Inability to deactivate sympathetic nervous system in brainstem infarct patients.

Catecholamine urinary excretion under basal conditions and after head down tilting (4 degrees) was studied in normo- and hypertensive controls and in patients with hemisphere and brainstem infarction, respectively. Both the normo- and hypertensive controls and patients with hemisphere infarction displayed a conspicuous decrease (about 40%) in noradrenaline (NA) urinary excretion after head down tilting. In contrast the patients with brainstem infarction increased NA urinary excretion after the manoeuvre, suggesting activation instead of deactivation of the sympathetic nervous system (SNS). In normo- and hypertensive controls the values of night NA excretion were lower than those of day NA excretion, whereas in brainstem infarct patients the night NA excretion was close to the day NA excretion. This finding also supports the view that the brainstem infarct patients are not able to deactivate their SNS during night recumbency. The SNS reactivity disorder of such patients if associated with impairment of autoregulation of cerebral circulation might generate an abnormal increase in cerebral circulation during night recumbency.