Reduction in regional cerebral blood flow during normal aging in man

Cerebral hemodynamics in patients with moyamoya disease. A study of regional cerebral blood flow by the 133Xe inhalation method

Regional cerebral blood flow was measured by the 133Xe inhalation method in 20 young patients with moyamoya disease and five young healthy volunteers. Most patients showed low values of mean hemispheric blood flow in both hemispheres. Regional cerebral blood flow was at a low value in the upper frontal region and at an almost average value in the posterotemporal and occipital regions, which was different from the "hyperfrontal" pattern in healthy volunteers. Regional cerebral blood flow was reduced evenly by hyperventilation. By 5% CO2 inhalation, regional cerebral blood flow was increased in the temporooccipital regions and was nearly unchanged or decreased in the frontal region.

Regional cerebral blood flow in hemiparkinsonian patients. Emission computerized tomography of inhaled 133Xenon before and after levodopa

Regional and mean cerebral blood flow (rCBF, CBF) were measured by tomography of inhaled 133Xe in 18 hemiparkinsonian patients before and after levodopa (L-dopa). Baseline mean CBF was 55 ml/ (100 g X min) after an L-dopa-free interval of at least 10 h (range 10-13) and remained unchanged at 56.1 ml/ (100 g X min) after optimal clinical improvement was achieved by L-dopa. However, L-dopa reduced rCBF significantly (P less than 0.05) in the striatum contralateral to the symptomatic limbs. In patients with adverse reactions such as hyperkinesias and on/off symptoms, flow tended to increase bilaterally in striatum and often markedly in midline structures anatomically related to globus pallidus and thalamus. Compared with a normal population, the subcortical rCBF distribution was asymmetrical with a reduced flow (-18%) in the striatum contralateral to the symptomatic limbs and in midline structures anatomically related to globus pallidus and thalamus (-12%). Cortical CBF was inverse related to the duration of Parkinson's disease (P less than 0.05), probably reflecting an increasing mental deterioration with time.

Age-related reductions in cerebral vasomotor reactivity and the law of initial value: a 4-year prospective longitudinal study

A group of 51 neurologically normal, middle-aged and elderly volunteers (aged 35-86 years; mean age 63.24 years) with and without risk factors for stroke were given annual tests of cerebral vasomotor reactivity to assess any changes in the cerebral vascular capacitance associated with advancing age that might alter cerebral vasomotor reactivity. Cerebral vasomotor reactivity was estimated as the difference in bihemisphere gray matter CBF measured by the 133Xe inhalation method in the steady state breathing room air, followed by a second measurement during inhalation of 100% oxygen. There were significant and progressive reductions in cerebral vasomotor reactivity during the 4-year longitudinal study. Positive linear correlations were apparent between initial steady-state mean bihemisphere gray matter CBF levels and degrees of vasomotor reactivity, suggesting that the Law of Initial Value plays an important role. This should be borne in mind when analyzing scores of cerebral vasomotor reactivity. In the present communication, analysis of covariance was used to correct for influences of initial CBF levels on vasomotor responses tested while breathing pure oxygen.

Regional cerebral blood flow characteristics of the Sturge-Weber syndrome

Four patients with the Sturge-Weber syndrome were studied using the non-invasive Xenon-133 inhalation technique. All four patients had decreased regional cerebral blood flow in the area of their lesion, and in two patients who were subsequently tested with 5% carbon dioxide inhalation, impaired vasomotor reactivity was documented. Diminished regional cerebral blood flow is consistent with previously described nuclide flow studies which demonstrated a delay in the initial perfusion blush in the region of the abnormal vasculature. The focal decrease in blood flow was greatest in the most severely affected patient, but was also prominent in the two younger patients, both of whom have excellent neurologic function. These studies suggest that localized decrease in blood flow and vasomotor dysfunction in Sturge-Weber syndrome can precede the occurrence of severe neurologic impairment and extensive cerebral atrophy and possibly be a major contributing factor in progressive dysfunction. A secondary observation was that the blood flow in the unaffected hemisphere was significantly greater in two children compared to the two adults and was similar to the age-related differences reported for normal children and adults.

Leptomeningeal metastases: reduction in regional cerebral blood flow and cognitive impairment

Twenty-six patients with recently diagnosed leptomeningeal metastases underwent multiple diagnostic procedures in order to assess possible cerebral parenchymal involvement. Pretreatment studies included detailed neurological examination, computed tomographic scan, electroencephalogram, neuropsychological assessment, psychiatric evaluation, and measurement of regional cerebral blood flow (rCBF) using the xenon 133 inhalation technique. At diagnosis 50% of the patients had symptoms and signs of cerebral dysfunction. Computed tomographic scanning and electroencephalography detected abnormalities in 42% and 58%, respectively. Scoring was abnormally low on at least three neuropsychological tests in 93% of the patients. The mean rCBF was reduced in 88% of patients by 16.1 +/- 2.5% (mean +/- SEM; range, 8 to 45%) compared with age-matched controls (p less than 0.001). rCBF was reduced and cognition was impaired in patients with or without overt cerebral manifestations. Neuropsychological testing and rCBF measurement may be helpful in early detection of cerebral dysfunction in patients with leptomeningeal metastases.

Functional brain imaging

Recent advances in brain imaging have allowed a regional examination of brain function using multiple-probe inert gas studies of cerebral blood flow, positron or single photon tomography. Inert gas blood flow methods using inhalation or injection of 133xenon have been used with multiple-probe systems to measure blood flow in 1 to 2 cm regions of lateral cortex. The sensitivity of these systems to neurophysiological stimuli and neurological diseases have been demonstrated in numerous studies of the normal resting state, memory and learning, motor activity and sensory input, dementia, and aphasia, to name some. Positron tomography utilizes cyclotron-produced, short-lived positron-emitting isotopes to label biologically active radiopharmaceuticals. Using positron tomographs capable of quantitative three-dimensional imaging and appropriate tracer-kinetic models, regional metabolic function, including glucose, oxygen, amino acid metabolism, and receptor-binding can be regionally studied throughout the brain. Clinical studies have been performed in dementia, schizophrenia, affective disorders, resting states, and sensory stimulation. Positron tomography offers potentially the greatest variety of studies and highest temporal and spatial resolution of any of the presently available functional brain-imaging modalities. Its principal drawback is the very high cost. Single photon tomography uses gamma-emitting isotopes such as 123iodine and 133xenon to image regional cerebral blood flow and recently receptor function. Although at present it does not have the variety of studies or the technical capabilities of positron tomography, it does provide three-dimensional studies with 1 to 2 cm resolutions throughout the brain at a considerably lower cost than positron tomography. In the future, magnetic resonance studies of blood flow or phosphorus metabolism may add a fourth modality.

Cerebral blood flow measurement in cerebrovascular occlusive diseases

In order to evaluate cerebral blood flow (CBF) patterns among individual patients with increased statistical confidence, CBF measurements were carried out using the 133Xe-inhalation method and external head detectors. F1 values representing gray matter flow from 3 to 6 head detectors were averaged to form 16 different regions for each cerebral hemisphere. Normative values were obtained from 46 healthy volunteers, and data from individual regions were analyzed for absolute blood flow rates (ml/100g/min), for concordance between right and left hemispheres and as percent of mean hemispheric flow. CBF measurements were then carried out among 37 patients with cerebrovascular occlusive diseases, and results were compared with normative values. A high incidence of abnormal flows were detected among symptomatic patients with intracranial arterial stenosis or occlusion and those with extracranial internal carotid artery occlusion. By using the above method for data analysis, it was possible to delineate hypoperfused areas among these patients. Even though the 133Xe-inhalation method has inherent limitations, this is a practical and safe method for measurement of CBF which can provide reliable information useful for management of patients with cerebrovascular occlusive diseases, particularly when the results are presented with statistical confidence.

Regional cerebral blood flow and oxygen consumption in human aging

The oxygen-15 continuous inhalation technique and PET were used to study the age-related changes in regional CBF and CMRO2. Twenty-seven patients, aged 19 to 76 years, free of any history of cerebral disease and vascular risk factors were examined in "resting state." CBF, CMRO2 and oxygen extraction fraction (OEF) values were calculated in seven different brain structures as well as in mean gray matter. Left-right ratios were also computed for all symmetrical structures analyzed. Mean gray CBF, but not mean gray CMRO2, decreased linearly with age (p less than 0.02). However, when younger subjects (less than or equal to 50 yrs) were compared to older subjects (greater than 50 yrs), an age-related matched decrease in CBF and CMRO2 was observed in mean gray matter (18% and 17%, p less than 0.05) and in all gray matter regions analyzed, particularly in frontal, temporo-sylvian and parieto-occipital cortex. White matter CBF and CMRO2 remained remarkably stable with advancing age. Although the possibility of methodological artifacts was considered, we favor progressive loss of cortical neurones and/or diminished activity of those remaining to explain our findings. In addition, age-related changes in cognitive activities might also be involved.

The effects of chronic cigarette smoking on cerebrovascular responsiveness to 5 per cent CO2 and 100 per cent O2 inhalation

Effects of chronic cigarette smoking on cerebrovascular responsiveness of volunteers at risk for stroke and not at risk for stroke were evaluated by serial measurements of cerebral blood flow using the 133Xe inhalation method. Resting gray matter blood flow values (Fg) measured while breathing room air were compared with Fg values measured during inhalation of either 5 per cent CO2 in air or 100 per cent O2. Changes in Fg values during inhalation of 5 per cent CO2 were used to estimate cerebral vasodilator capacitance, and those during inhalation of 100 per cent O2 were used to estimate cerebral vasoconstrictor capacitance. Results indicated that chronic cigarette smokers have both reduced vasodilator (P less than 0.01) and reduced vasoconstrictor (P less than 0.02) capacitance when compared with nonsmokers of the same ages regardless of whether or not other risk factors for stroke were present. Vasodilator capacitance to 5 per cent CO2 inhalation was reduced among smokers compared with nonsmokers of the same age by 48 per cent in non-risk subjects and 56 per cent in risk-factored subjects, while vasoconstrictor capacitance to 100 per cent O2 inhalation among smokers was decreased by 24 per cent in non-risk subjects and 34 per cent in risk-factored subjects. In risk-factored subjects, combined effects of smoking and other risks appeared to be additive.

Age-matched normal values and topographic maps for regional cerebral blood flow measurements by Xe-133 inhalation

The relationship between normal aging and regional cerebral blood flow (rCBF) computed as initial slope index (ISI) by Fourier method was investigated in 105 right-handed healthy volunteers (132 measurements) by Xe-133 inhalation method, and age-matched normal values were calculated. Mean brain ISI values showed significant negative correlation with advancing age (r = 0.70, p less than 0.001), and the regression line and its 95% confidence interval was Y = -0.32 (X - 19) + 63.5 +/- 11.2 (19 less than or equal to X less than or equal to 80). Regional ISI values also showed significant negative correlations for the entire brain (p less than 0.001). The regional reductions of ISI values with advancing age were significantly greater in the regional distribution of the middle cerebral arteries bilaterally, compared with regions in the distribution of the other arteries (p less than 0.05). Therefore, measured rCBF values for patients must be compared to age-matched normal values for mean hemispheric and each region examined. Two kinds of topographic maps, brain map showing rCBF compared to age-matched normal values and showing hemispheric differences were made by dividing patient's values by the 95% confidence limits for age-matched normal values and displaying laterality index calculated as follows, respectively. (formula; see text) These maps were useful for evaluating significantly decreased or increased regions and regional hemispheric differences.

Effects of aging on cerebral blood flow in dementia

Regional cerebral blood flow values were measured utilizing the 133Xe inhalation method in patients with multi-infarct dementia (MID) (n = 22, age 67.4 +/- 9.8 years), in patients with senile dementia of Alzheimer type (SDAT) (n = 36, age 63.8 +/- 8.0) and in age-matched normal healthy volunteers (n = 50, age 67.5 +/- 9.3). Mean hemispheric gray matter flow values were significantly reduced in MID (P less than 0.01) and SDAT (P less than 0.01) patients compared with age-matched normal volunteers. In normal volunteers, mean flow values showed gradual declines with advancing age (r = -0.44, P less than 0.005). In MID patients there were significant decreases in flow values with advancing age (r = -0.43, P less than 0.05), but flow values were consistently lower than in age-matched normals. Reductions of flow were most evident in the distribution of both middle cerebral arteries. Unlike MID patients, patients with SDAT had diffusely reduced flow values over all age ranges without correlation with advancing age. Reductions of mean flow values in both dementia groups were significantly correlated with severity of dementia (P less than 0.05 for both groups). Cerebral blood flow reductions related to the aging process also contribute to decreased cerebral perfusion in patients with MID. This is not true in SDAT, where the disease process itself pre-empts cerebral blood flow reductions attributable to aging.

A regional metabolic contrast method for the study of brain pathology

The use of 2-deoxyglucose for the measurement of regional cerebral glucose utilization in both animals and humans has gained widespread application. An attractive aspect of regional brain glucose metabolism is its apparent correlation with functional activity in neurons. Animal experiments suggest that this relationship is altered in brain lesions and that barbiturate anesthesia may be employed in the detection of brain regions where uncoupling of metabolism and neuronal function has occurred. A functional metabolic contrast technique is described that will permit determination of regional metabolism that is specifically attributable to neuronal activity. Areas of potential clinical application are discussed.

Effects of smoking on regional cerebral blood flow in neurologically normal subjects

The chronic effects of smoking on regional cerebral blood flow (CBF), and on serum lipids and lipoprotein levels in neurologically normal subjects, were studied. CBF was studied by the 133-Xenon inhalation method and gray matter flow was calculated following the method of Obrist et al. One hundred and eleven subjects, who had no abnormalities in neurological examinations nor in CT scans, were divided into two groups: smokers (37) and non-smokers (74). Those who had a smoking index (Number of cigarettes/day) X (years of smoking history) greater than 200 were designated as smokers. The mean smoking index of smokers was 760. Sixty-two of the 74 subjects in the non-smoking group had never smoked, and the mean smoking index of non-smokers was 17. In the male, CBF was significantly lower in smokers than in non-smokers (mean CBF, 12.5% lower in smokers, p less than 0.001). Increased reduction of CBF with advancing age was also observed. Compared to non-smokers, CBF in smokers was found to be significantly lower than the expected age matched value. Serum high density lipoprotein cholesterol values in smokers were significantly lower, and total cholesterol levels significantly higher than in non-smokers. We concluded that smoking chronically reduces CBF. Decrease of CBF in smokers was probably due to advanced atherosclerosis which produces vascular narrowing and raised resistance in cerebral blood vessels.

Regional cerebral blood flow and lateralized hemispheric dysfunction in depression

Cerebral blood flow is known as an indicator of cerebral metabolism. Using the 133Xenon inhalation method, we studied the regional cerebral blood flow (r-CBF) in patients with different subtypes of depression and in remission. A left frontal hypervascularization and a right posterior hypovascularization were found in major depressives, compared to normal subjects, minor depressives, and normothymic bipolar patients. These results tend to confirm the existence of cerebral dysfunction in both hemispheres in major depression, as reported by other authors using different techniques.

Correlations between regional cerebral blood flow and age-related brain atrophy: a quantitative study with computed tomography and the xenon-133 inhalation method

One hundred and two subjects (40 men and 62 women) neither having a history of neurologic deficits nor showing organic lesions on computed tomographic examination of the brain were studied. Ages of the subjects ranged from 26 to 81 years. Regional cerebral blood flow was measured by the xenon-133 inhalation method, and the volume percentage of brain with respect to the cranial cavity (craniocerebral index) was calculated by means of computer programs. Regional cerebral blood flow was computed as the fast component of two-compartmental analysis and as the initial slope index value. The percentage of each subject's craniocerebral index in relation to the standard for subjects with non-atrophied brains (brain volume index) was calculated as the indicator of brain atrophy. Both the mean brain fast component values and the mean brain initial slope index values correlated closely with the brain volume index in the elderly (r = 0.60, r = 0.62; P less than 0.0001 in each correlation coefficient). Low cerebral blood flow values coincided with loss of brain substance in the final stage of age-related brain atrophy, but not in the intermediate stage.

The comparative effects of organic brain disease on cerebral blood flow and measured intelligence

Raw scores for cerebral blood flow (CBF), determined by xenon 133 inhalation, and for Wechsler Adult Intelligence Scale (WAIS) were measured in five groups of 12 subjects each: young normals, aged normals, and patients with cerebrovascular disease without dementia, dementia with cerebrovascular disease, and degenerative brain disease. Important differences were present in the raw data according to age and sex. When these were adjusted, a quadratic model revealed a highly significant (p less than 0.0001, r = 0.86) correlation between CBF and measured intelligence score. We interpret these findings to indicate that in dementing illnesses the WAIS raw score reflects the severity of the brain disorder, regardless of cause, and that CBF is reduced as a function of the severity rather than the cause of the abnormality.

Age effects on focal cerebral blood flow changes produced by a test of right-left discrimination

The effects of age on focal cerebral blood flow changes resulting from the cognitive processing during right-left discrimination were examined. The pattern and amount of cortical flow were comparable for young and middle-aged subjects and consisted of flow increases in bilateral frontal, parietal and occipital regions. Task performance was negatively related to activation from left parietal and occipital channels. The frontal activation and the parietal correlation were attributed to the middle-aged subjects experiencing increased emotional arousal and attention to the right-left discrimination task due to hypothesized differences in cognitive effort and style, and/or novelty of formal examination situations.

CBF measured by the Xenon-133 inhalation technique and quantified EGG (qEEG) investigations in patients with unilateral internal carotid artery occlusion

The CBF measurements (Xenon-133, inhalation technique) and quantified EEG (qEEG) recordings of 20 patients with cerebrovascular disturbances due to an unilateral internal carotid artery occlusion were evaluated. One of the advantages of the inhalation method is the possibility of the simultaneous CBF measurement of both hemispheres. Special attention is paid to the difference in flow between the two hemispheres. The results of this investigation are compared with the findings of the qEEG studies. Furthermore the relationship between these results and the clinical state of the patient was studied. Although computer analysis revealed EEG abnormalities in 80% of the cases no correlation could be found between the grade of EEG abnormalities and the clinical data of the patient and/or the CBF parameters. A correlation was found between the asymmetry as well as the absolute values of the hemispheric flow and the clinical state. The question whether CBF measurements can provide a better insight into the pathophysiology of the blood flow pattern in patients with unilateral internal carotid artery occlusions was considered as well.

Subarachnoid haemorrhage: older patients have low cerebral blood flow

Daily estimations of hemispheral cerebral blood flow using the xenon-133 inhalation technique was made in 116 patients during the first three weeks after subarachnoid haemorrhage. The patients' cerebral perfusion on average remained less than the normal perfusion expected for their age (based on a single estimation of cerebral blood flow in 67 volunteers). On each separate day after subarachnoid haemorrhage cerebral blood flow was inversely related to the patient's age. Older patients seem especially at risk of developing cerebral ischaemia after subarachnoid haemorrhage. The clinical outcome was more often unfavourable in older patients--that is, in those who tended to have the lowest cerebral blood flow. Present results support the view that episodes of low cerebral blood flow lead to a poor outcome after subarachnoid haemorrhage. Because of the risk of inducing cerebral ischaemia great care should be exercised by physicians administering hypotensive drugs to older patients after subarachnoid haemorrhage.

Sex difference in brain atrophy during aging; a quantitative study with computed tomography

Brain atrophy in 154 men and 147 women without neurologic deficits was quantitatively studied by means of computed tomography. The ages ranged from 20 to 79 years. The volume percentage of brain to cranial cavity (Craniocerebral Index, or CCI) was calculated by means of computer programs available in CT systems. The mean CCI in the 20-39 age group was constant at 98.4 per cent in men and 98.7 in women, and this was considered the standard for the CCI in subjects with nonatrophied brains. The percentage of each subject's CCI in relation to this standard in both sexes (Brain Volume Index, or BVI) was calculated as the indicator of brain atrophy. The normal value for BVI was therefore 100 per cent in both sexes. A clear difference was observed between men and women in the process of brain atrophy with increasing age. In men a significant reduction in BVI began in the sixth decade of life (P less than 0.01); thereafter, the decline was gradual and steady through the eighth decade (P less than 0.05). In women, a significant reduction in BVI began in the fifth decade (P less than 0.01) and remained relatively constant during the fifth and sixth decades but declined significantly again in the seventh and eighth decades. In both sexes, remarkable individual differences in brain atrophy were characteristic.

rCBF in patients with carotid occlusion. Resting and hypercapnic flow related to collateral pattern

rCBF was measured by 133Xenon inhalation technique in 39 patients with unilateral carotid artery occlusion in a subacute-chronic stage. Resting flow values (ISI) varied between 23.7 and 52.4 ml/100 g/min. An almost constant finding was interhemispheric asymmetry, the degree of which was correlated with the severity of the initial symptoms. An ischemic focus was an insignificant finding. The CO2 response was normal in patients with angiographic signs of circle of Willis collateral flow and without significant contralateral carotid stenosis, whereas it was impaired in patients with a retrograde ophthalmic flow or collateral flow via the circle of Willis and contralateral carotid stenosis greater than or equal to 50%. It is concluded that the CO2 response in useful rCBF variable and may be applied for analysis of collateral flow capacity in patients with carotid artery occlusion considered for bypass surgery.

Effects of human aging on patterns of local cerebral glucose utilization determined by the [18F]fluorodeoxyglucose method

The [18F]fluorodeoxyglucose (FDG) scan method with positron emission computed tomography was used to determine patterns of local cerebral glucose utilization (LCMRglu) in 40 normal volunteer subjects aged 18 to 78 years. Throughout all the studies, each subject was quiet, without movement, with eyes open and ears unplugged, exposed only to ambient room light and sound. For the entire group, whole brain mean CMRglu was 26.1 +/- 6.1 mumol 100 g-1 min-1 (mean +/- SD, n = 40). At age 78, mean CMRglu was, on the average, 26% less than at age 18, an alteration of the same order as the variance among subjects at any age. The gradual decline of mean CMRglu with advancing age occurred at a faster rate than was reported for mean cerebral oxygen utilization, possibly due to increasingly altered pathways for glucose utilization, or to increasing oxidation of ketone bodies or other alternative substrates. Glucose utilization in the hemispheres was symmetrical and mean CMRglu of overall cortex, caudate, and thalamus was equal in individuals at all ages. The slopes of decline with age were similar when LCMRglu was averaged over zones corresponding to centrum semiovale, caudate, putamen, and frontal, temporal, parietal, occipital, and primary visual cortex. However, the metabolic ratio of superior frontal cortex to superior parietal cortex declined with age, possibly due to selective degeneration of superior frontal cortex or to differences between age groups in the sensory and cognitive response to the study. These results should be useful in distinguishing age from disease effects when the FDG scan method is used.

The effects of activation procedures on regional cerebral blood flow in humans

Regional cerebral blood flow (r-CBF) can be measured using 133XE and collimated detectors. The radionuclide can be administered either by inhalation or intracarotid injection. Comparison of blood flow determinations at rest and during performance of an activity identifies those brain regions that become active during the performance of the activity. Relatively specific patterns of r-CBF are observed during hand movements, sensory stimulation, eye movements, speech, listening, and reading. Regional CBF changes during reasoning and memorization are less specific and less well characterized. It is clear that brain lesions affect r-CBF responses to various activities, but this effect has not been well correlated with functional deficits or recovery of function. Regional CBF measurement gives information about brain activity and the functional response to experimental manipulation. This approach may well add to our understanding of normal, as well as pathologic, brain functioning.