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At least 739 records · Page 41Linked to original sources
PubMed2004

Abnormal alveolar attachments with decreased elastic fiber content in distal lung in fatal asthma.

Small airway disease is thought to contribute significantly to functional impairment caused by asthma. Functional evidence of airway-parenchyma uncoupling in asthma, such as loss of deep breath bronchodilator effect in bronchoconstrictive episodes and enhanced airway closure, has been previously demonstrated. Elastic fibers are essential to maintain adequate elastic recoil of the lungs. In this study, we hypothesized that alveolar attachments could be abnormal and that elastic fibers could be damaged in the distal lungs of patients with fatal asthma. For this purpose, we measured the number of abnormal alveolar attachments and quantified the content of elastic fibers in the adventitial layer of small airways and in the peribronchial and distal alveolar septa of 15 patients who died of asthma (FA) and 9 control subjects (CTRL). Our data (geometric mean [range]) showed an increased proportion of abnormal alveolar attachments per centimeter of basement membrane perimeter in fatal asthma (FA, 0.18 [0.03-4.00]; CTRL, 0.00 [0.00-0.12]; p < 0.001) and decreased elastic fiber content in the small airway adventitial layer (FA, 4.08 [2.22-11.46] microm; CTRL, 6.79 [5.62-10.0] microm; p = 0.01) and in the peribronchial alveoli (FA, 1.08 [0.46-1.91] microm; CTRL, 1.81 [1.22-1.74] microm; p = 0.003), but not in the distal alveoli. We propose that structural alterations at the peribronchiolar level might contribute to the pathogenesis of some functional abnormalities observed in patients with severe asthma.

Adult↗
PubMed1999

Evaluation of left atrial wall elasticity using acoustic microscopy.

Left atrial wall elasticity is one of the important factors regulating left atrial stiffness and functions. The authors evaluated left atrial wall elasticity by measuring the sound speed through the left atrial wall, based on the hypothesis that high elasticity tissues will yield larger sound speed values through the tissue, and examined age-associated changes in left atrial wall elasticity. Left atrium specimens were obtained from 30 normal subjects (age, 15-95 years) at autopsy. An acoustic microscope, operating at 450 MHz, was used to measure the sound speed in the endocardium and the myocardium of the left atrium. The sound speeds in endocardium and myocardium demonstrated significant correlation with age (r = 0.74, p<0.0001 and r = 0.47, p<0.01, respectively). These findings indicate that left atrial wall elasticity increased with advancing age. These changes may lead to deterioration of left atrial compliance and eventual left atrial failure in older subjects.

Adolescent↗
PubMed2006

Elasticity of the human false vocal fold.

OBJECTIVES: Very little is known about the elasticity of the human ventricular fold (false vocal fold). To better understand the potential role of the false fold in the fluid dynamics and aeroacoustics of phonation, we made some measurements on the elastic properties of human ventricular fold tissues in vitro. METHODS: Uniaxial tensile stress-strain characteristics of 6 male and 6 female false fold specimens were quantified with sinusoidal stretch-release deformation. Midcoronal sections of 3 specimens were examined to quantify the relative densities of collagen, elastin, seromucous glandular tissue, and adipose tissue by digital image analysis. RESULTS: Nonlinear stress-strain curves with hysteresis (viscous energy loss) were observed, with large interindividual differences. A hybrid linear-exponential model was used to determine the elastic modulus (tangent Young's modulus) of the false fold. On average, the male false fold was twice as stiff as the female at a tensile strain of 20% to 30%. CONCLUSIONS: This preliminary gender-related difference in elasticity could be attributed to a higher proportion of glandular tissue in the female false fold, due to the lower elastic modulus of glands. The present data allow one to develop a more comprehensive biomechanical model of phonation, for optimizing postoperative voice production following laryngeal reconstruction procedures.

Aged↗
PubMed1993

Elastography: elasticity imaging using ultrasound with application to muscle and breast in vivo.

Changes in tissue elasticity are generally correlated with its pathological state. In many cases, despite the difference in elasticity, the small size of a lesion or its location deep in the body preclude its detection by palpation. In general, such a lesion may or may not possess echogenic properties that would make it ultrasonically detectable. Elastography is an ultrasonic method for imaging the elasticity of compliant tissues. The method estimates the local longitudinal strain of tissue elements by ultrasonically assessing the one dimensional local displacements. This information can be combined with first order theoretical estimates of the local stress to yield a quantitative measure of the local elastic properties of tissue. The elasticity information is displayed in the form of a gray scale image called an elastogram. An experimental system for elastography in phantoms based on a single element transducer has been described previously [1]. Here we introduce a new elastography system based on a linear array transducer that is suitable for in vivo scanning. We describe tissue mimicking phantom experiments and preliminary in vivo breast and muscle elastograms confirming the feasibility of performing elastography in vivo. An elastogram of a breast containing an 8 mm palpable cancer nodule clearly shows the lesion. Elastograms and their corresponding sonograms show some similarities and differences in the depiction of tissue structures.

Adult↗
PubMed1998

Measuring the elastic modulus of small tissue samples.

Independent measurements of the elastic modulus (Young's modulus) of tissue are necessary step in turning elasticity imaging into a clinical tool. A system capable of measuring the elastic modulus of small tissue samples was developed. The system tolerates the constraints of biological tissue, such as limited sample size (< or = 1.5 cm3) and imperfections in sample geometry. A known deformation is applied to the tissue sample while simultaneously measuring the resulting force. These measurements are then converted to an elastic modulus, where the conversion uses prior calibration of the system with plastisol samples of known Young's modulus. Accurate measurements have been obtained from 10 to 80 kPa, covering a wide range of tissue modulus values. In addition, the performance of the system was further investigated using finite element analysis. Finally, preliminary elasticity measurements on canine kidney samples are presented and discussed.

Animals↗
PubMed1997

Physiologic aspects of drug therapy and large artery elastic properties.

Vasoactive drugs alter smooth muscle tone not only in arterial resistance vessels, but also in large conduit arteries. The resultant changes in smooth muscle tone alter both conduit vessel size and stiffness and hence influence pulsatile components of left ventricular afterload. The effects of smooth muscle relaxation and contraction on arterial elastic properties are complex and have not been fully characterized. Several recent studies have utilized a new intravascular ultrasound technique to study the effects of changes in smooth muscle tone on brachial artery elastic mechanics in normal human subjects in vivo. Smooth muscle relaxation with nitroglycerin improves isobaric brachial artery compliance without significantly altering arterial wall stiffness as measured by incremental elastic modulus (Einc). The improvement in compliance with smooth muscle relaxation is the net result of factors that: (1) increase wall stiffness (increased tension in parallel elastin and collagen fibers); (2) decrease wall stiffness (decreased tension in the smooth muscle and its associated series elastic component); and (3) increase vessel lumen size. Using a modified Maxwell model for the arterial wall, smooth muscle relaxation is also shown to shift the predominant elements contributing to wall stress and Einc from smooth muscle and the collagen fibers in series with the smooth muscle to collagen fibers in parallel with the smooth muscle. A better understanding of the mechanisms contributing to changes in arterial elastic mechanics following alterations in smooth muscle tone will help in developing pharmacologic therapies aimed at reducing pulsatile components of left ventricular afterload.

Arteries↗
PubMed2001

Monitoring of nonlinear respiratory elastance using a multiple linear regression analysis.

The elastic pressure/volume (P/V) curve obtained by the multiple linear regression (MLR) technique using a new model, was compared with the quasi-static P/V points obtained by the rapid airway occlusion technique. Seven infants were studied during mechanical ventilation using a pressure controlled mode. The resistive pressure was subtracted from airway opening pressure, thus determining the elastance related pressure, which was then plotted against the volume to make an MLR-elastance curve. Quasi-static P/V curves of the rapid occlusion technique were constructed by plotting the different inspiratory and expiratory volumes against the corresponding values of the quasi-static airway pressure. The calculated MLR-elastance curves closely fit the experimental quasi-static P/V points obtained by the occlusion technique. There were, however, some discrepancies due to the viscoelastic behaviour of the respiratory system. Although slightly altered by these discrepancies, the multiple linear regression-elastance curves did fit the observed quasi-static pressure/volume characteristics for use in clinical practice. The multiple linear regression technique may prove to be clinically useful by continuous monitoring of respiratory system mechanics during mechanical ventilation.

Airway Resistance↗
PubMed2001

Elastic properties of the lung and the chest wall in young and adult healthy pigs.

Understanding of the elastic pressure/volume (Pel/V) curve is still limited in health and disease. The aim of the present study was to elucidate the Pel/V curve and elastance of the respiratory system (ERS) lung (EL) and chest wall (ECW) in healthy pigs. Six young (20.8 kg) and seven adult (58.9 kg), anaesthetized, paralysed and ventilated pigs were studied. Pel/V curves were recorded at zero end-expiratory pressure (ZEEP) and at positive end-expiratory pressure (PEEP) up to 40 cmH2O with a computer controlled ventilator during an insufflation at a low, constant flow. Pel/V curves of the respiratory system showed a complex pattern in both young and adult pigs. During the insufflation, ERS decreased, increased, fell, and increased again. A second Pel/V curve recorded immediately after the first one showed lower elastance and only one early fall in ERS. ECW fell over the initial segment and was then nearly stable. Difference between 1st and 2nd curves reflected changes in EL caused by recruitment during the 1st insufflation. At PEEP, such signs of collapse and recruitment were reduced. A strong tendency to lung collapse contributes to a complex pattern of elastic pressure/volume curves. At low volumes and distending pressures the chest wall contributes significantly to changes in respiratory system elastance.

Aging↗
PubMed2006

Ultrastructural study of the filum terminale and its elastic fibers.

OBJECTIVE: The filum terminale (FT) is a fibrovascular band involved in the pathophysiology of tethered cord syndrome (TCS). Its morphological and ultrastructural properties remain largely unknown even though they are thought to play a role in the generation of TCS in adult patients with normal level conus medullaris. MATERIALS AND METHODS: Twenty fresh adult human cadavers had their fila measured and removed. Transversal and longitudinal sections of the proximal, middle, and distal thirds of FT were submitted to light microscopy analysis with four different techniques. Five fila were selected for longitudinal and transversal scanning electron microscopy analysis. RESULTS: The bulk of the FT is composed of 5- to 20-microm thick longitudinal bundles of Type 1 collagen separated by 3- to 10-microm intervals, although capillaries and other elements may be present. A delicate (0.05-1.5 microm) meshwork of predominantly Type 3 collagen transversal fibers connects these bundles. Abundant longitudinally oriented elastic and elaunin fibers are found inside collagen bundles. A complex tridimensional structure is evidenced on electron microscopy. CONCLUSION: The longitudinal arrangement of collagen bundles and the impressive amount of elastic and elaunin fibers should elicit considerable elastic properties to the FT. An altered elasticity mechanism has been proposed for TCS; further studies are needed with TCS patients to define whether the collagen structure, Type 1/Type 3 proportion, or elastic fiber content are altered, which could lead to new histopathological definitions of TCS, helping neurosurgeons in the difficult management of TCS patients with normal level conus medullaris.

Adult↗
PubMed2000

Energy storage by passive elastic structures in the mantle of sepia officinalis.

The passive elastic properties of the mantle of the cuttlefish Sepia officinalis have been characterized in experiments on intact mantle and on pieces cut from the mantle. The mantle was found to be very compliant over a wide range of circumferential strains, corresponding to a change in mantle circumferential strain of 0.45. Beyond this range of strain, the mantle was much stiffer, in both the circumferential direction, 0.542+/-0.025 MPa (mean +/- s.e.m., N=51) and through the thickness of the mantle wall, 0.152+/-0.041 MPa (N=11). Almost 80 % of the work done on the tissue during compression in the circumferential direction was recovered during elastic recoil of the tissue; this elastic work could contribute to refilling the mantle after a jet. Our estimates of the work done during a cycle of jetting and refilling show that such elastic work is small (approximately 1 %) compared with the contractile work done by the circular muscle fibres. However, although the elastic work is almost negligible in the overall energy budget, it is probably sufficient to power refilling of the mantle.

Animals↗
PubMed1989

Subepithelial elastic fibers in the bovine gastric mucosa.

The arrangement of subepithelial elastic fibers in the bovine gastric mucosa was studied by light and electron microscopy, with special reference to the elastic architecture of the cornified papillae. A common feature of their arrangement was that the fibers, derived from the elastic plexus in the deep layer of the lamina propria, extend perpendicularly toward the epithelium giving off the slender branches that end at the epithelial basement membrane. The connecting branches were observed electron microscopically in the form of oxytalan or slender elaunin fibers. The high frequency of fibers was found in the mucosa of the upper part of the ruminal atrium, the ruminal pillars, the reticular cristae and two kinds of cornified unguiculiform and omasal papillae. Each papilla consisted of the core of three-dimensional elastic network and numerous connecting-twigs arising from the superficial points of the network. The mucosae of the ruminal sacs, the floor of the reticular cells and the abomasum except the pyloric part were relatively poor in elastic fibers. These results suggest that the variation in fiber-arrangement may be relevant to the condition of mechanical stress inflicting on the gastric innersurface.

Animals↗
PubMed2006

Immunohistochemical characterization of elastic system fibers in rat molar periodontal ligament.

Among elastic system fibers, oxytalan fibers are known as a ubiquitous component of the periodontal ligament, but the localization and role of elastin-containing fibers, i.e., elastic and elaunin fibers, has yet to be clarified. In this study, we immunohistochemically investigated the localization of elastin and fibrillin, major proteins of elastin-containing fibers in the periodontal ligament of rat lower first molars. At the light microscope level, distribution of elastin-positive fibers was not uniform but often concentrated in the vicinity of blood vessels in the apical region of the ligament. In contrast, fibrillin-positive fibers were more widely distributed throughout the ligament, and the pattern of their distribution was comparable to the reported distribution of oxytalan fibers. At the ultrastructural level, assemblies or bundles of abundant fibrillin-containing microfibrils were intermingled with a small amount of elastin. This observation indicated that elastin-positive fibers observed under the light microscope were elaunin fibers. No mature elastic fibers, however, were found in the ligament. These results show that the major components of elastic system fibers in the periodontal ligament of the rat mandibular first molar were oxytalan and elaunin fibers, suggesting that the elastic system fibers play a role in the mechanical protection of the vascular system.

Animals↗
PubMed2006

Determining the ratio of the Gaussian curvature and bending elastic moduli of phospholipids from Q(II) phase unit cell dimensions.

A method is presented for measuring M, the ratio of the Gaussian (saddle splay) elastic modulus to the bending elastic modulus of a lipid monolayer. The ratio M is determined from measurements of the equilibrium bicontinuous inverted cubic (Q(II)) phase unit cell size in excess water as a function of temperature. The analysis includes the effect of a curvature elastic term that is second-order in the Gaussian curvature, K. Preliminary results using data on DOPE-Me validate the method. The fitted value of M is within 8% of the value estimated in an earlier treatment. The method can be used to measure changes in M due to addition of exogenous lipids and peptides to a host lipid system. The Gaussian elastic modulus has a substantial effect on the stability of fusion intermediates (stalks, hemifusion diaphragms, and fusion pores). Studying the effects of peptides and different lipids on M via this method may yield insights into how fusion protein moieties stabilize intermediates in membrane fusion in vivo. The contribution of the K2 curvature elastic term to the free energy of Q(II) phase and fusion pores explains some features of fusion pore stability and dynamics, and some peculiar observations concerning the mechanism of L(alpha)/Q(II) phase transitions.

Animals↗
PubMed2006

Evaluation of elastic properties of atomistic DNA models.

A number of intriguing aspects in dynamics of double-helical DNA is related to the coupling between its macroscopic and microscopic states. A link between the elastic properties of long DNA chains and their atom-level dynamics can be established by comparing the worm-like chain model of polymer DNA with the conformational ensembles produced by molecular dynamics simulations. This problem is complicated by the complexity of the DNA structure, the small size of DNA fragments, and relatively short trajectory durations accessible in computer simulations of microscopic DNA dynamics. A careful study of all these aspects has been performed by using longer DNA fragments and increased durations of MD trajectories as compared to earlier such investigations. Special attention is paid to the necessary conditions and criteria of time convergence, and the possibility to increase the sampling by using constrained DNA models and simplified simulation conditions. It is found that dynamics of 25-mer duplexes with regular sequences agrees well with the worm-like chain theory and that accurate evaluation of DNA elastic parameters requires at least two turns of the double helix and approximately 20-ns duration of trajectories. Bond length and bond-angle constraints affect the estimates within numerical errors. In contrast, simplified treatment of solvation can strongly change the observed elastic parameters of DNA. The elastic parameters evaluated for AT- and GC-alternating duplexes reasonably agree with experimental data and suggest that, in different basepair sequences, the torsional and stretching elasticities vary stronger than the bending stiffness.

Base Pairing↗
PubMed2000

Histomorphometrical study of the elastic fiber system in the anterior cerebral artery of man.

The aim of the present study was to quantify the distribution of the elastic fiber system within the wall of the anterior cerebral artery. The study is based on the works of Glynn (1940) and Stehbens (1989) concerning the incidence and origin of brain aneurysms and recent studies of the elastic fibers. The anterior cerebral artery was divided into three segments, S1, S2 and S3: S1 corresponds to the origin of the anterior cerebral artery, S2 is located at the junction of the anterior cerebral artery with the anterior communicating artery, and S3 at the junction of the rostrum and genu of the corpus callosum,which were submitted to routine histological procedures. A histomorphometrical study was undertaken using an estimation of the linear density (Ld) of the components of the fibrous elastic system which evaluates their full length in each segment. Data were analyzed using first order linear regression methods. The results show a decreasing quantity of elastic fibers in the three segments (S1>S2>S3). Study of the elastic fiber system may originate new concepts regarding the genesis of cerebral artery aneurysm.

Adult↗
PubMed1989

On the distribution of elastic fibers in the filiform papillae of Suncus murinus.

The distribution of elastic fibers in the filiform papillae of 1, 2, 3, 4 and 5 week-old and 6 month-old Suncus (Suncus murinus; insectivora) was examined by both Weigert's resorcin-fuchsin method and ultrastructural means. In the adult Suncus (6 months old), elastic fibers in the connective tissue core of the papillae were aligned perpendicularly to the epithelial surface and formed a palisade-like structure which encircled the margin of each connective tissue core. This characteristic structure was restricted to the filiform papillae in the anterior half of the lingual dorsum. In the filiform papillae of the posterior half, elastic fibers were markedly reduced and the palisade-like structure was not present. This characteristic pattern of elastic fiber distribution was established by 3 weeks of age. These observations reveal a characteristic structure consisting of elastic fibers in the connective tissue core of the filiform papillae and the regional distribution of this structure in the tongue. This suggests that the function of the structure in the connective tissue core is to protect against mechanical stress in mastication. The regional distribution of this structure may reflect the difference of mechanical strength between the anterior and posterior of the tongue caused by tongue movement during mastication.

Animals↗
PubMed1983

Viscoelastic behavior of human connective tissues: relative contribution of viscous and elastic components.

Stress-relaxation tests were performed at successive strain levels on strips of human aorta, skin, psoas tendon, dura mater, and pericardium. The elastic fraction, the equilibrium force divided by the initial force, was calculated at each strain increment. In the aorta, the elastic fraction decreased with strain and was modeled as the transfer of stress from elastic to collagen fibers, while in skin it increased with strain, probably due to the rearrangement of individual collagen fiber orientations, resulting in an aligned collagen network at high strains. The strain-independent elastic fractions for tendon, dura mater, and pericardium were similar, and approximately equal to the values found for aorta and skin at high strains. It was hypothesized that the elastic fraction is related to the type of fiber loaded, and the tissue geometry. This analysis may be useful in studying disease-induced changes in the mechanical properties of connective tissues.

Aged↗
PubMed1989

The application of Miller's elastic stain to glycol methacrylate tissue sections.

The application of Miller's dilute elastic stain followed sequentially by Gill's III hematoxylin and a fast green counterstain produced a reliable and consistent method for differentially staining elastic fibers, nuclei, muscle and collagen in glycol methacrylate tissue sections. Evaluation of different methods of fixation and conditions of staining on animal tissue sections showed that elastic fibers in both perfusion and immersion fixed tissues can be intensely stained. The stability of Miller's elastic stain offers the potential of a commercially available histological stain reagent for coarse and fine elastic fibers in glycol methacrylate tissue sections.

Acrylates↗