Abstract
We present a novel lens-based broadband near-infrared spectroscopy system to simultaneously measure cerebral changes in tissue oxygenation and haemodynamics via estimation of the changes in haemoglobin concentration; in addition to oxygen utilization via the measurement of the oxidation state of cytochrome-c-oxidase (CCO). We demonstrate the use of the system in a cohort of 6 newborn infants with neonatal encephalopathy in the Neonatal Intensive Care Unit for continuous measurement periods of up to 5 days. NIRS data was collected from above the frontal lobe on the left and right hemispheres simultaneously with systemic data to allow multimodal data analysis. This allowed us to study the NIRS variables in response to global pathophysiological events and we focused our analysis to spontaneous oxygen desaturations. We identified changes from the NIRS variables during 236 oxygen desaturations from over 212 hours of data with a change from the baseline to nadir of -12 ± 3%. There was a consistent negative change in the Δ[HbD] (= oxygenated - deoxygenated haemoglobin) and Δ[oxCCO] measurements, mean decreases were 3.0 ± 1.7μM and 0.22 ± 0.11μM, and a positive change in the Δ[HbT] (= oxygenated + deoxygenated haemoglobin) measurements across all subjects, mean increase was 0.85 ± 0.58μM. We have shown with a feasibility study that the relationship between haemoglobin oxygenation changes and CCO oxidation changes during these desaturation events was significantly associated with a magnetic resonance spectroscopy (MRS)-measured biomarker of injury severity (r = 0.91, p<0.01).
Highlights
Near-infrared spectroscopy (NIRS) is a non-invasive, non-ionizing technique that allows bedside in-vivo monitoring of changes of tissue chromophore concentrations and has been widely used in the study of both adult and neonatal brains [1]
This suggests that fitting the measured changes in near-infrared attenuation only for HHb and HbO2 would leave a chromophore with the spectral features of oxCCO unaccounted for
We have demonstrated the use of CYRIL in the Neonatal Intensive Care Unit (NICU) for continuous periods over 1-5 days, recording from 1 hour up to 16 hours per day, to simultaneously measure changes in cerebral oxygenation, haemodynamics and [oxCCO] in 6 newborn infants
Summary
Near-infrared spectroscopy (NIRS) is a non-invasive, non-ionizing technique that allows bedside in-vivo monitoring of changes of tissue chromophore concentrations and has been widely used in the study of both adult and neonatal brains [1]. NIRS has been used in neonatal studies as it is easy to apply on small infants undergoing intensive care It is relatively cheap and simple when compared with other cerebral monitoring techniques, such as magnetic resonance imaging (MRI) [2]. The cerebral fractional tissue oxygenation extraction (cFTOE), derived from the combination of rScO2 and systemic oxygen saturation (SpO2), is being used as a measure of oxygen consumption [5,6] These measurements are used as a surrogate for oxygenation and oxygen utilization by many researchers; they are complicated parameters that can be difficult to interpret as they are affected by several different variables, and have had limited success as a biomarker for brain injury [3]. Some groups combine measurements of cerebral blood flow (CBF) and oxygenation using two optical methods, frequency-domain NIRS combined with
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