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PubMed1996

A Study of the Stationary Volumetric Elastic Modulus during Dehydration and Rehydration of Stems of Pea Seedlings.

The relationship between cortical-cell turgor pressure (P) and tissue water mass (W) was determined for stem segments of pea (Pisum sativum L.) seedlings subjected to hydration and dehydration. This allowed a test for elastic hysteresis in the cortical cells. The P-W curves for dehydration and hydration were not coincident. In some experiments, the P-W curves exhibited a "roll-off" at high P, similar to the "plateau effect" sometimes observed in pressure-chamber studies. When hydration was followed by a 4-h dehydration, the tissue water mass (W0) at minimum turgor was reduced. This might reflect a reduction in apoplastic water mass and/or a contraction of the symplast during dehydration. Neglecting the decrease in W0 leads to underestimates of the stationary volumetric elastic modulus ([epsilon]stat). The result of an analysis that assumes W0 was constant during hydration suggests that there was no significant difference in [epsilon]stat between dehydration and hydration and, hence, no significant elastic hysteresis. However, a 16-h dehydration increased [epsilon]stat; this might be a response to water stress.

Journal Article↗
PubMed1984

Salinity Effects on Water Potential Components and Bulk Elastic Modulus of Alternanthera philoxeroides (Mart.) Griseb.

Pressure volume curves for Alternanthera philoxeroides (Mart.) Griseb. (alligator weed) grown in 0 to 400 millimolar NaCl were used to determine water potential (Psi), osmotic potential (psi(s)), turgor potential (psi(p)) and the bulk elastic modulus (epsilon) of shoots at different tissue water contents. Values of psi(s) decreased with increasing salinity and tissue Psi was always lower than rhizosphere Psi. The relationship between psi(p) and tissue water content changed because epsilon increased with salinity. As a result, salt-stressed plants had larger ranges of positive turgor but smaller ranges of tissue water content over which psi(p) was positive. To our knowledge, this is the first report of such a salinity effect on epsilon in higher plants. These increases in epsilon with salinity provided a mechanism by which a large difference between plant Psi and rhizosphere Psi, the driving force for water uptake, could be produced with relatively little water loss by the plant. A time-course study of response after salinization to 400 millimolar NaCl showed Psi was constant within 1 day, psi(s) and psi(p) continued to change for 2 to 4 days, and epsilon continued to change for 4 to 12 days. Changes in epsilon modified the capacity of alligator weed to maintain a positive water balance and consideration of such changes in other species of higher plants should improve our understanding of salt stress.

Journal Article↗
PubMed1998

Elastographic imaging of low-contrast elastic modulus distributions in tissue.

Elastography is a new ultrasonic imaging technique that produces images of the strain distribution in compliant tissues. This strain distribution is derived from ultrasonically estimated longitudinal internal motion induced by an external compression of the tissue. The displayed two-dimensional (2-D) images are called elastograms. In this paper, it is demonstrated that, when signal-to-noise ratio-enhancing techniques are used, elastography is capable of imaging low-contrast elastic modulus tissue structures with high contrast-to-noise ratios. This is demonstrated using both computer simulations and data obtained from 3 days postmortem ovine kidneys in vitro. The elastograms of such organs suggest that the modulus slowly decays from the renal cortex (RC) to the interior of the renal sinus (RS). Such modulus variation is corroborated by independent measurements of the Young's moduli. It is found that the RC is approximately twice as hard as the interior of the RS. We invoke our previous results on elastographic contrast-transfer efficiency to demonstrate that, at low contrast, the elastogram may be interpreted as a quantitative image of the relative Young's modulus distribution.

Animals↗
PubMed1993

Arterial elastic modulus for fixed and varied wall volume.

It is commonly assumed that a blood vessel maintains a constant wall volume over a wide range of intraluminal pressures. We have found that vessel wall volume decreases under increasing load. To determine the effect of decreasing wall volume on values of Elastic modulus (Em), two computer models were used. The first model held volume constant with measured values of rabbit carotid artery length and width while thickness was calculated. In the second model wall volume was allowed to vary with measured length, width and thickness. Em increased with increasing load in both models with higher values in the nonconstant volume model. Up to 30% loading, the difference was 11% or less; above 30% loading, the difference increased to over 100%.

Animals↗
PubMed1999

Carotid arterial stiffness as a surrogate for aortic stiffness: relationship between carotid artery pressure-strain elastic modulus and aortic pulse wave velocity.

Common carotid arterial (CCA) stiffness can be assessed during carotid ultrasonography, but its association with aortic stiffness, a well-defined cardiovascular risk factor, has not been clarified. This study examines the relationship between CCA and aortic stiffness. CCA pressure-strain elastic modulus (Ep) and aortic pulse wave velocity (APWV) were evaluated in 110 healthy volunteers (age 56.2 +/- 14.6 y) by B-mode and Doppler ultrasonography. CCA Ep increased linearly with age and was higher in men than in women (model r2 = 0.50, p < 0.001). APWV increased quadratically with age (model r2 = 0.54, p < 0.001), similarly for women and men. Both CCA Ep and APWV were linearly associated with systolic blood pressure (BP) (r = 0.53 and 0.46, respectively) but not with diastolic BP. A linear relationship was found between CCA Ep and APWV (APWV = 194.7 + 5.67 x Ep [model r2 = 0.42, p < 0.001]). CCA Ep was associated with APWV (p < 0.001) independent of age, gender, and BP (model r2 = 0.62, p < 0.001), and the most parsimonious model to explain APWV included CCA Ep and age (APWV = 601.73 - 15.64 x age + 0.223 x age2 + 2.69 x Ep [model r2 = 0.60, p < 0.001]). Thus, CCA Ep is moderately associated with APWV. CCA stiffness as assessed by B-mode may be useful as a surrogate for aortic stiffness.

Aortic Diseases↗
PubMed1992

Intraoperative measurement of the elastic modulus of the vocal fold. Part 1. Device development.

Although the concept of manipulating laryngeal biomechanics to improve vocal function is not new, there has been a recent proliferation in surgical techniques used to affect laryngeal function. These include methods which increase the stiffness of the vocal folds, medialize the vocal folds, alter the pitch by changing the tension of the vocal folds, and augment the tissues using injection of alloplastic materials. Despite these new and possibly revolutionary methods, no means are presently available to surgeons to intraoperatively evaluate and optimize results of a surgical intervention. This study involved the development of a device to measure the in vivo elastic modulus of the vocal folds.

Animals↗
PubMed2004

Modeling of elastic modulus evolution of cirrhotic human liver.

A micromechanics-based composite model is developed for the elastic behavior and its modulus evolution of cirrhotic human liver correlated with different pathological stages. Microstructurally, the cirrhotic liver is hypothesized to be pathologically elastic nodules embedded in the soft tissue matrix whose hyperelastic behavior is controlled by the Veronda-Westmann model. Under finite deformation, the total strain energy of the liver is collected through the combination of that in nodule particles and that in the tissue matrix. The overall constitutive relation of the pathological liver can further be established through the nonlinear hyperelasticity theory. Predictions of the elastic modulus and its pathological evolution are compared with available experimental data.

Computer Simulation↗
PubMed1998

Fibronectin expression and aortic wall elastic modulus in spontaneously hypertensive rats.

Recent studies have shown that large-artery wall remodeling per se does not reduce distensibility in hypertension, indicating qualitative or quantitative changes in arterial components. The aim of the study was to determine in 1-year-old spontaneously hypertensive rats (SHRs) the changes in the elastic properties of large arteries, as assessed by the incremental elastic modulus (E(inc)), and the changes in the extracellular matrix, including fibronectin (FN) and alpha5beta1-integrin. The relationship between E(inc) and circumferential wall stress was calculated from in vivo pulsatile changes in blood pressure and arterial diameter by using a high-resolution echo-tracking system at the site of the abdominal aorta and in vitro medial cross-sectional area. E(inc)-stress curves and FN and integrin alpha5-subunit contents were determined for each animal. Mean stress and E(inc) were higher in SHRs than in Wistar rats. However, in a common range of stress, E(inc)-stress curves for SHRs were superimposable on those for Wistar rats, indicating that wall materials in both strains have equivalent mechanical behavior. Immunohistochemistry indicated that total FN, EIIIA FN isoform, and alpha5-integrin increased in the SHRs aortas without changes in elastin and collagen densities. Total FN was also increased in SHRs as determined by Western blot analysis. No differences in FN and alpha5-subunit mRNAs were detected between SHRs and Wistar rats. These results indicate that the aortic wall material of SHRs and Wistar rats have equivalent mechanical properties, although in SHRs it is subjected to a higher level of stress. By increasing cell-matrix attachment sites, FN may participate in the mechanical adaptation of both cellular and matrix components in SHRs.

Animals↗
PubMed2006

Interrelationship between noninvasive predictors of atherosclerosis: transthoracic coronary flow reserve, flow-mediated dilation, carotid intima-media thickness, aortic stiffness, aortic distensibility, elastic modulus, and brachial artery diameter.

BACKGROUND: In this study, we searched for a correlation between transthoracic coronary flow reserve (CFR) and well-established surrogates of coronary atherosclerosis. METHODS: The study was conducted on 136 healthy subjects (mean age: 39.9 +/- 7.3 years) who were free of coronary risk factors. Transthoracic echocardiography was used to measure the aortic stiffness index (AoSI), aortic distensibility (AoD), and aortic elastic modulus (AoEM). High-resolution ultrasound was used to measure brachial artery endothelium-dependent and independent vasomotion and carotid intima-media thickness (IMT). In addition, transthoracic second harmonic Doppler echocardiography was used to measure CFR. RESULTS: All of the parameters significantly correlated with each other except brachial endothelium-independent dilation. CFR correlated significantly with brachial endothelium-dependent dilation (EDD) (r = 0.302, P < 0.01), carotid IMT (r =-0.388, P < 0.01), brachial artery diameter (r = 0.340, P < 0.01), AoD (r = 0.275, P < 0.01), AoS (r =-0.299, P < 0.01), and AoEM (r =-0.30,7 P < 0.01). Carotid IMT correlated significantly with brachial EDD and modestly with brachial artery diameter, AoD, AoS, and AoEM.In multivariate analysis, carotid IMT (beta=-0.323, P < 0.0001) and brachial artery diameter (beta = -0.259, P = 0.001) were significant independent predictors of CFR. The left ventricular mass index (beta= 0.371, P < 0.0001), brachial EDD (beta = -0.232, P = 0.002), and CFR (beta = -0.228, P = 0.003) were significant predictors for IMT. CONCLUSION: Transthoracic CFR correlated significantly with well-established noninvasive predictors of atherosclerosis, and we suggest that it can be used as a surrogate for coronary atherosclerosis.

Adult↗
PubMed2004

Elastic modulus of the thin filament under normal conditions and during heart failure.

We developed an original approach to prepare samples for electron microscopy in electric field allowing calculation of the Youngs modulus of the thin filament in a direction perpendicular to the axis of the filament (longitudinal to the protomer) under normal conditions and during heart failure induced by 10-day toxic and allergic myocarditis. Electric field stretches thin filaments in the transverse direction and the increase in its diameter linearly depends on the applied voltage. The elastic modulus was in inverse proportion to the applied voltage. We found that during heart failure thin filament had an extreme conformation and to a great extent lost its mobility.

Animals↗
PubMed2005

Noninvasive method for estimation of complex elastic modulus of arterial vessels.

Pulse wave velocity (PWV) is widely used for estimating the stiffness of an artery. It is well-known that a stiffened artery can be associated with various diseases and with aging. Usually, PWV is measured using the "foot-to-foot" method in which the travel time of the wave is measured over a distance. The "foot" of the pressure wave is not clear due to reflected waves and blood noise. Also, PWV is an average indicator of artery stiffness between the two measuring points and, therefore, does not identify local stiffness variations. We propose producing a bending wave in the arterial wall using low-frequency, localized ultrasound radiation force and measuring the wave velocity along the arterial wall. The wave velocity can be measured accurately over a few millimeters. A mathematical model for wave propagation along the artery is developed with which the Young's modulus of the artery can be determined from measured wave velocities. Experiments were conducted on a pig carotid artery cast in a tissue-mimicking gelatin. The wave velocity was measured by the phase change at a known distance for a given frequency. The measured wave velocity is about 3 m/s at 100 Hz and 6.5 m/s at 500 Hz. The real part of complex elastic modulus of the artery is estimated to be 300 kPa.

Animals↗
PubMed1983

Bending elastic modulus of red blood cell membrane derived from buckling instability in micropipet aspiration tests.

Observation of cell membrane buckling and cell folding in micropipette aspiration experiments was used to evaluate the bending rigidity of the red blood cell membrane. The suction pressure required to buckle the membrane surface initially was found to be about one-half to two-thirds of the pressure that caused the cell to fold and move up the pipet. A simple analytical model for buckling of a membrane disk supported at inner and outer radii correlates well with the observed buckling pressures vs. pipet radii. The buckling pressure is predicted to increase in inverse proportion to the cube of the pipet radius; also, the buckling pressure depends inversely on the radial distance to the toroidal rim of the cell, normalized by the pipet radius. As such, the pressure required to buckle the membrane with 1 X 10(-4) cm diam pipet would be about four times greater than with a 2 X 10(-4) cm pipet. This is the behavior observed experimentally. Based on analysis of the observed buckling data, the membrane bending or curvature elastic modulus is calculated to be 1.8 X 10(-12) dyn-cm.

Elasticity↗
PubMed1983

Estimation of the volumetric elastic modulus and membrane hydraulic conductivity of willow sieve tubes.

Severed aphid stylets were used to follow the kinetics of sieve tube turgor and osmotic pressure (pi) responses following step changes in water potential applied to the cambial surface of willow (Salix exigua Nutt.) bark strips. The kinetics of the turgor response were monitored with a pressure transducer. In separate experiments, the kinetics of the pi response were followed by freezing point determinations on stylet exudate. The sieve tube volumetric elastic modulus in the bark strips was about 21 bars, but may be higher in intact stems. The membrane hydraulic conductivity was about 5 x 10(-3) centimeters per second per bar; several factors make it difficult to estimate its value accurately. Differences in the turgor pressure (P) and pi responses, as well as the relatively more rapid initial turgor response to a water potential (psi) change, suggested a time-dependent component in sieve tube wall elasticity.Our observations were generally not supportive of the idea that sieve tubes might osmoregulate. However, the bark strip system may not be suitable for addressing that question.Separate measurements of psi, P, and pi demonstrate that the relationship predicted by the fundamental cell water potential equation, psi = P - pi, is applicable within experimental error (+/- 0.4 bar) to sieve tube water relations.

Journal Article↗
PubMed2004

Antifactor Xa activity correlates to thrombin generation time, platelet contractile force and clot elastic modulus following ex vivo enoxaparin exposure in patients with and without renal dysfunction.

Antifactor Xa activity is the gold standard monitoring parameter for low molecular weight heparin (LMWH) derivatives. It is frequently measured in high-risk populations, such as patients with renal dysfunction. Despite antifactor Xa monitoring, however, bleeding in renal dysfunction patients receiving LMWH remains a problem. This study determined the relationship between antifactor Xa activity and three novel coagulation monitoring parameters: thrombin generation time (TGT), platelet contractile force (PCF) and clot elastic modulus (CEM). This study also assessed the effect of renal dysfunction on these relationships. This was an ex vivo pharmacodynamic study of the relationship between antifactor Xa activity and TGT, PCF and CEM in subjects both with and without renal dysfunction. Thirty subjects completed this study (10 controls, 10 chronic kidney disease subjects, and 10 end-stage renal disease subjects receiving hemodialysis). Blood samples obtained from participants were spiked with increasing enoxaparin concentrations (0.25, 0.5, 1.0 and 3.0 IU mL(-1)). Samples were analyzed for TGT, PCF and CEM. The relationship between antifactor Xa activity and TGT, PCF and CEM was determined by Pearson's correlation. The effect of renal dysfunction on the relationship between antifactor Xa activity and TGT, PCF and CEM was determined by analysis of covariance. There is strong correlation between antifactor Xa activity and TGT, CEM and PCF. The presence of renal dysfunction significantly prolongs the TGT, and decreases the CEM relative to controls. These results suggest that patients with renal dysfunction have a greater pharmacodynamic response to LMWH, independent of the pharmacokinetics of LMWH.

Adult↗
PubMed1976

Ventricular elastic modulus as a function of age in the Syrian golden hamster.

Analysis of passive right and left ventricular pressure-volume curves for hearts of 72 Syrian golden hamsters studied in vitro showed increases in ventricular weight, volume, and compliance at mid-age. Both ventricles were filled by syringe pumps at a constant rate. Ventricular compliance (dV/dP) was determined by electronic differentiation of the intraventricular pressures and formation of the ratio (dV/dt)/(dP/dt) as a continuous function of intraventricular pressure between 0 and 30 mm Hg. By relating, with justification, the left ventricle to a thin-walled elastic sphere, ventricular elastic moduli, E, for different ages were compared at constant levels of myocardial wall stress, sigma. The elastic modulus E proved to be a linear function of sigma. The slope of the E-sigma plot yielded a stiffness constant, K, for each age group. Body weight, heart weight, end-diastolic volume, and dV/dP all varied by more than 200% up and then down as a function of age, but K was not a significant function of age. These results suggest that the aging heart does not normally undergo substantial alterations in passive properties that affect the muscle cells and fibers themselves, but rather that the observed changes in compliance are primarily attributable to alterations in ventricular size.

Aging↗
PubMed2006

Non-mineralized fibrocartilage shows the lowest elastic modulus in the rabbit supraspinatus tendon insertion: measurement with scanning acoustic microscopy.

The acoustic properties of rabbit supraspinatus tendon insertions were measured by scanning acoustic microscopy. After cutting parallel to the supraspinatus tendon fibers, specimens were fixed with 10% neutralized formalin, embedded in paraffin, and sectioned. Both the sound speed and the attenuation constant were measured at the insertion site. The 2-dimensional distribution of the sound speed and that of the attenuation constant were displayed with color-coded scales. The acoustic properties reflected both the histologic architecture and the collagen type. In the tendon proper and the non-mineralized fibrocartilage, the sound speed and attenuation constant gradually decreased as the predominant collagen type changed from I to II. In the mineralized fibrocartilage, they increased markedly with the mineralization of the fibrocartilaginous tissue. These results indicate that the non-mineralized fibrocartilage shows the lowest elastic modulus among 4 zones at the insertion site, which could be interpreted as an adaptation to various types of biomechanical stress.

Adaptation, Physiological↗
PubMed2002

Increased carotid wall elastic modulus and fibronectin in aldosterone-salt-treated rats: effects of eplerenone.

BACKGROUND: Previous studies have demonstrated the development of cardiac fibrosis in aldosterone (Aldo)-salt hypertensive rats. Our aim was to determine the effects of Aldo and the Aldo receptor antagonist eplerenone (Epl) on in vivo mechanical properties of the carotid artery using echo-tracking system. METHODS AND RESULTS: Aldo was administered (1 microg/h) in uninephrectomized Sprague-Dawley rats (SD) receiving a high-salt diet from 8 to 12 weeks of age. Uninephrectomized control SD rats received a normal salt diet without Aldo. Three groups of Aldo-salt rats were treated with 1, 10, or 30 mg/kg(-1) x d(-1) of Epl by gavage. Elasticity was measured by elastic modulus (Einc)-wall stress curves using medial cross-sectional area (MCSA). The structure of the arterial wall was analyzed by histomorphometry (elastin and collagen), immunohistochemistry (EIIIA fibronectin, Fn), and Northern blot (collagens I and III). Aldo produced increased systolic arterial pressure, pulse pressure, Einc, MCSA, and EIIIA Fn with no change in wall stress or elastin and collagen densities compared with controls without Aldo. No differences in collagen mRNA levels were detected between groups. Epl blunted the increase in pulse pressure in Aldo rats and normalized Einc-wall stress curves, MCSA, and EIIIA Fn. These effects were dose dependent and not accompanied by a reduction in wall stress. CONCLUSIONS: Aldo is able to increase arterial stiffness associated with Fn accumulation, independently of wall stress. The preventive effects of Epl suggest a direct role for mineralocorticoid receptors in mechanical and structural alterations of large vessels in rat hyperaldosteronism.

Aldosterone↗