Maximal Dilatation of Cerebral Vessels

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Abstract
It has been repeatedly observed that the cerebral vascular response to an increase in arterial carbon dioxide tension, as induced by inhalation of 5% to 7% carbon dioxide in normal subjects, produces a 50% to 75% increase in overall cerebral blood flow.1 On the other hand, a reduction below normal levels of the arterial carbon dioxide tension, as with passive or active hyperventilation,2,3 causes as much as a 50% reduction in cerebral blood flow. It has also been appreciated that the magnitude of these changes may show a marked individual variability, particularly as regards the effects of increased arterial carbon dioxide tension in patients with cerebral vascular disease.4,5 In this study, data are presented which suggest that the response to alterations in arterial carbon dioxide tension in patients with cerebral vascular disease may be conditioned by the resting state of the cerebral vessels. Method The subjects of