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Linear coupling between cerebral blood flow and oxygen consumption in activated human cortex.

ABSTRACT: The aim of this study was to test the hypothesis that, within a specific cortical unit, fractional changes in cerebral blood flow (CBF) and cerebral metabolic rate of oxygen consumption (CMR(O(2))) are coupled through an invariant relationship during physiological stimulation. This aim was achieved by simultaneously measuring relative changes in these quantities in human primary visual cortex (V1) during graded stimulation with patterns designed to selectively activate different populations of V1 neurons. Primary visual cortex was delineated individually in each subject by using phase-encoded retinotopic mapping. Flow-sensitive alternating inversion recovery MRI, in conjunction with blood oxygenation-sensitive MRI and hypercapnic calibration, was used to monitor CBF and CMR(O(2)). The stimuli used included (i) diffuse isoluminant chromatic displays; (ii) high spatial-frequency achromatic luminance gratings; and (iii) radial checkerboard patterns containing both color and luminance contrast modulated at different temporal rates. Perfusion responses to each pattern were graded by varying luminance and/or color modulation amplitudes. For all stimulus types, fractional changes in blood flow and oxygen uptake were found to be linearly coupled in a consistent ratio of approximately 2:1. The most potent stimulus produced CBF and CMR(O(2)) increases of 48 +/- 5% and 25 +/- 4%, respectively, with no evidence of a plateau for oxygen consumption. Estimation of aerobic ATP yields from the observed CMR(O(2)) increases and comparison with the maximum possible anaerobic ATP contribution indicate that elevated energy demands during brain activation are met largely through oxidative metabolism.

SUBMITTER: Hoge RD

PROVIDER: S-EPMC17795 | biostudies-literature | 1999 Aug

REPOSITORIES: biostudies-literature

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Linear coupling between cerebral blood flow and oxygen consumption in activated human cortex.

Hoge R D RD Atkinson J J Gill B B Crelier G R GR Marrett S S Pike G B GB

Proceedings of the National Academy of Sciences of the United States of America 19990801 16

The aim of this study was to test the hypothesis that, within a specific cortical unit, fractional changes in cerebral blood flow (CBF) and cerebral metabolic rate of oxygen consumption (CMR(O(2))) are coupled through an invariant relationship during physiological stimulation. This aim was achieved by simultaneously measuring relative changes in these quantities in human primary visual cortex (V1) during graded stimulation with patterns designed to selectively activate different populations of V ...[more]

PMID: 10430955

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Project description:UnlabelledAlthough it has been believed that brown adipose tissue (BAT) depots disappear shortly after the perinatal period in humans, PET imaging using the glucose analog (18)F-FDG has shown unequivocally the existence of functional BAT in adult humans, suggesting that many humans retain some functional BAT past infancy. The objective of this study was to determine to what extent BAT thermogenesis is activated in adults during cold stress and to establish the relationship between BAT oxidative metabolism and (18)F-FDG tracer uptake.MethodsTwenty-five healthy adults (15 women and 10 men; mean age ± SD, 30 ± 7 y) underwent triple-oxygen scans (H2(15)O, C(15)O, and (15)O2) as well as measurements of daily energy expenditure (DEE; kcal/d) both at rest and after exposure to mild cold (15.5°C [60°F]) using indirect calorimetry. The subjects were divided into 2 groups (high BAT and low BAT) based on the presence or absence of (18)F-FDG tracer uptake (standardized uptake value [SUV] > 2) in cervical-supraclavicular BAT. Blood flow and oxygen extraction fraction (OEF) were calculated from dynamic PET scans at the location of BAT, muscle, and white adipose tissue. Regional blood oxygen saturation was determined by near-infrared spectroscopy. The total energy expenditure during rest and mild cold stress was measured by indirect calorimetry. Tissue-level metabolic rate of oxygen (MRO2) in BAT was determined and used to calculate the contribution of activated BAT to DEE.ResultsThe mass of activated BAT was 59.1 ± 17.5 g (range, 32-85 g) in the high-BAT group (8 women and 1 man; mean age, 29.6 ± 5.5 y) and 2.2 ± 3.6 g (range, 0-9.3 g) in the low-BAT group (9 men and 7 women; mean age, 31.4 ± 10 y). Corresponding maximal SUVs were significantly higher in the high-BAT group than in the low-BAT group (10.7 ± 3.9 vs. 2.1 ± 0.7, P = 0.01). Blood flow values were significantly higher in the high-BAT group than in the low-BAT group for BAT (12.9 ± 4.1 vs. 5.9 ± 2.2 mL/100 g/min, P = 0.03) and white adipose tissue (7.2 ± 3.4 vs. 5.7 ± 2.3 mL/100 g/min, P = 0.03) but were similar for muscle (4.4 ± 1.9 vs. 3.9 ± 1.7 mL/100 g/min). Moreover, OEF in BAT was similar in the 2 groups (0.51 ± 0.17 in high-BAT group vs. 0.47 ± 0.18 in low-BAT group, P = 0.39). During mild cold stress, calculated MRO2 values in BAT increased from 0.97 ± 0.53 to 1.42 ± 0.68 mL/100 g/min (P = 0.04) in the high-BAT group and were significantly higher than those determined in the low-BAT group (0.40 ± 0.28 vs. 0.51 ± 0.23, P = 0.67). The increase in DEE associated with BAT oxidative metabolism was highly variable in the high-BAT group, with an average of 3.2 ± 2.4 kcal/d (range, 1.9-4.6 kcal/d) at rest, and increased to 6.3 ± 3.5 kcal/d (range, 4.0-9.9 kcal/d) during exposure to mild cold. Although BAT accounted for only a small fraction of the cold-induced increase in DEE, such increases were not observed in subjects lacking BAT.ConclusionMild cold-induced thermogenesis in BAT accounts for 15-25 kcal/d in subjects with relatively large BAT depots. Thus, although the presence of active BAT is correlated with cold-induced energy expenditure, direct measurement of MRO2 indicates that BAT is a minor source of thermogenesis in humans.

Dataset Information

Linear coupling between cerebral blood flow and oxygen consumption in activated human cortex.

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Linear coupling between cerebral blood flow and oxygen consumption in activated human cortex.

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