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Results for “Elastic Modulus”

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PubMed2005

The influence of circadian blood pressure changes on aortic distensibility and left ventricular diastolic function in hypertensive individuals.

BACKGROUND: Failure to decrease blood pressure (BP) normally during nighttime, which is called non-dipper, in hypertensive individuals is associated with higher cardiovascular morbidity and mortality. In addition, non-dipper BP leads to structural changes in the left ventricle; however, the influences of non-dipper BP on aortic elastic properties and left ventricular diastolic function have not been studied yet. METHODS: In this study, we evaluated aortic elastic properties and left ventricular diastolic function of 22 subjects with non-dipper hypertension, and 15 subjects with dipper hypertension using transthoracic second harmonic standard and tissue Doppler echocardiography (Acuson Sequoia C256). None of the subjects had any systemic disease or coronary risk factor except hypertension. RESULTS: Age, gender, body mass index, lipids, and standard echocardiographic findings including left ventricular mass index were similar between the groups. Office BP recordings were similar between non-dipper and dipper groups (147.9+/-6.1/93.9+/-4.3 vs. 144.0+/-8.0/93.0+/-3.7). Daytime and 24-h ambulatory BP measurements were similar within the groups, but nighttime BPs were significantly greater in non-dipper group than those were in dipper group. Left ventricular diastolic parameters obtained by both standard and tissue Doppler did not differ between the non-dipper and dipper groups. However, aortic distensibility was found to be slightly lower (4.1+/-2.4 vs. 4.9+/-1.9, p=0.08), and aortic stiffness index (6.3+/-0.5 vs. 6.1+/-0.4, p=0.08) and elastic modulus (6.2+/-2.5 vs. 4.8+/-2.3, p=0.08; groups non-dipper and dipper respectively) higher in non-dipper group than in dipper group. However, these differences were not statistically significant. CONCLUSION: Left ventricular remodeling and diastolic function were similar in patients with non-dipper and dipper hypertension. However, aortic elastic properties were slightly impaired in non-dipper hypertensives than those were in dipper ones, but these differences did not reach statistically significance.

Aorta, Thoracic↗

PubMed1997

Tissue equivalent vessel phantoms for intravascular ultrasound.

A tissue equivalent arterial vessel phantom has been developed for use in intravascular ultrasound imaging studies. The phantom material is constructed from a cross-linked gelatin matrix to which amorphous silica scattering particles are added. The ultrasonic properties (speed of sound, frequency-dependent attenuation coefficient and frequency-dependent backscatter coefficient) of the phantom material have been characterized at 42 MHz and correspond well with in vitro measurements of excised human arterial tissue. The mechanical properties of the cast vessel phantoms are controlled by varying the concentration of gelatin used in the matrix. Experimentally measured values of the circumferential Young's elastic modulus of hard and soft vessel phantoms agree well with values reported in the literature for human and canine arterial tissue for transmural pressures up to 100 mmHg. The phantoms are therefore suitable models for use in the development of new applications of intravascular ultrasound imaging, such as the assessment regional arterial elasticity.

Acoustics↗

PubMed1999

Noninvasive assessment of the viscoelasticity of peripheral arteries.

Currently used methods of examining the mechanical properties of blood vessel walls are either indirect or invasive, or measure vessel diameter and pressure waveforms at different sites. We developed a noninvasive technique to assess the mechanical properties and viscoelasticity of peripheral arteries. The pressure-strain elastic modulus (Ep) and the viscoelastic properties (energy dissipation ratio, EDR) of the common carotid artery (CCA), brachial artery (BA), radial artery (RA) and dorsalis pedis artery (DPA) were determined by means of palpating pressure and diameter distension waveforms extracted from high-resolution ultrasonography. The methodology was validated in vitro using an elastic tube phantom, as well as in vivo. In vivo study in 10 healthy volunteers (mean age 22 y) showed that the pressure-diameter curves were nonlinear, with an inflection at about 85-90 mmHg, and routed clockwise with slight hysteresis. The CCA (n = 5) had a mean diameter of 6.74 mm and the pulsatile diameter distension was 12.2%. The Ep calculated at the CCA was 0.44 x 10(6) dyne/cm2 with an EDR of 7.18%. The BA, RA and DPA (n = 10) had mean diameters of 3.91 mm, 2.21 mm and 2.12 mm; arterial strains of 4.60%, 4.25% and 8.91%; mean Ep of 1.39, 1.45, 0.90 x 10(6 )dyne/cm2; and mean EDRs of 6.34%, 6.15% and 5.60%, respectively. The method presented is relatively simple to implement clinically and has potential as a new diagnostic tool for detecting local vascular changes.

Adult↗

PubMed1987

Increased rigidity of red blood cell membrane in young spontaneously hypertensive rats.

The micropipette test was used to study the effects of age on the elasticity of red blood cell (RBC) membrane in spontaneously hypertensive rats (SHR) and age-matched normotensive Wistar-Kyoto rats (WKY), ranging from 3 to 23 weeks of age. The development of hypertension in the SHR started at 3 weeks and was fully established at 7 to 8 weeks. In the developmental phase of hypertension (3-5 weeks), the SHR showed a significant increase in RBC membrane elastic modulus (i.e., a decrease in RBC membrane deformability) when compared with the age-matched normotensive control rats (WKY). After the establishment of hypertension (7-8 weeks), however, the deformability of the RBC membrane of SHR improved and became comparable to that of the WKY. These results indicate that abnormal erythrocyte membrane elasticity is an early event in SHR and that adaptive recovery occurs when hypertension is fully developed.

Aging↗

PubMed2000

Mechanism of free radicals on the molecular fluidity and chemical structure of the red cell membrane damage.

This paper investigated the mechanism for the rheological dysfunction of red blood cell (RBC) caused by free radicals. Normal RBCs were collected from healthy volunteers. Fenton system was added to the RBCs and allowed to react for 30 minutes in vitro. The RBC membrane molecules were damaged due to the free radicals reaction. It was found that: (1) The protein configurations changed such as the ratio decreasing in alpha-helix and increasing in both of beta-sheet and coiled-coil; (2) -P=O/-P-O chemical group ratio in phospholipids increases; (3) the molecular rotational correlation times of proteins and lipids were extremely elevated; (4) the membrane shear elastic modulus was significantly enhanced. The present results support that the chemical structure changes led by free radicals are ultimately responsible for the reduction in molecular fluidity of RBC membrane.

Elasticity↗

PubMed1978

The effect of age on the distensibility of the abdominal aorta of man.

The variation with age in distensibility and the dimensions of the abdominal aorta at the bifurcation have been measured in 43 fresh human cadavers. The age range was from birth to 69 years, both sexes being represented. Patients with vascular disease were excluded. Barium sulfate infused into the aorta through an iliac artery enabled the change in diameter to be measured from a roentgenogram with change in pressure. Incremental strain value could thus be calculated. Strain value increased from 0.02 at birth to a maximum at the end of the first decade of life and then decreased to less than 0.01 by the age of 70 years. Aortas in the age group of four to 11 years showed less stiffness with increasing pressure than at other ages. Variations of strain with age correlate with alterations in the ratio of aortic wall collagen to elastin in the young. An increase in the thickness of the wall and an atheroma, in response to prolonged hemodynamic stress, account for increased stiffness in the older age groups. Other age and disease factors may play a part, but further work is required in man to examine the role of relative wall thickness, elastic modulus and alteration in wall structure in determining the variation of aortic distensibility with age reported herein.

Adolescent↗

PubMedDate not supplied

Segmental differences in geometric, elastic and contractile characteristics of small intramural coronary arteries of the rat.

The depedence of elastic and contractile properties on the caliber of small intramural coronary arteries was investigated in the rat in vitro. Different segments of the left anterior descending coronary artery branching system were prepared for microarteriography. The segments were cannulated at both ends, immersed in oxygenated normal Krebs Ringer (nKR) solution. Intraluminal pressure was changed at a rate of about 0.5 mm Hg/s between 0 and 150 mm Hg in repeated cycles. The outer diameter was continuously measured with microangiometry. Pressure-diameter curves were recorded after preconditioning pressure cycles in nKR, with PGF2alpha in the bath (7.5 x 10(-6) M), and in maximal relaxation with papaverine (2.8 x 10(-4) M). Biomechanical parameters were computed for vessels grouped according to their calibers (inner diameters: 50-150, 150-250, 250-350, >350 microm). Distensibility and contractility decreased with increasing caliber of the vessels, while the elastic modulus increased. Spontaneous tone was (at 100 mm Hg in mechanically preconditioned vessels) 18.8 +/- 4.5, 8.4 +/- 4.4, 9.7 +/- 3.7 and 8.3 +/- 3.8% in the four groups, respectively. PGF2alpha contraction was maximal around the 300- microm caliber. Our study is the first direct demonstration that intramural small coronary arteries exhibit characteristic variability in their elastic and contractile properties as a function of their caliber. Such differences may be important in segmentally specific control processes of the coronary microcirculation.

Animals↗

PubMed1995

Cancellous bone Young's modulus variation within the vertebral body of a ligamentous lumbar spine--application of bone adaptive remodeling concepts.

Bone remodeling theory based on strain energy density (SED) as the feedback control variable was used in conjunction with the finite element method to analyze the shape of the vertebral bodies within the ligamentous motion segment. The remodeling theory was once again applied to the altered two motion segments model to predict the Young's modulus distribution of the cancellous bone within the vertebral bodies. A three-dimensional finite element model of the two motion segments ligamentous lumbar spine (L3-5) was developed. Bone remodeling response (external as well as internal) of the motion segments to a uniaxial compressive load of 424.7 N was studied. The external shape of the converged model matched the normal shape of a vertebral body. The internal remodeling resulted in regional cancellous bone Young's moduli (or bone density) distributions similar to those reported in the literature; posterocentral regions of the vertebrae were predicted to have greater values of the elastic modulus than that of the outer regions. The results of the present study suggest that vertebral body assumes an adequate/optimum structure in terms of both its shape and its elastic moduli distribution within the cancellous region in response to the applied load. Extensions of the present model and its clinically relevant applications are discussed.

Adaptation, Physiological↗

PubMed1999

Effect of capping protein, CapZ, on the length of actin filaments and mechanical properties of actin filament networks.

We report on how physiological concentrations of capping protein shorten actin filaments and on the remarkably fluid nature of solutions of such short filaments even at the high concentrations that exist in cells. We measured the lengths of actin filaments formed by spontaneous polymerization of highly purified actin monomers by fluorescence microscopy after labeling with rhodamine-phalloidin. The length distributions are exponential with a mean of about 7 microm (2600 subunits). As observed previously with less quantitative assays, copolymerization with the actin capping protein, CapZ, reduces the length of the filaments. At cellular concentrations of capping protein, one filament forms for each molecule of capping protein and the population of filaments is uniformly short. Using CapZ to vary the length of actin filaments, we measured how their mechanical properties depend on length. The stiffness (elastic modulus) of actin filament networks depends steeply on the length, with long filaments contributing far out of proportion to their numbers to the stiffness. Even at physiological concentrations (300 microM), networks of filaments limited to lengths observed in cells with a 1 to 500 molar ratio of CapZ are more fluid and much less elastic than lower concentrations of longer actin filaments. Thus the high concentration of short actin filaments in cells must be crosslinked to produce the observed stiffness of the cortex.

Actins↗

PubMed1980

The fracture strength of amalgam overlying base materials.

Conclusions reached within the constraints of this study showed the following: 1. Fracture strength of Class II amalgam restorations decreased as the thickness of the bases increased. 2. Fracture strengths of amalgam restorations based with different thicknesses of zinc phosphate cement underline with 0.5 mm Dycal were not different from each other. 3. The strength of the restorations varied with the type of base. Zinc phosphate cement is equal to no base and superior to zinc phosphate cement plus Dycal, which is equal to Dycal. Dycal is superior to Cavitec, which is the same as Cavitec plus Dycal. 4. The base materials did not fracture. The amalgam restorations were stronger over a base with a higher modulus of elasticity, indicating that modulus of elasticity of a base is more important than compressive strength in supporting an amalgam restoration. 5. There is no advantage (no improvement in resistance to fracture of the amalgam restoration) to be gained from placing zinc phosphate cement over Dycal. 6. When a calcium hydroxide liner is not needed, the cements with a higher modulus of elasticity, such as zinc phosphate cement and reinforced ZOE, will provide for stronger amalgam restorations than Cavitec and unreinforced ZOE.

Calcium Hydroxide↗

PubMed2003

Differentiation of primary and secondary Raynaud's disease by carotid arterial stiffness.

INTRODUCTION: primary Raynaud's disease may be difficult to differentiate clinically from the secondary form with an underlying connective tissue, haematological, neurovascular or drug-induced disorder. We undertook a study to determine the elastic carotid and muscular femoral arterial biomechanical properties and intima-media thickness (IMT) in subjects with primary and secondary Raynaud's disease, to assess whether these parameters could differentiate the two conditions. METHODS: twenty patients with primary Raynaud's disease and 53 subjects with secondary Raynaud's associated with scleroderma (systemic sclerosis, SSc) had measurements of their carotid and femoral wall mechanics with a duplex scanner coupled to a Wall Track system. Their age, gender, body mass index, heart rate, systolic and diastolic blood pressures, presumed cardiovascular load, plasma creatinine, fasting cholesterol, triglyceride and glucose concentrations were also measured. RESULTS: the carotid elastic properties [mean (SD): elastic modulus: 560 (180) vs 1204 (558) mmHg,p <0.001 and stiffness index: 5.69 (1.35) vs 11.92 (6.4), p<0.001 for primary and secondary Raynaud's respectively] were significantly impaired in patients with secondary Raynaud's disease even after adjustment for potentially influencing physiological and biochemical variables. There were no statistical differences in the femoral elastic properties or the carotid and femoral IMTs between the two groups. CONCLUSION: Duplex determination of the carotid elasticity or stiffness is different in primary Raynaud's phenomenon compared with secondary Raynaud's associated with SSc. This may be a useful non-invasive tool, in addition to autoantibody markers and nail-fold capillaroscopy, to differentiate between the two forms of Raynaud's phenomenon.

Adult↗

PubMed1975

Cutaneous extensibility in pseudo-xanthoma elasticum.

In vivo skin elasticity was measured on unaffected forearm skin of twenty-five patients with pseudo-xanthoma elasticum and compared with age and sex-matched controls. The elastic modulus was raised in the recessive type I group and reduced in the dominant types I and II groups. No significant difference in skin thickness was found.

Adult↗

PubMed2004

Alternatives in polymerization contraction stress management.

Polymerization contraction stress of dental composites is often associated with marginal and interfacial failures of bonded restorations. The magnitude of stress depends on composite composition (filler content and matrix composition) and its ability to flow before gelation, which is related to the cavity configuration and curing characteristics of the composite. This article reviews variations among studies regarding contraction-stress-testing methods and contraction stress values of current composites, and discusses the validity of contraction stress studies in relation to results from microleakage tests. The effects of lower curing rates and alternative curing routines on contraction stress values are also discussed, as well as the use of low-elastic-modulus liners. Moreover, studies with experimental dimethacrylate-based composites and recent developments in low-shrinkage monomers are described.

Composite Resins↗

PubMed1975

The transcutaneous measurement of the elastic properties of the human saphenous vein femoropopliteal bypass graft.

The pressure-strain elastic modulus and compliance of 20 reversed saphenous femoropopliteal vein grafts have been measured by a noninvasive, ultrasonic method. The grafts had been in place for an average of 33.6 months, 11 days to 128 months. In this study no correlation was demonstrated between wall stiffness and duration of implantation. It is concluded that the elastic properties of vein grafts may remain stable for considerable periods of time.

Adult↗

PubMed1992

Non-invasive measurements of arterial compliance in hypertensive compared with normotensive adults.

AIM: To determine differences in arterial compliance attributable to hypertension. METHODS: Since measurements of arterial compliance have tended to vary in the past according to the method used, a new technique comprising carotid ultrasound and simultaneous, calibrated, carotid pressure waveform measurements was tested in 43 hypertensives and 43 control subjects matched for age, gender and body size. RESULTS: There was a significant reduction in compliance among the hypertensive patients, as estimated by the elastic modulus and the ratio of stroke volume to pulse pressure. However, when the non-linearity of the pressure-volume relationship and the impact of distending pressure were taken into account, by the arterial stiffness index and by the increase in arterial wall thickness associated with hypertension by Young's modulus, there were no significant differences in arterial compliance between the two groups.

Adult↗

PubMed2001

Nonlinear behavior of trabecular bone at small strains.

Study of the behavior of trabecular bone at strains below 0.40 percent is of clinical and biomechanical importance. The goal of this work was to characterize, with respect to anatomic site, loading mode, and apparent density, the subtle concave downward stress-strain nonlinearity, that has been observed recently for trabecular bone at these strains. Using protocols designed to minimize end-artifacts, 155 cylindrical cores from human vertebrae, proximal tibiae, proximal femora, and bovine proximal tibiae were mechanically tested to yield at 0.50 percent strain per second in tension or compression. The nonlinearity was quantified by the reduction in tangent modulus at 0.20 percent and 0.40 percent strain as compared to the initial modulus. For the pooled data, the mean +/- SD percentage reduction in tangent modulus at 0.20 percent strain was 9.07+/- 3.24 percent in compression and 13.8 +/- 4.79 percent in tension. At 0.40 percent strain, these values were 23.5 +/- 5.71 and 35.7+/- 7.10 percent, respectively. The magnitude of the nonlineari't depended on both anatomic site (p < 0.001) and loading mode (p < 0.001), and in tension was positively correlated with density. Calculated values of elastic modulus and yield properties depended on the strain range chosen to define modulus via a linear curve fit (p < 0.005). Mean percent differences in 0.20 percent offset yield strains were as large as 10.65 percent for some human sites. These results establish that trabecular bone exhibits nonlinearity at low strains, and that this behavior can confound intersite comparisons of mechanical properties. A nonlinear characterization of the small strain behavior of trabecular bone was introduced to characterize the initial stress-strain behavior more thoroughly.

Aged↗

PubMed2004

Phosphoryl choline introduces dual activity in biomimetic ionomers.

Dual activity of phosphoryl choline (PC) functional poly(trimethylene carbonate) (PTMC) was found which induces the zwitterionic biomimetic PC group to form physical cross-links with ionomers in the bulk, and at the same time enrich at the surface of cast films. The formation of zwitterionic domains from a bifunctional PC-PTMC-PC (ionomer) provided firm films with a low elastic modulus in contrast to the tacky PTMC starting material (Mn approximately 3900 g/mol) with poor mechanical performance. In addition, the ionomer possessed improved hemocompatible properties that was explained by the enrichment of PC at the surface, suggesting a way to tailor the mechanical performance of biodegradable PTMC-based ionomers while providing its bioactivity. Tailored elasticity while maintaining hemocompatibility of a biodegradable ionomer should be of particular interest for a variety of in vivo applications.

Biocompatible Materials↗

PubMed1997

Elastic protein-based materials in tissue reconstruction.

In natural tissues, cells form multiple attachment sites to their extracellular matrix. By means of those attachments, cells deform as the tissue deforms in response to the natural mechanical stresses and strains that the tissue must sustain during function. These mechanical forces are the energy input that instruct the cells to produce the extracellular matrix sufficient to sustain those forces. Thus, an ideal artificial material should have both the attachment sites for the natural cells and a compliance that matches the natural tissue. Elastic protein-based polymers have been designed to provide both cell attachment sites and to exhibit the required elastic modulus of the tissue to be replaced. Thus, this introduces the potential to design a temporary functional scaffolding that will be remodeled, while functioning, into a natural tissue. A feasibility study applies this concept to the problem of urinary bladder reconstruction in terms of the filling and emptying of a simulated bladder comprised of an elastic protein-based matrix containing cell attachment sites with human urothelial cells growing out onto the dynamic matrix. Furthermore, the elastic protein-based materials themselves have been designed to perform the set of energy conversions that occur in living organisms and, in particular, to convert mechanical energy into chemical energy with the result of chemical signals of the sort that could provide the stimuli to turn on the genes for producing the required extracellular proteins.

Animals↗