蠕变局部损伤开裂的有限元模型

建立了蠕变局部损伤法模型,并给出单元进入损伤态的判据和失效的临界拉伸应变条件,局部蠕变损伤理论的实质就是试样是多种不同蠕变性能材料的统一,并由蠕变应力再分布得到证实,应用有限元对双缺口圆试样作了蠕变局部损伤分析,启裂时间和断裂蠕变应变值均与实验结果相吻合。     

How defective spermatogenesis affects sperm DNA integrity

Spermatogenesis is the essential process to maintain and promote male fertility. It is extraordinarily complex with many regulatory elements and numerous steps. The process involves several cell types, regulatory molecules, repair mechanisms and epigenetic regulators. Evidence has shown that fertility can be negatively impacted by reduced sperm DNA integrity. Sources of sperm DNA damage include replication errors and causes of DNA fragmentation which include abortive apoptosis, defective maturation and oxidative stress. This review outlines the process of spermatogenesis, spermatogonial regulation and sperm differentiation; additionally, DNA damage and currently studied DNA repair mechanisms in spermatozoon are also covered.     

Multidisciplinary Approach to the Management of Extensive Dermato-fibro-sarcomas Involving the Chest Wall

Dermato-fibro-sarcomas are known for high-recurrence rates. The gold standard of management is surgical excision with clear margins. Such margins on the chest results in large defects which require complex reconstructive procedures. We report a case series of patients managed by a multidisciplinary team with good outcomes. A total of 12 patients with extensive dermato-fibro-sarcoma of the anterior chest wall were treated over a period of 5 years in our setting. The age range was 25 to 54 years. Skeletal defects were reconstructed with Prolene mesh and methyl acrylate cement in 10 of the 12 patients. Pedicle flaps were used in nine patients. All margins were clear of tumors, with the nearest margin being 1.5 cm. One patient had a recurrence. No donor-site morbidity was recorded in any of the patients.In conclusion, a multidisciplinary approach provides improved outcomes in the management of large dermato-fibro-sarcomas of the chest wall. With this approach, extensive dissection of the tumor is achieved, and reconstruction is performed with minimal complication.     

造血干/祖细胞的体外扩增培养研究

利用旋转壁式生物反应器(Rotating wall vessel,RWV)体外培养脐带血干细胞,使其大量扩增,以满足临床应用对造血干/祖细胞的数量与质量要求。从脐带血分离得到的单个核细胞(Mononuclear cells,MNC)在T-flask中培养24h,之后接种到RWV反应器中,培养200h。每24h细胞计数,测量培养基的pH和渗透压变化;在144h和197h测CD34 细胞含量并做CFU-GM半固体培养。有核细胞(Nucleated cells,NC)与CD34 细胞在第197h,分别扩增了435.5±87.6倍和32.7±15.6倍,CFU-GM(Colony-forming unit-granulocyte/macrophage)细胞扩增了21.7±4.9倍。整个培养过程中,RWV反应器中的pH和渗透压都保持在造血细胞最佳的扩增条件内,pH基本保持在7.2~7.4之间,渗透压基本保持在290~310mmol/kg之间。由于旋转壁式生物反应器(RWV)结构上的特殊性,可以保证细胞在悬浮流动的状态下生长,很好地模拟了脐带中的造血微环境,使脐带血造血干细胞在该反应器中短期内得到大量扩增。     

The impact of DNA damage, genetic mutation and cellular responses on cancer prevention, longevity and aging: observations in humans and mice

Over the past 5 years, data collected from the mouse suggest that pathways important for either preventing or resolving DNA damage are longevity assurance mechanisms whose critical overall function is somatic cell maintenance, a necessary part of cancer prevention. These pathways include those that reduce DNA damage levels caused by exogenous sources, replication errors and by-products of cellular respiration. Unresolved DNA damage leads to permanent mutations in the genetic code that may be oncogenic. Therefore, pathways that resolve DNA damage are important anti-cancer mechanisms. As an important line of defense, there are a variety of pathways that repair DNA damage. In addition, there are anti-cancer pathways that respond to DNA damage by either preventing cellular replication or inducing cell death. Genes in these pathways, termed longevity assurance genes (LAG), code for proteins that reduce cancer incidence and as a result assures a sufficiently long health span needed for reproduction. Data from mouse models, many that were originally designed to study cancer, are showing that a potential consequence of DNA damage and responses to DNA damage is aging; these models support the hypothesis that at least some aspects of normal aging are the consequence of anticancer mechanisms designed to deal with damaged DNA.     

Erworbene Bauchhöhlenmuskelstörungen

Zusammenfassung Die Bauchhöhle hat ein Faszienskelett, das durch ihren permanenten veränderhchen Ruhetonus verspannt gehalten wird. Zur Bauchhöhle gehören mit der seitlichen Bauchmuskulatur auch das Zwerchfell und der Beckenboden. Willkürliche und reflektorische Tonusänderungen bedingen ihre Verformung und ihren Verschluß oder ihre Eröffnung. Am Versuchstier haben wir diesen Ruhetonus schon in der Schwanzmuskulatur nachgewiesen, von der der Beckenboden des Menschen stammesgeschichtlich abstammt. Der Beckenboden bildet mit den Sphinkteren das anorektale Kontinenzorgan. Es ist, phylogenetisch erklärbar, bei der Frau viel schwächer entwickelt als beim Mann. Diese unterschiedliche Mächtigkeit ist his zu den Kernen des Rückenmarks, die diese Muskulatur steuern, zu verfolgen. Diese Asthenie des weiblichen Kontinenzorgans wird durch das Gebären und die Obstipation noch zusätzlich belastet. Das gleiche gilt für die Bauchdecke der Frau, die, wie hier nachgewiesen wird, nach einer Gravidität die gleichen, bleibenden Denervationserscheinungen ihrer Muskulatur erkennen läß t. Es sind die gleichen Schäden, die der Beckenboden mit den Sphinkteren erleidet. In schwereren Fällen ist neben der Inkontinenz also auch ein Schlotterbauch die Folge dieser Belastungen. Der ruhetonisierte Beckenboden kann das spastische Beckenbodensyndrom, die kontinente Obstipation, zur Folge haben. Sic kann psychotherapeutisch geheilt werden. Davon muß die inkontinente Obstipation unterschieden werden, die manchmal mit einem Mastdarmvorfall einhergeht. Bei ihr liegt das Hindernis im Darm. Sic kann in schweren Fällen durch eine Sigmaresektion gebessert werden. Die Denervationsinkontinenz ist am besten durch das operative Engerstellen des ganzen Levatortrichters zu bessern. Voraussetzung ist: Der gelähmte Beckenboden muß noch eine Restruheaktivität aufweisen.

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Acquired disturbances of muscles of the peritoneal cavity

The peritoneal cavity has a fascial skeleton that is kept under tension by permanent variable resting tone maintained by the abdominal muscles. The lateral abdominal muscles, the diaphragm and the pelvic floor are all components of this fasciomuscular support system. Voluntary and reflective changes in muscle tension allow the entry and exit of matter into and out of the spherical abdominal cavity by opening and closing of specialized wall segments called sphincters. We have previously demonstrated the existence of a resting tone in the tail muscles of mammals from which the human pelvic floor muscles are derived. The pelvic floor and its integrated sphincters form the anorectal organ of continence. This organ is much weaker in females than in males. The spinal centers that govern continence, contain in the female significantly fewer ganglion cells than the corresponding centers in the male. Childbirth and a commonly found tendency to develop constipation are additional stressors for the congenitally weaker female organ of continence. We explain in this paper why the abdominal wall and the pelvic floor may suffer stretch-induced denervation injuries during pregnancy and delivery. Such damage may persist in later life and can give rise to incontinence and flabby abdomen. Based on our work in this field, we found a new differentiation between continent and incontinent constipation. Continent constipation is caused by spasticity of the pelvic floor characterized by abnormally high sphincter activity. This spastic pelvic floor syndrome can be treated successfully by psychotherapeutic techniques. Incontinent constipation, in contrast, is always associated with subnormal activity of the sphincters and may be a cause of rectal prolapse. It can be treated successfully by anterior rectosigmoid resection. Incontinent constipation will also require operative approximation of the levators in many cases. Improvement cannot be expected to result from this procedure, however, unless the pelvic floor shows some residual resting activity.

Korrespondenz an: em. Prof. Dr. Dr. h. c. mult. F. Stelzner     

Finite Element Model Determination of Correction Factors Used for Measurement of Aortic Diameter via Conductance

Traditional methods for estimating the slope and offset volume V _P for determining real-time chamber volume by the conductance catheter technique are not suited to measurements made in the aorta due to the relatively low resistivity of the aortic wall. We developed three distinct three-dimensional finite element models of the conductance catheter and surrounding tissues in order to predict and V _P and to examine the nature of the electric field near the aortic wall. A heterogeneous isotropic model of the catheter, aorta and surrounding tissues accurately predicted the values of and V _P . A homogeneous anisotropic model was developed to examine the effects of anisotropy of blood and the layers of the aortic wall on measured values of resistance, and V _P . This model demonstrated that anisotropy of blood and aortic wall tissue can increase the values of both and V _P . Finally, a three-dimensional homogeneous isotropic rectangular model allowed examination of the effects of catheter position. This model showed small effects of catheter position on measured resistance (9.7% increase) and larger effects on (21.2% decrease) and V _P (41.9% increase). We conclude the following: the FEA models may lead to accurate estimate values of and V _P in vivo. The unique anisotropic conductive properties of the layers of the aortic wall contribute to the high observed values of and V _P in the aorta. Finally, catheter position has a proportionately greater effect on and V _P than on measured resistance. The results of this study should assist in the determination of aortic mechanical properties using conductance catheter measurements of vessel dimension. © 1999 Biomedical Engineering Society. PAC99: 8719Nn, 8719Rr, 8719Uv, 0270Dh, 8717Aa