Kinetic mechanisms to alter walking speed

A mechanism to modulate speed during human walking has not yet been proposed in the literature, even though changing walking speed is likely a necessary attribute of everyday ambulation. To understand how joint kinetics modulate walking speed 12 normal adults walked Fast (1.4 m/s), Slow (1.0 m/s), Accel (1.0–1.4 m/s) and Decel (1.4–1.0 m/s) trials while full body 3D kinematics and kinetics were collected. Reduced sagittal ankle plantarflexor moments were observed in Accel trials during early single limb stance (p < 0.001) and increased sagittal plantarflexor moments were seen in Decel trials during early single limb stance (p < 0.001) compared to steady speed walking. Modulating the sagittal ankle moment altered the center of pressure location and either attenuated (Accel) or accentuated (Decel) the early stance braking impulse to accelerate or decelerate the center of mass. The onset of walking speed changes occurred at 15% of the gait cycle and did not support the concept of “controlled falling”. Sagittal ankle push-off power appears a consequence of increased walking speed, but not the causative factor to increase walking speed.     

A Kinetic Model of Intervertebral Stress During Lifting

A biomechanical model of a simple lifting motion is presented in which the forces and moments of force acting about the L4-L5 vertebral articulation were determined from kinetic and kinematic data. Derivation of the forces due to motion permitted a unique method for estimating intervertebral stress during each phase of the lift and provided a logical extension to an earlier static model of intervertebral stress presented by Troup (13). The intervertebral force was found to have a maximum value of over 400 kg during the initial phase of the lift. By partitioning this force into its shearing and compressional components, it was possible to determine quantitatively the lumbar stress involved in lifting. The values are discussed briefly in relation to the aetiology of back injuries and some of the predictions and applications of the dynamic model are also considered.     

Kinetic modeling in support of radionuclide dose assessment

In this review, we trace the origins of mathematical modeling methods and pay particular attention to radiotracer applications. Nuclear medicine has been advanced greatly by the efforts of the Society of Nuclear Medicine's Medical Internal Radiation Dose Committee. Well-developed mathematical methods and tools have been created in support of a wide range of applications. Applications of mathematical modeling extend well beyond biology and medicine and are essential to analysis is a wide range of fields that rely on numerical predictions, eg, weather, economic, and various gaming applications. We start with the discovery of radioactivity and radioactive transformations and illustrate selected applications in biology, physiology, and pharmacology. We discuss compartment models as tools used to frame the context of specific problems. A definition of terms, methods, and examples of particular problems follows. We present models of different applications with varying complexity depending on the features of the particular system and function being analyzed. Commonly used analysis tools and methods are described, followed by established models which describe dosimetry along gastrointestinal and urinary excretory pathways, ending finally with a brief discussion of bone marrow dose. We conclude pointing to more recent, promising methods, not yet widely used in dosimetry applications, which aim at coupling pharmacokinetic data with other patient data to correlate patient outcome (benefits and risk) with the type, amount, kind and timing of the therapy the patient received.     

Kinetic analysis of forwards and backwards stair descent

The activity of descending stairs increases loading at the joints of the lower extremities as compared to walking, which may cause discomfort and or difficulties in completing the task. This study compared and contrasted the kinematics and kinetics of both forwards and backwards stair descent to those of level walking. We compared the support moments and moment powers of the lower limb joints while descending stairs forwards at a self-selected pace, backwards at a self-selected pace and forwards at the same pace as backwards. Participants were 10 healthy young adults (6 men and 4 women) aged 20–35 years. Sagittal plane kinematics and ground reaction forces were collected and moments of force computed using inverse dynamics. The ratio of stance/swing phase changed from 59:41 for normal level walking to between 65:35 and 70:30 for forward stair descent but backwards descent was 58:42. Stair descent produced larger double-peak support moments with reduced ankle plantar flexor and increased knee extensor moments as compared to level walking (>±95th-percentile confidence interval). The hip moments during stair descent were relatively small and highly variable. We observed significantly larger distances between the centres of pressure and the stair edges for backwards stair descent versus forwards stair descent. These results demonstrate that stair descent, even at a slower pace, requires greater power from the knee extensors than level walking but that backwards stair descent significantly reduced the peak knee power during midstance and provided a potentially safer means of descending stairs than forwards stair descent.     

Kinetic modeling in positron emission tomography.

Most PET kinetic modeling approaches have at their basis a compartmental model that has first-order, constant coefficients. The present article outlines the one-, two-, and three-compartment models used to measure cerebral blood flow, cerebral glucose metabolism, and receptor binding, respectively. The number of compartments of each model is based on specific knowledge of the physiological and/or biochemical compartments into which the tracer distributes. Additional physical and biochemical properties of the tracer distribution are considered in specifying the use of first-order rate constants. For example, in cerebral blood flow and receptor binding studies transport across the blood-brain barrier by diffusion can be modeled as a first-order process. A saturable carrier-mediated process or saturable enzyme catalyzed reaction, when tracer doses of the labeled substrate are used and the natural substrate is in steady-state, also results in first-order rate constants, as in glucose metabolism studies. The rate of ligand binding, on the other hand, depends on the concentrations of both substrate and available receptors. In order to appropriately model the reaction as pseudo first-order during a specified experimental interval, protocols are carefully designed to assure that the number of available binding sites remains approximately constant throughout the given interval. A broad array of scanning protocols is employed for kinetic analyses. These include single-scan approaches, which function like their autoradiographic counterparts in animal studies and are often called "autoradiographic" methods, which allow estimation of a single parameter. Dynamic scanning to obtain the time course of tissue activity allows simultaneous estimation of multiple parameters. Scanning may be conducted during a period of tracer uptake or after attainment of steady-state conditions. All quantitative modeling approaches share the common requirement that an arterial input function be measured or an appropriate surrogate be found. A vast array of methods is available for estimation of model parameters, both micro and macro. In the final analysis, it is the interaction among all elements of the PET study, including careful tracer selection, model specification, experimental protocol design, and sound parameter estimation methods, that determines the quantitative accuracy of the estimates of the physiological or biochemical process under study.     

Kinetic chain abnormalities in the athletic shoulder

Overhead activities require the shoulder to be exposed to and sustain repetitive loads. The segmental activation of the body's links, known as the kinetic chain, allows this to occur effectively. Proper muscle activation is achieved through generation of energy from the central segment or core, which then transfers the energy to the terminal links of the shoulder, elbow, and hand. The kinetic chain is best characterized by 3 components: optimized anatomy, reproducible efficient motor patterns, and the sequential generation of forces. However, tissue injury and anatomic deficits such as weakness and/or tightness in the leg, pelvic core, or scapular musculature can lead to overuse shoulder injuries. These injuries can be prevented and maladaptations can be detected with a thorough understanding of biomechanics of the kinetic chain as it relates to overhead activity.     

Kinetic asymmetries during running in male youth

ObjectivesA possible injury risk factor is limb asymmetry, which may differ across maturation given the adult growth spurt. The aim of this study is to quantify the magnitude of asymmetry in a number of kinetic variables during a running task in male youth of different maturity status.DesignQuantitative observational laboratory study.SettingSports performance laboratory.ParticipantsNon-injured youth athletes in pre-, mid-, and post-pubescent status.Main outcome measuresInter-limb leg asymmetries whilst sprinting on a non-motorized treadmill. Percent asymmetry was defined as: (Left leg − right leg)/right leg*100 = %asymmetry.ResultsHorizontal force presented limb asymmetries of 15.4, 14.8 and 14.7% for the pre-, mid- and post-PHV group respectively. Values for vertical force were higher (18.1, 20.2 and 20.8% respectively). Power asymmetries were 14.9, 15.8, and 15.5% respectively and work asymmetries were significant higher in pre-PHV participants (26.4%) compared to mid- (14.7%) and post-PHV (17.3%) participants.ConclusionsAs the population in this study was characterized as non-injured, asymmetries of 15–20% appeared typical during a running task in developmental athletes.     

HMME在不同溶液中光漂白反应动力学规律

目的 分析国产光敏剂血卟啉单甲醚（HMME）在不同溶液中光漂白反应动力学规律，加深对光漂白反应复杂反应过程的理解，并为HMME-PDT治疗微血管病变的数学建模研究提供实验依据和参数。 方法 根据光化学反应动力学原理，从理论上推导出在单纯溶液和复杂溶液（含可被光氧化的底物）中，单态氧介导的光漂白反应动力学方程，通过对实验测定的漂白数据（不同时间点的HMME浓度）进行拟合，进一步验证理论推导出光漂白反应动力学方程。 结果 HMME在单一溶液体系（PBS、DMSO）中的光漂白符合1级反应动力学过程，在含底物的复杂体系（白蛋白缓冲液、细胞悬液）中符合2级反应动力学过程。 结论 HMME在不同溶液体系中的光漂白遵循不同的反应动力学规律。根据化学反应动力学原理进行光漂白等复杂光化学反应过程的数学模拟是可行的，并有利于对复杂光化学反应过程的深入理解。     

Kinetic studies on oxidation of molecular tritium by soils

Molecular tritium oxidation by soil was investigated in the laboratory. The same oxidation mechanism was found for molecular tritium and hydrogen gas as the addition of hydrogen gas suppressed the oxidation rate of molecular tritium. Analyses by Michaelis—Menten kinetics showed apparent K_m values significantly lower at atmospheric hydrogen gas levels (below 2 ppm) than at elevated hydrogen gas levels. Soil temperature affected the oxidation rate as indicated by a change of V_max values with soil temperature while apparent K_m values remained constant. All soils from different locations had an oxidizing ability of molecular tritium and similar apparent K_m values. This indicated that oxidation is common in soils and similar enzymes are responsible for the oxidation of molecular tritium at atmospheric hydrogen levels.     

Kinetic modeling of PET-FDG in the brain without blood sampling

The aim in this work is to report a new method to calculate parametric images from a single scan acquisition with positron emission tomography (PET) and fluorodeoxyglucose (FDG) in the human brain without blood sampling. It is usually practical for research or clinical purposes to inject the patient in an isolated room and to start the PET acquisition only for some 10–20 min, about 30 min after FDG injection. In order to calculate the cerebral metabolic rates for glucose (CMRG), usually several blood samples are required. The proposed method considers the relation between the uptake of the tracer in the cerebellum as a reference tissue and the population based input curve. Similar results were obtained for CMRG values with the present method in comparison to the usual autoradiographic and the non-linear least squares fitting of regions of interest.     

CAR-T制备工艺中PD-1表达的动力学研究

目的 研究嵌合抗原受体T细胞(CAR-T)制备工艺中抗CD3/CD28磁珠和慢病毒对T细胞中程序性死亡因子1(PD-1)蛋白表达的影响,为改善其体内抗肿瘤活性研究提供理论依据.方法 筛选高表达PD-1细胞系,添加CAR-T制备工艺中抗CD3/CD28磁珠和慢病毒(CAR-GFP、CAR-CD19、CAR-CD30),流...     

慢性踝关节不稳患者三维步态动力学特征

目的:研究慢性踝关节不稳患者步态的三维动力学特征,探讨其运动功能变化及生物力学机制。方法:选择慢性踝关节不稳患者15名(实验组),依据其年龄、身高、体重匹配健康受试者15名(对照组)。采用三维动作捕捉系统和Visual 3D软件观测受试者步行时支撑期地面反作用力(GRF)及踝关节力矩的变化。结果:实验组在矢状轴、额状轴和垂直轴的GRF第1峰值较对照组差异均无统计学意义(P>0.05),但3个轴向的GRF第2峰值均较对照组小,其中矢状轴向前和垂直轴向上的GRF差异具有统计学意义(P<0.01)。踝关节力矩于矢状面、额状面、水平面的第1峰值分别是背伸、内翻和内收力矩,实验组较对照组差异均无统计学意义(P>0.05)。踝关节力矩于3个面的第2峰值分别是跖屈、外翻和外展力矩,实验组均较对照组小,其中跖屈和外展力矩差异具有统计学意义(P<0.05)。结论:慢性踝关节不稳患者步行过程中,于支撑末期向上、向前的地面反作用力以及踝跖屈、外展力矩降低,这可能是踝跖屈、外翻肌群肌肉功能不足所致,但导致踝关节跖屈功能不足的主要肌群尚需进一步明确。     

动态浊度法检测盐酸普鲁卡因注射液中的细菌内毒素

目的　建立盐酸普鲁卡因注射液中细菌内毒素的定量检测方法。方法　采用动态浊度法和“二点法”测定计算内毒素回收率。结果　将样品原液进行 1→ 16稀释 (1.2 5mg·ml-1)可消除其对鲎试验的抑制作用。结论　用“二点法”计算内毒素回收率 ,具有良好的可操作性和较强的可靠性。     

经尿道双极等离子汽化电切术治疗前列腺增生

目的观察经尿道双极等离子汽化电切术治疗前列腺增生症的疗效。方法采用英国GYRUS经尿道双极等离子汽化电切镜系统治疗前列腺增生症78例。结果术中出血少、无水中毒及尿失禁发生。结论双极等离子汽化电切镜系统治疗前列腺增生症,具有疗效显著,术野清晰,出血量少,并发症少,安全性高等优点,是治疗前列腺增生症较好的手术方法。     

Kinetic comparison of older men and women during walk-to-stair descent transition

Stair walking is one of the most challenging tasks for older adults, with women reporting higher incidence of falls. The purpose of this study was to investigate the gender differences in kinetics during stair descent transition. Twenty-eight participants (12 male and 16 female; 68.5 and 69.0 years of mean age, respectively) performed stair descent from level walking in a step-over-step manner at a self-selected speed over a custom-made three-step staircase with embedded force plates. Kinematic and force data were combined using inverse dynamics to generate kinetic data for gender comparison. The top and the first step on the staircase were chosen for analysis. Women showed a higher trail leg peak hip abductor moment (−1.0 N m/kg), lower trail leg peak knee extensor moment and eccentric power (0.74 N m/kg and 3.15 W/kg), and lower peak concentric power at trail leg ankle joint (1.29 W/kg) as compared to men (p < 0.05; −0.82 N m/kg, 0.89 N m/kg, 3.83 W/kg, and 1.78 W/kg, respectively). The lead leg knee eccentric power was also lower in women (p < 0.05). This decreased ability to exert knee control during stair descent transition may predispose women to a higher risk of fall.