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Force Decreased (force + decreased)
Selected AbstractsImproving vastus medialis obliquus function reduces pressure applied to lateral patellofemoral cartilageJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 5 2009John J. Elias Abstract The current study was performed to characterize how improving vastus medialis obliquus (VMO) function influences the pressure applied to patellofemoral cartilage. An additional focus was characterizing how lateral and medial cartilage lesions influence cartilage pressures. Ten knees were flexed to 40°, 60°, and 80° in vitro, and forces were applied to represent the VMO and other muscles of the quadriceps group while a thin film sensor measured joint pressures. The knees were loaded with a normal VMO force, with the VMO force decreased by approximately 50%, and with the VMO unloaded. After tests were performed with the cartilage intact, all tests were repeated with a 12-mm-diameter lesion created within the lateral cartilage, with the lateral lesion repaired with silicone, and with a medial lesion created. Based on a two-way repeated measures ANOVA and post-hoc tests, increasing the force applied by the VMO significantly (p,<,0.05) decreased the maximum lateral pressure and significantly increased the maximum medial pressure at each flexion angle. A lateral cartilage lesion significantly increased the maximum lateral pressure, while a medial lesion did not significantly influence the maximum medial pressure. Improving VMO function can reduce the pressure applied to lateral cartilage when lateral lesions are present. © 2008 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 27: 578,583, 2009 [source] Divergent effects of ephedrine and phenylephrine on cardiovascular hemodynamics of near-term fetal sheep exposed to hypoxemia and maternal hypotensionACTA ANAESTHESIOLOGICA SCANDINAVICA, Issue 7 2007T. Erkinaro Background:, We hypothesized that the administration of ephedrine and phenylephrine for maternal hypotension modifies cardiovascular hemodynamics in near-term sheep fetuses. Methods:, At 115,136 days of gestation, chronically instrumented, anesthetized ewes with either normal placental function or increased placental vascular resistance after placental embolization were randomized to receive boluses of ephedrine (n = 12) or phenylephrine (n = 12) for epidural-induced hypotension after a short period of hypoxemia. Fetal cardiovascular hemodynamics were assessed by Doppler ultrasonography at baseline, during hypotension and after vasopressor treatment. Results:, During hypotension, fetal PO2 decreased and proximal branch pulmonary arterial and pulmonary venous vascular impedances increased. Additionally, in the embolized fetuses, the time-velocity integral ratio between the antegrade and retrograde blood flow components of the aortic isthmus decreased. These parameters were restored to baseline conditions by ephedrine but not by phenylephrine. With phenylephrine, weight-indexed left ventricular cardiac output and ejection force decreased in the non-embolized fetuses, and the proportion of isovolumetric contraction time of the total cardiac cycle was elevated in the embolized fetuses. Conclusions:, After exposure to hypoxemia and maternal hypotension, ephedrine restored all fetal cardiovascular hemodynamic parameters to baseline. Phenylephrine did not reverse fetal pulmonary vasoconstriction or the relative decrease in the net forward flow through the aortic isthmus observed in fetuses with increased placental vascular resistance. Moreover, fetal left ventricular function was impaired during phenylephrine administration. [source] High temperature does not alter fatigability in intact mouse skeletal muscle fibresTHE JOURNAL OF PHYSIOLOGY, Issue 19 2009Nicolas Place Intense activation of skeletal muscle results in fatigue development, which involves impaired function of the muscle cells resulting in weaker and slower contractions. Intense muscle activity also results in increased heat production and muscle temperature may rise by up to ,6°C. Hyperthermia is associated with impaired exercise performance in vivo and recent studies have shown contractile dysfunction and premature fatigue development in easily fatigued muscle fibres stimulated at high temperatures and these defects were attributed to oxidative stress. Here we studied whether fatigue-resistant soleus fibres stimulated at increased temperature show premature fatigue development and whether increasing the level of oxidative stress accelerates fatigue development. Intact single fibres or small bundles of soleus fibres were fatigued by 600 ms tetani given at 2 s intervals at 37°C and 43°C, which is the highest temperature the muscle would experience in vivo. Tetanic force in the unfatigued state was not significantly different at the two temperatures. With 100 fatiguing tetani, force decreased by ,15% at both temperatures; the free cytosolic [Ca2+] (assessed with indo-1) showed a similar ,10% decrease at both temperatures. The oxidative stress during fatigue at 43°C was increased by application of 10 ,m hydrogen peroxide or tert-butyl hydroperoxide and this did not cause premature fatigue development. In summary, fatigue-resistant muscle fibres do not display impaired contractility and fatigue resistance at the highest temperature that mammals, including humans, would experience in vivo. Thus, intrinsic defects in fatigue-resistant muscle fibres cannot explain the decreased physical performance at high temperatures. [source] An in vitro study of non-axial forces upon the retention of an O-ring attachmentCLINICAL ORAL IMPLANTS RESEARCH, Issue 12 2009Renata Cristina Silveira Rodrigues Abstract: Objective: The purpose of this study was to evaluate the retention force of an O-ring attachment system in different inclinations to the ideal path of insertion, using devices to compensate angulations. Material and methods: Two implants were inserted into an aluminum base, and ball attachments were screwed to implants. Cylinders with O-rings were placed on ball attachments and connected to the test device using positioners to compensate implant angulations (0°, 7°, and 14°). Plexiglass bases were used to simulate implant angulations. The base and the test device were positioned in a testing apparatus, which simulated insertion/removal of an overdenture. A total of 2900 cycles, simulating 2 years of overdenture use, were performed and 36 O-rings were tested. The force required for each cycle was recorded with computer software. Longitudinal sections of ball attachment,positioner,cylinder with O-rings of each angulation were obtained to analyze the relationship among them, and O-ring sections tested in each angulation were compared with an unused counterpart. A mixed linear model was used to analyze the data, and the comparison was performed by orthogonal contrasts (,=0.05). Results: At 0°, the retention force decreased significantly over time, and the retention force was significantly different in all comparisons, except from 12 to 18 months. When the implants were positioned at 7°, the retention force was statistically different at 0 and 24 months. At 14°, significant differences were found from 6 and 12 to 24 months. Conclusions: Within the limitations of this study, it was concluded that O-rings for implant/attachments perpendicular to the occlusal plane were adequately retentive over the first year and that the retentive capacity of O-ring was affected by implant inclinations despite the proposed positioners. [source] Atom force microscopic characterisation of the interaction forces between bovine serum albumin and cross-linked alkylated chitosan membranes in media of different pHPOLYMER INTERNATIONAL, Issue 12 2002Wen Guang Liu Abstract Butyl, octyl and hexadecyl moieties were introduced into chitosan. The adhesion of bovine serum albumin (BSA) onto glucose aldehyde-crosslinked alkylated chitosan membranes in pH media was investigated by probing the force-displacement curves with BSA-coated Atom force microscope (AFM) tips. The results indicated that, at the isoelectric point (IP), the sample membranes exhibited higher adhesion forces; and deviating from IP ie at pH 2, pH 6, the adhesion forces decreased. The adhesion forces at pH 2 are less than those at pH 6 due to the presence of electrostatic repulsive and attractive interactions, respectively. Measurements of the adhesion force confirmed quantitatively that the introduction of hydrophobic side-chains to chitosan can facilitate protein adsorption; however, longer flexible side-chains can depress protein adsorption to a certain degree. From an analyses of the adhesion forces, it is proposed that protein adsorption can be tuned by adjusting the lengths of the introduced side-alkyl moieties. © 2002 Society of Chemical Industry [source] | |||||||||||||