Role of the medulla oblongata in plateau-wave development in dogs.

Plateau waves reflect both dilatation of the cerebral vessels and an increase in the cerebral blood volume under increased intracranial pressure (ICP). They are often associated with changes in arterial blood pressure (BP) and respiration, suggesting a role of the brain stem in their development. In experiments conducted on dogs in which intracranial hypertension was induced by occluding the neck veins, the authors stimulated the brain-stem reticular formation in the medulla oblongata and caudal pons to identify the brain sites that produce plateau-like responses. A rise in ICP was observed following stimulation of most areas of the brain stem and was associated with changes in arterial BP, cerebral perfusion pressure (CPP), cerebral blood flow (CBF), respiration, and pulse rate. The stimuli delivered to the medial reticular formation of the caudal medulla caused an arterial depressor response, a decrease in CPP and CBF, suppressed ventilation, and bradycardia; these responses were similar in many respects to plateau waves observed in clinical practice and almost corresponded to the depressor region of the vasomotor center. It is hypothesized that the medullary depressor area may play a role in eliciting cerebral vasomotor reaction concerned with the development of plateau waves in a state of increased ICP.