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Results for “Continuous Evolution”

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PubMed1994

Kinetics of compaction during lysozyme refolding studied by continuous-flow quasielastic light scattering.

We recently developed an experiment, termed continuous-flow quasielastic light scattering (QLS), that is capable of monitoring the time evolution of the hydrodynamic diameter of macromolecules or macromolecular assemblies in solution. Here we report the use of this method to directly monitor the kinetics of compaction of the polypeptide chain of hen egg white lysozyme (HEWL) when protein refolding is initiated by 10-fold dilution from 5 M guanidine hydrochloride (GuHCl) at pH 1.5, 23 degrees C. Previously, such information could only be obtained indirectly, by analysis of the kinetics of binding ans release of a fluorescent probe dye. Refolding was also monitored by UV difference absorption spectroscopy to characterize the time scale of the formation of the native environment around the aromatic side chains under the same conditions used in the continuous-flow QLS experiments. We find that HEWL becomes compact within 1 s after the initiation of refolding, the shortest time that is accessible with our first-generation instrument. This time scale is shorter than that for the recovery of the native absorbances in the aromatic region. These results provide direct evidence that the intermediate on the folding pathway of lysozyme is compact. The implications of these results for models of protein folding are discussed.

Animals↗

PubMedDate not supplied

Reform, change, and continuity in Finnish health care.

This article describes some essential aspects of the Finnish political and governmental system and the evolution of the basic institutional elements of the health care system. We examine the developments that gave rise to a series of health care reforms and reform proposals in the late 1980s and early 1990s and relate them to changes in health care expenditure, structure, and performance. Finally, we discuss the relationship between policy changes, reforms, and health system changes and the strength of neo-institutional theory in explaining both continuity and change. Much of the change in Finnish health care can be explained by institutional path dependency. The tradition of strong but small local authorities and the lack of legitimate democratic regional authorities as well as the coexistence of a dominant Beveridge-style health system with a marginal Bismarckian element explain the specific path of Finnish health care reform. Public responsibility for health care has been decentralized to smaller local authorities (known as municipalities) more than in any other country. Even an exceptionally deep economic recession in the early 1990s did not lead to systems change; rather, the economic imperative was met by the traditional centralized policy pattern. Some of the developments of the 1990s are, however, difficult to explain by institutional theory. Thus, there is a need for testing alternative theories as well.

Decision Making, Organizational↗

PubMed1977

Treatment of a flail injury of the chest. A case report with consideration of the evolution of therapy.

A patient with flail-chest injury, and associated abdominal and musculo-skeletal trauma, required several modes of mechanical ventilation in the Surgical Intensive Care Unit Ventilator modalities included mechanical ventilation with positive end-expiratory pressure (PEEP) and intermittent mandatory ventilation (IMV) with continuous positive airway pressure (CPAP) during 12 days of intensive respiratory care. This treatment has resulted from an evolution of ideas about pathophysiology and treatment of the flail-chest injury. Future developments portend a shorter duration of ventilatory support; alternatively, a radically new mode of therapy may simplify the care of the flail-chest injured patient.

Anesthesia↗

PubMed1999

Study of the evolution of the placenta and fetal pancreas in the pathophysiology of growth retardation intrauterine due to restricted maternal diet.

CONTEXT: Intrauterine growth retard (IUGR) continues to be a significant perinatology problem at the end of this century. The nature of the etiologic agent, the time when the attack occurred during pregnancy and its duration affect the type of IUGR. OBJECTIVE: To study the evolution of fetal pancreas and placenta between the 18th and 21st day of pregnancy in rats submitted to maternal protein-calorie restriction. DESIGN: Randomized controlled trial on laboratory animal. SAMPLE: Forty-one normoglycemic pregnant Wistar rats. INTERVENTION: Rats were divided into six experimental groups according to their access to food and date of cesarean section (18th or 21st day): control with free access to food; diet restricted to 25% introduced on 1st day of pregnancy; and diet restricted to 25% after the 3rd day of pregnancy. MAIN MEASUREMENTS: Newborn weight, placenta weight, histopathological study (morphological histochemistry). RESULTS: Maternal protein-calorie malnutrition caused intrauterine growth retard (IUGR) after the 18th day of pregnancy. Dietary restriction did not interfere with the morphology of the fetal pancreas and the immunohistochemical study of the placenta showed that glycogen stores were decreased between the 18th and 21st day in the control group and in a diet restricted to 25% from the first day of pregnancy. Dietary restriction after the 3rd day of pregnancy led to low placental glycogen concentrations on the 18th day and disappearance on the 21st day. CONCLUSION: The pathophysiology of IUGR due to maternal protein-calorie restriction in rats is related to lower placental weight and low placental glycogen stores.

Animals↗

PubMed2001

Nitrous oxide and dinitrogen emissions from soil under different water regimes and straw amendment.

In a laboratory study, soil amended with and without wheat straw (2.8 g kg(-1) soil) was incubated under 70% water holding capacity (WHC), continuously flooded and flooded/drained cycle conditions at 30 degrees C for 51 days. Dinitrogen and N2O evolution and ammonia volatilisation were measured during the incubation. Extractable NH4+-N and NO3--N were determined at the end of the incubation. Entrapped N2, N2O, and dissolved NH4+-N and NO3--N in drainage water were measured in the flooded/drained cycle treatment when the floodwater was drained. The results indicated that N loss through ammonia volatilisation was undetected in all treatments due to the low soil pH value (pHH2O= 5.87) and no air movement. The recovery of urea-15N as N2 was lowest in the continuously flooded treatments (0.75% and 0.96% with and without straw amendment, respectively), highest in the 70% WHC treatments (5.65% and 4.41%, respectively), and intermediate in the flooded/drained cycle treatments (1.79% and 2.65%, respectively). The recovery of urea-15N as N2O was in the same order as that of N2, negligible in the continuously flooded treatments, 0.01% and 0.07% in the flooded/drained cycle treatments, and 1.29% and 2.23% in the 70% WHC treatments, respectively. Peak N2O evolution rates were observed after the floodwater was drained but no substantial evolution was found after the soil was reflooded following drained periods. However, peak N2 evolution rates were observed after the onset of both drainage and re-flooding. Considerable quantities of N2 but no detectable N2O were entrapped in the flooded soil.

Agriculture↗

PubMed2002

[Endocavitary ablation for arrhythmias. New modalities of radiofrequency applications. New energy types].

Radiofrequency remains the reference energy type for catheter ablation of rhythm disorders. In the classic indications, which are atrial flutter or tachycardia, nodal re-entry and Wolff-Parkinson-White syndrome, this energy source has the best cost-efficiency-safety ratio, subject to strict conditions of use. Some new modalities of application have further improved performance, especially active irrigation of the electrode which allows induction of deeper lesions which is very useful for the ablation of difficult atrial flutters, epicardial fascicles of Kent and ischaemic ventricular tachycardias. The only emerging alternative energy type, in the framework of classical ablation, is cold, for which the principal advantages are the homogenous and slightly thrombogenic character for the lesion involved, and the possibility of reversible applications tests which are especially useful in the ablation of structures at risk. The situation is more open-ended concerning research on ablation for atrial fibrillation or the so-called new energy types, such as ultrasound and laser, whilst recognising a renewal in interest, especially for circumferential ablation of the pulmonary veins to isolate the ectopic venous foci. Mechanical energy such as luminous energy is emitted across a catheter balloon deployed at the orifice of the vein, perpendicular to its axis, aiming to reach a continuous circumferential lesion with a minimum of applications. Equally radiofrequency has been undergoing significant evolution for this application, such as by the development of porous catheter balloons with a liquid electrode, as well as by the development of deployable circumferential catheters. Ablation is use for atrial fibrillation, by endocavity atrial segmentation remains a field of research in which radiofrequency retains an important place. It is delivered via multi-electrode catheters according to the new application modalities, either pulsed or by phase interval, which secure better efficacy by better continuity of the line of block. Research is equally underway on the use of microwaves and cold in this application.

Atrial Fibrillation↗

PubMed1981

[Carcinoembryonic antigen (C.E.A.). Its value in the care of malignant tumours of the ovary (author's transl)].

The authors report on 466 serial levels of carcinoembryonic antigens (C.E.A.) carried out with the aim of surveying 44 patients who had malignant tumours of the ovaries : - one third of the cases had a positive level more than 10 ng per ml; - the presence and the serial level depend more on the histological nature of the tumour than the stage of its evolution; - when a serial level has been negative before treatment it has never become positive in in a definite and continuous manner when the tumour progresses. On the other hand, when the test is positive before any therapy is started then there is a good correlation between its clinical evolution, its response to treatment and the serial variations. Relying on their experience and on the results given in the literature, the authors suggest a scheme of practical use of levels of C.E.A. in the care of malignant tumours of the ovary.

Carcinoembryonic Antigen↗

PubMed2001

Rapid evolution of cis-regulatory sequences via local point mutations.

Although the evolution of protein-coding sequences within genomes is well understood, the same cannot be said of the cis-regulatory regions that control transcription. Yet, changes in gene expression are likely to constitute an important component of phenotypic evolution. We simulated the evolution of new transcription factor binding sites via local point mutations. The results indicate that new binding sites appear and become fixed within populations on microevolutionary timescales under an assumption of neutral evolution. Even combinations of two new binding sites evolve very quickly. We predict that local point mutations continually generate considerable genetic variation that is capable of altering gene expression.

Animals↗

PubMed1980

Evolution of membrane bioenergetics.

One of the first problems encountered by primitive cells was that of volume regulation; the continuous entry of ions, (eg, NaCl) and water in response to the internal colloid osmotic pressure threatening to destroy the cell by lysis. We propose that to meet this environmental challenge cells evolved an ATP-driven proton extrusion system plus a membrane carrier that would exchange external protons with internal Na+. With the appearance of the ability to generate proton gradients, additional mechanisms to harness this source of energy emerged. These would include proton-nutrient cotransport, K+ accumulation, nucleic acid entry, and motility. A more efficient system for the uptake of certain carbohydrates by vectorial phosphorylation via the PEP-phosphotransferase system probably appeared rather early in the evolution of anaerobic bacteria. The reversal of the proton-ATPase reaction to give net ATP synthesis became possible with the development of other types of efficient proton transporting machinery. Either light-driven bacterial rhodopsin or a redox system coupled to proton translocation would have served this function. Oxidation of one substrate coupled to the reduction of another substrate by membrane-bound enzymes evolved in such a manner that protons were extruded from the cell during the reaction. The progressive elaboration of this type of redox proton pump permitted the use of exogenous electron acceptors, such as fumarate, sulfate, and nitrate. The stepwise growth of these electron transport chains required the accretion of several flavoproteins, iron-sulfur proteins, quinones, and cytochromes. With modifications of these four basic components a chlorophyll-dependent photosynthetic system was subsequently evolved. The oxygen that was generated by this photosynthetic system from water would eventually accumulate in the atmosphere of the earth. With molecular oxygen present, the emergence of cytochrome oxidase would complete the respiratory chain. The proton economy of membrane energetics has been retained by most present-day microorganisms, mitochondria, chloroplasts, and cells of higher plants. A secondary use of the energy stored as an electrochemical difference of Na+ for powering membrane events probably also evolved in microorganisms. The exclusive age of the Na+ economy is distinctive of the plasma membrane of animal cells; the Na+-K+ ATPase sets up an electrochemical Na+ gradient that provides the energy for osmoregulation, Na+-nutrient co-transport, and the action potential of excitable cells.

Adenosine Triphosphatases↗

PubMed1996

[Crossed aphasia disclosed by central auditory disorder].

A 80-year-old woman, right-handed, suddenly felt the impression to be deaf. Besides, she presented language disorders of aphasic type relating to a sensorial transcortical aphasia. The case meets the diagnostic criteria for crossed aphasia. The magnetic resonance imaging showed a right temporo-parietal infarct. There was no sensorial or peripheral auditive disorder and no auditory agnosia of non verbal modality. During the evolution, the aphasic symptoms diminished partially and the subjective auditory deficit of the left ear continued. The integrated auditory evaluation (neuroacoustic test, study of auditory gnosia, dichotic listening test, evoked cortical auditory potentials) allowed the evidence of the characteristic disturbances of a right hemianacousia: loss of left hear in dichotic audition, decrease of amplitude of evoked right cortical auditory potentials. In the light of theories concerning auditory integration, one can explain this evolution. The initial aphasic comprehension disturbance expresses the alteration of the linguistic treatment of auditory information of the dominant hemisphere, here the right hemisphere. Subsequently, the linguistic disturbance regresses largely, letting persist the change of general auditory treatment. The representation of this general auditory treatment is hemispheric bilateral, the only right hemispheric damage shall result in hemianacousia.

Aged↗

PubMed1975

[Mauration of unitary responses to tonal stimulation in the cochlear nerve of the kitten].

The maturation of single auditory nerve fiber responses to long-duration (500 ms) tone-bursts was studied in kittens at various stages after birth. Spike discharges were examined as a function of three criteria. 10 Latency. Mean value of the "on" peak latency was about 25 ms at 1 to 3 days after birth. It then regressed, reaching 8 to 12 ms at the end of the first week, and 2 to 4 ms at 20 days. 20 Peristimulus histograms (PSTH). Evolution of PSTH revealed the characteristic sequence of unit reactivity to long duration stimuli (i.e. on, rhythmic, and continuous responses). Rhythmic responses is assumed up to now to be related to the immaturity of synaptic junctions below the hair cells. 30 interval histograms. The interspike interval histograms of the discharges showed a similar evolution. A bimodal distribution corresponding to the rhythmic mode of reactivity, appeared at the end of the first week.

Acoustic Stimulation↗

PubMed1992

Evolution of DNA damage in irradiated cells.

Ionizing radiation damage to a mammalian genome is modeled using continuous time Markov chains. Models are given for the initial infliction of DNA double strand breaks by radiation and for the enzymatic processing of this initial damage. Damage processing pathways include DNA double strand break repair and chromosome exchanges. Linear, saturable, or inducible repair is considered, competing kinetically with pairwise interactions of the DNA double strand breaks. As endpoints, both chromosome aberrations and the inability of cells to form clones are analyzed. For the post-irradiation behavior, using the discrete time Markov chain embedded at transitions gives the ultimate distribution of damage more simply than does integrating the Kolmogorov forward equations. In a representative special case explicit expressions for the probability distribution of damage at large times are given in the form used for numerical computations and comparisons with experiments on human lymphocytes. A principle of branching ratios, that late assays can only measure appropriate ratios of repair and interaction functions, not the functions themselves, is derived and discussed.

Cell Survival↗

PubMed1989

Evolution of DRGs and clinical information systems.

DRG definitions have evolved during the past decade and will continue to evolve as methods for evaluating severity data become available. The use of DRGs for hospital budgeting, payment and evaluation as well as the support of hospital utilization review and quality assurance activities requires that systems be available to insure data quality. A comprehensive and flexible clinical information system will be required by hospitals in order to manage under a DRG system.

Adult↗

PubMed1999

The low-density lipoprotein receptor family: genetics, function, and evolution.

With ever increasing sophistication in molecular biological approaches, the low-density lipoprotein receptor supergene family continues to grow rapidly. From the well-defined key role of these receptors in lipoprotein metabolism, the new members move the field into many different and diverse physiologic and developmental areas. We observe an expansion of the functional spectrum of the family members, which is due to 1) the binding to their extracellular domains of more and more components lacking homology to apolipoproteins, and 2) the recently uncovered interaction of the receptors' cytoplasmic tails with adaptor proteins that are part of signaling pathways. As this review attempts to describe, the task of delineation of the evolutionary history of the gene family may be aided by concepts that consider events, both divergent and convergent, within and between the intra- and extracellular domains.

Animals↗

PubMed1997

Evolution of left ventricular hypertrophy and function during long-term treatment of systemic hypertension with enalapril.

Continued treatment of hypertensive patients with enalapril reduced left ventricular (LV) hypertrophy steadily over a period of 5 years (by which time gross structural parameters were normal) and produced no further reduction during the following 2 years. Temporary suspension of treatment after 5-year follow-up gave rise to an increase in blood pressure, and to deterioration of LV isovolumic relaxation time and deceleration of the ventricular filling E wave, both of which chiefly reflect the active relaxation of the ventricle.

Adult↗

PubMed2006

Evolution of health information management and information technology in emergency medicine.

The implementation of information technology will continue to have important effects on the practice of emergency medicine. Patient registration and tracking systems, telemedicine electronic order entry systems, and the advent of electronic health records are some examples of applications that influence patient care in emergency departments. We review the literature regarding information technology advances in emergency medicine and outline the important role that emergency physicians play in developing and implementing a national health information technology strategy.

Australasia↗

PubMed1990

Preston M. Hickey memorial lecture. Ionic and nonionic iodinated contrast media: evolution and strategies for use.

The search for better radiopaque iodinated contrast material for intravascular use is continuing, but the recent development of new lower osmolality contrast media (LOCM), both ionic and nonionic, has dramatically affected the practice of radiology. The major issue retarding the introduction of LOCM into clinical practice in this country has been the increased cost of the media. Numerous preliminary assumptions and probabilities about the tolerance, efficacy, and overall safety of LOCM have been documented in scientific studies. The lower osmolality, reduced chemotoxicity, and high hydrophilicity of new compounds, particularly the nonionic variety compared with conventional high osmolality ionic agents (HOCM), offer a significant margin of safety to patients with known risk factors. Mounting data suggest that low or no risk patients are benefited as well, perhaps to an even greater degree. Costly trade-offs to the universal use of LOCM exist, therefore careful consideration of the advantages and disadvantages of LOCM for intravascular administration is required. This article, presented as the Preston M. Hickey Memorial Lecture to the Michigan Radiological Society in March of 1990, explores the historical development of iodinated intravascular contrast media, especially LOCM, and cites existing data that form the basis for various strategies for their use, that is, selective, universal, or nonvascular use. Better, safer, and less expensive contrast media are a realistic expectation in this new decade of technological promise. Reducing adverse side effects from the use of any new drug or technology must be our continued, collective goal.

Chemistry↗

PubMed1992

Adaptation and renewal of the gastrointestinal surgeon to meet the continuous challenge of modern gastroenterology.

The treatment of gastrointestinal diseases has entered into a period of rapid evolution. Gastroenterology has in the last 50 years evolved into a major specialty, covering not only complex clinical and diagnostic areas, but inclusive of sophisticated investigative work and major therapeutic endoscopic technology. Unfortunately, the evolution of gastrointestinal surgery has lagged behind. The scope of the gastrointestinal surgeon has become more limited, as potent pharmacotherapeutic probes, invasive radiological techniques and diagnostic and therapeutic endoscopic advances have been implemented. The development of minimally invasive surgical techniques has introduced a new era in surgical management. However, the establishment of new training programs and the acquisition of skills requiring the acquisition of costly equipment are major issues which surgical departments need to address. A novel training and programmatic configuration for the group of physicians involved in the management of gastrointestinal disease is required to meet this challenge. In particular, internists and surgeons must focus on the development of cost and time effective strategies for the management of clinical gastrointestinal disease. It seems likely, however, that adequate resources and management of these undertakings will only be forthcoming if corporate establishments, venture capital groups, medical health insurance institutions and national research agencies develop a consortium approach with medical schools to address these issues.

Education, Medical↗