The effect of carbon dioxide on cerebral blood flow was studied in ten patients with unilateral internal carotid obstruction. Inhalation of 5% carbon dioxide increased the cerebral blood flow significantly from 28.8 to 40.5 ml/100 gm of brain weight per minute (a 40% increase). A significant correlation was established between cerebral blood flow, neurological defects, and angiographic crossfilling. Increased cerebrovascular resistance in carotid obstruction is attributed to increased cerebrovascular tonus, which tends to preserve pressure gradients all along the cerebral arterial tree in the presence of a decreased volume of inflow. Carbon dioxide inhalation increased the cerebral blood flow by virtue of reduction of this cerebrovascular resistance, thereby serving to reduce stasis in less efficiently perfused arteries. Intermittent inhalation of 5% carbon dioxide in air is recommended as an adjunct to vascular surgery in treatment of unilateral carotid obstructions.
Hegedus SA, Shackelford RT. Carbon Dioxide and Obstructed Cerebral Blood Flow: Correlation Between Cerebral Blood Flow, Crossfilling, and Neurological Findings. JAMA. 1965;191(4):279–282. doi:10.1001/jama.1965.03080040021004
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