A mechanical model for adjustable passive stiffness in rabbit detrusor

2006 ◽  
Vol 101 (4) ◽  
pp. 1189-1198 ◽  
Author(s):  
John E. Speich ◽  
Kevin Quintero ◽  
Christopher Dosier ◽  
Lindsey Borgsmiller ◽  
Harry P. Koo ◽  
...  
Keyword(s):  
Steady State ◽  
Mechanical Model ◽  
Strain Softening ◽  
Slow Component ◽  
Viscoelastic Model ◽  
Passive Force ◽  
Passive Stiffness ◽  
Cross Link ◽  
Force Relaxation ◽  
Adjustable Passive Stiffness

Strips of rabbit detrusor smooth muscle (DSM) exhibit adjustable passive stiffness characterized by strain softening: a loss of stiffness on stretch to a new length distinct from viscoelastic behavior. At the molecular level, strain softening appears to be caused by cross-link breakage and is essentially irreversible when DSM is maintained under passive conditions (i.e., when cross bridges are not cycling to produce active force). However, on DSM activation, strain softening is reversible and likely due to cross-link reformation. Thus DSM displays adjustable passive stiffness that is dependent on the history of both muscle strain and activation. The present study provides empirical data showing that, in DSM, 1) passive isometric force relaxation includes a very slow component requiring hours to approach steady state, 2) the level of passive force maintained at steady state is less if the tissue has previously been strain softened, and 3) tissues subjected to a quick-release protocol exhibit a biphasic response consisting of passive force redevelopment followed by force relaxation. To explain these and previously identified characteristics, a mechanical model for adjustable passive stiffness is proposed based on the addition of a novel cross-linking element to a hybrid Kelvin/Voigt viscoelastic model.

Adjustable passive length-tension curve in rabbit detrusor smooth muscle

2007 ◽  
Vol 102 (5) ◽  
pp. 1746-1755 ◽  
Author(s):  
John E. Speich ◽  
Christopher Dosier ◽  
Lindsey Borgsmiller ◽  
Kevin Quintero ◽  
Harry P. Koo ◽  
...  
Keyword(s):  
Smooth Muscle ◽  
Strain Softening ◽  
Muscle Length ◽  
Strain History ◽  
Total Force ◽  
Detrusor Smooth Muscle ◽  
Passive Force ◽  
Passive Stiffness ◽  
Active Force ◽  
Length Changes

Until the 1990s, the passive and active length-tension ( L-T) relationships of smooth muscle were believed to be static, with a single passive force value and a single maximum active force value for each muscle length. However, recent studies have demonstrated that the active L-T relationship in airway smooth muscle is dynamic and adapts to length changes over a period of time. Furthermore, our prior work showed that the passive L-T relationship in rabbit detrusor smooth muscle (DSM) is also dynamic and that in addition to viscoelastic behavior, DSM displays strain-softening behavior characterized by a loss of passive stiffness at shorter lengths following a stretch to a new longer length. This loss of passive stiffness appears to be irreversible when the muscle is not producing active force and during submaximal activation but is reversible on full muscle activation, which indicates that the stiffness component of passive force lost to strain softening is adjustable in DSM. The present study demonstrates that the passive L-T curve for DSM is not static and can shift along the length axis as a function of strain history and activation history. This study also demonstrates that adjustable passive stiffness (APS) can modulate total force (35% increase) for a given muscle length, while active force remains relatively unchanged (4% increase). This finding suggests that the structures responsible for APS act in parallel with the contractile apparatus, and the results are used to further justify the configuration of modeling elements within our previously proposed mechanical model for APS.

scholarly journals Rhythmic contraction generates adjustable passive stiffness in rabbit detrusor

2010 ◽  
Vol 108 (3) ◽  
pp. 544-553 ◽  
Author(s):  
Atheer M. Almasri ◽  
Paul H. Ratz ◽  
Hersch Bhatia ◽  
Adam P. Klausner ◽  
John E. Speich
Keyword(s):  
Kinase Inhibitor ◽  
Smooth Muscles ◽  
Physiological Role ◽  
Passive Tension ◽  
Passive Stiffness ◽  
Vascular Smooth Muscles ◽  
Rhythmic Contraction ◽  
Length Changes ◽  
Changes Over Time ◽  
Adjustable Passive Stiffness

The length-tension ( L-T) relationships in airway and vascular smooth muscles have been shown to adapt with length changes over time. Our prior studies have shown that the active and passive L-T relationships in rabbit detrusor smooth muscle (DSM) can adapt and that DSM exhibits adjustable passive stiffness (APS) characterized by a passive L-T curve that is a function of strain and activation history. The present study demonstrates that passive tension due to APS can represent a substantial fraction of total tension over a broad length range. Our previous studies have shown that maximal KCl-induced contractions at short muscle lengths generate APS that is revealed by increased pseudo-steady-state passive tension at longer lengths compared with previous measurements at those lengths. The objective of the present study was to determine the mechanisms involved in APS generation. Increasing the number of KCl-induced contractions or the duration of a contraction increased the amount of APS generated. Furthermore, a fraction of APS was restored in calcium-free solution and was sensitive to the general serine and threonine protein kinase inhibitor staurosporine. Most importantly, rhythmic contraction (RC) generated APS, and because RC occurs spontaneously in human bladder, a physiological role for RC was potentially identified.

scholarly journals Correction to Mechanics of a Dual Cross-Link Gel with Dynamic Bonds: Steady State Kinetics and Large Deformation Effects

2016 ◽  
Vol 49 (11) ◽  
pp. 4378-4378 ◽  
Author(s):  
Jingyi Guo ◽  
Rong Long ◽  
Koichi Mayumi ◽  
Chung-Yuen Hui
Keyword(s):  
Steady State ◽  
Large Deformation ◽  
Cross Link ◽  
Steady State Kinetics

scholarly journals Studies on dielectric relaxation in relation to viscosity of some anilines, phenol, and their binary mixtures at microwave frequencies

2019 ◽  
Vol 97 (2) ◽  
pp. 210-215
Author(s):  
C.V. Maridevarmath ◽  
G.H. Malimath
Keyword(s):  
Relaxation Time ◽  
Steady State ◽  
Dynamic Viscosity ◽  
Room Temperature ◽  
Viscoelastic Model ◽  
Frictional Resistance ◽  
Nonlinear Behaviour ◽  
Viscoelastic Relaxation ◽  
Microwave Frequencies ◽  
Loss Formula

In the present work, the study of variation of relaxation time (τ) with viscosity of the medium (η) is carried out on four polar samples: 2-Nitroaniline, 4-Bromoaniline, 4-Chloroaniline, 4-Chlorophenol, and also on the binary mixture of 2-Nitroaniline + 4-Bromoaniline at room temperature by using microwave bench operating at a frequency of 9.59 GHz. In this regard, the different parameters like dielectric constant ([Formula: see text]), dielectric loss ([Formula: see text]), relaxation time (τs), macroscopic steady state viscosity (ηs), dynamic viscosity (ηd), and viscoelastic relaxation time (τve) were determined for all the systems. It is observed that the relaxation time (τs) increases with the increase in the viscosity of the medium for all the systems. Plots of log(τs) versus log(ηs) for all the systems show that variation of relaxation time is found to be nonlinear in the higher viscosity regions. This suggests the failure of Debye’s theory at these regions. Further, the nonlinear behaviour of relaxation time with the viscosity is explained by using the viscoelastic model suggested by Barlow et al. (Proc. R. Soc. A 309, 473 (1969). doi: 10.1098/rspa.1969.0053 ). It is also observed that macroscopic steady state viscosity (ηs) values are greater than the dynamic viscosity (ηd), and viscoelastic relaxation time (τve) values were found to be lower compared to the relaxation time (τs). These results suggest that the effective frictional resistance experienced by the molecules during reorientation is lower and the measured values of macroscopic steady state viscosity (ηs) are frequency dependent.

Sodium tracer kinetics and transmembrane flux in tissue-cultured chick heart cells

1982 ◽  
Vol 243 (3) ◽  
pp. C169-C176 ◽  
Author(s):  
D. M. Wheeler ◽  
C. R. Horres ◽  
M. Lieberman
Keyword(s):  
Steady State ◽  
Slow Component ◽  
Heart Cells ◽  
Kinetic Measurements ◽  
Considerable Difficulty ◽  
Control Value ◽  
Na Efflux ◽  
Nonmuscle Cells ◽  
Chick Heart ◽  
Efflux Kinetics

Considerable difficulty has been encountered in defining the physiological significance of sodium tracer kinetic measurements in cardiac muscle. In this study, 24Na+ efflux experiments were performed by directly monitoring tissue radioactivity during the superfusion of growth-oriented embryonic chick heart cells in tissue cultured. The cellular 24Na+ efflux from contractile preparations exhibited at least two exponential components whereas noncontractile, fibroblastlike preparations had a single efflux component similar in rate to the slower component of the contractile preparations. We concluded that the slow component represents efflux from nonmuscle cells, whereas the faster component reflects the muscle cell compartment. The mean Na+ efflux rate constants for contractile preparations (beating 150 min-1) were 3.1 and 0.35 min-1. Intracellular Na+ concentrations, as determined by isotope uptake and by flame photometry, were 18 and 16 mM for contractile and nonmuscle preparations, respectively. The steady-state, transmembrane fluxes are 98 and 5 pmol . cm-2 . s-1 for muscle and nonmuscle cells, respectively. The Na+ efflux kinetics in 10(-4) M ouabain were reduced by approximately 16% from the control value. These findings indicate that the greater part of the steady-state Na+ efflux in cultured heart cells is due to mechanisms other than the Na+-K+ pump.

scholarly journals CHEMO-MECHANICAL MODEL FOR PREDICTING THE LIFETIME OF EPDM RUBBERS

2019 ◽  
Vol 92 (4) ◽  
pp. 722-748 ◽  
Author(s):  
Xavier Colin ◽  
Mouna Ben Hassine ◽  
Moussa Nait-Abelaziz
Keyword(s):  
Mechanical Behavior ◽  
Thermal Aging ◽  
Mechanical Model ◽  
Degradation Kinetics ◽  
Weight Changes ◽  
Cross Link ◽  
Elementary Reactions ◽  
Industrial Material ◽  
Macromolecular Network ◽  
Concentration Changes

ABSTRACT A chemo-mechanical model has been developed for predicting the long-term mechanical behavior of EPDM rubbers in a harsh thermal oxidative environment. Schematically, this model is composed of two complementary levels: The “chemical level” calculates the degradation kinetics of the macromolecular network that is introduced into the “mechanical level” to deduce the corresponding mechanical behavior in tension. The “chemical level” is derived from a realistic mechanistic scheme composed of 19 elementary reactions describing the thermal oxidation of EPDM chains, their stabilization against oxidation by commercial antioxidants but also by sulfide bridges, and the maturation and reversion of the macromolecular network. The different rate constants and chemical yields have been determined from a heavy thermal aging campaign in air between 70 and 170 °C on four distinct EPDM formulations: additive free gum, unstabilized and stabilized sulfur vulcanized gum, and industrial material. This “chemical level” has been used as an inverse resolution method for simulating accurately the consequences of thermal aging at the molecular (concentration changes in antioxidants, carbonyl products, double bonds, and sulfide bridges), macromolecular (concentration changes in chain scissions and cross-link nodes), and macroscopic scales (weight changes). Finally, it gives access to the concentration changes in elastically active chains from which are deduced the corresponding changes in average molar mass MC between two consecutive cross-link nodes. The “mechanical level” is derived from a modified version of the statistical theory of rubber elasticity, called the phantom network theory. It relates the elastic and fracture properties to MC if considering the macromolecular network perfect, and gives access to the lifetime of the EPDM rubber based on a relevant structural or mechanical end-of-life criterion. A few examples of simulations are given to demonstrate the reliability of the chemo-mechanical model.

Investigation of Flow Stress Behavior and Microstructural Evolution of 7050 Al Alloy

2007 ◽  
Vol 546-549 ◽  
pp. 1065-1068 ◽  
Author(s):  
You Ping Yi ◽  
Hua Chen ◽  
Yong Cheng Lin
Keyword(s):  
Steady State ◽  
Strain Softening ◽  
Type Equation ◽  
Al Alloy ◽  
Compression Tests ◽  
Hollomon Parameter ◽  
Deformation Behaviors ◽  
Three Stages ◽  
Increasing Temperature ◽  
State Stress

The plastic deformation behaviors of 7050 Al alloy were investigated by compression tests at temperatures ranging of 250°C450°C under constant strain rates of 0.01s−1, 1s−1 and 10s−1. The results showed that all the flow curves consisted of three stages, i.e. strain-hardening, strain-softening and steady state-strain. Initially, the stress rises steeply at microstrain deformation, and then increases at a decreased rate, followed by a strain-softening until a steady state stress. The stress level decreases with increasing deformation temperature and decreasing strain rate, which can be represented by a Zener-Hollomon parameter in an exponent-type equation, 1 19 7.202 σ p 80.71 sinh (1.64 10 Z) = ⋅ −  × − ⋅ −  . Elongated grains with serrations developed in the grain boundaries were observed; the dynamic recrystallization (DRX) occurs with increasing temperature and dislocation density, and the shape of grain at steady state is nearly equiaxial. It can be concluded that the DRX phenomenon is sensitive to the temperature and the dynamic flow softening is mainly as the result of dynamic recovery and DRX.

Force Recovery After Activated Stretching in Whole Skeletal Muscle: Transient Aspects of Force Enhancement

2008 ◽  
Author(s):  
Ryan A. Koppes ◽  
David T. Corr
Keyword(s):  
Skeletal Muscle ◽  
Steady State ◽  
Isometric Force ◽  
Underlying Mechanism ◽  
Mechanical Work ◽  
Force Enhancement ◽  
Transient Phenomena ◽  
Force Depression ◽  
Force Relaxation ◽  
In Situ Experiments

The enhancement of isometric force after active stretching is a well-accepted and demonstrated characteristic of skeletal muscle in both whole muscle [1,2] and single-fiber preparations [1,3], but its mechanisms remain unknown. Although traditionally analyzed at steady-state, transient phenomena caused, at least in part, by cross-bridge kinetics may provide novel insight into the mechanisms associated with force enhancement (FE). In order to identify the transient aspects of FE and its relation to stretching speed, stretching amplitude, and muscle mechanical work, a post hoc analysis of in situ experiments in soleus muscle tendon units of anesthetized cats [2] was conducted. The period immediately following stretching, at which the force returns to steady-state, was fit using an exponential decay function. The aims of this study were to analyze and quantify the effects of stretching amplitude, stretching speed, and muscle mechanical work on steady-state force enhancement (FEss) and transient force relaxation rate after active stretching. The results of this study were interpreted with respect to prior force depression (FD) experiments [4], to identify if the two phenomena exhibited similar transient and steady-state behaviors, and thus could be described by the same underlying mechanism(s).

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