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PubMed1997

Parasitism-induced Effects on Host Growth and Metabolic Efficiency in Tobacco Hornworm Larvae Parasitized by Cotesia congregata.

Parasitism by the braconid wasp Cotesia congregata affects the growth of Manduca sexta larvae in a parasitoid 'dose-dependent' fashion. Following parasitization of fourth-instar larvae, more heavily parasitized larvae grew larger compared to those containing fewer parasitoids due to an increase in host dry weight. The differences in host mass appeared to arise after oviposition. A 'dose-dependent' enhancement of host dry weight would appear nutritionally beneficial for the parasitoids developing in more 'crowded' hosts. The efficiencies of conversion of ingested and digested food to body mass and the approximate digestibility of the diet ingested by the host caterpillar did not vary significantly with clutch size although parasitoids took slightly longer to develop in the more heavily parasitized hosts. Larval parasitoids developing in the presence of many competitors weighed up to 50% less than those developing in hosts with fewer endoparasitoids, although the weight of adult female parasitoids did not vary significantly with wasp clutch size. The maximum number of emerging wasps was 200 parasitoids, possibly representing the host's 'carrying capacity' for larvae parasitized in the fourth-instar. The ratio of emerging to non-emerging parasitoids decreased as parasitoid clutch size increased, with few or none emerging from very heavily parasitized hosts containing more than 400 parasitoids. Copyright 1997 Elsevier Science Ltd. All right reserved

Journal Article↗
PubMed1984

Decreased response of plasma immunoreactive erythropoietin to "available oxygen" in anemia of prematurity.

Erythropoietin, hemoglobin, hematocrit, oxygen affinity (P50), and reticulocyte counts were measured weekly starting at 1 week of age in 10 very-low-birth-weight infants and on a single occasion in 15 healthy men. In the adults, "available oxygen" (derived from oxygen carrying capacity and P50) averaged 13.1 ml/dl blood and the mean erythropoietin level was 15.2 mU/ml. Erythropoietin levels in the infants were inversely related to concentration of hemoglobin, P50, and available oxygen. However, despite the much lower mean "available oxygen" of 9.3 ml/dl in the infants compared with that in adults (P less than 0.001), the mean erythropoietin value of 8.2 mU/ml in the infants was less than in adults (P less than 0.001). Furthermore, the erythropoietin response to decreased "available oxygen" was lowest in the least mature infants. VLBW infants often develop clinical evidence of hypoxia during the anemia of prematurity. The relatively low erythropoietin levels in relation to "available oxygen" are compatible with a decreased erythropoietin response to hypoxia compared with that in adults. Such a difference in response could be a contributing factor to the anemia of prematurity.

Adult↗
PubMed1999

Anemic hypoxia in moderate intracerebral hemorrhage: the alterations of cerebral hemodynamics and brain metabolism.

To determine the influence of anemic hypoxia on cerebral hemodynamics and brain metabolism during pathological conditions of the brain, moderate-sized intracerebral hemorrhage (ICH) was created in canines with and without preoperatively inducing chronic anemia. The changes in cerebral perfusion pressure (CPP) and cerebral blood flow velocities (CBFv) were evaluated as well as the determinations for cerebral extraction fraction of oxygen (CEO2), arteriovenous oxygen content difference (AVDO2) and lactate (Lac) concentrations through the arterial and superior sagittal sinus (SSS) samples. Before ICH production, anemic animals (n = 8) showed a significant reduction in cerebral AVDO2 and arteriovenous Lac difference (AVDLac) but had higher CBFv as well as CEO2 than did nonanemic animals (n = 8). The CBFv began to decrease within 30 min after ICH in anemic but not in nonanemic animals, and the difference between the two groups was found to be significant at 2 h (P<0.05). Following ICH, anemic group also showed coupling reductions in CEO2 and AVDO2, indicating a decreased cerebral metabolic rate for oxygen (CMRO2) relative to the baseline data, compared with a constant CMRO2 in nonanemic group in which the CEO2, AVDO2, and CBFv remained relatively normal. Moreover, compared to the baseline data, a significant increase of the AVDLac was found in anemic but not in nonanemic group, although the former had lower Lac concentrations of the SSS than did the latter group throughout the whole observation period. We conclude that, in cases with chronically reduced Hct, cerebral hemodynamics and oxygenation remain in favorable conditions, thus decreasing Lac production of the brain. The findings suggest a lowered metabolic demand of the brain tissue due to reduced cerebral O2-carrying capacity. During the early phase of moderate ICH, the regulation capacity in cerebral hemodynamics and brain oxygenation tend to deteriorate in profound anemic hypoxia, which consequently leads to enhancing at least modest anaerobic glycolysis.

Anemia↗
PubMed2003

Baseline criteria and the evolution of hosts and parasites: D0, R0 and competition for resources between strains.

Our understanding of the evolution of diseases has been greatly aided by the use of baseline criteria. Here we examine the theoretical and biological relationships of the well known baseline criteria for the evolution of disease (R0) and the recently introduced corresponding criterion for the evolution of resistance in hosts (D0). We show that there is a formal theoretical equivalence between the two criteria and discuss the characteristics of seperability that determine whether the criteria define the course of evolution. These theoretical determinants correspond biologically to whether strains compete for resources or not. We discuss the biological application of the criteria and argue that D0 may be less widely applicable than R0, but does determine the evolution of resistance in populations with fixed carrying capacities.

Animals↗
PubMed1997

Prey dominance in discrete predator-prey systems with a prey refuge.

The effects of a prey refuge in a multiprey discrete system with predation is studied. We demonstrate the stable coexistence of species that would otherwise exclude each other without a prey refuge. With a prey refuge, we show that an endangered prey not only recovers from the brink of extinction, but also dominates the system. We invent notions of dominance that guarantee the extinction of all the dominated prey in the system. With the extermination of most of its prey, the predator either coexists with the dominant prey or is driven to extinction. By using a precise mathematical definition, we obtain that a prey with a sufficiently high carrying capacity persists in a predator-prey system with a prey refuge.

Animals↗
PubMed1997

Optimal harvesting from a population in a stochastic crowded environment.

We study the (Ito) stochastic differential equation [equation: see text] as a model for population growth in a stochastic environment with finite carrying capacity K > 0. Here r and alpha are constants and Bt denotes Brownian motion. If r > or = 0, we show that this equation has a unique strong global solution for all x > 0 and we study some of its properties. Then we consider the following problem: What harvesting strategy maximizes the expected total discounted amount harvested (integrated over all future times)? We formulate this as a stochastic control problem. Then we show that there exists a constant optimal "harvest trigger value" x* epsilon (0, K) such that the optimal strategy is to do nothing if Xt < x* and to harvest Xt-x* if Xt > x*. This leads to an optimal population process Xt being reflected downward at x*. We find x* explicitly.

Environment↗
PubMed1998

Optimal harvesting policy for single population with periodic coefficients.

In this paper, we examine the exploitation of single population modeled by time-dependent Logistic equation with periodic coefficients. First, it is shown that the time-dependent periodic Logistic equation has a unique positive periodic solution, which is globally asymptotically stable for positive solutions, and we obtain its explicit representation. Further, we choose the maximum annual-sustainable yield as the management objective, and investigate the optimal harvesting policies for constant harvest and periodic harvest. The optimal harvest effort that maximizes the annual-sustainable yield, the corresponding optimal population level, the corresponding harvesting time-spectrum, and the maximum annual-sustainable yield are determined, and their explicit expressions are obtained in terms of the intrinsic growth rate and the carrying capacity of the considered population. Our interesting and brief results generalize the classical results of Clark for a population described by the autonomous logistic equation in renewable resources management.

Conservation of Natural Resources↗
PubMed1999

Variable effort fishing models in random environments.

We study the growth of populations in a random environment subjected to variable effort fishing policies. The models used are stochastic differential equations and the environmental fluctuations may either affect an intrinsic growth parameter or be of the additive noise type. Density-dependent natural growth and fishing policies are of very general form so that our results will be model independent. We obtain conditions on the fishing policies for non-extinction and for non-fixation at the carrying capacity that are very similar to the conditions obtained for the corresponding deterministic model. We also obtain conditions for the existence of stationary distributions (as well as expressions for such distributions) very similar to conditions for the existence of an equilibrium in the corresponding deterministic model. The results obtained provide minimal requirements for the choice of a wise density-dependent fishing policy.

Animals↗
PubMed1992

Use of blood transfusion in management of anemia.

Transfusion of red blood cells is useful in restoring oxygen-carrying capacity in patients with symptomatic anemia. In general, physicians should avoid transfusing blood based on hemoglobin concentration alone. Instead, they should focus on the impact of anemia on the patient's symptoms and level of activity. The concern for HIV infection and viral hepatitis has only served to highlight the potential risks associated with homologous transfusion therapy. These concerns should be carefully considered, along with possible alternatives, before a decision is made to transfuse. It is important to define the cause of anemia and to institute appropriate corrective therapy. The availability of recombinant human erythropoietin offers an option in selected patients to reduce or eliminate the need for red blood cell transfusion.

Anemia↗
PubMed2001

Techniques for blood administration in sickle cell patients.

Transfusion therapy provides many benefits to Individuals with sickle cell disease but may lead to cardiovascular complications, alloimmunization, exposure to infection, and iron overload. Simple transfusion is used to increase oxygen-carrying capacity. Chronic simple transfusion is useful in preventing a number of complications in sickle cell disease. Acute erthrocyte exchange transfusion can reduce the percentage of cells containing sickle hemoglobin while decreasing volume overload and minimizing hyperviscosity. Chronic erythrocyte exchange transfusion reduces iron loading but Increases donor exposure. Directed odnation may reduce alloimmunization and exposure to infection.

Anemia, Sickle Cell↗
PubMed1992

Fluid and electrolyte management in the pediatric surgical patient.

The following is a quick guide to the perioperative fluid program discussed 1. Always assess the state of fluid repletion in any patient presenting for surgical management (Note: This does not necessarily mean operative management). 2. If the patient is hypovolemic or if there is the possibility of hypovolemia and you are uncertain, restore volumes equal to 25% of the patient's blood volume with a fluid push made up of an osmotically active electrolyte solution modified for the additional requirements of red cell carrying capacity or clotting factors. If this results in a urine output and correction of hypoperfusion or hypotension, maintain an increased fluid administration program until a stable urine output and good perfusion are achieved. If the patient is normovolemic at the time of presentation, particularly if the patient is having an elective operative procedure and does not have an intravenous line in place, calculate the insensible losses that will occur during the time of fluid restriction before surgery and correct at least 50% of these during the operative procedure. 3. Develop the postoperative fluid program as a combination of 24-hour insensible loss replacement (maintenance fluid), restoration of measured losses, and an estimate (guess) as to the volume requirements for third-space fluid shifts. Restore blood losses if appropriate or administer additional volumes of balanced electrolyte solution at a 3-to-1 ratio to replace measured blood loss. 4. Total the insensible loss measurement, the measured losses, and the estimate of third-space requirement and divide this volume by 24 to get an initial hourly fluid administration rate. 5. Select the most osmotically active fluid that you intend to use and administer it first at the calculated rate. Carefully monitor the patient's urine output. 6. Increase or decrease the fluid administration rate to bring the hourly urine output within the guidelines for the appropriate hourly urine output (milliliters) for the particular patient based on size (kilograms). 7. When the urine output falls within the appropriate range, maintain that rate of fluid administration, and recalculate the volumes required because of insensible loss, measured loss, and third-space shifts by subtracting the amount of fluid already administered from the volume that will be required in the remainder of the 24 hours; this will yield the volumes of additional maintenance, measured loss, and third-space fluids that will make up the remainder of the fluids needed for the 24 hours.(ABSTRACT TRUNCATED AT 400 WORDS)

Child, Preschool↗
PubMed2003

Allee effects, extinctions, and chaotic transients in simple population models.

Discrete time single species models with overcompensating density dependence and an Allee effect due to predator satiation and mating limitation are investigated. The models exhibit four behaviors: persistence for all initial population densities, bistability in which a population persists for intermediate initial densities and otherwise goes extinct, extinction for all initial densities, and essential extinction in which "almost every" initial density leads to extinction. For fast-growing populations, these models show populations can persist at high levels of predation even though lower levels of predation lead to essential extinction. Alternatively, increasing the predator's handling time, the population's carrying capacity, or the likelihood of mating success may lead to essential extinction. In each of these cases, the mechanism behind these disappearances are chaotic dynamics driving populations below a critical threshold determined by the Allee effect. These disappearances are proceeded by chaotic transients that are proven to be approximately exponentially distributed in length and highly sensitive to initial population densities.

Alleles↗
PubMed2003

Metapopulation dynamics with quasi-local competition.

Stepping-stone models for the ecological dynamics of metapopulations are often used to address general questions about the effects of spatial structure on the nature and complexity of population fluctuations. Such models describe an ensemble of local and spatially isolated habitat patches that are connected through dispersal. Reproduction and hence the dynamics in a given local population depend on the density of that local population, and a fraction of every local population disperses to neighboring patches. In such models, interesting dynamic phenomena, e.g. the persistence of locally unstable predator-prey interactions, are only observed if the local dynamics in an isolated patch exhibit non-equilibrium behavior. Therefore, the scope of these models is limited. Here we extend these models by making the biologically plausible assumption that reproductive success in a given local habitat not only depends on the density of the local population living in that habitat, but also on the densities of neighboring local populations. This would occur if competition for resources occurs between neighboring populations, e.g. due to foraging in neighboring habitats. With this assumption of quasi-local competition the dynamics of the model change completely. The main difference is that even if the dynamics of the local populations have a stable equilibrium in isolation, the spatially uniform equilibrium in which all local populations are at their carrying capacity becomes unstable if the strength of quasi-local competition reaches a critical level, which can be calculated analytically. In this case the metapopulation reaches a new stable state, which is, however, not spatially uniform anymore and instead results in an irregular spatial pattern of local population abundance. For large metapopulations, a huge number of different, spatially non-uniform equilibrium states coexist as attractors of the metapopulation dynamics, so that the final state of the system depends critically on the initial conditions. The existence of a large number of attractors has important consequences when environmental noise is introduced into the model. Then the metapopulation performs a random walk in the space of all attractors. This leads to large and complicated population fluctuations whose power spectrum obeys a red-shifted power law. Our theory reiterates the potential importance of spatial structure for ecological processes and proposes new mechanisms for the emergence of non-uniform spatial patterns of abundance and for the persistence of complicated temporal population fluctuations.

Competitive Behavior↗
PubMed2003

Genetic stability of attenuated mengovirus vectors with duplicate primary cleavage sequences.

Short poly(C)-tract Mengoviruses have proven vaccine efficacy in many species of animals. A novel vector for the delivery of foreign proteins was created by insertion of a second autoproteolytic primary cleavage cassette linked to a multiple cloning site (MCS) into an attenuated variant of Mengo. Nineteen cDNAs from foreign sequences that ranged from 39 to 1653 bases were cloned into the MCS. The viral reading frame was maintained and translation resulted in dual, autocatalytic excision of the foreign peptides without disruption of any Mengo proteins. All cDNAs except those with the largest insertions produced viable virus. Active proteins such as GFP, CAT, and SIV p27 were expressed within infected cells. Relative to parental Mengo, the growth kinetics and genetic stability of each vector was inversely proportional to the size of the inserted sequence. While segments up to 1000 bases could be carried, inserts greater than 500-600 bases were usually reduced in size during serial passage. The limit on carrying capacity was probably due to difficulties in virion assembly or particle stability. Yet for inserts less than 500-600 bases, the Mengo vectors provided an effective system for the delivery of foreign epitopes into cells and mice.

Animals↗
PubMed2003

Extinction risk to bird populations caused by DDT exposure.

The impact of toxic chemicals on wild animals and plants can be quantified in terms of the enhanced risk of population extinction. To illustrate a method for doing this, we estimated such impact for two bird species: herring gull (Larus argentatus) in Long Island, NY, and sparrowhawk (Accipiter nisus) in eastern England, when they were exposed to DDT (p,p(')-dichlorodiphenyltrichloroethane) and its metabolites (called DDTs). The method we used is based on a formula of the mean time to population extinction derived for a stochastic differential equation (the canonical model). The intrinsic rate of natural population growth was estimated from an exponentially growing population, and the intensity of the environmental fluctuation was estimated from the magnitude of population size fluctuation. The effect of exposure to DDTs in reducing the population growth rate was evaluated based on an age-structured population model, by assuming that age-specific fertility is density-dependent and sensitive to DDTs exposure, but age-specific survivorship is not. The results are expressed in terms of the risk equivalent--the decrease in carrying capacity K that causes the same enhancement of extinction risk as chemical exposure at a given level. The risk equivalent can be used in mitigation banking.

Animals↗
PubMed2002

Population, environment, disease, and survival: past patterns, uncertain futures.

Societies are exploring what sustainable development means for development choices. Increasingly, we recognise that human population health is not just an input to socioeconomic development, but is an essential outcome, and, over time, a marker of sustainability. There has been recent attention to how stocks of social and human capital precondition gains in population health. However, recognition of how environmental change can limit health and survival has been slower. Over many millennia, disease and longevity profiles in populations have reflected changes in environmental conditions and, often, excedances of carrying capacity. Today, population growth and the aggregated pressures of consumption and emissions are beginning to impair various global environmental systems. The research tasks in detecting, attributing, and projecting the resultant health effects are complex. Have recent health gains, in part, depended on depleting natural environmental capital? Population health sciences have a crucial contribution to make to the sustainability project.

Ecology↗
PubMed1995

Systemic haemodynamics and oxygenation during haemodilution in children.

Transfusion of homologous blood should be avoided when possible, and one technique that diminishes perioperative requirement for donor blood is haemodilution. In children its effects on systemic haemodynamics and systemic oxygenation have not been reported. Six children aged 4-12 yr were anaesthetised for major surgery and blood was withdrawn to reduce packed cell volume to 25%. Cardiac index increased from 3.1 (SD 0.5) L min-1 m-2 at baseline to 4.4 (0.5) L min-1 m-2 at the end of surgery, when packed cell volume was 16 (1)%; this change, compensating for the decline in oxygen carrying capacity, was associated with a fall in systemic vascular resistance and a rise in stroke volume. Oxygen extraction from haemoglobin rose from 0.22 (0.05) to 0.33 (0.06). Perioperative blood loss was 40% of circulating blood volume; however, owing to reinfusion of autologous blood (and use of a cell saver in three patients), the haemoglobin one day after operation was only 19% lower than preoperatively (9.9 [1.5] vs 12.5 [2.5] g/dL). In this study, children seemed at least as able as adults to compensate for the effects of haemodilution, which allowed major surgery without transfusion of homologous blood.

Anesthesia↗
PubMed1999

Meta-analyses of the effectiveness of erythropoietin for end-stage renal disease and cancer.

Anemia, a decreased oxygen-carrying capacity of the blood, develops frequently in patients with end-stage renal disease (ESRD) or cancer. Given the wide variation in clinical response to erythropoietin in the treatment of anemia associated with these diseases, 2 meta-analyses of its effectiveness were undertaken. Databases (MEDLINE and International Pharmaceutical Abstracts) were searched to identify relevant articles. Search terms included erythropoietin, anemia, end-stage renal disease, cancer, multiple myeloma, and myelodysplastic syndrome. Searches were limited to human subjects and the English language. Reference lists of identified articles were reviewed for further articles of interest. The primary author (W.A.M.) selected the articles, and 2 researchers, working independently, extracted the necessary data. Articles had to meet the following criteria to be included in the meta-analyses: (1) Articles must have dealt with treatment of subjects with documented anemia. (2) Studies must have been original research with sample size > or =10. (3) Abstracts could be included if the full research manuscript was unavailable. (4) Patients could not be concurrently receiving other growth factors. (5) The quality of the selected articles must have been assessed by 2 independent researchers. A clinical response to erythropoietin was defined as a 0.06 increase in hematocrit or a 20 g/L increase in hemoglobin. Thirty-nine of the 76 identified articles were included in the meta-analyses. The effectiveness of erythropoietin was calculated at 87% for ESRD, 79% for multiple myeloma, 40% for solid tumor cancer, and 13% for myelodysplastic syndrome. Both subgroup and sensitivity analyses were performed.

Anemia↗