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51.
Levy C Landesberg A 《American journal of physiology. Heart and circulatory physiology》2004,286(1):H434-H441
Various mechanisms have been suggested to explain cardiac force-length Ca2+ relations. The existence of a cooperativity mechanism, whereby cross-bridge (XB) recruitment is affected by the number of active XBs, suggests that the force response to length oscillations should lag length oscillations. Consequently, the oscillatory force response should be larger during shortening than during lengthening. To test this prediction, force responses to large-sarcomere length (SL) oscillations (36.7 +/- 16.0 nm) at different SLs (n = 6) and frequencies (n = 7) were studied in intact tetanized trabeculae dissected from rat right ventricle (n = 13). Stable tetani were obtained by utilizing 30 microM cyclopiazonic acid in Krebs-Henseleit solution containing 6 mM extracellular Ca(2+) at 25 degrees C. SL was measured by laser diffraction techniques (Dalsa). Force was measured by silicone strain gauge. Instantaneous dynamic stiffness during large oscillations was measured by superimposing additional fast (50 or 200 Hz) and small-amplitude (2.25 +/- 0.25 nm) oscillations. The force responses lagged the SL oscillations at slow frequencies (112 +/- 41 ms at 1 Hz), and counterclockwise hystereses were obtained in the force-length plane: the force was higher during shortening than during lengthening. The delay in the force response decreased as the frequency of the SL oscillation was increased. Clockwise hysteresis, where the force preceded the SL, was obtained at frequencies >4 Hz. Similar hysteresis characteristics were obtained in the force-SL and stiffness-SL planes. Maximal lag was observed at the shortest SL, and the delay decreased with sarcomere elongation: 131.1 +/- 31.7 ms at 1.78 +/- 0.03 microm vs. 14.7 +/- 18.5 ms at 1.99 +/- 0.015 microm. The results establish the ability of cardiac fiber to adapt XB recruitment to changes in prevailing loading conditions. This study supports the stipulated existence of a cooperativity mechanism that regulates XB recruitment and highlights an additional method to characterize regulation of the force-length relation. 相似文献
52.
Nicola Theis Amir A. Mohagheghi Thomas Korff 《Journal of electromyography and kinesiology》2012,22(6):947-953
Tendon stiffness is calculated by dividing changes in tendon force by tendon elongation. For this purpose, participants are commonly asked to perform a maximal muscle contraction (“active” method). Alternatively tendon elongation can be achieved by means of a passive joint rotation (“passive” method). The purpose of this study was to compare Achilles tendon stiffness obtained from both methods across different tendon strain rates. Twenty adults performed a series of ramped maximum isometric plantarflexions of different durations. Passive ankle rotations of different angular velocities were also performed. Achilles tendon stiffness was obtained from a combination of motion analysis, isokinetic dynamometry and ultrasonography and compared across methods at three strain rates. At all strain rates, tendon stiffness obtained from the active method was 6% greater compared to the passive method. In spite of this systematic bias, there was good agreement between the methods. Intraclass correlation coefficients were greater than 0.98, and more than 95% of data points fell into the 95% confidence intervals. This agreement will be acceptable in many research contexts. We also found a linear increase in tendon stiffness with increasing strain rate, which must be taken into consideration when interpreting or reporting tendon stiffness. 相似文献
53.
Mohd Amir Taj Mohammad Kartikay Prasad Gulam Mustafa Hasan Vijay Kumar Ravins Dohare 《Journal of biomolecular structure & dynamics》2020,38(15):4625-4634
Communicated by Ramaswamy H. Sarma 相似文献
54.
AIMS: The objective of the study was to assess the pharmacodynamic equivalence of LHRH analogue triptorelin 3-month and 28-day SR formulations. METHODS: Patients with documented locally advanced or metastatic prostate cancer were randomized to receive one injection of the 3-month formulation (n = 63) or three injections at 28-day intervals of the 28-day formulation (n = 68). Group-chemical castration rates defined as the percentage of patients reaching a testosterone plasma level =0.5 ng/ml were compared at D84 (i.e., 3 x 28 days). Testosterone, LH and triptorelin plasma profiles, and change from baseline in plasma PSA were assessed over 3 months (from baseline to D91). RESULTS: Chemical castration rates were 98 and 96% in the 3-month and 28-day formulation groups, respectively, with confidence interval (two-sided 94.2% CI) of [-8.1%; 9.6%]. Median times to reach chemical castration were 18.8 and 18.5 days (p = 0.86, log rank), respectively. Ratios for mean peak plasma levels and AUC(91) of the two formulations for both testosterone and LH fell within the [0.80; 1.25] equivalence interval. Mean PSA decreases from baseline at D91 were 91.0 and 91.7%, respectively (p = 0.73). CONCLUSION: Treatments with the two triptorelin formulations over 3 months are pharmacologically equivalent. 相似文献
55.
Andre Serra Bley Jo?o Carlos Ferrari Correa Amir Curcio Dos Reis Nayra Deise Dos Anjos Rabelo Paulo Henrique Marchetti Paulo Roberto Garcia Lucareli 《PloS one》2014,9(5)
Asymmetry in the alignment of the lower limbs during weight-bearing activities is associated with patellofemoral pain syndrome (PFPS), caused by an increase in patellofemoral (PF) joint stress. High neuromuscular demands are placed on the lower limb during the propulsion phase of the single leg triple hop test (SLTHT), which may influence biomechanical behavior. The aim of the present cross-sectional study was to compare kinematic, kinetic and muscle activity in the trunk and lower limb during propulsion in the SLTHT using women with PFPS and pain free controls. The following measurements were made using 20 women with PFPS and 20 controls during propulsion in the SLTHT: kinematics of the trunk, pelvis, hip, and knee; kinetics of the hip, knee and ankle; and muscle activation of the gluteus maximus (GM), gluteus medius (GMed), biceps femoris (BF) and vastus lateralis (VL). Differences between groups were calculated using three separate sets of multivariate analysis of variance for kinematics, kinetics, and electromyographic data. Women with PFPS exhibited ipsilateral trunk lean; greater trunk flexion; greater contralateral pelvic drop; greater hip adduction and internal rotation; greater ankle pronation; greater internal hip abductor and ankle supinator moments; lower internal hip, knee and ankle extensor moments; and greater GM, GMed, BL, and VL muscle activity. The results of the present study are related to abnormal movement patterns in women with PFPS. We speculated that these findings constitute strategies to control a deficient dynamic alignment of the trunk and lower limb and to avoid PF pain. However, the greater BF and VL activity and the extensor pattern found for the hip, knee, and ankle of women with PFPS may contribute to increased PF stress. 相似文献
56.
The online photoreaction of the rose bengal photosensitized luminol–copper (II) chemiluminescence (CL) system was used for the determination of β-nicotinamide adenine dinucleotide (NADH) and ethanol (EtOH) in pharmaceutical formulations combined with a flow injection technique. NADH can significantly enhance the CL emission of the reaction. For EtOH, alcohol dehydrogenase in soluble form was utilized in the presence of nicotinamide adenine dinucleotide resulting in NADH production. The limit of detection (3σ blank, 𝑛 = 3) of 4.0 × 10−8 and 2.17 × 10−5 M, and linear range 1.3 × 10−7 to 2.5 × 10−5 M (R2 = 0.9998, n = 6) and 0.11–2.17 × 10−3 M (R2 = 0.9996, n = 6) were obtained for NADH and EtOH respectively. The injection rate was 100 h−1 with a relative standard deviation (n = 3) of 1.5–4.8% in the range studied for both analytes. The procedure was satisfactorily applied to pharmaceutical formulations with recoveries in the range 91.6 ± 3.0% to 110 ± 2.0% for NADH and 88 ± 3.0% to 95.4 ± 4.0% for EtOH. The results obtained were very consistent and did not differ considerably from the reported approaches at a 95% confidence limit. The possible mechanism of the CL reaction is also explained briefly. 相似文献
57.
A detailed 3D anatomical model of the patellofemoral joint was developed to study the tracking, force, contact and stability characteristics of the joint. The quadriceps was considered to include six components represented by 15 force vectors. The patellar tendon was modeled using four bundles of viscoelastic tensile elements. Each of the lateral and medial retinaculum was modeled by a three-bundle nonlinear spring. The femur and patella were considered as rigid bodies with their articular cartilage layers represented by an isotropic viscoelastic material. The geometrical and tracking data needed for model simulation, as well as validation of its results, were obtained from an in vivo experiment, involving MR imaging of a normal knee while performing isometric leg press against a constant 140 N force. The model was formulated within the framework of a rigid body spring model and solved using forth-order Runge-Kutta, for knee flexion angles between zero and 50 degrees. Results indicated a good agreement between the model predictions for patellar tracking and the experimental results with RMS deviations of about 2 mm for translations (less than 0.7 mm for patellar mediolateral shift), and 4 degrees for rotations (less than 3 degrees for patellar tilt). The contact pattern predicted by the model was also consistent with the results of the experiment and the literature. The joint contact force increased linearly with progressive knee flexion from 80 N to 210 N. The medial retinaculum experienced a peak force of 18 N at full extension that decreased with knee flexion and disappeared entirely at 20 degrees flexion. Analysis of the patellar time response to the quadriceps contraction suggested that the muscle activation most affected the patellar shift and tilt. These results are consistent with the recent observations in the literature concerning the significance of retinaculum and quadriceps in the patellar stability. 相似文献
58.
59.
Hossein Jafari Mansoorian Amir Hossein Mahvi Ahmad Jonidi Jafari Mohammad Mehdi Amin Ahmad Rajabizadeh Narges Khanjani 《Enzyme and microbial technology》2013,52(6-7):352-357
Electricity generation from microbial fuel cells which treat food processing wastewater was investigated in this study. Anaerobic anode and aerobic cathode chambers were separated by a proton exchange membrane in a two-compartment MFC reactor. Buffer solutions and food industry wastewater were used as electrolytes in the anode and cathode chambers, respectively. The produced voltage and current intensity were measured using a digital multimeter. Effluents from the anode compartment were tested for COD, BOD5, NH3, P, TSS, VSS, SO4 and alkalinity. The maximum current density and power production were measured 527 mA/m2 and 230 mW/m2 in the anode area, respectively, at operation organic loading (OLR) of 0.364 g COD/l.d. At OLR of 0.182 g COD/l.d, maximum voltage and columbic efficiency production were recorded 0.475 V and 21%, respectively. Maximum removal efficiency of COD, BOD5, NH3, P, TSS, VSS, SO4 and alkalinity were 86, 79, 73, 18, 68, 62, 30 and 58%, respectively. The results indicated that catalysts and mediator-less microbial fuel cells (CAML-MFC) can be considered as a better choice for simple and complete energy conversion from the wastewater of such industries and also this could be considered as a new method to offset wastewater treatment plant operating costs. 相似文献
60.