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Ischaemic brain damage induced by rapid lowering of arterial pressure in hypertension
Insights
Hypertensive baboons tolerated lower mean arterial pressures (MAP) before brain damage occurred compared to normotensive animals. This suggests hypertension may protect against hypotension-induced ischemic brain injury.
Area of Science:
- Cardiovascular Physiology
- Neurology
- Renal Hypertension
Background:
- Chronic hypertension alters cerebrovascular autoregulation.
- Understanding tolerance to hypotension in hypertensive states is crucial for patient safety.
Purpose of the Study:
- To compare the tolerance to induced hypotension and resultant ischemic brain damage between normotensive and renovascular hypertensive baboons.
- To investigate the role of cerebral vascular resistance in hypotension tolerance.
Main Methods:
- Monitoring mean arterial pressure (MAP) and cerebral blood flow in normotensive and hypertensive baboons.
- Inducing hypotension using trimetaphan, head-up tilt, and blood withdrawal until isoelectric electroencephalogram (EEG).
- Assessing ischemic brain damage post-hypotension.
Main Results:
- Hypertensive baboons required a significantly higher MAP (32 mmHg) to achieve an isoelectric EEG compared to normotensive baboons (19 mmHg).
- Cerebral blood flow reduction was similar in both groups.
- Ischemic brain damage occurred in most animals of both groups, particularly in arterial boundary zones.
Conclusions:
- Cerebral resistance vessels in chronic hypertension may limit the extent of tolerable hypotension.
- Hypertension might offer a degree of protection against severe hypotension-induced ischemic brain injury.
Abstract:
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.