Central nervous system glucose utilization rate during oxygen-induced respiratory changes at 2 atmospheres oxygen in the rat.

Hyperbaric oxygenation (HBO) at pressures higher than 3 atmospheres absolute (ATA) primarily affects the CNS, while at lower pressures, the respiratory functions are predominantly changed. Due to the outstanding respiratory manifestations of HBO at pressures lower than 3 ATA O2, the possible overlapping neurological effects of oxygen toxicity may not be easily identified. However, rats exposed for 1 and 4 h to 2 ATA O2 have shown increases in the regional cerebral metabolic rate for glucose (rCMRgl) when neither visible signs of respiratory nor nervous distress were observed. The purpose of the present study was to differentiate between the CNS and the respiratory effects of HBO at 2 ATA during development of the early signs of the respiratory distress. Changes in the rCMRgl measured by [14C]-2-deoxyglucose (2-DG) autoradiographic technique and respiratory frequency (Rf) were used as criteria for determination of CNS and respiratory effects of HBO, respectively. The results demonstrate no differences in the rCMRgl (28 major structures examined) among 3 groups of conscious rats exposed to 2 ATA O2 and normoxia at 1 and 2 ATA. At the same time a significant reduction was found in the Rf of the oxygen-exposed rats. In conclusion the respiratory system at 2 ATA O2 is apparently affected earlier than, and independent from the CNS. However, due to limited resolution power of the [14C]2-DG technique, the effect of HBO on certain undetected central respiratory control centers cannot yet be ruled out.