Computed tomography and positron emission transaxial tomography evaluations of normal aging and Alzheimer's disease

Senile dementia and Alzheimer's disease. Brain blood flow and metabolism

Dementia of Alzheimer type is not form of accelerated aging. Blood flow, oxygen consumption and glucose utilization of the normally aged brain are maintained unchanged from the 3rd to the 7th decade of life. Thereafter, these parameters may decrease. Brain blood flow and oxidative metabolism is reduced in dementia of Alzheimer type and thus is different from the aged-matched mentally healthy subjects. There is evidence that the predominant impairment among these parameters may occur in cerebral glucose metabolism. This disturbance may precede changes in cerebral oxygen consumption and blood flow. Cerebral hypometabolism of glucose is accentuated in the temporo-parietal cortex. This finding may be helpful in diagnosing dementia of Alzheimer type.

Abnormalities of regional brain metabolism in Alzheimer's disease and their relation to functional impairment

Resting brain metabolism in patients with Alzheimer's disease (AD) has consistently been demonstrated to be reduced. Moreover, the magnitude of the reduction is related to the severity of dementia. Positron emission tomography (PET), which provides regional metabolic rates for glucose in cross-sectional slices of brain, has demonstrated three alterations in AD that are related to functional deficits. First, whole brain metabolic rate is reduced, and these reductions are related to overall severity of dementia. Second, regional metabolic rates in the association cortices demonstrate relatively greater reductions than are observed in the primary sensory and motor cortices, corresponding to marked impairment of higher cognitive function and relative sparing of sensory and motor function. Third, regional metabolic rates in the association cortices demonstrate increased left-right asymmetry relative to controls. Greater metabolic asymmetry is accompanied by disproportionate neuropsychological deficits in either language or visuospatial function, depending on whether the left or right cerebral hemisphere, respectively, has a lower metabolic rate.

Longitudinal course of normal aging and progressive dementia of the Alzheimer's type: a prospective study of 106 subjects over a 3.6 year mean interval

Elderly, community residing subjects (N = 106; mean age = 70.6 +/- 6.02 years) with cognitive functioning consistent with normal aging or dementia of the Alzheimer's type (DAT), were followed over a 3.6 year mean interval (range = 2.78 to 5.12 years). All subjects were assessed at baseline on the Global Deterioration Scale (GDS), a global clinical instrument reflecting the continuum of cognitive dysfunction from normal aging to severe DAT. At follow-up subjects were reassessed with respect to mortality, institutionalization and clinical change, defined as at least a two-point change on the 7-point GDS. Our results suggest that patients at deterioration levels GDS greater than or equal to 4, are more likely to show negative outcomes, specifically, institutionalization (Ps less than .001), death (Ps less than .01), or, for the community residing remainder, clinical deterioration (Ps less than .05), than subjects from less impaired (GDS = 2 or GDS = 3) subject groups. Seventy-six per cent of subjects at deterioration levels four or greater (N = 34) had negative outcomes at follow-up, whereas ninety percent of subjects with deterioration levels less than four (N = 72) did not.

Cerebral blood flow and brain atrophy correlated by xenon contrast CT scanning

Correlations between cerebral blood flow (CBF) measured during stable xenon contrast CT scanning and standard CT indices of brain atrophy were investigated in the patients with senile dementia of Alzheimer type, multi-infarct dementia and idiopathic Parkinson's disease. Compared to age-matched normal volunteers, significant correlations were found in patients with idiopathic Parkinson's disease between cortical and subcortical gray matter blood flow and brain atrophy estimated by the ventricular body ratio, and mild to moderate brain atrophy were correlated with stepwise CBF reductions. However, in patients with senile dementia of Alzheimer type and multi-infarct dementia, brain atrophy was not associated with stepwise CBF reductions. Overall correlations between brain atrophy and reduced CBF were weak. Mild degrees of brain atrophy are not always associated with reduced CBF.

The effect of age on glucose and energy metabolism in brain cortex of rats

It is well documented that the mature human brain oxidizes only glucose to obtain energy under physiological, nonstarved conditions. Through adulthood to the beginning of senescence, the balance between oxygen and glucose consumption of the brain was found to be unchanged as the basis for energy production. Beyond the age of 70 yr, however, cerebral glucose consumption appears to decrease. In the present study, the effect of advancing age on glucose and energy metabolism in brain cortex of rats was investigated. The study was carried out in male Wistar rats, 6 (young adult), 12 (adult), 24 and 30 (both aged) mth of age. Male Wistar rats may be designated as being 'aged' from 24 mth of life onwards. Intermediates of glycolysis, tricarboxylic acid cycle and energy-rich compounds were measured by means of sensitive standard enzymatic methods under steady-state conditions of arterial normotension, normoxemia, normocapnia and normothermia in anesthesia with 0.5 vol% halothane and nitrous oxide/oxygen 70:30. The 12-mth-old adult rats served as controls. The glucose concentration in brain cortex was found to be about 1.5 times higher in 6-mth-old than in 12-mth-old animals but did not differ in the 12-, 24-, and 30-mth-old rats. Besides glucose, fructose-1,6-phosphate and ATP decreased from young adult to adult rats while pyruvate, malate and creatine phosphate diminish with advancing age. A tendency to reduction with aging was also evident in glucose-6-phosphate, fructose-1, 6-diphosphate, and lactate. The fall in substrate concentrations may be attributed to the reduced activity of enzymes acting in glucose breakdown. It is concluded that glucose and energy metabolism may diminish with the process of normal aging, but that the reduction is of only moderate extent.

Relations between neuropsychological and cerebral metabolic asymmetries in early Alzheimer's disease

Regional CMRglc (rCMRglc) values were determined with positron emission tomography (PET) in 10 patients with mild to moderate clinically diagnosed Alzheimer's disease (AD) and in 26 healthy controls. rCMRglc in frontal, parietal, and temporal association cortices were significantly more laterally asymmetrical in AD patients than in controls (p less than 0.05). Furthermore, lateral asymmetry of rCMRglc in AD patients but not in the control subjects correlated significantly with asymmetry of language and visuospatial functions such that lower left than right rCMRglc was associated with relatively greater impairment of language and vice versa. The results demonstrate that discrepancies between language and visuospatial deficits in patients with early AD are related to asymmetrical reductions in cerebral cortical glucose metabolism.

Cerebral blood flow and metabolism in normal human aging, pathological aging, and senile dementia

A review and a reappraisal are presented of earlier data on cerebral circulatory and metabolic studies in normal active elderly men (Group I) of mean age 71 years, compared with normal young subjects of mean age 21 years, conducted at the National Institutes of Health, Bethesda, MD, U.S.A., during 1956-1958. There was no significant difference in the mean CBF and cerebral metabolic rate for oxygen (CMRO2) values between the two populations; i.e., these important parameters did not fall with chronological aging per se. There was significant depression in the mean cerebral metabolic rate for glucose (CMRG) value (by approximately 23%) in the aged compared with the young. Newer methods using positron emission tomography and appropriate isotopes have confirmed these findings in normal aging in human subjects and experimental animals. As expected, MABP and cerebral vascular resistance (CVR) were significantly elevated in the normal aged. MABP was even more elevated in elderly hypertensive subjects, and the CVR more elevated in the subjects with arteriosclerosis (Group II), who also showed a small but significant fall in CBF and in internal jugular venous PO2. The CBF showed a more pronounced fall in senile aged patients with chronic brain syndrome (Group III), in whom the CMRO2 also showed a marked drop (by approximately 22%); the CMRG fell still further (approximately 40% of that in the young). Of the few aged subjects followed up after a lapse of 11 years by a repeat estimation of the same physiological and psychological parameters and of the EEG, most showed clear worsening, together with a fall in overall physical and intellectual performance, probably related to a rise in CVR and an increase in atherosclerosis with aging.(ABSTRACT TRUNCATED AT 250 WORDS)

Human brain glucose utilization and cognitive function in relation to age

Brain oxidative metabolism was examined with positron emission tomography and [18F]2-deoxy-D-glucose in 40 healthy men aged 21 to 83 years, under conditions of reduced visual and auditory stimulation. The mean cerebral metabolic rate for glucose (CMRglc) equaled 4.6 to 4.7 mg X 100 gm-1 X min-1 and did not correlate significantly with age (p greater than 0.05). Regional cerebral metabolic rates for glucose (rCMRglc) and Q ratios (rCMRglc/CMRglc), which had lower coefficients of variation than did rCMRglc, also did not correlate with age. Hyperfrontality of cerebral metabolism was absent at all ages. Age decrements were demonstrated in the error score on the Benton Revised Visual Retention Test and in the Performance Subtest scaled score of the Wechsler Adult Intelligence Scale (WAIS) but not in the Verbal Subtest scaled score of the WAIS. The cognitive test scores did not correlate with brain metabolic rates. The results indicate that brain oxidative metabolism, when measured under resting conditions with reduced sensory input, is not reduced in relation to age in healthy men. Furthermore, no significant relations between intelligence and resting cerebral metabolism are evident.

Circulating vitamins in Alzheimer's dementia as compared with other dementias

Blood levels of 12 vitamins were compared in 55 patients with Alzheimer's disease and 58 control subjects (10 intellectually alert, 12 depressed, 28 multi-infarct dementias, 8 with other specific dementias). No significant differences in vitamin blood levels were found between the Alzheimer's disease group and the control groups either individually or in total. Conventional parenteral vitamin treatment of seven patients with vitamin deficits did not benefit their cognitive state. Conventional vitamin malnutrition did not seem to contribute to the disability in these subjects.