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 (SaO2) in the range of 85-99% and of carbon dioxide tension (PaCO2) in the range of 4.3-9.6 kPa. No relation was found between changes in SaO2 and CytO2]. Alterations in PaCO2 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) mumol.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) mumol/ml. These results define a fraction of cerebral cytochrome oxidase in the newborn infant that is oxidized after an increase in PaCO2 but demonstrate that a change in SaO2 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.