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PubMed2003

Measurement of the elastic modulus of rabbit nasal septal cartilage during Nd:YAG (lambda = 1.32 microm) laser irradiation.

BACKGROUND AND OBJECTIVES: The objective of this study was to quantitatively measure changes in the elastic moduli of rabbit nasal septal cartilage during laser heating. While the efficacy of laser cartilage reshaping has been established for use in nasal surgery, few studies have investigated the temperature-dependent viscoelastic behavior of cartilage. STUDY DESIGN/MATERIALS AND METHODS: Cyclic force versus displacement curves were generated during the Nd:YAG laser (lambda = 1.32 microm, 10 second exposure time, 21.22 W/cm2) irradiation of cartilage specimens secured in cantilevered geometry. Samples were irradiated three times with 30 second cooling intervals between each laser exposure. Measurements were recorded before, during, and after laser irradiation, and then following complete rehydration in normal saline (NS) for 1 hour at 25 degrees C. Elastic modulus was calculated assuming linear viscoelastic behavior. RESULTS: The elastic modulus in native tissue decreased during and after successive laser exposures from about 6 to 3.5 MPa. After rehydration, the modulus returned to near-baseline value. Surface temperature reached a maximum of 65 degrees C. CONCLUSIONS: The laser irradiation of cartilage using parameters similar to those used in reshaping does not produce significant irreversible changes in the mechanical properties of the tissue. Measurement of the elastic modulus is an effective means of characterizing alterations in cartilage mechanical behavior during and after laser heating.

Animals↗
PubMed1994

Elastic wall properties and collagen content in the ureter: an experimental study in pigs.

We used an impedance planimetric method to look at elastic wall properties of ureter in ten anaesthetized pigs. A balloon was stepwise inflated and deflated in the ureteropelvine junction, in the mid-ureter, and in the intramural part of the ureter at the ureterovesical junction with pressures up to 70 cmH2O, while the pressure and balloon cross-sectional area (Bcsa) were measured simultaneously. The elastic wall parameters were calculated from these measurements. At sacrifice, tissue samples were collected for analysis of collagen content of the ureteral wall. A non-linear clockwise relation (hysteresis loops) between Bcsa and balloon pressure was demonstrated. At maximal inflation of the balloon, the Bcsa, wall tension, and compliance were 35.28 +/- 3.52, 38.44 +/- 3.23, and 61.36 +/- 8.09 mm2, 230.71 +/- 12.82, 242.38 +/- 10.49, and 302.17 +/- 20.03 cmH2O x m, and 0.167 +/- 0.047, 0.124 +/- 0.002, and 0.182 +/- 0.040 mm2 x cmH2O-1 in the intramural part of the ureter, middle part, and ureteropelvine junction, respectively. The collagen content was 0.3249 +/- 0.0077, 0.3301 +/- 0.0066, and 0.3457 +/- 0.0060 mg x mg-1 dry defatted weight in the intramural part, in the middle, and in the ureteropelvine junction, respectively. The collagen content of the ureteropelvine junction was significantly higher than that of the middle of ureter (P < 0.02) and than that of the intramural part (P < 0.05). No significant correlations were found between the elastic parameters at maximal inflation of the balloon and the collagen content (P < 0.10). In conclusion the elastic wall properties were significantly different in the three ureteral segments and the collagen content of the ureteropelvine junction differed from that of the two distal locations. However, no relationship between the wall properties and the collagen content was found.

Animals↗
PubMed1978

Studies of elastic tissue formation in the developing bovine ligamentum nuchae.

The foetal ligamentum nuchae showed two distinct stages of development, each characterised by its cell population and fibre products. Fibroblasts of the early phase have extensive ergastoplasm apparently associated with collagen production; those of the late phase have an "attenuated" cytoplasm and coincide with an increase of elastic tissue content. The elastic fibre comprised a core of fine elastin fibrils (100--130 nm diameter) and a surrounding mantle of microfibrillar protein. As development proceeded, the elastin fibrils appeared to coalesce with each other and also with elastin fibrils from adjacent fibres to form composite mature elastic fibre--a process which was accompanied by a loss of microfibrils. A characteristic of elastic fibres from adult ligament, not apparent in the foetal tissue, was that of bifurcation.

Animals↗
PubMed1996

Towards a molecular understanding of the elasticity of titin.

Vertebrate striated muscle behaves elastically when stretched and this property is thought to reside primarily within the giant filamentous protein, titin (connectin). The elastic portion of titin comprises two distinct structural motifs, immunoglobulin (Ig) domains and the PEVK titin, which is a novel motif family rich in proline, glutamate, valine and lysine residues. The respective contributions of the titin Ig and the PEVK sequences to the elastic properties of the molecule have been unknown so far. We have measured both the passive tension in single, isolated myofibrils from cardiac and skeletal muscle and the stretch-induced translational movement of I-band titin antibody epitopes following immunofluorescent labelling of sites adjacent to the PEVK and Ig domain regions. We found that with myofibril stretch, I-band titin does not extend homogeneously. The Ig domain region lengthened predominantly during small stretch, but such lengthening did not result in measurable passive tension and might be explained by straightening, rather than by unfolding, of the Ig repeats. At moderate to extreme stretch, the main extensible region was found to be the PEVK segment whose unravelling was correlated with a steady passive tension increase. In turn, PEVK domain transition from a linearly extended to a folded state appears to be principally responsible for the elasticity of muscle fibers. Thus, the length of the PEVK sequence may determine the tissue-specificity of muscle stiffness, whereas the expression of different Ig domain motif lengths may set the characteristic slack sarcomere length of a muscle type.

Amino Acid Sequence↗
PubMed2001

Relationship of hydraulic impedance and elasticity in the pulmonary artery of maturing newborn pigs.

The current study determined the dynamic stress-strain elastic moduli (E(Y)) and characteristic impedances (Z(0(2-7Hz))) of the main pulmonary artery in open-chest, anesthetized newborn pigs at 2 days, 2 weeks, and 3 months of age. E(Y) and Z(0(2-7Hz)) were compared to those values derived from the Womersley and Moens-Korteweg equations (denoted E(W-MK) and Z(0W-MK), respectively) to test the validity of these equations in describing the elasticity of the intact newborn pulmonary artery. E(Y) was defined as the ratio of stress to strain. The current study hypothesized that: (1) E(Y) and E(W-MK) are numerically similar, and therefore the Womersley and Moens-Korteweg equations accurately describe the viscoelastic properties of the main pulmonary artery of the newborn pig, and (2) that both E(Y) and Z(0) are elevated at birth and undergo a steady decline with maturation. E(Y) was not significantly different from E(W-MK), while Z(0(2-7Hz)) was nearly identical to Z(0W-MK) in all groups. The elastic modulus peaked (P < 0.001) in 2-week-old pigs compared with both younger and older animals, while Z(0(2-7Hz)) decreased with increasing age (48 h = 1237 +/- 251 [SEM] dyn s cm(-5), 2-week = 433 +/- 95 dyn s cm(-5), 3 month = 162 +/- 17 dyn s cm(-5), P < 0.001). These experiments validate the Womersley and Moens-Korteweg equations as accurately describing the elastic properties of the intact newborn pig pulmonary artery. These data also demonstrate that a diminution in Z(0) may occur even with increased wall stiffness, as observed in our 2-week-old pigs.

Age Factors↗
PubMed1987

Noninvasive measurement of arterial blood pressure and elastic properties using photoelectric plethysmography technique.

The objective of this paper is to review our developed method for measuring noninvasively the arterial blood pressure as well as the mechanical properties of the vascular system in a thin portion of the biological segment such as human fingers or small animal extremities like rat tails and rabbit forelegs. This measurement is based on a principle called the 'volume-oscillometric method'. During the gradual change in cuff pressure, the amplitude of consecutive arterial volume pulsations associated with pulse pressure shows change characteristically due to the nonlinearity of arterial pressure-volume(P-V) relation. Arterial pressure can be accurately determined by detecting this characteristic change in the amplitude, while the arterial elastic properties such as P-V relationship and volume elastic modulus can be noninvasively obtained as a function of arterial transmural pressure, provided that the arterial volume changes are quantitatively determined during this pressure measurement. The validity and accuracy of this pressure and elasticity measurement with photoelectric plethysmography technique for detecting arterial volume changes are clearly demonstrated on the in vitro and in vivo experiments. Considering the simplicity and practicability of this measurement using the photoelectric plethysmography, we present a new portable instrument for the long-term ambulatory monitoring of indirect arterial pressure and a handy fully-automatic instrument for the noninvasive measurement of arterial elastic properties, and a few examples obtained by each instrument are also described.

Animals↗
PubMed1993

Elastic properties of the titin filament in the Z-line region of vertebrate striated muscle.

The characteristics of the titin filament in the vicinity of the Z-line were investigated using immunoelectron microscopy. We used monoclonal titin antibodies T-11 and T-12 on single fibres of frog skeletal muscle, and on Z-line-extracted fibres. It is well established that the I-band region of titin is elastic. We find, however, that the elastic properties are not uniform. The T-12 epitope, which binds near the Z-line at the N1-line level, hardly changes position relative to the Z-line as the sarcomere is stretched. This demonstrates the functional inextensibility of the N1-Z-line region. After extreme stretch (above 6-microns sarcomere length), this zone finally does elongate; thus, the titin molecule in this region is intrinsically elastic. The functional inextensibility seen at shorter sarcomere lengths may, therefore, be a result of binding of titin to the actin filament in the zone near the Z-line. When the Z-line was extracted, the T-12 epitope remained in the same position as in the unextracted fibres; it did not retract from the Z-line. Failure to retract implies that functional anchoring of titin is not exclusive to the Z-line, but includes some site closer to the A-band. Combined with the results of the above-mentioned stretch experiment, this result implies a likely binding of titin to the thin filament either focally at the N1 line or all along the entire N1-Z region. Thus, this region of titin is functionally stiff, but intrinsically elastic.

Animals↗
PubMed1992

The elastic deformability of closed multilayered membranes is the same as that of a bilayer membrane.

The elastic behavior of closed multilayered membranes is analyzed with the assumption that the constituent layers are in close contact but are unconnected in the sense that they are free to slide by one another. The system exhibits three independent elastic deformation modes for any number of the constituent layers equal to or larger than two. These are the area expansivity of the membrane neutral surface, and the local and non-local membrane bending. The corresponding elastic moduli are expressed in terms of the elastic moduli of the constituent layers, their areas, and distances between their neutral surfaces. Closed multilayered membranes only differ from a closed bilayer membrane in that for any of their shapes some of the constituent layers are expanded and some compressed.

Elasticity↗
PubMed1991

Early preclinical diagnosis of dominant pseudoxanthoma elasticum by specific ultrastructural changes of dermal elastic and collagen tissue in a family at risk.

The preferred description for the Grönblad-Strandberg syndrome, pseudoxanthoma elasticum (PXE), refers only to the cutaneous aspect of the disease, although the skin is the least severely involved organ. The potential catastrophic manifestation of this heterogeneous heritable disorder is described in a dominant pedigree where mother and grandmother died because of major vascular problems. The family requested predictive testing of the three children. Diagnosis of PXE is usually performed by morphological examination of skin lesions, which reveal incrustations formed by inorganic ions (mainly calcium) and various organic (degraded?) materials in the elastin moiety of the elastic fibers. The ubiquitous elastic fibers in other organs and arteries may be similarly involved. Moreover, there is co-involvement of collagen fibrils at the electron microscopical level. The three adolescent siblings did not show any clinical PXE symptoms. However, ultrastructural investigation of overtly normal skin in predilection sites gave a positive diagnosis for this dominant PXE type. Dermal connective tissue showed a specific aberrant pattern: elastin of elastic fibers regularly contained small foci of calcification resembling those in perilesional skin of the mother and other PXE patients; in collagen bundles adjacent to altered elastic fibers, collagen fibrils occurred with thickened diameters and flower-like contours; ground substance material was increased. The possible pathogenetic mechanism and problems posed by predictive testing of adult-onset diseases are discussed.

Adolescent↗
PubMed1987

The occurrence of elastic system fibres in the matrix of normal articular cartilage.

Normal articular cartilages from the weight-bearing areas of the femoral condyles of the knee joints of 11 patients (3-20 years old) and of 35 Schwarzkopf sheep (3 months to 2 years old) were studied using the electron microscope. The study has shown that the matrix of normal articular cartilage is not only composed of collagen fibrils and proteoglycans, but also contains two types of elastic system fibres. Small elastic fibres can be identified in the superficial and lower radiate zones of cartilage of man and sheep. Similar to elastic fibres in other tissues, they consist of a central amorphous core and are surrounded by aggregates of 10 nm microfibrils. Another type of elastic system fibres, oxytalan fibres, are found in the intermediate and upper radiate zones of the articular cartilage.

Adolescent↗
PubMed1980

A quantitative analysis of elastic, entropic, electrostatic, and osmotic forces within relaxed skinned muscle fibers.

The elastic behavior of mechanically skinned skeletal muscle fibers in relaxing solution is modelled using equations developed by Flory (1953) for the elasticity of non-biological polymers. Mechanically, the relaxed skinned fiber is considered to be a semi-crystalline network of inextensible polymer chains, which are periodically cross-linked and which are bathed in an aqueous medium. We consider (1) configurational elastic forces in the network, (2) entropic forces due to mixing of polymer and water, (3) electrostatic forces due to fixed charges on the muscle proteins and mobile charges in the bathing solution, and (4) compressive forces due to large colloids in the bathing solution. Van der Waals forces are not considered since calculations show that they are probably negligible under our conditions. We derive an expression which relates known quantities (ionic strength, osmotic compressive pressure, and fiber width), experimentally estimated quantities (fixed charge density and volume fraction of muscle proteins), and derived quantities (concentration of cross-links and a parameter reflecting the interaction energy between protein and water). The model was tested by comparison with observed changes in skinned fiber width under a variety of experimental conditions which included changes in osmotic compressive pressure, pH, sarcomere length, and ionic strength. Over a wide range of compressive pressure (0-36 atm) the theory predicted the nonlinear relation between fiber width and logarithm of pressure. The direction and magnitude of the decrease in width when pH was decreased to 4 could be modelled assuming the fixed charge density on the protein network was 0.34 moles of electrons per liter protein, a value in accordance with the estimates of others. The relation between width and sarcomere length over the complete range of compressive pressures could be modelled with the assumption that the number of cross-links increases somewhat with sarcomere length. Changes of width with ionic strength were modelled assuming that increasing salt concentration both increased the electrostatic shielding of fixed charges and decreased the number of cross-links. The decrease of fiber width in 1% glutaraldehyde was modelled by assuming that the concentration of crosslinks increased by some 10%. The theory predicted the order of magnitude but not the detailed shape of the passive tension-length relation which may indicate that, as with non-biological polymers, the theory does not adequately describe the behavior of semi-crystalline networks at high degrees of deformation. In summary, the theory provides a semiquantitative approach to an understanding of the nature and relative magnitudes of the forces underlying the mechanical behavior of relaxed skinned fibers. It indicates, for instance, that when fibers are returned to near their in vivo size with 3% PVP, the forces in order of their importance are: (elastic forces) approximately (entropic forces) greater than (electrostatic forces) approximately (osmotic compressive forces).

Animals↗
PubMed1977

[Electron microscopic examination of the morphogenesis of the elastic fibre in elastosis senilis and pseudoxanthoma elasticum (author's transl)].

We undertook to investigate the elastic and collagenous fibers of senile elastosis (s.E.) and pseudoxanthoma elasticum (P.e.). This was done by comparing the above with normal skin under the electron microscope. The main difference is the increasing occurance of a fine granular-filamentous substance composed of microfibrils of varying thicknesses. A new formation arises as this substance is excreted by the activated fibroblasts and the combines extracellulary with the pathological elastic fibers. In the case of P.e. there is an additional calcification. It seems that with the elastogenesis of s.E. small elastic fibers are formed. P.e., in contrast, shows irregular electron-dense reticular sheets with numerous holes. The alteration of collagen observed in both diseases is considered as the primary change (which arises in both cases through the fine granular-filamentous material). In both diseases it is a matter of alterations of the little vessels, in endothel and basement membranes. We find here the same fine granular-filamentous substance in the elastic fibers of lamina interna, where as in P.e. we can see the calcification.

Adult↗
PubMed1989

Elastic fibres in patients with systemic sclerosis. A morphological study.

Dermal elastic fibres in biopsies taken from sun-exposed involved digital skin and sun-protected uninvolved skin on the medial aspect of the upper arms from 13 patients with systemic sclerosis were examined by light and transmission electron microscopy. For controls, biopsies were taken from similar sites from 4 age- and sex-matched healthy volunteers and 4 patients with primary Raynaud's phenomenon. On light microscopy only the control digital biopsies showed mild actinic changes of the elastic fibres whereas in all the biopsies from patients with systemic sclerosis identical changes of thickening, clumping and fragmentation of the elastic fibres were observed. Quantitative assessment of the dermal elastic fibres using microdensitometry and video image analysis showed no significant difference between the patients and controls. On electron microscopy more advanced abnormalities similar to those seen in actinic damage and chronological aging were found in the biopsies from all the patients with systemic sclerosis compared to the controls.

Adult↗
PubMed1988

The length dependence of the series elasticity of pig bladder smooth muscle.

Strips of urinary bladder smooth muscle were subjected to a series of quick release measurements. Each measurement consisted of several releases and resets to the original length, made during one contraction. The complete length-force characteristic of series elasticity was quantified by estimating H, the amplitude of quick release necessary to reduce the active force to exactly zero, and Db, a measure for the deviation of the characteristic from a straight line. By measuring a series of contractions at increasing stretched strip lengths, the length dependence of these parameters was studied. It was found that H depends linearly on stretched strip length. On average H/length amounted to 0.04. Db decreased when strips were stretched, i.e. a straight line was more closely approximated. Both parameter dependencies support the concept of two separate elastic mechanisms, a linear true passive elasticity in series with a non-linear elasticity in the cross-bridges. For the latter, H amounts to 3.8% of the initial strip length.

Animals↗
PubMed1990

Deposition and remodelling of elastic fibres in chronic hepatitis.

A longitudinal study of elastic fibres was conducted in liver biopsies from 21 patients with chronic viral hepatitis. Biopsies were taken at the start of treatment with alpha-interferon, and after 6 months or 1 year of treatment. No elastic fibres could be detected in portal tracts or fibrous septa when inflammation and necrosis were present, whatever the duration of the disease. Once the liver lesions had healed, elastic fibres were synthesized. Fibres were of two types and patterns: at first, they were thin, long and parallel to each other. Later, they were thicker, shorter and tortuous and were closely wrapped around thick bundles of collagen fibres. These findings suggest that the deposition of elastic fibres acts as a marker of healing in chronic active hepatitis and that their remodelling occurs concomitantly with the deposit of large bundles of collagen fibres.

Biopsy↗
PubMed2003

Mechanisms governing the visco-elastic responses of living cells assessed by foam and tensegrity models.

The visco-elastic properties of living cells, measured to date by various authors, vary considerably, depending on the experimental methods and/or on the theoretical models used. In the present study, two mechanisms thought to be involved in cellular visco-elastic responses were analysed, based on the idea that the cytoskeleton plays a fundamental role in cellular mechanical responses. For this purpose, the predictions of an open unit-cell model and a 30-element visco-elastic tensegrity model were tested, taking into consideration similar properties of the constitutive F-actin. The quantitative predictions of the time constant and viscosity modulus obtained by both models were compared with previously published experimental data obtained from living cells. The small viscosity modulus values (10(0)-10(3) Pa x s) predicted by the tensegrity model may reflect the combined contributions of the spatially rearranged constitutive filaments and the internal tension to the overall cytoskeleton response to external loading. In contrast, the high viscosity modulus values (10(3)-10(5) Pa x s) predicted by the unit-cell model may rather reflect the mechanical response of the cytoskeleton to the bending of the constitutive filaments and/or to the deformation of internal components. The present results suggest the existence of a close link between the overall visco-elastic response of micromanipulated cells and the underlying architecture.

Actin Cytoskeleton↗
PubMed1989

Elasticity changes in the large arteries of human limbs in response to cycle ergometry performed with upper and lower limbs.

At rest and after cycle ergometry the elastic properties of the large arteries of limbs of healthy men were examined using an original non-invasive quantitative oscillometric method. It has been shown that in response to muscle work performed with the legs there is a decrease of the effective inner radius, and an increase of the characteristic impedance modulus and bulk modulus and of the elastic resistance of the intact and relaxed wall in the large arteries in the upper limbs. All these changes testify to an increase of vascular tension in the upper limbs. In response to work performed with the hands, there is an increase of the effective inner radius of large arteries of the upper limbs, a large increase of the pulsatile blood volume increment of the intact vessels and a decrease of the characteristic impedance modulus, of the bulk modulus and of the elastic resistance of the intact arterial wall. These changes indicate a decrease of the vascular tension of these arteries. In response to work performed either with the legs or with the hands a decrease of the effective inner radius of large arteries and an increase of the elastic resistance of the relaxed arterial wall were observed in the lower limbs, all these changes indicating relatively small changes in tone of these vessels. It is concluded that the wall tension of large arteries supplying blood to the muscles of non-working limbs is increased. Vascular tension changes in the arteries in working limbs are accounted for by the superimposition of centrally originating vasoconstriction with local vasodilatation, which also affects large arteries.

Adult↗
PubMed1993

In vivo evaluation of visco-elasticity in a biological tube. Part 2. Application of a mechanical model.

Based on a theoretical model, the urethral stress-relaxation response following a sudden forced dilatation was studied in ten healthy female volunteers. The energy dissipation following a sudden urethral dilatation proved to follow the function Y = Z + C alpha e-t/tau alpha + C beta e-t/tau beta. Hence, a mechanical model was chosen, consisting of two Maxwell elements and one Hooke element coupled in parallel. The decay in force following deformation may be described as F = F(o) exp (-t.E/eta) for each Maxwell element. Thus, it was possible to determine the elastic E and viscous eta coefficients for the participating mechanical equivalents in the model, and thereby quantitatively describe the visco-elastic properties in the urethra. The reproducibility of the elastic and the viscous coefficients proved to be fairly high, and they seemed to be unaffected by the size of dilatation. On the other hand, the rate of dilatation clearly influenced the computed parameters. However, this phenomenon was easily explained by the duration of the deformation, which allowed the viscous elements to move before any measurements were performed. The present method permits in vivo evaluation of the elastic and viscous properties of the urethra, as well as other accessible biological tubes, and may be of value in the description of normal physiological and pathophysiological behaviour of the structures studied.

Adult↗