Oxygen deprivation, typically the result of a combination of hypoxia and hypoperfusion, is often the primary event setting off a biochemical cascade that leads to irreversible brain injury in perinatal encephalopathy. The long-term objective of this project is the development of a novel near-infrared spectroscopy (NIRS) device for the continuous monitoring of the regional tissue saturation (St02), arterial saturation (Sa02), and venous saturation (Sv02) in the neonate's brain. Such a device could potentially detect brain tissue compromise before the development of irreversible structural damage, thus allowing for timely and specific intervention. The novelty of our approach relates to the hypothesis that an appropriate temporal analysis of NIRS data can yield three different oxygenation measurements: (1) St02 from the temporal average of the optical signal; (2) Sa02 from the oscillating component of the optical absorption at the pulse frequency; (3) Sv02 from the oscillating component of the optical absorption at the respiratory frequency. The short-term goals of this project are to characterize NIRS measurements of cerebral oxygenation and to identify the most effective practical implementation of NIRS (in terms of instrumentation and data processing) for non-invasive cerebral oximetry. In particular, we aim to 1 ) investigate the relationship between the local measurements of the hemoglobin oxygenation in the cerebral tissue, in the arterial vascular compartment, and in the venous vascular compartment, and 2) perform spatially resolved measurements of cerebral oxygenation to localize areas of brain damage. To achieve our short-term goals, we propose to perform measurements on an animal model (piglets) where we can induce changes in the hemoglobin oxygenation levels over a large range, where we can perform hemodilution experiments, where we can induce focal brain injury, and where we have access to invasive readings of Sa02 and Sv02 from the gas analysis of blood samples. Finally we will test our proposed NIRS approach to cerebral oximetry on human neonates. The completion of this study will lead to the characterization of NIRS oximetry of the brain, to the development of multimode optical oximetry (simultaneous local measurement of St02, Sa02, and Sv02), and to the identification of the most effective approach to the non-invasive. continuous monitoring of cerebral oxygenation in neonates.
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