The subject has recently been studied by James, Millar&Purves who measured the cerebral vascular response to hypoxia with all nerves intact and following division or stimulation of the vagus and cervical sympathetic nerves. The effect of sympathectomy (...) is seen to consist of an elevation of both grey and white matter blood flow 40-50 per cent above control over the range of PaO2 tested, 35 to 440 mmHg. When the cervical sympathetic nerve as stimulated at constant frequency and intensity, cortical flow was reduced to control levels.
The Physiology of the Cerebral Circulation (Monographs of the Physiological Society) by M. J. Purves (Hardcover - May 31, 1972)