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Experimental bilateral deep temporal epilepsy. Effects of ablation of one focus and of different brain lesions
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Experimental investigation on cerebral circulation: autoregulatory mechanisms
No full textBrain dysfunction is a frequent complication of sepsis, usually defined as "sepsis-associated encephalopathy" (SAE). Its pathophysiology is complex and related to numerous processes and pathways, while the exact mechanisms producing neurological impairment in septic patients remain incompletely elucidated. Alterations of the cerebral blood flow (CBF) may represent a key component for the development of SAE. Reduction of CBF may be caused by cerebral vasoconstriction, either induced by inflammation or hypocapnia. Endothelial dysfunction associated with sepsis leads to impairment of microcirculation and cerebral metabolic uncoupling that may further reduce brain perfusion so that CBF becomes inadequate to satisfy brain cellular needs. The natural autoregulatory mechanisms that protect the brain from reduced/ inadequate CBF can be impaired in septic patients, especially in those with shock or delirium, and this further contributes to cerebral ischemia if blood pressure drops below critical thresholds. Sedative agents alter cerebro-vascular reactivity and may significantly reduce CBF. Although disorders of brain perfusion and alteration of CBF and cerebral autoregulation are frequently observed in humans with sepsis, their exact role in the pathogenesis of SAE remains unknown. Brain perfusion can further become inadequate due to cerebral microcirculatory dysfunction, as evidenced in the experimental setting. Microvascular alterations can be implicated in the development of electrophysiological abnormalities observed during sepsis and contribute to neurological alterations in septic animals. The aim of this review is to provide an update on the pathophysiology of brain perfusion in sepsis, with a particular focus on human clinical investigation and novel tools for CBF monitoring in septic patients
Cerebral blood flow autoregulation during intracranial hypertension: a simple, purely hydraulic mechanism?
No full textOBJECTIVE:
In this paper, we re-propose the role of a hydraulic mechanism, acting where the bridging veins enter the dural sinuses in cerebral blood flow (CBF) autoregulation.
MATERIALS AND METHODS:
We carried out an intraventricular infusion in ten albino rabbits and increased intracranial pressure (ICP) up to arterial blood pressure (ABP) levels. We measured CBF velocity by an ultrasound probe applied to a by-pass inserted in a carotid artery and recorded ICP by an intraventricular needle. Diastolic and pulsatile ICP and ABP values were analyzed from basal conditions up to brain tamponade and vice versa.
CONCLUSIONS:
A biphasic pattern of pulsatile intracranial pressure (pICP) was observed in all trials. Initially, until the CBF velocity remained constant, pICP increased (from 1.2 to 5.4 mmHg) following a rise in diastolic intracranial pressure (dICP); thereafter, in spite of a further rise in dICP, pICP decreased (2.87 mmHg) following CBF velocity reduction until intracranial circulation arrest (pICP=1.2 mmHg). A specular pattern was observed when the intraventricular infusion was stopped and CBF velocity returned to basal levels. These findings can be interpreted as indicating a hydraulic mechanism. Initially, when CBF is still constant, pICP rise is due to an increase in venous outflow resistance; subsequently, when CBF decreases following a further increase in venous outflow resistance, the vascular engorgement produces an arteriolar vasodilation. This vasodilation determines an increase in vascular wall stiffness, thus reducing pulse transmission to surrounding subarachnoid spaces.In this paper, we re-propose the role of a hydraulic mechanism, acting where the bridging veins enter the dural sinuses in cerebral blood flow (CBF) autoregulation.We carried out an intraventricular infusion in ten albino rabbits and increased intracranial pressure (ICP) up to arterial blood pressure (ABP) levels. We measured CBF velocity by an ultrasound probe applied to a by-pass inserted in a carotid artery and recorded ICP by an intraventricular needle. Diastolic and pulsatile ICP and ABP values were analyzed from basal conditions up to brain tamponade and vice versa.A biphasic pattern of pulsatile intracranial pressure (pICP) was observed in all trials. Initially, until the CBF velocity remained constant, pICP increased (from 1.2 to 5.4 mmHg) following a rise in diastolic intracranial pressure (dICP); thereafter, in spite of a further rise in dICP, pICP decreased (2.87 mmHg) following CBF velocity reduction until intracranial circulation arrest (pICP = 1.2 mmHg). A specular patter..
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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