Cerebral hemodynamics and metabolism in subjects over 90 years of age

Database for physiologically based pharmacokinetic (PBPK) modeling: physiological data for healthy and health-impaired elderly

Physiologically based pharmacokinetic (PBPK) models have increasingly been employed in chemical health risk assessments. By incorporating individual variability conferred by genetic polymorphisms, health conditions, and physiological changes during development and aging, PBPK models are ideal for predicting chemical disposition in various subpopulations of interest. In order to improve the parameterization of PBPK models for healthy and health-impaired elderly (herein defined as those aged 65 yr and older), physiological parameter values were obtained from the peer-reviewed literature, evaluated, and entered into a Microsoft ACCESS database. Database records include values for key age-specific model inputs such as ventilation rates, organ volumes and blood flows, glomerular filtration rates, and other clearance-related processes. In total, 528 publications were screened for relevant data, resulting in the inclusion of 155 publications comprising 1051 data records for healthy elderly adults and 115 data records for elderly with conditions such as diabetes, chronic obstructive pulmonary disease (COPD), obesity, heart disease, and renal disease. There are no consistent trends across parameters or their associated variance with age; the gross variance in body weight decreased with advancing age, whereas there was no change in variance for brain weight. The database contains some information to inform ethnic and gender differences in parameters; however, the majority of the published data pertain to Asian (mostly Japanese) and Caucasian males. As expected, the number of records tends to decrease with advancing age. In addition to a general lack of data for parameters in the elderly with various health conditions, there is also a dearth of information on blood and tissue composition in all elderly groups. Importantly, there are relatively few records for alveolar ventilation rate; therefore, the relationship between this parameter and cardiac output (usually assumed to be 1:1) in the elderly is not well informed by the database. Despite these limitations, the database represents a potentially useful resource for parameterizing PBPK models for the elderly to facilitate the prediction of dose metrics in older populations for application in risk assessment.

Stroke risk and age do not predict behavioral activation of brain blood flow

Twenty-four neurologically normal subjects, 12 in their twenties and 12 in their sixties, were included in a protocol that studied the relationship of resting cerebral blood flow and cerebral blood flow activation by neuropsychological testing to age and stroke risk factors. Both age and a stroke risk index were predictive of a reduced resting cerebral blood flow. Despite this, cerebral blood flow activation relative to resting flow was preserved. Subclinical lesions of deep white matter are proposed to explain the apparently paradoxical result that resting cerebral blood flow is decreased by factors that damage cerebral vessels, while cerebral vascular reactivity is unimpaired.

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.

Cerebral blood flow and metabolic rate of oxygen, glucose, lactate, pyruvate, ketone bodies and amino acids

The cerebral blood flow (CBF) and cerebral metabolic rate (CMR) of oxygen, glucose, lactate, pyruvate, ketone bodies, and 24 amino acids were examined in 10 healthy subjects, five 21-24 and five 55-65 years old. The subjects were free from drugs. The results of psychometric and neurological examinations were negative. CBF was determined with the nitrous oxide method on the subjects who were awake and normocapnic and had fasted overnight. No differences were found between the young and the old groups except in arterial levels of four amino acids, viz. aspartic acid, methionine, lysine, and tryptophan. In the whole group of 10 subjects, a significant cerebral net uptake (expressed as median values in mumol X kg-1 X min-1) was found not only for oxygen (1719) and glucose (248), but also for acetoacetate (4.3), D-beta-hydroxybutyrate (6.2), arginine (2.0), leucine (5.2), and isoleucine (1.2). There was a significant net release of lactate (-28). CBF was positively correlated to the CMR of oxygen and D-beta-hydroxybutyrate. Arterial concentrations and CMR were positively correlated for ketone bodies, glutamic acid, proline and taurine. It is of particular interest that the whole group of healthy subjects showed a significant cerebral uptake of branched-chain and dibasic amino acids.

The EEG in centenarians

1. The EEGs of ten centenarians were described. 2. In most healthy centenarians, posterior dominant rhythms are within the lower part of the alpha range (average 8.62 c/sec). 3. Although slowing of the posterior dominant rhythm at age 100 is greater than in younger groups, there is no evidence in this study of a progressive decrease in frequency during the two decades between 80 and 100 years. 4. Most records of centenarians contained other abnormalities, either of diffuse slowing or of slow wave foci, the latter most often in the left temporal area. 5. The relationship of the observed EEG changes to the process of aging as distinct from reduced cerebral metabolism and blood flow resulting from disease is discussed.