Sequential changes and recoveries of the motor evoked potential in experimental acute intracranial hypertension

The D- and I-waves of the motor evoked potential (MEP) were investigated as a monitor for acute intracranial hypertension in 20 dogs. Intracranial pre ssure (ICP) was raised by inflation of an extradural balloon. The MEP elici ted by electrical transcortical stimulation were recorded during inflation and deflation of the balloon. The D-waves were linearly suppressed accordin g to the ICP level, however, the I-waves and the ICP level did not correlat e. Each wave disappeared in the animals kept about 50 mmHg or more, whose p upils were dilated. In the animals kept under 60 mmHg, the amplitude of the D-wave recovered proportionate to the period during which the amplitude wa s suppressed less than 50%. The changes of the MEP have some relation to hi stopathological changes. The results demonstrate that the D-wave of MEP is a useful monitor for intracranial hypertension.