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At least 955 records · Page 53Linked to original sources
PubMed2004

Relationship between reduced elasticity of extracardiac vessels and left main stem coronary artery disease.

OBJECTIVES: To investigate the elastic properties of medium-size extracardiac arteries and veins between patients with and without left main stem coronary artery disease. METHODS: The compliance, distensibility, and incremental elastic modulus (iEmod) of the internal thoracic arteries (n=53), long saphenous veins (n=38), and radial arteries (n=35) from 74 patients undergoing coronary surgery were studied in organ baths. Twenty-four patients had left main stem (LMS) disease and 50 non-LMS coronary disease. RESULTS: Internal thoracic arteries from patients with LMS presented significantly lower compliance (-17%) and distensibility (-18%) and significantly higher iEmod (19%) than internal thoracic arteries from patients with non-LMS disease. Radial arteries from patients with LMS presented higher iEmod (50%) than radial arteries from patients with non-LMS disease. Furthermore, long saphenous veins from patients with LMS had reduced compliance (-45%), reduced distensibility (-40%) and increased iEmod (34%) compared to those from patients with non-LMS disease. CONCLUSIONS: LMS coronary disease is associated with a significantly reduced elasticity of extracardiac arteries and veins compared to non-LMS coronary disease. This finding suggests that widespread vascular elasticity defects may play a role in the development of LMS disease and be responsible for the higher incidence of early and late cardiovascular morbidity observed in this condition.

Coronary Artery Disease↗
PubMed2005

Effect of lipid-containing, positively charged nanoemulsions on skin hydration, elasticity and erythema--an in vivo study.

Dry skin and other skin disorders such as atopic dermatitis are characterized by impaired stratum corneum (SC) barrier function and by an increase in transepidermal water loss (TEWL) leading to a decrease in skin hydration. The possibility that dermatological and cosmetic products containing SC lipids could play a part in the restoration of disturbed skin barrier function is of great interest in the field of dermatology and cosmetics. The aim of the present study was to evaluate the effect of positively charged oil/water nanoemulsions (PN) containing ceramide 3B and naturally found SC lipids (PNSC) such as ceramide 3, cholesterol, and palmitic acid on skin hydration, elasticity, and erythema. Creams of PNSC were compared to PN creams, to creams with negatively charged o/w nanoemulsion and SC lipids (NNSC) and to Physiogel cream, a SC lipid containing formulation, which is already on the market. The formulations (PN, PNSC, and NNSC) were prepared by high-pressure homogenization. After adding Carbopol 940 as thickener, particle size and stability of the creams were not significantly changed compared to the nanoemulsions. The studies were carried out on three groups, each with 14 healthy female test subjects between 25 and 50 years of age, using Corneometer 825, Cutometer SEM 575 and Mexameter 18 for measurements of skin hydration, elasticity, and erythema of the skin, respectively. The creams were applied regularly and well tolerated throughout the study. All formulations increased skin hydration and elasticity. There was no significant difference between PNSC and Physiogel. However, PNSC was significantly more effective in increasing skin hydration and elasticity than PN and NNSC indicating that phytosphingosine inducing the positive charge, SC lipids and ceramide 3B are crucial for the enhanced effect on skin hydration and viscoelasticity.

Administration, Topical↗
PubMed2006

Elastic modulus measurements from individual lactose particles using atomic force microscopy.

The elastic modulus of pharmaceutical materials affects a number of pharmaceutical processes and subsequently formulation performance and is currently assessed by bulk methods, such as beam bending of compacts. Here we demonstrate the accurate measurement of the elastic modulus of alpha monohydrate lactose from the dominant (011) face of single crystals using atomic force microscopy (AFM) as 3.45+/-0.90GPa. The criteria to ensure this data is recorded within the elastic limit and can be modelled using Hertzian theory are established. We compare and contrast this AFM method to a permanent indentation technique based upon a much larger Berkovich pyramidal indenter on a lactose compact and the wider literature. Finally the AFM was utilized to study the elastic response of amorphous lactose, demonstrating that the physical state of the amorphous material changes under repeated loading and behaves in a more crystalline manner under repeated force measurements, suggesting a pressure induced phase transition. The AFM based approach demonstrated has the significant advantages of requiring minimal sample, no need for producing a compact, being non-destructive in that no permanent indent is required and providing a technique capable of detecting variations in material properties across a single particle or a number of particles.

Chemistry, Pharmaceutical↗
PubMed2004

The dependence of transversely isotropic elasticity of human femoral cortical bone on porosity.

The objective of this study was to examine the dependence of the elastic properties of cortical bone as a transversely isotropic material on its porosity. The longitudinal Young's modulus, transverse Young's modulus, longitudinal shear modulus, transverse shear modulus, and longitudinal Poisson's ratio of cortical bone were determined from eighteen groups of longitudinal and transverse specimens using tensile and torsional tests on a servo-hydraulic material testing system. These cylindrical waisted specimens of cortical bone were harvested from the middle diaphysis of three pairs of human femora. The porosity of these specimens was assessed by means of histology. Our study demonstrated that the longitudinal Young's and shear moduli of human femoral cortical bone were significantly (p<0.01) negatively correlated with the porosity of cortical bone. Conversely, the elastic properties in the transverse direction did not have statistically significant correlations with the porosity of cortical bone. As a result, the transverse elastic properties of cortical bone were less sensitive to changes in porosity than those in the longitudinal direction. Additionally, the anisotropic ratios of cortical bone elasticity were found to be significantly (p<0.01) negatively correlated with its porosity, indicating that cortical bone tended to become more isotropic when its porosity increased. These results may help a number of researchers develop more accurate micromechanics models of cortical bone.

Adult↗
PubMed2005

Elastic properties of an intact and ACL-ruptured knee joint: measurement, mathematical modelling, and haptic rendering.

An analytical, dynamic model of the human knee joint has been developed to simulate the unloaded knee joint behaviour in 6 degrees of freedom. It is based on extensive robot-based measurements of the elastic properties of a human cadaver knee joint. The measured data are compared with data from the literature to ensure that a proper database for modelling is used. The analytical modelling of the passive elastic joint properties is done with Local Linear Model Trees. The deduced knee joint model incorporates passive elastic properties of the internal knee joint structures, passive elastic muscle forces, damping forces, gravitational forces, and external forces. There are two sets of parameters, one simulating the movement of the intact knee joint, and a second simulating the knee joint with ruptured anterior cruciate ligament. The dynamic model can be easily processed in real-time. It is implemented in the haptic display of the Munich Knee Joint Simulator (MKS), which enables a person to move a plastic leg driven by a robot manipulator and feel the simulated knee joint force. Orthopaedic physicians judged the performance of the dynamic knee joint model by executing physical knee joint tests at the MKS.

Anterior Cruciate Ligament↗
PubMed2005

Comparison of elastic versus nonelastic compression in bilateral venous ulcers: a randomized trial.

BACKGROUND: There is controversy regarding the effectiveness of elastic vs nonelastic compression in the healing of venous leg ulcers. To gain insight into this controversy, we randomly compared a four-layer elastic bandage with a nonelastic garment (CircAid) in patients with venous leg ulcers. METHODS: Twenty-four extremities of 12 patients with bilateral leg ulcers were randomized to have a four-layer elastic bandage in 1 extremity and a nonelastic compression garment CircAid in the contralateral limb. The CEAP classification in 22 extremities was C(6 S); ES; A(D6,14,15,P18); PR; 1 extremity in 2 patients was C(6 S); E(S); A(D 6,14,15,P18); PRO. There were seven men and five women. Age ranged from 45 to 82 years, with a mean of 61 years. All patients had postthrombotic leg ulcers diagnosed clinically by duplex ultrasonography (n = 8) or by phlebography (n = 4). Every 4 weeks, patients had the ulcer area measured in square centimeters by a computerized scanning method and had the limb girth measured in centimeters at the foot, ankle, and calf. The ankle-brachial index was determined in all cases. Color photographs of the ulcer areas were taken monthly to assess healing progress. All patients were compliant. Results were assessed at 12 weeks. A patient satisfaction sheet was filled out by the patient, who circled one of the following scores: 3, very satisfied; 2, moderately satisfied; and 1, not satisfied. Cox proportional hazards models or paired t tests were used for comparison. RESULTS: The 24 limbs were randomized and divided into 2 groups of 12 each. Group A received CircAid, and group B, a four-layer elastic bandage. Duplex scanning showed a pattern of reflux in 11 limbs of each group. One limb in each group had a pattern of obstruction documented by air plethysmography (n = 2). Phlebography demonstrated the anatomic site in both limbs. The initial ulcer area in group A was 48.98 +/- 14.13 cm2 and was 50.08 +/- 18.30 cm2 in group B (P = .9285). The ulcer healing rate was significantly faster in group A compared with group B (hazard ratio, 0.56; 95% confidence interval, 0.33-0.96; P = .0173). Ulcers with hemodynamic obstruction had a protracted course when compared with the contralateral limbs with reflux. There was no significant difference in girth reduction between groups A and B (hazard ratio, 2.36; 95% confidence interval, 0.30-18.52; P = .3580). The ankle-brachial index was normal (> or = 1.0) in all patients. CONCLUSIONS: In compliant patients, venous leg ulcers randomized to nonelastic compression had a significantly faster healing rate per week than ulcers treated by the conventional four-layer compression system.

Aged↗
PubMed2005

Understanding the elasticity of fibronectin fibrils: unfolding strengths of FN-III and GFP domains measured by single molecule force spectroscopy.

While it is well established that fibronectin (FN) matrix fibrils are elastic, the mechanism of fibril elasticity during extension is still debated. To investigate the molecular origin of FN fibril elasticity, we used single molecule force spectroscopy (SMFS) to determine the unfolding behavior of a recombinant FN-III protein construct that contained eight FN-III domains ((1-8)FN-III) and two green fluorescent protein (GFP) domains. FN-III domains were distinguished from GFP domains by their shorter unfolding lengths. The unfolding strengths of both domains were determined for a wide range of pulling rates (50 to 1,745 nm/s). We found that the mechanical stabilities of FN-III and GFP domains were very similar to each other over the entire range of pulling speeds. FN fibrils containing GFP remain brightly fluorescent, even when stretched, meaning that GFP domains remain largely folded. Since GFP and FN-III have equal unfolding strengths, this suggests that FN-III domains are not extensively unraveled in stretched FN fibrils. Our results thus favor an alternative model, which invokes a conformational change from a compact to an extended conformation, as the basis for FN fibril elasticity.

Elasticity↗
PubMed2004

Modelling liver tissue properties using a non-linear visco-elastic model for surgery simulation.

In this work, we introduce an extension of the linear elastic tensor-mass method allowing fast computation of non-linear and visco-elastic mechanical forces and deformations for the simulation of biological soft tissue. We aim at developing a simulation tool for the planning of cryogenic surgical treatment of liver cancer. Percutaneous surgery simulation requires accurate modelling of the mechanical behaviour of soft tissue, and previous experimental characterizations have shown that linear elasticity is only a coarse approximation of the real properties of biological tissues. We first show that our model can simulate different types of non-linear and visco-elastic mechanical behaviours at speeds which are compatible with real-time applications. Then an experimental setup is presented which was used to characterize the mechanical properties of deer liver tissue under perforation by a biopsy needle. Experimental results demonstrate that a linear model is not suitable for simulating this application, while the proposed model succeeds in accurately modelling the axial load measured on the needle.

Animals↗
PubMed2006

Elastic fibres and vascular structure in hypertension.

Blood vessels are dynamic structures composed of cells and extracellular matrix (ECM), which are in continuous cross-talk with each other. Thus, cellular changes in phenotype or in proliferation/death rate affect ECM synthesis. In turn, ECM elements not only provide the structural framework for vascular cells, but they also modulate cellular function through specific receptors. These ECM-cell interactions, together with neurotransmitters, hormones and the mechanical forces imposed by the heart, modulate the structural organization of the vascular wall. It is not surprising that pathological states related to alterations in the nervous, humoral or haemodynamic environment-such as hypertension-are associated with vascular wall remodeling, which, in the end, is deleterious for cardiovascular function. However, the question remains whether these structural alterations are simply a consequence of the disease or if there are early cellular or ECM alterations-determined either genetically or by environmental factors-that can predispose to vascular remodeling independent of hypertension. Elastic fibres might be key elements in the pathophysiology of hypertensive vascular remodeling. In addition to the well known effects of hypertension on elastic fibre fatigue and accelerated degradation, leading to loss of arterial wall resilience, recent investigations have highlighted new roles for individual components of elastic fibres and their degradation products. These elements can act as signal transducers and regulate cellular proliferation, migration, phenotype, and ECM degradation. In this paper, we review current knowledge regarding components of elastic fibres and discuss their possible pathomechanistic associations with vascular structural abnormalities and with hypertension development or progression.

Animals↗
PubMed2005

Arterial elasticity measurement in renal transplant patients under anticalcineurin immunosuppression.

INTRODUCTION: Calcineurin inhibitors may be associated with decreased arterial elasticity and increased vascular risk. We measured pulse wave velocity (PWV) in large or small arteries as an index of elasticity. The aim of our study was to determine aortic and radial arterial elasticity in 30 stable kidney transplant patients treated with calcineurin inhibitor immunosuppression. PATIENTS AND METHODS: In stable kidney transplant patients we determined the usual biochemical parameters as well as lipid profiles, 24-hour blood pressure (BP) monitoring (CBPM) using a chronobiological program (Garapa), and PWV with a HDI-PWV CR-2000 monitor. RESULTS: Sixteen patients received cyclosporine (CsA, G-1) and 14 tacrolimus (G-2) immunosuppression. There were no baseline differences regarding age (G-1: 56 +/- 12 years, G-2: 56 +/- 14 years), renal transplant follow-up (G-1: 7 +/- 3 years, G-2: 7.5 +/- 3 years), Systolic BP, pulse pressure or plasma creatinine (G-1: 163 +/- 35 umol/L, G-2: 173 +/- 26 umol/L). Patients in the G-1 showed higher diastolic BP (79 +/- 11 vs 74 +/- 8 mm Hg), greater proteinuria (1.26 +/- 0.4 vs 0.6 +/- 0.2 g/d, P < .05), total cholesterol (5.51 +/- 1.2 mmol/L) and low-density lipoprotein (3.08 +/- 0.3 vs 2.99 +/- 0.3 mmol/L, P = NS). Aortic arterial elasticity was decreased in G-1 patients (10.4 +/- 6 vs 14.3 +/- 2 mL/mm Hg x10, P < .05) as well as that in the radial artery (G-1: 5.52 +/- 1 vs 5.57 +/- 1.2 mL/mm Hg x100, P = NS). Almost 100% of the patients presented normal diurnal BP with high nocturnal BP in a nondipper pattern in both groups. CONCLUSION: Calcineurin immunosuppression may contribute to arterial stiffness in kidney transplant patients. No differences between CsA or tacrolimus were observed in our study. CBPM and PWV are useful tools to evaluate subclinical atherosclerosis in renal transplant patients.

Adult↗
PubMed2004

Staging deep venous thrombosis using ultrasound elasticity imaging: animal model.

Deep venous thrombi undergo progressive hardening with age. However, the evolution rate remains poorly characterized by both invasive and noninvasive techniques. In a previous study (Emelianov et al. 2002), we demonstrated the potential of ultrasound elasticity imaging to noninvasively detect and age thrombus using a rat-based model. Knowing that thrombi harden over time is useful, but the value of the technique relies on whether the age of a thrombus can be predicted from strain estimates, and how accurate these predictions are. The objective of the present study is to answer these two questions. In the previous study, thrombus elasticity changes were monitored only on day 3, 6 and 9 after surgically induced formation of thrombosis in rat inferior vena cavas. In this study, ultrasound elasticity imaging was performed on two independent groups of rats (16 in total) starting from day 3 through day 10 with more temporal samples through the thrombus maturation process. For each rat, thrombus hardness was quantified at each scan interval by measures of normalized strains and reconstructed relative Young's moduli. In both groups, strain magnitudes exhibit progressive decrease as clots age. The relationship between the normalized strain and the clot age was developed from the first group and evaluated by the second group. Statistical analysis showed that the age estimation accuracy is within 0.8 day. If further research can successfully transfer the animal clot-hardening model to human patients, we believe that elasticity imaging will become a key component of venous compression ultrasound for effective diagnosis and treatment of deep venous thrombosis.

Animals↗
PubMed2005

Correspondence of ultrasound elasticity imaging to direct mechanical measurement in aging DVT in rats.

Previous ultrasound elasticity imaging experiments supported a generally accepted concept that the hardness of deep venous thrombi increases with thrombus aging. Results also showed that this noninvasive imaging technique can accurately predict thrombus age through strain estimates, in a well-controlled animal study. In the present study, as an alternative means to characterize elastic properties of thrombi, we used a direct mechanical measurement system to estimate Young's modulus of ex vivo thrombi. Unlike conventional indentation tests, the device uses a specific compression geometry for cylindrical tissue specimens. We also proposed an approximation scheme to retrieve Young's modulus from force-displacement measurements made using the device. Finite element simulations and calibrations on tissue-mimicking phantoms validated the system. Then, using two groups of rats with surgically-induced thrombi, we further investigated the correlation between Young's modulus measured ex vivo and elasticity images reconstructed in vivo. This comparison was accomplished by converting the intrathrombus strains measured in the in vivo studies into Young's modulus estimates using a model-based approach. Good agreement between time-dependent Young's modulus estimates observed in vivo and direct measurements of Young's modulus using the mechanical device helps to confirm the ability of elasticity imaging to age deep venous thrombi for efficient treatment.

Aging↗
PubMed2000

Impaired elastogenesis in Hurler disease: dermatan sulfate accumulation linked to deficiency in elastin-binding protein and elastic fiber assembly.

Hurler disease resulting from a deficiency in alpha-L-iduronidase, which causes an accumulation of dermatan sulfate and heparan sulfate glycosaminoglycans, is characterized by connective tissue and skeletal deformations, cardiomyopathy, cardiac valve defects, and progressive coronary artery stenosis. In this report, we present evidence that accumulation of dermatan sulfate but not heparan sulfate moieties is linked to impaired elastic fiber assembly that, in turn, contributes substantially to the development of the clinical phenotype in Hurler disease. Our data suggest that dermatan sulfate-bearing moieties bind to and cause functional inactivation of the 67-kd elastin-binding protein, a molecular chaperone for tropoelastin, which normally facilitates its secretion and assembly into elastic fibers. We demonstrate that, in contrast to normal skin fibroblasts and cells from Sanfilippo disease, which accumulate heparan sulfate, Hurler fibroblasts show reduced expression of elastin-binding protein and do not assemble elastic fibers, despite an adequate synthesis of tropoelastin and sufficient production of a microfibrillar scaffold of elastic fibers. Because cultured Hurler fibroblasts proliferate more quickly than their normal counterparts and the addition of exogenous insoluble elastin reduces their proliferation, we suggest that cell contacts with insoluble elastin play an important role in controlling their proliferation.

Adolescent↗
PubMed1999

A micromechanics model of the elastic properties of human dentine.

A generalized, self-consistent model of cylindrical inclusions in a homogeneous and isotropic matrix phase was used to study the effects of tubule orientation on the elastic properties of dentine. Closed-form expressions for the five independent elastic constants of dentine were derived in terms of tubule concentration, and the Young's moduli and Poisson ratios of peri- and intertubular dentine. An atomic-force microscope indentation technique determined the Young's moduli of the peri- and intertubular dentine as approx. 30 and 15 GPa, respectively. Over the natural variation in tubule density found in dentine, there was only a slight variation in the axial and transverse shear moduli with position in the tooth, and there was no measurable effect of tubule orientation. It was concluded that tubule orientation has no appreciable effect on the elastic behaviour of normal dentine, and that the elastic properties of healthy dentine can be modelled as an isotropic continuum with a Young's modulus of approx. 16 GPa and a shear modulus of 6.2 GPa.

Dentin↗
PubMed2000

Effect of chain length and unsaturation on elasticity of lipid bilayers.

Micropipette pressurization of giant bilayer vesicles was used to measure both elastic bending k(c) and area stretch K(A) moduli of fluid-phase phosphatidylcholine (PC) membranes. Twelve diacyl PCs were chosen: eight with two 18 carbon chains and degrees of unsaturation from one double bond (C18:1/0, C18:0/1) to six double bonds per lipid (diC18:3), two with short saturated carbon chains (diC13:0, diC14:0), and two with long unsaturated carbon chains (diC20:4, diC22:1). Bending moduli were derived from measurements of apparent expansion in vesicle surface area under very low tensions (0.001-0.5 mN/m), which is dominated by smoothing of thermal bending undulations. Area stretch moduli were obtained from measurements of vesicle surface expansion under high tensions (>0.5 mN/m), which involve an increase in area per molecule and a small-but important-contribution from smoothing of residual thermal undulations. The direct stretch moduli varied little (< +/-10%) with either chain unsaturation or length about a mean of 243 mN/m. On the other hand, the bending moduli of saturated/monounsaturated chain PCs increased progressively with chain length from 0.56 x 10(-19) J for diC13:0 to 1.2 x 10(-19) J for diC22:1. However, quite unexpectedly for longer chains, the bending moduli dropped precipitously to approximately 0.4 x 10(-19) J when two or more cis double bonds were present in a chain (C18:0/2, diC18:2, diC18:3, diC20:4). Given nearly constant area stretch moduli, the variations in bending rigidity with chain length and polyunsaturation implied significant variations in thickness. To test this hypothesis, peak-to-peak headgroup thicknesses h(pp) of bilayers were obtained from x-ray diffraction of multibilayer arrays at controlled relative humidities. For saturated/monounsaturated chain bilayers, the distances h(pp) increased smoothly from diC13:0 to diC22:1 as expected. Moreover, the distances and elastic properties correlated well with a polymer brush model of the bilayer that specifies that the elastic ratio (k(c)/K(A))(1/2) = (h(pp) - h(o))/24, where h(o) approximately 1 nm accounts for separation of the headgroup peaks from the deformable hydrocarbon region. However, the elastic ratios and thicknesses for diC18:2, diC18:3, and diC20:4 fell into a distinct group below the correlation, which showed that poly-cis unsaturated chain bilayers are thinner and more flexible than saturated/monounsaturated chain bilayers.

Biophysical Phenomena↗
PubMed2001

Elastic constants of polymer-grafted lipid membranes.

The surface expansion that is induced by the lateral pressure in the brush region of lipid membranes containing grafted polymers is deduced from the scaling and mean-field theories for the polymer brush, together with the equation of state for a lipid monolayer at the equivalence pressure with fluid lipid bilayers. Depending on the length and mole fraction of the polymer lipid, the membrane expansion can be appreciable. Direct experimental evidence for this lateral expansion comes from recent spin-label measurements with lipid membranes containing poly(ethylene glycol)-grafted lipids. The expansion in lipid area modifies the elastic constants of the polymer-grafted membranes in a way that opposes the direct elastic response of the polymer itself. Calculations as a function of polymer lipid content indicate that the net change in isothermal area expansion modulus of the membrane is negative but small, in contrast to previous predictions. A similar situation applies to the curvature elastic moduli of membranes containing short polymer lipids. For longer polymer lipids, however, the direct contribution of the polymer brush to the bending elastic constants dominates, and the increase in bending moduli with increasing polymer lipid content rapidly exceeds the basal values of the bare lipid membrane. The spontaneous (or intrinsic) curvature of the component monolayer of polymer lipid-containing membranes is calculated for the first time. The polymer brush contribution to spontaneous curvature scales quadratically with the polymer length, and at least quadratically with the mole fraction of polymer lipid.

Elasticity↗
PubMed1967

Wave propagation in a viscous fluid contained in an orthotropic elastic tube.

The problem of pressure wave propagation through a viscous fluid contained in an orthotropic elastic tube is considered in connection with arterial blood flow. Solutions to the fluid flow and elasticity equations are obtained for the presence of a reflected wave. Numerical results are presented for both isotropic and orthotropic elastic tubes. In particular, the pressure pulse, flow rate, axial fluid velocity, and wall displacements are plotted vs. time at various stations along the ascending aorta of man. The results indicate an increase in the peak value of the pressure pulse and a decrease in the flow rate as the pulse propagates away from the heart. Finally, the velocity of wave propagation depends mainly on the tangential modulus of elasticity of the arterial wall, and anisotropy of the wall accounts in part for the reduction of longitudinal movements and an increase in the hydraulic resistance.

Aorta↗
PubMed1973

The anisotropic elastic properties of the sarcolemma of the frog semitendinosus muscle fiber.

Tension and curvature of the sarcolemmal tube of the frog muscle fiber were measured at different extensions and were used to calculate the anisotropic elastic properties of the sarcolemma. A model was derived to obtain the four parameters of the elasticity matrix of the sarcolemma. Sarcolemmal thickness was taken as 0.1 mum. Over the range of reversible sarcolemmal tube extension, the longitudinal elastic modulus E(L) = 6.3 x 10(7) dyn/cm(2), the circumferential modulus E(c) = 0.88 x 10(7) dyn/cm(2), the longitudinal Poisson's ratio sigma(L) = 1.2, and the circumferential Poisson's ratio sigma(c) = 0.18. At tubular rest length E(L) = 1.2 x 10(7) dyn/cm(2). The sarcolemma is less extensible in the longitudinal direction along the fiber axis than in the circumferential direction. It can be extended reversibly to 48% of its rest length, equivalent to extending the intact fiber from a sarcomere length of 3 mum to about 4.5 mum. The sarcolemma does not contribute to intact fiber tension at fiber sarcomere lengths <3 mum, and between 3 and 4 mum its contribution is about 20%. It also exerts a pressure on the myoplasm, which can be calculated by means of the model. The longitudinal elastic modulus of the whole fiber is 1 x 10(5) dyn/cm(2) at a sarcomere length of 2.33 mum.

Animals↗