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 ( {Mathematical expression}_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 ( {Mathematical expression}_c), arterial acid-base chemistry and glucose, as well as {Mathematical expression}_CBF distribution (r {Mathematical expression}_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 {Mathematical expression}_c and f_b decreased and BP_s increased similarly in the two groups. Total {Mathematical expression}_CBF and r {Mathematical expression}_CBF decreased to the same extent in both groups, and the r {Mathematical expression}_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.