Leenders KL, Perani D, Lammertsma AA, et alCerebral blood flow, blood volume and oxygen utilization: normal values and effect of age. Brain 113:27-47
ABSTRACT Regional cerebral blood flow (CBF), oxygen extraction ratio (OER), oxygen utilization (CMRO2) and blood volume (CBV) were measured in a group of 34 healthy volunteers (age range 22-82 yrs) using the 15O steady-state inhalation method and positron emission tomography. Between subjects CBF correlated positively with CMRO2, although the interindividual variability of the measured values was large. OER was not dependent on CMRO2, but highly negatively correlated with CBF. CBV correlated positively with CBF. When considering the values of all the regions of interest within a single subject, a strict coupling between CMRO2 and CBF, and between CBF and CBV was found, while OER was constant and independent of CBF and CMRO2. In 'pure' grey and white matter regions CMRO2, CBF and CBV decreased with age approximately 0.50% per year. In other regions the decline was less evident, most likely due to partial volume effects. OER did not change or showed a slight increase with age (maximum in the grey matter region 0.35%/yr). The results suggest diminished neuronal firing or decreased dendritic synaptic density with age.
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- "Due to the nature of our study, a dichotomous comparison between young and old subject-groups, we could not evaluate the pattern of age-related decreases in oxygen metabolism. Some earlier studies have found this decrease to be linear and starting at a young age [Leenders et al., 1990; Marchal et al., 1992] while others found the oxygen metabolism to remain stable up to 40 years of age, after which point it substantially declined [Devous, Sr. et al., 1986]. Future studies should include subjects across a wide range of ages to investigate this property. "
ABSTRACT: Blood oxygenation-level dependent (BOLD) magnetic resonance imaging signal changes in response to stimuli have been used to evaluate age-related changes in neuronal activity. Contradictory results from these types of experiments have been attributed to differences in cerebral blood flow (CBF) and cerebral metabolic rate of oxygen (CMRO2 ). To clarify the effects of these physiological parameters, we investigated the effect of age on baseline CBF and CMRO2 . Twenty young (mean ± sd age, 28 ± 3 years), and 45 older subjects (66 ± 4 years) were investigated. A dual-echo pseudocontinuous arterial spin labeling (ASL) sequence was performed during normocapnic, hypercapnic, and hyperoxic breathing challenges. Whole brain and regional gray matter values of CBF, ASL cerebrovascular reactivity (CVR), BOLD CVR, oxygen extraction fraction (OEF), and CMRO2 were calculated. Whole brain CBF was 49 ± 14 and 40 ± 9 ml/100 g/min in young and older subjects respectively (P < 0.05). Age-related differences in CBF decreased to the point of nonsignificance (B=-4.1, SE=3.8) when EtCO2 was added as a confounder. BOLD CVR was lower in the whole brain, in the frontal, in the temporal, and in the occipital of the older subjects (P<0.05). Whole brain OEF was 43 ± 8% in the young and 39 ± 6% in the older subjects (P = 0.066). Whole brain CMRO2 was 181 ± 60 and 133 ± 43 µmol/100 g/min in young and older subjects, respectively (P<0.01). Age-related differences in CBF could potentially be explained by differences in EtCO2 . Regional CMRO2 was lower in older subjects. BOLD studies should take this into account when investigating age-related changes in neuronal activity. Hum Brain Mapp, 2015. © 2015 Wiley Periodicals, Inc. © 2015 Wiley Periodicals, Inc.Human Brain Mapping 07/2015; DOI:10.1002/hbm.22891 · 6.92 Impact Factor
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- "Accurate exploration of our environment requires that we know both the spatial location and the relative timing of sensory information. Such abilities decline with age (Evans et al., 1992; Stevens and Choo, 1996) and reflect the overall physiological, structural, and metabolic changes that occur in the elderly (Raz et al., 2005; Terry et al., 1987; Leenders et al., 1990). Therefore in recent years there has been much interest in a number of reports showing that training can improve perceptual abilities even in adults (Gilbert et al., 2001; Seitz and Dinse, 2007; Citri and Malenka, 2008). "
ABSTRACT: High frequency electrical stimulation of an area of skin on a finger improves two-point spatial discrimination in the stimulated area, likely depending on plastic changes in the somatosensory cortex. However, it is unknown whether improvement also applies to temporal discrimination. Twelve young and ten elderly volunteers underwent the stimulation protocol onto the palmar skin of the right index finger. Somatosensory temporal discrimination threshold (STDT) was evaluated before and immediately after stimulation as well as 2.5h and 24h later. There was a significant reduction in somatosensory temporal threshold only on the stimulated finger. The effect was reversible, with STDT returning to the baseline values within 24h, and was smaller in the elderly than in the young participants. High frequency stimulation of the skin focally improves temporal discrimination in the area of stimulation. Given previous suggestions that the perceptual effects rely on plastic changes in the somatosensory cortex, our results are consistent with the idea that the timing of sensory stimuli is, at least partially, encoded in the primary somatosensory cortex. Such a protocol could potentially be used as a therapeutic intervention to ameliorate physiological decline in the elderly or in other disorders of sensorimotor integration. Copyright © 2015. Published by Elsevier Ireland Ltd.Clinical neurophysiology: official journal of the International Federation of Clinical Neurophysiology 07/2015; DOI:10.1016/j.clinph.2015.06.023 · 2.98 Impact Factor
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- "comparison, the brain is about 5% blood by volume (Leenders et al., 1990). Consequently, much more activity in a liver voxel is contained in the blood compartment. "
ABSTRACT: Kinetic analysis is a tool used to glean additional information from positron emission tomography (PET) data by exploiting the dynamics of tissue metabolism. The standard irreversible and reversible two compartment models used in kinetic analysis were initially developed to analyse brain PET data. The application of kinetic analysis to PET of the liver presents the opportunity to move beyond the generic standard models and develop physiologically informed pharmacokinetic models that incorporate structural and functional features in particular to the liver. In this paper, we develop a new compartment model, called the tubes model, which is informed by the liver׳s sinusoidal architecture, high fractional blood volume, high perfusion rate, and large hepatocyte surface area facing the space of Disse. The tubes model distributes tracer between the blood and intracellular compartments in more physiologically faithful proportions than the standard model, producing parametric images with improved contrast between healthy and neoplastic tissue.Journal of Theoretical Biology 11/2014; 365. DOI:10.1016/j.jtbi.2014.10.028 · 2.30 Impact Factor