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Near infrared spectroscopy for evaluation of cerebral oxygenation

Peter Rasmussen

Summary / Abstract

Normal brain function requires continuous oxygen (O2) supply and near-infrared spectroscopy (NIRS) monitors the capillary-oxygenation-level-dependent (COLD) signal as cerebral haemoglobin oxygenation (ScO2). This thesis work provides evidence that ScO2 follows the calculated capillary O2 saturation (ScapO2) obtained by integration of arterio-jugular differences and a transcranial
Doppler based estimate of changes in cerebral blood flow (CBF) both at rest and during exercise. The NIRS response was also evaluated during electroconvulsive therapy (ECT), where the ScO2 became reduced when ECT caused extreme bradycardia and marked reduction in cerebral perfusion, while ScO2 was maintained when bradycardia was prevented by prior administration of glycopyrrolate. At rest and during maximal whole-body exercise in healthy volunteers, ScO2 tracked ScapO2 with manipulation of both the arterial O2 content and CBF. It is of functional importance that handgrip strength correlated with ScO2, ScapO2 and, accordingly, with the calculated mitochondrial O2 tension. In conclusion, NIRS is capable of monitoring the cerebral ScapO2 non-invasively at rest and during exercise and responds to an acute reduction in cerebral perfusion. Thus, NIRS offers an estimate of cerebral COLD under conditions where arterial and jugular venous catheterisation, or functional magnetic resonance imaging (fMRI), is not feasible, or practical as during surgery, work in the industry, and whole-body exercise.