The effect of severe hypoxia on the blood-cerebrospinal fluid barrier of dogs was evaluated from the rate of passage of radioiodinated human serum albumin from plasma to cisternal fluid. Hypoxia was induced by intratracheal administration of varying mixtures of O2 and N2 or by use of a Smith-Jones pressure chamber. Radioiodinated albumin was injected intravenously and cisternal fluid and plasma samples were obtained at various intervals thereafter in experimental and control animals. Hypoxia maintained for 1 hour or longer resulted in a marked increase in the concentration ratio (cisternal fluid radioactivity)/(plasma radioactivity). The concentration ratio was frequently higher after 4 hours of hypoxia than after 24–48 hours in control animals. The slope of CSF albumin-I131 concentration as a function of time for the hypoxic animals was about five times that for the control animals. It is concluded that changes in rate of passage of albumin from plasma into cisternal fluid reflect alterations in the permeability of the blood-cerebrospinal fluid barrier to albumin.

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