<p>This dissertation recruited 24 premature infants born less than 32 weeks gestational age over a one year time period from October 2010 to 2011. The goals were to longitudinally measure cerebral oxygen saturation, evaluate how environmental variables controlled by nursing, positioning and noise, affect cerebral oxygen saturations, and examine the relationship between cerebral oxygen saturation and two currently measured vital signs.</p><p>Using mixed general linear models, findings from this dissertation showed the developmental trajectory of cerebral oxygen saturation values in premature infants' began in the high 70s during the first two days of life and then significantly decreased into the mid-60s over several weeks during hospitalization in a neonatal intensive care unit (NICU). The trajectory of cerebral oxygen saturation during the first week of life in those infants who developed an IVH did not significantly differ from those infants without IVH. At this time, use of cerebral oxygen saturation to identify those infants at risk for IVH during the first week of life cannot be supported, but findings may indicate that cerebral oxygen saturation monitoring could potentially monitor the severity of the impact of IVH later during hospitalization as those infants with an IVH had significantly lower cerebral oxygen saturation values after the third week of life. In this case, cerebral oxygen saturation might help to understand the long-term degree of neurological damage. </p><p>Heart rate and peripheral oxygenation were chosen as the two physiologic variables to compare to cerebral oxygen saturation and average cerebral oxygen saturation was lower with higher heart rate and higher with higher peripheral oxygenation. Peripheral oxygenation that is already routinely measured in premature infants appears to not provide an accurate measure of the changes in cerebral oxygen saturation. Cerebral oxygen saturation monitoring is highly suggested for those infants who are at risk for neurological damage such as infants with hypoxic-ischemic encephalopathy or seizures since peripheral oxygenation does not appear to be an appropriate proxy for cerebral oxygenation.</p><p>Finally, sound and positioning were chosen to represent two frequently encountered components of the neonatal intensive care environment that also influence infant cerebral oxygen saturation. A peak in sound from the ambient sound level was only 5 decibels and found to not significantly affect cerebral oxygen saturation values. A neutral position considered the gold standard-- supine, head midline--was compared to five other positions widely used by NICU nurses. However, results showed positions with a turned head did not significantly change cerebral oxygen saturation from the neutral position. Yet, differences in cerebral oxygen saturation were found between two lateral positions (left lateral and right lateral, head elevated 15°) with an elevated head measuring lower cerebral oxygen saturation levels.</p> / Dissertation

Continuous monitoring of blood perfusion and oxygenation is essential in assessing the health of a transplanted organ. Particularly, monitoring the perfusion and oxygenation of the organ during the two-week period after the transplant procedure is crucial in detecting a sustained loss in perfusion or a reduction in oxygen saturation before these changes render irreversible damage to the organ or patient. Pulse oximetry is a clinically accepted method of monitoring the arterial oxygen saturation of a patient in a non-invasive manner. Pulse oximeters exploit the wavelength-dependent absorption of oxygenated and deoxygenated hemoglobin to measure a patient's arterial oxygen saturation. However, traditional pulse oximeters do not provide perfusion information and produce erroneous oxygen saturation measurements under low perfusion levels. An optical blood perfusion and oxygenation sensor, based on a modified reflectance pulse oximeter, has been developed for in situ monitoring of transplanted organs. To reduce the number of animal experiments, phantoms that mimic the optical and anatomical properties of liver parenchyma have also been developed. In this work, in vitro data was gathered from dye solutions mimicking oxygenated blood that were pumped through single and multi-layer phantoms mimicking liver parenchyma and through a phantom mimicking the portal vein. A portion of the phantom data was compared to data collected from in vivo occlusion studies performed on female swine to assess the ability of the phantoms to mimic the response observed with changes in blood perfusion through liver parenchyma. Both the single layer and multilayer phantoms showed a similar response to changes in perfusion as the in vivo case. With each phantom, the signal increased linearly with increases in perfusion, but the multilayer phantom showed a higher sensitivity (approximately 30% higher) to changes in perfusion than the single layer phantom. This higher sensitivity would provide the ability to measure smaller changes in perfusion and increase the resolution of the sensor. Also, both parenchymal phantoms showed similar trends in the oxygenation studies, with the R value decreasing with increasing oxygenation. While the observations in this research demonstrate the ability to use both phantoms for in vitro experiments, the results show the multilayer phantom is a better option for mimicking perfusion because it displays similar occlusion patterns as the liver parenchyma in vivo, a higher sensitivity to changes in perfusion than the single layer phantom, and it is only slightly more complex in design (contains only two more layers of sinusoids) than the single layer phantom.

There has been extensive research investigating the differences between global and local feature discrimination. The role that global and local feature discrimination has in sustained attention tasks however has been relatively neglected. In the current research, participants were required to perform a sustained attention task requiring them to engage in either global or local shape stimuli discrimination. Reaction times to local feature discrimination revealed a quadratic trend with time-on-task, with performance levels showing a decline before returning to initial levels towards the end of the task. This trend was not found in the global shape discrimination condition. Functional near-infrared spectroscopy (fNIRS) was employed to assess hemispheric cerebral oxygenation during the tasks. It was found in both conditions that there was greater oxygenation in the right hemisphere compared to the left hemisphere. It was also found that right hemisphere oxygenation increased with time-on-task. Left hemisphere oxygenation decreased during the global task, while it increased during the local task with time on task. Total cerebral oxygenation, collapsed over both hemispheres, increased more over time in the local discrimination task than the global discrimination task. The performance data and the fNIRS results suggest an increased utilization of bilateral cognitive resources with time-on-task in the local discrimination condition, but not in the global discrimination condition. Results and implications are discussed.

Akademisk avhandling--Gothenburg. / Bibliography: p. 69-74.

Made available in DSpace on 2014-06-11T19:31:09Z (GMT). No. of bitstreams: 0 Previous issue date: 2003-02-14Bitstream added on 2014-06-13T21:02:17Z : No. of bitstreams: 1 bechara_jn_dr_jabo.pdf: 522049 bytes, checksum: 69aeded0d4620c6c2721ab82f9614fd2 (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Os principais fatores a serem considerados durante a anestesia em eqüinos são a depressão cardiovascular e ventilatória e suas implicações hemodinâmicas. O objetivo do presente estudo foi o de avaliar duas modalidades ventilatórias na espécie eqüina e as repercussões destes modos de ventilação nos parâmetros ventilatórios, hemodinâmicos e mecânica respiratória. Foram utilizados 19 eqüinos clinicamente sadios, em decúbito lateral, aleatoriamente divididos em dois grupos, sendo que no Grupo I foi realizada a ventilação com pressão positiva intermitente e, no Grupo II com pressão controlada. O experimento foi dividido em duas fases, sendo que na primeira foram avaliados os parâmetros ventilatórios e de mecânica respiratória e, na segunda fase, além desses, também foram avaliados os parâmetros hemodinâmicos. Observou-se melhora dos parâmetros de ventilação em relação aos momentos de ventilação espontânea, quando empregou-se a ventilação controlada. Não foram observadas alterações hemodinâmicas e de oxigenação quando comparados os diferentes momentos num mesmo grupo, porém os valores da pressão venosa central e da pressão da artéria pulmonar foram superiores no grupo da ventilação com pressão positiva intermitente. Concluiu-se que não há diferença entre a ventilação com pressão positiva intermitente e a ventilação com pressão controlada em eqüinos clinicamente saudáveis. / The most important factors to be considered in equine anesthesia are the cardiovascular and ventilatory depressions and further hemodynamic failure. The purpose of the present study was to evaluate two modes of mechanical ventilation in horses and their repercussion on ventilatory and hemodynamic parameters and respiratory mechanics also. Nineteen healthy horses in lateral recumbency, were randomly assigned into two groups. In Group I, intermittent positive pressure ventilation was used and, in Group II, pressure controlled ventilation. The experiment was divided into two phases, in the first ventilatory parameters and respiratory mechanics were evaluated and in the second phase, hemodynamic parameters were also measured. A significant improvement was observed in ventilatory parameters when compared controlled to spontaneous ventilation. No changes in hemodynamic and oxygenation parameters were observed, but central venous pressure and pulmonary arterial pressure were higher with intermittent positive pressure ventilation. In conclusion, there is no difference between intermittent positive pressure ventilation and pressure controlled ventilation in healthy horses.

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No description available.

Hypolimnetic oxygenation systems, such as linear bubble-plume diffusers, are used to improve raw water quality. Linear bubble-plume diffusers were installed in Spring Hollow Reservoir (SHR) and Carvins Cove Reservoir (CCR). Diffusers induce mixing that aids distribution of oxygen throughout the hypolimnion. The induced mixing also creates an undesirable effect by increasing hypolimnetic oxygen demand (HOD). Nevertheless, oxygenation systems are commonly used and long-term oxygenation is hypothesized to actually decrease HOD. Increased oxygen concentrations in combination with the induced mixing affect the location of the oxic/anoxic boundary relative to the sediment water interface. If the oxic/anoxic boundary is pushed beneath the sediment/water interface, the concentrations of soluble iron and manganese in the bulk water are reduced. This work was performed to further validate a recently published bubble-plume model that predicts oxygen addition rates and the elevation in the reservoir where the majority of the oxygen is added. Also, the first field observations of a theoretically expected secondary plume are presented. Model predicted addition rates were compared to observed accumulation rates to evaluate HOD over a wide range of applied gas flow rates. Observations in both reservoirs showed evidence of horizontal spreading that correlated well with plume-model predictions and of vertical spreading below diffuser elevations, showing oxygen penetration into the sediment. Experimental observations of a theoretically expected secondary plume structure also correlated well with model predictions. Plume-induced mixing was shown to be a function of applied gas flow rates, and was observed to increase HOD. HOD was also observed to be independent of bulk hypolimnion oxygen concentration, indicating that the increase in oxygen concentration is not the cause of the increased HOD. Long-term oxygenation resulted in an overall decrease in background HOD as well as a decrease in induced HOD during diffuser operation. Elevated oxygen concentrations and mixing, which occur naturally during destratification and artificially during oxygenation, were observed to coincide with low dissolved metal concentrations in CCR. Movement of the oxic/anoxic boundary out of the sediment, which is also common during stratified periods, appears to facilitate transport of reduced Mn to the overlying waters. Hypolimnetic oxygenation increased oxygen concentrations throughout the hypolimnion, including down to the SWI, and induced mixing, although not to the extent observed during destratification. Subsequently, elevated Mn concentrations were observed to be restricted to the benthic waters located immediately over the sediments, while bulk (hypolimnion) water Mn concentrations remained low. The good agreement between the model and the experimental data show that the model can be used as a predictive tool when designing and operating bubble-plume diffusers. Linear bubble-plume diffusers provide sufficient horizontal and vertical spreading to enable oxygen to reach the sediments. Hypolimnetic oxygenation, despite the increased HOD, is a viable method to manage the negative consequences of hypolimnetic anoxia in water-supply reservoirs. / Ph. D.

Lakes and reservoirs exhibit a number of mixing and transport mechanisms. Understanding the transport is crucial to understanding and predicting constituent and density structures. Transport in waterbodies can be natural, such as seiche-induced boundary mixing or advectively-driven inflows. Hypolimnetic oxygenation using bubble-plumes also leads to enhanced mixing. Whether natural or plume-induced, increased mixing will alter the waterbody properties. Conversely, the density structure affects the behavior of plumes as well as inflowing and outflowing water. For example, stratification resulting from impounding a river can result in nutrient and suspended solids retention. Similarly, operation of plumes can induce mixing in the hypolimnion, resulting in warming, increased nutrient transport, and resuspension of settled particles. Modeling is extremely useful in determining the effects of dams on water quality constituents, enhanced transport, and the performance of mitigation techniques, such as hypolimnetic oxygenation. In this work, a variety of modeling techniques are used to evaluate natural and man-made mixing mechanisms. These include simple temperature and mass budgets, a two-dimensional lake model, and a two-phase plume model. A bubble-plume and plume-enhanced mixing was studied in Lake Hallwil. It was found that the plume-lake interaction was much more complex then previously expected, and knowledge of the seiche- and plume-enhanced near-field was necessary to accurately model the plume performance. A two-dimensional lake model was then coupled with a linear-plume model to accurately predict not only the plume performance, but also the plume-enhanced mixing in Spring Hollow Reservoir. The same two-dimensional lake model, used in conjunction with data analysis, demonstrated that the Iron Gate I Reservoir was not a significant sink for suspended solids, with only the large, adjacent side bay (Orsova Bay) thought to be the permanent sink. Furthermore, significant stratification did not develop, preventing substantial primary productivity. While the impoundment did change the water quality characteristics, the extent is much less than previously expected. The modeling methods presented here and the coupled plume-reservoir model should be useful tools for the design, modeling and greater understanding of bubble-plumes and other transport-related phenomena in lakes and reservoirs. / Ph. D.

The purpose of this research was to apply a discrete-bubble model to predict the performance of several hypolimnetic oxygenators. The model is used to predict the oxygen transfer rate in a hypolimnetic oxygenator based on the initial bubble size formed at the diffuser. The discrete-bubble model is based on fundamental principles, and therefore could also be applied to other mass transfer applications involving the injection of bubbles into a fluid. The discrete-bubble model has been applied to a linear bubble-plume diffuser, a full-lift hypolimnetic aerator and the Speece Cone with promising results. The first step in this research was to investigate the principals of bubble formation at a submerged orifice, bubble rise velocity and bubble mass transfer. The discrete-bubble model is then presented. The model traces a single bubble rising through a fluid, accounting for changes in bubble size due to mass transfer, temperature and hydrostatic pressure. The bubble rise velocity and mass transfer coefficients are given by empirical correlations that depend on the bubble size. Bubble size is therefore recalculated at every increment and the values for the bubble rise velocity and mass transfer coefficients are continually updated. The discrete-bubble model is verified by comparison to experimental data collected in large-scale oxygen transfer tests. Finally, the discrete-bubble model is applied to the three most common hypolimnetic oxygenation systems: the Speece Cone, the bubble-plume diffuser, and the full-lift hypolimnetic oxygenation systems. The latter being presented by Vickie Burris in her thesis, <i>Hypolimnetic Aerators: Predicting Oxygen Transfer and Water Flow Rate</i>. / Master of Science