俄罗斯开发出新式人工心脏瓣膜

俄罗斯专家最近利用坚固而且具有惰性的热解碳开发出一种由3个瓣叶组成的人工心脏瓣膜。瓣膜病病人接受这种人工心脏瓣膜移植治疗后,可有效避免红细胞溶解及血栓形成等瓣膜移植引发的副作用。     

新型机械心脏瓣膜的研究

目前临床使用的各种机械心脏瓣膜的主要问题是血栓栓塞和与抗凝治疗有关的出血,其缺陷在于瓣膜开启时,碟片和支架将瓣膜的整个血流通道分隔成三至四个较小的血流通道。在这种受阻隔的血流通宫,形成容易诱发血栓的高剪应力区、紊流和滞流区。我们研制的两种机械心脏瓣膜在瓣膜开启时,没有任何支架和碟片分隔瓣膜的血流通道,使血流与天然心脏瓣膜中的相类似,可减少对血液的危害,从而可减少换瓣病人对抗凝治疗的依赖程度。     

组织工程方法在人工心脏瓣膜领域中的应用

将组织工程的思想与方法应用于人工心脏瓣膜领域有望克服现有瓣膜的不足,具有良好的应用前景。然而,实现组织工程心脏瓣膜仍然存在许多挑战。该文介绍了组织工程瓣膜的定义及发展,讨论了常用的组织工程瓣膜的材料学研究与制备方法、调控瓣膜再细胞化的手段以及相应的挑战。基于细胞支架、种子细胞、生物活性因子三要素制备的组织工程瓣膜目前大多仅处于基础研究阶段。更具应用推广价值的组织工程瓣膜研究方向是基于异种心包膜或瓣叶交联的组织工程瓣膜,包括提高交联的生物瓣膜的抗钙化性能,制备脱离不良溶剂保存的可预装干燥瓣膜,以及探索新型的生物瓣膜交联方式。     

全软成形环与缘对缘瓣膜成形术在心脏瓣膜关闭不全成形术中的疗效比较

目的:观察和比较全软成形环与缘对缘瓣膜成形术在心脏瓣膜关闭不全成形术中的疗效。方法:回顾性研究我院行心脏瓣膜关闭不全成形术患者80例,随机分为Ⅰ组与Ⅱ组,每组各40例。第Ⅰ组患者在行心脏瓣膜关闭不全成形术中使用全软成形环进行治疗,第Ⅱ组患者在手术过程进行缘对缘瓣膜成形术。比较治疗前后两组患者二尖瓣口、二尖瓣环面积和收缩期及舒张期二尖瓣环周径、左心室内径、心搏出量、射血速率、射血时间及临床有效率。结果:治疗后,两组二尖瓣形态、左心室内经、心搏出量、射血速率及射血时间均较治疗前有所改善(P0.05);且与第Ⅱ组相比,第Ⅰ组患者二尖瓣口面积、心搏出量及射血速率较大,二尖瓣环的面积、收缩期及舒张期二尖瓣环周径、左心室内径较小,射血时间明显缩短(P0.05)。第Ⅱ组治疗总有效率为95%,较第Ⅰ组(62.5%)显著升高,差异具有统计学意义(P0.05)。结论:与缘对缘瓣膜成形术相比,全软成形环在心脏瓣膜关闭不全成形术中的疗效更好,其机制可能与增大二尖瓣口面积、心搏出量及射血速率,减小二尖瓣环的面积、收缩期及舒张期二尖瓣环周径、左心室内径,缩短射血时间有关。     

清除牛心包组织内细胞的方法

置换生物心脏瓣膜的病人一般不需抗凝治疗。但由于生物心脏瓣膜的逐渐损坏,术后５年至１０年需行再次换瓣手术。根据生物心脏瓣膜的病理检查发现,瓣叶的钙化变性是瓣膜原发性失功的主要形式,而瓣膜内的残存细胞和细胞碎片则起了重要的初始钙化源的作用。     

兰州飞控仪器总厂—立项新型心脏瓣膜生产线

_,,_。、./J。J、,二,琢现日丁班日在兰州飞控仪器总厂立项。该厂是“人工心脏瓣膜”定点生产厂家,这次立项生产的CL型系列人工心脏瓣膜,用于置换人体心脏内发生病变的心脏瓣膜,使患者重建血液循环动力功能。据悉,该项目拟建设一条年产一万只全炭双叶型人工机械心脏瓣膜生产线,一条年产一万只CL标准和短柱型人工机械心脏瓣膜生产线,以及人工机械心脏瓣膜流体力学及物理兰州飞控仪器总厂——立项新型心脏瓣膜生产线     

牦牛心包材料的生化组成

牦牛是我国重要的生物资源,用牦牛心包缝制的心脏瓣膜可用于置换病变严重或坏死的天然心脏瓣膜.本文分析了牦牛心包材料的生化组成,从其生化组成上论证了牦牛心包用作心脏瓣膜材料的可行性.     

超声心动图检测人工心脏瓣膜功能的价值

自从1951年开展人工心脏瓣膜置换,迄今已有30余年。换瓣适应症的选择,要求系列的观察瓣膜的质地、性能和左室的功能。超声心动图对瓣膜病的诊断经历了M型、二维、脉冲,连续多普勒超声及彩色多普勒的发展过程。近年来,经食道超声、负荷多普勒超声及术中超声越来越得到了广泛应用。本文对各种估价人工瓣的超声心动图方法及一些功能指标的价值进行综述。     

室间隔缺损介入封堵和外科手术对瓣膜功能影响的对比研究

目的:通过对介入封堵治疗的室间隔缺损患者进行中长期临床随访,并和同期行外科修补手术的室间隔缺损患者进行对比,分析两种术式对心脏瓣膜功能的影响。方法:选择行介入封堵治疗患者279例(介入组),行外科手术修补治疗患者243例(手术组)。利用超声心动图检查瓣膜反流发生情况及随访转归情况,并对两组瓣膜反流的发生率进行对比研究。结果:术后短期介入组二尖瓣反流发生率较手术组高(P0.05),三尖瓣和主动脉瓣反流发生率两组相比无统计学差异。中长期随访中,三尖瓣反流、主动脉瓣反流以及二尖瓣反流两组相比均无统计学差异。结论:室间隔缺损介入封堵治疗疗效确切,安全性高,创伤较小。术前利用超声心动图对患者的严格筛选,术中熟练轻柔稳定的操作和适合封堵器的选择是减少介入封堵术后发生瓣膜反流最重要的因素。     

80岁以上老年人冠状动脉旁路移植术合并瓣膜置换手术的临床分析

目的:总结老年患者行冠状动脉旁路移植术(CABG)合并瓣膜置换(VR)手术的特点及经验。方法:上海交通大学附属第一人民医院心血管外科2001年11月至2010年3月对60例年龄大于80的患者施行冠状动脉搭桥+瓣膜置换手术,男33例,女27例。年龄80-87岁,平均年龄(83.77±2.45)岁。均为冠心病合并瓣膜病变患者。其中36例患者行冠状动脉旁路移植+二尖瓣置换手术,15例患者行冠状动脉旁路移植+主动脉瓣置换手术,9例患者行冠状动脉旁路移植+双瓣置换手术,同时8例患者行三尖瓣成形手术,3例患者行射频消融手术,1例升主动开成形术。置换生物瓣膜者51例,置换机械瓣膜者9例。CABG平均搭桥(2.13±0.75)根,搭桥材料为左乳内动脉与大隐静脉。结果:全组早期死亡9例(15%),1例死于术后出血,1例死于多器官功能衰竭,7例死于术后心衰。早期生存51例(85%),出现术后并发症10例,其中2例发生胸腔积液,1例心包填塞,3例肺部感染,1例心房扑动后发生室颤,3例二次开胸止血。给予相应对症治疗后痊愈出院。门诊随访49例,随访时间1～60个月,心功能I级2例、Ⅱ级29例、Ⅲ级18例、Ⅳ级0例(NYHA分级)。结论:对老年患者行冠脉搭桥+瓣膜置换手术,只要掌握手术适应证,充分作好术前准备、术中及术后处理,手术治疗可以取得良好效果。     

Common features of analogous replacement histone H3 genes in animals and plants

Phylogenetic analysis of histone H3 protein sequences demonstrates the independent origin of the replacement histone H3 genes in animals and in plants. Multiple introns in the replacement histone H3 genes of animals in a pattern distinct from that in plant replacement H3 genes supports this conclusion. It is suggested that replacement H3 genes arose at the same time that, independently, multicellular forms of animals and of plants evolved. Judged by the degree of invariant and functionally constrained amino acid positions, histones H3 and H4, which form together the tetramer kernel of the nucleosome, have co-evolved with equal rates of sequence divergence. Residues 31 and 87 in histone H3 are the only residues that consistently changed across each gene duplication event that created functional replacement histone H3 variant forms. Once changed, these residues have remained invariant across divergent speciation. This suggests that they are required to allow replacement histone H3 to participate in the assembly of nucleosomes in non–S-phase cells. The abundant occurrence of polypyrimidine sequences in the introns of all replacement H3 genes, and the replacement of an intron by a polypyrimidine motif upstream of the alfalfa replacement H3 gene, suggests a function. It is speculated that they may contribute to the characteristic cell-cycle-independent pattern of replacement histone H3 genes by binding nucleosome-excluding proteins.     

Trans-kingdom conjugation offers a powerful gene targeting: tool in yeast

Gene targeting is one of the powerful techniques used to investigate eukaryotic genes. In a typical eukaryotic microbe, Saccharomyces cerevisiae yeast, we examined trans-kingdom conjugation between Escherichia coli bacterium and yeast as a gene targeting tool. Here, it is shown that trans-kingdom conjugation effectively induced gene replacement even on yeast's target loci (e.g. ura3-52 allele) which is never targeted by conventional transformation. This clearly indicates that trans-kingdom conjugation offers a very powerful gene targeting tool in yeasts. In fact, Southern hybridization analysis of transconjugants distinctly verified the accuracy in the conjugative gene replacement. The efficiency of gene replacement was about 0.4×10⁻⁷ per recipient yeast. This is enough to sustain gene targeting with gene replacement by trans-kingdom conjugation. We also discuss the mechanism of conjugative gene replacement.     

Ovarian hormone replacement to aged ovariectomized female rats benefits acquisition of the morris water maze

Ovarian steroids have been suggested to aid in preserving cognitive functioning during aging in both humans and other animals. Spatial memory relies heavily on the hippocampus, a structure that is sensitive to the influence of both ovarian hormones and aging. The present study investigated the outcome of ovarian hormone replacement during aging on performance in a spatial version of the Morris water maze. Female rats were ovariectomized at 14 months of age and received one of three types of replacement prior to testing at 16 months: acute estrogen replacement (2 days), chronic estrogen replacement (28 days), or chronic replacement of both estrogen and progesterone (28 days). Control animals, which did not receive replacement hormones, displayed significant overnight forgetting during acquisition of the task. Ovarian hormone replacement, both acute and chronic, prevented forgetting. Previous studies have demonstrated that high levels of ovarian hormones are detrimental to performance of young adult female rats on this task (Warren and Juraska, 1997; Chesler and Juraska, 2000). The current study found an opposite effect during aging: ovarian hormone replacement was beneficial. This suggests that animal models of menopause, aimed at exploring the protective effects of hormone replacement therapy on cognition during human female aging, require the use of aged female animals.     

From Embryo to Adult: The Complete Development and Unusual Replacement of the Dentition of the Tammar Wallaby (Macropus eugenii)

Unlike their reptile-like ancestors with continuous tooth replacement, mammals have evolved to replace each tooth either only once, or not at all. In previous large-scale comparative studies, it has been suggested that this tooth replacement only occurs from a successional dental lamina produced lingually to the primary tooth. This study aims to document the complete tooth development and replacement pattern of the tammar wallaby (Macropus eugenii). The tammar wallaby is a diprotodont marsupial, a group defined by their two procumbent lower incisors. To provide a comprehensive documentation of the spatio-temporal pattern of tooth development, we used Lugol’s Iodine staining and microCT scanning (diceCT) of embryos and pouch young into adulthood, resulting in high resolution 3D models for both soft and mineralised stages of development for all tooth positions. Our results reveal that the eponymous lower incisors are the successional generation at the third incisor locus, where the primary dentition initiates but never erupts. Furthermore, we track the development of the only replacement tooth, the permanent third premolar (P3), from initiation to eruption, and found it develops from the primary dental lamina, mesial to the dP3. This is contrary to the conventional view of lingual replacement from successional lamina in mammals. Our findings indicate that no functional tooth replacement occurs in the tammar wallaby, and expands the diversity of tooth replacement patterns found in mammals. We also conclude that since almost all marsupial and placental mammals produce replacement teeth from the distalmost deciduous premolar, this tooth should be considered homologous in these two groups.

     

The ‘Widow Effect’ and its Consequences for Reproduction in Burying Beetles,Nicrophorus vespilloides (Coleoptera: Silphidae)

Burying beetles tend their young on small vertebrate carcasses, which serve as the sole source of food for the developing larvae. Single females are as proficient at rearing offspring as male-female pairs, yet males opt to remain with their broods throughout most of the larval development. One potential benefit of a male's extended residency is that it affords him the opportunity of additional copulations with the female, which could ensure his paternity in a replacement brood should the female's first egg clutch fail to hatch. We tested this hypothesis by manipulating males' access to their mates during the production of replacement clutches, using genetic colour markers to determine the paternity of offspring. Females were induced to produce a replacement brood by removing their first clutch of eggs. In one experimental treatment, we removed the female's mate upon the removal of her first egg clutch (‘widowed’ females); in a second treatment, the female was permitted to retain her mate up until she produced a replacement clutch. There was no significant difference in paternity between males removed from females before the initiation of replacement clutches and those permitted to remain with their mates. However, widowed females produced fewer offspring in replacement broods than did females permitted to retain their mates. This difference occurred primarily because a significantly greater proportion of widowed females opted not to produce a replacement clutch, a result we refer to as the ‘widow effect’. This widow effect was further shown in those replicates in which females of both treatments produced replacement clutches: widowed females took significantly longer to produce a replacement clutch than did females permitted to retain their mates. The loss of her mate could be a signal to a female that a take-over of the carcass is imminent. Her reluctance to produce a replacement clutch under these circumstances might constitute a strategy by which she conserves carrion for a subsequent reproductive attempt with an intruding male successful at ousting her previous mate. Regardless of its functional significance, the widow effect favours the extended residency of males and therefore contributes to the selective maintenance of male parental care.     

A decade of fertility below replacement level in Singapore

This paper discusses fertility trends in Singapore during the decade 1975-1984. Fertility 1st dropped below the replacement level in 1975 when the gross reproduction rate reached 1.006 and fell further to the low of 0.772 in 1984. During the same period all of the 3 main races, Chinese, Malays, and Indians, experienced fertility below replacement level. The shortfall in the number of births required to ensure replacement fertility increased during the decade until it approached 1/4 in 1984. This indicates that Singapore has more than achieved its national demographic goal of fertility to attain 0 growth and to stabilize the population in the future. This study shows that the newly introduced population policies designed to improve the quality of the population may well in practice lead to fewer births. A declining population in the 21st century is very likely.     

Targeted neuronal death affects neuronal replacement and vocal behavior in adult songbirds

In the high vocal center (HVC) of adult songbirds, increases in spontaneous neuronal replacement correlate with song changes and with cell death. We experimentally induced death of specific HVC neuron types in adult male zebra finches using targeted photolysis. Induced death of a projection neuron type that normally turns over resulted in compensatory replacement of the same type. Induced death of the normally nonreplaced type did not stimulate their replacement. In juveniles, death of the latter type increased recruitment of the replaceable kind. We infer that neuronal death regulates the recruitment of replaceable neurons. Song deteriorated in some birds only after elimination of replaceable neurons. Behavioral deficits were transient and followed by variable degrees of recovery. This raises the possibility that induced neuronal replacement can restore a learned behavior.     

Immunoglobulin V gene replacement is caused by the intramolecular DNA deletion mechanism.

Circular DNA resulting from V gene replacement was studied with an A-MuLV transformed cell line containing ablts. This cell line undergoes V gene replacement at elevated temperatures in the immunoglobulin (Ig) heavy chain (H) gene. Examination of circular DNA revealed that a heptamer-related sequence (TACTGTG) within the coding region of VDJ was joined to the recombination signal sequence (RSS) of a germline VH segment. This provides direct evidence for a intramolecular DNA deletion mechanism for V gene replacement. In the pre-B cell line as well as in in vivo lymphocytes, unusual circular DNAs were found which were structurally similar to the V gene replacement circles. They represented excision products of the deletion type recombination between one complete RSS and a heptamer-like sequence in the Ig H region.     

Donation: a new, facile method of gene replacement in yeast

Summary We describe here a new method for the introduction of non-selectable alleles into Saccharomyces cerevisiae, gene replacement by donation. This method only requires the availability of an autonomously replicating, selectable plasmid containing the allele to be introduced into yeast. The plasmid is digested at a restriction site (or sites) within this allele, and introduced into yeast by transformation. In the course of double-strand break repair, the entering plasmid donates genetic information to the chromosome, replacing the chromosomal allele in a gene conversion-like event. Gene replacement events are identified by a phenotypic screen of the transformants. When necessary, the transforming plasmid may be subsequently lost by segregation during permissive growth. We have studied several parameters affecting the utility of this protocol as a method of gene replacement. Together with our previous results, the results show gene replacement by donation to be a useful, facile method, yielding gene replacement in up to 1.5% of transformants.     

Paleoecology of benthic community replacement

The literature of community paleoecology is filled with examples in which long-term environmentally-controlled faunal transitions are misidentified as forms of ecologic succession. This has obscured a fundamental community-level process - community replacement - involving gradual to abrupt substitution of one benthic community for another as a result of subtle to sharp changes in habitats over subevolutionary time. In gradually changing environments, replacement takes place through conformational reorganization of species-abundance distributions within established communities, yielding sequences of slightly different fossil associations. Environments that change very rapidly drastically feature a different type of community replacement involving species turnover, wherein environmental tolerance limits of community members are closely approached or exceeded. Paleoecologists should be alert to the strong likelihood that many temporal transitions involving autochthonous fossil associations are, in fact, community replacement sequences.