Developmental changes in cerebral optical parameters in neonates using near-infrared time-resolved spectroscopy

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We used a portable three-wavelength near-infrared time-resolved spectroscopy (TRS) system to measure the light absorption coefficient (μa), light reduced scattering coefficient (μ's), hemoglobin (Hb) concentration and Hb oxygen saturation (SO2) in the brain. In a basic study using a piglet hypoxic model, the relationship between differential pathlength factor (DPF) and hemoglobin oxygenation state in the brain was investigated. In a clinical study using neonates, the developmental changes in those parameters were investigated.(1)Measurement of cerebral light pathlength by TRS in a piglet model of hypoxiaWe investigated the relationships of mean light pathlength with arterial (SaO2) and sagittal sinus venous Hb oxygen saturation (SvO2) in the brain under the condition of stepwise hypoxia loading. The ratio of mean light pathlength to interoptode distance is defined as the DPF. At FiO2 of 0.21, the DPF values at 761,795 and 835 nm were estimated to be 5.02±0.36, (mean±SD), 5.31±0.32 and 4.92±0.34,respectively. There was a significant positive linear correlation between DPF at 761 and 795 nm and SaO2. The DPF and SvO2 also showed a significant positive linear correlation at 761 and 795 nm. The factors influencing the DPF were increase in deoxyHb and decrease in oxyHb during hypoxia.(2)Measurement of cerebral optical parameter,802 and cerebral blood volume by TRS in the developing brainThe subjects were 19 neonates whose gestational age was 25 to 41 weeks. The DPF values at 761,795 and 835 nm were estimated to be 4.9±0.52,5.02±0.53 and 4.64±0.46,respectively. The values of μ's at each wavelength were 6.30±1.30,6.04±1.11 and 6.37±1.45/cm respectively. The CBV was 2.2±0.6 ml/100g, which is similar to the value previously reported. The SO2 was 73±4.0% under 95-100% of SpO2. The SO2 and postconceptual weeks showed a significant negative linear relationship. The reason for this is the increase in cerebral oxygen consumption with development of the brain.