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Lennart Persson

Publications and source records attributed to Lennart Persson.

At least 19 recordsLinked to original sources
PubMed2006

Continuous monitoring of cerebral metabolism in traumatic brain injury: a focus on cerebral microdialysis.

PURPOSE OF REVIEW: This review highlights recent advances in cerebral microdialysis as a tool for neurochemical monitoring of patients with traumatic brain injury. RECENT FINDINGS: Progress in microdialysis research has come from validation studies of microdialysis biomarkers and clinical outcome in large cohorts of traumatic brain injury patients and by combining microdialysis with other methods, such as positron emission tomography, magnetic resonance spectroscopy, brain tissue oximetry and electrophysiology. The combination of rapid-sampling microdialysis and electrocorticography has revealed complex, transient fluctuations of microdialysis glucose and lactate and depolarization-like events that may affect the secondary injury process. The use of microdialysis to monitor global cerebral metabolic events (related to intracranial hypertension or reduced cerebral perfusion pressure for example) as opposed to focal events in peri-lesional brain tissue need to be clearly distinguished and the microdialysis catheter location verified by neuroimaging to ensure proper data interpretation. Differences in microdialysis biomarker levels between grey and white matter following traumatic brain injury need clarification. SUMMARY: Microdialysis is established as a neurochemical research tool in neurointensive care, particularly in combination with other monitoring methods, and contributes to a growing knowledge of secondary injury mechanisms in traumatic brain injury. The value of microdialysis as a tool in routine neurointensive care decision-making remains unclear.

Brain Injuries↗
PubMed2005

Bistability and an Allee effect as emergent consequences of stage-specific predation.

The Allee effect, a reduction of individual fitness at low population density that can lead to sudden and unannounced extinctions, has been shown to come about through a number of mechanisms, usually associated with group behavior or mate search. Recent papers show that it may arise through size-selective predation, without explicit assumptions relating individual fitness to population density. It arises from the shift that a predator induces in the population stage distribution of its prey. We study the parameter conditions that lead to such an emergent Allee effect. The emergent Allee effect occurs under fairly broad conditions. We show that stage-specific predation can also induce bistability between alternative states where both prey and predator are present. A perturbation analysis on the equilibria shows that all equilibria are highly robust to changes in predator density. Our work shows that when size-specific interactions are taken into account, bistabilities and catastrophic collapses are possible even in purely exploitative food webs, which has substantial implications for questions related to food web theory and conservation issues.

Animals↗
PubMed2005

Assessment of systemic inflammation markers to differentiate a stable from a deteriorating clinical course in patients with febrile neutropenia.

In this study, we evaluated the predictive values of procalcitonin (PCT), C-reactive protein (CRP), interleukin-6 (IL-6) and serum amyloid A (SAA) for determining the clinical course in febrile neutropenic patients. Daily plasma analyses during the fever course were performed in 101 episodes with fever and chemotherapy-induced neutropenia (neutrophil count <0.5 x 10(9)/L). Procalcitonin (PCT) and IL-6 values were significantly higher in febrile episodes in patients who developed complications. Procalcitonin with a cut-off value of < or =0.4 ng/mL or IL-6 < or =50 pg/mL 3 d after fever onset indicated daily high negative predictive values (NPVs) (91-100%) for episodes with complications. No marker could predict deterioration; however, daily low plasma concentrations of PCT or IL-6 during the first 8 d of fever were found to be a good predictor of no subsequent complications in neutropenic patients and therefore to be a helpful tool for limiting anti-microbial therapy.

Adolescent↗
PubMed2005

Relationship between cerebral blood flow and oxygen metabolism, and extracellular glucose and lactate concentrations during middle cerebral artery occlusion and reperfusion: a microdialysis and positron emission tomography study in nonhuman primates.

OBJECT: Changes in lactate and glucose levels in the brain may be used to monitor a dynamic ischemic process. The authors related extracellular concentrations of glucose and lactate to regional cerebral blood flow (rCBF) and cerebral metabolic rate of oxygen (CMRO2) in a model of ischemia. METHODS: Transient (2 hours) middle cerebral artery occlusion (MCAO) was performed in eight macaque monkeys. Extracellular measurements of glucose and lactate levels using microdialysis (two probes in each brain) and sequential positron emission tomography measurements were performed during MCAO and reperfusion. Glucose and lactate levels were related to rCBF and CMRO2 as well as the pathophysiological categories of severe ischemia and penumbra. In probe regions characterized by severe ischemia, there were significant changes in glucose and lactate levels and the lactate/glucose ratio. In probe regions distinguished by penumbra, only lactate levels increased significantly and, in general, the changes were smaller and transient. This difference between severe ischemic and penumbral regions was significant for all microdialysis parameters. There was a significant correlation between glucose, and CBF and CMRO2. Lactate concentration was correlated with CMRO2. CONCLUSIONS: Extracellular glucose levels might be limited by rCBF, whereas lactate levels were more related to CMRO2. Lactate concentration is a better marker of irreversible ischemia than glucose concentration, although near-zero levels of glucose during MCAO probably signals near-complete cessation of rCBF. In situations with elevated lactate levels, glucose may help to discriminate between partial and severe ischemia.

Animals↗
PubMed2004

Predicting shifts in dynamics of cannibalistic field populations using individual-based models.

The occurrence of qualitative shifts in population dynamical regimes has long been the focus of population biologists. Nonlinear ecological models predict that these shifts in dynamical regimes may occur as a result of parameter shifts, but unambiguous empirical evidence is largely restricted to laboratory populations. We used an individual-based modelling approach to predict dynamical shifts in field fish populations where the capacity to cannibalize differed between species. Model-generated individual growth trajectories that reflect different population dynamics were confronted with empirically observed growth trajectories, showing that our ordering and quantitative estimates of the different cannibalistic species in terms of life-history characteristics led to correct qualitative predictions of their dynamics.

Animals↗
PubMed2004

Population dynamic theory of size-dependent cannibalism.

Cannibalism is characterized by four aspects: killing victims, gaining energy from victims, size-dependent interactions and intraspecific competition. In this review of mathematical models of cannibalistic populations, we relate the predicted population dynamic consequences of cannibalism to its four defining aspects. We distinguish five classes of effects of cannibalism: (i) regulation of population size; (ii) destabilization resulting in population cycles or chaos; (iii) stabilization by damping population cycles caused by other interactions; (iv) bistability such that, depending on the initial conditions, the population converges to one of two possible stable states; and (v) modification of the population size structure. The same effects of cannibalism may be caused by different combinations of aspects of cannibalism. By contrast, the same combination of aspects may lead to different effects. For particular cannibalistic species, the consequences of cannibalism will depend on the presence and details of the four defining aspects. Empirical evidence for the emerged theory of cannibalism is discussed briefly. The implications of the described dynamic effects of cannibalism are discussed in the context of community structure, making a comparison with the community effects of intraguild predation.

Animals↗
PubMed2004

Use of inflammatory markers for early detection of bacteraemia in patients with febrile neutropenia.

The aim of the study was to evaluate the ability of procalcitonin, C-reactive protein, serum amyloid A, interleukin-6 and interleukin-8 to predict bacteraemia during the 2 first d of fever in neutropenic patients. A total of 94 febrile neutropenic episodes in 60 patients were studied. Plasma samples were analysed at 10-h intervals from the onset of fever. Clinical events were categorized into 4 groups: 1) bacteraemia caused by other agents than coagulase-negative staphylococci (non-CNS bacteraemia) (n = 21), 2) coagulase-negative staphylococci bacteraemia (n = 15), 3) microbiologically or clinically documented infection without bacteraemia (n = 26) and 4) fever of unknown origin (n = 32). In non-CNS bacteraemia all markers, except for serum amyloid A, showed significantly higher levels compared to patients with fever of unknown origin (p < 0.05). For non-CNS bacteraemia the highest negative predictive value was found for procalcitonin (94%), followed by interleukin-6 (89%), C-reactive protein (88%) and interleukin-8 (87%). Procalcitonin, with a cut-off level of 1.4 ng/ml during 10-20 h after fever onset, showed the highest positive predictive value (67%) for a non-CNS bacteraemia. In conclusion, the value of the analysed markers to predict a non-CNS bacteraemia in neutropenic patients was limited due to low sensitivity and positive predictive value. However, procalcitonin, interleukin-6, C-reactive protein, and interleukin-8 could give useful information for the clinician in excluding a non-CNS bacteraemia.

Adolescent↗
PubMed2003

Emergent Allee effects in top predators feeding on structured prey populations.

Top predators that forage in a purely exploitative manner on smaller stages of a size-structured prey population have been shown to exhibit an Allee effect. This Allee effect emerges from the changes that predators induce in the prey-population size distribution and represents a feedback of predator density on its own performance, in which the feedback operates through and is modified by the life history of the prey. We demonstrate that these emergent Allee effects will occur only if the prey, in the absence of predators, is regulated by density dependence in development through one of its juvenile stages, as opposed to regulation through adult fecundity. In particular, for an emergent Allee effect to occur, over-compensation is required in the maturation rate out of the regulating juvenile stage, such that a decrease in juvenile density will increase the total maturation rate to larger/older stages. If this condition is satisfied, predators with negative size selection, which forage on small prey, exhibit an emergent Allee effect, as do predators with positive size selection, which forage on large adult prey. By contrast, predators that forage on juveniles in the regulating stage never exhibit emergent Allee effects. We conclude that the basic life-history characteristics of many species make them prone to exhibiting emergent Allee effects, resulting in an increased likelihood that communities possess alternative stable states or exhibit catastrophic shifts in structure and dynamics.

Age Factors↗
PubMed2003

Gigantic cannibals driving a whole-lake trophic cascade.

Trophic cascades have been a central paradigm in explaining the structure of ecological communities but have been demonstrated mainly through comparative studies or experimental manipulations. In contrast, evidence for shifts in trophic cascades caused by intrinsically driven population dynamics is meager. By using empirical data of a cannibalistic fish population covering a 10-year period and a size-structured population model, we show the occurrence of a dynamic trophic cascade in a lake ecosystem, in which the community over time alternates between two different configurations. The intrinsically driven change in the size structure of the fish population from a dominance of stunted individuals to a dominance of gigantic cannibals among adult individuals is the driving force behind distinct abundance switches observed in zooplankton and phytoplankton. The presence of the phase with gigantic cannibals depends critically on the energy they extract from their victims, allowing strong reproduction for a number of years.

Animals↗
PubMed2003

On the issue of early and aggressive treatment in grade 2 gliomas.

PURPOSE: To study the effects of surgery and timing of radiotherapy on patient survival in grade 2 gliomas. METHODS: One hundred and eighty-nine patients with diffuse astrocytomas, oligoastrocytomas, and oligodendrogliomas, World Health Organization grade 2, treated between 1982 and 2000 were identified. The impact of treatment given and clinical parameters were studied in univariate- and multivariate survival analyses. RESULTS: Median survival for the whole patient sample was 6.4 years and the 5-year survival rate was 60%. Macroscopic total resection was beneficial in the univariate analysis (P=0.03) but not when adjusting for confounders. Early subtotal resection did not prolong survival. Early radiotherapy was associated with a shorter survival time compared to delayed or no irradiation (P=0.004). However, this difference was mainly due to an unequal distribution of prognostic factors and was not significant in the multivariate analysis. The most important predictors for long survival time were young age ( P<0.001), oligodendroglioma histology ( P<0.001), and small tumour size ( P=0.02). CONCLUSIONS: Early conventional treatment with surgery and radiotherapy had no positive effect on patient survival. This opens up the possibility of trying and evaluating other first-line treatment regimens in this disease.

Adult↗
PubMed2003

Competition in size-structured populations: mechanisms inducing cohort formation and population cycles.

In this paper we investigate the consequences of size-dependent competition among the individuals of a consumer population by analyzing the dynamic properties of a physiologically structured population model. Only 2 size-classes of individuals are distinguished: juveniles and adults. Juveniles and adults both feed on one and the same resource and hence interact by means of exploitative competition. Juvenile individuals allocate all assimilated energy into development and mature on reaching a fixed developmental threshold. The combination of this fixed threshold and the resource-dependent developmental rate, implies that the juvenile delay between birth and the onset of reproduction may vary in time. Adult individuals allocate all assimilated energy to reproduction. Mortality of both juveniles and adults is assumed to be inversely proportional to the amount of energy assimilated. In this setting we study how the dynamics of the population are influenced by the relative foraging capabilities of juveniles and adults. In line with results that we previously obtained in size-structured consumer-resource models with pulsed reproduction, population cycles primarily occur when either juveniles or adults have a distinct competitive advantage. When adults have a larger per capita feeding rate and are hence competitively superior to juveniles, population oscillations occur that are primarily induced by the fact that the duration of the juvenile period changes with changing food conditions. These cycles do not occur when the juvenile delay is a fixed parameter. When juveniles are competitively superior, two different types of population fluctuations can occur: (1) rapid, low-amplitude fluctuations having a period of half the juvenile delay and (2) slow, large-amplitude fluctuations characterized by a period, which is roughly equal to the juvenile delay. The analysis of simplified versions of the structured model indicates that these two types of oscillations also occur if mortality and/or development is independent of food density, i.e. in a situation with a constant juvenile developmental delay and a constant, food-independent background mortality. Thus, the oscillations that occur when juveniles are more competitive are induced by the juvenile delay per se. When juveniles exert a larger foraging pressure on the shared resource, maturation implies an increase not only in adult density, but also in food density and consequently fecundity. Our analysis suggests that this correlation in time between adult density and fecundity is crucial for the occurrence of population cycles when juveniles are competitively superior.

Animals↗
PubMed2003

Cerebral blood flow and metabolism after cardiopulmonary resuscitation. A pathophysiologic and prognostic positron emission tomography pilot study.

BACKGROUND: Prolonged coma is not an uncommon clinical problem following resuscitation from cardiac arrest. Early and precise prediction of outcome is highly desirable for ethical and economical reasons. The aims of this study were to use positron emission tomography (PET) to investigate the regional dynamic changes of cerebral blood flow and metabolism during the early period after cardiopulmonary resuscitation (CPR) in unconscious patients and to evaluate if PET may be a potential prognostic evaluator. METHODS AND RESULTS: PET and Glasgow Coma Scale examinations were sequentially performed on days 1, 3 and 7 in seven patients remaining comatose post CPR. Each PET included regional determinations of cerebral blood flow (rCBF), oxygen metabolism (rCMRO(2)), oxygen extraction ratio (rOER), and cerebral blood volume (rCBV). One patient was excluded due to complex trauma problems. Three patients remained unconscious until death and three woke up. All patients initially exhibited low CMRO(2) and CBF. Increased OER was only found exceptionally and when present was predominantly in focal areas. The comatose patients showed progressive depression of CMRO(2) and after 1 week had lower CMRO(2) than those patients who woke up. This difference was most pronounced in the putamen and occipital cortex. Two of the seven patients developed large focal infarcts. CONCLUSIONS: An initially low CMRO(2) was common to all patients. Early development of subclinical focal ischemic lesions was also common. The progressive depression of CMRO(2) over the first week in those patients remaining unconscious may be an indication of prolonged but not necessarily permanent coma. Further studies are required to identify pathophysiological features that can predict the long-term clinical outcome in patients who remain unconscious after 1 week.

Aged↗
PubMed2003

Brain trauma.

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Brain Injuries↗
PubMed2002

Size-dependent life-history traits promote catastrophic collapses of top predators.

Catastrophic population collapses such as observed in many exploited fish populations have been argued to result from depensatory growth mechanisms (i.e., reduced reproductive success at low population densities, also known as Allee effect). Empirical support for depensation from population-level data is, however, hard to obtain and inconclusive. Using a size-structured, individual-based model we show that catastrophic population collapses may nonetheless be an intrinsic property of many communities, because of two general aspects of individual life history: size- and food-dependent individual growth and individual mortality decreasing with body size. Positive density dependence, characteristic for depensatory growth mechanisms and catastrophic behavior, results as a direct and robust consequence of the interplay between these individual life-history traits, which are commonly found in many species.

Animals↗