Age-related changes in regional cerebral blood flow and brain volume in healthy subjects

Interaction of age and APOE genotype on cerebral blood flow at rest

We investigated the impact of APOE genotype on cerebral blood flow (CBF) in older and younger adults. Forty cognitively normal older adults (16 ε4 carriers, 24 non-ε4 carriers) and 30 younger adults (15 ε4 carriers, 15 non-ε4 carriers) completed a resting-state whole-brain pulsed arterial spin labeling magnetic resonance scan. Main effects of aging were demonstrated wherein older adults had decreased gray matter CBF corrected for partial volume effects compared to younger adults in widespread brain regions. Main effects of APOE genotype were also observed wherein ε4 carriers displayed greater CBF in the left lingual gyrus and precuneus than non-carriers. An interaction between age and APOE genotype in the left anterior cingulate cortex (ACC) was characterized by reduced CBF in older ε4 carriers and increased CBF in young ε4 carriers. Increased CBF in the left ACC resulting from the interaction of age group and APOE genotype was positively correlated with executive functioning in young ε4 adults (r = 0.61, p = 0.04). Results demonstrate APOE genotype differentially impacts cerebrovascular function across the lifespan and may modify the relationship between CBF and cognition. Findings may partially support suggestions that the gene exerts antagonistic pleiotropic effects.

Differences between middle cerebral artery blood velocity waveforms of young and postmenopausal women

OBJECTIVE

We characterized middle cerebral artery (MCA) blood flow velocity waveforms measured by transcranial Doppler ultrasonography in premenopausal (26.6 +/- 6.1 years, mean +/- SD) and postmenopausal (54.0 +/- 3.6 years) women, of whom six were receiving hormone therapy (PM-HT) and seven were not (PM-non-HT). We hypothesized that feature points on MCA waveforms are altered in postmenopausal women compared with those in young women.

DESIGN

A short protocol involved maintaining end-tidal PO2 at euoxia (88 mm Hg) and end-tidal PCO2 at 1.5 mm Hg above eucapnic values using a dynamic end-tidal forcing system. Doppler data for the velocity spectral outline (Vp) were collected every 10 ms, and velocity waveform analyses were done on a beat-by-beat basis. Waveform features were identified over each cardiac cycle, including the average Vp (VCYC), maximum acceleration (AMAX), and the ratio of the velocity at the reflected wave and the velocity at peak systole (VR:VMAX).

RESULTS

VCYC was unchanged between premenopausal and postmenopausal women (69.4 +/- 9.6 and 67.5 +/- 11.1 cm/s, respectively). AMAX was significantly higher (P = 0.007) in premenopausal women (987.9 +/- 280.7 cm/s) compared with postmenopausal women (743.1 +/- 100.3). Conversely, VR:VMAX was significantly smaller (P < 0.001) in premenopausal women (0.90 +/- 0.09) compared with postmenopausal women (1.11 +/- 0.05). In postmenopausal women, the reflected wave is higher than the maximum velocity at peak systole, suggesting the presence of a shoulder in the MCA waveform.

CONCLUSIONS

Further investigations are required to assess whether this waveform analysis can provide insight into pathophysiologic changes in cerebral hemodynamics with aging.

Carotid atherosclerosis is associated with brain atrophy in Japanese elders

BACKGROUND

The relation between atherosclerosis and brain atrophy remains unclear in patients with risk factors for cardiovascular diseases.

OBJECTIVE

This study was performed to clarify the relation between brain atrophy and carotid atherosclerosis.

METHODS

A total of 142 patients (78 women and 64 men, mean age 74 years) with no neurologic disturbances were studied. Brain atrophy was evaluated on the basis of the brain atrophy index (BAI, BAI = brain parenchyma/intracranial space A 100%), calculated by means of digitized computed tomographic scans obtained at the level of the basal ganglia. Carotid atherosclerosis was evaluated on the basis of the plaque score (PS), defined as the sum of all plaque heights in both carotid arteries, intima-media thickness (IMT), and vessel diameter (VD) of the common carotid artery as assessed by ultrasonography.

RESULTS

Age negatively correlated with BAI in both men (r = -0.587, p < 0.001) and women (r = -0.724, p < 0.001). PS of the carotid artery also negatively correlated with BAI in men (r = -0.502, p < 0.001) as well as women (r = -0.480, p < 0.001). VD and IMT of the right carotid artery negatively correlated with BAI in women (VD; -0.256, p < 0.05, IMT; -0.216, p < 0.05) but not in men. Other characteristics were unrelated to BAI. Multiple regression analysis showed that age and PS were independent predictors of brain atrophy in both sexes. The percentage of variance of BAI values explained by this model in women (51.9%) was much greater than that in men (35.5%).

CONCLUSION

Carotid atherosclerosis may be a useful morphological index of brain atrophy.

Voxel-based morphometry of human brain with age and cerebrovascular risk factors

The objectives of this study were to evaluate the correlations of the volumes of the gray matter and white matter with age, and the correlations of the tissue probabilities of the gray matter and white matter with age and several cerebrovascular risk factors. We obtained magnetic resonance (MR) images of the brain and clinical information from 769 normal Japanese subjects. We processed the MR images automatically by correcting for inter-individual differences in brain size and shape, and by segmenting the MR images into the gray matter and white matter. Volumetry of the brain revealed a significant negative correlation between the gray matter volume and age, which was not observed between white matter volume and age. Voxel-based morphometry showed that age, systolic blood pressure, and alcohol drinking correlated with the regional tissue probabilities of the gray matter and white matter.

Neuroanatomical database of normal Japanese brains

To develop a high-resolution in vivo human neuroanatomy database for Japanese brains, a data set on 1547 normal subjects between the ages of 16 and 79 years has been collected. First, we determined individual reference brains of normal Japanese for each age and gender group. We found there exists cross-generational changes in brain shape, that is, the young generation has a shorter and wider brain than the older generation. Second, we determined the effect of aging on the volume of gray matter and white matter by voxel based morphometry. A significant negative correlation between the gray matter volume and age was observed. We assume that this kind of database is quite useful to investigators who are engaged in basic neuroscience, clinical diagnostics and evaluation of neuropsychiatric disorders in patients.

Magnetic resonance abnormalities and cardiovascular disease in older adults. The Cardiovascular Health Study

BACKGROUND AND PURPOSE

Cerebral magnetic resonance imaging often detects abnormalities whose significance is unknown. The prevalence and correlates of findings such as ventricular enlargement, sulcal widening, and increased white matter signal intensity were examined in 303 men and women aged 65 to 95 years participating in a multicenter study of cardiovascular disease.

METHODS

Cerebral magnetic resonance imaging was performed and interpreted according to a standard protocol, and findings were correlated with measures of cardiovascular disease and its risk factors.

RESULTS

Measures of cerebral atrophy increased with age and were greater in men than in women (each P < .01). Ventricular enlargement and sulcal widening were associated with prior stroke, hypertension, diabetes, and white race (each P < .03). Extent of white matter hyperintensity was associated with age, prior stroke, hypertension, and use of diuretics (each P < .004). On multivariate analysis, age, male gender, white race, and prior stroke retained strong associations with increased ventricular and sulcal scores. After adjustment for age, prior stroke, and other risk factors, white matter hyperintensity was associated with atherosclerosis as measured by increased internal carotid artery thickness on ultrasound.

CONCLUSIONS

Cerebral atrophy and white matter hyperintensity are common in the elderly and are associated with age, prior stroke, and known cardiovascular risk factors. Though these findings have been suggested to represent normal aging, their wide variability and associations with cardiovascular disease argue against their inevitability with advancing age and support the need to identify modifiable risk factors for these abnormalities.

Periventricular hyperintensity on magnetic resonance imaging correlated with brain ageing and atrophy

Fifty-two patients with cerebrovascular risk factors without neurological abnormalities were reviewed with respect to periventricular hyperintensity (PVH) on T2-weighted magnetic resonance imaging (MRI); brain atrophy was also assessed by CT and T1-weighted MRI. Extensive PVH showed a stronger correlation with age-related atrophy than mild or absent PVH. The relative volume of brain affected by PVH, calculated by computer, also correlated with brain atrophy, especially ventricular enlargement. The effects of PVH on brain ageing and atrophy is discussed.

CBF measured by Xe-CT: approach to analysis and normal values

Normal reference values and a practical approach to CBF analysis are needed for routine clinical analysis and interpretation of xenon-enhanced computed tomography (CT) CBF studies. We measured CBF in 67 normal individuals with the GE 9800 CT scanner adapted for CBF imaging with stable Xe. CBF values for vascular territories were systematically analyzed using the clustering of contiguous 2-cm circular regions of interest (ROIs) placed within the cortical mantle and basal ganglia. Mixed cortical flows averaged 51 +/- 10ml.100g-1.min-1. High and low flow compartments, sampled by placing 5-mm circular ROIs in regions containing the highest and lowest flow values in each hemisphere, averaged 84 +/- 14 and 20 +/- 5 ml.100 g-1.min-1, respectively. Mixed cortical flow values as well as values within the high flow compartment demonstrated significant decline with age; however, there were no significant age-related changes in the low flow compartment. The clustering of systematically placed cortical and subcortical ROIs has provided a normative data base for Xe-CT CBF and a flexible and uncomplicated method for the analysis of CBF maps generated by Xe-enhanced CT.

Gender differences in age effect on brain atrophy measured by magnetic resonance imaging

A prospective sample of 69 healthy adults, age range 18-80 years, was studied with magnetic resonance imaging scans (T2 weighted, 5 mm thick) of the entire cranium. Volumes were obtained by a segmentation algorithm that uses proton density and T2 pixel values to correct field inhomogeneities ("shading"). Average (+/- SD) brain volume, excluding cerebellum, was 1090.91 ml (+/- 114.30; range, 822.19-1363.66), and cerebrospinal fluid (CSF) volume was 127.91 ml (+/- 57.62; range, 34.00-297.02). Brain volume was higher (by 5 ml) in the right hemisphere (P less than 0.0001). Men (n = 34) had 91 ml higher brain and 20 ml higher CSF volume than women (n = 35). Age was negatively correlated with brain volume [r(67) = -0.32, P less than 0.01] and positively correlated with CSF volume (r = 0.74, P less than 0.0001). The slope of the regression line with age for CSF was steeper for men than women (P = 0.03). This difference in slopes was significant for sulcal (P less than 0.0001), but not ventricular, CSF. The greatest amount of atrophy in elderly men was in the left hemisphere, whereas in women age effects were symmetric. The findings may point to neuroanatomic substrates of hemispheric specialization and gender differences in age-related changes in brain function. They suggest that women are less vulnerable to age-related changes in mental abilities, whereas men are particularly susceptible to aging effects on left hemispheric functions.

Regional cerebral blood flow measurements in the diagnosis of dementia

The Xenon-133 regional cerebral blood flow technique (rCBF) was used to assess cortical perfusion in a group of 15 elderly patients (mean age = 79.1, SD = 8.7) with a probable diagnosis of Dementia of the Alzheimer type (DAT). Nine had mild DAT and six were in the moderate stages of DAT. These patients were compared with 15 age and sex matched normal elderly controls (mean age = 75.1, SD = 5.6). RCBF was measured in each patient and control at rest with eyes closed. The DAT patients had significantly lower mean global CBF than normal controls (t = -4.63, p less than 0.0001). In addition, a further 15 normal elderly subjects aged 60 to 92 were assessed and combined with the original 15 to allow calculation of a normal range of rCBF for elderly individuals. Seventy-three per cent of the DAT patients fell below the lower limit of the normal range (39.3 - 59.3 ISI units). These results show the possible usefulness of rCBF as an aid in the diagnosis of early DAT.