Influence of age on length and passive elastic stiffness characteristics of the calf muscle-tendon unit of women.
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BACKGROUND AND PURPOSE: Therapeutic stretching of the calf muscle-tendon unit is used to increase its length and to ameliorate decreased dorsiflexion range of motion (ROM), but the influence of age on the passive properties of the calf muscle-tendon unit has not been studied adequately The purpose of this study was to examine the influence of age on length and passive elastic stiffness (PES) characteristics of the calf muscle-tendon unit when stretched through the full, available dorsiflexion ROM. SUBJECTS: Twenty-four younger women (aged 20-39 years), 24 middle-aged women (aged 40-59 years), and 33 older women (aged 60-84 years) participated. METHODS: An isokinetic dynamometer was used to passively stretch the right calf muscle-tendon unit from relaxed plantar flexion to the maximal angle of available dorsiflexion at 5(us-1. The maximal passive resistive torque was measured, and passive angle-torque curves were constructed for a full ROM from an initial angle of passive resistive torque to the maximal dorsiflexion angle. The full ROM represented length extensibility. The average PES was calculated for this full stretch ROM and for the first half and the last half of this stretch ROM. The maximal passive dorsiflexion angle, maximal passive resistive torque, angular change for the full stretch ROM, and average PES for the full stretch ROM and the first half and the last half of the full stretch ROM were examined for group differences and their relationships with age. RESULTS: The maximal passive dorsiflexion angle, maximal passive resistive torque, angular change for the full stretch ROM, and average PES within the last half of the full stretch ROM were less for the older women than for the younger women. Age was negatively associated with these variables. CONCLUSION AND DISCUSSION: Decreased maximal passive dorsiflexion ROM in older women was associated with decreased maximal passive resistive torque, decreased calf muscle-tendon unit length extensibility, and decreased average PES within the last half of their available passive dorsiflexion ROM. (+info)
Intracellular elasticity and viscosity in the body, leading, and trailing regions of locomoting neutrophils.
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To investigate the mechanisms underlying pseudopod protrusion in locomoting neutrophils, we measured the intracellular stiffness and viscosity in the leading region, main body, and trailing region from displacements of oscillating intracellular granules driven with an optical trap. Experiments were done in control conditions and after treatment with cytochalasin D or nocodazole. We found 1) in the body and trailing region, the granules divided into a "fixed" population (too stiff to measure) and a "free" population (easily oscillated; fixed fraction 65%, free fraction 35%). By contrast, the fixed fraction in the leading region was <5%. 2) In the body and trailing region, there was no difference in stiffness or viscosity, but both were sharply lower in the leading region (respectively, 20-fold and 5-fold). 3) Neither cytochalasin D nor nocodazole caused a decrease in stiffness, but both treatments markedly reduced the fixed fraction in the body and trailing region to <20% and <40%, respectively. These observations suggest a discrete lattice structure in the body and trailing region and suggest that the developing pseudopod has a core that is more fluidlike, in the sense of a much lower viscosity and an almost total loss of stiffness. This is consistent with the contraction/solation hypothesis of pseudopodial formation. (+info)
Elastic properties and composition of the aortic wall in old spontaneously hypertensive rats.
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We hypothesized that age-linked changes in the composition and elastic properties of the arterial wall occur earlier in hypertensive than in normotensive rats. We evaluated the consequences of hypertension and aging on aortic mechanics, geometry, and composition in 3-, 9-, and 15-month-old awake Wistar-Kyoto rats (WKY) (normotensive) and spontaneously hypertensive rats (SHR) (hypertensive). The elastic modulus of the thoracic aorta, calculated from aortic pulse wave velocity and geometry, was higher in young and adult SHR than in age-matched WKY, as was wall stress; however, isobaric pulse wave velocity and pulse wave velocity-pressure curves were similar. Elastic modulus, isobaric pulse wave velocity, and the slope of the pulse wave velocity-pressure curve dramatically increased in old SHR compared with age-matched WKY; there was no further elevation of blood pressure or wall thickness. Fibrosis did not develop with age in SHR, and the ratio of elastin to collagen decreased in a similar fashion with aging in both strains. In conclusion, although elastic properties of the aortic wall are not intrinsically modified in young and adult SHR in comparison to age-matched WKY, aging is associated with a dramatic stiffening of the aortic wall in old SHR but not in WKY. Changes in blood pressure, aortic wall geometry, or scleroprotein composition do not appear to explain this age-linked aortic stiffening in SHR, suggesting that other mechanisms of disorganization of the media may be involved. (+info)
Functional and morphological heterogeneity of emphysema and its implication for selection of patients for lung volume reduction surgery.
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Lung volume reduction surgery (LVRS) in patients with advanced pulmonary emphysema aims to alleviate symptoms and enhance quality of life by improving respiratory mechanics. The theoretical concepts of the operation predict the greatest functional benefit in patients with marked hyperinflation, and with airflow obstruction due to loss of elastic recoil. Consistent observations in several centres, have confirmed these expectations. To achieve maximal reduction in lung volume at the least cost of functional tissue, resection is targeted to the lung zones with the most severe destruction by emphysema, leaving zones with relatively well-preserved tissue intact. Heterogeneity in emphysema distribution as assessed by visual scoring of the chest computed tomography scan according to a simple grading system has been shown to correlate with LVRS outcome variables. Therefore, evaluation of lung volume reduction surgery candidates has to include the functional and morphological characteristics of the emphysema as well as a general assessment of perioperative risk. However, the knowledge of potential predictive factors of lung volume reduction surgery outcome is so far based on retrospective analysis of highly selected patients. Therefore, many questions in respect of the selection of ideal candidates for this procedure remain unanswered at the present time. (+info)
Alteration of cross-linking amino acids of elastin in human aorta in association with dissecting aneurysm: analysis using high performance liquid chromatography.
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Elastic fiber is one of the major component of the extracellular matrix, which provides the resilience to many tissues. Elasticity is an important property of human aorta, and this elastic property decreases in various pathological conditions such as dissecting aneurysm (DA). Since the cross-linking structures in elastin are responsible for this elasticity, we studied the alteration of various cross-linking amino acids in human aorta associated with DA by a new method using high-performance liquid chromatography (HPLC). Materials were obtained from non-atherosclerotic areas of thoracic aorta of 27 autopsy cases which had no particular aortic disease and 19 cases of DA at replacement operation. After acid hydrolysis, SEP-PAK silica-gel column and Fe3+/activated charcoal column pretreatment were carried out for analysis of desmosine (DES), isodesmosine (ISDES), neodesmosine (NEO), oxodesmosine (OXO) and isooxodesmosine (ISOXO), and for analysis of aldosine (ALD), respectively. These prepared samples were applied to the reversed-phase HPLC column. We also analyzed pyridinoline (PYR), a major cross-linking amino acid of collagen as an index of fibrosis. All crosslinks of elastin were decreased in DA as compared to the age-matched control. The decrease of ISOXO was marked. The increase of PYR and PYR/(DES+ISDES) were not statistically significant. It is suggested oxidative degradation on elastin crosslinks occur in DA, and the ratio of collagen to elastin didn't contribute to the pathogenesis of DA. (+info)
Enzyme dynamics and activity: time-scale dependence of dynamical transitions in glutamate dehydrogenase solution.
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We have examined the temperature dependence of motions in a cryosolution of the enzyme glutamate dehydrogenase (GDH) and compared these with activity. Dynamic neutron scattering was performed with two instruments of different energy resolution, permitting the separate determination of the average dynamical mean square displacements on the sub-approximately 100 ps and sub-approximately 5 ns time scales. The results demonstrate a marked dependence on the time scale of the temperature profile of the mean square displacement. The lowest temperature at which anharmonic motion is observed is heavily dependent on the time window of the instrument used to observe the dynamics. Several dynamical transitions (inflexions of the mean squared displacement) are observed in the slower dynamics. Comparison with the temperature profile of the activity of the enzyme in the same solvent reveals dynamical transitions that have no effect on GDH function. (+info)
Desmin filaments studied by quasi-elastic light scattering.
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We studied polymers of desmin, a muscle-specific type III intermediate filament protein, using quasi-elastic light scattering. Desmin was purified from chicken gizzard. Polymerization was induced either by 2 mM MgCl(2) or 150 mM NaCl. The polymer solutions were in the semidilute regime. We concluded that the persistence length of the filaments is between 0.1 and 1 microm. In all cases, we found a hydrodynamic diameter of desmin filaments of 16-18 nm. The filament dynamics exhibits a characteristic frequency in the sense that correlation functions measured on one sample but at different scattering vectors collapse onto a single master curve when time is normalized by the experimentally determined initial decay rate. (+info)
Adhesion-induced receptor segregation and adhesion plaque formation: A model membrane study.
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A model system to study the control of cell adhesion by receptor-mediated specific forces, universal interactions, and membrane elasticity is established. The plasma membrane is mimicked by reconstitution of homophilic receptor proteins into solid supported membranes and, together with lipopolymers, into giant vesicles with the polymers forming an artificial glycocalix. The homophilic cell adhesion molecule contact site A, a lipid-anchored glycoprotein from cells of the slime mold Dictyostelium discoideum, is used as receptor. The success of the reconstitution, the structure and the dynamics of the model membranes are studied by various techniques including film balance techniques, micro fluorescence, fluorescence recovery after photobleaching, electron microscopy, and phase contrast microscopy. The interaction of the functionalized giant vesicles with the supported bilayer is studied by reflection interference contrast microscopy, and the adhesion strength is evaluated quantitatively by a recently developed technique. At low receptor concentrations adhesion-induced receptor segregation in the membranes leads to decomposition of the contact zone between membranes into domains of strong (receptor-mediated) adhesion and regions of weak adhesion while continuous zones of strong adhesion form at high receptor densities. The adhesion strengths (measured in terms of the spreading pressure S) of the various states of adhesion are obtained locally by analysis of the vesicle contour near the contact line in terms of elastic boundary conditions of adhesion: the balance of tensions and moments. The spreading pressure of the weak adhesion zones is S approximately 10(-9) J/m(2) and is determined by the interplay of gravitation and undulation forces whereas the spreading pressure of the tight adhesion domains is of the order S approximately 10(-6) J/m(2). (+info)