Role of the medullary vasomotor centre in the development of plateau waves.

Plateau waves can sometimes be found in various neurosurgical patients with increased intracranial pressure (ICP). In spite of the clinical importance of the waves, the precise mechanism producing them is still obscure. It has been reported that the waves are often accompanied by a reduction of arterial blood pressure (ABP) and suppression of respiration, suggesting a role of the brain stem in their development. In this study, we induced intracranial hypertension in dogs by occluding the neck veins, then stimulated the pressor and depressor areas of the brain stem, observing changes of ICP, ABP, cerebral blood flow (CBF), respiration and heart rate. Stimulation of the brain stem usually caused an increase in the ICP accompanied by variations of the ABP, CBF, respiration and heart rate. These variations were divided into two types: Type I and Type II. Type I which was induced by the stimulation of the pressor area of the brain stem comprised an arterial pressor response, an increase of CBF, hyperventilation and bradycardia. Type II which was caused by stimulation of the depressor area, included declines of the ABP and CBF, respiratory suppression and bradycardia. Of these, variations observed in Type II were similar in many respects to the plateau waves observed in clinical practice. We suggest that the depressor area of the medullary vasomotor centre may play an important role in eliciting the cerebral vasomotor reaction in the development of plateau waves in intracranial hypertension.