Impact of 70% nitrous oxide administration on regional distribution of brain blood flow in unmedicated healthy swine

Abstract

Regional distribution of brain blood flow was examined in 11 healthy, spontaneously breathing swine using 15 micron in diameter radionuclide-labeled microspheres that were injected into the left atrium. Measurements were made during inhalation of 30% O2/70% nitrogen (control) and at 15, 45, 75, and 120 min of 30% O2/70% nitrous oxide breathing. The animals were surgically prepared 10-12 days before the hemodynamic study. Arterial blood-gas tensions, arterial pH, mean aortic pressure, and cardiac output remained near their respective control values during exposure to 70% nitrous oxide. Control values of blood flow in the cerebrum, cerebellum, and the brain stem were 68.5 +/- 4.7, 75.6 +/- 4.2, and 54.2 +/- 4.0 ml . min-1 X 100 g-1, respectively. At 15 min of exposure to nitrous oxide, blood flow in the cerebrum, cerebellum, and the brain stem was 169, 127, and 145% of the control values, respectively. For the caudate nuclei and the corpus callosum, the corresponding figures were 141 and 131% of control, while that for remainder of the cerebrum was 178% of the control value. In the medulla, pons, and thalamus-midbrain, blood flow was 151, 157, and 141% of the respective control values. In all regions of the porcine brain, elevated levels of blood flow persisted throughout the 2 h of exposure to 70% nitrous oxide and no marked fluctuations occurred. It is concluded that administration of 70% nitrous oxide to healthy pigs caused pronounced cerebrovascular vasodilatation in all regions of the brain. This persisted throughout the 2 h of its administration.