Bi-hemispheric CBF and Its CO2 Reactivity of TIAs and Completed Strokes in ICA Occlusions

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Bi-hemispheric cerebral blood flow (CBF) measurements during rest and hyperventilation, with intra-arteria1 ¹³³Xe injection method, were investigated in 19 cases, angiographically diagnosed as unilateral internal carotid artery (ICA) occlusion, including 8 cases with TIAs and 11 cases with completed strokes as the onset. Indices of cerebral vascular resistance and CO₂ reactivity with decreasing arterial\PCO₂ were also investigated.

A significant decrease (P < 0.05) of hemispheric mean CBF was noted in the ischemic hemisphere, but normal flow values in the unaffected hemisphere and preserved CO₂ responsiveness during hyperventilation were observed in both the affected and unaffected hemispheres in patients with TIAs. Moreover, a direct relationship between CBF and blood pressure, observed in 11 cases with completed strokes, was not recognized in 8 cases with TIAs.

A degree of the abnormalities of the affected hemisphere in cerebral circulation was suggested to be somewhat different between TIAs and completed strokes in ICA occlusions, and bi-hemispheric CBF measurements would be an useful method for evaluating the various indices of the CBF in ICA occlusions.     

Cerebral blood flow and CO2 reactivity in transient ischemic attacks: comparison between TIAs due to the ICA occlusion and ICA mild stenosis

Hemispheric mean cerebral blood flow (CBF), together with its CO2 reactivity in response to hyperventilation, was investigated in 18 patients with transient ischemic attacks (TIAs) by intraarterial 133Xe injection method in a subacute-chronic stage of the clinical course. In 8 patients, the lesion responsible for symptoms was regarded as unilateral internal carotid artery (ICA) occlusion, and in 10 patients, it was regarded as unilateral ICA mild stenosis (less than 50% stenosis in diameter). Resting flow values were significantly (P less than 0.05) decreased in the affected hemisphere of TIA due to the ICA occlusion as compared with the unaffected hemisphere of the same patient, regarded as the relative control. It was not decreased in the affected hemisphere of TIA due to the ICA mild stenosis as compared with the control. With respect to the responsiveness of CBF to changes in PaCO2, it was preserved in both TIAs, due to the ICA occlusion and ICA mild stenosis. Vasoparalysis was not observed in either types of TIAs in the subacute-chronic stage. However, in the relationship of blood pressure and CO2 reactivity, expressed as delta CBF(%)/delta PaCO2, pressure-dependent CO2 reactivity as a group was observed with significance (P less than 0.05) in 8 cases of TIA due to the ICA occlusion, while no such relationship was noted in 10 cases of TIA due to the ICA mild stenosis. Moreover, clinical features were different between TIAs due to the ICA occlusion and ICA mild stenosis, i.e., more typical, repeatable TIA (6.3 +/- 3.7 times) with shorter duration (less than 30 minutes) was observed in TIAs due to the ICA mild stenosis, while more prolonged, less repeatable TIA (2.4 +/- 1.4 times) was observed in TIAs due to fixed obstruction of the ICA. From these observations, two different possible mechanisms as to the pathogenesis of TIA might be expected, e.g., TIA of microembolic origin due to the ICA mild stenosis, and TIA of hemodynamic origin due to fixed obstruction of the ICA, for whom the bypass surgery might be beneficial, i.e., all TIAs are not based on the same mechanism.     

Cerebral Blood Flow and CO2 Reactivity in Transient Ischemic Attacks: Comparison between TIAs due to the ICA Occlusion and ICA Mild Stenosis

Hemispheric mean cerebral blood flow (CBF), together with its CO₂ reactivity in response to hyperventilation, was investigated in 18 patients with transient ischemic attacks (TIAs) by intraarterial ₁₃₃Xe injection method in a subacute-chronic stage of the clinical course. In 8 patients, the lesion responsible for symptoms was regarded as unilateral internal carotid artery (ICA) occlusion, and in 10 patients, it was regarded as unilateral ICA mild stenosis <50% stenosis in diameter). Resting flow values were significantly (P < 0.05) decreased in the affected hemisphere of TIA due to the ICA occlusion as compared with the unaffected hemisphere of the same patient, regarded as the relative control. It was not decreased in the affected hemisphere of TIA due to the ICA mild stenosis as compared with the control. With respect to the responsiveness of CBF to changes in Pa_CO2, it was preserved in both TIAs, due to the ICA occlusion and ICA mild stenosis. Vasoparalysis was not observed in either types of TIAs in the subacute-chronic stage. However, in the relationship of blood pressure and CO₂ reactivity, expressed as ΔCBF(%)/ΔPa_CO2, pressure-dependent CO₂ reactivity as a group was observed with significance (P < 0.05) in 8 cases of TIA due to the ICA occlusion, while no such relationship was noted in 10 cases of TIA due to the ICA mild stenosis. Moreover, clinical features were different between TIAs due to the ICA occlusion and ICA mild stenosis, i.e., more typical, repeatable TIA (6.3 ± 3.7 times) with shorter duration (<30 minutes) was observed in TIAs due to the ICA mild stenosis, while more prolonged, less repeatable TIA (2.4 ± 1.4 times) was observed in TIAs due to fixed obstruction of the ICA. From these observations, two different possible mechanisms as to the pathogenesis of TIA might be expected, e.g., TIA of microembolic origin due to the ICA mild stenosis, and TIA of hemodynamic origin due to fixed obstruction of the ICA, for whom the bypass surgery might be beneficial, i.e., all TIAs are not based on the same mechanism.     

Xenon/CT CBF measurements as valuable diagnostic tool in a case of bilateral occlusive cerebrovascular disease associated with intracranial aneurysm

A patient with the coincidental occurrence of a right internal carotid artery (ICA) stenosis and asymptomatic ipsilateral infraclinoidal ICA aneurysm is presented. CBF measurements including testing of the cerebrovascular reserve capacity (CRC) demonstrated a compromise of cerebral blood flow (CBF) within the anterior circulation of the affected side. We treated the patient in one operation by aneurysm clipping and subsequent carotid endarterectomy (CEA). 10 months later she presented with an occlusion of the contralateral ICA. CBF measurements showed sufficient resting flow and CRC on both sides. One year later repeat measurements disclosed a lowered resting CBF and diminished CRC on the affected side. Extracranial/Intracranial (EC/IC) artery bypass improved both symptoms and CBF/CRC values. The authors propose to treat symptomatic ICA stenosis and concurrent silent ipsilateral intracranial aneurysms at once if the patient is eligible for aneurysm surgery. CBF measurements should be performed before surgery. In a medically compromised patient carotid endarterectomy alone appears to be justifiable. In cases of symptomatic aneurysm and concurrent ICA stenosis a CEA can be added to aneurysm clipping to improve the hemodynamic situation for a better postoperative management. Xenon/CT investigations are suitable to provide important cerebral blood flow information. Together with angiography and clinical judgment it allows to identify patients with hemodynamic insufficiency. These are suitable candidates for an operative procedure to augment cerebral blood flow and to improve symptoms.     

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 < 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 (<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.     

Effect of glycerol on cerebral blood flow in chronic cerebral ischemic disease

The change of cerebral blood flow (CBF) after glycerol infusion was analyzed in 10 cases of lacunar infarction and 11 cases of ischemic disease of major artery: 6 cases of internal carotid artery occlusion and 5 cases of middle cerebral artery occlusion. In lacunar infarction, CBF increased generally except for the corona radiata and the increased ratio was about 20%. In cases with ischemic disease of a major artery, the CBF tended to increase in the non-affected hemisphere after glycerol infusion. But CBF did not always increase in the affected hemisphere; rather it decreased in the temporal and parietal lobes and especially in the corona radiata. The blood flow of the affected hemisphere might be stealed to the non-affected hemisphere after glycerol infusion. This phenomenon might be caused by a poor cerebrovascular reserve capacity of the maximally dilated vessels in the affected side.     

Cerebral perfusion imaging with N-isopropyl-(123I) P-iodoamphetamine (123I-IMP): its planar imaging and semiquantitative analysis in cases with internal carotid occlusion

Occlusion of internal carotid artery (ICA) is one of the most common cause of stroke, and the single common arterial lesion considered for extraintracranial bypass. The symptoms of ICA occlusion are not uniform; some shows transient ischemic attacks (TIAs), others completed stroke at the onset. So, measurement of cerebral blood flow might be needed to evaluate the prognosis, or to select surgical candidate in ICA occlusion. Several methods, such as Xe-133 intracarotid method, Xe-133 inhalation method etc, have been applied for the assessment of cerebral blood flow in cases with ICA occlusion. No previous report was found by the newly developed 123I-IMP in this connection. The purpose of the present study is first to demonstrate the feasibility of 123I-IMP planar brain scintigraphy and its semiquantitative analysis in 17 cases with ICA occlusion. After intravenous injection of 3 mCi of 123I-IMP, brain scintigrams were obtained from anterior, Towne, vertex, posterior, right lateral and left lateral views, and were recorded on magnetic tape and Poraloid films. Semiquantitative analysis was performed as a percent index of asymmetry (PIA) from the difference of each hemispheric count in the scintigrams by use of on-lined minicomputer system. Clinical manifestations of these 17 cases were, completed stroke in 10, TIAs in 4, and no neurological symptom in 3. 123I-IMP brain scintigrams demonstrated low flow lesion in 10 out of 10 completed stroke, in 2 out of 4 TIAs and normal perfusion in all cases with no neurological symptoms.(ABSTRACT TRUNCATED AT 250 WORDS)     

Regional cerebral blood flow, diaschisis, and steal after stroke

Regional CBF was measured by 133Xe inhalation in unilateral cerebral infarction, carotid TIAs, and normal volunteers. Regional CBF values were bilaterally and symmetrically reduced in patients measured within 3 weeks after stroke. Later, rCBF values returned toward normal in the contralateral hemisphere of patients with infarction and in both hemispheres with carotid TIAs. In cases with carotid occlusive disease, flow reduction was seen in the contralateral posterior cerebral artery distribution, with hyperemia in ipsilateral occipital lobe caused by interhemispheric steal. Brainstem-cerebellar flow values were increased following acute cerebral infarction if patients were alert but reduced if consciousness was impaired.     

Regional Cerebral Blood Flow,Diaschisis, and Steal After Stroke

Regional CBF was measured by ¹³³Xe inhalation in unilateral cerebral infarction, carotid TIAs, and normal volunteers. Regional CBF values were bilaterally and symmetrically reduced in patients measured within 3 weeks after stroke. Later, rCBF values returned toward normal in the contralateral hemisphere of patients with infarction and in both hemispheres with carotid TIAs. In cases with carotid occlusive disease, flow reduction was seen in the contralateral posterior cerebral artery distribution, with hyperemia in ipsilateral occipital lobe caused by interhemispheric steal. Brainstem-cerebellar flow values were increased following acute cerebral infarction if patients were alert but reduced if consciousness was impaired.     

Effect of nimodipine on cerebral blood flow and cerebrovascular reactivity after subarachnoid haemorrhage

The aim of the present study was to investigate the effect of nimodipine on autoregulation of cerebral blood flow (CBF), CO2 reactivity and cerebral oxygen metabolism (CMRO2) in patients with subarachnoid haemorrhage (SAH). Eight patients with severe SAH were studied with repeated CBF and CMRO2 measurements on the first day of the bleeding and after at least 12 h of treatment of nimodipine. An initial resting study, an autoregulation study and a hyperventilation study was performed. CBF was measured using the 133-Xenon intravenous method. CMRO2 was calculated as AVDO2 x CBF. Nimodipine did not significantly change CBF and CMRO2 in the initial resting study. After induced arterial hypotension intact autoregulation was found before as well as after treatment with nimodipine. Beneficial effects of nimodipine were found on CO2 reactivity and CMRO2 during hypotension that may be explained as a positive effect on cerebral ischaemia.     

Cerebral blood flow and CO2 reactivity in patients with transient ischemic attack]

To elucidate the changes in cerebral blood flow (CBF) and CO2 reactivity in patients with transient ischemic attack (TIA), 10 patients with TIA and 5 healthy adults (controls) underwent two consecutive CBF measurements (i.e. the first measurement during room air inhalation and the second measurement during 5%CO2 inhalation). Hemispheric mean CBF was determined by each CBF measurement using 133Xenon inhalation method. CO2 reactivity was evaluated by analysing delta CBF (= mean CBF during hypercapnea-mean CBF at rest) and delta CBF/delta PaCO2. The resting mean CBF values in the bilateral hemispheres (i.e. both of the affected and unaffected hemispheres) were significantly lower in TIA patients than controls (p less than 0.05). Inhalation of 5%CO2 significantly increased mean CBF in TIA patients bilaterally, however the mean CBF value during hypercapnea was again significantly lower in TIA patients than controls (p less than 0.05). CO2 reactivity in TIA patients was not significantly different from controls (p greater than 0.05). The result demonstrated that TIA patients have a chronic and global cerebral oligemia with normal CO2 reactivity. The chronic and global cerebral oligemia may develop a transient ischemic neurological symptom by being superimposed with local decrease of CBF.     

Assessment of cerebral haemodynamic reserve: correlation between PET parameters and CO2 reactivity measured by the intravenous 133 xenon injection technique.

Regional cerebral blood flow (CBF), oxygen utilisation, fractional oxygen extraction (OER) and cerebral blood volume (CBV) were measured by positron emission tomography (PET) in 21 patients with occlusive carotid artery disease. In the same patients, measurements of cerebral CO2 reactivity were performed using the intravenous xenon-133 technique. A significant correlation was found in symptomatic hemispheres between the CBF/CBV ratio and CO2 reactivity. Four patients had significant increases in OER and this was associated with a reduction in CBF/CBV ratio implying exhaustion of haemodynamic reserve. CO2 reactivity was reduced below 1.5% mm Hg in all four cases with raised OER but only in two cases with normal OER. In patients with CO2 reactivities above 1.5% mm Hg, OER was normal in all cases. It is concluded that measurements of CO2 reactivity provide a satisfactory method for assessing cerebral haemodynamic reserve.     

Cerebral hemodynamics measured with simultaneous PET and near-infrared spectroscopy in humans

Near-infrared spectroscopy (NIRS) enables continuous non-invasive quantification of blood and tissue oxygenation, and may be useful for quantification of cerebral blood volume (CBV) changes. In this study, changes in cerebral oxy- and deoxyhemoglobin were compared to corresponding changes in CBF and CBV as measured by positron emission tomography (PET). Furthermore, the results were compared using a physiological model of cerebral oxygenation. In five healthy volunteers changes in CBF were induced in a randomized order by hyperventilation or inhalation of 6% CO(2). Arterial content of O(2) and CO(2) was measured several times during each scanning. Changes in deoxyhemoglobin (deltaHb), oxyhemoglobin (deltaHbO(2)) and total hemoglobin (deltaHb(tot)) were continuously recorded with NIRS equipment. CBF and CBV was also determined in MRI-coregistered PET-slices in regions determined by the placement of the two optodes, as localized from the transmission scan. The PET-measurements showed an average CBV of 5.5+/-0.74 ml 100 g(-1) in normoventilation, with an increase of 29% during hypercapnia, whereas no significant changes were seen during hyperventilation. CBF was 51+/-10 in normoventilation, increased by 37% during 6% CO(2) and decreased by 25% during hyperventilation. NIRS showed significant increases in oxygenation during hypercapnia, and a trend towards decreases during hyperventilation. Changes in CBV measured with both techniques were significantly correlated to CO(2) levels. However, deltaCBV(NIRS) was much smaller than deltaCBV(PET), and measured NIRS parameters smaller than those predicted from the model. It is concluded that while qualitatively correct, NIRS measurements of CBV should be used with caution when quantitative results are needed.     

Long-term assessment of cerebral perfusion following STA-MCA by-pass in patients

A prospective study of mean hemispheric cerebral blood flow (CBF) correlated with clinical status has now been completed for the past 54 months. Thirty-eight patients underwent superficial temporal to middle cerebral artery (STA-MCA) by-pass. They were compared with 22 patients with similar arteriographic lesions and clinical symptoms, treated medically throughout the same interval of time. Assignment to either treatment group was not randomized but depended solely on choice of patient or treating physician. Both groups were matched for age, clinical symptoms, angiographic abnormalities, and CBF values. All patients had proximal occlusion of one internal carotid artery or intracranial occlusive disease of the internal carotid or middle cerebral arteries. CBF measurements and clinical evaluations were repeated at regular intervals up to 54 months following surgery or institution of medical treatment. Mean follow up interval after STA-MCA by-pass was 28.7 months and for medical treatment was 29.7 months. Mean hemispheric CBF values for STA-MCA patients became significantly increased 2 weeks after operation. After that, CBF flow values decreased. At 24 months after surgery, flow values for surgically treated patients were significantly higher than among those treated medically, although there were no differences in flow values between the two groups at 3, 6, 12, 36 and 48 months. Prospective clinical evaluations after STA-MCA by-pass were as follows: 12 (32%) improved with cessation of TIAs and/or neurological improvement, 16 (42%) remained unchanged, 7 (18%) deteriorated (due to new or recurrent strokes) and 3 (8%) expired. Clinical results were the same for medical treatment: 6 (27%) improved, 10 (46%) unchanged, 4 (18%) deteriorated due to new or recurrent stroke, and 2 (9%) expired.     

Comparison between the photoelectric method and H2 clearance method for measuring cerebrocortical blood flow in cats

The photoelectric method using carbon black as a nondiffusible tracer of blood was compared with the hydrogen clearance (H2) method in nine anesthetized cats. A photoelectric apparatus and H2 electrode were applied to a small region of the cerebral cortex (left ectosylvian gyrus) for simultaneous measurement of the regional CBF. The values of CBF(H2) and CBF(photoelectric) were 50.7 +/- 19.2 and 52.1 +/- 14.5 ml.100 g-1.min-1, respectively. CBF(H2) and CBF(photoelectric) were found to correlate well (r = 0.588, p less than 0.01) when changes in CBF were induced by CO2 inhalation, exsanguination, hyperventilation, and occlusion of the middle cerebral artery. The correlation between CBF(H2) and CBF(photoelectric) was much better in the case of intraindividual comparisons (r = 0.957, p less than 0.01). In addition to its merits in common with the H2 clearance method, such as handiness, low cost, and strict regionality, the photoelectric method displayed the following advantages: time-to-time measurements of CBF (less than 20 s), immediate display of the microcirculatory flow pattern, and simultaneous monitoring of cerebral blood volume. However, measurements from deep structures of the brain are better performed by the H2 method despite the disadvantage of the use of a potentially explosive gas.     

Vascular responses in cerebrovascular "Moyamoya" disease--evaluated by positron emission tomography

We investigated cerebral blood flow and metabolism, and cerebral vascular response in 9 patients with cerebrovascular Moyamoya disease or unilateral Moyamoya phenomenon using positron emission tomography (PET). The subjects consisted of 5 men and 4 women, and were from 9 to 60 years old. Five patients had bilateral occlusion in the carotid fork with Moyamoya vessels (fulfilled the criteria of cerebrovascular Moyamoya disease), and four patients had unilateral Moyamoya phenomenon. The PET scanner used was the HEADTOME III, of which spatial resolution in clinical use was 10 mm full width at half-maximum (FWHM) in the image plane. Cerebral blood flow (CBF), cerebral metabolic rate of oxygen (CMRO2), cerebral oxygen extraction fraction (OEF), and cerebral blood volume (CBV) were measured in resting state by the 15O-labelled gases steady state method in every patient and 22 normal controls (17 men and 5 women, and from 26 to 64 years old). Consecutively cerebral vascular responses were measured by H215O autoradiographic method in resting state, hypercapnia, hypocapnia, and hypertension. Forced hypercapnia, hypocapnia, and hypertension were achieved by 7% CO2 inhalation, hyperventilation, and venous infusion of angiotensin II, respectively. CMRO2 of the whole brain was significantly lower in patients than in normal controls (p less than 0.05), and CBV of the lentiform nucleus significantly increased in patients (p less than 0.01). This reflected Moyamoya vessels in the basal ganglionic regions. In 3 of 5 patients with bilateral Moyamoya vessels, CBF and CMRO2 in the symptomatic cerebral hemisphere were lower than that in the nonsymptomatic hemisphere.(ABSTRACT TRUNCATED AT 250 WORDS)     

CBF before and after extracranial-intracranial bypass surgery in patients with ischemic cerebrovascular disease studied with 133Xe-inhalation tomography

Cerebral blood flow (CBF) was studied by 133Xenon inhalation tomography in 22 patients with symptoms of ischemic cerebrovascular disease before and after establishment of an extracranial-intracranial bypass shunt. Selection of patients for shunting was based on angiographically demonstrated arterial occlusions and on the finding of focal low flow areas corresponding to the clinical symptoms, that consisted mainly of minor stroke with good remission and with or without subsequent TIAs. It was required that the area of low flow should clearly exceed the CT lesion present in practically all cases. Following surgery, the permanent neurologic deficits remained unchanged, while the TIAs stopped in all but one case. Two patients showed a definite increase of CBF in the low flow area while another two showed a questionable increase. All the other cases, 18 of the 22, showed an unchanged tomographic flow map with no trend towards diminution in extension or severity of the focal hypoperfused area. A persistent low flow in areas with no corresponding CT lesion following alleviation of a possible flow impediment is interpreted to represent an incomplete infarction or diaschisis.     

Cerebral blood flow, cerebral oxygen metabolism, cerebral glucose metabolism, and tissue pH in human acute cerebral infarction using positron emission tomography

It is necessary for treatment and deciding prognosis to make clear about changes of cerebral blood flow and metabolism in acute cerebral infarction. This preliminary PET study was designed to investigate physiological and biochemical changes in acute cerebral infarction by positron emission tomography (PET). PET studies were performed in six patients with acute cerebral infarction within 48 hours after onset of stroke using continuous inhalation of C15O2 for cerebral blood flow (CBF), 15O2 for cerebral metabolic rate for oxygen (CMRO2), 11CO for cerebral blood volume, the intravenous injection of 11C-dimethyloxazolidinedione for tissue pH and the intravenous injection of 18F-fluorodeoxyglucose for cerebral metabolic rate for glucose (CMRGlu). Metabolic coupling index (MCI) image was made from CBF image and CMRGlu image to investigate relation between CBF and CMRGlu. Also oxygen glucose index (OGI) image was made from CMRO2 image and CMRGlu image to investigate relation between CMRO2 and CMRGlu. Preliminary results demonstrate that reduction of CBF, CMRO2, and CMRGlu in the affected cortex except for reperfusion case. Increase of OER was recognized four of six cases. Patterns of MCI and OGI in the cortex which CMRO2 value is less than 65 mumol/100 g/min were different from those in the cortex which CMRO2 value is more than 65. MCI of the affected cortex (CMRO2 less than 65) decreased relative to that of the cortex (CMRO2 greater than or equal to 65). OGI of the affected cortex (CMRO2 less than 65) significantly decreased in comparison with that of the cortex (CMRO2 greater than or equal to 65).(ABSTRACT TRUNCATED AT 250 WORDS)     

Cerebral blood flow responses to inhaled carbon dioxide in schizophrenia

Carbon dioxide (CO2) is a potent cerebrovasodilator; even mild changes in CO2 are associated with marked changes in cerebral blood flow (CBF). We measured CBF before and after 5% CO2 inhalation in 19 medicated patients with schizophrenia and 16 normal volunteers. Another group of 16 volunteers had 2 CBF measurements under resting conditions. Although both patients and controls showed marked CBF increase during CO2 inhalation, the CBF response was significantly less in the patients. Change in CBF per mm of CO2 was lower in the patients. The second group of controls did not show significant differences between the 2 resting CBF measurements.     

Higher cerebral function and hemispheric blood flow during awake carotid artery balloon test occlusions

OBJECTIVES: Measures capable of detecting early alterations of brain function during acute cerebral ischaemia have not been adequately defined. Internal carotid artery (ICA) test occlusions provide a well controlled environment to investigate the effects of reversible acute hemispheric hypoperfusion on brain function. A continuous time estimation task was developed that reliably demonstrated alterations in higher cerebral function before development of any deficits in elementary neurological function during ICA balloon catheter test occlusions. In the present study, we hypothesised that alterations in our behavioural task would correlate significantly with absolute level of ipsilateral CBF. METHODS: Twenty five patients underwent awake ICA test occlusions during which sustained attention and ipsilateral CBF were measured simultaneously using our time estimation task and the intracarotid 133Xe washout method. Alteration in sustained attention was correlated with CBF after occlusion using Fisher's exact test. RESULTS: Deterioration in sustained attention was significantly associated with ipsilateral CBF below 30 ml/g/min (Fisher's exact test, p=0.047). Changes in individual patients' performance on the behavioural task correlated in real time with changes occurring either at the point of occlusion or at a specific threshold of induced hypotension. Sensitivity for our behavioural test in predicting CBF was 75%; specificity 70%. CONCLUSIONS: Monitoring sustained attention during carotid balloon test occlusions seems to be a sensitive means to detect decreases in CBF as measured by 133Xe washout. Correlation between higher cerebral function and CBF can allow more detailed investigations of physiological relations between cerebral haemodynamics and brain function in human conditions of cerebral ischaemia.