Role of the posterior hypothalamus in the development of acute brain swelling.

Destructive stereotaxic lesions were made in the posterior hypothalamus, unilaterally or bilaterally, in 26 dogs. In 21 dogs the intracranial pressure (ICP) was maintained in normal range, and in five dogs the ICP was artificially elevated to 300 to 400 mm h2o, preceding the procedures to the hypothlamus. Arterial oxygen and carbon dioxide pressure ((PaO2 and PaCO2) were maintained in the normal range. Before and after each procedure, systemic arterial pressure (SAP) was elevated by intravenous injection of norepinephrine (5 X 10(-3) mg/kg) to determined whether the ICP increases coincidentally with elevation of the systemic arterial pressure. The intracranial pressure/mean arterial pressure ratio of elevation by injection of norepinephrine was not significant regardless of the level of the ICP, or of uni-or bilateral lesions of the hypothalamus. The authors conclude that dysfunction of posterior hypothalamus does not play a specific role in the development of vasomotor paralysis leading to acute brain swelling, under conditons of normal or moderately raised ICP with normal PaCO2 and Pato2 levels.