SEARCH · PubMed Health

Results for “environmental variability”

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 973 records · Page 54Linked to original sources

PubMed2004

Age, gender, and urban-rural differences in the correlates of physical activity.

BACKGROUND: The majority of the population is inactive, and strategies to date for promoting regular physical activity have been limited in their effectiveness. Further research is needed to identify correlates of physical activity in different subgroups to design more efficacious interventions. This study sought to identify correlates of physical activity across men and women, urban and rural geographical locations, and four distinct age groups (18-25; 26-45; 46-59; and 60+). METHODS: This study employed data from a large provincial household random sample (N = 20,606) of Canadians. Analyses were utilized to examine the amount of variance explained in self-reported physical activity by a number of demographic and/or biological, psychological, behavioral, social, and environmental variables within each subgroup. RESULTS: Proportion of friends who exercise, injury from past physical activity, educational level, perceived health status, and alcohol consumption were among the strongest correlates across subgroups. CONCLUSIONS: A number of correlates were identified as being significant across all subgroups examined. Most differences in the correlates of physical activity were found within different age groups rather than among urban and rural residents and gender.

Adult↗

PubMed2006

Correlates of physical activity in a national sample of children aged 9-13 years.

BACKGROUND: Physical activity (PA) is critical for children's normal growth and development. The purpose of this study was to assess potential correlates of physical activity in a US national sample of youth aged 9-13 years. METHODS: A nationally representative telephone survey of parent-child pairs was conducted from April through June 2002. The questions assessed organized and free-time physical activity behavior and psychosocial and environmental variables that are potentially related to youth physical activity. RESULTS: Children's positive outcome expectations or beliefs about the benefits of participating in physical activity and parent's beliefs that participating in physical activity is important were related to participation in both organized and free-time physical activity. Children's perception of parental support and parent's reports of direct support were strongly related to organized physical activity. Feeling safe, having lots of places to be active, and parental participation with their child were strongly related to free-time physical activity. CONCLUSIONS: Messages and interventions aiming to increase children and adolescent's participation in organized and free-time physical activity should continue to focus on promoting the benefits that are associated with being active, the importance of parental support, and the provision of safe and enjoyable opportunities to be active.

Adolescent↗

PubMed1997

Environment-behavior relations, behavior therapy and the process of persuasion and attitude change.

The phenomena described by the cognitive dissonance literature, especially to explain attitude change, have important relevance to understanding certain aspects of therapy. Contrary to popular beliefs, these phenomena can be described in behavior-analytic terms. To do so requires an analysis of learning histories that select and maintain consistency in what individuals say and do. An understanding of the environmental variables that produce consistency can then be applied to the kinds of attitude change and stability found in the cognitive dissonance literature that have therapeutic importance.

Attitude↗

PubMed1990

Asthma attack periodicity: a study of hospital emergency visits in Vancouver.

Attendances at the emergency departments of the nine acute care hospitals serving the Vancouver region, with a population of just under a million people, were recorded from July 1, 1984 to October 31, 1986. Of about 25,500 visits a month, 2.7% were for respiratory conditions; and of these, 41.3% were for asthma. Data from 11 air monitoring stations were also tabulated on a daily basis, giving mean maximal hourly values for SO2, NO2, and O3; daily aerosol sulfate measurements from one station were also analyzed, together with daily temperature data and measurements of the coefficient of haze. In 3 consecutive years, a peak in asthma attendances was noted, starting in the last week of September, and continuing for 3 weeks. In these periods, weekly visits for asthma reached 130 patients; during the rest of the year, the weekly visits for asthma varied between 30 and 90. This peak affected children and adults between the ages of 15 and 60, but no increase was seen in those over 60 years. Although pollution levels increased sharply in the fall, a day-by-day analysis showed that the rise in asthma attendances preceded the increase in NO chi and SO2 levels for the region, expressed as the mean of the hourly maxima across all stations. It seems unlikely that a specific pollen is responsible for this, or that house mite replication is the cause. Soya beans are not shipped out of Vancouver. The cause of the peak has not been identified. Variations in emergency visits by day of the week have been recorded; in children and in those aged 15-60, more visits occur on Sundays than on other days, but this does not occur in those over 60. There is no significant variation in environmental data by day of the week. Intercorrelations between environmental variables and emergency visits have been calculated separately for the periods May 1 to October 31, and November 1 to April 31. SO2, NO2, and SO4 are strongly intercorrelated in both periods; ozone is strongly related to temperature, but less strongly correlated to sulfate than is the case in Southern Ontario. In summer, total emergency visits (but not respiratory visits) are strongly correlated with temperature in all age groups (the hotter the day, the more visits occur); but respiratory visits are not related to temperature, ozone, or NO2 levels. However, in the 15-60 age group, asthma and respiratory visits are correlated in summer with SO2 and SO4 levels (P = less than 0.001).(ABSTRACT TRUNCATED AT 400 WORDS)

Adolescent↗

PubMed1992

The effect of ozone associated with summertime photochemical smog on the frequency of asthma visits to hospital emergency departments.

A retrospective study using ambient ozone, temperature, and other environmental variables and their effect on the frequency of hospital visits for asthma was conducted in New Jersey, an area that often exceeds the allowable national standard for ozone. Data on emergency department visits for asthma, bronchitis, and finger wounds (a nonrespiratory control) were analyzed for the period May through August for 1988 and 1989. Asthma visits were correlated with temperature while the correlation between asthma visits and ozone concentration was nonsignificant. However, when temperature was controlled for in a multiple regression analysis, a highly significant relationship between asthma visits and ozone concentration was identified. Between 13 and 15% of the variability of the asthma visits was explained in the regression model by temperature and ambient ozone levels. This association, when compared to similar studies in Canada, shows the contribution of ozone to asthma admissions to be stronger in areas with higher ozone concentrations. Thus, among regions with periodic accumulations of ozone in the ambient atmosphere, an exposure-response relationship may be discernible. This supports the need to attain air quality standards for ozone to protect individuals in the general population from the adverse health effects caused by ambient ozone exposure.

Asthma↗

PubMed2001

Environmental, cultural and social changes and their influence on parasite infections.

The changes taking place within the societies, cultures and the environments in which we live are massive and complex. By referring to simple epidemiological models it is possible to build an objective framework with which to look at these changes in terms of their likely impact on the epidemiology of parasitic diseases within human communities. These parameters are listed for hosts and both micro- and macroparasites, as are epidemiologically significant cultural, social and environmental variables. Changes in these variables may be either detrimental or beneficial to human health and may, in addition, interact in complex ways. Examples of the complexity of changes which can influence epidemiology are provided for a cultural template of the population living in the north-east of Thailand.

Animals↗

PubMed2002

The ecology of cutaneous leishmaniasis in Nizzana, Israel: infection patterns in the reservoir host, and epidemiological implications.

We conducted an extensive interdisciplinary study in an emerging focus of cutaneous leishmaniasis in the Western Negev Desert of Israel between July 1998 and February 2000. The aims of the this study were to determine (1) the reservoir hosts, (2) the distribution of the pathogen within the host range, (3) the associations of host, vector, and pathogen within defined habitats, (4) the demographic distribution of the pathogen within the host populations, and (5) to apply the newly acquired epizootiological data to explain morbidity patterns in humans. Fourteen square (60 m width) sampling plots were delimited in three types of habitats each with a different kind of substrate: loess, sand, and sand-loess ecotone. Rodents and sand flies were trapped and several environmental variables were measured. Leishmania infections in rodents were detected microscopically in stained smears of ear tissue and by a Leishmania-specific polymerase chain reaction. Results indicate that, contrary to previous reports, Psammomys obesus and not Meriones crassus is the main reservoir host in the region. Additional rodents (12 Gerbillus dasyurus and two M. crassus) were also found positive for Leishmania DNA. Prevalence of Leishmania infections amongst P. obesus was highest in loess habitats (65%), intermediate in the sandy-loess ecotone (20%), and 0% in the sandy habitats. Psammomys obesus individuals in the loess habitat of the Nizzana ruins were larger, on average (probably older), than those in the sandy habitat of the Mt. Keren junction. Sand fly density was positively correlated to soil moisture being higher in the relatively humid plots of Nizzana ruins and much lower in the drier sandy soil of Mt. Keren. Elucidation of fundamental ecological factors affecting this disease has helped explain an apparent discrepancy between the distribution of the disease in the zoonotic system and among humans.

Animals↗

PubMed1999

Long-term effects of short-term provision of protein-enriched diets on resistance to nematode infection, and live-weight gain and wool growth in sheep.

Weaner sheep that had been hand-fed on diets containing increasing concentrations of protein for a 9-week period (when uninfected, or infected with Haemonchus contortus) were studied during the next 69 weeks when put on to pasture as a single, unsupplemented flock. During the 9-week period, groups of 12 sheep (six infected, six uninfected) were offered one of five iso-energetic (9.0 MJ kg(-1)) diets containing 10, 13, 16, 19 or 22% crude protein. All sheep were treated with anthelmintic at the end of the 9 weeks and then put out to pasture for 69 weeks, where they were all subject to the same environmental variables including nematode larval challenge. During the grazing period, animals that had previously received the higher protein diets consistently had higher live-weight gain and wool production, higher antibody responses to both H. contortus and Trichostrongylus colubriformis antigenic challenge in vitro, and lower faecal nematode egg counts than did the lambs previously offered the lower protein diets. Faecal egg counts of the grazing sheep that had been artificially infected with H. contortus while being hand-fed were similar to those of the uninfected sheep and there was no interaction between previous infection and dietary protein concentration. We conclude that short periods of enhanced post-weaning nutrition can have long-term and perhaps life-long effects on production.

Animals↗

PubMed2000

Roles of experimental marine ecology in coastal management and conservation.

The paper reviews the main findings of rocky shore and subtidal nearshore experimental marine ecology (EME) in cold and temperate marine ecosystems during the past four decades. It analyzes the role of EME in coastal management and conservation. The historical development of strategies for managing single or multispecies fisheries are reviewed. The published results show over-exploitation and depletion of more than 60% of the fish stocks and a lack of connection between the management of fisheries and results derived from experimental marine ecology. This is mainly due to: (a) the different temporal and spatial scale at which most marine ecologists and fishery managers operate; (b) the lack of long-term fishery monitoring and adaptive techniques for management; and (c) limitations in the design of experiments on fisheries. Large-scale oceanic perturbations, due to combinations of excessive resource exploitation and environmental variability coupled with present trends in management approaches are discussed. Modern approaches and tools for management of fisheries, such as Adaptive Management (AM), Territorial User Rights in Fisheries (TURFs), Individual Transferrable Quotas and Non-Transferrable Quotas (ITQs, INTQs) are discussed in the context of small-scale fisheries and EME. Published views on limits of applied ecological research with regards to management of fisheries are discussed. Linkages between EME, marine conservation and the establishment of Marine Protected Areas (MPAs) and experimental exclusions of humans are highlighted. Results derived from MPAs, such as: (a) species or community trophic cascades, and (b) the role of key-stone species and species interaction strengths, are discussed. It is concluded that the role of EME in conservation has been greater than has been the case in management of fisheries. The potential to link EME, conservation and the management of fisheries is exemplified through the proposed establishment in Chile of a connected network of Scientific Reserves, MPAs and TURFs sites. The final conclusion is that to cross-fertilize EME, conservation and management, there are three main challenges: (1) to end the traditional view of approaching the management of fisheries and marine conservation as contradictory/antagonizing issues; (2) to improve communications between experimental marine ecology and the management of fisheries through the implementation of experimentation and adaptive management; (3) to improve linkages between marine conservation, the management of fisheries and social sciences.

Journal Article↗

PubMed2001

Fish fauna of the Severn Estuary. Are there long-term changes in abundance and species composition and are the recruitment patterns of the main marine species correlated?

Fish were collected from the intake screens of the Oldbury Power Station in the Severn Estuary in each week between early July 1972 and late June 1977 and at least twice monthly between early January 1996 and late June 1999. The annual catches, after adjustment to a common sampling effort, demonstrate that the abundance of fish at Oldbury was far greater in the 1990s than 1970s, mainly due to marked increases in the numbers of certain marine species, such as sand goby, whiting, bass, thin-lipped grey mullet, herring, sprat and Norway pout. These increases may reflect the great improvement that occurred in the water quality of the Severn Estuary between these decades. The only species that declined markedly in abundance was poor cod. Modest declines in flounder and River lamprey paralleled those occurring elsewhere in the UK. The species composition in the two decades also differed, reflecting changes not only in the relative abundances of the various marine estuarine-opportunistic species, which dominated the ichthyofauna, but also in those of the suite of less abundant species in the estuary. The cyclical changes undergone each year by the species composition of the fish fauna of the Severn Estuary reflect sequential intra-annual changes in the relative abundances of species representing each of the marine, diadromous and freshwater categories. New approaches have been developed to test whether or not large sets of correlations between patterns of recruitment amongst abundant marine species (internal correlations), and between those patterns and salinity and water temperature within the estuary (cross-correlations), were significant. The correlation profile analyses found no evidence that the annual recruitment strengths of these species were either intercorrelated, or correlated with either one or a combination of both of the above environmental variables. Yet, the timings of the recruitment of these species into the estuary were intercorrelated, i.e. a slightly earlier or later than normal immigration by one species in a given year was paralleled by the same trend in other species. However, this association in recruitment times could be linked neither to salinity nor water temperature within the estuary, nor to a combination of these two variables. These results indicate that, while the factors that influence the annual recruitment strengths of the juveniles of different marine species vary, inter-annual differences in the phasing of events that regulate spawning times and/or larval dispersal influence, in the same direction, the times when marine species are recruited into the estuary.

Journal Article↗

PubMed1993

Relation of infant feeding practices, cigarette smoke exposure, and group child care to the onset and duration of otitis media with effusion in the first two years of life.

The relation of infant feeding practices, cigarette smoke exposure, and group child care to the onset and duration of otitis media with effusion (OME) was evaluated in a cohort of 698 healthy infants prospectively monitored by tympanometry in the home every 2 to 4 weeks until 2 years of age. Except for an experimental group of children who were offered early tube placement, the study children received conventional care from their personal physician or clinic. We used LISREL, a structural equation modeling procedure (computer software), to explore associations between environmental variables and OME onset and duration while controlling for interrelations among the variables. Supine feeding position and early initiation of group child care were associated with earlier onset of OME. Shorter duration of breast-feeding, increased packs of cigarettes smoked per day in the home, and increased hours per week in group child care were associated with an increase in the amount of time with OME during one or more of the age blocks studied (birth to 6, 6 to 12, 12 to 18, and 12 to 24 months). For a decrease in the amount of time with OME during the first 2 years of life, prolonged breast-feeding and upright feeding position should be encouraged, and cigarette smoke exposure should be minimized. Limiting early child care in large groups might also be advisable.

Breast Feeding↗

PubMed1989

The primary sex ratio under environmental sex determination.

The ESS primary sex ratio (male/female) under environmental sex determination (ESD) is shown to be equal to the ratio of the average fertility of a female to the average fertility of a male. Thus, depending upon how male and female fertility change over the environmental variable causing ESD, the primary sex ratio may be either male or female biased, or neither. The primary sex ratio thus contains information as to how male and female fertilities change with the environment.

Animals↗

PubMed2001

Loss of heterozygosity in somatic cells of the mouse. An important step in cancer initiation?

Loss of heterozygosity (LOH) of tumour suppressor genes is a crucial step in the development of sporadic and hereditary cancer. Recently, we and others have developed mouse models in which the frequency and nature of LOH events at an autosomal locus can be elucidated in genetically stable normal somatic cells. In this paper, an overview is presented of recent studies in LOH-detecting mouse models. Molecular mechanisms that lead to LOH and the effects of genetic and environmental variables are discussed. The general finding that LOH of a marker gene occurs frequently in somatic cells of the mouse without deleterious effects on cell viability, suggests that also tumour suppressor genes are lost in similar frequencies. LOH of tumour suppressor genes may thus be an initiating event in cancer development.

Animals↗

PubMed2003

Childhood and adolescent psychologic development.

Child and adolescent psychologic development is a complex process that is governed by the interactions of multiple biologic, genetic, sociocultural, and environmental variables. Viewed from an ecological context, the individual influences, and is influenced by, a multilayered set of systems, including the family, school, neighborhood, and peer group, as well as the more indirect effects of the workplace, health care and social services systems, and the larger cultural belief and value systems of the society in which the individual lives. This article reviews the major developmental themes and transitions through which children and adolescents must move on the path to adulthood. Primary developmental tasks are reviewed within each age period from birth to adulthood, along with a discussion of several risk factors that present challenges to normal development at the individual, family, community, and societal levels. The important roles of pediatricians and other health care professionals in helping children and families negotiate these developmental challenges is also reviewed.

Adolescent↗

PubMed1999

Environmental lighting has a selective influence on ethanol intake in rats.

The effect of lighting condition on levels of absolute ethanol intake were systematically examined in the present study. Wistar rats were exposed to one of three lighting conditions: constant light, constant dark, and a standard 12/12 light/dark cycle. The animals were acclimatized to lighting conditions for 2 weeks prior to ethanol (EtOH) acquisition with water and food available ad lib. EtOH was then presented in increasing concentrations from 2% (v/v; 95% with tap water) to 10% on alternate days in free choice with water. Immediately following the acquisition phase, a maintenance period was initiated that began with everyday presentations of 10% EtOH solution in free choice with water. After 10 days, lighting conditions for the constant light and dark groups were switched to normal lighting (12/12 light/ dark). EtOH and water intake were recorded for an additional 10 days. Rats exposed to constant light during EtOH acquisition and maintenance consumed less EtOH during the maintenance period than rats exposed to normal lighting conditions. When lighting conditions were switched to a normal cycle, water consumption increased significantly but EtOH intake did not change. Rats living in constant dark during EtOH acquisition and maintenance consumed less EtOH during the acquisition period when compared with rats living in normal lighting conditions. Unlike animals trained under constant lighting, switching to normal lighting conditions had no effect on EtOH or water intake. There were no differences in water consumption levels among the groups during acquisition and maintenance, suggesting a specificity of the effects of lighting condition on EtOH intake. The present study, therefore, has attempted to show that an environmental variable such as lighting may exert a selective influence on EtOH self-selection in rats.

Alcohol Drinking↗

PubMed2003

The age-structured lottery model.

The lottery model of competition between species in a variable environmental has been influential in understanding how coexistence may result from interactions between fluctuating environmental and competitive factors. Of most importance, it has led to the concept of the storage effect as a mechanism of species coexistence. Interactions between environment and competition in the lottery model stem from the life-history assumption that environmental variation and competition affect recruitment to the adult population, but not adult survival. The strong role of life-history attributes in this coexistence mechanism implies that its robustness should be checked for a variety of life-history scenarios. Here, age structure is added to the adult population, and the results are compared with the original lottery model. This investigation uses recently developed shape characteristics for mortality and fecundity schedules to quantify the effects of age structure on the long-term low-density growth rate of a species in competition with its competitor when applying the standard invasibility coexistence criterion. Coexistence conditions are found to be affected to a small degree by the presence of age structure in the adult population: Type III mortality broadens coexistence conditions, and type I mortality makes them narrower. The rates of recovery from low density for coexisting species, and the rates of competitive exclusion in other cases, are modified to a greater degree by age structure. The absolute rates of recovery or decline of a species from low density are increased by type I mortality or early peak reproduction, but reduced by type III mortality or late peak reproduction. Analytical approximations show how the most important effects can be considered as simple modifications of the long-term low-density growth rates for the original lottery model.

Age Factors↗

PubMed2003

Bulking in activated sludge plants treating paper mill wastewaters.

As part of a larger project to examine the causes of bulking in activated sludge plants treating wastewaters from paper mills, two laboratory-scale activated sludge plants were run in parallel. This was to evaluate the impact of variable environmental and operational parameters on the sludge ecology, and in particular, on the filamentous bacteria in the sludge. A survey of paper mills in the UK showed that there was a significant difference between the activated sludge plants at the paper mills using virgin fibre and those using recycled fibre. An examination of samples from activated sludge plants at the paper mills showed that there did not appear to be any significant correlation between filament abundance and the settlement characteristics as measured by stirred specific volume index (SSVI). The surface charge carried by the sludge particles was also measured and it was found that this parameter was better related to the SSVI. Similar results were found for samples from the laboratory plants. Seven different sets of operational conditions were applied to the laboratory-scale plants. These were aimed at simulating the conditions noted for the full-scale plants during the mill survey. The effects of low dissolved oxygen and low organic loading rates were examined. The effect of inorganic sulphur compounds and volatile fatty acids was studied. A change in raw material from virgin fibre to recycled fibre (corrugated paper) caused an immediate and continuous deterioration in settlement. Divalent cations, calcium and magnesium, were found to be successful in controlling settlement in the final clarifier.

Environmental Monitoring↗

PubMed2000

Some local environmental effects on mercury emission and absorption at a soil surface.

The purpose of this study was to quantify effects of some local environmental variables on the soil surface exchanges of total gaseous mercury (TGM), under controlled conditions. A dynamic flux chamber with a Tekran mercury analyzer was used to quantify TGM emissions from, and absorption by, a clean, fine sandy loam soil with very low mercury content inside of a building and in a low TGM environment, outside. Simultaneous measurements of mercury flux, air and soil temperatures, ozone concentration, humidity, soil moisture and solar radiation were made. Controlled applications of water were made to change soil H2O content and measure the response of mercury flux. Air-soil exchanges were highly dependent on soil temperature (r2 = 0.78) and the mercury concentration gradient between the TGM in the soil pores and the ambient TGM above the soil surface (r2 = 0.98 for absorption and r2 = 0.408 for emissions). Correlations with air temperature and ozone levels are explained by the relationships of these variables with soil temperature. No detectable correlation was found with solar radiation or humidity. Wet soil maintained higher rates of soil TGM emission and decreased soil absorption. Emissions increased with increasing soil H2O, peaked at approximately field capacity, and then decreased slightly until saturation.

Air Pollutants↗