[Pressure waves induced by electrical stimulation of upper pons and lower midbrain in dogs with experimental subarachnoid hemorrhage]

Neurogenic mechanisms of pressure waves were investigated by means of electrical stimulation of the upper pons and the lower midbrain of 32 dogs in which subarachnoid hemorrhage had experimentally been made. The dogs were slightly anesthetized, immobilized and artificially respired. After subarachnoid infusion of red blood cells, continuous recordings of systemic blood pressure (SBP), intracranial pressure (ICP) and cerebral perfusion pressure (CPP) were made simultaneously. At the stage of increased ICP, pressure waves were induced by electrical stimulation of the upper pons and the lower midbrain from 6 to 12 mm rostral to external auditory meatus. Stimulation parameters, i.e., intensity, duration and frequency, were kept constant at 0.1 mA, 1 msec and 40-50 Hz, respectively, throughout experiments. The induced pressure waves were classified into three types: fast, slow and plateau waves. Fast waves had a duration of 10-30 sec, being associated with a marked increase in SBP. They were induced by stimulation of 41 points in various portions of the pontine and mesencephalic tegmentum. Slow waves had a duration of 30 sec to 3 min, being associated with no change or a decrease in SBP. They were induced by stimulation of 12 points in the rostral pontine reticular formation and the mesencephalic reticular formation. Plateau waves had a duration of 3 min or more, being associated with no change or a decrease in SBP. They were induced by stimulation of 2 points in the mesencephalic reticular formation 2 mm lateral to the red nucleus, where slow waves had been induced at the early stage.(ABSTRACT TRUNCATED AT 250 WORDS)