Ischaemic brain damage induced by rapid lowering of arterial pressure in hypertension.

Mean arterial pressure (MAP) and cerebral blood flow were monitored in six normotensive [MAP = 99 +/- 3 mmHg (s.e.m.)] and seven baboons with renovascular hypertension (MAP = 140 +/- 5 mmHg). Arterial pressure was decreased sufficiently rapidly and for a sufficient time, as determined by the electroencephalogram (EEG), to result in ischaemic brain damage. Using a combination of a bolus injection of trimetaphan, head-up tilt and acute withdrawal of blood, an isoelectric EEG was achieved at a higher MAP in the hypertensive (32 +/- 2 mmHg) than in the normotensive (19 +/- 1 mmHg: P less than 0.001) animals. Cerebral blood flow decreased to an equivalent degree in both groups. Ischaemic brain damage accentuated in the arterial boundary zones was seen in five normotensive and six hypertensive animals. This is further evidence that the resistance vessels in chronic hypertension may limit the degree of hypotension (therapeutic or accidental) that can be tolerated by the hypertensive patient.