It has long been recognized that hyperventilation produces symptoms of central nervous system origin, and the clinical manifestations of this disorder have been extensively reviewed.1-5 Estimation of cerebral circulatory and metabolic changes during active and passive hyperventilation were first made by Kety and Schmidt,6 whose measurements were performed during the latter half of a 20-minute period of hyperventilation. Under these conditions, in 5 normal young subjects there was a consistent decrease in the rate of cerebral blood flow, an increase in cerebral vascular resistance, and a slight increase in mean arterial pressure.
In the present study, we were particularly interested in investigating the changes in cerebral hemodynamics induced by relatively brief periods (1 to 2 minutes) of active hyperventilation. In view of the marked changes which were found to occur in cerebral hemodynamics of subjects with normal cerebral circulatory status, it was decided to extend the study to