SEARCH · PubMed Health

Results for “Continuous Evolution”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 919 records · Page 51Linked to original sources

PubMed2005

A robust and fast method of sampling and analysis of delta13C of dissolved inorganic carbon in ground waters.

The stable carbon isotopic composition of dissolved inorganic carbon (delta13C(DIC)) is traditionally determined using either direct precipitation or gas evolution methods in conjunction with offline gas preparation and measurement in a dual-inlet isotope ratio mass spectrometer. A gas evolution method based on continuous-flow technology is described here, which is easy to use and robust. Water samples (100-1500 microl depending on the carbonate alkalinity) are injected into He-filled autosampler vials in the field and analysed on an automated continuous-flow gas preparation system interfaced to an isotope ratio mass spectrometer. Sample analysis time including online preparation is 10 min and overall precision is 0.1 per thousand. This method is thus fast and can easily be automated for handling large sample batches.

Air Pollutants↗

PubMed1991

Rudolf Schoenheimer and the concept of the dynamic state of body constituents.

In 1935 Rudolf Schoenheimer (1898-1941) introduced the isotopic tracer technique in metabolic research. The results of his experiments led to a new view of metabolism and nutrition and the evolution of a concept of "continual regeneration," i.e., of continual release and uptake of substances by the cell and, thus, of a "dynamic state of body constituents." This dynamic view of metabolism can be traced back to the thinking of some investigators of the 19th and early 20th century, notably C. Bernard and F. G. Hopkins. It was Schoenheimer, however, who provided clear experimental evidence of the dynamic concept of metabolism.

Body Composition↗

PubMed2006

Evolutionary origin and maintenance of coexpressed gene clusters in mammals.

Gene order is not random with regard to gene expression in mammals: coexpressed genes, and in particular housekeeping genes, are clustered along chromosomes more often than expected by chance. To understand the origin of these clusters and to quantify the impact of this phenomenon on genome organization, we analyzed clusters of coexpressed genes in the human and mouse genomes. We show that neighboring genes experience continuous concerted expression changes during evolution, which leads to the formation of coexpressed gene clusters. The pattern of expression within these clusters evolves more slowly than the genomic average. Moreover, by studying gene order evolution, we show that some clusters are maintained by natural selection and, therefore, have a functional significance. However, we also demonstrate that some coexpressed gene clusters are the result of neutral coevolution effects, as illustrated by the clustering of genes escaping inactivation on the X chromosome. Moreover, we show that, although statistically significant, constraints on gene orders have a limited impact on mammalian genome organization, affecting only 3-5% of the pool of human and murine genes. It had been hypothesized that coexpressed gene clusters might correspond to large chromatin domains. In contradiction, we find that most of these clusters contain only 2 genes whose coexpression may be due to transcriptional read-through or the activity of bidirectional promoters.

Animals↗

PubMed2002

The significance of telomerase activation and cellular immortalization in human cancer.

Repression of telomerase in the somatic tissues of humans, and probably other long-lived mammals, appears to have evolved as a powerful protective barrier against cancer. Immortalization in vitro of normal human cells that lack telomerase involves the reactivation of telomerase or, rarely, an alternative (ALT) mechanism for maintaining telomeres. Inactivation of the effectors of replicative senescence, i.e. genes encoding one or more elements of the p16/pRB and/or ARF/p53/p21 anti-proliferative pathways, is required for telomerase depression leading to immortalization. Regulation of telomerase in normal human cells is mediated primarily by transcriptional repression of hTERT, the gene encoding the catalytic subunit of telomerase. Rodent cells do not possess stringent controls on telomerase activity in the soma and this explains why they are so readily immortalized and transformed in culture compared with their human counterparts. Because active telomerase has been found to exist in the proliferative compartments of self-renewing tissues, it is not yet clear whether the telomerase present in 90% of human cancers exists as a consequence of selection of pre-existing telomerase-positive cells during carcinogenesis or through induction of hTERT expression in cells in which it is normally tightly repressed. In support of the latter, chromosome transfer techniques have revealed the presence of genes on normal human chromosomes that are able to extinguish hTERT transcription in cancer cells and induce them to undergo senescence. It is clear that telomerase is obligatory for continuous tumour cell proliferation, clonal evolution and malignant progression. Telomerase therefore represents an attractive target at which to aim new anti-cancer drugs. Results with a variety of telomerase inhibitory strategies in human cancer cells have confirmed that its functional inactivation results in progressive telomere shortening, leading to growth arrest and/or cell death through apoptosis. Promising candidate small molecule inhibitors are beginning to emerge that will form the basis for anti-telomerase drug development.

Animals↗

PubMed1999

Continuous professional development for anaesthetists.

Anaesthesia, as well as the whole of medicine, is involved in a revolution not only technical but also economic, because of the need for cost-containment in healthcare delivery. Continuing medical education, primarily devoted to updating knowledge and skills, is moving rapidly towards continuous professional development. A permanent evolution of practitioners is mandatory in order that they are able to adapt their practice to technical, ethical and economic changes, integrated in a team-working and multidisciplinary approach to patient care.

Journal Article↗

PubMed1986

Medical psychotherapy: an evolving concept.

The term "medical psychotherapy" is gaining ascendancy in its use to describe the approach to therapeutic intervention used by psychiatrists who conceptualize their function as being at the more medical end of the spectrum of psychiatric practice styles. The following definition represents an attempt to crystallize a model that is in an active stage of evolution. I hope to stimulate continued debate and refinement of the concept.

Humans↗

PubMed2005

New techniques and technologies for pediatric cataract surgery.

PURPOSE OF REVIEW: This paper surveys the literature from April 2004 to April 2005 and addresses trends in pediatric cataract surgery techniques. RECENT FINDINGS: The evolution of pediatric cataract surgery continues, with many adult cataract surgical techniques being applied to children with minor technical adjustments. More and more, surgeons are implanting intraocular lenses in younger children. One of the most widely reported technologic advances in 2004-2005 was the use of hydrophobic acrylic intraocular lenses in children. Predicting axial growth, and refractive change that accompanies it, is one of the major remaining challenges for the long-term care of children who have had cataract surgery. SUMMARY: Automation and intraocular lenses have helped to provide better anatomic and functional outcome for cataract surgery in children. Two major challenges in the coming years will be to find a way to obviate invasive procedures like posterior capsulotomy and vitrectomy and to study the growth of eyes in a well designed prospective study that will help to design new intraocular lens power calculation formulas specifically suited for children's eyes.

Cataract Extraction↗

PubMed2006

Impact of HIV-1 pol diversity on drug resistance and its clinical implications.

PURPOSE OF REVIEW: HIV knowledge is based on subtype B, common in resource-rich settings, whereas globally non-B subtypes predominate. Inter-subtype pol diversity encompasses multiple genotypic differences among HIV variants, the consequence of which is unknown. This review summarizes publications from the past year relevant to the impact of HIV diversity on drug resistance evolution and its potential clinical implications. RECENT FINDINGS: The benefit of antiretroviral therapy in non-B infected patients is ongoing, though subtype heterogeneity in rates of disease progression is observed. Pol inter-subtype diversity is high, and known subtype B drug resistance mutations occur in non-B subtypes. New mutations and subtype-specific mutation rates are identified, however, unexplained drug susceptibilities are seen, and additional insight is offered on structural pathogenic mechanisms of resistance in non-B subtypes. These differences may affect genotypic interpretation and our ability to apply drug resistance to patient care. SUMMARY: Current evidence suggests good treatment response and comparable drug resistance evolution in HIV-1 B and non-B infected patients, with increasingly emerging differences. Impact of inter-subtype diversity on drug susceptibility and on evolution of drug resistance should continue to be a major research focus to increase our understanding and ability to improve global patient care.

Algorithms↗

PubMed1976

Estimated Drainage of Carbon from the Tricarboxylic Acid Cycle for Protein Synthesis in Suspension Cultures of Paul's Scarlet Rose Cells.

The amount of carbon (mumoles of carbon atoms) drained from the tricarboxylic acid cycle for protein synthesis was compared with mumoles of CO(2) released from the cycle at 2-day intervals during the growth of suspension cultures of Paul's Scarlet rose. We concluded that during the period of most rapid protein synthesis (day 0-4) one-sixth as much carbon was drained from the tricarboxylic acid cycle for protein synthesis as was released as CO(2). By day 8, one-thirtieth of the amount of carbon released as CO(2) was incorporated into protein. Net protein synthesis stopped on day 8, but the evolution of CO(2)/culture continued at its maximum rate until day 10.Similar ratios were calculated based on the recovery of (14)C in protein versus CO(2) following a 3-hr provision of labeled substrates to 3-day-old cells (age of maximum protein synthesis). Provision of acetate-1-(14)C and acetate-2-(14)C indicated from one-eighth to an equal amount of carbon was incorporated into protein as was released as CO(2). When (14)C-labeled intermediates of the tricarboxylic acid cycle were provided, the ratio of (14)C incorporated into protein versus that evolved in CO(2) ranged from 1/0.9 to 1/4.9.Following a critical analysis of the methods used, it was concluded that during periods of rapid protein synthesis, a conservative estimate of the amount of carbon drained from the tricarboxylic acid cycle for protein synthesis was one-fourth of the amount evolved as CO(2) from the cycle.

Journal Article↗

PubMed1979

Biosynthesis of Photosystem II Reaction Centers, Antenna and Plastoquinone Pool in Greening Cells of Cyanidium caldarium Mutant III-C.

Dark-grown etiolated cells of Cyanidium caldarium mutant III-C lacking >/=99% of their normal chlorophyll content and inactive for photosynthesis were greened in continuous light. Measurements of oxygen evolution and fluorescence kinetics indicate that during greening: (a) the photosystem II (PSII) antenna containing between 30 and 40 chlorophyll a per center undergoes little change in size from 5% of the centers synthesized per cell to fully active cells; (b) energy transfer between PSII centers appears very early in the greening process; (c) the plastoquinone pool size per PSII center (about 14 equivalents) does not vary during greening and has already attained full size after synthesis of only 13% of the full complement of centers.The PSII centers, antenna chlorophyll and plastoquinone are integrated into the membrane with constant stoichiometry throughout at least 90% of the greening process. These components are integrated such that in regions of the membrane containing active PSII centers, their density in the membrane hardly changes over the same period. The center-antenna complex and possibly the plastoquinone pool as well are organized into unit structures containing 40 chlorophyll a and 7 plastoquinones, respectively. Energy transfer between centers in PSII appears following aggregation of the center-antenna units.

Journal Article↗

PubMed1987

The UK National External Quality Assessment Scheme in Blood Group Serology. Compatibility testing 1983-1984: the influence of variables in test procedures on detection of incomplete antibodies.

Error rates in exercises in compatibility testing varied between 3% and 36% over the six years 1979-1984. Evolution of serological procedures was continuous through this period but without clear evidence of improvement in performance of antibody detection although performance in the UK appears to be comparable with that elsewhere. Relationships have been established between a number of variables of reagents and techniques, and their performance. The influence of some variables is reasonably clear but there appear to be interactions between certain variables in their effects on performance, and interpretation is less straightforward. A test for agglutination of enzyme treated cells together with an antiglobulin test appears to be the most reliable combination for detection of incomplete antibodies in compatibility testing although one stage enzyme techniques are an inevitable compromise between reliability and convenience. Compatibility testing should not be considered in isolation from antibody screening in determining the optimum combination of tests for pretransfusion antibody detection.

Agglutination Tests↗

PubMed2005

Novel genetic basis of field-evolved resistance to Bt toxins in Plutella xylostella.

Insecticidal toxins from Bacillus thuringiensis (Bt) are widely used to control pest insects, but evolution of resistance threatens their continued efficacy. The most common type of Bt resistance ('Mode 1') is characterized by recessive inheritance, > 500-fold resistance to at least one Cry1A toxin, negligible cross-resistance to Cry1C, and reduced binding of Bt toxins to midgut membrane target sites. Mutations affecting a Cry1A-binding midgut cadherin protein are linked to laboratory-selected Mode 1 resistance in Heliothis virescens and Pectinophora gossypiella. Here we show that field-evolved Mode 1 resistance in the diamondback moth, Plutella xylostella, has a different genetic basis, indicating that screening for resistance in the field should not be restricted to a previously proposed DNA-based search for cadherin mutations.

Animals↗

PubMed1978

Changes in the cyclic AMP content during growth and development of Acetabularia.

The 3',5'-adenosine monophosphate (cyclic-AMP) content of the unicellular alga Acetabularia has been examined at various developmental stages. It has been found that very young algae, less than 10mm in length, have a high cAMP content [more than 7 pmoles per 100 mg wet weight (WW)], but that with the growth of the algae, the cAMP content decreases rapidly, reaching the low level of 0.5--1.0 pmoles per 100mg WW. The cAMP content remains at this level until cap differentiation, after which an increase in cAMP content accompanies cap enlargement. It has been shown that these results are unlikely to be affected by changes in the cAMP content induced by variations in circadian rhythm. Treatment with theophylline (2.10(-3) M), a phosphodieterase inhibitor, results in an increase in the cAMP content and delays growth and cap formation. Experiments on the effects of theophylline upon the circadian rhythm of oxygen evolution have shown that the continuous presence of theophylline in the culture medium does not induce a phase shift in the rhythm. The cAMP content of anucleate Acetabularia shows development stage variations parallel to that of the whole algae.

Acetabularia↗

PubMed2003

Endovascular therapies for vascular disease.

Endovascular techniques including angioplasty, stenting, and endoluminal stent grafts represent important therapeutic options for the treatment of vascular disease. Technologic advances have allowed for the treatment of aneurysmal disease as well as extra-cranial carotid disease that previously required surgical methods. The success of various endovascular therapies varies based on anatomic location and extent of disease. The clinical results in different arterial segments are increasingly recognized in the published literature. The aortoiliac arterial bed appears to respond most favorably, with less favorable results observed in the infra-inguinal and infrapopliteal locations. There is increasing evidence that stent-supported carotid angioplasty using cerebral protection will play an important future role in the treatment of carotid artery stenosis. Less invasive techniques to treat abdominal aortic aneurysms with endoluminal stent grafts have dramatically changed the available therapeutic options. Improved devices and delivery systems will likely increase the number of patients who can be successfully treated in this manner. The evolution of endovascular therapies will continue to change the way we treat vascular disease.

Aneurysm↗

PubMed2003

Assessing quality in the cardiac catheterization laboratory.

Quality assurance and improvement have increasingly been the focus of health care providers, third-party payers, and patients. Because cardiovascular procedures are common, easily identifiable with claims data, and account for a relatively large proportion of health care expenditures, particular attention has been paid to quality assurance in the setting of the diagnostic and interventional cardiac catheterization laboratory. The structure, process, and outcomes domains of quality measurement in the interventional laboratory involve the maintenance of volume standards, the availability of surgical backup, consistent tracking of procedural outcomes and complications so they can be compared with national standards, and the application of evidence-based therapy. Quality assurance i the diagnostic laboratory revolves around the clinical proficiency of the operators, the maintenance and management of catheterization laboratory equipment, and the presence of a continuous quality improvement program. The evolution of interventional equipment and techniques along with the establishment of national registries has led to a gradual improvement in the quality of percutaneous coronary intervention. Given the dynamic nature of cardiology, adaptable quality assurance and quality improvement programs will remain the foundation of successful catheterization labs.

Benchmarking↗

PubMed1990

Genomic variation of Trypanosoma cruzi: involvement of multicopy genes.

By using improved pulsed field gel conditions, the karyotypes of several strains of the protozoan parasite Trypanosoma cruzi were analyzed and compared with those of Leishmania major and two other members of the genus Trypanosoma. There was no difference in chromosome migration patterns between different life cycle stages of the T. cruzi strains analyzed. However, the sizes and numbers of chromosomal bands varied considerably among T. cruzi strains. This karyotype variation among T. cruzi strains was analyzed further at the chromosomal level by using multicopy genes as probes in Southern hybridizations. The chromosomal location of the genes encoding alpha- and beta-tubulin, ubiquitin, rRNA, spliced leader RNA, and an 85-kilodalton protein remained stable during developmental conversion of the parasite. The sizes and numbers of chromosomes containing these sequences varied among the different strains analyzed, implying multiple rearrangements of these genes during evolution of the parasites. During continuous in vitro cultivation of T. cruzi Y, the chromosomal location of the spliced leader gene shifted spontaneously. The spliced leader gene encodes a 35-nucleotide RNA that is spliced in trans from a 105-nucleotide donor RNA onto all mRNAs in T. cruzi. The spliced leader sequences changed in their physical location in both the cloned and uncloned Y strains. Associated with the complex changes was an increase in the infectivity of the rearranged variant for tissue culture cells. Our results indicate that the spliced leader gene clusters in T. cruzi undergo high-frequency genomic rearrangements.

Animals↗

PubMed1996

A methyl-accepting protein involved in multiple-sugar chemotaxis by Cellulomonas gelida.

Tethered-cell and capillary assays indicated that L-methionine is required by Cellulomonas gelida for its normal cell motility pattern and chemotaxis and that S-adenosylmethionine is involved in sugar chemotaxis by this cellulolytic bacterium. In addition, in vivo methylation assays showed that several proteins were methylated in the absence of protein synthesis. The incorporated methyl groups were alkali sensitive. Of special interest was the observation that the methylation level of a 51,000-Mr protein increased two- to fivefold upon addition of various sugar attractants and decreased after the removal of the attractants. The increase was less pronounced in mutants defective in sugar chemotaxis and appeared to be specifically involved with sugar chemotaxis. Furthermore, cell fractionation and in vitro methylation assays demonstrated that the 51,000-Mr protein is located in the cytoplasmic membrane. These results suggest that a specific methyl-accepting chemotaxis protein is involved in multiple-sugar chemotaxis by C gelida. During chemotaxis, the changes of methylesterase activity in C gelida cells were similar to those in Escherichia coli RP437 cells, as determined by a continuous-flow assay for methanol evolution. Thus, the mechanism of methyl-accepting chemotaxis protein-mediated chemotaxis of the gram-positive C. gelida appears to be similar to that of the gram-negative E. coli rather than to that of other gram-positive bacteria, such as Bacillus subtilis.

Bacterial Proteins↗

PubMedDate not supplied

AAPM/RSNA physics tutorial for residents. Topics in US: B-mode US: basic concepts and new technology.

Ultrasonography (US) has been used in medical imaging for over half a century. Current US scanners are based largely on the same basic principles used in the initial devices for human imaging. Modern equipment uses a pulse-echo approach with a brightness-mode (B-mode) display. Fundamental aspects of the B-mode imaging process include basic ultrasound physics, interactions of ultrasound with tissue, ultrasound pulse formation, scanning the ultrasound beam, and echo detection and signal processing. Recent technical innovations that have been developed to improve the performance of modern US equipment include the following: tissue harmonic imaging, spatial compound imaging, extended field of view imaging, coded pulse excitation, electronic section focusing, three-dimensional and four-dimensional imaging, and the general trend toward equipment miniaturization. US is a relatively inexpensive, portable, safe, and real-time modality, all of which make it one of the most widely used imaging modalities in medicine. Although B-mode US is sometimes referred to as a mature technology, this modality continues to experience a significant evolution in capability with even more exciting developments on the horizon.

Health Physics↗