QUANTIFICATION OF CONCENTRATION CHANGES IN NEONATAL HUMAN CEREBRAL OXIDIZED CYTOCHROME-OXIDASE

The oxygenation of cerebral cytochrome oxidase in vivo was investigated in eight newborn preterm infants. Near-infrared spectroscopy was used to quantify changes in the concentration of oxidized cytochrome oxidase ([CytO2]) observed during alterations in arterial oxygen saturation (Sa(o2)) in the range of 85-99% and of carbon dioxide tension (Pa(CO2)) in the range of 4.3-9.6 kPa. No relation was found between changes in Sa(O2) and [CytO2]. Alterations in Pa(CO2) were positively related both to changes in [CytO2] and total cerebral hemoglobin concentration ([Hb]t). The changes in [CytO2] ranged from 0.09 to 0.33 (median 0.21) mu-mol.l-1.kPa-1. The ratio [CytO2]/[Hb]t ranged from 0.06 to 0.12 (median 0.08). The relation of DELTA[CytO2] to the change in cerebral blood volume (DELTA-CBV) was calculated: DELTA[CytO2]/DELTA-CBV ranged from 0.09 to 0.18 (median 0.11) mu-mol/ml. These results define a fraction of cerebral cytochrome oxidase in the newborn infant that is oxidized after an increase in Pa(CO2) but demonstrate that a change in Sa(O2) in the range studied was not sufficient by itself to change [CytO2]. They differ from results of studies in adults; this may reflect significant differences between adult and neonatal brain.