[Intracranial pressure irregularities induced by bulbar stimulation in experimental subarachnoid hemorrhage]

Neurogenic mechanisms of pressure waves were investigated in dogs with acute intracranial hypertension. After subarachnoid infusion of hemolyzed red blood cells, simultaneous recordings of both systemic blood pressure (SBP) and intracranial pressure (ICP) were made continuously. Pressure waves could be induced by electrical stimulation of the medulla oblongata at the stage of increased ICP. Induced pressure waves were specific at the site of the stimulation. These pressure waves were classified into 3 types, consisting of fast waves, slow waves and rebound waves. The fast waves had a duration of 10-30 seconds, being accompanied by a marked increase of SBP. These waves were induced by stimulation of various portions of the lateral reticular formation. The slow waves had a duration of 30 seconds to 3 minutes, being accompanied by a decrease or little change of SBP. These waves were induced by stimulation of the lateral portion of lateral reticular formation. The rebound waves had a duration of 30 seconds to 3 minutes, followed by a decrease of SBP. These waves were induced by stimulation of the lateral area of the solitary tract nucleus. At the end stage of intracranial hypertension, electrical stimulation of all of these sites induced changes of ICP depending on SBP. Slow waves were increase the intracranial pressure during arterial depressor responses indicating primary cerebral vasodilatation. It is suggested from these data that cerebral vascular tonus is concerned with the lateral portion of lateral reticular formation.