The Effect of Hypercapnia on Brain Permeability to Protein

Abstract

HYPERCAPNIA is known to influence the penetration of a variety of substances into the brain. Investigations have ranged from the effect of carbon dioxide inhalation on the regional uptake of trifluoroiododomethane labeled with radioactive iodine (¹³¹I),¹ a rapidly penetrating compound that essentially measures blood flow, to the entry of viruses and colloidal carbon,² particles that ordinarily have limited access to the central nervous system. In addition, the accumulation of various drugs³ and ions^4,5 has been studied in the hypercapnic animal. An analysis of the results of these latter experiments has required consideration of enhanced blood flow, changes in ionization of drugs secondary to increased hydrogen ion activity, and alteration in the degree of metabolic incorporation or binding in brain and plasma. Other studies have implied a pathological increase in blood-brain permeability to plasma proteins. Clemedson et al⁶ exposed rabbits, guinea pigs, and cats