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排序方式: 共有5772条查询结果,搜索用时 31 毫秒
51.
Dr. B. K. van Kreel N. Cox-Reyven P. Soeters 《Medical & biological engineering & computing》1998,36(3):337-345
Multifrequency bio-electronic impedance analysis (MF BIA) measurements are taken from a heterogeneous group of patients, varying
in size between obese and slim. The measuring system uses four electrodes: two current and two potential electrodes. Three
new models are developed to calculate total body water (TBW) from the BIA data, and the resulting TBW values are compared
with TBW determined by D2O dilution. The results demonstrate that the most simple model provides the best TBW values. For individual patients, TBW
can be determined by means of bioimpedance measurement with an accuracy of 3 litres. In the most simple model (model 1), the
body is electrically represented by a cylinder, and corrections are made for the amount of fat. This is an extension of the
model used by Xitron. In the more advanced models (2 and 3), the body is represented by a cylinder for the trunk, and truncated
cones represent the arms and legs. In model 2, ΔTBW amounts to 3 litres. It is shown that the resistance of the trunk is proportional
to the square root of the length. In model 3, it is assumed that subcutaneous fat is a poor conductor if electric current.
An equation is developed that describes the partition of subcutaneous fat, and the fat layer is then removed from the cones
representing arms and legs and from the cylinder that models the trunk. 相似文献
52.
We develop tidal-ventilation pulmonary gas-exchange equations that allow pulmonary shunt to have different values during expiration and inspiration, in accordance with lung collapse and recruitment during lung dysfunction (Am. J. Respir. Crit. Care Med. 158 (1998) 1636). Their solutions are tested against published animal data from intravascular oxygen tension and saturation sensors. These equations provide one explanation for (i) observed physiological phenomena, such as within-breath fluctuations in arterial oxygen saturation and blood-gas tension; and (ii) conventional (time averaged) blood-gas sample oxygen tensions. We suggest that tidal-ventilation models are needed to describe within-breath fluctuations in arterial oxygen saturation and blood-gas tension in acute respiratory distress syndrome (ARDS) subjects. Both the amplitude of these oxygen saturation and tension fluctuations, and the mean oxygen blood-gas values, are affected by physiological variables such as inspired oxygen concentration, lung volume, and the inspiratory:expiratory (I:E) ratio, as well as by changes in pulmonary shunt during the respiratory cycle. 相似文献
53.
G. D. Tansley R. J. Edwards C. R. Gentie 《Medical & biological engineering & computing》1988,26(2):175-185
The paper aims to present the strengths and weaknesses of computational fluid mechanics (CFM) compared with existing in vitro
haemodynamic techniques such as LDA, hot-wire anemometry and static pressure measurement, and to discuss the application of
CFM to the analysis of prosthetic heart valve flow. It presents a brief summary of existing methods used in analysing in vitro
heart valve flow (along with CFM), the special problems inherent in each method and the quantities each is capable of giving.
The analysis then goes on to present examples of information yielded by CFM. It also contains a brief discussion of the data
requirements for the analysis of heart valve performance and the clinical relevance of fluid dynamic occurrences. The conclusion
drawn is that CFM has a major role to play in the analysis of prosthetic heart valve flow and design because of the improved
availability of data afforded and the increased correlation between CFM and clinical flow regimes, due to the ability to consider
realistic models of blood. 相似文献
54.
目的:建立能反应自身免疫特点的1型糖尿病动物模型,为进一步研究该病发病机理奠定基础。方法:将16只NOD.Scid小鼠随机分为两组,实验组小鼠腹腔注射发病NOD小鼠脾细胞,对照组注射未发病NOD小鼠脾细胞;每日测定血糖和体重;当出现重度糖尿病临床表现时处死,其余小鼠细胞过继后10周处死,经组织学观察和细胞因子ELISA测定。结果:实验组小鼠发病率为8/8,对照组为0/8;胰岛炎性积分分别为2.5±0.2,0;实验组IL-2、IL-10、IFN-γ水平分别为60.7pg/ml、15.5pg/ml、20.2ng/ml,对照组为2.4pg/ml、17.5pg/ml、3.2ng/ml。结论:在NOD.Scid小鼠体内一次性过继发病NOD小鼠脾细胞后5~10周可成功建立1型糖尿病的小鼠模型。 相似文献
55.
M. A. Helal K. C. Watts A. E. Marble 《Medical & biological engineering & computing》1993,31(6):562-568
A hydrodynamic model for the part of the human arterial network below the renal arteries has been constructed using specially
fabricated distensible tubes and a pulsatile pump to simulate an aortoiliac bypass. The experiments and the computer model
indicated that no ‘steal’ occurred due to the insertion of the bypass graft. Also, the results showed that the length of the
stenosis had a non-systematic apparent effect on the physiological significance of the obstruction and that the kinetic power
represented only a small percentage of the total power. The total power efficiency of the bypass graft was unaffected by its
elastic properties. The experimental investigation also indicated that the pressure drop across the stenosis was considerably
larger than the drop calculated using the Poiseuille flow relationship when the stenosis was severe. Therefore, a critical
arterial stenosis value cannot be defined as an obstruction of a constant percentage reduction of luminal area. It varies
directly with the effective cross-sectional area and inversely with the flow rate. The value of angiography in assessing the
functional significance of any arterial stenosis is there-fore limited. A better method for evaluation requires quantitative
measurements of local blood pressure and blood flow, not only at rest, but also under conditions creating augmented flows
due to exercise. 相似文献
56.
Björn Jonson Rolf Nilsén Hans-Göran Karlsson 《Medical & biological engineering & computing》1975,13(2):209-213
The relationship between the arterial blood pressure and the volume of the arteries within a segment of an extremity is nonlinear. The present paper shows how the flow and volume pulsations of the arteries within a limb segment can be simulated taking this property into account. An electrical model was constructed comprising one resistor and two voltage dependent ‘capacitors’, the latter corresponding to the pressure dependent elasticity, or compliance, of the arteries. Adequate simulations were obtained over a wide pressure range, which is impossible with linear models. The nonlinear, i.e. pressure dependent, relationship between the volume and pressure of arteries, observed under static conditions, must also be taken into consideration when studying pulsatile events with models whether mathematical or physical. 相似文献
57.
将人机交互领域中研究的唇读技术应用于康复工程之中,设计了一个基于视觉语言的语音合成系统。该系统特别针对后天致残,丧失语音能力的人设计,采用了一种特定条件下的汉语可视语音数据库。不同于现有的数据库,该数据库的设计具有以下特点:采用了非对称唇形轮廓模型,提取了嘴唇突出度的信息;针对汉语音节的特点,增强了汉字音节中信息变化过程;兼顾未来唇读技术的发展,以音节为基本元素,具有可扩充性。采用运动检测和数学形态学的办法提取唇动图像序列中的唇形区域,并从中提取非对称唇形轮廓模型特征参数,同时通过计算部分参数对时间的差分,来获得唇形轮廓的动态信息。基于隐马尔可夫模型的学习和识别实验表明,该数据库的设计方法合理,所选的唇动特征用能够将识别效果平均提高25%。 相似文献
58.
59.
Dr. Zsolt Szabó Henning Vosberg Charles A. Sondhaus Ludwig E. Feinendegen 《European journal of nuclear medicine and molecular imaging》1985,11(6-7):265-274
Examination of the input-output events in functioning organs by the use of the impulse-response function (IRF) for a radioactive tracer is gaining more and more ground in nuclear medicine. This study summarizes the development of deconvolution analysis, laying special stress on the model-free approach. System linearity and time invariance are discussed, and means of eliminating noise in IRFs originating from the input and organ-time-activity curves are outlined. Typical IRFs are illustrated by flow diagrams, time-domain curves, and their representation by Laplace transforms. The cases of nondiffusible and diffusible tracers as well as parenchymally extracted and transported substances are discussed. Methods for the derivation of models and for the calculation of physiologically important parameters from theIRFs are suggested.At present, a guest scientist at the Institute for Medicine, Nuclear Research Center Jülich, Jülich, Federal Republic of Germany 相似文献
60.
Eleven acetylsalicylic acid (ASA) formulations were administered to 26 healthy volunteers in a cross-over design. The properties of the preparations differed from conventional, effervescent, buffered to buccal. The objectives of this study were:
- 1 Consideration of the general aspects of a biopharmaceutical study: which parameter for which biopharmaceutic characteristic?
- 2 Measurement of the kinetic parameters of ASA: first-pass effect, mean residence time, mean appearance time, total body clearance, apparent volume of distribution, half-lives, etc.
- 3 Comparison of the formulations.