Grey Matter Perfusion in Clinically Isolated Syndrome and Relapsing-Remitting Multiple Sclerosis

Die vorliegende Studie vergleicht Merkmale der mittels Kernspin-Tomografie bestimmten zerebralen Perfusion in verschiedenen Regionen der Grauen Substanz von Patienten mit klinisch isoliertem Syndrom und Patienten mit schubförmig-remittierender Multipler Sklerose. Als Marker der klinischen Schwere der Erkrankung wurden das normalisierte Hirnvolumen und der erreichte Wert auf der Expanded Disability Status Scale verwendet. In einem simplen Gruppenvergleich findet sich ein keiner der betrachteten Regionen ein Unterschied im Hinblick auf die lokale Perfusion. Die Ergebnisse einer simultanen Korrelationsanalyse suggerieren jedoch, dass es durchaus Unterschiede in der lokalen Perfusion der Grauen Substanz gibt. Die Ergebnisse dieser Studie legen daher nahe, dass einfache Gruppenvergleiche nur schlecht geeignet sind, um Variationen der regionalen Perfusion zu erfassen. Zusammengefassend legt die vorliegende Studie nahe, dass der den hämodynamischen Veränderungen bei Patienten mit klinisch isoliertem Syndrom und schubförmig-remittierender Multipler Sklerose zu Grunde liegende Mechanismus eher diffus als fokal ist und darüber hinaus einer gewissen (zeitlichen) Entwicklung unterliegt.This study compares magnetic resonance imaging-derived cerebral grey matter perfusion characteristics in patients diagnosed with clinically isolated syndrome and patients diagnosed with relapsing-remitting multiple sclerosis. Normalized brain volume and the Expanded Disability Status Scale were used as markers of disease severity. There is no difference between both subject subgroups with respect to perfusion parameters in any of the analysed grey matter regions in a simple group comparison. However, the results from the simultaneous correlation analysis indicate that there is a difference in local perfusion between the two groups of patients. This study therefore suggests that simply group comparisons are not a suitable tool to analyse regional perfusion metrics. In summary, the results of this study suggest that the underlying mechanism responsible for hemodynamic changes in clinically isolated syndrome and relapsing-remitting multiple sclerosis is diffuse rather than focal and is subject to some sort of (temporal) evolution. 2017-10-1

Production and emissions of oceanic nitrous oxide

This study calculates N2O production rates (N2OPR) based on concentration measurements and Transit Time Distribution (TTD) calculations. New parameterisations of N2OPR based on an apparent oxygen consumption rate (AOUR and temperature or depth, respectively, are developed and applied to calculate N2O production the entire ocean. A global annual subsurface N2O production of ~3±1 Tg N and a global annual organic carbon remineralisation rate of 17.6 Pg are estimated. The N2O flux to the mixed layer (F_grad) and the N2O emissions to the atmosphere via gas exchange (F_gasex) are calculated or the central North Atlantic. The mean F_grad is found to be significantly smaller than the mean F_gasex. A possible reason for this is the seasonality of surface pN2O/F_gasex, as a seasonally-resolved, integrated estimate of F_gasex significantly reduces the difference between the two flux estimates. There is no conclusive evidence for a biological N2O source in the mixed layer

Produktion und Emissionen von ozeanischem Distickstoffmonoxid

This study calculates N2O production rates (N2OPR) based on concentration measurements and Transit Time Distribution (TTD) calculations. New parameterisations of N2OPR based on an apparent oxygen consumption rate (AOUR and temperature or depth, respectively, are developed and applied to calculate N2O production the entire ocean. A global annual subsurface N2O production of ~3±1 Tg N and a global annual organic carbon remineralisation rate of 17.6 Pg are estimated. The N2O flux to the mixed layer (F_grad) and the N2O emissions to the atmosphere via gas exchange (F_gasex) are calculated or the central North Atlantic. The mean F_grad is found to be significantly smaller than the mean F_gasex. A possible reason for this is the seasonality of surface pN2O/F_gasex, as a seasonally-resolved, integrated estimate of F_gasex significantly reduces the difference between the two flux estimates. There is no conclusive evidence for a biological N2O source in the mixed layer.In dieser Studie werden, basierend auf Konzentrationsmessungen und Transit Time Distributions (TTD) N2O Produktionsraten (N2OPR) berechnet. Neue Parameterisierungen für N2OPR abhängig von einer Sauerstoffverbrauchsrate (AOUR) und der Temperatur bzw. der Tiefe werden entwickelt und zur Berechnung der N2O-Produktion im Weltozean verwendet. Dabei wird die globale jährliche N2O-Produktion auf ~3±1 Tg N und die jährliche Remineralisationsrate von organischem Kohlenstoff auf 17.6 Pg geschätzt. Der N2O-Fluss in die Mischungsschicht (F_grad) und der N2O-Fluss in die Atmosphäre (F_gasex) werden für den zentralen Nord-Atlantik berechnet. Der mittlere F_grad ist signifikant kleiner als der mittlere F_gasex. Ein möglicher Grund ist der zyklische Jahresgang von pN2O/F_gasex, da eine integrierte Schätzung die Differenz zwischen den verschiedenen Flüssen deutlich reduziert. Es gibt keine zwingenden Hinweise auf biologische N2O-Produktion in der Mischungsschicht

North Atlantic production of nitrous oxide in the context of changing atmospheric levels

We use transit time distributions calculated from tracer data together with in situ measurements of N(2)O to estimate the concentration of biologically produced N(2)O ([N(2)O](xs)) and N(2)O production rates in the central North Atlantic Ocean. Our approach to estimation of N(2)O production rates integrates the effects of potentially varying production and decomposition mechanisms along the transport path of a water mass. We find that previously used approaches overestimate the oceanic equilibrium N(2)O concentrations by 8-13% and thus underestimate the strength of N(2)O sources in large parts of the water column. Thus the quantitative characteristics of the [N(2)O](xs)/AOU relationship used as an indicator of nitrification are distorted. We developed a new parameterization of N(2)O production during nitrification depending linearly on AOU and exponentially on temperature and depth, which can be applied to calculate N(2)O production due to nitrification in the entire ocean including oxygen minimum zones

Global oceanic production of nitrous oxide

We use transient time distributions calculated from tracer data together with in situ measurements of nitrous oxide (N2O) to estimate the concentration of biologically produced N2O and N2O production rates in the ocean on a global scale. Our approach to estimate the N2O production rates integrates the effects of potentially varying production and decomposition mechanisms along the transport path of a water mass.We estimate that the oceanic N2O production is dominated by nitrification with a contribution of only approximately 7 per cent by denitrification. This indicates that previously used approaches have overestimated the contribution by denitrification. Shelf areas may account for only a negligible fraction of the global production; however, estuarine sources and coastal upwelling of N2O are not taken into account in our study. The largest amount of subsurface N2O is produced in the upper 500 m of the water column. The estimated global annual subsurface N2O production ranges from 3.1+/-0.9 to 3.4+/-0.9 Tg N yr^-1. This is in agreement with estimates of the global N2O emissions to the atmosphere and indicates that a N2O source in the mixed layer is unlikely. The potential future development of the oceanic N2O source in view of the ongoing changes of the ocean environment (deoxygenation, warming, eutrophication and acidification) is discussed

Association of Retinal and Macular Damage with Brain Atrophy in Multiple Sclerosis

Neuroaxonal degeneration in the central nervous system contributes substantially to the long term disability in multiple sclerosis (MS) patients. However, in vivo determination and monitoring of neurodegeneration remain difficult. As the widely used MRI-based approaches, including the brain parenchymal fraction (BPF) have some limitations, complementary in vivo measures for neurodegeneration are necessary. Optical coherence tomography (OCT) is a potent tool for the detection of MS-related retinal neurodegeneration. However, crucial aspects including the association between OCT- and MRI-based atrophy measures or the impact of MS-related parameters on OCT parameters are still unclear. In this large prospective cross-sectional study on 104 relapsing remitting multiple sclerosis (RRMS) patients we evaluated the associations of retinal nerve fiber layer thickness (RNFLT) and total macular volume (TMV) with BPF and addressed the impact of disease-determining parameters on RNFLT, TMV or BPF. BPF, normalized for subject head size, was estimated with SIENAX. Relations were analyzed primarily by Generalized Estimating Equation (GEE) models considering within-patient inter-eye relations. We found that both RNFLT (p = 0.019, GEE) and TMV (p = 0.004, GEE) associate with BPF. RNFLT was furthermore linked to the disease duration (p<0.001, GEE) but neither to disease severity nor patients' age. Contrarily, BPF was rather associated with severity (p<0.001, GEE) than disease duration and was confounded by age (p<0.001, GEE). TMV was not associated with any of these parameters. Thus, we conclude that in RRMS patients with relatively short disease duration and rather mild disability RNFLT and TMV reflect brain atrophy and are thus promising parameters to evaluate neurodegeneration in MS. Furthermore, our data suggest that RNFLT and BPF reflect different aspects of MS. Whereas BPF best reflects disease severity, RNFLT might be the better parameter for monitoring axonal damage longitudinally. Longitudinal studies are necessary for validation of data and to further clarify the relevance of TMV