Contribution of the inflow arteries to alterations in total cerebrovascular resistance in the rabbit

Effect of internal carotid artery reperfusion in combination with Tenecteplase on clinical scores and hemorrhage in a rabbit embolic stroke model

In the present study, we used a modification of the rabbit small clot embolic stroke model (RSCEM), a multiple infarct ischemia model to achieve reperfusion (REP) through the internal carotid artery (ICA) following small clot embolization. We determined if increasing regional cortical blood flow (RCBF) following an embolic stroke is beneficial to neurological outcome. We compared this to cerebral reperfusion induced by the administration of the thrombolytic Tenecteplase (TNK, 1.5 mg/kg, IV bolus) in the presence or absence of REP. In this study, we also measured the incidence of ICH following REP and thrombolytic treatment. Following embolization, RCBF was reduced to 48-55% of baseline. When REP was induced by removal of a CCA ligature, RCBF initially increased to 185% of baseline. REP (P(50)=1.18+/-0.43 mg) had no effect on embolization-induced behavior measured 24 h following embolization compared to control (P(50)=1.01+/-0.48 mg). However, TNK treatment (2-hours post-embolization) in the absence or presence of REP (initiated 2 h following embolization) significantly (p<0.05) increased the group P(50) to 2.92+/-0.55 mg and 2.42+/-0.40 mg, respectively. In addition, ICH was increased in the REP (42%, p<0.05) and REP-TNK (35%, p>0.05) group compared to either the control group (5.5%) or TNK group (10%). This study show that reperfusion of ICA can increase RCBF following embolization, but this is not associated with improved neurological outcome measured using quantal analysis. However, TNK administration significantly increased behavioral outcome when given 2 h following embolization; an increase that is not affected by combining TNK with REP.

Principles of cerebral oxygenation and blood flow in the neurological critical care unit

Cerebrovascular disease and trauma are leading causes of death in the United States. In addition to the initial insult to the brain, disturbances of cerebral oxygenation and metabolism underlie many of the secondary pathophysiological processes that increase both morbidity and mortality. Therefore, researchers and clinicians have sought to obtain a more thorough understanding of the physiological and biochemical principles of cerebral oxygenation and metabolism. New technologies capable of offering continuous and quantitative assessment of cerebral oxygenation may improve clinical outcomes. In this article, we review the physiological principles of cerebral metabolism, cerebral blood flow and their metabolic coupling, and cerebral oxygenation, with particular emphasis on variables that could be monitored and managed in an intensive care unit setting.

An experimental study of cerebrovascular resistance, pressure transmission, and craniospinal compliance

To successfully match the treatment to the cause for raised intracranial pressure (ICP) after a severe head injury, it is important to know the underlying mechanism at a given moment for the raised pressure. In particular, it is important to distinguish between active cerebral vasodilation, indicating functional autoregulation, and a passive vascular dilation as the cause for raised ICP. An experimental study was performed in feline models of diffusely raised ICP (n = 6), of active arterial vasodilation caused by arterial hypercarbia (n = 6), and of passive arterial dilation caused by pharmacologically induced arterial hypertension (n = 6) to determine if wave form analysis of ICP can distinguish active from passive arteriolar vasodilation. Pulsatile pressure transmission from the blood pressure pulse to the ICP pulse (cerebrovascular pressure transmission [CVPT]), cerebrovascular resistance, and craniospinal compliance were measured simultaneously at each level of raised ICP, arterial hypercarbia, and arterial hypertension. Arterial hypercarbia, caused by both 5 and 10% inspired CO2 increased low-frequency CVPT, which was followed by an increasingly negative phase shift between the blood pressure and ICP wave form (P < 0.05). Diffusely raised ICP caused by intraventricular infusion of mock cerebrospinal fluid caused increased low-frequency CVPT (P < 0.01) but resulted in no overall change in phase shift, although the sign of the phase shift remained negative. After arterial hypertension, caused by the infusion of angiotensin II, where there was loss of myogenic tone, an increased low-frequency CVPT was accompanied by a positive phase shift (P < 0.01). These data demonstrate it may be possible to distinguish active arteriolar vasodilation from a passive loss of autoregulatory vascular tone through simultaneous measurement of the low-frequency CVPT and phase shift. Analysis of the ICP wave form provides information relevant to the management of raised ICP.

Central nervous system monitoring. What helps, what does not

The ICU monitoring of CNS function can make a difference in the clinical outcome. No single technique addresses the multiple issues that arise in the ICU setting, especially for the polytrauma patient. Multimodality approaches combining assessment of cerebral blood flow, electrophysiologic parameters, and intracranial pressure, when appropriate, with cardiac and respiratory monitors are being developed at a number of traumatology centers world wide. Experience needs to be gained to establish the best combination of these modalities. Pending this, selected use of intracranial pressure monitoring combined with EEG and transcranial Doppler ultrasound provides reliable immediate assessment and ongoing monitoring of CNS structures.