed by the melanocytes. The present findings suggest that the choroidal melanocytes have a close relationship with the elastic fibers, as has been reported with dermal melanocytes and elastic fibers.

Animals↗
PubMed1989

[Elasticity and deviation angle of toothbrush in Korean adults].

The purpose of this experiment was to establish a simple and general recommendation criteria to evaluate the toothbrush whether it was usable or not. We gave 94 adults the same toothbrushes and required them to use only those toothbrushes and recollected them after 4 weeks' use. Then, we determined elasticity loss, deformation degree and deviation angle of the used toothbrushes. From the above data, we compared and analyzed the correlation between loss of elasticity loss and deviation angle. The obtained results were as follows: 1. In Korean adults, there was no statistical difference between elasticity loss and deviation angle according to both age and sex group (p greater than 0.05). 2. There was no statistical correlationship between elasticity loss and deviation angle (r = 0.15, p greater than 0.05). 3. It was regarded that the determination of deviation angle was more simple method than that of elasticity loss for the evaluation of useful period of toothbrush. 4. In Korean adults, the average usable period of toothbrush was estimated about 1 month.

Adult↗
PubMed1989

Corneal topography and elasticity in normal and keratoconic eyes. A methodological study concerning the pathogenesis of keratoconus.

One eye of 27 patients with keratoconus and 37 normals were examined by photokeratoscopy and topographic pachometry to obtain informations about the corneal shape and thickness profile. The progressive alteration of corneal topography in keratoconus may be based on elastic deformation. Through a distention, predominantly of the central area, increasing large differences between central and peripheral thickness appear. Simultaneously the area of the corneal surface increases into a more elliptical corneal shape. In keratoconus relative to normals, the study demonstrates, an alteration of, as well as a correlation between, the corneal shape and thickness profile in accordance with the elastic hypothesis. Based on corneal topography determination, intraocular pressure measurements and a derived elastic theory the corneal tissue mass (M), tissue strength (Young's Modulus in steady state Y(s) , and the ocular rigidity (E) were determined. Y(s) and E was found to be significantly decreased, whereas M seems to be equal in keratoconus compared with normals. Histologically cornea consists of an amorphous matrix in which the collagen fibers are embedded. E seems to reflect the immediate elastic response of the collagen fibers (Y(i], which, however, may be relaxed in steady state. Y(s) seems to reflect the elastic response of the matrix, which consists of matrix compression and sliding of collagen fibers. Thus the biomechanical alteration of cornea in keratoconus may be introduced by increased sliding fo collagen fibers due to reduced attachment to Bowman's layer and altered synthesis of the matrix substance.

Adolescent↗
PubMed1988

[Do elastic corpuscles appear prenatally? Histological studies of the skin of embryos and fetuses].

There have been descriptions of corpuscular structures in the human skin since the turn of the century. These bodies 3-20 micron in size are situated in the zone connecting the epidermis and corium. They can be readily visualized with resorcinol-fuchsin staining according to Weigert and are regarded as morphological variants of the elastic fiber system. According to the investigations we have carried out so far on the skin of babies, infants and adults, these elastic globes exhibit the following distribution pattern: abundant occurrence on the limbs, only scanty occurrence on the trunk and the hands. With increasing age, a numerical increase of elastic globes can be demonstrated in babies and in infants. In adults, there is an opposite tendency in the hands and feet. Here, the frequency of elastic globes decreases with increasing age. To clarify the question as to whether precursors of elastic globes are present, the skin of 35 embryos and fetuses was systematically examined for their occurrence and the results of the investigation are discussed.

Elastic Tissue↗
PubMed1988

The circulating alpha 1-antitrypsin-elastase complex attacks the elastic lamina of blood vessels. An immunohistochemical study.

The aim of the study was to determine the destination of the alpha 1-antitrypsin-elastase complex, which is found in circulating blood after the peroral administration of elastase. The complex was made in vitro by mixing hog pancreatic elastase with human alpha 1-antitrypsin and then injected intravenously into rats and mice. Tissues taken at various times after injection were subjected to histochemical staining using an antibody against elastase. Light microscope observations revealed dense deposition of reaction products in the elastic lamina of the arterioles; moderate or slight deposits were seen in the tissues surrounding arteries, in the tubular epithelial cells of the proximal convoluted tubules in the kidney, and in the pancreatic ducts. Immunoelectron microscopy revealed heavy deposition of the reaction product in the elastic lamina of the small arteries and arterioles; some dissolution of the elastic fibers was also evident. Pinocytic uptake of the alpha 1-antitrypsin-elastase complex was observed on the abluminal surface of endothelial cells and in smooth-muscle cells bordering the elastic lamina of arterioles. The endothelial cells of the arteries and arterioles retained their normal morphological appearance, although local desquamation was observed in some animals. The results indicate that, when the alpha 1-antitrypsin-elastase complex is present in the circulating blood, it is incorporated into the elastic lamina through the endothelial layer. This results in liquefaction of the lamina, desquamation of endothelial cells and leakage of the complex into the perivascular tissues via the vascular walls. However, some of the complex seems to be excreted very quickly from the kidneys.

Animals↗
PubMed1988

Determination of the elastic properties of the cervix.

The elastance of the uterine cervix of nonpregnant women was measured by placing a 3- or 4-cm compliant balloon in the cervical canal and determining its pressure-volume characteristic while filling with up to 5 mL of sterile water at a rate of 12 mL/minute. The mean elastance for 247 patients who had previously suffered either one or more spontaneous midterm pregnancy losses, preterm birth, or three or more early spontaneous abortions was significantly lower than that of 42 controls who did not meet these criteria. Elastances were significantly lower in groups having a clinically observed patulous cervix or laceration, or a clinically diagnosed incompetent cervix, than in the normal cervix group. No significant difference was found between the follicular and luteal phases for 64 regularly cycling women. Values were significantly reduced in women showing a widened cervix on a hysterosalpingogram when compared with those with a normal-appearing cervix. When larger Hegar dilators were passed without resistance, the elastance was generally lower, although there was not always good correlation between the largest dilator passed and elastance.

Catheterization↗
PubMedDate not supplied

[Elasticity of the skin in chronic venous insufficiency].

The results of our measurements of skin elasticity at the level of the calf, show that the existence of a cutaneous pump is unlikely. In addition, they are not consistent with the suggestion that the skin acts as an elastic stocking. In case of chronic venous insufficiency (CVI), the loss of elasticity which is demonstrated, is probably secondary to a persisting dermal edema. In patients with essential varicosities, a significant loss of elasticity is only noted in case of reticular varicosities. Essential truncular varicosities are not accompanied with a significant loss of elasticity. It is therefore highly likely that truncular varicosities and reticular varicosities do not have the same etiology.

Chronic Disease↗
PubMed1986

Dynamic splinting: a systematic approach to the selection of elastic traction.

Elastic traction is an important but occasionally misapplied component of upper-extremity dynamic splints. Information regarding a systematic approach for selection of elastic traction has been limited. A biomechanical analysis of dynamic splinting methods was done to identify factors that might help educate therapists in the proper application of elastic traction. Material properties of elastic traction were measured with a mechanical testing system capable of accurately identifying physical properties of various substances. Results of this analysis indicated that specific spring constant values for clinically used bands ranged from 134 to 531 g, original length values ranged from 0.7 to 3.2 in., the consistency of bands labeled as identical by the manufacturer was generally very good, and each band's ability to maintain its material properties with repeated elongation was similar from band to band and showed gradual diminution after several hundred repetitions. These data were combined with theoretical constructs of splint fabrication to devise a simple and logical method for analysis and determination of elastic traction requirements for various diagnostic applications. A goniometer, ruler, and spring scale are the only tools necessary to perform the analysis. Simple charts depicting forces and moments provide identification of the appropriate rubber band for application.

Arthritis, Rheumatoid↗