Cerebral Blood Flow Dynamics Research Articles

1313 Unilateral lesion of the hippocampal ca1 subfield due to transient forebrain ischemia plus unilateral hyperthermia, and its dynamics of cerebral blood flow and brain temperature

A brief sub-lethal ischaemic stimulus has been reported to protect against subsequent ischaemic damage in vivo, and in vitro following periods of hypoxia or oxygen–glucose deprivation (OGD). Preconditioning against neurotoxic stimuli has been linked to N-methyl-d-aspartate (NMDA) receptors, since receptor blockade prevents the protection afforded by OGD, and low doses of NMDA treatment are capable of preconditioning. The current study demonstrated that NMDA preconditioning also protects against 3-nitropropionic acid (3-NPA), a generator of both excitotoxic and oxidative damage, in addition to glutamate. Cerebellar granule neuronal (CGN) cultures prepared from 8-day neonatal Sprague–Dawley rats were maintained for 8 days prior to NMDA stimulation for 6 h. At 9 days in vitro (DIV), preconditioned and control cultures were subjected to a toxic insult (1 μM–10 mM glutamate or 1 μM–10 mM 3-NPA). Neuronal viability was assessed by use of a fluorescein diacetate assay. Protection was effective with 100 μM NMDA preconditioning for 6 h against 1–100 μM glutamate, and also against 1–500 μM 3-NPA. The study demonstrates that NMDA preconditioning can be beneficial against excitotoxic treatments, even when these are potentially complicated by associated oxidative damage and metabolic compromise, as is the case for 3-NPA.

PS-27-4 Progression of dementia of Alzheimer type and cerebral blood flow dynamics; a three-year follow-up study

PS-27-4 Progression of dementia of Alzheimer type and cerebral blood flow dynamics; a three-year follow-up study

Postsurgical observations of mean hemispheric cerebral blood flow with patients receiving high-flow EC-IC bypass using a radial artery graft: (preliminary report, one-year observation of 10 hemispheres)

BACKGROUND When we encounter an inaccessible internal carotid artery lesion, we sacrifice the inaccessible internal carotid artery and, at the same time, establish a high-flow extracranial-to-intracranial arterial bypass (EC-IC bypass). Questions and concerns remain, however, about the dynamics of the patient's cerebral blood flow postoperatively. METHOD Ten hemispheres from 9 patients had received radial artery grafting as an EC-IC bypass with the simultaneous obstruction of the internal carotid artery. Their mean hemispheric cerebral blood flow (mCBF) was measured longitudinally during 1 year after surgery by single photon emission computed tomography (SPECT) and a 133Xenon-inhalation method. RESULTS The serial mCBF values of the five hemispheres with giant aneurysm or paracavernous meningioma were attenuated during the postoperative 3-month period and then returned to the normal range. In only one case did the postoperative reduction of mCBF fail to return to normal; in addition there was a memory disturbance that had developed and progressed. Five hemispheres with the ICA stenosis did not present reduction in mCBF. In three out of five hemispheres, transient elevation of mCBF at 1 month after surgery was observed. CONCLUSIONS We conclude from our study that the internal carotid artery can be safely substituted by the radial artery graft from the view point of cerebral blood flow.

Validation of Continuous Thermal Measurement of Cerebral Blood Flow by Arterial Pressure Change

A thermal measurement system to monitor cerebral blood flow (CBF) continuously from the cortical surface is evaluated in vivo. It has a temperature resolution of better than 0.001 degrees C (1 m degrees C) and can compensate for baseline temperature fluctuations in the brain tissue. A new approach has been developed to test the capability of monitoring dynamic CBF response. Transient CBF changes associated with changes in mean arterial blood pressure (MABP) caused by repeated bolus norepinephrine injections are used to examine the response of the measurement system in both the heated mode, sensitive to flow, and the unheated mode, sensitive only to temperature. Experiments on 13 rats demonstrate that changes in the MABP are closely correlated with those of temperature difference in the heated mode. Regression analysis shows a mean slope of 0.9 m degrees C/mm Hg in the heated mode, which is significantly different from zero (p < 0.002) and from the mean slope in the unheated mode (p < 0.002). This indicates that flow signal in the system output can be distinguished from the baseline thermal fluctuations. Thus, the system can be used to detect and study dynamic perfusion changes from the brain surface with minimal tissue damage. Furthermore, analysis of the data shows that the transient flow signal before autoregulation is linearly correlated with changes in MABP.

Rapid changes in extracellular glucose levels and blood flow in the striatum of the freely moving rat

The dynamics of regional cerebral blood flow and brain extracellular glucose were studied in the freely moving rat. These two variables were measured in the striatum during and following both mild tail pinch and resistant stress. Blood flow was monitored using a refinement of the hydrogen clearance technique that allowed repeated measurements at 5-min intervals. A slow stream of hydrogen was directed at the rat's snout for 10–20 s through lightweight tubing attached to the animal's head and detected at a chronically implanted platinum electrode. Extracellular glucose was monitored with microdialysis in a separate group of animals using an on-line, enzyme-based assay that provided 2.5-min time resolution. Mean striatal blood flow 24 h following implantation was 89.9 ± 2.5 ml ·(100g) −1·min −1. A 5-min tail pinch caused flow to increase immediately to 169.5 ± 20 ml ·(100g −1·min −1. In contrast, there was no change in blood flow during restraint stress, although there was a small increase following the end of the stress. Significant increases in blood flow were also observed in the striatum during periods of eating and grooming. Extracellular glucose levels increased following both forms of stress, to a maximum of 170 ± 22% of baseline with restraint compared to 110 ± 2% with tail pinch. In both cases, the increase occured after the stress had ended and persisted while blood flow returned to basal levels.

Assessing the Effects of Antihypertensive Medication on Cerebral Blood Flow: Demonstration in Internal Carotid Artery Occlusion

Dynamic cerebral blood flow (CBF) studies using acetazolamide or hypercapnia as a vasodilatory challenge have attempted to evaluate intracranial hemodynamics. We report two patients with asymptomatic internal carotid artery occlusion in whom the vasodilatory stimulus was a single oral dose of antihypertensive medication (prazosin hydrochloride or enalapril maleate). In both patients, changes in regional CBF occurred that were larger than those seen in nine normal controls. One patient experienced an improvement in regional CBF with a reduction in probe pair asymmetry. In the other patient, who had bilateral carotid artery disease, a decrease in regional CBF in all 16 probes (mean decrease 12 percent) and an accentuation of the predose asymmetry were observed. Both patients remained asymptomatic throughout the study. Assessing these effects on cerebral circulation may help identify patients at risk for iatrogenic focal cerebral ischemia and provide information regarding the functional status of the cerebral vasculature.

Cerebral blood flow: assessment with dynamic contrast-enhanced T2*-weighted MR imaging at 1.5 T.

The authors assessed regional cerebral blood flow dynamics with magnetic resonance (MR) imaging enhanced with gadolinium diethylenetriaminepentaacetic acid (DTPA). After bolus administration of Gd-DTPA, rapid T2*-weighted gradient-echo images were acquired. Image acquisition time ranged from 2 to 3 seconds. The signal intensity (SI) of brain tissue and blood vessels markedly decreased during the first pass of contrast agent through the brain due to the local field inhomogeneity caused by the concentrated paramagnetic contrast agent. The method was used in 18 subjects with no cerebrovascular disease and 32 patients with stroke, vascular stenosis, arteriovenous malformation, and cerebral neoplasm. Comparison with intracranial angiography was performed in three patients and with single-photon emission computed tomography of blood flow in four. The change in T2* relaxation rate was approximately linearly related to the dose of contrast agent. The SI change increased as the echo time was lengthened. Regions in cerebral infarcts, metastases, and arteriovenous malformations showed different enhancement patterns than those of edema around a lesion and of normal brain tissue. Abnormal circulation times in patients with vascular stenoses were demonstrated. The method provides information about cerebral blood flow dynamics not available from conventional MR imaging and MR angiography.

Neurosurgical applications of ion beams

The program at Donner Pavilion has applied nuclear medicine research to the diagnosis and radiosurgical treatment of life-threatening intracranial vascular disorders that affect more than half a million Americans. Stereotactic heavy-charged-particle Bragg peak radiosurgery, using narrow beams of heavy ions, demonstrates superior biological and physical characteristics in brain over X-and γ-rays, viz., improved dose distribution in the Bragg peak and sharp lateral and distal borders and less scattering of the beam. Examination of CNS tissue response and alteration of cerebral blood-flow dynamics related to heavy-ion Bragg peak radiosurgery is carried out using three-dimensional treatment planning and quantitative imaging utilizing cerebral angiography, computerized tomography (CT), magnetic resonance imaging (MRI), cine-CT, xenon X-ray CT and positron emission tomography (PET). Also under examination are the physical properties of narrow heavy-ion beams for improving methods of dose delivery and dose distribution and for establishing clinical RBE/LET and dose-response relationships for human CNS tissues. Based on the evaluation and treatment with stereotactically directed narrow beams of heavy charged particles of over 300 patients, with cerebral angiography, CT scanning and MRI and PET scanning of selected patients, plus extensive clinical and neuroradiological followup, it appears that Stereotactic charged-particle Bragg peak radiosurgery obliterates intracranial arteriovenous malformations or protects against rebleeding with reduced morbidity and no mortality. Discussion will include the method of evaluation, the clinical research protocol, the Stereotactic neuroradiological preparation, treatment planning, the radiosurgery procedure and the protocol for followup. Emphasis will be placed on the neurological results, including the neuroradiological and clinical response and early and late delayed injury in brain leading to complications (including vasogenic edema, arterial occlusion, venous thrombosis and radiation necrosis). Clinical results in both children and adults will be illustrated and health outcome will be related to the advantages of charged-particle treatment planning, the radiosurgical procedure, dose distribution and dose localization.

Heavy Charged-Particle Bragg Peak Radiosurgery for Intracranial Vascular Disorders

The program at Donner Pavilion has applied nuclear medicine research to the diagnosis and radiosurgical treatment of life-threatening intracranial vascular disorders that affect approximately one million Americans. Stereotactic heavy-ion Bragg peak radiosurgery, using narrow beams of heavy ions (helium), demonstrates superior biological and physical characteristics in brain over X and gamma rays and protons, viz., improved dose distribution in the Bragg peak, sharp lateral and distal borders, and less multiple scattering and range straggling for the same residual range in CNS tissue. Examination of CNS tissue response and alteration of cerebral blood-flow dynamics related to heavy-ion Bragg peak radiosurgery is being undertaken using three-dimensional treatment planning and quantitative imaging utilizing cerebral angiography, computerized tomography (CT), magnetic resonance imaging (MRI), cine-CT, xenon X-ray CT, and positron emission tomography (PET). Also under examination are the physical properties of narrow heavy-ion beams for improving methods of dose delivery and dose distribution and for establishing clinical RBE/LET and dose-response relationships for human CNS tissues. Based on the evaluation and treatment with stereotactically directed narrow beams of heavy ions of over 130 patients, with cerebral angiography and CT scanning, and with MRI and radioisotope scanning of selected patients, plus extensive clinical and neuroradiological follow-up, it appears that heavy-ion radiosurgery obliterates intracranial arteriovenous malformations or protects against rebleeding with reduced morbidity and mortality.

The hemodynamic component of compensation in the brain after unilateral blocking of the somatosensory cortex

In experiments on anesthetized and waking cats the dynamics of the cerebral blood flow was investigated by a thermoelectric method in one hemisphere during experimental injury to the somatosensory area of the opposite hemisphere. Temporary cold blocking of this area of the cortex gives rise to definite hemodynamic distorbances in the opposite hemisphere, namely a biphasic vascular response: an initial decrease in the blood supply followed by a long after-effect of an increase in the blood flow. Similar vascular responses also were observed after unilateral extirpation of the somatosensory cortex. Vascular responses of this type are evidence of increased activity of the cortical structures in the intact hemisphere and can be regarded as a compensatory response to local injury of particular areas of the cortex.

Evaluation of functional reversibility of ischemic brain --to select appropriate patients with completed stroke for STA-MCA bypass surgery.

The purpose of this paper is to present a new method by which the functional reversibility of the ischemic brain can be evaluated by changes of somatosensory evoked potentials (SEP) in induced-hypertension. The method (called functional SEP test) was useful in selecting appropriate candidates of completed stroke for superficial temporal artery (STA)—middle cerebral artery (MCA) anastomosis. To evaluate the grade of reversible hypofunction of ischemic brain, cerebral blood flow (CBF) dynamics and SEPs during induced-hypertension were measured before, during and after operation in 19 completed stroke patients with main trunk occlusion of MCA. As control studies, cerebral angiographies and CBF studies were performed in 29 conservatively treated cases. Furthermore, preoperative angiographical findings, STA-MCA shunt flow and blood pressure of STA and MCA were examined respectively in surgically treated cases. From these studies, our present criteria for bypass operation evolved as follows: 1) Mean CBF value is in 25 to 32 ml/ 100g/min without global loss of autoregulation and CO2-reactivity; 2) Amplitude of initial component of SEP is augmented 2 times or more during induced-hypertension than at rest state; 3) The N1-amplitude ratio of the normal side to the affected side is above 0.5 at rest state and increased approximately to normal value, i.e., 1.0 by induced-hypertension; and 4) The STA-MCA shunt flow through STA is in 40 to 90 ml/min and the MCA blood pressure is in 40 to 60 mmHg.

Cerebral blood flow dynamics in hypotension and cardiac arrest.

Cerebral blood flow dynamics in hypotension and cardiac arrest.

Neurosurgical aspects of occlusive cerebral vascular disease.

The surgeon's interest in cerebral vascular disease began in the last century with the concern for hemorrhagic collections on the surface of the brain-the epidural and subdural hematomas. In this century, with the development and use of cerebral angiography since the thirties, cerebral aneurysms and their intracranial complications have gained increasing attention. Of more than academic interest, many aneurysms are now amenable to surgical treatment. More recently, patients having a socalled “cerebral vascular accident,” or “stroke syndrome,” have been referred to the neurosurgeon for evaluation. By collaboration, the radiologist also is involved in seeking a physiologic explanation for the dysfunction associated with cerebral vascular insufficiency and/or failure. Such collaboration is based mainly upon the application of the radiologic technic of angiography. This revealing premortem pathophysiologic roentgen procedure is disclosing new and important information concerning the dynamics of cerebral blood flow, information which was unavailable to the pathologist in the past. Postmortem studies of dead brains with collapsed vessels, ignoring the crucial factor of the carotid and vertebral artery inflow, have been misleading. This brief presentation concerns the evaluation of the “stroke syndrome” from a neurosurgical point of view, based upon angiographic studies correlated with the clinical aspects of the various abnormalities in cerebral blood flow. Diagnosis It has been of considerable interest to observe the multiplicity of causes for a stroke or “cerebrovascular accident,” terms still commonly used to finalize a transfer to the morgue or a nursing home. Some rather striking observations have been made as a result of a study of “stroke” patients admitted to a cerebral vascular ward for purposes of a neurological work-up, including angiographic studies.