Simultaneous Bedside Assessment of Global Cerebral Blood Flow and Effective Cerebral Perfusion Pressure in Patients with Intracranial Hypertension

Background: We examined a bedside technique transcerebral double-indicator dilution (TCID) for global cerebral blood flow (CBF) as well as the concept of effective cerebral perfusion pressure (CPPeff) during different treatment options for intracranial hypertension, and compared global CBF and CPPeff with simultaneously obtained conventional parameters. Methods: Twenty-six patients developing intracranial hypertension in the course of traumatic brain injury or subarachnoid hemorrhage were prospectively analyzed using a combined assessment during elevated ventilation (n=15) or osmotherapy (hypertonic saline or mannitol). For calculation of global CBF, injections of ice-cold indocyanine green boluses were performed and temperature and dye concentration changes were monitored in the thoracic aorta and the jugular bulb. CBF was then calculated according to the mean transit time principle. Estimation of CCP, the arterial pressure at which cerebral blood flow becomes zero, was performed by synchronized registration of corresponding values of blood flow velocity in the middle cerebral artery and arterial pressure and extrapolation to zero-flow velocity. CPPeff was calculated as mean arterial pressure minus critical closing pressure (CPPeff=MAPc−CCP). Results: Elevated ventilation causes a decrease in both ICP (P<0.001) and CBF (P<0.001). While CPPconv increased (P<0.001), CPPeff decreased during this observation (P=0.002). Administration of osmotherapeutic agents resulted in a decrease of ICP (P<0.001) and a temporary increase of CBF (P=0.052). CPPconv and CPPeff showed no striking difference under osmotherapy. Conclusion: TCID allows repeated measurements of global CBF at the bedside. Elevated ventilation lowered and osmotherapy temporarily raised global CBF. In situations of increased vasotonus, CPPeff is a better indicator of blood flow changes than conventional CP

Do we miss the hot spots? ? The use of very high resolution aerial photographs to quantify carbon fluxes in peatlands

International audienceAccurate determination of carbon balances in heterogeneous ecosystems often requires the extrapolation of point based measurements. The ground resolution (pixel size) of the extrapolation base, e.g. a land-cover map, might thus influence the calculated carbon balance, in particular if biogeochemical hot spots are small in size. In this paper, we test the effects of varying ground resolution on the calculated carbon balance of a boreal peatland consisting of hummocks (dry), lawns (intermediate) and flarks (wet surfaces). The generalizations in lower resolution imagery led to biased area estimates for individual micro-site types. While areas of lawns and hummocks were stable below a threshold resolution of ~60 cm, the maximum of the flark area was located at resolutions below 25 cm and was then decreasing with coarsening resolution. Using a resolution of 100 cm instead of 6 cm led to an overestimation of total CO2 uptake of the studied peatland area (approximately 14 600 m2) of ~6% and an underestimation of total CH4 emission of ~11%. To accurately determine the surface area of scattered and small-sized micro-site types in heterogeneous ecosystems (e.g. flarks in peatlands), a minimum ground resolution appears necessary. In our case this leads to a recommended resolution of 25 cm, which can be derived by conventional airborne imagery. The usage of high resolution imagery from commercial satellites, e.g. Quickbird, however, is likely to underestimate the surface area of biogeochemical hot spots. It is important to note that the observed resolution effect on the carbon balance estimates can be much stronger for other ecosystems than for the investigated peatland where the relative hot spot area of the flarks is very small and their hot spot characteristics with respect to CH4 and CO2 fluxes is rather modest

Reflexões sobre a prática docente na perspectiva etnomatemática

Este artigo tem como objetivo relatar a experiência vivida pelos autores no desenvolvimento de minicursos propostos ao longo do ano de 2010. Tais atividades tiveram por objetivo discutir a prática docente interagindo com os saberes discentes e a cultura cotidiana, assim como os princípios esperados numa formação dentro da perspectiva etnomatemática. O artigo foi construído a partir da análise das respos-tas de um questionário de avaliação proposto aos participantes ao final das atividades

Identification of linear relationships from noisy data using errors-in-variables models-relevance for reconstruction of past climate from tree-ring and other proxy information

Reliable paleoclimate reconstructions are needed to assess if the recent climatic changes are unusual compared to pre-industrial climate variability. Here, we focus on one important problem in climate reconstructions: Transfer functions relating proxies (predictors) and target climatic quantities (predictands) can be seriously biased when predictand and predictor noise is not adequately accounted for, resulting in biased amplitudes of reconstructed climatic time series. We argue for errors-in-variables models (EVM) for unbiased identification of linear structural relationships between noisy proxies and target climatic quantities by (1) introducing underlying statistical concepts and (2) demonstrating the potential biases of using the EVM approach, the most commonly used direct ordinary least squares (OLS) regression, inverse OLS regression, or the reduced major axis method ('variance matching') with a simulation example of artificial noise-disturbed sinusoidal time series. We then develop an alternative strategy for paleoclimate reconstruction from tree-ring and other proxy data, explicitly accounting for the identified problem

Vertical distributions of ozone in the lower stratosphere over Antarctica and their relations to the spring depletion

Abstract - Three year observations of vertical ozone distributions (1985 - 1987) are analyzed, which have been gained by means of electrochemical ozone sondes (OSE-3) at GEORG FORSTER station (71°S; 12°E). This material and additional data of other stations are used to discuss the primary chemical origin of the spring time ozone depletion in connection with dynamically conditioned variations of ozone distribution in the southern polar stratosphere. A mean pattern featured by three typical time periods of the ozone depletion using the height-time variations of pronounced maxima of the vertical ozone distribution is drawn to localize the chemical active regionDuring spring in 1987 the ozone variations are discussed in more detail to separate different dynamical impacts like an irregular outflow of ozone into the troposphere and the control of vertical ozone distribution by dynamics of the southern polar stratospheric vortex itself. The special dynamical preconditions rendered it possible to use the height variations of stratospheric ozone as an indicator for the verticl diabatic circulation inside the polar stratospheric vortex

Dipole source localization and fMRI of simultaneously recorded data applied to somatosensory categorization

In this study, the feasibility of dipole source localization (DSL) and coregistration with functional magnetic resonance imaging (fMRI) activation patterns on the basis of simultaneously acquired data is demonstrated. Brain activity was mapped during the performance of a somatosensory single reaction and a choice reaction task at high spatiotemporal resolution in six healthy subjects. The choice reaction task required a categorization of two different stimulus intensities, whereas for the single reaction task merely the perception of a tactile stimulus had to be confirmed by the subjects. An offline artifact correction algorithm was applied to 32-channel EEG data that were acquired between subsequent MRI scans. Using a multiple dipole approach, five distinct dipole sources were identified within areas of the somatosensory system. Coregistration of fMRI and DSL showed consistent spatial activation patterns with a mean distance of 9.2 ± 6.8 mm between dipole sources and fMRI activation maxima. However, since the number of fMRI activation sites exceeded the number of cerebral dipole sources, it was not possible to assign a dipole source to each fMRI activation site. Dipole moment time courses were consistent with previously reported results of similar experiments. A comparison of brain activation patterns during the two tasks with both fMRI and DSL indicated an involvement of the contralateral secondary somatosensory cortex in somatosensory categorization

Valence characterisation of the subsurface region in SmB6\mathrm{SmB_{6}}

Samarium hexaboride (SmB6), which lies in the mixed valence regime in the Anderson model, has been predicted to possess topologically protected surface states. The intensive investigations on SmB6 have brought up the long-standing questions about the discrepancy between the surface and bulk electronic properties in rare earth compounds in general. Here, we investigate and eventually clarify this discrepancy in the particular case of SmB 6by the photoemission core-level spectra. We focus on the change in both Sm and B states depending on time, temperature, probing depth and surface termination on the cleaved (1 0 0) surface. Our spectra show that the unusual time-dependent change in the Sm valence occurs within aperiod of hours, which is not related to the adsorption of residual gases. Moreover, we observe a reduction of the surface feature in the B and Sm states on the same timescale accompanied by the formation of a subsurface region. Thus, it indicates the relatively slow charge redistribution between the surface and subsurface regions. Our findings demonstrate that the f states is strongly involved in the surface relaxation