Effects of carbon dioxide inhalation on cerebral blood flow and oxygen tissue level in spontaneously hypertensive rabbits.

Abstract

Background and Purpose: Because previous studies have yielded conflicting results, this study was designed to investigate the efficiency of cerebrovascular reactivity to carbon dioxide in hypertension associated with moderate diffuse cerebral ischemic lesions.Methods: The effects of carbon dioxide inhalation on mean arterial blood pressure, heart and respiration rates, cerebral cortical blood flow, polarographically detected oxygen currents (oxygen availability), and cerebral electrical activity were compared in 14 spontaneously hypertensive and 16 normotensive rabbits anesthetized with urethane and ar-chloralose. Blood flow was measured with the hydrogen clearance and thermal clearance methods.Results: In the resting state the frequency of electrical activity shifted to slower components, the levels of oxygen availability and cerebral blood flow were lower (p<0.01), and the ratio of the two latter parameters was greater (p<0.01) in hypertensive rabbits than in normotensive animals. Carbon dioxide inhalation induced more marked increases in cerebral blood flow, respiration rate, and oxygen availability in hypertensive (p<0.01) than in normotensive (p<0.05) rabbits. The ratio of oxygen availability to cerebral blood flow decreased (p<0.01) in the former and did not change significantly in the latter group. The carbon dioxide-induced rise in blood flow was also slower and more protracted in hypertensive rabbits (p<0.01). Histological investigation revealed groups of neurons with ischemic changes in the cortex of the hypertensive rabbits.