Oxygen saturation | EPFL Graph Search

Oxygen saturation (symbol SO2) is a relative measure of the concentration of oxygen that is dissolved or carried in a given medium as a proportion of the maximal concentration that can be dissolved in that medium at the given temperature. It can be measured with a dissolved oxygen probe such as an oxygen sensor or an optode in liquid media, usually water. The standard unit of oxygen saturation is percent (%). Oxygen saturation can be measured regionally and noninvasively. Arterial oxygen saturation (SaO2) is commonly measured using pulse oximetry. Tissue saturation at peripheral scale can be measured using NIRS. This technique can be applied on both muscle and brain. In medicine Oxygen saturation (medicine) In medicine, oxygen saturation refers to oxygenation, or when oxygen molecules (O2) enter the tissues of the body. In this case blood is oxygenated in the lungs, where oxygen molecules travel from the air into the blood. Oxygen saturation ((O2) sats) measures the perc

Local in vivo optical measurements of neurometabolic and neurovascular coupling mechanisms in the rodent cortex

Elena Migacheva

This thesis introduces a novel approach for in vivo separation and quantification of spatio-temporal dynamics of optical coefficients (absorption, scattering), oxygen saturation (SO2) and haemoglobin concentrations within rat brain somatosensory cortex under baseline and neuronal stimulation conditions. The quantification of mentioned parameters became possible due to design of a novel optical setup for localized spatio-temporally-resolved (within ∼ 1 mm3 at 10 Hz) reflectance spectroscopy (STRReS) measurements at small source-detector separations. The possibility to automatically take into account the light propagation path lengths in tissue using Monte Carlo modeling, defines the novelty of this approach and its perspectives for brain research. This kind of corrections is currently limited or inaccurate with existing techniques like optical intrinsic signal imaging. In particular, the main aim of this thesis is to explore and better understand the local spatio-temporal characteristics of neurovascular and neurometabolic coupling mechanisms within in vivo rat cerebral cortex at initial and subsequent stages of neuronal stimulation with using STRReS technique. It has been proven theoretically (with Monte Carlo simulations) and experimentally (from in vivo rat brain cortex), that STRReS measurements are suitable from in vivo somatosensory cortex under neuronal stimulation conditions. As a part of this research, we have validated theoretically and experimentally the biological importance of new optical parameter ”gamma” (parameter of the phase function), which is nessesary to take into account for accurate optical coefficients extraction. On the other side, the STRReS technique was not found to be helpful to determine differential factors corrections for improvement of optical intrinsic signal imaging analysis due to differences in experiment’s geometries. Finally, it has been shown that temporal dynamics of reflectance is strongly influenced by light scattering variations within 500-900 nm range. Specifically, the shape of reflectance dynamics at 600 and 610 nm differs significantly from deoxy-haemoglobin concentration dynamics at initial stage of neural activation. For this reason, it is important always to take into account the variations of both components of reflectance signal: absorption and scattering. Additionally, an initial delay of 1 s was found in SO2 and haemoglobin concentrations dynamics. The interpretation of this delay, however, is strongly dependent on the origin of scattering signal. Our results are well correlated with ”metabolic” hypothesis of underlying neurovascular and neurometabolic coupling mechanisms, assuming that the scattering signal has a non-vascular origin at 500-599 nm. Nevertheless, the ”neurogenic” hypothesis is not completely excluded as far as the scattering signal has a vascular origin at 500-599 nm.

EPFL2012

Improved framework to estimate travel time and derived distributions in hydrological control volumes

Mitra Asadollahi

Crossing properties of soil saturation, defined as the duration and excursion of soil saturation below and above certain thresholds, are key variables to ecosystem functioning and evolution by primarily influencing the plant and soil microbes physiological dynamics. Under climate change, the variability in the precipitation patterns is expected to be more ubiquitous and directly translate to a shift in soil saturation levels. This, in turn, will influence crossing properties of soil saturation and thus be expected to leave a mark on ecosystems. However, the lack of a deep understanding of the links between biological processes and the change in soil saturation patterns hinders foretelling the impact of climate variability on ecohydrological systems even at the smallest scale, that is, the level of a single plant.To that end, this thesis presents experimental results from laboratory soil column experiments and extensive computational studies on the interactions between soil saturation and biological activities, that is, plants and microbes. To this aim, the depth-time soil saturation patterns are mapped by means of modeling the transport processes of relevance and experimental tools at a minimal hydrological control volume in search for upscaling methods. In this context, two modeling approaches can be employed. Physically based models that explicitly represent transport processes with high costs of application at larger scales. Age-based models that rely on generic functions with a focus on time past since arrival, that is, the age of event water in the storage. This thesis work combines models (HYDRUS-1D as physically based and tran-SAS as age-based) with soil column experimental data and Bayesian inference methods to explore the links between age characteristics and transport processes. In this thesis, data from four different experimental designs on monthly to yearly timescale under varied environmental conditions are examined in terms of tracer type, precipitation pattern, vegetation, soil type, resolution and type of collected data. Of the modeled data, two sets of results from specific experiments were carried out within the framework of this thesis.This thesis addresses also the role of the balance between dispersive and convective forces, known as Péclet number, in controlling the shape of age functions in drainage. While sole reliance on drainage flow and tracer data (reflective of Péclet number) suffice to capture age dynamics in drainage, un- certainties may arise for predictions on (evapo)transpiration. This thesis deals also with the role of root distributions as controls in determining the age to root uptake and shows plants with similar uniform-equivalent root distribution render very similar age dynamics. It was shown in this thesis that nitrate consumption by microbes can be linked to age characteristics of a conservative tracer and that the relation between microbial respiration and soil saturation may bear more complexity than is currently integrated in most models. Overall, this thesis lays steps to the development of modeling tools with high predictive power for soil saturation by originating upscaling methods and bridging the gaps between physically based and age-based models with a view on the consequences of (possi- bly changing) variable soil saturation on adaptations of microbial communities and their metabolic product.

EPFL2022