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Modelos matemáticos aplicados na avaliação da mecânica respiratória em camundongos com desafios de agonista da musculatura lisa.; Mathematical models applied in the assessment of respiratory mechanics in mice with smooth muscle´s agonist challenges.

Aoki, Fabio Gava
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 14/02/2013 PT
Relevância na Pesquisa
36.05%
Modelos matemáticos são utilizados como ferramentas na avaliação da mecânica respiratória para a compreensão da fisiologia e patologias do sistema respiratório. A presente pesquisa visou avaliar, através da aplicação de modelos matemáticos, a mecânica respiratória em camundongos submetidos à metacolina. Deu-se ênfase no modelo linear de compartimento único e suas variantes não lineares. Camundongos C57BL/6 (n = 8) foram traqueostomizados, ventilados mecanicamente (flexiVent, SCIREQ, Canadá) e perturbações em volume foram aplicadas para a modelagem do sistema respiratório. O protocolo experimental foi elaborado de forma a se analisar a variação dos parâmetros respiratórios durante a aplicação do agente broncoativo e também se verificou a divisão do sinal quasi-senoidal em expirações e inspirações durante a técnica de oscilação forçada (FOT) com perturbação de frequência 2,5 Hz. Com base nisso, uma rotina computacional própria foi desenvolvida para a análise dos experimentos realizados no ventilador mecânico e foram pesquisadas as vantagens e desvantagens dos modelos matemáticos aplicados. Os resultados demonstraram um aumento no desvio padrão dos parâmetros do modelo linear unicompartimental e suas variantes não lineares após a aplicação do broncoconstritor. Acredita-se que esta grande variação nos parâmetros esteja relacionada com o enrijecimento do parênquima e da heterogeneidade da ventilação pulmonar após a utilização da droga. Devido à correlação dos parâmetros do modelo com a fisiologia ocorrer somente no modelo linear...

Efeitos do alongamento da musculatura respiratória com a técnica de alongamento passivo e contração-relaxamento na mecânica ventilatória e capacidade funcional de pacientes com doença pulmonar obstrutiva crônica; Effects of respiratory muscle stretching with passive and hold-relax techniques on ventilatory mechanics and functional capacity in patients with chronic obstructive pulmonary disease

Wada, Juliano Takashi
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 13/02/2015 PT
Relevância na Pesquisa
36.17%
Os pacientes com doença pulmonar obstrutiva crônica (DPOC), devido à obstrução brônquica e redução da retração elástica pulmonar apresentam o aumento do recrutamento da musculatura respiratória, predispondo à incoordenação toracoabdominal, aumentando o trabalho respiratório, provocando fadiga e dispnéia. O alongamento dos músculos respiratórios (AMR) poderia diminuir a atividade muscular, melhorar a sua capacidade contrátil e a mobilidade da caixa torácica otimizando a ventilação pulmonar, entretanto, estes efeitos nos músculos respiratórios permanecem desconhecidos. Objetivo: Avaliar os efeitos da adição do AMR associados à reabilitação pulmonar na mecânica ventilatória, na capacidade funcional e na atividade muscular em pacientes com DPOC. Método: Estudo randomizado e controlado incluiu 30 pacientes com DPOC que foram distribuídos aleatoriamente para os grupos: tratado (GT, n = 15) e controle (GC, n = 15). Todos os pacientes foram submetidos a 24 sessões de treinamento aeróbico duas vezes por semana. Além disso, o GT recebeu AMR e o GC recebeu o alongamento dos membros superiores e inferiores, antes dos exercícios aeróbicos. Foram avaliados: teste da capacidade funcional (teste de caminhada de 6 minutos...

Improved systolic ventricular function with normal myocardial mechanics in compensated cardiac hypertrophy

Okoshi, Katashi; Okoshi, Marina Politi; Matsubara, Beatriz Bojikian; Gonçalves, Giancarlo; Barros, Reginaldo; Cicogna, Antonio Carlos
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 297-307
ENG
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36.04%
There still controversy about the relation between changes in myocardial contractile function and global left ventricular (LV) performance during stable concentric hypertrophy. To clarify this, we analyzed LV function in vivo and myocardial mechanics in vitro in rats with pressure overload-induced cardiac hypertrophy. Male Wistar rats (70 g) underwent ascending aorta stenosis for 8 weeks (group AAS, n=9). LV performance was assessed by transthoracic echocardiography under light anesthesia. Myocardial function was studied in isolated papillary muscle preparation during isometric contraction. The data were compared with age- and sex-matched sham-operated rats (group C, n=9). LV weight-to-body weight ratio (C: 2.0 ± 0.5 mg/g; AAS: 3.3 ± 0.7 mg/g), LV relative wall thickness (C: 0.19 ± 0.02; AAS; 0.34 ± 0.10), and LV fractional shortening (C: 54 ± 5%; AAS: 70 ± 8%) were increased in the group AAS (p<0.05). Echocardiographic analysis also indicated a significant association (r=0.74; p<0.001) between percent fractional shortening and LV relative wall thickness. The performance of AAS isolated muscle revealed that active tension (C: 6.6 ± 1.7 g/mm 2; AAS: 6.5 ± 1.5 g/mm 2) and maximum rate of tension development (C: 69 ± 21 g/mm 2/s; AAS: 69 ± 18 g/mm 2) were not significantly different from group C (p>0.05). In conclusion: 1) Compensated pressure-overload myocardial hypertrophy is associated with preserved myocardial function and increased ventricular performance; 2) The improved LV function might be due to the ventricular remodeling characterized by an increased relative wall thickness. Copyright © 2002 By PJD Publications Limited.

Reduced effect of pH on skinned rabbit psoas muscle mechanics at high temperatures: implications for fatigue.

Pate, E; Bhimani, M; Franks-Skiba, K; Cooke, R
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 01/08/1995 EN
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36.11%
1. Inhibition of actomyosin function by decreased pH has been proposed to account for much of the depression of muscle function during fatigue. The clearest support for this hypothesis has been from studies of skinned skeletal muscle fibre mechanics at low temperatures (< or = 15 degrees C). 2. We re-examined the effect of decreased pH (7.0-6.2) on skinned mammalian skeletal fibre mechanics at low (10 degrees C) and high (30 degrees C) temperatures, using recently developed protocols that allow reproducible mechanical data to be obtained at higher temperatures. 3. At 10 degrees C we duplicated previous observations of a significant inhibition of maximum shortening velocity (Vmax) and isometric tension (Po) by acidosis. In contrast, at the higher temperature, we found only a very minimal effect of acidosis on Vmax and a threefold reduction in the decrease in Po. 4. Thus at temperatures only slightly below physiological for mammalian skeletal muscle systems, pH plays a much less important role in the process of muscle fatigue at the cross-bridge level than has been suggested by data obtained at physiologically unrealistic temperatures.

Imaging Two-Dimensional Displacements and Strains in Skeletal Muscle during Joint Motion by Cine DENSE MR

Zhong, Xiaodong; Epstein, Frederick H.; Spottiswoode, Bruce S.; Helm, Patrick A.; Blemker, Silvia S.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
36.06%
The objective of this study was to apply cine magnetic resonance imaging (MRI) using displacement encoding with stimulated echoes (DENSE) to measure the dynamic two-dimensional (2D) displacement and Lagrangian strain fields in the biceps brachii muscle. Six healthy volunteers underwent cine DENSE MRI during repeated elbow flexion against the load of gravity. Displacement encoded dynamic images of the upper arm were acquired with spatial and temporal resolutions of 1.9 × 1.9 mm2 and 30 ms, respectively. Pixel-wise Lagrangian displacement and strain fields were calculated from the measured images. We extracted first and second principal strains (E1 and E2) along the centerline and anterior regions of the muscle. E1 and E2 were relatively uniform along the anterior region. However, E1 and E2 were both nonuniform along the centerline region – normalized values for E1 and E2 varied over the ranges of 0.27 to 1.35, and 0.45 to 2.36, respectively. The directions of the first and second principal strains varied throughout the muscle and showed that the direction of principal shortening is not necessarily aligned with fascicle direction. This study demonstrates the utility of cine DENSE MR imaging for analyzing skeletal muscle mechanics and provides data describing the in vivo mechanics of muscle tissue to a level of detail that has not been previously possible.

Large-scale Models Reveal the Two-component Mechanics of Striated Muscle

Jarosch, Robert
Fonte: Molecular Diversity Preservation International (MDPI) Publicador: Molecular Diversity Preservation International (MDPI)
Tipo: Artigo de Revista Científica
Publicado em 18/12/2008 EN
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36.06%
This paper provides a comprehensive explanation of striated muscle mechanics and contraction on the basis of filament rotations. Helical proteins, particularly the coiled-coils of tropomyosin, myosin and α-actinin, shorten their H-bonds cooperatively and produce torque and filament rotations when the Coulombic net-charge repulsion of their highly charged side-chains is diminished by interaction with ions. The classical “two-component model” of active muscle differentiated a “contractile component” which stretches the “series elastic component” during force production. The contractile components are the helically shaped thin filaments of muscle that shorten the sarcomeres by clockwise drilling into the myosin cross-bridges with torque decrease (= force-deficit). Muscle stretch means drawing out the thin filament helices off the cross-bridges under passive counterclockwise rotation with torque increase (= stretch activation). Since each thin filament is anchored by four elastic α-actinin Z-filaments (provided with force-regulating sites for Ca2+ binding), the thin filament rotations change the torsional twist of the four Z-filaments as the “series elastic components”. Large scale models simulate the changes of structure and force in the Z-band by the different Z-filament twisting stages A...

Significant Impact on Muscle Mechanics of Small Nonlinearities in Myofilament Elasticity

Månsson, Alf
Fonte: The Biophysical Society Publicador: The Biophysical Society
Tipo: Artigo de Revista Científica
Publicado em 22/09/2010 EN
Relevância na Pesquisa
45.94%
Important mechanisms in muscle contraction have recently been reevaluated based on analyses that rely on the assumption of linear myofilament elasticity. However, the present theoretical study shows that nonlinearity of this elasticity, even when so minor that it may be difficult to detect in experimental data, could have great impact on the interpretation of muscle mechanical experiments. This is illustrated by using simulated stiffness and strain-versus-force data for muscle fibers shortening at different constant velocities. There is substantial quantitative agreement, for this condition, between models with distributed myofilament compliance and models where the compliance of the myofilaments and the actomyosin cross-bridges are lumped together into two separate elastic elements acting in series. The data thus support the usefulness of the latter, simpler, type of model in the analysis. However, most importantly, the data emphasize the importance of caution before reevaluating fundamental mechanisms of muscle contraction based on analyses relying on the assumption of linear myofilament elasticity.

Chronic heart failure decreases cross-bridge kinetics in single skeletal muscle fibres from humans

Miller, Mark S; VanBuren, Peter; LeWinter, Martin M; Braddock, Joan M; Ades, Philip A; Maughan, David W; Palmer, Bradley M; Toth, Michael J
Fonte: Blackwell Science Inc Publicador: Blackwell Science Inc
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
46.1%
Skeletal muscle function is impaired in heart failure patients due, in part, to loss of myofibrillar protein content, in particular myosin. In the present study, we utilized small-amplitude sinusoidal analysis for the first time in single human skeletal muscle fibres to measure muscle mechanics, including cross-bridge kinetics, to determine if heart failure further impairs contractile performance by altering myofibrillar protein function. Patients with chronic heart failure (n = 9) and controls (n = 6) were recruited of similar age and physical activity to diminish the potentially confounding effects of ageing and muscle disuse. Patients showed decreased cross-bridge kinetics in myosin heavy chain (MHC) I and IIA fibres, partially due to increased myosin attachment time (ton). The increased ton compensated for myosin protein loss previously found in heart failure patients by increasing the fraction of the total cycle time myosin is bound to actin, resulting in a similar number of strongly bound cross-bridges in patients and controls. Accordingly, isometric tension did not differ between patients and controls in MHC I or IIA fibres. Patients also had decreased calcium sensitivity in MHC IIA fibres and alterations in the viscoelastic properties of the lattice structure of MHC I and IIA fibres. Collectively...

Caenorhabditis elegans Body Mechanics Are Regulated by Body Wall Muscle Tone

Petzold, Bryan C.; Park, Sung-Jin; Ponce, Pierre; Roozeboom, Clifton; Powell, Chloé; Goodman, Miriam B.; Pruitt, Beth L.
Fonte: The Biophysical Society Publicador: The Biophysical Society
Tipo: Artigo de Revista Científica
Publicado em 20/04/2011 EN
Relevância na Pesquisa
36.2%
Body mechanics in the nematode Caenorhabditis elegans are central to both mechanosensation and locomotion. Previous work revealed that the mechanics of the outer shell, rather than internal hydrostatic pressure, dominates stiffness. This shell is comprised of the cuticle and the body wall muscles, either of which could contribute to the body mechanics. Here, we tested the hypothesis that the muscles are an important contributor by modulating muscle tone using optogenetic and pharmacological tools, and measuring animal stiffness using piezoresistive microcantilevers. As a proxy for muscle tone, we measured changes in animal length under the same treatments. We found that treatments that induce muscle contraction generally resulted in body shortening and stiffening. Conversely, methods to relax the muscles more modestly increased length and decreased stiffness. The results support the idea that body wall muscle activation contributes significantly to and can modulate C. elegans body mechanics. Modulation of body stiffness would enable nematodes to tune locomotion or swimming gaits and may have implications in touch sensation.

Differential modulation of right ventricular strain and right atrial mechanics in mild vs. severe pressure overload

Voeller, Rochus K.; Aziz, Abdulhameed; Maniar, Hersh S.; Ufere, Nneka N.; Taggar, Ajay K.; Bernabe, Noel J.; Cupps, Brian P.; Moon, Marc R.
Fonte: American Physiological Society Publicador: American Physiological Society
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
45.85%
Increased right atrial (RA) and ventricular (RV) chamber volumes are a late maladaptive response to chronic pulmonary hypertension. The purpose of the current investigation was to characterize the early compensatory changes that occur in the right heart during chronic RV pressure overload before the development of chamber dilation. Magnetic resonance imaging with radiofrequency tissue tagging was performed on dogs at baseline and after 10 wk of pulmonary artery banding to yield either mild RV pressure overload (36% rise in RV pressure; n = 5) or severe overload (250% rise in RV pressure; n = 4). The RV free wall was divided into three segments within a midventricular plane, and circumferential myocardial strain was calculated for each segment, the septum, and the left ventricle. Chamber volumes were calculated from stacked MRI images, and RA mechanics were characterized by calculating the RA reservoir, conduit, and pump contribution to RV filling. With mild RV overload, there were no changes in RV strain or RA function. With severe RV overload, RV circumferential strain diminished by 62% anterior (P = 0.04), 42% inferior (P = 0.03), and 50% in the septum (P = 0.02), with no change in the left ventricle (P = 0.12). RV filling became more dependent on RA conduit function...

Contribution of myocardium overlying the anterolateral papillary muscle to left ventricular deformation

Itoh, Akinobu; Stephens, Elizabeth H.; Ennis, Daniel B.; Carlhall, Carl-Johan; Bothe, Wolfgang; Nguyen, Tom C.; Swanson, Julia C.; Miller, D. Craig; Ingels, Neil B.
Fonte: American Physiological Society Publicador: American Physiological Society
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
45.89%
Previous studies of transmural left ventricular (LV) strains suggested that the myocardium overlying the papillary muscle displays decreased deformation relative to the anterior LV free wall or significant regional heterogeneity. These comparisons, however, were made using different hearts. We sought to extend these studies by examining three equatorial LV regions in the same heart during the same heartbeat. Therefore, deformation was analyzed from transmural beadsets placed in the equatorial LV myocardium overlying the anterolateral papillary muscle (PAP), as well as adjacent equatorial LV regions located more anteriorly (ANT) and laterally (LAT). We found that the magnitudes of LAT normal longitudinal and radial strains, as well as major principal strains, were less than ANT, while those of PAP were intermediate. Subepicardial and midwall myofiber angles of LAT, PAP, and ANT were not significantly different, but PAP subendocardial myofiber angles were significantly higher (more longitudinal as opposed to circumferential orientation). Subepicardial and midwall myofiber strains of ANT, PAP, and LAT were not significantly different, but PAP subendocardial myofiber strains were less. Transmural gradients in circumferential and radial normal strains...

Effects of increased preload on the force-frequency response and contractile kinetics in early stages of cardiac muscle hypertrophy

Haizlip, Kaylan M.; Bupha-Intr, Tepmanas; Biesiadecki, Brandon J.; Janssen, Paul M. L.
Fonte: American Physiological Society Publicador: American Physiological Society
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
45.85%
Numerous studies have aimed to elucidate markers for the onset of decompensatory hypertrophy and heart failure in vivo and in vitro. Alterations in the force-frequency relationship are commonly used as markers for heart failure with a negative staircase being a hallmark of decompensated cardiac function. Here we aim to determine the functional and molecular alterations in the very early stages of compensatory hypertrophy through analysis of the force-frequency relationship, using a novel isolated muscle culture system that allows assessment of force-frequency relationship during the development of hypertrophy. New Zealand white male rabbit trabeculae excised from the right ventricular free wall were utilized for all experiments. Briefly, muscles held at constant preload and contracting isometrically were stimulated to contract in culture for 24 h, and in a subset up to 48 h. We found that, upon an increase in the preload and maintaining the muscles in culture for up to 24 h, there was an increase in baseline force produced by isolated trabeculae over time. This suggests a gradual compensatory response to the impact of increased preload. Temporal analysis of the force-frequency response during this progression revealed a significant blunting (at 12 h) and then reversal of the positive staircase as culture time increased (at 24 h). Phosphorylation analysis revealed a significant decrease in desmin and troponin (Tn)I phosphorylation from 12 to 24 h in culture. These results show that even very early on in the compensatory hypertrophy state...

Phenomenological consequences of sectioning and bathing on passive muscle mechanics of the New Zealand white rabbit tibialis anterior

Abraham, Adam C.; Kaufman, Kenton R.; Haut Donahue, Tammy L.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
36.1%
Skeletal muscle tissue provides support and mobility of the musculoskeletal system. Numerical modeling of muscle tissue aids in understanding disease pathophysiology, however, the effectiveness is dependent on accurately accounting for various tissue phenomena. Muscle modeling is made difficult due to the multitude of constituents that contribute to elastic and viscous mechanisms. Often, deterministic single fiber or fiber bundle studies are undertaken to examine these contributions. However, examination of whole, intact and structurally altered tissue and comparison to findings at the myofibril scale can help elucidate tissue mechanics. Stress relaxation tests at 10% strain were performed on 28 New Zealand White rabbits tibialis anterior muscles for whole, intact muscle and sub-sectioned muscle samples. Additionally, to aid in examining viscous effects sub groups were tested with and without a phosphate buffered saline bath. The steady-state elastic modulus was not significantly different between groups. Interestingly, sectioning did result in a negative Poisson’s ratio. Additionally, sectioning resulted in altering the viscous tissue response as the time to reach steady-state was significantly faster than whole muscle samples (p < 0.05)...

Mechanical and energetic properties of papillary muscle from ACTC E99K transgenic mouse models of hypertrophic cardiomyopathy

Song, Weihua; Vikhorev, Petr G.; Kashyap, Mavin N.; Rowlands, Christina; Ferenczi, Michael A.; Woledge, Roger C.; MacLeod, Kenneth; Marston, Steven; Curtin, Nancy A.
Fonte: American Physiological Society Publicador: American Physiological Society
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
46%
We compared the contractile performance of papillary muscle from a mouse model of hypertrophic cardiomyopathy [α-cardiac actin (ACTC) E99K mutation] with nontransgenic (non-TG) littermates. In isometric twitches, ACTC E99K papillary muscle produced three to four times greater force than non-TG muscle under the same conditions independent of stimulation frequency and temperature, whereas maximum isometric force in myofibrils from these muscles was not significantly different. ACTC E99K muscle relaxed slower than non-TG muscle in both papillary muscle (1.4×) and myofibrils (1.7×), whereas the rate of force development after stimulation was the same as non-TG muscle for both electrical stimulation in intact muscle and after a Ca2+ jump in myofibrils. The EC50 for Ca2+ activation of force in myofibrils was 0.39 ± 0.33 μmol/l in ACTC E99K myofibrils and 0.80 ± 0.11 μmol/l in non-TG myofibrils. There were no significant differences in the amplitude and time course of the Ca2+ transient in myocytes from ACTC E99K and non-TG mice. We conclude that hypercontractility is caused by higher myofibrillar Ca2+ sensitivity in ACTC E99K muscles. Measurement of the energy (work + heat) released in actively cycling heart muscle showed that for both genotypes...

Effect of levosimendan on the contractility of muscle fibers from nemaline myopathy patients with mutations in the nebulin gene

de Winter, Josine M; Joureau, Barbara; Sequeira, Vasco; Clarke, Nigel F; van der Velden, Jolanda; Stienen, Ger JM; Granzier, Henk; Beggs, Alan H; Ottenheijm, Coen AC
Fonte: BioMed Central Publicador: BioMed Central
Tipo: Artigo de Revista Científica
EN_US
Relevância na Pesquisa
46.01%
Background: Nemaline myopathy (NM), the most common non-dystrophic congenital myopathy, is characterized by generalized skeletal muscle weakness, often from birth. To date, no therapy exists that enhances the contractile strength of muscles of NM patients. Mutations in NEB, encoding the giant protein nebulin, are the most common cause of NM. The pathophysiology of muscle weakness in NM patients with NEB mutations (NEB-NM) includes a lower calcium-sensitivity of force generation. We propose that the lower calcium-sensitivity of force generation in NEB-NM offers a therapeutic target. Levosimendan is a calcium sensitizer that is approved for use in humans and has been developed to target cardiac muscle fibers. It exerts its effect through binding to slow skeletal/cardiac troponin C. As slow skeletal/cardiac troponin C is also the dominant troponin C isoform in slow-twitch skeletal muscle fibers, we hypothesized that levosimendan improves slow-twitch muscle fiber strength at submaximal levels of activation in patients with NEB-NM. Methods: To test whether levosimendan affects force production, permeabilized slow-twitch muscle fibers isolated from biopsies of NEB-NM patients and controls were exposed to levosimendan and the force response was measured. Results: No effect of levosimendan on muscle fiber force in NEB-NM and control skeletal muscle fibers was found...

3D movement and muscle activity patterns in a violin bowing task

Wales, Jennifer.
Fonte: Brock University Publicador: Brock University
Tipo: Electronic Thesis or Dissertation
ENG
Relevância na Pesquisa
36.1%
Objective: Overuse injuries in violinists are a problem that has been primarily analyzed through the use of questionnaires. Simultaneous 3D motion analysis and EMG to measure muscle activity has been suggested as a quantitative technique to explore this problem by identifying movement patterns and muscular demands which may predispose violinists to overuse injuries. This multi-disciplinary analysis technique has, so far, had limited use in the music world. The purpose of this study was to use it to characterize the demands of a violin bowing task. Subjects: Twelve injury-free violinists volunteered for the study. The subjects were assigned to a novice or expert group based on playing experience, as determined by questionnaire. Design and Settings: Muscle activity and movement patterns were assessed while violinists played five bowing cycles (one bowing cycle = one down-bow + one up-bow) on each string (G, D, A, E), at a pulse of 4 beats per bow and 100 beats per minute. Measurements: An upper extremity model created using coordinate data from markers placed on the right acromion process, lateral epicondyle of the humerus and ulnar styloid was used to determine minimum and maximum joint angles, ranges of motion (ROM) and angular velocities at the shoulder and elbow of the bowing arm. Muscle activity in right anterior deltoid...

Ultrastructural and cellular basis for the development of abnormal myocardial mechanics during the transition from hypertension to heart failure

Shah, Sanjiv J.; Aistrup, Gary L.; Gupta, Deepak K.; O'Toole, Matthew J.; Nahhas, Amanda F.; Schuster, Daniel; Chirayil, Nimi; Bassi, Nikhil; Ramakrishna, Satvik; Beussink, Lauren; Misener, Sol; Kane, Bonnie; Wang, David; Randolph, Blake; Ito, Aiko; Wu, M
Fonte: American Physiological Society Publicador: American Physiological Society
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
45.97%
Although the development of abnormal myocardial mechanics represents a key step during the transition from hypertension to overt heart failure (HF), the underlying ultrastructural and cellular basis of abnormal myocardial mechanics remains unclear. We therefore investigated how changes in transverse (T)-tubule organization and the resulting altered intracellular Ca2+ cycling in large cell populations underlie the development of abnormal myocardial mechanics in a model of chronic hypertension. Hearts from spontaneously hypertensive rats (SHRs; n = 72) were studied at different ages and stages of hypertensive heart disease and early HF and were compared with age-matched control (Wistar-Kyoto) rats (n = 34). Echocardiography, including tissue Doppler and speckle-tracking analysis, was performed just before euthanization, after which T-tubule organization and Ca2+ transients were studied using confocal microscopy. In SHRs, abnormalities in myocardial mechanics occurred early in response to hypertension, before the development of overt systolic dysfunction and HF. Reduced longitudinal, circumferential, and radial strain as well as reduced tissue Doppler early diastolic tissue velocities occurred in concert with T-tubule disorganization and impaired Ca2+ cycling...

The role of intrinsic muscle mechanics in the neuromuscular control of stable running in the guinea fowl

Daley, Monica A; Voloshina, Alexandra; Biewener, Andrew A
Fonte: Blackwell Science Inc Publicador: Blackwell Science Inc
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
36.1%
Here we investigate the interplay between intrinsic mechanical and neural factors in muscle contractile performance during running, which has been less studied than during walking. We report in vivo recordings of the gastrocnemius muscle of the guinea fowl (Numida meleagris), during the response and recovery from an unexpected drop in terrain. Previous studies on leg and joint mechanics following this perturbation suggested that distal leg extensor muscles play a key role in stabilisation. Here, we test this through direct recordings of gastrocnemius fascicle length (using sonomicrometry), muscle–tendon force (using buckle transducers), and activity (using indwelling EMG). Muscle recordings were analysed from the stride just before to the second stride following the perturbation. The gastrocnemius exhibits altered force and work output in the perturbed and first recovery strides. Muscle work correlates strongly with leg posture at the time of ground contact. When the leg is more extended in the drop step, net gastrocnemius work decreases (−5.2 J kg−1versus control), and when the leg is more flexed in the step back up, it increases (+9.8 J kg−1versus control). The muscle's work output is inherently stabilising because it pushes the body back toward its pre-perturbation (level running) speed and leg posture. Gastrocnemius length and force return to level running means by the second stride following the perturbation. EMG intensity differs significantly from level running only in the first recovery stride following the perturbation...

A dynamic model of smooth muscle contraction.

Gestrelius, S; Borgström, P
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /07/1986 EN
Relevância na Pesquisa
36.06%
A dynamic model of smooth muscle contraction is presented and is compared with the mechanical properties of vascular smooth muscle in the rat portal vein. The model is based on the sliding filament theory and the assumption that force is produced by cross-bridges extending from the myosin to the actin filaments. Thus, the fundamental aspects of the model are also potentially applicable to skeletal muscle. The main concept of the model is that the transfer of energy via the cross-bridges can be described as a 'friction clutch' mechanism. It is shown that a mathematical formulation of this concept gives rise to a model that agrees well with experimental observations on smooth muscle mechanics under isotonic as well as isometric conditions. It is noted that the model, without any ad hoc assumptions, displays a nonhyperbolic force-velocity relationship in its high-force portion and that it is able to maintain isometric force in conditions of reduced maximum contraction velocity. Both these findings are consistent with new experimental observations on smooth muscle mechanics cannot be accounted for by the classical Hill model.

Alongamento muscular; Stretching muscle. Pt. II - Mechanical interactions

Durigon, Odete de Fátima Sallas
Fonte: Universidade de São Paulo. Faculdade de Medicina Publicador: Universidade de São Paulo. Faculdade de Medicina
Tipo: info:eu-repo/semantics/article; info:eu-repo/semantics/publishedVersion; ; Formato: application/pdf
Publicado em 07/12/1995 POR
Relevância na Pesquisa
45.89%
O autor analisa os aspectos da mecânica muscular envolvidos nos procedimentos de alongamento bem como alguns dos mecanismos dos efeitos deste tipo de trabalho sobre a estrutura do músculo.; The autor analize the aspects of muscle mechanics envolved in the stretching procedures and the mechanisms of these effects on the muscle structure.