计算机辅助组织工程在组织支架仿生建模和设计中的应用

计算机辅助组织工程(CATE)可以帮助进行复杂组织支架的建模,设计和制造,使很多用于改善替代材料力学及生物学性能的新方法得以实施。CATE通过获取组织的生物学、生物力学及生物化学信息,进行界面的设计、模拟和组织的制作。本文将讲述CATE在骨组织工程支架仿生设计中的应用:介绍运用CATE进行仿生建模,解剖结构重建,组织支架设计,定量CT分析,有限元分析和支架的自由挤压沉积制作。     

A physicomathematical approach to the structure of the mandible

Summary Classical methods of anatomical study and experimentation have reached an endpoint with respect to the advancement of our knowledge of certain aspects of bone, i.e. its mechanical properties, investigation of the constraints acting on bone and the organization of bone allowing resistance to such mechanical stress. Indeed, current knowledge is rather limited regarding bone as a material. Furthermore, bone from the cadaver cannot be considered a reliable source of study material since its physicochemical composition and mechanical properties are highly different from those of living bone. The types of experimentation used to date, although allowing to study the phenomena occuring on the surface of the bone, do not allow to evaluate those that occur within the bone without modification of its mechanical features. Finally, the number and complexity of the parameters to be taken into account in this respect largely supersede the possibilities of classical study techniques.Accordingly, new types of methodology are required to evaluate the many parameters involved, to perform the corresponding computations and resolve the great number of unknown variables. Such methodology must allow experimentation to be performed without modifying the object of study and to determine the phenomena occuring within the bone itself, i.e. the mandible.A method of computer assisted simulation of a physicomathematical model was used to analyse the structural properties of the mandible. This method was based on that used for the computation and elaboration of large metal structures (offshore drilling platforms), structures submitted to special stress (resistance to force 7 earthquake of the new extension to the radioactive waste disposal factory at the Hague) or aeronautical structures composed of composite material.

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Approche physico-mathématique structurale de la mandibule

Résumé L'étude des propriétés mécaniques de l'os, celle des contraintes qu'il subit, la manière dont il est organisé pour résister à ces contraintes s'avèrent déboucher sur une impasse si l'on se contente des méthodes classiques d'études et d'expérimentations.En effet, nous n'avons actuellement qu'une connaissance très limitée de l'os en qualité de matériau. Le matériau d'expérimentation, l'os de cadavre ne peut être considéré comme fiable, sa constitution physico-chimique et ses propriétés étant par trop différentes de celles de l'os vivant. Le type même des expérimentations utilisées, s'il permet bien d'étudier ce qui se passe à la surface de l'os ne permet pas de prendre en compte ce qui se passe à l'intérieur de celui-ci sans en modifier les caractéristiques mécaniques. Enfin, le nombre et la complexité des paramètres à prendre en compte dépassent largment les possibilités des techniques classiques. C'est pourquoi, il est nécessaire de faire appel à des méthodologies nouvelles capables de prendre en compte un nombre très élevé de paramètres, de les calculer et de résoudre un nombre très important d'inconnues. Ces méthodologies doivent permettre l'expérimentation sans modifier l'objet de l'expérience et de calculer ce qui se passe à l'intérieur même de la mandibule.Cette méthode de simulation sur modèle physico-mathématique par informatique utilisée pour le calcul et l'élaboration des grandes structures métalliques (plate-forme off shore), celui de structures placées dans des conditions de contraintes particulières (prise en compte des tremblements de terre de magnitude 7 pour l'extension de l'usine de La Hague) ou bien celui des structures aéronautiques à matériaux composites a été ici appliquée à l'étude structurale de la mandibule.

     

微机心电场仿真模型与仿真研究

心电场仿真是心电理论研究的前沿课题。本文讨论首次在IBM-PC/AT微机上实现的一个完整的心电场仿真模型。其中,人体和心脏的单元分割精度与国外最近的研究相同,采用边界元法求解心电场电位,并提出一种新的心脏兴奋传播仿真算法,提高了仿真速度。应用该模型对正常心脏和病变心脏进行了仿真研究,仿真结果与临床测量结果是一致的。     

利用计算机对肺及纵膈肿瘤照射野的设计探讨

胸部肿瘤以往多采用二野前后对穿照射及前后野加水平野照射,使其脊髓及胸骨受量偏高,纵膈剂量低,高剂量区常位于靶区之外,剂量分布不合理。放射治疗时,要求减少脊髓,正常肺及胸骨的受量(后者尤其对青少年),提高靶区的致死量。作者利用Philips-oss治疗计划系统,选择肺癌及纵膈肿瘤各一例。根据胸部的解剖位置,采用三野成角加楔形板,经治疗计划系统内存参数处理后,绘制出剂量分布曲线,其优点是靶区内剂量分布均匀。在肺癌及纵膈肿瘤达到致死量的同时,脊髓,正常肺组织及胸骨受量减少或为零。     

医学文献检索虚拟课堂

本文就《医学文献检索》虚拟课堂的建设提出了构想,包括实现技术、硬软件需求和课堂内容组织等。并提供了建设实例。     

Left-ventricular pressure gradients: a computer-model simulation

Both invasive left-ventricular pressure measurements and non-invasive colour M-mode echographic measurements have shown the existence of intraventricular pressure gradients (IVPGs) during early filling. The mechanisms responsible for these IVPG cannot be completely explained by the experiments. Therefore a one-dimensional numerical model is developed and validated. The model describes filling (both velocities and pressures) along a left ventricular (LV) base-apex axis. Blood-wall interaction in the left ventricle with moving boundaries is taken into account. The computational results for a canine heart indicate that the observed IVPGs during filling are the consequence of a complex interaction between, on the one hand, pressure waves travelling in the LV and, on the other hand, LV geometry, relaxation and compliance. The computational results indicate the pressure dependency of wavespeed (0.77-1.90 m-1 s) for different mean intraventricular pressures (0.88-5.00 mmHg) and IVPGs up to 2 mmHg, independent of the ratio of end systolic volume and equilibrium volume. Increasing relaxation rate not only decreases minimum basal pressure (2.8 instead of 3.6 mmHg) but also has a strong influence on the time delay between the minimum basal and apical pressures (14 ms instead of 49 ms). The results sustain the hypothesis that pressure-wave propagation determines IVPGs and that IVPGs are no proof of elastic recoil.     

World Wide Web and Internet: applications for radiologists

Global exchange of information is one of the major sources of scientific progress in medicine. For management of the rapidly growing body of medical information, computers and their applications have become an indispensable scientific tool. Approximately 36 million computer users are part of a worldwide network called the Internet or “information highway” and have created a new infrastructure to promote rapid and efficient access to medical, and thus also to radiological, information. With the establishment of the World Wide Web (WWW) by a consortium of computer users who used a standardized, nonproprietary syntax termed HyperText Markup Language (HTML) for composing documents, it has become possible to provide interactive multimedia presentations to a wide audience. The extensive use of images in radiology makes education, worldwide consultation (review) and scientific presentation via the Internet a major beneficiary of this technical development. This is possible, since both information (text) as well as medical images can be transported via the Internet. Presently, the Internet offers an extensive database for radiologists. Since many radiologists and physicians have to be considered “Internet novices” and, hence, cannot yet avail themselves of the broad spectrum of the Internet, the aim of this article is to present a general introduction to the WWW/Internet and its applications for radiologists. All Internet sites mentioned in this article can be found at the following Internet address: http://www.univie.ac.at/radio/radio.html (Department of Radiology, University of Vienna) Received: 2 February 1998; Revision received: 11 June 1998; Accepted: 27 July 1998     

Sodium channel blockade enhances dispersion of the cardiac action potential duration

Summary The goal of this study was to elucidate the causes why the proarrhythmic activity of sodium channel blocking drugs is enhanced during the post-infarction period. Therefore, we studied the effects of a reduction in sodium conductance on the action potential duration and its dispersion in a simulated array of 1600 ventricular myocytes. Cardiac tissue is known to possess anisotropic properties with regard to the intercellular electrical resistance (R). Infarction as well as aging causes deposition of collagen in the cardiac tissue, thereby inducing zones of high electrical resistance leading to a non-uniform anisotropy (Spach et al., Circ Res 62811, 1988). For our study an array of 40*40 ventricular myocytes was simulated using Beeler-Reuter-algorithms. Physical tissue properties were assumed to be either a) uniform anisotropic (i.e., all longitudinal R=5000 cm, all transversal R=20000 cm; UA) or b) non-uniform anisotropic (i.e., transversal R for the inner 10*10 cells was set to 10¹⁰ cm; NUA). Mean action potential duration (APD) was increased under UA (287 ms, dispersion: 0,8 ms) when compared to NUA (285 ms, disp.: 3,2 ms). Assuming a 25% decrease in sodium conductance, we found the total activation time (TAT) to be increased (from 99 to 139 ms), indicating slowing of conduction, APD to be shortened (from 287 to 259 ms), and the APD-dispersion to be increased (from 0.8 to 29 ms) in UA. These changes were more pronounced in the case of NUA: increase in TAT from 103 to 150 ms, APD-shortening from 285 to 214 ms and a marked increase in APD-Dispersion from 3.2 to 53 ms). From these results it is concluded that a) the effects of a reduced sodium conductance are more pronounced in NUA tissue, and b) that the resulting increase in dispersion may provoke arrhythmia by local differences in APD.This may be one of the mechanisms underlying the increased proarrhythmic risk of class I antiarrhythmic drugs in the postinfarction period.     

How do normal subjects learn a simple adaptative task: How and why do paranoid schizophrenic patients fail?

Summary The authors studied the behavior of normal subjects and paranoid schizophrenic patients in a simple problem-solving situation. The schizophrenics were divided into two sample groups, one of individuals under treatment and the other of individuals not under treatment.The learning process involved in this problem-solving situation is very similar to an instrumental conditioning, and can be understood by means of the following assumptions: (1) the subjects use decision functions in reacting to the stimuli, although they may be not fully aware of this; (2) learning is the result of successive transformations of these decisions in the course of time; (3) the changes have specific probabilities and are related to (a) those responses which are made to the latest stimuli, and (b) a differential probability for decision functions which were effective, or only interrupted painful reinforcement, or were completely ineffective.In schizophrenics further factors of importance were (1) an inertia factor and (2) the rigidly continued use of unsuccessful or only partially successful decision criteria.The authors used a systems theory based on Galois field theory and a calculus of operators specifying three groups of subjects. A computer program based on these hypotheses was tested in a simulation experiment.The statistical evaluation of the results showed a congruence between the theoretical approach and the experimental data.This work was carried out with financial support from the Institute de Alta Cultura, Lisbon, between 1970 and 1974     

Programming a predictive rormula for angina and other risk factors in patients with cardiac diseases undergoing noncardiac operations

We programmed a formula which predicts the incidence of either myocardial infarction or cardiac death during the postoperative period. The original formula was proposed by Shah et al, based on their own data and analysis. The program is simple and is written in a language called Quick Basic. The use of this program is also simple. Such a program has improved the use of this analysis substantially. The program has been posted on to a few Computer network services as a free software.(Suwa K, Ogura S: Programming a predictive formula for angina and other risk factors in patients with cardiac diseases undergoing non-cardiac operations. J Anesth 6: 241–242, 1992)