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Cerebral blood flow in untreated and treated hypertension
1Department of Medicine and Nephrology B, Herlev Hospital, Denmark.
Insights
Cerebral blood flow (CBF) remains stable in hypertensive and normotensive individuals. However, chronic hypertension and certain medications can affect the blood pressure limits of CBF autoregulation.
Area of Science:
- Neurology
- Cardiovascular Medicine
- Pharmacology
Background:
- Cerebral blood flow (CBF) autoregulation is crucial for maintaining brain perfusion despite blood pressure fluctuations.
- Hypertension is known to alter the physiological limits of CBF autoregulation.
Purpose of the Study:
- To investigate the impact of hypertension and antihypertensive treatments on cerebral blood flow (CBF) and its autoregulation.
- To evaluate the effects of specific drug classes, including converting enzyme inhibitors and calcium antagonists, on CBF autoregulation.
Main Methods:
- The study likely involved comparative analysis of CBF and autoregulation parameters in hypertensive versus normotensive individuals.
- Pharmacological interventions were assessed for their influence on intracranial pressure and autoregulation limits.
Main Results:
- CBF is comparable in hypertensive and normotensive individuals without neurological deficits.
- Chronic hypertension shifts the autoregulation limits to higher pressures, necessitating careful blood pressure management during acute reductions.
- Cerebral vasodilators and some calcium antagonists can impair autoregulation and increase intracranial pressure.
Conclusions:
- Converting enzyme inhibitors may improve autoregulation during hypotension and retain benefits with chronic use.
- Antihypertensive therapy can lead to re-adaptation of CBF autoregulation towards normal.
- Long-term pharmacological effects of antihypertensive drugs on the cerebral circulation require further investigation.
Abstract:
Cerebral blood flow (CBF) is the same in hypertensive and normotensive man without neurological deficit. Chronic hypertension shifts the lower and upper blood pressure limits of CBF autoregulation towards higher pressure. Acute blood pressure reduction will lower CBF only if the pressure is taken below the lower limit of autoregulation. Added to this, some drugs are cerebral vasodilatators and have the potential for paralysing autoregulation and raising intracranial pressure, an effect also seen with at least some calcium antagonists. Converting enzyme inhibitors improve autoregulation during hypotension, probably by releasing angiotensin II dependent tone in the larger cerebral resistance vessels. With chronic antihypertensive treatment, CBF autoregulation may re-adapt towards normal. Converting enzyme inhibitors when given chronically probably retain their beneficial effect on the lower limit of autoregulation. Apart from this, it is uncertain whether there are chronic pharmacological effects of antihypertensive drugs directly on the cerebral circulation.