Impact of 70% Nitrous Oxide Administration on Regional Distribution of Brain Blood Flow in Unmedicated Healthy Swine

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Abstract
Regional distribution of brain blood flow as examined in 11 healthy, spontaneously breathing swine using 15 .mu.m in diameter radionuclide-labeled microspheres that were injected into the left atrium. Measurements were made during inhalation of 30% O2/70% N (control) and at 15, 45, 75 and 120 min of 30% O2/70% N2O 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 remains near their respective control values during exposure to 70% N2O. 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 .cntdot. min-1 .cntdot. 100 g-1, respectively. At 15 in of exposure to N2O, 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% N2O and no marked fluctuations occurred. Administration of 70% N2O to healthy pigs caused pronounced cerebrovascular vasodilatation in all regions of the brain. This persisted throughout the 2 h of its administration.

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