Effect of exposure to oxygen at 101 and 150 kPa on the cerebral circulation and oxygen supply in conscious rats

Hyperbaric oxygen at pressures of 300 to 500 kPa has been shown to induce changed distribution of cerebral blood flow ( _CBF) in rats, in places reducing the supply of the supplementary O₂. Thus, in the present study, the effect of hyperoxia at 101 (group 1, n = 9) and 150 (group 2, n = 9) kPa OZ on cerebral blood flow distribution and central haemodynamics was tested in conscious, habituated rats. During the control period the systolic arterial pressure (BP_s), heart rate (f _c), breathing frequency (f _b), cardiac output ( _c), arterial acid-base chemistry and glucose, as well as _CBF distribution (r _CBF) were similar in the two groups of animals. During O₂ exposure, the acid-base chemistry remained unchanged. The haemoglobin decreased in group 2, but remained unchanged in group 1. The f _c decreased rapidly in both groups during the change in gas composition, after which f _c remained constant both in group 1 and in group 2, for whom pressure was increased. The _c and f _b decreased and BP_s increased similarly in the two groups. Total _CBF and r _CBF decreased to the same extent in both groups, and the r _CBF changes were equally scattered. In group 1, breathing of pure O₂ did not increase the O₂ supply to any cerebral region except to the thalamus and colliculi after 60 min, whereas the O₂ supply to the hypothalamus decreased and remained low. In group 2, the O₂ supply was unchanged compared to the control period in all regions. These findings agree with previous observations during exposures to higher O₂ pressures. In air after O₂ exposure the acid-base chemistry remained normal. The f _c and f _b increased to higher levels than during the control period. The BP_s remained high. The brain blood flows were increased, inducing elevated O₂ supply to several brain regions compared to the control period. In conclusion, O₂ supply to the central nervous system was found to be in the main unchanged during breathing of O₂ at 101 kPa and 150 kPa.