Hans Christian Engell

Regional cerebral blood flow in patients with transient ischemic attacks studied by Xenon-133 inhalation and emission tomography.

Cerebral blood flow CBF was studied in 14 patients with transient ischemic attacks TIA and arteriosclerotic neck vessel disease. CBF was measured by a rapidly rotating single photon emission computerized tomograph using Xenon-133 inhalation. This method yields images of 3 brain slices depicting CBF with a spatial resolution of 1.7 cm. Based primarily on the clinical evidence and on the angiographical findings embolism was considered the pathogenetic factor in 10 cases, whereas chronic hemodynamic insufficiency rendered symptomatic by postural factors probably accounted for the symptoms in 4 patients. Of the 14 patients, all studied days to weeks after the most recent TIA, four showed hypoperfused areas on the CBF-tomograms and with roughly the same location hypodense areas on CT-scanning, i.e. areas of complete infarction. However, an additional five patients showed reduction of CBF in areas with no abnormality on the CT-scan. The abnormal blood flow pattern was found to be unchanged after clinically successful reconstructive vascular surgery. This suggests the presence of irreversible ischemic tissue damage without gross emollition (incomplete infarction). It is concluded, that TIAs are often harmful events, as no less than 9 of the 14 patients studied had evidence of complete and/or incomplete infarction. Thorough examination and rational therapy should be instituted as soon as possible to prevent further ischemic lesions.

Hemodynamic effect of carotid endarterectomy.

Cerebral blood flow was measured by the intravenous xenon-133 technique at rest and during cerebral vasodilation with acetazolamide in 32 patients before and after uncomplicated carotid endarterectomy. The results were compared with the internal carotid artery perfusion pressure measured during surgery. A significant improvement in side-to-side cerebral blood flow asymmetry occurred in 6 patients studied at baseline and in 11 patients during provoked cerebral vasodilation. These patients all belonged to a group of 14 patients who, in addition to a severe stenosis of the internal carotid artery, presented a reduction in cerebral perfusion pressure of at least 20%. No improvements occurred in 18 patients with no or only minor reduction in perfusion pressure, irrespective of the degree of stenosis. These findings indicate an improved perfusion reserve following carotid endarterectomy in most patients with marked reduction in perfusion pressure, whereas only some of these patients will experience an improvement in baseline cerebral blood flow.

Cerebral Blood Flow and Internal Carotid Artery Flow During Carotid Surgery

In a series of 17 patients operated on for stenosis of the internal carotid artery, measurement of the blood flow in the internal carotid artery by a squarewave electromagnetic flowmeter was performed simultaneously with measurement of the regional cerebral blood flow (rCBF) by the 133Xenon injection technique. The measurements were made before and after endarterectomy. On completion of endarterectomy there was significant increase in mean internal carotid artery flow (ICAF), from 133 ml/min to 212 ml/min (P < 0.05), whereas mean rCBF remained unaltered. The ratio ICAF/rCBF gives brain substance in grams supplied by the internal carotid artery. The mean value of this ratio increased significantly from 231 gm to 452 gm after endarterectomy (P < 0.01). Thus cerebral hemodynamics tended to the normal postoperatively.

Evaluation of the regional cerebral vasodilatory capacity before carotid endarterectomy by the acetazolamide test

To estimate the regional perfusion pressure and possibly the stump pressure during carotid endarterectomy, cerebral blood flow (CBF) measurements including a vasodilatory test were performed preoperatively. CBF was measured by 133Xe inhalation and emission tomography. An intravenous dose of 1g acetazolamide (Diamox) was used as cerebral vasodilator. Thirty-six patients with a clinical history of previous strokes (9 cases) or transient ischaemic attacks (27 cases) were studied. Nine of the patients showed occlusion of the contralateral internal carotid artery (ICA). The percent flow increase induced by Diamox in the ipsilateral hemisphere correlated to the ICA pressure was measured before clamping (n = 32, r = 0.55, p less than 0.001). In 12 of the 36 patients, Diamox caused a significant change in the flow distribution indicating a restricted regional vasodilatory capacity and a reduced regional perfusion pressure. In addition, these 12 patients showed a low stump pressure (less than 50 mmHg). However, 8 additional patients had uniform CBF increases at the Diamox test, but showed low stump pressures. It is concluded, that preoperative tests of the cerebral vasodilational capacity can be used to identify most patients with a low ICA pressure, and a substantial fraction of patients that will develop a low stump pressure upon ICA clamping during operation. In these patients with abnormal Diamox tests surgical reconstruction is particularly indicated, but, at the same time the perioperative risks are presumably highest in this group.

Cerebral blood flow before and after carotid endarterectomy.

From the Surgical Laboratory of Circulatory Research, Dept. D. and the Dept. of Anesthesiology. Rigshospitalet, Copenhagen, Denmark. Presented at the 13th Scientific Session of the International College of Angiology, Copenhagen, Denmark, June 29 to July 4 1971. The prime object of carotid endarterectomy is to prevent damage due to emboli arising from an atheromatous process in the artery. In case of severe arterial stenosis endarterectomy may further prevent total occlusion of the artery at a later stage. In a previous publication6 it was shown that endarterectomy of severely stenosed internal carotid arteries resulted in increased flow through the artery, while mean regional cerebral blood flow (rCBF) of the hemisphere remained unaltered, i.e. a greater amount of brain tissue was fed by the carotid artery following operation. Unchanged cerebral blood flow after carotid endarterectomy was also found by O’Brien et al.l° and by Adams, Smith & lvyliel in smaller series of 10 and 17 patients, respectively. In this study the effect of carotid endarterectomy on cerebral hemodynamics has been evaluated peroperatively by simultaneous measurements of rCBF, internal carotid artery flow (ICA flow) , mean arterial blood pressure peripheral in the internal carotid artery (ICA pressure), and in the radial artery (MABP).

Measurement of cerebral blood flow by intravenous xenon-133 technique and a mobile system. Reproducibility using the Obrist model compared to total curve analysis.

The recent development of a mobile 10 detector unit, using i.v. Xenon-133 technique, has made it possible to perform repeated bedside measurements of cerebral blood flow (CBF). Test-retest studies were carried out in 38 atherosclerotic subjects, in order to evaluate the reproducibility of CBF level and side-to-side asymmetry. Data were analysed according to the Obrist model and the results compared with those obtained using a model correcting for the air passage artifact. Reproducibility was of the same order of magnitude as reported using stationary equipment. The side-to-side CBF asymmetry was considerably more reproducible than CBF level. Using a single detector instead of five regional values averaged as the hemispheric flow increased standard deviation of CBF level by 10-20%, while the variation in asymmetry was doubled. In optimal measuring conditions the two models revealed no significant differences, but in low flow situations the artifact model yielded significantly more stable results. The present apparatus, equipped with 3-5 detectors covering each hemisphere, offers the opportunity of performing serial CBF measurements in situations not otherwise feasible.

Staged bilateral carotid endarterectomy

In a series of 56 staged bilateral carotid endarterectomies, new neurologic symptoms developed in 5% and 20% following the first and second procedure, respectively. All complications were transient or minor. The incidence of postendarterectomy hypertension was significantly higher following the second procedure, when operations were staged less than 3 weeks apart. A correlation between these hypertensive episodes and the occurrence of new neurologic symptoms could not be shown. However, as this correlation has been proved in several other reports, bilateral carotid endarterectomy is advised to be staged at least 3 weeks apart. In addition, a conservative attitude towards contralateral asymptomatic lesions is proposed.

Noninvasive xenon-133 measurements of cerebral blood flow using stationary detectors compared with dynamic emission tomography

Repeated bedside measurements of CBF have been made possible by the recent development of a mobile unit with 10 stationary detectors using the intravenous xenon-133 method. To evaluate this technique, comparative CBF studies at rest and following the application of a cerebral vasodilatory stimulus (acetazolamide, 1 g i.v.) were performed with the mobile equipment and with xenon-133 single-photon emission inhalation tomography in patients with cerebrovascular disease. The CBF level and the flow response to acetazolamide as determined with the two methods were well correlated, although at low flow levels the stationary detectors yielded somewhat lower CBF values than did emission tomography. Considering the side-to-side asymmetry, an excellent correlation was obtained. Using the initial slope index, the stationary detectors revealed quantitatively 83% of the interhemispheric asymmetry and 63% of the asymmetry in the middle cerebral artery territory shown with the tomograph. As illustrated by a case history, the nontomographic CBF unit used in this study may provide reliable and useful information in patients with occlusive cerebrovascular disease by performing repeated CBF studies and challenging the cerebral circulation with acetazolamide.

Peroperative Cerebral Blood Flow Measurements Cerebral 133Xenon Clearance during Reconstruction of the Carotid and Subclavian Arteries

Cerebral blood flow (CBF), 133Xe intraarterial injection technique, measured in 9 patients subjected to carotid surgery. During clamping CBF was reduced, and neurological complications occurred when CBF decreased to 20–30 ml/100g-min during periods of 15–35 min. In cases of total occlusion of the internal carotid and of subclavian steal, 133Xe clearance gave valuable information.

Carotid artery disease and low cerebral perfusion pressure: symptomatology, operative risk and outcome.

Direct internal carotid artery blood pressure measurements in patients undergoing carotid endarterectomy identified 49 patients, among 239 consecutive cases (21%), who had a reduction in perfusion pressure of 20% or more. The clinical history, objective findings and angiographic data were compared with those of a control group of a further 49 patients selected from the remaining patients operated on over the same period. The two groups were compared for short- and long-term outcome of surgery. We were unable to delineate a symptomatic neurological profile that identified patients with low perfusion pressures. Surgery in patients with low perfusion pressures seemed to be associated with an increased complication rate (12% versus 4%), although this was not statistically significant. Definite postoperative improvements in persisting neurological deficits were observed only in one patient. Long-term results were equal in the two groups with an annual stroke risk of 3%.