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Near-Infrared Spectroscopy (NIRS) instruments most often measures the reflected NIR attenuation at a couple of wavelengths, to quantify the concentration of the oxygenated and deoxygenated hemoglobin ([HbO2], [HHb]) and provide information about the brain oxygen levels. Of particular interest are the changes in brain oxygenation due to neuronal activity as they can provide us with an indirect measurement of brain function. For several years now we have been developing technology that extend NIRS instrumentation by allowing measuring hundreds of NIR wavelengths. The technique is called broadband near-infrared spectroscopy (or bNIRS). The bNIRS system measures changes in light attenuation, reflected back from the head, over 308 near-infrared (NIR) wavelengths (610nm-918nm). This allow us to quantify the changes in brain tissue [HbO2], [HHb] and the concentration changes in the oxidation state of cerebral cytochrome-c-oxidase ([oxCCO]). CCO is an enzyme in the electron transport chain of the mitochondrial catalyzing more than 95% of oxygen to produce ATP.
In my talk I will discuss how we have been using this technology both in our preclinical and clinical investigations in perinatal hypoxic-ischemia. In particular, I will introduce our clinical study in newborns with Hypoxic-Ischemic (HI) injury undergoing therapeutic hypothermia. In 24 neonates, 54 episodes of spontaneous decreases in peripheral oxygen saturation (desaturations) were recorded between 6h and 81h after birth. As determined by magnetic resonance spectroscopy derived lactate/N-acetyl-aspartate (MRS-measured Lac/NAA) 8 newborns had unfavorable and 16 newborns had favorable outcomes after HI. We demonstrated that a strong relationship between cerebral metabolism (bNIRS-measured oxCCO) and oxygenation was associated with unfavorable outcome; this is likely to be due to a lower cerebral metabolic rate and mitochondrial dysfunction in severe encephalopathy. In addition, uniquely we have obtained these results using a non-invasive bedside technique, bNIRS, in the first 4 days of life.
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