Techn. Univ., Diss.--Chemnitz, 2004. / Literaturverz. S. 141 - 151.

Peridynamics is a reformulation of classical continuum mechanics that utilizes integral equations in place of partial differential equations to remove the difficulty in handling discontinuities, such as cracks or interfaces, within a body. Damage is included within the constitutive model; initiation and propagation can occur without resorting to special crack growth criteria necessary in other commonly utilized approaches. Predicting damage and residual strengths of composite materials involves capturing complex, distinct and progressive failure modes. The peridynamic laminate theory correctly predicts the load redistribution in general laminate layups in the presence of complex failure modes through the use of multiple interaction types.This study presents two approaches to obtain the critical peridynamic failure parameters necessary to capture the residual strength of a composite structure. The validity of both approaches is first demonstrated by considering the residual strength of isotropic materials. The peridynamic theory is used to predict the crack growth and final failure load in both a diagonally loaded square plate with a center crack, as well as a four-point shear specimen subjected to asymmetric loading.This study also establishes the validity of each approach by considering composite laminate specimens in which each failure mode is isolated. Finally, the failure loads and final failure modes are predicted in a laminate with various hole diameters subjected to tensile and compressive loads.

This thesis presents the software program for multilayer structural elements design. The main users of the software should be bachelor and master students of mechanical technology department and their professors as well. The program can be successfully applied for computations of mechanical characteristics of the real (industrial) problems. This program is able to choose the multilayer structural elements type and its mechanical and geometrical parameters. While the program is running the user can watch the calculated values of the parameters, plots of the main dependencies and explanations of main operations being performed with the program variables. The algorithm of the program assumes that the model multilayer structural elements is idealized, i.e. uniaxial stretching, which is simple and quite adequate. The program is developed for training purposes, so the algorithm used is idealized and not sophisticated but preserving the main features of multilayer structural elements calculation. There is given a comparison of the program with the similar one calculating two materials composite developed by foreign researchers. The program calculates three most often used multilayer structural elements structures (there is no limit of the amount of layers). The presented original program is written in Microsoft programming language Visual Basic 6 and can be used on computers running Windows 9x/Me/Xp.

Spontaneous term labour is associated with increased inflammatory events in the myometrium including cytokine production and leukocyte infiltration. We hypothesized that mechanical stretch of the uterine wall by the growing fetus facilitates peripheral leukocyte transendothelial migration into the term pregnant myometrium through the release of various cytokines. The current study demonstrated that static mechanical stretch directly induces secretion of multiple cytokines and chemokines by human myometrial smooth muscle cells. Stretch-induced cytokines (1) increased vascular permeability; (2) enhanced leukocyte adhesion to the endothelium of the surrounding uterine microvasculature by (3) inducing the expression of endothelial cell adhesion molecules; and (4) directed the transendothelial migration of peripheral neutrophils. Our data provide a direct proof of mechanical regulation in leukocyte recruitment from the uterine blood vessels, which represents a putative mechanism for the leukocyte infiltrate seen in the myometrium during labour and postpartum involution.

Spontaneous term labour is associated with increased inflammatory events in the myometrium including cytokine production and leukocyte infiltration. We hypothesized that mechanical stretch of the uterine wall by the growing fetus facilitates peripheral leukocyte transendothelial migration into the term pregnant myometrium through the release of various cytokines. The current study demonstrated that static mechanical stretch directly induces secretion of multiple cytokines and chemokines by human myometrial smooth muscle cells. Stretch-induced cytokines (1) increased vascular permeability; (2) enhanced leukocyte adhesion to the endothelium of the surrounding uterine microvasculature by (3) inducing the expression of endothelial cell adhesion molecules; and (4) directed the transendothelial migration of peripheral neutrophils. Our data provide a direct proof of mechanical regulation in leukocyte recruitment from the uterine blood vessels, which represents a putative mechanism for the leukocyte infiltrate seen in the myometrium during labour and postpartum involution.

During rhythmic arm cycling soleus H-reflex amplitudes are reduced by modulation of group Ia presynaptic inhibition (Frigon et al, 2004). This reflex suppression is graded with the frequency of arm cycling (Loadman & Zehr 2007; Hundza & Zehr 2009) and 0.8 Hz is the minimum frequency to significantly reduce the soleus H-reflex (Hundza & Zehr 2009). Despite the data on modulation of the soleus H-reflex amplitude induced by rhythmic arm cycling, comparatively little is known about the modulation of stretch reflexes due to remote limb movement. Therefore, the present study was intended to explore the effect of arm cycling on stretch and H-reflex amplitudes in the soleus muscle. In so doing, additional information on the mechanism of action during rhythmic arm cycling would be revealed. Although both reflexes share the same afferent pathway, we hypothesized that stretch reflex amplitudes would be less suppressed by arm cycling because they are less inhibited by presynaptic inhibition (Morita et al, 1998). Failure to reject this hypothesis would add additional strength to the argument that Ia presynaptic inhibition is the mechanism modulating soleus H-reflex amplitude during rhythmic arm cycling. Participants were seated in a customized chair with feet strapped to footplates. Three motor tasks were performed: static control trials and arm cycling at 1 and 2 Hz. Soleus H-reflexes were evoked using single 1 ms pulses of electrical stimulation delivered to the tibial nerve at the popliteal fossa. A constant M-wave and ~6% MVC activation of soleus was maintained across conditions. Stretch reflexes were evoked using a vibratory shaker (ET-126; Labworks Inc). The shaker was placed over the triceps surae tendon and controlled by a custom written LabView program (single sinusoidal pulse at 100Hz). Results demonstrated that rhythmic arm cycling that was effective for conditioning soleus H-reflexes did not show a suppressive effect on the amplitude of the soleus stretch reflex. We suggest this indicates that stretch reflexes are less sensitive to conditioning by rhythmic arm movement, as compared to H-reflexes, due to the relative insensitivity of Ia presynaptic inhibition. / Graduate

The monosynaptic connection between the locust forewing stretch receptor (fSR) and the first basalar motoneuron (BAl) is part of a sensory pathway involved in flight. The fSR is a single sensory afferent, triggered during wing elevation, that makes central connections with the wing depressor motoneuron, BAl. The fSR/BAl synapse in Locusta migratoria was used as a model to study the modulation of cholinergic synaptic transmission. Electrophysiological experiments indicate that presynaptic muscarinic cholinergic receptors are involved in the down-regulation of acetylcholine release from the fSR terminals and at least some of these are located on and activate GABAergic intemeurons that inhibit the fSR. These experiments are supported by electron microscopical (EM) immunocytochemical (ICC) studies, which show that the fSR receives synaptic inputs from neurons immunoreactive (IR) for GABA.Additional EM ICC studies reveal that the fSR also receives synaptic inputs from glutamate-IR neurons. The EM ICC studies also showed that neurons that are not immunoreactive for GABA or glutamate are presynaptic to the fSR and its postsynaptic member, suggesting that the fSR/BAl synapse is modulated by other neuromodulators. Further electrophysiological studies revealed that the biogenic amines, octopamine and dopamine are potentially capable of modulating the fSR/BAl synapse, by suppressing the postsynaptic response of BAl to ACh (at least in part). The biogenic amine, 5- hydroxytryptamine (5HT) is also potentially capable of modulating the fSR/Bal synapse but may act through octopamine receptors. This is supported by confocal microscopical ICC studies, which show that the neuropil region containing the fSR/BAl synapses is octopamine-IR but not 5HT-LR. These results indicate that a range of neuromodulators acting via different mechanisms interact to modulate cholinergic synaptic transmission between the fSR and BAl.

Master of Philosophy (MPhil) / Background: Physical deconditioning is often associated with chronic pain and is believed to be a result of gradual movement inhibition and reduction of physical activities. It is common for chronic pain sufferers to present with limited muscle extensibility and poor tolerance to physical movement. Exercises are therefore prescribed to assist in regaining muscle extensibility, strength, fitness and endurance. Of particular interest is stretch, a type of exercise aimed at increasing muscle extensibility. Stretch is commonly prescribed as part of physical rehabilitation in pain management programs, yet little is known of its effectiveness in the chronic pain population. Aim: The aim of this randomised controlled trial was to investigate the effects of a three-week stretch program on muscle extensibility and stretch tolerance in patients with chronic musculoskeletal pain. Methods: Thirty adults with pain persisting for at least three months and limited hamstring muscle extensibility were recruited from patients enrolled in a multidisciplinary pain management program at a Sydney Hospital. A within-subject design was used, with one leg of each participant randomly allocated to an experimental (stretch) condition and the other to a control (no stretch) condition. The hamstring muscles of the experimental leg were stretched for one minute a day over a three-week period, whilst the hamstring muscles of the control leg were not stretched during this time. This intervention was embedded within a pain management program and supervised by physiotherapists. Primary outcome measures were muscle extensibility and stretch tolerance, reflected by passive hip flexion angles produced with standardised and non-standardised torques, respectively. Initial measures were taken prior to the first stretch on day one and final measures were taken one to two days after the last stretch. A blinded assessor was used for all testing. Results: After three weeks of intervention, stretch did not increase muscle extensibility (mean between-group difference in hip flexion was 1 degree; 95% CI -2 to 4 degrees) but did improve stretch tolerance (mean between-group difference in hip flexion was 8 degrees; 95% CI 5 to 10 degrees). Conclusion: Three weeks of stretch increases tolerance to the discomfort associated with stretch but does not change muscle extensibility in patients with chronic musculoskeletal pain. This study provides support for the ongoing incorporation of stretch in pain management programs, where stretch may be conceptualised as a graded exposure to movement and assisting in the restoration of normal activity and function.

Master of Philosophy (MPhil) / Background: Physical deconditioning is often associated with chronic pain and is believed to be a result of gradual movement inhibition and reduction of physical activities. It is common for chronic pain sufferers to present with limited muscle extensibility and poor tolerance to physical movement. Exercises are therefore prescribed to assist in regaining muscle extensibility, strength, fitness and endurance. Of particular interest is stretch, a type of exercise aimed at increasing muscle extensibility. Stretch is commonly prescribed as part of physical rehabilitation in pain management programs, yet little is known of its effectiveness in the chronic pain population. Aim: The aim of this randomised controlled trial was to investigate the effects of a three-week stretch program on muscle extensibility and stretch tolerance in patients with chronic musculoskeletal pain. Methods: Thirty adults with pain persisting for at least three months and limited hamstring muscle extensibility were recruited from patients enrolled in a multidisciplinary pain management program at a Sydney Hospital. A within-subject design was used, with one leg of each participant randomly allocated to an experimental (stretch) condition and the other to a control (no stretch) condition. The hamstring muscles of the experimental leg were stretched for one minute a day over a three-week period, whilst the hamstring muscles of the control leg were not stretched during this time. This intervention was embedded within a pain management program and supervised by physiotherapists. Primary outcome measures were muscle extensibility and stretch tolerance, reflected by passive hip flexion angles produced with standardised and non-standardised torques, respectively. Initial measures were taken prior to the first stretch on day one and final measures were taken one to two days after the last stretch. A blinded assessor was used for all testing. Results: After three weeks of intervention, stretch did not increase muscle extensibility (mean between-group difference in hip flexion was 1 degree; 95% CI -2 to 4 degrees) but did improve stretch tolerance (mean between-group difference in hip flexion was 8 degrees; 95% CI 5 to 10 degrees). Conclusion: Three weeks of stretch increases tolerance to the discomfort associated with stretch but does not change muscle extensibility in patients with chronic musculoskeletal pain. This study provides support for the ongoing incorporation of stretch in pain management programs, where stretch may be conceptualised as a graded exposure to movement and assisting in the restoration of normal activity and function.

Thesis (M.Eng.). / Written for the Dept. of Biomedical Engineering. Title from title page of PDF (viewed 2009/06/17). Includes bibliographical references.