[Intermittent focal cerebral ischemia in hypotension due to pacemaker syndrome]

A pacemaker syndrome manifested as transient sensoric aphasia in a 68-year-old woman with a VVI-pace-maker implanted after SA-block. The attack occurred during long-term blood pressure recording and Holter monitoring. Borderline hypotension was documented during ventricular pacing which induced a retrograde excitation of the atrium. Clinical investigations excluded any intracranial abnormality, any source of embolism or stenosis of extra- and intracranial cerebral arteries. Cerebral blood flow measurements revealed a significant increase during pacing at elevated heart rate. Therefore, a device for AV-sequential pacing was implanted and basic pacing rate was elevated. The present case report indicates that focal and not only global cerebral ischemia can be produced by an impairment of systemic hemodynamics due to hypotension and a pacemaker syndrome. Improvement of cerebral blood flow during pacing is an unexpected finding contrasting with the concept of autoregulation. In addition, pacemaker implantation should be discussed in patients with transient cerebral perfusion deficits if an improvement of cerebral blood flow is documented along with rising heart rate.

Time course of myocardial and cerebral blood flow during stable but hemodynamically compromising ventricular tachycardias. Laboratory investigations

Myocardial and cerebral blood flow were determined with radiolabeled microspheres in 20 Sprague-Dawley rats during sinus rhythm and during stable but hemodynamically compromising ventricular tachycardias. In addition, in 10 animals the measurements were performed at hypotension induced by exsanguination. In controls (n = 10), myocardial and cerebral blood flow were 5.14 +/- 0.6 and 1.03 +/- 0.3 ml/g per minute, respectively. The range of myocardial blood flow values was markedly enlarged after onset of tachycardia induced by epicardial pacing. The mean values of myocardial blood flow were 5.80 +/- 1.9 ml/g per minute (n.s.) after 1 min and 7.46 +/- 3.9 ml/g per minute (n.s.) after 5 min. Cerebral blood flow, however, significantly decreased after 1 min (0.57 +/- 0.1 ml/g per minute, P < 0.01) and after 5 min (0.71 +/- 0.3 ml/per minute, P < 0.05). In contrast, 1 min after exsanguination myocardial blood flow significantly decreased (4.03 +/- 1.5 ml/g per minute, P < 0.05) and recovered after 5 min (6.06 +/- 1.2 ml/g per minute, n.s.) Cerebral blood flow was below control levels 1 min (0.70 +/- 0.2 ml/g per minute, P < 0.05) after onset of hypotension due to exsanguination and returned to normal values with the next 4 min (0.90 +/- 1 ml/g per minute, n.s.). The results suggest that stable but hemodynamically compromising ventricular tachycardias markedly affect cerebral blood flow, whereas in most cases myocardial blood flow is maintained within normal ranges, or even increases. An augmented myocardial autoregulation can be concluded from the autoregulatory index. This maintainance of regulatory ability might be due to the increase of myocardial oxygen consumption at decreased coronary perfusion pressure during tachycardias. In contrast, during hypovolemic hypotension, myocardial as well as cerebral blood flow decreased. During stable but hemodynamically compromising ventricular tachycardias, cerebral blood flow initially drops drastically and recovers slowly over the next 5 min. This finding contrasts with the results of hypovolemic and drug-induced hypotension models.

[Cerebral circulation in patients with dilated cardiomyopathy and aortic valve diseases]

The present study was performed in order to investigate the effect of dilated cardiomyopathy and severe aortic valve disease on cerebral blood flow. Cerebral perfusion was determined in 39 healthy volunteers representing two control groups of different age (77.7 +/- 8.7; 79.7 +/- 8.1 ml/100 g/min), in 7 patients with dilated cardiomyopathy (64.0 +/- 4.7 ml/100 g/min), in 11 patients with severe aortic stenosis (71.1 +/- 14.8 ml/100 g/min), and in 6 patients with severe aortic regurgitation (54.6 +/- 5.8 ml/100 g/min). Regional cerebral blood flow was measured with the 133Xenon inhalation method. Cerebral blood flow in severe aortic regurgitation patients (p = 0.006) was markedly and significantly reduced versus controls, whereas in dilated cardiomyopathy patients (p = 0.197) and in patients with severe aortic stenosis (p = 0.111) cerebral blood flow was not significantly reduced. A chronic adaptation of cerebral blood flow to the profound reduction of cardiac output is assumed in dilated cardiomyopathy patients. The collapsing pulse and the maximal reduction of mean arterial blood pressure in severe aortic regurgitation patients cause the reduction of autoregulatory capacity of cerebral blood flow with subsequent decrease of brain perfusion. Measurement of cerebral blood flow appears to be suitable for evaluation of perfusion deficits due to cardiac abnormalities. It provides an additional parameter for estimating the indication of valve replacement in patients with aortic valve disease.

Reduction of cerebral blood flow with induced tachycardia in rats and in patients with coronary artery disease and premature ventricular contractions

A reduction of cerebral blood flow (CBF) was observed in experimental studies in rats immediately after the onset of parasystolic rhythm or with stable, but haemodynamically compromising, tachycardias. Based on these data and with a view to studying the effects of premature ventricular contractions (PVCs) on the cerebral circulation in humans, CBF was measured using the 133-Xenon inhalation method in 24 age matched human controls (group A1: age 58.5 +/- 6.2 years; group A2: 52.2 +/- 7.8 years) in nine coronary artery disease (CAD) patients without PVCs (B), in 11 CAD patients with frequent PVCs (> 300.h-1) (C) and in nine patients, after exclusion of CAD by angiography, also with frequent PVCs (> 300.h-1) (D). Holter monitoring was performed during the CBF measurement. CBF determined in the human control groups A1 and A2 was 79.9 +/- 9.9 ml.100 g.-1 min-1 and 81.5-13.0 ml. 100 g-1 min-1, respectively. CBF was 74.1 +/- 13.6 ml . 100 g.-1 min-1 (P = 0.267 vs A1) in group B, 65.8 +/- 11.8 ml.100 g-1 min-1 (P = 0.004 vs A1) in group C and 74.2 +/- 15.6 ml.100 g.-1 min-1 (P = 0.218 vs A2) in group D. The significant reduction of CBF in CAD patients with frequent PVCs suggests that arrhythmias have a significant impact on CBF. Non-CAD patients with frequent PVCs did not show significant CBF decreases in comparison with controls. One can hypothetize that an impairment of electrical postextrasystolic potentiation, due to premature ventricular depolarization, and hence myocardial dysfunction leads to CBF reduction in CAD patients. The CBF reduction with CAD could also reflect concomitant coronary and cerebral arteriosclerosis.

Evaluation of erectile dysfunction with the sympathetic skin response in comparison to bulbocavernosus reflex and somatosensory evoked potentials of the pudendal nerve

Sympathetic skin response (SSR) was investigated in 60 normal subjects (mean age 37.7 +/- 15.9) and 30 patients (mean age 47.2 +/- 12.0) referred from the department of urology for further electrophysiological evaluation of erectile dysfunction (ED). SSR was present in all normal subjects. Mean latency in the lower extremities was 2.16 +/- 0.20 sec. The coefficient of variance for repeated measurements in individual subjects was 10%. The latencies correlated slightly positively with the height of the subjects (r = 0.271, p < 0.05), but not with age. SSR in patients was compared to the bulbocavernosus reflex (BCR) and somatosensory evoked potentials (SSEP) of the pudendal nerve. All patients had a complete urological work-up with evaluation of hormonal function, pharmacotesting and Dopplersonography, as well as pharmacocavernosography and measurement of nocturnal penile tumescence if indicated. Six patients were diagnosed to have functional impotence, 4 dysfunctions were probably of vascular origin, 5 were neurogenic and 15 of the mixed type of vascular and neurogenic origin. Diabetes mellitus was the underlying disease in 14. In the two groups with neurogenic involvement (5 neurogen, 15 mixed) 14 of 20 patients had a pathological BCR, 12 had pathological SSEP and 9 had an absent SSR. Of these 9 patients two showed normal BCR and SSEP. Sensitivity for neurogenic dysfunction was 70% for the BCR, 60% for the BCR and SSEP, but that it detects some patients with erectile dysfunction, in whom other parameters are not pathological.(ABSTRACT TRUNCATED AT 250 WORDS)

Carotid artery stenosis and tachyarrhythmias: regional cerebral blood flow during high-rate ventricular pacing after one vessel occlusion in rats

The aim of the present study was to investigate the effect of hypotensive tachycardias on cerebral blood flow (CBF) in the presence of significant carotid stenosis. The experiments were performed in 57 spontaneously breathing rats during arterial normoxia and normocapnia anesthetized with thiobarbital. CBF was determined with radiolabeled microspheres during control conditions (normofrequent sinus rhythm, normotension; group A; n = 15), during high-rate left ventricular pacing (660-840 ppm) at normotension (group B1; n = 13), borderline hypotension (group B2; n = 15) and severe hypotension (group B3; n = 7). In addition, CBF measurements were performed during borderline hypotension induced by hemorrhage (group C; n = 7). Global CBF was 1.09 +/- 0.29 ml g-1 min-1 in group A, 0.93 +/- 0.40 in group B1, 0.68 +/- 0.31 in group B2 (P < 0.05 vs. A), 0.42 +/- 0.16 in group B3 (P < 0.05 vs. A) and 0.83 +/- 0.2 in group C. The highest CBF values were found in the cerebellum (A; 1.43 +/- 0.5 ml g-1 min-1) and the lowest in the postocclusive tissue of the ipsilateral hemisphere (A; 0.74 +/- 0.2 ml g-1 min-1). In all groups a 15% mean CBF reduction in the right hemispherical cerebrum in comparison to the left hemisphere was observed (P < 0.01). In contrast, hemispherical CBF of the cerebellum did not differ. The CBF blood pressure relationship shifted to lower CBF values, the threshold of CBF regulation shifted to higher blood pressure values in the tissue regions distal to the occluded vessel during hypotensive tachycardias.(ABSTRACT TRUNCATED AT 250 WORDS)

Specific recognition of arteriovenous malformations using Xenon-133 RCBF technique

With respect to the methodology of the atraumatic Xenon-133 technique the problem whether or not the proposed and introduced arterial artifact (AA) truely represents radiation from intravascular volume and to what extent it affects regional cerebral blood flow (rCBF) calculation is unresolved. We performed rCBF measurements in 22 patients with angiomas to clarify this issue in those patients known to have pathologically enlarged intracranial vessels. P4--the parameter suggested to represent the AA--as well as the conventional blood flow parameter for gray matter (F1) were compared to those of 50 volunteers using four criteria of abnormality: 1. intrahemispheric distribution, 2. interhemispheric differences of homologous detector pairs, 3. differences of mean hemispheric values, 4. visual evaluation of CBF maps. 19 of the 22 patients with angioma fulfilled at least two of the four criteria of abnormality, in comparison to 1 of 50 volunteers. P4's sensitivity for detecting angiomas proved to be higher (86%) than the perfusion parameters of gray matter. Focal increase of P4 proved to be highly specific for the presence of arteriovenous malformation (AVM, specifity 98%). A true arterial artifact exists in most instances in the presence of an AVM. Disregarding AA in the algorithm for calculation rCBF leads to an artificial overestimation of tissue flow in the region of the AVM.

Myocardial and cerebral hemodynamics during tachyarrhythmia-induced hypotension in the rat

BACKGROUND

The different vulnerabilities of heart and brain to hypotension and hypoxia have been discussed. Hemorrhagic or cardiogenic hypotension appears to cause greater cerebral lesions than drug-induced hypotension. The present model was established to evaluate myocardial blood flow (MBF) and function of the heart and cerebral blood flow (CBF) during tachyarrhythmias and to characterize the capacity of blood flow regulation in the heart and brain during tachycardia-induced borderline hypotension.

METHODS AND RESULTS

MBF and CBF were determined with radiolabeled microspheres. Coronary and central venous oxygen tensions were measured to estimate myocardial and cerebral oxygen consumption (MVO2 and CVO2). Measurements were performed in 62 Sprague-Dawley rats during sinus rhythm and high-rate left ventricular pacing and after hemorrhage. In control rats, MBF and CBF were 5.08 +/- 1.07 and 1.09 +/- 0.29 mL.g-1.min-1. MBF increased (7.21 +/- 1.98 mL.g-1.min-1, P < .05), whereas CBF decreased (0.99 +/- 0.29 mL.g-1.min-1, P = NS) during normotensive high-rate pacing. MBF and CBF dropped to 4.27 +/- 2.24 mL.g-1.min-1 (P = NS) and 0.68 +/- 0.29 mL.g-1.min-1 (P < .05) during pacing-induced borderline hypotension and decreased further during severe hypotension (1.77 +/- 0.81 mL.g-1.min-1, P < .01; 0.45 +/- 0.18 mL.g-1.min-1, P < .01). During borderline hypotension due to hemorrhage, MBF and CBF were 4.05 +/- 0.95 mL.g-1.min-1 (P = NS) and 0.71 +/- 0.23 mL.g-1.min-1 (P < .05). MVO2 and CVO2 were 72.7 +/- 15.4 and 12.7 +/- 3.3 mL.100 g-1.min-1 in control rats. MVO2 increased during normotensive pacing (100.3 +/- 27.4 mL.100 g-1.min-1, P = NS). Mean MVO2 was reduced during pacing-induced borderline hypotension (64.1 +/- 35.6 mL.100 g-1.min-1, P = NS) and severe hypotension (29.8 +/- 15.4 mL.100 g-1.min-1, P < .05). CVO2 decreased in correlation to CBF. Coronary and cerebrovascular resistance and autoregulation indexes indicated a maintenance of MBF regulation and a failure of CBF regulation during borderline hypotensive tachycardias. These results show a dissociation of MBF and CBF after onset of hypotensive tachycardias. Thus, brain tissue appears to be jeopardized at an earlier stage than myocardial muscle during tachyarrhythmias.

CONCLUSIONS

The proposed hypotension model is suitable to analyze tachyarrhythmia-induced hemodynamic changes and end-organ perfusion in the presence of myocardial dysfunction. It has the potential to test therapeutic strategies in the treatment of tachycardias.

Immersion and perfusion staining with 2,3,5-triphenyltetrazolium chloride (TTC) compared to mitochondrial enzymes 6 hours after MCA-occlusion in primates

2,3,5-triphenyltetrazolium chloride (TTC) is commonly applied in rodents and cats as a marker of infarcted tissue as early as 20 min after the onset of focal ischaemia. At this stage it is suggested that it reflects hypoperfusion rather than failure of respiratory chain. Immersion of brain slices in TTC solution is preferable in comparison to perfusion with TTC in order to ensure, that enough TTC enters the post-occlusion tissue. We compared immersion technique versus perfusion technique 6 h after permanent occlusion of the left middle cerebral artery in 18 baboons. In addition, we assessed the function of the respiratory chain enzymes of stained and unstained tissue in three baboons. The immersion technique revealed an absence of TTC staining limited to subcortical structures in two animals. In seven experiments TTC indicated involvement of almost the entire MCA territory. The extent of the ischaemic lesion indicated by the perfusion technique was very similar. Tissue samples from the presumed infarcted areas revealed normal mitochondrial function. We conclude that perfusion and immersion technique do not cause significant different ischaemic delineation 6 h after middle cerebral artery occlusion. TTC staining appears to be a reliable method of evaluating volume of infarction in primates. Furthermore, absence of TTC staining 6 h after stroke onset is caused by energy or oxygen depletion rather than by mitochondrial injury.

[Effect of frequent ventricular extrasystole on brain circulation in patients with coronary heart disease]

Animal experiments using the microsphere method indicate a 8% reduction of mean cerebral blood flow during parasystolic rhythm induced by ventricular pacing in comparison to a control group with sinus rhythm. The parasystolic rhythm causes changes of systemic arterial blood pressure, which are comparable to the hemodynamic effects of frequent premature ventricular contractions. Because a reduction of cerebral blood flow induced by frequent premature ventricular beats can be assumed by the results of the laboratory investigations, cerebral blood flow was determined in a clinical study in 19 coronary artery disease patients and in 11 healthy, age-adjusted volunteers using the 133Xenon-inhalation method, in order to investigate the effect of ventricular ectopics on cerebral perfusion. Simultaneously Holter monitoring was performed during cerebral blood flow measurements. Cerebral blood flow was estimated by the initial slope index, which is calculated from the early decay of the clearance curve, and by the mean cerebral blood flow index, which is calculated by the stochastic method. Grey matter blood flow is estimated by the two-compartment analysis. Cerebral blood flow in coronary artery disease patients is reduced versus controls. The initial slope indices were 45.2 +/- 5.1 s-1 and 57.4 +/- 7.2(-1), respectively (p < 0.01). In patients with frequent ventricular ectopic activity (739/h) an additional reduction of cerebral blood flow was observed. The initial slope index was 42.6 +/- 6.3 s-1 (p < 0.01). The reduction of cerebral blood flow in coronary artery disease patients is partially due to the coincidence of coronary and cerebral artery disease. Frequent ventricular premature contractions might cause an additional reduction.

[Sympathetic skin response--physiologic principles, normal values and clinical use]

Sympathetic skin reflex (SSR) was evaluated in the lower extremities of 60 normal volunteers aged 17 to 72 (mean age 38 +/- 16 years, 28 females, 32 males). SSR was obtainable in all volunteers and most often consisted of a biphasic wave with initial negative deflection. Mean latency was 2.16 +/- 0.20 s. Mean variation in a second repetitive measurement was 0.21 +/- 0.14 s. The SSR was not age- or sex dependent. There was a weak positive correlation of the SSR with the height of the volunteers (r = 0.271; p = 0.037). SSR was investigated in 39 patients with polyneuropathy (age 59 +/- 18). SSR was pathological in 51% on one or both legs. There was no correlation of the SSR to the aetiology nor to the type of lesion (axonal versus demyelinating polyneuropathy) nor to clinical symptoms. The applicability of the SSR is reviewed from the literature regarding polyneuropathy, erectile dysfunction, central degenerative diseases, multiple sclerosis, sympathetic reflex dystrophies, spinal and peripheral nerve lesions. SSR is briefly compared to alternative methods. SSR appears to be a reasonable method to describe a small section of the autonomic nervous system (sympathetic sudomotor function) and to calculate group differences. There appears to be no close correlation to any of the autonomic disturbances in individual patients.

Sympathetic skin response abnormalities in amyotrophic lateral sclerosis

The sympathetic skin response (SSR) was evaluated in 25 patients with amyotrophic lateral sclerosis (ALS) to assess for involvement of the autonomic nervous system. Twenty-two age-matched normals and 6 patients with muscular dystrophy served as controls. The SSR was intact in all normal volunteers and all patients with muscular dystrophy. The mean SSR latency in the ALS patients was prolonged compared to that of normals (2.29 +/- 0.28 versus 2.13 +/- 0.16 s, P < 0.05). The SSR was absent in one or both legs of 10 ALS patients (40%). Absence or abnormal latency of SSR in patients with ALS without clinical findings of autonomic failure suggests involvement of the autonomic nervous system in addition to the motor system.

PET study of changes in local brain hemodynamics and oxygen metabolism after unilateral middle cerebral artery occlusion in baboons

Local cerebral hemodynamics and oxygen metabolism were measured by positron emission tomography (PET) with the oxygen-15 (15O) steady-state method in baboons, immediately before (T0), 1 (T1), and 3-4 (T2) h after permanent middle cerebral artery occlusion (MCAO). At T1, there was a marked fall in both cerebral blood flow (CBF) and the CBF/cerebral blood volume (CBV) ratio in the occluded territory; these changes were sustained at T2, indicating stable reduction in cerebral perfusion pressure and lack of spontaneous reperfusion within this time range. Compared with preocclusion conditions, the oxygen extraction fraction (OEF) in the occluded territory was elevated at both T1 and T2, indicative of a persistent oligemia/ischemia for up to 3 h after MCAO. At T2, however, this OEF increase had lessened, concomitantly with a decline in cerebral metabolic rate of oxygen (CMRO2). This impairment of oxidative metabolism occurred earlier in the deep, compared with the cortical, MCA territories; in the latter, the CMRO2 was essentially preserved at T1 and only moderately reduced at T2, possibly suggesting prolonged viability. Finally, no significant changes in CBF or CMRO2 were observed in the contralateral MCA territory in this time range after MCAO. Despite methodological limitations (mainly partial volume effects related to PET imaging, which may have resulted in an underestimation of true changes and an overlooking of heterogeneous changes) our study demonstrates the feasibility of the combined PET-MCAO paradigm in baboons; this experimental approach should be valuable in investigating the pathophysiology and therapy of acute stroke.

CO2 reactivity in the ischaemic core, penumbra, and normal tissue 6 hours after acute MCA-occlusion in primates

Testing vasoreactivity with CO2 or Diamox is a common diagnostic procedure for the study of haemodynamics in stroke patients. CO2 reactivity (CO2R) was tested in 5 baboons six hours after permanent occlusion of the left middle cerebral artery (MCA) in order to attain new insights into interpretation of vasoreactivity tests. Using the microsphere method, cerebral blood flow (CBF) was determined in the various vascular territories as well as in the centre of the ischemia, the penumbra and the remaining MCA-tissue. CBF decreased significantly in the affected MCA in all animals and in addition in the contralateral cerebellum in one animal (p < 0.05). In addition, the left anterior cerebral artery (ACA) demonstrated a similar decrease. During hypercapnia CBF increased in all areas with the exception of the left, occluded MCA territory. Thus CO2 enhanced the difference between ischaemic and non-ischaemic tissue (i.e., tissue with diaschisis). Mean CO2 R was 3.37 ml/100 g/min/mmHg in the right MCA, 0.16 in the left. While the left ACA demonstrated a decreased perfusion during normocapnia in a similar range to the MCA territory, only CO2R was able to identify precisely the territory of the occluded vessel. CO2 R was zero or negative in the ischaemic core, close to zero in the penumbra and profoundly decreased in the remaining MCA tissue. The overall CO2 R of the MCA was almost zero, suggesting vasoparalysis in response to hypercapnia in the core and penumbra and exhausted CO2 R even in non-infarcted, non-penumbral tissue. One animal displayed a negative CO2 R equivalent to an intracerebral steal-phenomenon.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood flow and clinical course in patients with ischemic stroke without cerebrospecific therapy

To evaluate the course of cerebral tissue perfusion in patients with acute focal cerebral ischemia of the supratentorial compartment regional cerebral blood flow (rCBF) was measured on day 0, 7, 14, 21, and 28 in 132 patients using the 133 Xenon stationary inhalation technique. Ischemic events of the brainstem and hemorrhagic complications were excluded. The clinical status was evaluated using a modified Mathew score. In 34 patients no hemodilution, anti-edema therapy, or Ca(++)-antagonists were used but otherwise best medical therapy was applied. These patients represented the so called "natural course" of cerebral ischemia. In 30/34 patients on day 0 (within 16 hours after onset of symptoms) focal flow abnormalities were found in the involved side. In 9 of these 30 patients and in 1 of the remaining ischemia was observed in the contralateral side. rCBF above normal (relative luxury perfusion) despite pathologic neurologic findings was observed in 8/34 patients on day 3-7. Eight patients presented on day 3-7 with normal flow which later became ischemic again without evidence of another symptomatic episode. Correlation between severity of clinical findings and actual rCBF was low from day 3 to 7 but close on day 0. From day 14-21 hemispheric CBF correlated well with the total neurologic score but focal clinical findings had a lower correlation with focal flow as compared to day 0 and day 28. Contralateral ischemia was never found after day 14. In 5 other cases with "natural course" described above, a transitory decrease of rCBF below the initial ischemia level was found between day 3 and 14.(ABSTRACT TRUNCATED AT 250 WORDS)

Hemodilution in cerebral infarcts

To evaluate the effect of hypervolemic hemodilution on cerebral blood flow (CBF) two protocols have been performed: A) Ten randomly selected baboons have been treated with either low molecular dextrane (10 ml/kg) or normal saline (10 ml/kg). Regional cerebral ischemia was produced in all baboons. CBF increased selectively in the ischemic territory but not in the normally perfused tissue. B) Forty patients with acute cerebral ischemia were treated on day onset of symptoms with either dextrose, low molecular weight dextrane, hydroxyethyl starch or pentoxifylline. After intravenous infusion of the substances CBF increased only in the groups treated with dextrane- or starch-solution. Ischemic tissue benefitted more from hypervolemic hemodilution than normally perfused tissue. It was concluded that hypervolemic hemodilution leads to increase of cerebral blood flow, more in ischemic than in normally perfused brain tissue.

Effect of stable xenon on regional cerebral blood flow and the electroencephalogram in normal volunteers

We evaluated the effects of breathing 35% stable xenon in 65% oxygen on regional cerebral blood flow and the electroencephalogram in 20 normal volunteers. We measured blood flow in 32 brain regions over both hemispheres with the xenon-133 intravenous injection technique in two protocols. In the first protocol (n = 10), a baseline study was followed by a second study during 5 minutes of breathing stable xenon; in the other protocol (n = 8), the baseline study was followed by a second study after 5 minutes of breathing stable xenon. Two volunteers were excluded due to excessive movements during the inhalation of stable xenon. Some of the remaining 18 volunteers had varying alterations of consciousness accompanied by electroencephalogram changes. After stable xenon inhalation the electroencephalogram returned to normal within 2-3 minutes. During stable xenon inhalation mean +/- SD PECO2 dropped significantly from 39.4 +/- 4.4 to 33.3 +/- 5.4 mm Hg in the first protocol and from 39.4 +/- 2.6 to 34.8 +/- 4.1 mm Hg in the second protocol due to hyperventilation in 13 volunteers. Mean regional cerebral blood flow increased significantly by 13.5-25.4% without correction for PECO2. In the first protocol regional cerebral blood flow increased by greater than 12% in 11-14 (depending on the flow parameter) of the 20 hemispheres. In the second protocol regional cerebral blood flow increased by greater than 12% in 9-13 of the 16 hemispheres. We conclude that cautious interpretation is necessary in the assessment of regional cerebral blood flow with 35% xenon-enhanced computed tomography.

Effect of flunarizine on cerebral blood flow in baboons with or without focal cerebral ischaemia

In baboons with or without regional cerebral ischaemia (achieved by transorbital clip of the middle cerebral artery), cerebral blood flow (CBF) was measured using the intra-arterial Xenon-133 technique during steady-state, slight hypotension, and hypocapnia before and after administration of various doses of the calcium antagonist flunarizine (0.5 mg kg-1, 1.0 mg kg-1, or 10 micrograms kg-1 min-1 over 30 min). In normal baboons flunarizine did not alter CBF significantly, but at reduced blood pressure it increased CBF by 19.9% owing to exaggerated vasodilatory autoregulation. During hypocapnia flunarizine impaired the physiological reduction in CBF owing to reduced vasoconstriction. In baboons with cerebral ischaemia, CBF measurements were stable and comparable with those in a control group using an arterial clip unless flunarizine was added. In a group of five flunarizine-treated animals, mean CBF after positioning of the clip was higher than in the control group. However, the increase in mean CBF varied significantly between animals, indicating that a secondary reduction in CBF due to postischaemic pathophysiological processes was not prevented consistently.

Cerebral blood flow and rheologic alterations by hyperosmolar therapy in patients with brain oedema

Cerebral blood flow was assessed as initial slope index by 133-Xenon inhalation in 36 patients with brain tumours subjected to osmotic dehydration. The following solutions were employed: I. 20% mannitol, II. 40% sorbitol, III. 10% glycerol. Parameters affecting blood rheologic properties as Hct, plasma viscosity, red blood cell aggregation and fluidity were simultaneously studied. CBF which was reduced in the oedematous hemisphere with brain tumour increased during infusion and thereafter by mannitol or sorbitol, respectively. The blood flow response to glycerol was more delayed, less intense, but maintained longer. Hct and plasma viscosity were significantly reduced by all osmotic agents, while red blood cell fluidity fell and aggregation rose under mannitol. It is concluded that sorbitol (40%) is superior for emergency treatment with high ICP, whereas glycerol seems to be preferable to improve cerebral blood flow in oedematous brain.

An intravascular technique to occlude the middle cerebral artery in baboons

A technique is described for occlusion of the middle cerebral artery in the baboon by an intravascular approach. A torque catheter is introduced under fluroscopic control into the internal carotid artery by transfemoral catheterization. In conjunction with a guide wire an infusion microcatheter with increasing stiffness from the distal tip to the proximal shaft is positioned in the proximal part of the middle cerebral artery via the introducer system. N-Butyl-2-cyanoacrylate-monomers are injected into the microcatheter for permanent occlusion of the middle cerebral artery. The procedure was successfully completed in 21 out of 24 baboons. In 3 baboons the occlusion could not be achieved since the torque catheter could not pass proximal extreme tortuosities of possibly arterisclerotic internal carotid arteries. Infarcts in the 21 animals were confirmed by computerized tomography and/or autopsies in all animals.

Abnormalities of interictal cerebral perfusion in classic but not common migraine

Regional cerebral blood flow (rCBF) was measured as gray matter blood flow using the 133Xe inhalation technique in 50 pain-free headache patients: Eight patients having classic migraine with normal computed tomograms were matched to patients having common migraine and to normal controls. Interictal rCBF was determined at least 6 days after the last migraine attack and more than 24 hours before the next one. There were no between-group differences for age, PCO2, mean hemispheric blood flow, interindividual and intraindividual variabilities, hyperfrontality, or rCBF symmetry. However, when subjects were classified as to overall abnormal perfusion, a significant number (n = 4, p less than 0.04) of patients with classic migraine had rCBF abnormalities, whereas only one such patient was seen in the group with common migraine. Patients with classic migraine had abnormal mean hemispheric blood flows or disturbed intrahemispheric rCBF patterns. Oligemic and hyperemic regions topographically corresponded to the clinical symptoms in one patient. We conclude that during migraine attacks and interictally there is an instability of rCBF control in patients with classic but not common migraine.

Effect of stable xenon in room air on regional cerebral blood flow and electroencephalogram in normal baboons

Measurement of regional cerebral blood flow (rCBF) was performed in 6 healthy baboons during ventilation with 35% stable xenon in artificial air. rCBF was measured with the intraarterial xenon-133 method. EEG was recorded continuously. All CBF areas of interest over one hemisphere reacted in the same way. Mean flow increased during short-term exposure to stable xenon and decreased if stable xenon inhalation was continued for at least 24 minutes. EEG showed a decrease of alpha- and beta-wave patterns a short time after the start of stable xenon inhalation without further changes over the period when rCBF finally decreased. CO2 reactivity increased in most animals, and autoregulation to mild arterial hypotension was significantly impaired with increased flow. It is concluded that 35% stable xenon in artificial air increases rCBF after short-term exposure and decreases rCBF after longer exposure. EEG changes were noted after short-term exposure. rCBF and EEG recovered rapidly after the end of stable xenon inhalation.