Differences in the time course of regional cerebral hemo-dynamics of gray and white matter during experimental hypertension.

Investigations concerned with the pathogenesis of hypertensive encephalopathy have reported two opposing changes in cerebral hemodynamics during induced hypertension: (1) vasospasm or vasoconstriction of the leptomeningeal arteries and (2) increase of cerebral blood flow which has been termed "breakthrough" of the cerebral autoregulation. To resolve this apparent conflict, continuous measurements of focal cerebral flow and oxygen availability were made in 17 baboons by the use of implanted platinum electrodes placed in both gray and white matter during induced hypertension. Autoregulation was initially well maintained in gray matter followed by "breakthrough" but the autoregulatory response was poorly maintained in the cerebral white matter. The vasoconstriction of the leptomeningeal arteries reported in earlier investigations from observations made through a skull window appears to be due to a marked autoregulatory response to hypertension rather than vasospasm. The autoregulatory response appears to be efficient in gray matter but relatively deficient in white matter.