Cerebrovascular and brain metabolism reviews
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Cerebrovasc Brain Metab Rev · Jan 1993
ReviewHemorrhagic transformation after cerebral ischemia: mechanisms and incidence.
Hemorrhagic infarction and cerebral hematoma are feared events that may follow cerebral ischemia. Newly developed thrombolytic agents may be effective stroke therapy, but may also promote hemorrhagic complications after ischemic stroke. It is therefore critically important to understand the true incidence of hemorrhagic transformation after ischemic stroke, and to identify if possible the mechanisms underlying the phenomenon. ⋯ Experimental and clinical evidence support the notion that hemorrhage results from augmented collateral circulation into the ischemic zone, perhaps in concert with hypertension. Recanalization and distal migration of the thrombus are not factors that are associated with transformation. Pharmacologic recanalization using thrombolytic drugs are not likely to be associated with hemorrhage if reperfusion is accomplished very soon after the onset of neurologic symptoms.
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Cerebrovasc Brain Metab Rev · Jan 1992
ReviewTherapeutic modulation of brain temperature: relevance to ischemic brain injury.
Hypothermia was first applied therapeutically as a local anesthetic and later was used to achieve organ protection during procedures necessitating circulatory interruption. Profound whole-body hypothermia, typically carried out in conjunction with extracorporeal bypass, has long been employed during cardiac and neurosurgical operative procedures. More recently, studies in small-animal experimental models of cerebral ischemia have provided persuasive evidence that even small decreases in brain temperature confer striking protection against ischemic neuronal injury. ⋯ The measurement of brain temperature is now practicable in neurosurgical patients requiring invasive monitoring, and human studies have shown that cortical and cerebroventricular temperatures may exceed systemic temperatures. Mild to moderate decreases in brain temperature are neuroprotective in cerebral ischemia, while mild elevations of brain temperature are markedly deleterious in the setting of ischemia or injury. It is anticipated that controlled clinical trials of therapeutic brain temperature modulation will be undertaken over the next several years.
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Cerebrovasc Brain Metab Rev · Jan 1991
ReviewCurrent concepts of pathophysiology and management of cerebral vasospasm following aneurysmal subarachnoid hemorrhage.
Approximately 10 in 100,000 persons suffer rupture of a saccular intracranial aneurysm annually, and roughly 60% of these will survive the initial catastrophe in reasonable neurological condition. Of the many ensuing complications of aneurysmal subarachnoid hemorrhage, the most frustrating continues to be a form of delayed-onset cerebral arterial narrowing known as vasospasm. Because it is caused by thick subarachnoid blood clots coating the adventitial surface of cerebral arteries, the distribution and severity of vasospasm correlates closely with location and volume of subarachnoid hematoma as visualized on computed tomography (CT). ⋯ Several treatments from the latter category, namely, hypertensive, hypervolemic hemodilutional therapy and the calcium channel blocker nimodipine, have proven moderately effective and are in widespread clinical use. It has also been possible to mechanically dilate vasospastic vessels with transluminal angioplasty improving cerebral blood flow to ischemic brain. However we are still in need of an effective agent to prevent arterial narrowing, and several hopeful candidates in this category of treatment are clot lytic agent tissue plasminogen activator (rt-PA) and an inhibitor of iron-dependent peroxidation, 21-aminosteroid U74006F (tirilazad mesylate).
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Autoregulation of blood flow denotes the intrinsic ability of an organ or a vascular bed to maintain a constant perfusion in the face of blood pressure changes. Alternatively, autoregulation can be defined in terms of vascular resistance changes or simply arteriolar caliber changes as blood pressure or perfusion pressure varies. While known in almost any vascular bed, autoregulation and its disturbance by disease has attracted particular attention in the cerebrovascular field. ⋯ In chronic hypertension, the limits of autoregulation are shifted toward high blood pressure. Acute hypertensive encephalopathy, on the other hand, is thought to be due to autoregulatory failure at very high pressure. In long-term diabetes mellitus there may be chronic impairment of CBF autoregulation, probably due to diabetic microangiopathy.