[Sympathetic tonus of the cerebral vessels]

The bilateral cervical sympathectomy in anesthetized cats with initial arterial pressure (AP) 80--115 mm Hg increased the total blood flow while decreasing the local cerebral blood flow. In initial AP 116--135 mm Hg no effect on the total cerebral blood flow occurred while the local cerebral blood flow diminished insignificantly. If the AP was 136--180 mm Hg, the sympathectomy effect was only revealed after preliminary activation of the sympathetic nervous system. The effect of the sympathectomy depends on initial cerebral vascular tone, the perfusion pressure being one of the major factors.