Effect of age on muscle functions investigated with surface electromyography.

The purpose of this study was to investigate changes in the surface electromyographic (EMG) signal as a means of defining age-related central and peripheral mechanisms affecting muscle fatigue. Spectral and temporal variables of the surface EMG signal were studied during voluntary isometric contractions of the dominant biceps brachii muscle in a group of 8 healthy elderly men (age range 67-86 years) and a group of 10 healthy young men (age range 23-34 years). The maximal torque developed and the rate of decrease (slope) of spectral variables and conduction velocity (CV) were statistically higher in the young subjects than in the elderly subjects. Motor unit (MU) CV distribution was also estimated from the surface EMG signal and no statistical difference was observed in its variance between the two groups. These results confirm previous findings from the tibialis anterior muscle. Thus, changes in fiber type distribution and decrease in MU firing rate with aging may be factors determining the decrease in maximal voluntary contraction torque and in myoelectric manifestations of muscle fatigue.     

砂片邻面去釉及其临床治疗中的评估

目的：评估砂片邻面去釉技术在正畸治疗过程中的短期患龋率及安全性，疗程问题。方法：采用直丝弓矫治技术结合砂片邻面去釉进行矫治。结果：本组患者经过砂片邻面去釉结束矫治后1年，未见邻面龋的发生。结论：在严格选择临床适应症，规范操作，并积极防龋处理的前提下，砂片邻面去釉技术在正畸治疗过程中是安全的。     

中心静脉压评价左心室功能价值的探讨

本文采用微导管法在20例受试者中监测了中心静脉压,观察其与左心室功能——心指数、每搏功、射血分数之间的相关关系.结果表明,在心肌缺血、心脏效能降低时,中心静脉压与左心室功能之间无相关关系.     

亲水膜的表面改性及在膜蒸馏中的应用

膜的微孔性和疏水性是水溶液膜蒸馏的两个基本条件,迄今人们均采用疏水性高分子材料制成疏水微孔膜用于膜蒸馏研究。本文采用辐照接枝聚合和等离子体表面聚合的方法,将亲水的醋酸纤维素微孔膜和硝酸纤维素微孔膜表面疏水化改性,成功地用于膜蒸馏研究,大大扩展了疏水微孔膜的材料来源。实验结果表明,亲水膜表面改性得到的疏水膜,其膜蒸馏性能不低于疏水材料制成的膜,尤其是等离子体聚合法可以实现多种特殊单体在多孔的材料表面聚合,成为制备高性能疏水微孔膜的有效手段,为膜蒸馏的深入发展和实用化创造了有利条件。     

Mechanics of the pleural space: Fundamental concepts

The transmission of forces from the respiratory muscles to the lung across the extremely thin pleural space has been poorly understood because of the difficulty of accurately measuring pleural liquid and pleural surface pressure (lung static recoil or transpulmonary pressure). Recent results using relatively noninvasive techniques have indicated that the vertical gradient in pleural liquid pressure is not hydrostatic, that pleural liquid pressure is closely related to lung recoil, and that there exists a very thin but continuous pleural liquid layer. These findings contradict concepts based on hydrostatic equilibrium and on the distinction between pleural liquid and pleural surface pressure due to pleural contact. Pleural liquid pressure is not in hydrostatic equilibrium because the difference between the vertical gradient in pleural liquid pressure and the effect of gravity is always balanced by a pressure loss due to a viscous flow within the pleural space. Fluid lubrication of the pleural surfaces is the primary function of the pleural space. The mechanical interaction between the lung and the chest wall is coupled to the dynamics of liquid within the pleural space, which is viewed as a flow-through system. Homeostasis is achieved in such a system by the adjustment of the viscous flow within the pleural space and the outflow absorption rate by lymphatics to the microvascular filtration rate across pleural capillaries.     

肺表面活性物质表面张力动态测试

本文论述了肺表面活性物质表面张力动态检测的意义和测试原理,介绍了表面张力动态测试仪结构和性能,最后比较分析了测试结果。     

氨基甲酸钼和钙化合物对脂摩擦性能的影响及其表面膜组成

研究了氨基甲酸钼(MoDTC)和钙化合物在润滑脂中的配伍性。添加MoDTC和钙化合物后,鋰和钙基脂的物理、化学性能仅发生轻微变化。四球机和MM200摩擦机试验表明:MoDTC添加石油磺酸钙或碳酸钙,在减磨和提高承载能力方面有增效作用。利用俄歇和光电子能谱仪,发现表面膜主要由MoS_2,MoO_3,FeS_2,CaCO_3和CaSO_4等组成。正是这种表面膜使得MoDTC和钙化合物具有增效作用。     

Benefits of Smaller Electrode Surface Area (4 mm2) on Steroid-Eluting Leads

The purpose was to test whether a reduction of pacemaker electrode surface area below 8 mm2 improves leads that elute steroid from the electrode tip to the surrounding myocardium. A standard-sized 8 mm2 lead with 1 mg dexamethasone was implanted in 12 patients and a lead with 4 mm2 electrode surface area and 0.5 mg dexamethasone in ten patients. Pacing threshold, impedance, and sensing threshold were measured at implantation and after 1, 4, and 12 weeks. Pacing thresholds were similar for both groups and were always less than or equal to 0.8 V at 0.5 msec pulse duration in all patients. Impedance was significantly higher (P less than 0.05) for the 4 mm2 lead (implantation: 726 +/- 119 ohms; 1 week: 596 +/- 71 ohms; 4 weeks: 624 +/- 68 ohms; 12 weeks: 643 +/- 56 ohms) than for the 8 mm2 lead (implantation: 422 +/- 43 ohms; 1 week: 402 +/- 48 ohms; 4 weeks: 439 +/- 57 ohms; 12 weeks: 449 +/- 61 ohms). R wave amplitudes did not differ between both groups; no sensing failure occurred at 5 mV sensitivity. Compared to the 8 mm2 lead the reduction of surface area to 4 mm2 did not influence pacing threshold, but resulted in a higher pacing impedance. The amount of pacing energy was lower in the smaller-sized electrode. For clinical impact, low pacing threshold and high impedance leads are the condition to implant pulse generators with smaller battery capacity.     

Finite element modelling of forearm skin wrinkling

Background/purpose: Human skin is a complex multilayered material. Although there are many numerical models of skin in existence, which accurately simulate several of its complex mechanical characteristics, there are very few models that simulate wrinkling – a phenomenon common to all human skin. The purpose of this study was to develop a multilayer model of skin, which could simulate wrinkling more realistically than the existing models in the literature. Method: The skin on the volar forearm was wrinkled by displacing two tabs, which were attached to the skin surface towards each other. Eight volunteers were used in the experiment. The profiles of the wrinkles were measured using a customised laser profilometer system. The maximum range and average roughness of the wrinkle profiles were calculated. The multilayer model of skin consisted of the stratum corneum, dermis and underlying hypodermis. The constitutive equations for each layer were implemented into a finite element model and the wrinkling experiments were simulated. The results of the model were compared with the results of the experiments. Results: The size of the wrinkles predicted by the model fell within the range of the wrinkle sizes measured in the experiments. The maximum range and average roughness differed by 34% and 43% from the corresponding mean experimental results, respectively. The results show that the proposed three‐layer skin model simulates wrinkling more realistically than either a single or a two‐layer model. Conclusion: A three‐layer model of skin has been developed and validated under the harsh conditions of wrinkling. It has been shown that a three‐layer model better simulates the wrinkling of skin as compared with models of fewer layers. The model has several applications, including simulating skin aging and the design of more realistic artificial skin. The model can also be used to study the interaction of surgical scalpels or razors with human skin with a view to improving their design.     

Formulation Optimization of Propranolol Hydrochloride Microcapsules Employing Central Composite Design

A central composite design was employed to produce microcapsules of propranolol hydrochloride by o/o emulsion solvent evaporation technique using a mixture of cellulose acetate butyrate as coat material and span-80 as an emulsifier. The effect of formulation variables namely levels of cellulose acetate butyrate (X₁) and percentage of Span-80 (X₂) on encapsulation efficiency (Y₁), drug release at the end of 1.5 h (Y₂), 4 h (Y₃), 8 h (Y₄), 14 h (Y₅), and 24 h (Y₆) were evaluated using the F test. Mathematical models containing only the significant terms were generated for each response parameter using multiple linear regression analysis and analysis of variance. Both the formulation variables exerted a significant influence (P <0.05) on Y₁ whereas the cellulose acetate butyrate level emerged as the lone factor which significantly influenced the other response parameters. Numerical optimization using desirability approach was employed to develop an optimized formulation by setting constraints on the dependent and independent variables. The experimental values of Y₁, Y₂, Y₃, Y₄, Y₅, and Y₆ for the optimized formulation was found to be 92.86±1.56% w/w, 29.58±1.22%, 48.56±2.56%, 60.85±2.35%, 76.23±3.16% and 95.12±2.41%, respectively which were in close agreement with those predicted by the mathematical models. The drug release from microcapsules followed first order kinetics and was characterized by Higuchi diffusion model. The optimized microcapsule formulation developed was found to comply with the USP drug release test-1 for extended release propranolol hydrochloride capsules.