Sequential changes and recoveries of the motor evoked potential in experimental 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 pressure (ICP) was raised bvy inflation of an extradural balloon. The MEP elicited by electrical transcortical stimulation were recorded during inflation and deflation of the balloon. The D-waves were linearly suppressed according to the ICP level, however, the I-waves and the ICP level did not correlate. Each wave disappeared in the animals kept about 50 mmHg or more, whose pupils were dilated. In the animals kept under 60 mmHg, the amplitude of the D-wave recovered proportionate to the period during which the amplitude was suppressed less than 50%. The changes of the MEP have some relation to histopathological changes. The results demonstrate that the D-wave of MEP is a useful monitor for intracranial hypertension.