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Biomedical subjects

E Post

Publications and source records attributed to E Post.

At least 19 recordsLinked to original sources
PubMed2001

Pervasive influence of large-scale climate in the dynamics of a terrestrial vertebrate community.

BACKGROUND: Large-scale climatic variability has been implicated in the population dynamics of many vertebrates throughout the Northern Hemisphere, but has not been demonstrated to directly influence dynamics at multiple trophic levels of any single system. Using data from Isle Royale, USA, comprising time series on the long-term dynamics at three trophic levels (wolves, moose, and balsam fir), we analyzed the relative contributions of density dependence, inter-specific interactions, and climate to the dynamics of each level of the community. RESULTS: Despite differences in dynamic complexity among the predator, herbivore, and vegetation levels, large-scale climatic variability influenced dynamics directly at all three levels. The strength of the climatic influence on dynamics was, however, strongest at the top and bottom trophic levels, where density dependence was weakest. CONCLUSIONS: Because of the conflicting influences of environmental variability and intrinsic processes on population stability, a direct influence of climate on the dynamics at all three levels suggests that climate change may alter stability of this community. Theoretical considerations suggest that if it does, such alteration is most likely to result from changes in stability at the top or bottom trophic levels, where the influence of climate was strongest.

Abies↗
PubMed2001

Metathesis-based monoliths: influence of polymerization conditions on the separation of biomolecules.

Monolithic materials were prepared by transition metal-catalyzed ring-opening metathesis copolymerization of norborn-2-ene and 1,4,4a,5,8,8a-hexahydro-1,4,5,8-exo,endo-dimethanonaphthalene within the confines of surface-derivatized borosilicate columns in the presence of the porogenic solvents toluene and 2-propanol using Cl2(PCy3)2Ru(=CHPh) (1) as initiator. Relevant physicochemical data of the porous structure (specific surface area (sigma), pore volume (Vp), volume fraction of pores (epsilon(p)), and intermicroglobule volume (epsilon(z))) of the monolithic columns were determined by inverse size exclusion chromatography in tetrahydrofuran. Mean particle diameters were determined via electron microscopy. The influence of variations in polymerization conditions in terms of stoichiometry of the monomers and porogenic solvents on the chromatographic separation of the oligodeoxynucleotides dT12-dT18 and eight model proteins (ribonuclease A, insulin, cytochrome c, lysocyme, alpha-lactalbumin, alpha-chymotrypsinogen, beta-lactoglobulin B, catalase) were studied. Also, the role of additional phosphine on the entire polymerization setup and the associated chromatographic separations was elucidated. Relevant chromatographic data as well as differences between the separation of oligodeoxynucleotides and proteins may directly be attributed to the above-mentioned physicochemical properties of the metathesis-based monoliths. Finally, DSC-TGA-MS investigations on various monoliths of different composition and age were carried out in order to provide information on stability and oxidation behavior.

Animals↗
PubMed2001

The timing of life-history events in a changing climate.

Although empirical and theoretical studies suggest that climate influences the timing of life-history events in animals and plants, correlations between climate and the timing of events such as egg-laying, migration or flowering do not reveal the mechanisms by which natural selection operates on life-history events. We present a general autoregressive model of the timing of life-history events in relation to variation in global climate that, like autoregressive models of population dynamics, allows for a more mechanistic understanding of the roles of climate, resources and competition. We applied the model to data on 50 years of annual dates of first flowering by three species of plants in 26 populations covering 4 degrees of latitude in Norway. In agreement with earlier studies, plants in most populations and all three species bloomed earlier following warmer winters. Moreover, our model revealed that earlier blooming reflected increasing influences of resources and density-dependent population limitation under climatic warming. The insights available from the application of this model to phenological data in other taxa will contribute to our understanding of the roles of endogenous versus exogenous processes in the evolution of the timing of life-history events in a changing climate.

Anemone↗
PubMed2001

Treatment as usual (TAU) control practices in the PROSPECT Study: managing the interaction and tension between research design and ethics.

The use of treatment as usual (TAU) as a control condition may pose the considerable challenge of maintaining both scientific rigor and meeting high ethical standards in experiments on human subjects. The authors illustrate the tension and explore the relationship between research design and ethics, especially the interaction between the two, in the NIMH-funded PROSPECT study (Prevention of Suicide in Primary Care Elderly - Collaborative Trial). The goal of PROSPECT is to determine whether placement of a depression health specialist in primary care practices will have a favorable impact on rates of depression, hopelessness and suicidal ideation in elderly primary care patients with major or persistent minor depression. PROSPECT randomly assigns practices either to an intervention arm (which includes the provision of depression health specialists) or to an enhanced care arm (TAU, with the addition of screening and assessment services). TAU, enhanced by the provision of screening and assessment services, is to be used as a benchmark for measuring the effectiveness of PROSPECT's intervention. However, TAU in the epidemiological and clinical literature has also been linked to high rates of suicide in the elderly related to unrecognized and untreated or under-treated depression. The authors present their approach to managing the tension, or interaction, between the use of TAU for scientific and public health purposes and the requirement for beneficence, that is, the duty to assure the safety of human subjects in research and to do no harm. Through enhancements of TAU, by the provision of information to primary care physicians concerning the psychiatric status of their patients, the investigators attempt to meet the challenge of maintaining rigor and meeting high ethical standards.

Aged↗
PubMed2001

An empirical Bayes approach to estimating the relation of mortality to exposure to particulate matter.

As part of its assessment of the health risks associated with exposure to particulate matter (PM), the U.S. Environmental Protection Agency analyzed the risks associated with current levels, and the risk reductions that might be achieved by attainment of alternative PM standards, in two locations in the United States, Philadelphia, and Los Angeles. The concentration-response function describing the relation between a health endpoint and ambient PM concentrations is an important component, and a source of substantial uncertainty, in such risk analyses. In the absence of location-specific estimates, the concentration-response functions necessary for risk assessments in Philadelphia and Los Angeles must be inferred from the available information in other locations. Although the functional form of the concentration-response relations is assumed to be the same everywhere, the value of the PM coefficient in that function may vary from one location to another. Under this model, a distribution describes the probability that the PM coefficient in a randomly selected location will lie in any range of interest. An empirical Bayes estimation technique was used to improve the estimation of location-specific concentration-response functions relating mortality to short-term exposure to particles of aerodynamic diameter less than or equal to 2.5 microm (PM-2.5), for which functions have previously been estimated in several locations. The empirical Bayes-adjusted parameter values and their SEs were used to derive an estimate of the distribution of PM-2.5 coefficients for mortality associated with short-term exposures. From this distribution, distributions of relative risks corresponding to different specified changes in PM-2.5 concentrations could be derived.

Air Pollutants↗
PubMed2001

Reproductive asynchrony increases with environmental disturbance.

While it is widely recognized that the manner in which organisms adjust their timing of reproduction reflects evolutionary strategies aimed at minimizing offspring mortality or maximizing reproductive output, the conditions under which the evolutionarily stable strategy involves synchronous or asynchronous reproduction is a matter of considerable discord. A recent theoretical model predicts that whether a population displays reproductive synchrony or asynchrony will depend on the relative scales of intrinsic regulation and environmental disturbance experienced by reproducing individuals. This model predicts that, under conditions of negligible competition and large-scale environmental perturbation, evolution of a single mixed strategy will result in asynchronous reproduction. We tested this prediction using empirical data on large-scale climatic fluctuation and the annual timing of reproduction by three species of flowering plants covering 1300-population-years and four degrees of latitude in Norway. In agreement with model predictions, within populations of all three species reproductive asynchrony increased with the magnitude of large-scale climatic perturbation, but bore no relation to the strength of local density dependence. These results suggest that mixed evolutionarily stable strategies can arise from the interplay of combinations of agents of selection and the scale at which they operate; hence it is fruitless to associate synchronous versus asynchronous timing with particular single factors like climate, competition, or predation.

Climate↗
PubMed1999

Common dynamic structure of canada lynx populations within three climatic regions

Across the boreal forest of Canada, lynx populations undergo regular density cycles. Analysis of 21 time series from 1821 onward demonstrated structural similarity in these cycles within large regions of Canada. The observed population dynamics are consistent with a regional structure caused by climatic features, resulting in a grouping of lynx population dynamics into three types (corresponding to three climatic-based geographic regions): Pacific-maritime, Continental, and Atlantic-maritime. A possible link with the North Atlantic Oscillation is suggested.

Journal Article↗
PubMed1999

Environmental variation shapes sexual dimorphism in red deer.

Sexual dimorphism results from dichotomous selection on male and female strategies of growth in relation to reproduction. In polygynous mammals, these strategies reflect sexual selection on males for access to females and competitive selection on females for access to food. Consequently, in such species, males display rapid early growth to large adult size, whereas females invest in condition and early sexual maturity at the expense of size. Hence, the magnitude of adult size dimorphism should be susceptible to divergence of the sexes in response to environmental factors differentially influencing their growth to reproduction. We show that divergent growth of male and female red deer after 32 years of winter warming and 15 years of contemporaneously earlier plant phenology support this prediction. In response to warmer climate during their early development, males grew more rapidly and increased in size, while female size declined. Conversely, females, but not males, responded to earlier plant phenology with increased investment in condition and earlier reproduction. Accordingly, adult size dimorphism increased in relation to warmer climate, whereas it declined in relation to forage quality. Thus, the evolutionary trajectories of growth related to reproduction in the sexes (i) originate from sexual and competitive selection, (ii) produce sexual size dimorphism, and (iii) are molded by environmental variation.

Animal Feed↗
PubMed1998

Population dynamics of Norwegian red deer: density-dependence and climatic variation.

We present a model on plant-deer climate interactions developed for improving our understanding of the temporal dynamics of deer abundance and, in particular, how intrinsic (density-dependent) and extrinsic (plants, climate) factors influence these dynamics. The model was tested statistically by analysing the dynamics of five Norwegian red deer populations between 1964 and 1993. Direct and delayed density-dependence significantly influenced the development of the populations: delayed density-dependence primarily operated through female density, whereas direct density-dependence acted through both female and male densities. Furthermore, population dynamics of Norwegian red deer were significantly affected by climate (as measured by the global weather phenomenon, the North Atlantic Oscillation: NAO). Warm, snowy winters (high NAO) were associated with decreased deer abundance, whereas the delayed (two-year) effect of warm, snowy winters had a positive effect on deer abundance. Our analyses are argued to have profound implications for the general understanding of climate change and terrestrial ecosystem functioning.

Animals↗
PubMed1997

Global climate change and phenotypic variation among red deer cohorts.

The variability of two fitness-related phenotypic traits (body weight and a mandibular skeletal ratio) was analysed among cohorts and age-classes of red deer in Norway. Phenotypic variation among cohorts was pronounced for calves, yearlings and reproductively mature adults. Fluctuations in cohort-specific mean body weights and skeletal ratios of adults correlated with global climatic variation in winter conditions influenced by the North Atlantic Oscillation while cohorts were in utero. Red deer born following warm winters were smaller than those born after cold winters, and this inter-cohort variability persisted into adulthood. Phenotypic variation among cohorts of red deer influenced by climate change may pose consequences for fitness of cohorts since body size and condition contribute to reproductive success and survival in male and female red deer. In particular, the recent trend of increasingly warm winters in northern Europe and Scandinavia may lead to reduced body size and fecundity of red deer, and perhaps other ungulates, in those areas.

Animals↗
PubMed1996

The effects of cold, touch, and chemical stimulation of the anterior faucial pillar on human swallowing.

Cold stimulation of the oropharyngeal mucosa, including the faucial pillar region, is used a specific technique for the treatment of swallowing disorders. The physiological mechanisms underpinning this clinical technique are unclear. Thermal (cold), chemical (saline, glucose and water), mechanical (light touch) and feigned stimulation of the faucial pillar were assessed for their effects on the latency to swallow and the repetitive frequency of swallowing. There was no significant difference between these variables following light stimulation of the faucial pillar with a metal probe warmed to body temperature compared with feigned stimulation. However, cold touch stimulation evoked a significant increase in swallowing latency and repetitive frequency compared to feigned stimulation. The results suggest the existence of thermo-sensitive receptors in the faucial pillars that evoke swallowing when stimulated by cold touch. The clinical and physiological importance of these findings are discussed.

Adult↗
PubMed1994

[Leprosy in The Netherlands in the period 1970-1991].

OBJECTIVE: To inventory the changes in leprosy epidemiology in the Netherlands. DESIGN: Retrospective. SETTING: Academic Medical Centre (Amsterdam) and University Hospital Dijkzigt (Rotterdam), the Netherlands. METHOD: The medical records of all new leprosy patients in the period 1970-1991 were analysed. RESULTS: Between 1970 and 1991, 622 new leprosy patients were registered; 371 men (59.6%) and 251 women (40.4%). Most patients came from Surinam (73.3%) and Indonesia (7.2%). The mean time lapse between onset and treatment in the Netherlands was 10.1 years. Switching from monotherapy to combination therapy (1979) had no effect on the incidence of reversal reactions (cellular hypersensitivity in immunologically unstable patients), but did affect the incidence of erythema nodosum leprosum during the treatment. CONCLUSION: Leprosy in the Netherlands is an important disease, mainly from Surinam. The main advantage of combination therapy is the shortened duration of treatment. The treatment of choice is the one recommended by the WHO, the combination therapy with rifampicin administration once a month, because of the few adverse effects.

Adult↗
PubMed1994

Alcoholic beverages and breast cancer: some observations on published case-control studies.

We identified 38 case-control studies investigating possible associations between alcoholic beverage consumption and cancer of the female breast. Each study was characterized according to design features such as: control type (hospital or community based), risk factors controlled for, matching strategy, and statistical power. We examined the effect of these design variables on several outcome variables including identification of any significant elevation in odds ratio and characterization of any dose-response effect. The major finding of this study is that of a striking difference between hospital and community based controlled studies with respect to (1) the level of any estimated dose-response effect, and (2) the finding of statistically significant elevations in odds ratios at levels of consumption below 4 drinks per week. In summary, the generally weak associations reported in these case-control studies along with the measurement and/or selection biases implied by our findings would lead one to the conclusion that present evidence does not support a causal association. This conclusion seems to be in accord with results from cohort studies and with similar conclusions from several other reviews.

Alcohol Drinking↗
PubMed1987

Continent urostomy: a clinical experience in 20 patients.

Urinary diversion via a continent ileal reservoir (modified Kock's procedure) was performed in 20 patients. Primary continent urostomy construction was carried out in 6 patients. Previous urinary diversion was present in 12 patients. Two patients were referred to us because a previous attempt to construct a continent reservoir urostomy had failed. There was no operative mortality. Three early complications occurred in 3 patients. Leakage from a uretero-enteric anastomosis in one patient and necrosis of a continence-providing valve in another patient necessitated reoperation. Late complications causing malfunction of the nipple valves required revisional surgery in 2 patients. Stoma stricture developed in 1 patient after 5 months and could be corrected surgically. The functional results were excellent. Continence was achieved without reflux to the upper urinary tract. Instead of a Kock pouch, an S-pouch was used. The continence and antireflux-providing valves were stapled to the reservoir wall. Slippage of the nipple valves did not occur. All our patients had consistently positive urine cultures and were without complaints. In a few cases, stone formation was observed usually on the staples at the tip of the valve. The stones were removed by forceps during endoscopy of the reservoir.

Adult↗
PubMed1985

[Prune belly syndrome].

Referring to a patient operated on the third day of life for pyeloureteral stenosis the 'prune belly' syndrome is described. The syndrome is delineated by urinary tract anomalies, undescended testicles and a prune like abdominal wall. Several other anomalies are commonly seen. In this patient the megaureters, the vesicoureteral reflux and megacystis are considered part of the syndrome. The pyeloureteral stenosis was only seen once before in a succumbed newborn.

Abnormalities, Multiple↗