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1
Bogle, Jamie M., David A. Zapala, Robin Criter e Robert Burkard. "The Effect of Muscle Contraction Level on the Cervical Vestibular Evoked Myogenic Potential (cVEMP): Usefulness of Amplitude Normalization". Journal of the American Academy of Audiology 24, n. 02 (febbraio 2013): 077–88. http://dx.doi.org/10.3766/jaaa.24.2.2.
Testo completoAbstract (sommario):
Background: The cervical vestibular evoked myogenic potential (cVEMP) is a reflexive change in sternocleidomastoid (SCM) muscle contraction activity thought to be mediated by a saccular vestibulo-collic reflex. CVEMP amplitude varies with the state of the afferent (vestibular) limb of the vestibulo-collic reflex pathway, as well as with the level of SCM muscle contraction. It follows that in order for cVEMP amplitude to reflect the status of the afferent portion of the reflex pathway, muscle contraction level must be controlled. Historically, this has been accomplished by volitionally controlling muscle contraction level either with the aid of a biofeedback method, or by an a posteriori method that normalizes cVEMP amplitude by the level of muscle contraction. A posteriori normalization methods make the implicit assumption that mathematical normalization precisely removes the influence of the efferent limb of the vestibulo-collic pathway. With the cVEMP, however, we are violating basic assumptions of signal averaging: specifically, the background noise and the response are not independent. The influence of this signal-averaging violation on our ability to normalize cVEMP amplitude using a posteriori methods is not well understood. Purpose: The aims of this investigation were to describe the effect of muscle contraction, as measured by a prestimulus electromyogenic estimate, on cVEMP amplitude and interaural amplitude asymmetry ratio, and to evaluate the benefit of using a commonly advocated a posteriori normalization method on cVEMP amplitude and asymmetry ratio variability. Research Design: Prospective, repeated-measures design using a convenience sample. Study Sample: Ten healthy adult participants between 25 and 61 yr of age. Intervention: cVEMP responses to 500 Hz tone bursts (120 dB pSPL) for three conditions describing maximum, moderate, and minimal muscle contraction. Data Collection and Analysis: Mean (standard deviation) cVEMP amplitude and asymmetry ratios were calculated for each muscle-contraction condition. Repeated measures analysis of variance and t-tests compared the variability in cVEMP amplitude between sides and conditions. Linear regression analyses compared asymmetry ratios. Polynomial regression analyses described the corrected and uncorrected cVEMP amplitude growth functions. Results: While cVEMP amplitude increased with increased muscle contraction, the relationship was not linear or even proportionate. In the majority of cases, once muscle contraction reached a certain “threshold” level, cVEMP amplitude increased rapidly and then saturated. Normalizing cVEMP amplitudes did not remove the relationship between cVEMP amplitude and muscle contraction level. As muscle contraction increased, the normalized amplitude increased, and then decreased, corresponding with the observed amplitude saturation. Abnormal asymmetry ratios (based on values reported in the literature) were noted for four instances of uncorrected amplitude asymmetry at less than maximum muscle contraction levels. Amplitude normalization did not substantially change the number of observed asymmetry ratios. Conclusions: Because cVEMP amplitude did not typically grow proportionally with muscle contraction level, amplitude normalization did not lead to stable cVEMP amplitudes or asymmetry ratios across varying muscle contraction levels. Until we better understand the relationships between muscle contraction level, surface electromyography (EMG) estimates of muscle contraction level, and cVEMP amplitude, the application of normalization methods to correct cVEMP amplitude appears unjustified.
2
ZLATANOV, BOYAN. "Error estimates for approximating best proximity points for cyclic contractive maps". Carpathian Journal of Mathematics 32, n. 2 (2016): 265–70. http://dx.doi.org/10.37193/cjm.2016.02.15.
Testo completoAbstract (sommario):
We find a priori and a posteriori error estimates of the best proximity point for the Picard iteration associated to a cyclic contraction map, which is defined on a uniformly convex Banach space with modulus of convexity of power type.
3
Beirão da Veiga, L., C. Canuto, R. H. Nochetto, G. Vacca e M. Verani. "Adaptive VEM: Stabilization-Free A Posteriori Error Analysis and Contraction Property". SIAM Journal on Numerical Analysis 61, n. 2 (10 marzo 2023): 457–94. http://dx.doi.org/10.1137/21m1458740.
Testo completo
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Canuto, Claudio, e Davide Fassino. "Higher-order adaptive virtual element methods with contraction properties". Mathematics in Engineering 5, n. 6 (2023): 1–33. http://dx.doi.org/10.3934/mine.2023101.
Testo completoAbstract (sommario):
<abstract><p>The realization of a standard Adaptive Finite Element Method (AFEM) preserves the mesh conformity by performing a completion step in the refinement loop: In addition to elements marked for refinement due to their contribution to the global error estimator, other elements are refined. In the new perspective opened by the introduction of Virtual Element Methods (VEM), elements with hanging nodes can be viewed as polygons with aligned edges, carrying virtual functions together with standard polynomial functions. The potential advantage is that all activated degrees of freedom are motivated by error reduction, not just by geometric reasons. This point of view is at the basis of the paper [L. Beirão da Veiga et al., "Adaptive VEM: stabilization-free a posteriori error analysis and contraction property", SIAM Journal on Numerical Analysis, vol. 61, 2023], devoted to the convergence analysis of an adaptive VEM generated by the successive newest-vertex bisections of triangular elements without applying completion, in the lowest-order case (polynomial degree $ k = 1 $). The purpose of this paper is to extend these results to the case of VEMs of order $ k\ge2 $ built on triangular meshes. The problem at hand is a variable-coefficient, second-order self-adjoint elliptic equation with Dirichlet boundary conditions; the data of the problem are assumed to be piecewise polynomials of degree $ k-1 $. By extending the concept of global index of a hanging node, under an admissibility assumption of the mesh, we derive a stabilization-free a posteriori error estimator. This is the sum of residual-type terms and certain virtual inconsistency terms (which vanish for $ k = 1 $). We define an adaptive VEM of order $ k $ based on this estimator, and we prove its convergence by establishing a contraction result for a linear combination of (squared) energy norm of the error, (squared) residual estimator, and (squared) virtual inconsistency estimator.</p></abstract>
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Bokhove, O., A. Kalogirou e W. Zweers. "From Bore–Soliton–Splash to a New Wave-to-Wire Wave-Energy Model". Water Waves 1, n. 2 (novembre 2019): 217–58. http://dx.doi.org/10.1007/s42286-019-00022-9.
Testo completoAbstract (sommario):
AbstractWe explore extreme nonlinear water-wave amplification in a contraction or, analogously, wave amplification in crossing seas. The latter case can lead to extreme or rogue-wave formation at sea. First, amplification of a solitary-water-wave compound running into a contraction is disseminated experimentally in a wave tank. Maximum amplification in our bore–soliton–splash observed is circa tenfold. Subsequently, we summarise some nonlinear and numerical modelling approaches, validated for amplifying, contracting waves. These amplification phenomena observed have led us to develop a novel wave-energy device with wave amplification in a contraction used to enhance wave-activated buoy motion and magnetically induced energy generation. An experimental proof-of-principle shows that our wave-energy device works. Most importantly, we develop a novel wave-to-wire mathematical model of the combined wave hydrodynamics, wave-activated buoy motion and electric power generation by magnetic induction, from first principles, satisfying one grand variational principle in its conservative limit. Wave and buoy dynamics are coupled via a Lagrange multiplier, which boundary value at the waterline is in a subtle way solved explicitly by imposing incompressibility in a weak sense. Dissipative features, such as electrical wire resistance and nonlinear LED loads, are added a posteriori. New is also the intricate and compatible finite-element space–time discretisation of the linearised dynamics, guaranteeing numerical stability and the correct energy transfer between the three subsystems. Preliminary simulations of our simplified and linearised wave-energy model are encouraging and involve a first study of the resonant behaviour and parameter dependence of the device.
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Waldrop, T. G., e R. W. Stremel. "Muscular contraction stimulates posterior hypothalamic neurons". American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 256, n. 2 (1 febbraio 1989): R348—R356. http://dx.doi.org/10.1152/ajpregu.1989.256.2.r348.
Testo completoAbstract (sommario):
Recent studies have suggested that the subthalamic locomotor region (STLR) of the posterior hypothalamus is involved in modulating cardiorespiratory responses to feedback from contracting muscles. The purpose of this study was to determine whether neurons in this hypothalamic region alter their discharge frequency during contraction of hindlimb muscles. Stainless steel electrodes were used to record single-unit activity of STLR neurons during static and rhythmic contractions of hindlimb muscles in anesthetized cats. Recordings were also made from neurons in areas outside but surrounding the subthalamic locomotor region. Contraction of the triceps surae muscles was induced by stimulation of the peripheral cut ends of the L7 and S1 ventral roots. Both static and rhythmic contractions of the triceps surae evoked an increase in the discharge rate of the majority of the STLR cells studied. Two types of excitatory responses were observed: 1) abrupt increases in discharge frequency at the onset of muscular contraction and 2) a delayed more gradual increase in firing. Most of the cells that responded to muscular contraction could be activated by mechanical probing of the triceps surae muscles. However, the changes in discharge frequency were unrelated to changes in arterial pressure occurring during muscular contraction. Most of the neurons located outside the STLR were slightly inhibited by or did not respond to muscular contraction. Thus input from contracting muscles exerts predominantly an excitatory effect on neurons in the posterior hypothalamus. These results are consistent with other studies which have concluded that this hypothalamic site is involved in influencing the cardiorespiratory responses to muscular contraction.
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Zlatanov, Boyan. "On a generalization of tripled fixed or best proximity points for a class of cyclic contractive maps". Filomat 35, n. 9 (2021): 3015–31. http://dx.doi.org/10.2298/fil2109015z.
Testo completoAbstract (sommario):
We enrich the known results about tripled fixed points and tripled best proximity points. We generalize the notion of ordered pairs of cyclic contraction maps and we obtain sufficient conditions for the existence and uniqueness of fixed (or best proximity) points. We get a priori and a posteriori error estimates for the tripled fixed points and for the tripled best proximity points, provided that the underlying Banach space has modulus of convexity of power type in the case of best proximity points, obtained by sequences of successive iterations. We illustrate the main result with an example.
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Khoromskij, Boris, e Sergey Repin. "Rank Structured Approximation Method for Quasi-Periodic Elliptic Problems". Computational Methods in Applied Mathematics 17, n. 3 (1 luglio 2017): 457–77. http://dx.doi.org/10.1515/cmam-2017-0014.
Testo completoAbstract (sommario):
AbstractWe consider an iteration method for solving an elliptic type boundary value problem {\mathcal{A}u=f}, where a positive definite operator {\mathcal{A}} is generated by a quasi-periodic structure with rapidly changing coefficients (a typical period is characterized by a small parameter ϵ). The method is based on using a simpler operator {\mathcal{A}_{0}} (inversion of {\mathcal{A}_{0}} is much simpler than inversion of {\mathcal{A}}), which can be viewed as a preconditioner for {\mathcal{A}}. We prove contraction of the iteration method and establish explicit estimates of the contraction factor q. Certainly the value of q depends on the difference between {\mathcal{A}} and {\mathcal{A}_{0}}. For typical quasi-periodic structures, we establish simple relations that suggest an optimal {\mathcal{A}_{0}} (in a selected set of “simple” structures) and compute the corresponding contraction factor. Further, this allows us to deduce fully computable two-sided a posteriori estimates able to control numerical solutions on any iteration. The method is especially efficient if the coefficients of {\mathcal{A}} admit low-rank representations and if algebraic operations are performed in tensor structured formats. Under moderate assumptions the storage and solution complexity of our approach depends only weakly (merely linear-logarithmically) on the frequency parameter \frac{1}{\epsilon}.
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CASCON, J. MANUEL, RICARDO H. NOCHETTO e KUNIBERT G. SIEBERT. "DESIGN AND CONVERGENCE OF AFEM IN H(DIV)". Mathematical Models and Methods in Applied Sciences 17, n. 11 (novembre 2007): 1849–81. http://dx.doi.org/10.1142/s0218202507002492.
Testo completoAbstract (sommario):
We design an adaptive finite element method (AFEM) for mixed boundary value problems associated with the differential operator A-∇div in H(div, Ω). For A being a variable coefficient matrix with possible jump discontinuities, we provide a complete a posteriori error analysis which applies to both Raviart–Thomas ℝ𝕋n and Brezzi–Douglas–Marini 𝔹𝔻𝕄n elements of any order n in dimensions d = 2, 3. We prove a strict reduction of the total error between consecutive iterates, namely a contraction property for the sum of energy error and oscillation, the latter being solution-dependent. We present numerical experiments for ℝ𝕋n with n = 0, 1 and 𝔹𝔻𝕄1 which document the performance of AFEM and corroborate as well as extend the theory.
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Haberl, Alexander, Dirk Praetorius, Stefan Schimanko e Martin Vohralík. "Convergence and quasi-optimal cost of adaptive algorithms for nonlinear operators including iterative linearization and algebraic solver". Numerische Mathematik 147, n. 3 (5 febbraio 2021): 679–725. http://dx.doi.org/10.1007/s00211-021-01176-w.
Testo completoAbstract (sommario):
AbstractWe consider a second-order elliptic boundary value problem with strongly monotone and Lipschitz-continuous nonlinearity. We design and study its adaptive numerical approximation interconnecting a finite element discretization, the Banach–Picard linearization, and a contractive linear algebraic solver. In particular, we identify stopping criteria for the algebraic solver that on the one hand do not request an overly tight tolerance but on the other hand are sufficient for the inexact (perturbed) Banach–Picard linearization to remain contractive. Similarly, we identify suitable stopping criteria for the Banach–Picard iteration that leave an amount of linearization error that is not harmful for the residual a posteriori error estimate to steer reliably the adaptive mesh-refinement. For the resulting algorithm, we prove a contraction of the (doubly) inexact iterates after some amount of steps of mesh-refinement/linearization/algebraic solver, leading to its linear convergence. Moreover, for usual mesh-refinement rules, we also prove that the overall error decays at the optimal rate with respect to the number of elements (degrees of freedom) added with respect to the initial mesh. Finally, we prove that our fully adaptive algorithm drives the overall error down with the same optimal rate also with respect to the overall algorithmic cost expressed as the cumulated sum of the number of mesh elements over all mesh-refinement, linearization, and algebraic solver steps. Numerical experiments support these theoretical findings and illustrate the optimal overall algorithmic cost of the fully adaptive algorithm on several test cases.
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Botterman, B. R., G. A. Iwamoto e W. J. Gonyea. "Classification of motor units in flexor carpi radialis muscle of the cat". Journal of Neurophysiology 54, n. 3 (1 settembre 1985): 676–90. http://dx.doi.org/10.1152/jn.1985.54.3.676.
Testo completoAbstract (sommario):
Motor units in the cat flexor carpi radialis (FCR) muscle, one of two primary wrist flexors, were classified into three groups: slow twitch, fatigue resistant (S); fast twitch, fatigue resistant (FR); and fast twitch, fatigue sensitive (FF). Classification was based on 1) the ratio of the tension-time area produced by a train of stimuli delivered at 40 pps and the maximum tension-time area (A40/Amax), and 2) the cumulative force index (CFI), calculated from a series of trains (40 pps) delivered intermittently for a period of 4 min. The CFI is defined as the ratio between the force accumulated in the last 2 min of stimulation to the first 2 min of stimulation. Motor units with values for A40/Amax greater than 0.50 were classified as type S units, and less than 0.50 as type F. A40/Amax is essentially equivalent to the "sag" profile of an unfused tetanus in its ability to separate units into "slow" and "fast" contracting units. In general, units with area ratios less than 0.50 had twitch contraction times less than 25 ms, whereas units with area ratios greater than 0.50 had contraction times greater than 25 ms. Separation of type F units into two groups was based on the CFI, with ratios less than or equal to 0.75 corresponding to type FF units and greater than 0.75 as type FR units. Type S units also had CFIs greater than 0.75. Based on this classification scheme, 40.4% of FCR motor units were type S, 37.5% type FR, and 22.1% type FF. The a priori assumption of three motor-unit types based on the distributions of A40/Amax and CFI was evaluated by cluster analysis. The analysis supported the assumption of three primary groups of motor units. Furthermore, when cluster formation proceeded to the point where only three clusters remained in the analysis, each of these clusters consisted exclusively of one type of unit (i.e., S, FR, or FF). The validity of the classification scheme was further tested by stepwise discriminant analysis. Units classified as types S, FR, and FF were predicted to be classified with 100% accuracy. All units had a high probability (a posteriori) of having group membership in their originally classified group (P greater than 0.99 for 129 units; P greater than 0.90 for 7 units). The duration of potentiated twitch contractions for type FR and FF units was found to be less than reported for most populations of hindlimb units.(ABSTRACT TRUNCATED AT 400 WORDS)
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Gong, Wei, Zhiyu Tan e Zhaojie Zhou. "Optimal convergence of finite element approximation to an optimization problem with PDE constraint*". Inverse Problems 38, n. 4 (2 marzo 2022): 045004. http://dx.doi.org/10.1088/1361-6420/ac4f5c.
Testo completoAbstract (sommario):
Abstract We study in this paper the optimal convergence of finite element approximation to an optimization problem with PDE constraint. Specifically, we consider an elliptic distributed optimal control problem without control constraints, which can also be viewed as a regularized inverse source problem. The main contributions are two-fold. First, we derive a priori and a posteriori error estimates for the optimization problems, under an appropriately chosen norm that allows us to establish an isomorphism between the solution space and its dual. These results yield error estimates with explicit dependence on the regularization parameter α so that the constants appeared in the derivation are independent of α. Second, we prove the contraction property and rate optimality for the adaptive algorithm with respect to the error estimator and solution errors between the adaptive finite element solutions and the continuous solutions. Extensive numerical experiments are presented that confirm our theoretical results.
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Okai, Liria Akie, e André Fabio Kohn. "Quantifying the Contributions of the Flexor Digitorum Brevis Muscle on Postural Stability". Motor Control 19, n. 3 (luglio 2015): 161–72. http://dx.doi.org/10.1123/mc.2013-0066.
Testo completoAbstract (sommario):
Surprisingly little attention has been devoted to the role played by the intrinsic muscles of the human foot. The aim of this study was to quantify the capabilities of the flexor digitorum brevis (FDB) muscle to contribute to upright postural control. The approaches consisted of analysis of the effects of FDB contraction elicited by external electrical stimulation and quantification of the magnitude of FDB torque generation. The results showed the FDB can produce significant changes in static posture by itself as shown by changes in the center of pressure. Moreover, the FDB contribution to counterbalance the gravity’s toppling force was estimated at around 14.5% of the total required active torque at the ankle to keep the subject from falling. A posteriori functional analysis during horizontal perturbations showed high and self-sustained activity of FDB. These results demonstrated that the FDB has a significant capability of contributing to postural control.
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Buffa, Annalisa, e Carlotta Giannelli. "Adaptive isogeometric methods with hierarchical splines: Error estimator and convergence". Mathematical Models and Methods in Applied Sciences 26, n. 01 (2 novembre 2015): 1–25. http://dx.doi.org/10.1142/s0218202516500019.
Testo completoAbstract (sommario):
The problem of developing an adaptive isogeometric method (AIGM) for solving elliptic second-order partial differential equations with truncated hierarchical B-splines of arbitrary degree and different order of continuity is addressed. The adaptivity analysis holds in any space dimensions. We consider a simple residual-type error estimator for which we provide a posteriori upper and lower bound in terms of local error indicators, taking also into account the critical role of oscillations as in a standard adaptive finite element setting. The error estimates are properly combined with a simple marking strategy to define a sequence of admissible locally refined meshes and corresponding approximate solutions. The design of a refine module that preserves the admissibility of the hierarchical mesh configuration between two consecutive steps of the adaptive loop is presented. The contraction property of the quasi-error, given by the sum of the energy error and the scaled error estimator, leads to the convergence proof of the AIGM.
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Napadow, Vitaly J., Qun Chen, Van J. Wedeen e Richard J. Gilbert. "Biomechanical basis for lingual muscular deformation during swallowing". American Journal of Physiology-Gastrointestinal and Liver Physiology 277, n. 3 (1 settembre 1999): G695—G701. http://dx.doi.org/10.1152/ajpgi.1999.277.3.g695.
Testo completoAbstract (sommario):
Our goal was to quantify intramural mechanics in the tongue through an assessment of local strain during the physiological phases of swallowing. Subjects were imaged with an ultrafast gradient echo magnetic resonance imaging (MRI) pulse sequence after the application of supersaturated magnetized bands in the x and y directions. Local strain was defined through deformation of discrete triangular elements defined by these bands and was depicted graphically either as color-coded two-dimensional strain maps or as three-dimensional octahedra whose axes correspond to the principal strains for each element. During early accommodation, the anterior tongue showed positive strain (expansive) in the anterior-posterior direction ( x), whereas the middle tongue showed negative strain (contractile) in the superior-inferior direction ( y). During late accommodation, the anterior tongue displayed increased positive x-direction and y-direction strain, whereas the posterior tongue displayed increased negative y-direction strain. These findings were consistent with contraction of the anterior-located intrinsic muscles and the posterior-located genioglossus and hyoglossus muscles. During propulsion, posterior displacement of the tongue was principally associated with positive strain directed in the x and y directions. These findings were consistent with posterior passive stretch in the midline due to contraction of the laterally inserted styloglossus muscle, as well as contraction of the posterior located transversus muscle. We conclude that MRI of lingual deformation during swallowing resolves the synergistic contractions of the intrinsic and extrinsic muscle groups.
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Wood, C. E. "ACTH, cortisol, and renin responses to arterial hypotension in sheep". American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 251, n. 1 (1 luglio 1986): R18—R22. http://dx.doi.org/10.1152/ajpregu.1986.251.1.r18.
Testo completoAbstract (sommario):
This study was designed to investigate adrenocorticotropin (ACTH), cortisol, and renin responses to nitroprusside-induced hypotension in adult sheep. Five sheep were surgically prepared with carotid arterial skin loops at least 1 yr before these experiments. After catheterization of the carotid arteries and external jugular veins the sheep were infused with nitroprusside intravenously at rates of 0, 10, 15, or 20 micrograms . kg-1 . min-1 for 10 min. Nitroprusside produced significantly dose-related decreases in mean arterial pressure and increases in heart rate, plasma ACTH and cortisol concentrations, and plasma renin activity. Hematocrit was significantly increased in the 10- and 20-micrograms . kg-1 . min-1 groups during nitroprusside, probably reflecting contraction of the spleen. After the end of the period of hypotension, hematocrit was significantly decreased in all nitroprusside infusion groups, probably reflecting transcapillary movement of fluid into the vascular space. A posteriori analysis of the data suggests that the ACTH response to nitroprusside infusion was better predicted by the nadir in mean arterial pressure and that the renin activity response was better predicted by the initial rate of decrease of mean arterial pressure during nitroprusside infusion.
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Templeton, G. H., G. B. Seibert, M. Ramanathan, S. S. Cassidy e R. Johnson. "Left ventricular coordinate systems". American Journal of Physiology-Heart and Circulatory Physiology 257, n. 3 (1 settembre 1989): H1025—H1031. http://dx.doi.org/10.1152/ajpheart.1989.257.3.h1025.
Testo completoAbstract (sommario):
Three-dimensional kinematics of radiopaque markers in anterior, posterior, septal, and lateral regions of a major equatorial plane were evaluated in anesthetized dogs by biplane fluoroscopy. Stationary coordinate systems measured marker locations recorded during diastole and systole from a contractile origin at the center of contraction at end systole and from a geometric origin at the intersection with the equatorial plane of the ventricular long axis at end diastole. A time-indexed system measured marker locations at end diastole and at end systole, respectively, from the locations of the geometric origin at end diastole and end systole. Compared to the stationary system with the geometric origin, both the stationary system with the contractile origin and the time-indexed system reduced the variability of the radial components of the contractile displacements between ventricular regions. In contrast to the other two systems, the system with the contractile origin reduced circumferential components to values not significantly different from zero. These results indicate that 1) abnormally contracting regions of the ventricle may be located and their size measured by determining the region where the radial component differs from that in the rest of the equatorial plane and 2) rotation in a major equatorial plane of the ventricle is significant, but the influence of rotation can be minimized by referencing ventricular dimensions to a coordinate system with an origin at the center of contraction.
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Call, Jarrod A., Michael D. Eckhoff, Kristen A. Baltgalvis, Gordon L. Warren e Dawn A. Lowe. "Adaptive strength gains in dystrophic muscle exposed to repeated bouts of eccentric contraction". Journal of Applied Physiology 111, n. 6 (dicembre 2011): 1768–77. http://dx.doi.org/10.1152/japplphysiol.00942.2011.
Testo completoAbstract (sommario):
The objective of this study was to determine the functional recovery and adaptation of dystrophic muscle to multiple bouts of contraction-induced injury. Because lengthening (i.e., eccentric) contractions are extremely injurious for dystrophic muscle, it was considered that repeated bouts of such contractions would exacerbate the disease phenotype in mdx mice. Anterior crural muscles (tibialis anterior and extensor digitorum longus) and posterior crural muscles (gastrocnemius, soleus, and plantaris) from mdx mice performed one or five repeated bouts of 100 electrically stimulated eccentric contractions in vivo, and each bout was separated by 10–18 days. Functional recovery from one bout was achieved 7 days after injury, which was in contrast to a group of wild-type mice, which still showed a 25% decrement in electrically stimulated isometric torque at that time point. Across bouts there was no difference in the immediate loss of strength after repeated bouts of eccentric contractions for mdx mice (−70%, P = 0.68). However, after recovery from each bout, dystrophic muscle had greater torque-generating capacity such that isometric torque was increased ∼38% for both anterior and posterior crural muscles at bout 5 compared with bout 1 ( P < 0.001). Moreover, isolated extensor digitorum longus muscles excised from in vivo-tested hindlimbs 14–18 days after bout 5 had greater specific force than contralateral control muscles (12.2 vs. 10.4 N/cm2, P = 0.005) and a 20% greater maximal relaxation rate ( P = 0.049). Additional adaptations due to the multiple bouts of eccentric contractions included rapid recovery and/or sparing of contractile proteins, enhanced parvalbumin expression, and a decrease in fiber size variability. In conclusion, eccentric contractions are injurious to dystrophic skeletal muscle; however, the muscle recovers function rapidly and adapts to repeated bouts of eccentric contractions by improving strength.
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Cooper, Donald S., Maisie Shindo, Malcolm H. Hast, Uttam Sinha e Dale H. Rice. "Dynamic Properties of the Posterior Cricoarytenoid Muscle". Annals of Otology, Rhinology & Laryngology 103, n. 12 (dicembre 1994): 937–44. http://dx.doi.org/10.1177/000348949410301203.
Testo completoAbstract (sommario):
The aim of this research was to investigate the contractile properties of the posterior cricoarytenoid (PCA) muscle. Simultaneous measurements were made of the isometric force, temperature, and electromyographic activity of the dorsal cricoarytenoid muscle of anesthetized dogs during supramaximal stimulation of the recurrent laryngeal nerve for twitch and tetanic contraction. The conduction delay between stimulation of the recurrent nerve at the level of the larynx and the onset of the muscle action potential averaged 2.0 ± 0.2 milliseconds (ms), and the latent period between the onset of electrical activity of the muscle and the onset of contraction had a mean duration of 3.3 ± 0.8 ms. The mean of isometric contraction times found was 33.3 ± 2.0 ms, shorter than most previous studies of canine PCA muscle. Tetanic frequency defined as smooth contraction was higher than previous estimates. Considerations of scaling of physiological time based on animal mass were applied to analysis of the experimental findings to make possible systematic comparison of previous findings across species and animal size.
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Knight, D. R., Y. T. Shen, J. X. Thomas, W. C. Randall e S. F. Vatner. "Sympathetic activation induces asynchronous contraction in awake dogs with regional denervation". American Journal of Physiology-Heart and Circulatory Physiology 255, n. 2 (1 agosto 1988): H358—H365. http://dx.doi.org/10.1152/ajpheart.1988.255.2.h358.
Testo completoAbstract (sommario):
To determine effects of regional left ventricular (LV) denervation on regional contractile responses to sympathetic activation, dogs with posterior LV wall denervation (posterior wall-denervated group) and dogs with innervated posterior LV walls (intact group) were studied during excitement, exercise, bilateral sympathetic nerve stimulation, and norepinephrine infusion. In intact conscious dogs, all modes of sympathetic activation increased the magnitude and decreased the time of onset of systolic wall thickening (WT) similarly in the anterior and posterior wall. In the denervated group, excitement failed to increase posterior WT during systole but instead elicited asynchronous contraction, i.e., postsystolic WT, as well as delayed onset of contraction. Asynchronous contraction was not observed with excitement after beta-adrenergic receptor blockade. Asynchronous contraction of the posterior wall was also observed during the initial phase of exercise in conscious dogs and during bilateral stellate stimulation in anesthetized dogs in the posterior wall-denervated group. In comparison to neural activation, adrenergic receptor activation with norepinephrine (0.2 microgram/kg-1.min-1 iv) induced a supersensitive increase in systolic WT in the denervated posterior wall (36 +/- 5%) compared with the anterior wall (17 +/- 2%) and a delay in the end of contraction in the anterior region. Thus asynchronous contraction can be elicited in dogs with regional LV denervation as a result of an early and enhanced contraction in the innervated region during neural sympathetic activation. The reverse was observed with systemic administration of norepinephrine because of catecholamine supersensitivity in the denervated posterior wall.
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Bauer, R. M., G. A. Iwamoto e T. G. Waldrop. "Ventrolateral medullary neurons modulate pressor reflex to muscular contraction". American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 257, n. 5 (1 novembre 1989): R1154—R1161. http://dx.doi.org/10.1152/ajpregu.1989.257.5.r1154.
Testo completoAbstract (sommario):
Cardiorespiratory alterations during exercise are mediated through feedback from contracting muscles and descending drive from rostral brain sites such as the posterior hypothalamus. The role of medullary sites, which process this information, was examined in this study. In anesthetized cats, muscular contraction elicited by stimulation of L7 and S1 ventral roots and electrical stimulation of sites in the posterior hypothalamus both evoked increases in arterial pressure, heart rate, and minute ventilation. The reflex increase in arterial pressure produced by muscular contraction was attenuated significantly 15-20 min after bilateral microinjections of an excitatory amino acid (EAA) receptor antagonist, kynurenic acid (KYN), into the ventrolateral medulla (VLM). The reflex increase in arterial pressure evoked by muscular contraction returned to control levels 90 min after VLM microinjections of KYN. Microinjection of KYN into the VLM had no effect on the cardiorespiratory responses to posterior hypothalamic stimulation. These findings suggest that neurons in the VLM modulate the reflex pressor response evoked by muscular contraction. This reflex may be mediated through an interaction with EAA receptors on neurons in the VLM.
22
Yoganathan, Ajit P., Jack D. Lemmon, Young H. Kim, Peter G. Walker, Robert A. Levine e Carol C. Vesier. "A Computational Study of a Thin-Walled Three-Dimensional Left Ventricle During Early Systole". Journal of Biomechanical Engineering 116, n. 3 (1 agosto 1994): 307–14. http://dx.doi.org/10.1115/1.2895735.
Testo completoAbstract (sommario):
A numerical study was conducted to solve the three-dimensional Navier-Stokes equations for time-dependent flow in a compliant thin-walled, anatomically correct left ventricle during early systole. Model parameters were selected so that the simulation results could be compared to clinical data. The results produced endocardial wall motion which was consistent with human heart data, and velocity fields consistent with those occurring in a normally-contracting left ventricle. During isovolumetric contraction the posterior wall moved basally and posteriorly, while the septal wall moved apically and anteriorly. During ejection, the short axis of the left ventricle decreased 1.1 mm and the long axis increased 4.2 mm. At the end of the isovolumetric contraction, most of the flow field was moving form the apex toward the base with recirculation regions at the small pocket formed by the concave anterior leaflet, adjacent to the septal wall and near the left ventricular posterior wall. Fluid velocities in the outflow tract matched NMR data to within 10 percent. The results were also consistent with clinical measurements of mitral valve-papillary muscle apparatus displacement, and changes in the mitral valve annular area. The results of the present study show that the thin-walled, three-dimensional left ventricular model simulates observed normal heart phenomena. Validation of this model permits further studies to be performed which involve altered ventricular function due to a variety of cardiac diseases.
23
Cheeney, Gregory, Jose M. Remes-Troche, Ashok Attaluri e Satish S. C. Rao. "Investigation of anal motor characteristics of the sensorimotor response (SMR) using 3-D anorectal pressure topography". American Journal of Physiology-Gastrointestinal and Liver Physiology 300, n. 2 (febbraio 2011): G236—G240. http://dx.doi.org/10.1152/ajpgi.00348.2010.
Testo completoAbstract (sommario):
Desire to defecate is associated with a unique anal contractile response, the sensorimotor response (SMR). However, the precise muscle(s) involved is not known. We aimed to examine the role of external and internal anal sphincter and the puborectalis muscle in the genesis of SMR. Anorectal 3-D pressure topography was performed in 10 healthy subjects during graded rectal balloon distention using a novel high-definition manometry system consisting of a probe with 256 pressure sensors arranged circumferentially. The anal pressure changes before, during, and after the onset of SMR were measured at every millimeter along the length of anal canal and in 3-D by dividing the anal canal into 4 × 2.1-mm grids. Pressures were assessed in the longitudinal and anterior-posterior axis. Anal ultrasound was performed to assess puborectalis morphology. 3-D topography demonstrated that rectal distention produced an SMR coinciding with desire to defecate and predominantly induced by contraction of puborectalis. Anal ultrasound showed that the puborectalis was located at mean distance of 3.5 cm from anal verge, which corresponded with peak pressure difference between the anterior and posterior vectors observed at 3.4 cm with 3-D topography ( r = 0.77). The highest absolute and percentage increases in pressure during SMR were seen in the superior-posterior portion of anal canal, reaffirming the role of puborectalis. The SMR anal pressure profile showed a peak pressure at 1.6 cm from anal verge in the anterior and posterior vectors and distinct increase in pressure only posteriorly at 3.2 cm corresponding to puborectalis. We concluded that SMR is primarily induced by the activation and contraction of the puborectalis muscle in response to a sensation of a desire to defecate.
24
Kieser, D. C., E. Savage e P. Sharplin. "A Positive Quadriceps Active Test, without the Quadriceps Being Active". Case Reports in Orthopedics 2019 (28 dicembre 2019): 1–4. http://dx.doi.org/10.1155/2019/6135632.
Testo completoAbstract (sommario):
Case. A 55-year-old male with a chronic isolated grade 3 PCL injury who demonstrates a positive quadriceps active test without activating his quadriceps musculature. Conclusion. Gravity and hamstring contraction posteriorly translate the tibia into a subluxed position. Subsequent gastrocnemius contraction with the knee flexed causes an anterior tibial translation by virtue of the mass enlargement of the gastrocnemius muscular bulk, the string of a bow effect, and the anterior origin of the gastrocnemius in relation to the posterior border of the subluxed tibia aided by the normal posterior tibial slope.
25
Bokhove, Onno, Anna Kalogirou, David Henry e Gareth P. Thomas. "A novel wave-energy device with enhanced wave amplification and induction actuator". International Marine Energy Journal 3, n. 1 (14 maggio 2020): 37–44. http://dx.doi.org/10.36688/imej.3.37-44.
Testo completoAbstract (sommario):
A novel wave-energy device is presented. Both a preliminary proof-of-principle of a working, scaled laboratory version of the energy device is shown as well as the derivation and analysis of a comprehensive mathematical and numerical model of the new device. The wave-energy device includes a convergence in which the waves are amplified, a constrained wave buoy with a (curved) mast and direct energy conversion of the buoy motion into electrical power via an electro-magnetic generator. The device is designed for use in breakwaters and it is possible to be taken out of action during severe weather. The new design is a deconstruction of elements of existing wave-energy devices, such as the TapChan, IP wave-buoy and the Berkeley Wedge, put together in a different manner to enhance energy conversion and, hence, efficiency. The idea of wave-focusing in a contraction emerged from our work on creating and simulating rogue waves in crossing seas, including a "bore-soliton-splash". Such crossing seas have been recreated and modelled in the laboratory and in simulations by using a geometric channel convergence. The mathematical and numerical modelling is also novel. One monolithic variational principle governs the dynamics including the combined (potential-flow) hydrodynamics, the buoy motion and the power generation, to which the dissipative elements such as the electrical resistance of the circuits, coils and loads have been added a posteriori. The numerical model is a direct and consistent discretisation of this comprehensive variational principle. Preliminary numerical calculations are shown for the case of linearised dynamics; optimisation of efficiency is a target of future work.
26
Clark, Robert A., e Joseph L. Demer. "Functional morphometry demonstrates extraocular muscle compartmental contraction during vertical gaze changes". Journal of Neurophysiology 115, n. 1 (1 gennaio 2016): 370–78. http://dx.doi.org/10.1152/jn.00825.2015.
Testo completoAbstract (sommario):
Anatomical studies demonstrate selective compartmental innervation of most human extraocular muscles (EOMs), suggesting the potential for differential compartmental control. This was supported by magnetic resonance imaging (MRI) demonstrating differential lateral rectus (LR) compartmental contraction during ocular counterrolling, differential medial rectus (MR) compartmental contraction during asymmetric convergence, and differential LR, inferior rectus (IR), and superior oblique (SO) compartmental contraction during vertical vergence. To ascertain possible differential compartmental EOM contraction during vertical ductions, surface coil MRI was performed over a range of target-controlled vertical gaze positions in 25 orbits of 13 normal volunteers. Cross-sectional areas and partial volumes of EOMs were analyzed in contiguous, quasi-coronal 2-mm image planes spanning origins to globe equator to determine morphometric features correlating best with contractility. Confirming and extending prior findings for horizontal EOMs during horizontal ductions, the percent change in posterior partial volume (PPV) of vertical EOMs from 8 to 14 mm posterior to the globe correlated best with vertical duction. EOMs were then divided into equal transverse compartments to evaluate the effect of vertical gaze on changes in PPV. Differential contractile changes were detected in the two compartments of the same EOM during infraduction for the IR medial vs. lateral (+4.4%, P = 0.03), LR inferior vs. superior (+4.0%, P = 0.0002), MR superior vs. inferior (−6.0%, P = 0.001), and SO lateral vs. medial (+9.7%, P = 0.007) compartments, with no differential contractile changes in the superior rectus. These findings suggest that differential compartmental activity occurs during normal vertical ductions. Thus all EOMs may contribute to cyclovertical actions.
27
Sasada, Syusaku, Toshiki Tazoe, Tsuyoshi Nakajima, E. Paul Zehr e Tomoyoshi Komiyama. "Effects of Leg Pedaling on Early Latency Cutaneous Reflexes in Upper Limb Muscles". Journal of Neurophysiology 104, n. 1 (luglio 2010): 210–17. http://dx.doi.org/10.1152/jn.00774.2009.
Testo completoAbstract (sommario):
The functional coupling of neural circuits between the upper and lower limbs involving rhythmic movements is of interest to both motor control research and rehabilitation science. This coupling can be detected by examining the effect of remote rhythmic limb movement on the modulation of reflex amplitude in stationary limbs. The present study investigated the extent to which rhythmic leg pedaling modulates the amplitude of an early latency (peak 30–70 ms) cutaneous reflex (ELCR) in the upper limb muscles. Thirteen neurologically intact volunteers performed leg pedaling (60 or 90 rpm) while simultaneously contracting their arm muscles isometrically. Control experiments included isolated isometric contractions and discrete movements of the leg. ELCRs were evoked by stimulation of the superficial radial nerve with a train of rectangular pulses (three pulses at 333 Hz, intensity 2.0- to 2.5-fold perceptual threshold). Reflex amplitudes were significantly increased in the flexor carpi radialis and posterior deltoid and significantly decreased in the biceps brachii muscles during leg pedaling compared with that during stationary isometric contraction of the lower leg muscles. This effect was also sensitive to cadence. No significant modulation was seen during the isometric contractions or discrete movements of the leg. Additionally, there was no phase-dependent modulation of the ELCR. These findings suggest that activation of the rhythm generating system of the legs affects the excitability of the early latency cutaneous reflex pathways in the upper limbs.
28
Conrad, P. A., K. A. Giuliano, G. Fisher, K. Collins, P. T. Matsudaira e D. L. Taylor. "Relative distribution of actin, myosin I, and myosin II during the wound healing response of fibroblasts." Journal of Cell Biology 120, n. 6 (15 marzo 1993): 1381–91. http://dx.doi.org/10.1083/jcb.120.6.1381.
Testo completoAbstract (sommario):
Myosin I is present in Swiss 3T3 fibroblasts and its localization reflects a possible involvement in the extension and/or retraction of protrusions at the leading edge of locomoting cells and the transport of vesicles, but not in the contraction of stress fibers or transverse fibers. An affinity-purified polyclonal antibody to brush border myosin I colocalizes with a polypeptide of 120 kD in fibroblast extracts. Within initial protrusions of polarized, migrating fibroblasts, myosin I exhibits a punctate distribution, whereas actin is diffuse and myosin II is absent. Myosin I also exists in linear arrays parallel to the direction of migration in filopodia and microspikes, established protrusions, and within the leading lamellae of migrating cells. Myosin II and actin colocalize along transverse fibers in the lamellae of migrating cells, while myosin I displays no definitive organization along these fibers. During contractions of actin-based fibers, myosin II is concentrated in the center of the cell, while the distribution of myosin I does not change. Thus, myosin I is found at the correct location and time to be involved in the extension and/or retraction of protrusions and the transport of vesicles. Myosin II-based contractions in more posterior cellular regions could generate forces to separate cells, maintain a polarized cell shape, maintain the direction of locomotion, maximize the rate of locomotion, and/or aid in the delivery of cytoskeletal/contractile subunits to the leading edge.
29
Tanoi, Chiharu, Yoshio Suzuki, Masato Shibuya, Kenichiro Sugita, Kaoru Masuzawa e Masahisa Asano. "Mechanism of the Enhanced Vasoconstrictor Responses to Endothelin-1 in Canine Cerebral Arteries". Journal of Cerebral Blood Flow & Metabolism 11, n. 3 (maggio 1991): 371–79. http://dx.doi.org/10.1038/jcbfm.1991.77.
Testo completoAbstract (sommario):
Vasoconstrictor effects of endothelin-1 (ET) were investigated in endothelium-denuded strips of cerebral (basilar and posterior cerebral) and mesenteric arteries of the dog. ET produced a concentration-dependent contraction in these arteries. Contractile responses to lower concentrations (below 3 × 10−10 M) of ET were significantly greater in the cerebral arteries than in the mesenteric artery. Inhibition by nifedipine of the contractile responses to ET was greater in the basilar artery than in the mesenteric artery. After the inhibition by 10−7 M nifedipine, the remaining responses to ET were similar in the two arteries. Cerebral arteries, but not the mesenteric artery, relaxed significantly from the resting level when placed in a Ca2+ -free solution containing 0.1 m M EGTA (0-Ca solution). Readdition of Ca2+ to the cerebral arteries placed in the 0-Ca solution caused a biphasic contraction that was sensitive to nifedipine. When 10−9 M ET was introduced before the Ca2+-induced contraction, this peptide produced only a very small contraction, but enhanced the Ca2+-induced contraction. The extent of the enhancement induced by ET was much greater in the cerebral arteries than in the mesenteric artery. These results indicate that the enhanced responses to ET in the cerebral arteries were dependent to a large extent on Ca2+ influx through voltage-dependent Ca2+ channels (VDCs). It is likely that the VDCs in these arteries are more activated in the resting state than those in the mesenteric artery.
30
Morano, Alexander A., Ilzat Ali e Jeffrey D. Dvorin. "Elucidating the Spatio-Temporal dynamics of the Plasmodium falciparum basal complex". PLOS Pathogens 20, n. 6 (3 giugno 2024): e1012265. http://dx.doi.org/10.1371/journal.ppat.1012265.
Testo completoAbstract (sommario):
Asexual replication of Plasmodium falciparum occurs via schizogony, wherein 16–36 daughter cells are produced within the parasite during one semi-synchronized cytokinetic event. Schizogony requires a divergent contractile ring structure known as the basal complex. Our lab has previously identified PfMyoJ (PF3D7_1229800) and PfSLACR (PF3D7_0214700) as basal complex proteins recruited midway through segmentation. Using ultrastructure expansion microscopy, we localized both proteins to a novel basal complex subcompartment. While both colocalize with the basal complex protein PfCINCH upon recruitment, they form a separate, more basal subcompartment termed the posterior cup during contraction. We also show that PfSLACR is recruited to the basal complex prior to PfMyoJ, and that both proteins are removed unevenly as segmentation concludes. Using live-cell microscopy, we show that actin dynamics are dispensable for basal complex formation, expansion, and contraction. We then show that EF-hand containing P. falciparum Centrin 2 partially localizes to this posterior cup of the basal complex and that it is essential for growth and replication, with variable defects in basal complex contraction and synchrony. Finally, we demonstrate that free intracellular calcium is necessary but not sufficient for basal complex contraction in P. falciparum. Thus, we demonstrate dynamic spatial compartmentalization of the Plasmodium falciparum basal complex, identify an additional basal complex protein, and begin to elucidate the unique mechanism of contraction utilized by P. falciparum, opening the door for further exploration of Apicomplexan cellular division.
31
Campanelli, J. T., e R. H. Scheller. "Histidine-rich basic peptide: a cardioactive neuropeptide from Aplysia neurons R3-14". Journal of Neurophysiology 57, n. 4 (1 aprile 1987): 1201–9. http://dx.doi.org/10.1152/jn.1987.57.4.1201.
Testo completoAbstract (sommario):
We have previously demonstrated that neurons R3-14 of the Aplysia abdominal ganglia specifically express a gene encoding a 108-amino acid neuropeptide precursor. This precursor is postranslationally processed by cleavage of a signal sequence and two internal dibasic residues resulting in three peptides. The peptide products are colocalized in dense core granules throughout the R3-14 processes that innervate the efferent vein of the gill and the auricle. Gel filtration and reverse phase high-pressure liquid chromatography (rpHPLC) were used to purify a 4.9-kDa peptide produced by the R3-14 neurons. We call this peptide the histidine-rich basic peptide (HRBP), which reflects its primary structure. In vitro tension measurements of cannulated Aplysia hearts revealed dose-dependent cardioexcitatory actions of HRBP. HRBP increased both beat frequency and amplitude with a threshold of 10(-7) M. HRBP increased the amplitude of ventricular contractions in a dose-dependent manner, whereas the frequency of contraction is unaffected. In contrast both the amplitude and frequency of auricular contractions were enhanced. High concentrations of HRBP also had a positive tonotropic effect on the auricle. HRBP was also demonstrated to have actions on tissue of the gut. Circular muscles of the crop adjacent to the anterior gizzard showed infrequent spontaneous contractions. Both HRBP and acetylcholine (ACh) induced repetitive contractions of this muscle. Circular muscles of the posterior gizzard had a high degree of spontaneous activity when continually perfused. Contraction amplitude and frequency was increased by HRBP and ACh, whereas contractility was inhibited by Phe-Met-Arg-Phe-amide (FMRFamide).
32
Lafleur, J., D. Zytnicki, G. Horcholle-Bossavit e L. Jami. "Declining inhibition elicited in cat lumbar motoneurons by repetitive stimulation of group II muscle afferents". Journal of Neurophysiology 70, n. 5 (1 novembre 1993): 1805–10. http://dx.doi.org/10.1152/jn.1993.70.5.1805.
Testo completoAbstract (sommario):
1. The aim of the present experiments was to verify whether group II inputs from gastrocnemius medialis (GM) muscle could elicit declining inhibitions similar to those observed during GM contractions in a variety of lumbar motoneurons of the cat spinal cord. Motoneurons were recorded intracellularly in chloralose- or pentobarbitone-anesthetized preparations during electrical stimulation of GM nerve with repetitive trains. 2. With strengths in the group I range, repetitive stimulation evoked the usual Ia excitation in homonymous motoneurons and excitatory postsynaptic potential (EPSP) amplitudes remained constant throughout the stimulation sequence. In synergic plantaris motoneurons lacking an excitatory connection with Ia afferents from GM, the same stimulation, kept at a constant strength throughout the stimulation sequence, elicited rapidly decreasing inhibitory potentials reminiscent of those evoked by GM contractions. 3. In motoneurons of pretibial flexors, quadriceps, and posterior biceps-semitendinosus, the stimulation strength required to observe declining inhibitions resembling those produced by GM contractions was 4-8 times group I threshold, engaging group II in addition to group I fibers. 4. These results show that input from GM group II plus group I afferents can elicit inhibitory effects in a variety of motoneurons. Such observations support the hypothesis that messages from spindle secondary endings and/or nonspecific muscle receptors activated during contraction might contribute to the widespread inhibition caused by GM contractions. 5. Inasmuch as constant input in group II and group I afferents evoked declining inhibitory potentials, the origin of the decline must be central, which suggests that the rapid reduction of contraction-induced inhibitions also depended on a central mechanism.
33
Kambhampati, Srinivas B. S., e Bharat Guthikonda. "The pushed quadriceps active test – A modification of the quadriceps active test to diagnose PCL deficiency". Journal of Arthroscopic Surgery and Sports Medicine 2 (30 giugno 2021): 128–30. http://dx.doi.org/10.25259/jassm_9_2021.
Testo completoAbstract (sommario):
Quadriceps active (QA) test has been described and well known for the diagnosis of posterior cruciate ligament (PCL) deficiency. We describe a modification of the QA test to diagnose PCL deficiency. Pushed QA test consists of two components where the examiner pushes the proximal tibia posteriorly with the knee flexed <90° in the first part of the test translating the tibia posteriorly like in the posterior drawer test while the patient reduces the translation actively by contracting the quadriceps in the second part like in the QA test.
34
Martin, Adam C., Michael Gelbart, Rodrigo Fernandez-Gonzalez, Matthias Kaschube e Eric F. Wieschaus. "Integration of contractile forces during tissue invagination". Journal of Cell Biology 188, n. 5 (1 marzo 2010): 735–49. http://dx.doi.org/10.1083/jcb.200910099.
Testo completoAbstract (sommario):
Contractile forces generated by the actomyosin cytoskeleton within individual cells collectively generate tissue-level force during epithelial morphogenesis. During Drosophila mesoderm invagination, pulsed actomyosin meshwork contractions and a ratchet-like stabilization of cell shape drive apical constriction. Here, we investigate how contractile forces are integrated across the tissue. Reducing adherens junction (AJ) levels or ablating actomyosin meshworks causes tissue-wide epithelial tears, which release tension that is predominantly oriented along the anterior–posterior (a-p) embryonic axis. Epithelial tears allow cells normally elongated along the a-p axis to constrict isotropically, which suggests that apical constriction generates anisotropic epithelial tension that feeds back to control cell shape. Epithelial tension requires the transcription factor Twist, which stabilizes apical myosin II, promoting the formation of a supracellular actomyosin meshwork in which radial actomyosin fibers are joined end-to-end at spot AJs. Thus, pulsed actomyosin contractions require a supracellular, tensile meshwork to transmit cellular forces to the tissue level during morphogenesis.
35
Ramirez-Estudillo, Abel, Karla Torres-Navarro, Sergio Rojas-Juárez, Ximena Ramirez-Galicia, Berenice Palafox-Cornejo e Adriana Galicia-Castillo. "Case Report: Fibroglial Retinal Tissue in Contractile Morning Glory Disc Anomaly". Case Reports in Ophthalmology 12, n. 2 (11 giugno 2021): 525–30. http://dx.doi.org/10.1159/000510958.
Testo completoAbstract (sommario):
The purpose of the present case is to describe a patient with tractional retinal detachment (RD) associated with contractile morning glory: a 17-year-old female, with a history of failed surgery for RD when she was 2 years old in her right eye (OD), nystagmus, and a limited visual acuity in the left eye (OS). The slit lamp examination showed phthisis bulbi in OD and the anterior segment was unremarkable in OS. Dilated fundus examination revealed a tractional RD in the posterior pole and peripapillary and preretinal fibrosis without evidence of intravitreal dispersion of retinal pigment epithelial cells. After surgery treatment, the RD resolved and the posterior segment showed a staphylomatous excavation around the optic disc anomaly with irregular contractions that folded the macular area. This were unrelated to light, breathing, or eye movements. Although morning glory disc anomaly is associated with RD, the early diagnosis can reverse structural changes. In this case, the rare association with contractile movements was found posterior to the pars plana vitrectomy after all the fibroglial epiretinal tissue was removed.
36
Esbaugh, A. J., M. Hazel e D. P. Toews. "Aspects of lymph-heart function in Rana catesbeiana". Canadian Journal of Zoology 80, n. 12 (1 dicembre 2002): 2125–30. http://dx.doi.org/10.1139/z02-210.
Testo completoAbstract (sommario):
The effect of voluntary dives on the posterior lymph heart rate of the bullfrog, Rana catesbeiana, was tested and compared with the blood-heart rate (n = 6). This was performed by cannulating the posterior lymph heart and femoral artery simultaneously. Blood-heart rates during submergence were significantly lower (α = 0.05) then pre-submergence rates at all sampling times. In contrast, the lymph hearts showed significantly lower rates only during the first and last submergence intervals. It is believed that the lymph-heart bradycardia found during these intervals is due in part to the physiological "preparations" for diving by the frog. Further information regarding posterior lymph heart contractions was gained by cannulating two posterior lymph hearts on one side of the frog (n = 5). It was found that these hearts beat within 100 ms of each other between 66 and 97% of the time (α = 0.05). The combined contraction of the three posterior lymph hearts could facilitate the movement of lymph through the outflow valve and into the venous circulation. This study represents the first time the axial coordination of homolateral lymph hearts has been shown to extend to the multiple posterior lymph hearts.
37
Lentle, R. G., G. W. Reynolds, C. M. Hulls e J. P. Chambers. "Advanced spatiotemporal mapping methods give new insights into the coordination of contractile activity in the stomach of the rat". American Journal of Physiology-Gastrointestinal and Liver Physiology 311, n. 6 (1 dicembre 2016): G1064—G1075. http://dx.doi.org/10.1152/ajpgi.00308.2016.
Testo completoAbstract (sommario):
We used spatiotemporal mapping of strain rate to determine the direction of propagation and amplitudes of the longitudinal and circumferential components of antrocorporal (AC) contractions and fundal contractions in the rat stomach maintained ex vivo and containing a volume of fluid that was within its normal functional capacity. In the region of the greater curvature the longitudinal and circular components of AC contractions propagated synchronously at right angles to the arciform geometric axis of the stomach. However, the configuration of AC contractions was U shaped, neither the circular nor the longitudinal component of contractions being evident in the upper proximal corpus. Similarly, in the distal upper antrum of some preparations, circumferential components propagated more rapidly than longitudinal components. Ongoing “high-frequency, low-amplitude myogenic contractions” were identified in the upper proximal gastric corpus and on the anterior and posterior wall of the fundus. The amplitudes of these contractions were modulated in the occluded stomach by low-frequency pressure waves that occurred spontaneously. Hence the characteristics of phasic contractions vary regionally in the antrum and corpus and a previously undescribed high-frequency contractile component was identified in the proximal corpus and fundus, the latter being modulated in synchrony with cyclic variation in intrafundal pressure in the occluded fundus.
38
Devost, Dominic, e Hans H. Zingg. "Novel in vitro system for functional assessment of oxytocin action". American Journal of Physiology-Endocrinology and Metabolism 292, n. 1 (gennaio 2007): E1—E6. http://dx.doi.org/10.1152/ajpendo.00529.2005.
Testo completoAbstract (sommario):
One of the classical biological actions mediated by the posterior pituitary hormone oxytocin (OT) is contraction of the uterus at parturition. Moreover, premature activation of the OT system is thought to contribute to preterm labor, a major clinical problem in obstetrical practice. However, the molecular mechanisms linking activation of the OT receptor (OTR) to myometrial contractions are not fully understood. Here, we describe an in vitro system that should serve as a useful tool to study this question at a cellular level. The system consists of a collagen lattice contraction assay and two different human myometrial cell lines: a cell clone from a telomerase-immortalized human myometrial cell population (hTERT-C3) as well as a cell line derived from a primary culture of human myometrial cells (M11). Using this approach, we observed that 1 nM OT promoted an almost maximal effect on cell contraction in both cell lines tested. Furthermore, this dose-dependent, OT-induced contraction was antagonized by the specific OTR antagonist d(CH2)5[Tyr(Me)2,Thr4,Tyr-NH29]OVT as well as the clinically used antagonist atosiban. This cell line-based contraction assay enables the application of molecular tools aimed at suppressing or overexpressing specific genes. It is also amenable to high-throughput testing approaches. Therefore, this system represents a powerful and improved experimental model that should facilitate the study of the molecular signal transduction pathways involved in the uterotonic actions of OT.
39
Wagner, Jamie, Erik Allman, Ashley Taylor, Kiri Ulmschneider, Timothy Kovanda, Bryne Ulmschneider, Keith Nehrke e Maureen A. Peters. "A calcineurin homologous protein is required for sodium-proton exchange events in the C. elegans intestine". American Journal of Physiology-Cell Physiology 301, n. 6 (dicembre 2011): C1389—C1403. http://dx.doi.org/10.1152/ajpcell.00139.2011.
Testo completoAbstract (sommario):
Caenorhabditis elegans defecation is a rhythmic behavior, composed of three sequential muscle contractions, with a 50-s periodicity. The motor program is driven by oscillatory calcium signaling in the intestine. Proton fluxes, which require sodium-proton exchangers at the apical and basolateral intestinal membranes, parallel the intestinal calcium flux. These proton shifts are critical for defecation-associated muscle contraction, nutrient uptake, and longevity. How sodium-proton exchangers are activated in time with intestinal calcium oscillation is not known. The posterior body defecation contraction mutant ( pbo-1) encodes a calcium-binding protein with homology to calcineurin homologous proteins, which are putative cofactors for mammalian sodium-proton exchangers. Loss of pbo-1 function results in a weakened defecation muscle contraction and a caloric restriction phenotype. Both of these phenotypes also arise from dysfunctions in pH regulation due to mutations in intestinal sodium-proton exchangers. Dynamic, in vivo imaging of intestinal proton flux in pbo-1 mutants using genetically encoded pH biosensors demonstrates that proton movements associated with these sodium-proton exchangers are significantly reduced. The basolateral acidification that signals the first defecation motor contraction is scant in the mutant compared with a normal animal. Luminal and cytoplasmic pH shifts are much reduced in the absence of PBO-1 compared with control animals. We conclude that pbo-1 is required for normal sodium-proton exchanger activity and may couple calcium and proton signaling events.
40
Lloyd, R., L. Jugé e L. Bilston. "O043 Investigating Upper-Airway Mechanics with Computational Tongue Models". Sleep Advances 4, Supplement_1 (1 ottobre 2023): A16—A17. http://dx.doi.org/10.1093/sleepadvances/zpad035.043.
Testo completoAbstract (sommario):
Abstract With the use of computational models of the oral cavity, we aim to understand how changes in the morphology of the oral cavity and changes the stiffness of the tongue affect the movement of the posterior surface of the tongue. Anatomical and diffusion weighted imaging from 20 healthy individuals (10M:10F, Age: 22-54years, BMI: 17-30kg/m²), were used to develop 3D models of the tongue including the fibre orientations of the tongue muscles. All models were aligned and scaled to match the volume of the average subject's mandible, so that only differences in shape were modelled. The muscles of the tongue were modelled as transversely isotropic, with a shear moduli of 2.9 and 1.0kPa, parallel and perpendicular to the muscle fibre direction, respectively. Each individual participant model was prescribed an active contraction producing 50kPa of stress in the horizontal component of the genioglossus. The influence of initial hyoid position on the average anterior displacement of the posterior surface of the tongue was assessed with linear regression. On average the contraction moved the posterior tongue 4.0±0.7mm anteriorly. For every millimetre of hyoid elevation, anterior tongue displacement (i.e. airway dilation) decreased by 0.1mm. These initial models demonstrate that the automated modelling pipeline can identify how structural differences alter the efficacy of dilator muscles. Future implementations of these models will also incorporate experimentally measured pharyngeal pressures, and temporal and spatial patterns of muscle activations based on experimental data, to assess the how variation in the coordinated contractions contributes to airway collapse.
41
Mørk, Halvor K., Ivar Sjaastad, Ole M. Sejersted e William E. Louch. "Slowing of cardiomyocyte Ca2+ release and contraction during heart failure progression in postinfarction mice". American Journal of Physiology-Heart and Circulatory Physiology 296, n. 4 (aprile 2009): H1069—H1079. http://dx.doi.org/10.1152/ajpheart.01009.2008.
Testo completoAbstract (sommario):
Deterioration of cardiac contractility during congestive heart failure (CHF) is believed to involve decreased function of individual cardiomyocytes and may include reductions in contraction magnitude and/or kinetics. We examined the progression of in vivo and in vitro alterations in contractile function in CHF mice and investigated underlying alterations in Ca2+ homeostasis. Following induction of myocardial infarction (MI), mice with CHF were examined at early (1 wk post-MI) and chronic (10 wk post-MI) stages of disease development. Sham-operated mice served as controls. Global and local left ventricle function were assessed by echocardiography in sedated animals (∼2% isoflurane). Excitation-contraction coupling was examined in cardiomyocytes isolated from the viable septum. CHF progression between 1 and 10 wk post-MI resulted in increased mortality, development of hypertrophy, and deterioration of global left ventricular function. Local function in the noninfarcted myocardium also declined, as posterior wall shortening velocity was reduced in chronic CHF (1.2 ± 0.1 vs. 1.9 ± 0.2 cm/s in sham). Parallel alterations occurred in isolated cardiomyocytes since contraction and Ca2+ transient time to peak values were prolonged in chronic CHF (115 ± 6 and 158 ± 11% sham values, respectively). Surprisingly, contraction and Ca2+ transient magnitudes in CHF were larger than sham values at both time points, resulting from increased sarcoplasmic reticulum Ca2+ content and greater Ca2+ influx via L-type channels. We conclude that, in mice with CHF following myocardial infarction, declining myocardial function involves slowing of cardiomyocyte contraction without reduction in contraction magnitude. Corresponding alterations in Ca2+ transients suggest that slowing of Ca2+ release is a critical mediator of CHF progression.
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Padda, Bikram S., Sung-Ae Jung, Dolores Pretorius, Charles W. Nager, Debbie Den-Boer e Ravinder K. Mittal. "Effects of pelvic floor muscle contraction on anal canal pressure". American Journal of Physiology-Gastrointestinal and Liver Physiology 292, n. 2 (febbraio 2007): G565—G571. http://dx.doi.org/10.1152/ajpgi.00250.2006.
Testo completoAbstract (sommario):
The role of pelvic floor muscle contraction in the genesis of anal canal pressure is not clear. Recent studies have suggested that vaginal distension increases pelvic floor muscle contraction. We studied the effects of vaginal distension on anal canal pressure in 15 nullipara asymptomatic women. Anal pressure, rest, and squeeze were measured using station pull-through manometry techniques with no vaginal probe, a 10-mm vaginal probe, and a 25-mm vaginal probe in place. Rest and squeeze vaginal pressures were significantly higher when measured with the 25-mm probe compared with the 10-mm probe, suggesting that vaginal distension enhances pelvic floor contraction. In the presence of the 25-mm vaginal probe, rest and squeeze anal pressures in the proximal part of the anal canal were significantly higher compared with no vaginal probe or the 10-mm vaginal probe. On the other hand, distal anal pressures were not affected by any of the vaginal probes. Ultrasound imaging of the pelvic floor revealed that vaginal distension increased the anterior-posterior length of the puborectalis muscle. Atropine at 15 μg/kg had no influence on the rest and squeeze anal pressures with or without vaginal distension. Our data suggest that pelvic floor contractions increase pressures in the proximal part of the anal canal, which is anatomically surrounded by the puborectalis muscle. We propose that pelvic floor contraction plays an important role in the fecal continence mechanism by increasing anal canal pressure.
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Towse, Theodore F., Jill M. Slade e Ronald A. Meyer. "Effect of physical activity on MRI-measured blood oxygen level-dependent transients in skeletal muscle after brief contractions". Journal of Applied Physiology 99, n. 2 (agosto 2005): 715–22. http://dx.doi.org/10.1152/japplphysiol.00272.2005.
Testo completoAbstract (sommario):
The signal intensity (SI) in gradient-echo, echo-planar magnetic resonance images (repetition time/echo time = 1,000/40) of anterior tibialis muscle in active [estimated energy expenditure 42.4 ± 3.7 (SD), n = 8] vs. sedentary (32.3 ± 0.6 kcal·kg−1·day−1, n = 8) young adult (18–34 yr old) human subjects was measured after single, 1-s-duration maximum voluntary ankle dorsiflexion contractions. There was no difference between groups in anterior tibial muscle cross-sectional area or peak force. In both groups there was a transient increase in anterior tibialis muscle SI, which peaked 5–7 s after the end of each contraction. The magnitude of the SI transient was over threefold greater [5.5 ± 1.0 (SE) vs. 1.5 ± 0.4%] and persisted twice as long (half-recovery time 5.4 ± 0.4 vs. 2.7 ± 0.3 s) in the active subjects. In the same subjects, blood flow in popliteal, anterior tibial, and posterior tibial arteries was measured by cardiac-gated CINE magnetic resonance angiography before and after 2 min of dynamic, repetitive ankle dorsiflexion exercise. There was no difference between groups in resting or postexercise flow in anterior tibial artery, although popliteal and posterior tibial artery flow after exercise tended to be greater in the active group. The results indicate that transient hyperemia and oxygenation in muscle after single contractions are enhanced by chronic physical activity to a greater extent than peak muscle blood flow.
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Xu, Liang, Xi Wei Xie e Jost B. Jonas. "Posterior Vitreous Contraction After Cerebral Sinus Thrombosis". Ophthalmic Surgery, Lasers, and Imaging 40, n. 6 (1 novembre 2009): 600–601. http://dx.doi.org/10.3928/15428877-20091030-13.
Testo completo
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van der Pas, Stéphanie, Botond Szabó e Aad van der Vaart. "Adaptive posterior contraction rates for the horseshoe". Electronic Journal of Statistics 11, n. 2 (2017): 3196–225. http://dx.doi.org/10.1214/17-ejs1316.
Testo completo
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Reiß, Markus, e Johannes Schmidt-Hieber. "Posterior contraction rates for support boundary recovery". Stochastic Processes and their Applications 130, n. 11 (novembre 2020): 6638–56. http://dx.doi.org/10.1016/j.spa.2020.06.005.
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Gao, Chao, e Harrison H. Zhou. "Rate-optimal posterior contraction for sparse PCA". Annals of Statistics 43, n. 2 (aprile 2015): 785–818. http://dx.doi.org/10.1214/14-aos1268.
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Shen, Weining, e Subhashis Ghosal. "Posterior Contraction Rates of Density Derivative Estimation". Sankhya A 79, n. 2 (19 giugno 2017): 336–54. http://dx.doi.org/10.1007/s13171-017-0105-7.
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Ghosh, Prasenjit, Debdeep Pati e Anirban Bhattacharya. "Posterior Contraction Rates for Stochastic Block Models". Sankhya A 82, n. 2 (14 ottobre 2019): 448–76. http://dx.doi.org/10.1007/s13171-019-00180-5.
Testo completo
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Hartley, Olan, Tanvi Shanbhag, Derek Smith, Antonio Grimm, Ziad Salameh, Santosh K. Tadakamadla, Frank Alifui-Segbaya e Khaled E. Ahmed. "The Effect of Stacking on the Accuracy of 3D-Printed Full-Arch Dental Models". Polymers 14, n. 24 (13 dicembre 2022): 5465. http://dx.doi.org/10.3390/polym14245465.
Testo completoAbstract (sommario):
The objective of this study was to assess the effect of stacking on the dimensional and full-arch accuracy of 3D-printed models, utilising a standardised assessment methodology. A previously validated methodology involving a standard tessellation language image (STL) reference model, comprising seven spheres on a horseshoe base resembling a dental arch, was used. Six 3D-designed STL models were prepared, optimised, and stacked horizontally using 3D Sprint software. The stacking file was transferred to the NextDent 5100 printer to build the physical models. To assess accuracy, a coordinate measuring machine (CMM) measured the diameter of the spheres n=210, and twenty-one vectors extended between the centres of each of the seven spheres (n = 630). When compared to the reference model, significant differences were observed for dimensional (p = 0.006) and full-arch accuracy (p = 0.006) for all stacked models. Additionally, significant differences were observed between the stacked models for the dimensional accuracy between the posterior (p = 0.015), left posterior (p = 0.005) and anteroposterior (p = 0.002). The maximum contraction was observed in the fourth stacked model, which demonstrated the highest median deviation and least precision within the full-arch (MD = 666 μm, IQR = 55 μm), left posterior (MD = 136 μm, IQR = 12 μm), posterior (MD = 177 μm, IQR = 14 μm) and anteroposterior (MD = 179 μm, IQR = 16 μm) arch segments. In general, the anterior and left posterior arch segments recorded the highest contractions with a median deviation of 34 μm and 29 μm, and precision of 32 μm and 22 μm, respectively. Statistically significant differences were observed between the stacked models in terms of dimensional accuracy that were within clinically acceptable thresholds. The greatest contraction was noted in the fourth model, displaying the least full-arch accuracy compared to the other models. Stacked, additively manufactured, full arch models are a viable alternative for diagnostic, orthodontic, and single-unit prosthodontic applications. In contrast, caution should be exercised when utilising stacked models for full arch high accuracy prosthodontic applications. Further research is needed to assess the impact of additional variables including different printers and resins.