PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “balancing selection”

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 757 records · Page 42Linked to original sources
PubMed2006

Modeling and phantom studies of ultrasonic wall shear rate measurements using coded pulse excitation.

Wall shear rate (WSR) is the derivative of blood velocity with respect to vessel radius at the endothelial cell (EC) surface. The product of WSR and blood viscosity is the wall shear stress (WSS) that has been identified as an important factor for atherosclerosis development. High echo signal-to-noise ratio (eSNR) and high spatial resolution are crucial for minimizing the errors in WSR estimates. By transmitting coded pulses with time-bandwidth product greater than one, high eSNR from weak blood scatter can be achieved without increasing instantaneous power or sacrificing spatial resolution. This paper summarizes a series of measurements in a straight tube (5-mm diameter), constant velocity flow phantom using a 10 MHz transducer (60% bandwidth, f/1.5) imaged with a 72 degrees Doppler angle, 125 MHz sampling frequency and 1 kHz pulse repetition frequency. Measurements were made using a frequency-modulated (FM) code, phase-modulated (PM) codes, and uncoded broadband and narrow band pulse transmissions. Both simulation and experimental results show that coded-pulse excitation increases accuracy and precision in WSR estimation for laminar flow over a broad range of peak velocity values when compared to standard pulsing techniques in noise-limited conditions (eSNR < 30 dB). The code sequence and its length are selected to balance range lobe suppression with eSNR and echo coherence enhancements to minimize WSR errors. In our study, the combination of an eight bit Optimal coded pulse with a Wiener compression filter yielded the highest WSR estimation performance.

Animals↗
PubMedDate not supplied

Osteoporosis: nutrition.

Nutrition has important potential for the prevention and treatment of osteoporosis. Ensuring the adequacy of calcium intake is central to any program of osteoporosis control, but it must be considered in the context of the many factors, including other nutrients, diseases, and drugs, which influence calcium absorption, utilization, and excretion. The dietary consumption of calcium by large segments of the U.S. population remains inadequate. More attention must be paid not only to increasing calcium intake, but also to maximizing its availability from food sources and its retention by the body. As individuals age, it becomes increasingly difficult to maintain adequate calcium balance; dietary selection must be made with special care for older persons to ensure that all of the nutrients are consumed in sufficient quantities and that neither excessive weight loss nor weight gain occurs.

Adolescent↗
PubMed1993

Anesthetic considerations in patients with hyperparathyroidism.

Although there is controversy over which patients should undergo parathyroidectomy, some patients clearly benefit from the procedure. This case illustrates typical findings in a patient with a parathyroid adenoma. Preoperative hydration and electrolyte balance and selection of anesthetic drugs that were easily titrated was associated with a smooth intraoperative course on this patient. Mild hypocalcemia postoperatively was quickly recognized and treated.

Adenoma↗
PubMed1989

Digestibility of protein and amino acids in selected foods as determined by a rat balance method.

Values (%) for true digestibility of crude protein and individual amino acids in 20 selected foods were determined by the rat balance (fecal) method. The products were fed as the sole source of protein in diets containing 8% crude protein (N x 6.25). Lowest true protein digestibility values (79-84) were obtained for pinto beans, kidney beans and lentils; intermediate values (89-92) were obtained for chick peas, beef stew, skim milk (over heated), rolled oats, whole wheat cereal, and pea protein concentrate; and highest values (94-100) were obtained for sausage, macaroni-cheese, rice-wheat gluten cereal, skim milk, tuna, soy isolate, peanut butter, chicken frankfurters, beef salami, casein and casein + methionine. In animal foods, peanut butter and soy isolate, the differences between true digestibility of crude protein and most individual amino acids were less than 5%. However, the values for true digestibility of methionine and cystine were up to 44% lower than those of crude protein in pinto beans, kidney beans, lentils, chick peas and pea concentrate. In these legumes, digestibility of crude protein was not a good predictor of digestibility of the limiting amino acids.

Amino Acids, Essential↗
PubMed2001

The influence of glucose-insulin-kalium mixture (GIK) on the selected parameters of acid-base balance in acute myocardial infarction.

The aim of the paper was assessing the influence of polarizing GIK mixture on the selected indicators of acid-base equilibrium in patients with acute myocardial infarction treated fibrinolytically. The patients had arterial blood taken in order to check pH, partial pressure of oxygen and carbon dioxide, and the content of bicarbonates. Changes in the examined parameters in the group obtaining GIK and in the one obtaining placebo were subject to critical analysis. Changes in gasometric parameters taking place under the influence of GIK administered to patients were also analysed according to the site of infarction. It was observed that after 24 hours from the beginning of infusion pH increased and pCO2 decreased in comparison to the initial examination. These changes did not depend on the kind of applied infusion (GIK or physiological saline infusion), no significant changes in bicarbonates being observed. However, after applying GIK infusion, an increase in oxygen pressure in comparison with the control group was observed, and differences between the groups were within the boundaries of significance. Neither was there observed any influence of infarction site on changes in the assessed parameters of acid-base equilibrium in the group treated with GIK nor in the one receiving placebo.

Acid-Base Equilibrium↗
PubMed2003

A critical review of selective serotonin reuptake inhibitor-associated bleeding: balancing the risk of treating hepatitis C-infected patients.

BACKGROUND: Selective serotonin reuptake inhibitors (SSRIs) are increasingly being used to treat interferon-associated side effects in patients receiving hepatitis C virus (HCV) therapy. Because there is an increased risk of bleeding in HCV-infected patients who have developed cirrhosis and either portal hypertension or hepatic failure or both, we critically reviewed the literature on SSRI-associated bleeding. DATA SOURCES AND STUDY SELECTION: We performed a MEDLINE search of literature from 1966 to the present using hemorrhage, SSRI, and antidepressants as search terms and followed up on relevant citations. We reviewed 6 retrospective studies, 5 of which were case-control studies, and 18 case reports of bleeding in 37 people. Our review is supplemented with a case report of a possible connection between SSRI treatment and a fatal gastrointestinal bleed in an HCV-infected man. DATA SYNTHESIS: Bleeding events in 12/18 reports (67%) describing 19/24 people (79%) were closely associated with the use of SSRIs. CONCLUSION: Combining aspirin or nonsteroidal anti-inflammatory drugs with SSRIs for the treatment of interferon-associated neuropsychiatric side effects increases the risks of hemorrhage in patients with HCV who have developed cirrhosis and either portal hypertension or hepatic failure or both. We recommend that clinicians exercise caution when prescribing medications that can promote spontaneous bleeding to patients with multiple risk factors for internal hemorrhage.

Analgesics↗
PubMed2004

A three-dimensional flow control concept for single-cell experiments on a microchip. 1. Cell selection, cell retention, cell culture, cell balancing, and cell scanning.

An ideal microchip for single-cell experiments should be able to allow us to culture cells, to select any desired single cell from a group, to retain the cell for convenient cellular signal detection, and to deliver any buffer or reagent directly to the cell at any time during continual detection and observation. Most importantly, any negative impact on the live cell should be minimized. To accomplish all these functions, we developed a three-dimensional liquid flow control concept and employed special liquid flow fields to manipulate and retain a single yeast cell freely in the chip. A zero-speed point was controlled to retain the cell for three-dimensional cell balancing and cell scanning. A dispersive flow delivered reagents at a high speed to very near the cell and provided them to the cell at a low speed. No force stronger than its gravitational force was exerted on the cell, which could be balanced on different positions on an arc-sloping wall, thus minimizing any negative impact on the cell due to strong liquid flows. Specifically, we demonstrate on-chip single-cell culture, cell wall removal, and reagent delivery. Subsequently, single-cell fluorescence detection was performed, and noise filtering and background correction were applied for data processing.

Cell Culture Techniques↗
PubMed2005

Mass-balance estimation of heavy metals and selected anions at a landfill receiving MSWI bottom ash and mixed construction wastes.

An estimation of the heavy metal and anion mass-balance was made for municipal solid waste incinerator bottom ash deposited at a construction and industrial waste landfill. The mass-balance was found by comparing the content of metals and anions in the landfill leachate to the metal and anion content in the deposited bottom ash. The discharge of heavy metals ranged from 0.001% for Pb to 0.55% for Cr, which is approximately at the same level as in regular municipal solid waste (MSW) landfills. Landfilled organic material and silicates from construction waste might have contributed to the retention of metals. Chloride, and to a lesser extent sulphate, appeared to be readily released from the landfill. It was estimated that a mass corresponding to 80% of the Cl- and 18% of the SO(4)2- in the bottom ash was discharged annually. Low retention, especially of chloride, may lead to a rapid decline in the discharge of this ion in the future when the landfilling of bottom ash is discontinued.

Anions↗
PubMed2003

The evolution of parasite recognition genes in the innate immune system: purifying selection on Drosophila melanogaster peptidoglycan recognition proteins.

Genes involved in the recognition of parasites by the acquired immune system are often subject to intense selection pressures. In some cases, selection to recognize a diverse range of parasites has resulted in high levels of polymorphism, while elsewhere the protein sequence has changed rapidly under directional selection. We tested whether parasite recognition genes in the innate immune system show similar patterns of evolution. We sequenced seven peptidoglycan recognition protein genes (PGRPs) from 12 lines of Drosophila melanogaster and one line of D. simulans and used a variety of tests to determine whether the observed mutations were selectively neutral. We were unable to detect either balancing or directional selection. This suggests that the molecular cues used by insects to detect parasites are highly conserved and probably under strong functional constraints which prevent their evolving to evade the host immune response. Therefore, interactions between these genes are unlikely to be the focus of host-parasite coevolution, at least in Drosophila. We also found evidence of gene conversion occurring between two genes, PGRP-SC1A and PGRP-SC1B.

Amino Acid Sequence↗
PubMed2004

Molecular population genetics and the search for adaptive evolution in plants.

The first papers on plant molecular population genetics were published approximately 10 years ago. Since that time, well over 50 additional studies of plant nucleotide polymorphism have been published, and many of these studies focused on detecting the signature of balancing or positive selection at a locus. In this review, we discuss some of the theoretical and statistical issues surrounding the detection of selection, with focus on plant populations, and we also summarize the empirical plant molecular population genetics literature. At face value, the literature suggests that a history of balancing or positive selection in plant genes is rampant. In two well-studied taxa (maize and Arabidopsis) over 20% of studied genes have been interpreted as containing the signature of selection. We argue that this is probably an overstatement of the prevalence of natural selection in plant genomes, for two reasons. First, demographic effects are difficult to incorporate and have generally not been well integrated into the plant population genetics literature. Second, the genes studied to date are not a random sample, so selected genes may be overrepresented. The next generation of studies in plant molecular population genetics requires additional sampling of local populations, explicit comparisons among loci, and improved theoretical methods to control for demography. Eventually, candidate loci should be confirmed by explicit consideration of phenotypic effects.

Evolution, Molecular↗
PubMed2001

Balance in cluster randomized trials.

This paper explores the role of balancing covariates between treatment groups in the design of cluster randomized trials. General expressions are obtained for two criteria to evaluate designs for parallel group studies with two treatments. The first is the variance of the estimated treatment effect and the second is the extent to which the estimated treatment effect is changed by adjusting for covariates. It is argued that the second of these is more important for cluster randomized trials. Methods of obtaining balanced designs from covariates which are available at the start of a study are proposed. An imbalance measure is used to compare the extent to which designs balance important covariates between the arms of a trial. Several approaches to selecting a well balanced design are possible. A method that randomly selects one member from the class of designs with acceptable bias will allow randomization inference as well as model-based inference. The methods are illustrated with data from a trial of school-based sex education.

Adolescent↗
PubMed1984

Sodium and potassium intake and balance in adults consuming self-selected diets.

Twenty eight adults, 12 men and 16 women, participated in a 1-yr study designed to assess daily nutrient intake accurately. All subjects lived at home, consumed self-chosen diets, and maintained a detailed daily dietary record throughout the year. During four 7-day balance studies, one in each season of the year, meals, beverages, urine, and feces were analyzed for sodium and potassium content by atomic absorption spectrometry. Total intakes averaged 3.4 g/day for sodium and 2.8 g/day for potassium. The Na:K ratio for all diets analyzed averaged 1.3. Nutrient densities of sodium and potassium were 1.8 and 1.5 g/1000 kcal, respectively. Apparent absorptions of sodium and potassium were 98 and 85%, respectively, and did not change significantly over the wide range of intakes. Average urinary excretions of sodium and potassium were 86 and 77% of total intake, respectively. Mean metabolic balances were positive for sodium, +0.47 g/day, and potassium, +0.28 g/day. The data of this study provide useful information concerning the dietary intakes, excretions, and balances of sodium and potassium for adults based on analytic determination.

Adult↗
PubMed2006

Intron length and accelerated 3' gene evolution.

Genetic evolution depends in part upon a balance between negative selection and environmentally driven mutation. To explore whether this balance is affected by gene structure, we have used phylogenetic data mining to compare gene compositions across a range of species. Here we show that genomes of higher species exhibit a greater frequency of 5' CpG islands and of CpG-->TpG/CpA transitions. This latter mutational pattern exhibits a 5'-to-3' trend in higher species, consistent with a length-dependent effect on methylation-dependent CpG suppression. Associated strand asymmetry (TpG>CpA) declines with gene length, implying attenuation of transcription-coupled repair 3' to introns. A sharp 3' rise in coding region single-nucleotide polymorphism frequency further supports a mechanistic role for intron length in promoting genetic variation by reducing repair and/or weakening negative selection. Consistent with this, the Ka/Ks ratio of 3' exons exceeds that of centrally located exons in intron-containing, but not in intronless, genes (p<0.0003). We conclude that the efficiency of transcription-coupled repair decreases with gene length, suggesting in turn that 3' gene evolution is accelerated both by introns and by gene methylation.

3' Untranslated Regions↗
PubMed2002

Signatures of random and selective mass extinctions in phylogenetic tree balance.

Current models of diversification with evolving speciation rates have trouble mimicking the extreme imbalance seen in estimated phylogenies. However, these models have not incorporated extinction. Here, we report on a simple simulation model that includes heritable and evolving speciation rates coupled with mass extinctions, Random (but not selective) mass extinctions, coupled with evolving among-lineage variation in speciation rates, increase imbalance of postrecovery clades. Thus, random mass extinctions are plausible contributors to the imbalance of modern clades. Paleontological evidence suggests that mass extinctions are often random with respect to ecological and morphological traits, consistent with our simulations. In contrast, evidence that the current anthropogenic mass extinction is phylogenetically selective suggests that the current extinction episode may be qualitatively different from past ones in the way it reshapes future biotas.

Biological Evolution↗
PubMed1982

Cerebrospinal fluid hydromechanics in adult patients with benign noncommunicating hydrocephalus: one-hour test shunting and balanced cerebrospinal fluid infusion test to select patients for intracranial bypass operation.

Cerebrospinal fluid (CSF) pressure and absorption were determined in 12 patients with benign noncommunicating hydrocephalus. An extracorporeal communication of plastic tubing between the ventricular system and the lumbar subarachnoid space was established to imitate the hydromechanical condition after an intracranial bypass operation. This extracorporeal shunt, which in effect was an externalized Torkildsen shunt, served first as a test shunt for 1 hour and then as a route for the constant rate CSF infusion test. The total CSF absorptive capacity was thus determined under a condition of balanced CSF pressure between the proximal and distal compartment. Four patients, whose tests showed normal CSF pressure and absorption, were selected for intracranial bypass operation. Follow-up examination showed a normal clinical condition, reduction of the ventricular system, normal CSF pressure, and normal CSF absorption in all 4 patients. The other 8 patients, whose tests indicated impaired CSF absorption, were treated by ventriculoatrial shunting. The tests were valid in selecting patients for intracranial bypass operation.

Adolescent↗
PubMed2003

Genetic regulation of feed intake and energy balance in poultry.

Intensive selection by poultry breeders over many generations for economically important production traits such as growth rate and meat production has been accompanied by significant changes in feed intake and energy balance. For example, the modern commercial broiler, selected for rapid growth and enhanced muscle mass, does not adequately regulate voluntary feed intake to achieve energy balance. When given unrestricted access to feed, broilers exhibit hyperphagia leading to an excessive accumulation of energy (fat) stores, making these birds prone to obesity and other health-related problems. Humoral and neural pathways have been identified and studied in mammals that link appetite and energy balance. A series of highly integrated regulatory mechanisms exists for both of these processes involving complex interactions between peripheral tissues and the central nervous system. Within the central nervous system, the brainstem and the hypothalamus play critical roles in the regulation of feed intake and energy balance. Genes encoding key regulatory factors such as hormones, neuropeptides, receptors, enzymes, transcription factors, and binding/transport proteins constitute the molecular basis for regulatory systems that derive from integrated sensing, signaling, and metabolic pathways. However, we do not yet have a complete understanding of the genetic basis for this regulation in poultry. This review examines what is currently known about the regulation of feed intake and energy balance in poultry. A better understanding of the genes associated with controlling feed intake and energy balance and how their expression is regulated by nutritional and hormonal stimuli will offer new insights into current poultry breeding and management practices.

Animal Husbandry↗
PubMed2001

[Selected parameters of the oxidative-antioxidative balance in children with bronchial asthma exacerbations].

The aim of this study was to evaluate the involvement of selected parameters of oxidative-antioxidative system in children with bronchial asthma exacerbations. In my study the intensity of lipid peroxidation was calculated by the contents of malolonic dialdehyd in plasma. In order to evaluate activity of antioxidative system I investigated vitamin E concentration and total antioxidants status in serum, as well as activity of glutathione peroxidase and superoxide dismutase in blood. My study was performed on 32 children treated for exacerbations of bronchial asthma. The control group consisted of 27 healthy children. The study has revealed that children suffering from bronchial asthma exhibit disturbances in the oxidative-antioxidative balance, manifested by increased oxidative activity and by changes in certain parameters of the antioxidative system. It should be emphasized that disturbances in the oxidative/antioxidative balance were observed in the period of clinical exacerbation of asthma, as well as in the period of clinical remission. This fact may constitute further evidence for a prolonged existence of minimal inflammation in the respiratory tract in bronchial asthma.

Acute Disease↗