scholarly journals Model of Blood–Brain Transfer of Oxygen Explains Nonlinear Flow-Metabolism Coupling During Stimulation of Visual Cortex

2000 ◽  
Vol 20 (4) ◽  
pp. 747-754 ◽  
Author(s):  
Manouchehr S. Vafaee ◽  
Albert Gjedde
Keyword(s):  
Blood Flow ◽  
Oxygen Consumption ◽  
Visual Cortex ◽  
Metabolic Rate ◽  
Oxygen Diffusion ◽  
Visual Stimulation ◽  
Blood Oxygenation ◽  
Nonlinear Flow ◽  
Diffusion Capacity ◽  
Positron Emission

The coupling between cerebral metabolic rate of oxygen (CMRO2) and blood flow (CBF) in response to visual stimulation was evaluated by means of a model of oxygen delivery. The model predicted a nonlinear relationship between stimulus-evoked changes of oxygen consumption and blood flow. The magnitude of the CMRO2/CBF ratio index ( IO2) was used to indicate the degree of flow-metabolism coupling prevailing in specific areas of the brain during physiological stimulation. Therefore, the index provided a measure of the blood oxygenation level dependent (BOLD) magnetic resonance contrast. To evaluate the changes of IO2 in response to visual stimulation, the model was applied to the effect of a changing flicker rate of a visual stimulus on the magnitudes of CBF, CMRO2, and oxygen diffusion capacity, in the human brain. Positron emission tomography (PET) was used to measure the CBF and the CMRO2 in 12 healthy volunteers who viewed a cross-hair (baseline) or a yellow-blue annular checkerboard reversing at frequencies of 1, 4, or 8 Hz. The magnitude of CBF in the primary visual cortex increased as a function of the checkerboard reversal rate and reached a maximum at the frequency of 8 Hz ( z = 16.0), while the magnitude of CMRO2 reached a maximum at 4 Hz ( z = 4.0). Therefore, the calculated IO2 was lower at 8 Hz than at 1 and 4 Hz, in contrast to the oxidative metabolic rate that reached its maximum at 4 Hz. The model explained the increase of oxygen consumption as the combined effect of increased blood flow and increased oxygen diffusion capacity in the region of visual activation.

scholarly journals Striatal and Cortical BOLD, Blood Flow, Blood Volume, Oxygen Consumption, and Glucose Consumption Changes in Noxious Forepaw Electrical Stimulation

2010 ◽  
Vol 31 (3) ◽  
pp. 832-841 ◽  
Author(s):  
Yen-Yu I Shih ◽  
Hsiao-Ying Wey ◽  
Bryan H De La Garza ◽  
Timothy Q Duong
Keyword(s):  
Blood Flow ◽  
Oxygen Consumption ◽  
Metabolic Rate ◽  
Blood Volume ◽  
Functional Imaging ◽  
Cerebral Blood Volume ◽  
Glucose Consumption ◽  
Blood Oxygenation ◽  
Cerebral Metabolic Rate ◽  
Positron Emission

Recent reports showed noxious forepaw stimulation in rats evoked an unexpected sustained decrease in cerebral blood volume (CBV) in the bilateral striatum, whereas increases in spike activity and Fos-immunoreactive cells were observed. This study aimed to further evaluate the hemodynamic and metabolic needs in this model and the sources of negative functional magnetic resonance imaging (fMRI) signals by measuring blood oxygenation-level-dependent (BOLD), cerebral-blood-flow (CBF), CBV, and oxygen-consumption (i.e., cerebral metabolic rate of oxygen (CMRO2)) changes using an 11.7-T MRI scanner, and glucose-consumption (i.e., cerebral metabolic rate of glucose (CMRglc)) changes using micro-positron emission tomography. In the contralateral somatosensory cortex, BOLD, CBF, CBV, CMRO2 ( n=7, P<0.05), and CMRglc ( n=5, P<0.05) increased. In contrast, in the bilateral striatum, BOLD, CBF, and CBV decreased ( P<0.05), CMRO2 decreased slightly, although not significantly from baseline, and CMRglc was not statistically significant from baseline ( P>0.05). These multimodal functional imaging findings corroborate the unexpected negative hemodynamic changes in the striatum during noxious forepaw stimulation, and support the hypothesis that striatal hemodynamic response is dominated by neurotransmitter-mediated vasoconstriction, overriding the stimulus-evoked fMRI signal increases commonly accompany elevated neuronal activity. Multimodal functional imaging approach offers a means to probe the unique attributes of the striatum, providing novel insights into the neurovascular coupling in the striatum. These findings may have strong implications in fMRI studies of pain.

scholarly journals Effects of Acetazolamide on Cerebral Blood Flow, Blood Volume, and Oxygen Metabolism: A Positron Emission Tomography Study with Healthy Volunteers

2001 ◽  
Vol 21 (12) ◽  
pp. 1472-1479 ◽  
Author(s):  
Hidehiko Okazawa ◽  
Hiroshi Yamauchi ◽  
Kanji Sugimoto ◽  
Hiroshi Toyoda ◽  
Yoshihiko Kishibe ◽  
...  
Keyword(s):  
Positron Emission Tomography ◽  
Blood Flow ◽  
Cerebral Blood Flow ◽  
Metabolic Rate ◽  
Blood Volume ◽  
Cerebral Blood Volume ◽  
Capillary Blood ◽  
Emission Tomography ◽  
Positron Emission ◽  
Capillary Blood Volume

To evaluate changes in cerebral hemodynamics and metabolism induced by acetazolamide in healthy subjects, positron emission tomography studies for measurement of cerebral perfusion and oxygen consumption were performed. Sixteen healthy volunteers underwent positron emission tomography studies with15O-gas and water before and after intravenous administration of acetazolamide. Dynamic positron emission tomography data were acquired after bolus injection of H215O and bolus inhalation of15O2. Cerebral blood flow, metabolic rate of oxygen, and arterial-to-capillary blood volume images were calculated using the three-weighted integral method. The images of cerebral blood volume were calculated using the bolus inhalation technique of C15O. The scans for cerebral blood flow and volume and metabolic rate of oxygen after acetazolamide challenge were performed at 10, 20, and 30 minutes after drug injection. The parametric images obtained under the two conditions at baseline and after acetazolamide administration were compared. The global and regional values for cerebral blood flow and volume and arterial-to-capillary blood volume increased significantly after acetazolamide administration compared with the baseline condition, whereas no difference in metabolic rate of oxygen was observed. Acetazolamide-induced increases in both blood flow and volume in the normal brain occurred as a vasodilatory reaction of functioning vessels. The increase in arterial-to-capillary blood volume made the major contribution to the cerebral blood volume increase, indicating that the raise in cerebral blood flow during the acetazolamide challenge is closely related to arterial-to-capillary vasomotor responsiveness.

scholarly journals Eccentricity Mapping of the Human Visual Cortex to Evaluate Temporal Dynamics of Functional T1ρ Mapping

2015 ◽  
Vol 35 (7) ◽  
pp. 1213-1219 ◽  
Author(s):  
Hye-Young Heo ◽  
John A Wemmie ◽  
Casey P Johnson ◽  
Daniel R Thedens ◽  
Vincent A Magnotta
Keyword(s):  
Blood Flow ◽  
Visual Cortex ◽  
Temporal Dynamics ◽  
Occipital Cortex ◽  
Hemodynamic Response ◽  
Proton Exchange ◽  
Blood Oxygenation ◽  
Human Visual Cortex ◽  
Tissue Metabolism ◽  
Oxygenation Level

Recent experiments suggest that T1 relaxation in the rotating frame ( T1ρ) is sensitive to metabolism and can detect localized activity-dependent changes in the human visual cortex. Current functional magnetic resonance imaging (fMRI) methods have poor temporal resolution due to delays in the hemodynamic response resulting from neurovascular coupling. Because T1ρ is sensitive to factors that can be derived from tissue metabolism, such as pH and glucose concentration via proton exchange, we hypothesized that activity-evoked T1ρ changes in visual cortex may occur before the hemodynamic response measured by blood oxygenation level-dependent (BOLD) and arterial spin labeling (ASL) contrast. To test this hypothesis, functional imaging was performed using BOLD, and ASL in human participants viewing an expanding ring stimulus. We calculated eccentricity phase maps across the occipital cortex for each functional signal and compared the temporal dynamics of T1ρ versus BOLD and ASL. The results suggest that T1ρ changes precede changes in the two blood flow-dependent measures. These observations indicate that T1ρ detects a signal distinct from traditional fMRI contrast methods. In addition, these findings support previous evidence that T1ρ is sensitive to factors other than blood flow, volume, or oxygenation. Furthermore, they suggest that tissue metabolism may be driving activity-evoked T1ρ changes.

Increased oxygen consumption in human visual cortex: response to visual stimulation

2009 ◽  
Vol 98 (2) ◽  
pp. 85-89 ◽  
Author(s):  
M. S. Vafaee ◽  
S. Marrett ◽  
E. Meyer ◽  
A. C. Evans ◽  
A. Gjedde
Keyword(s):  
Oxygen Consumption ◽  
Visual Cortex ◽  
Visual Stimulation ◽  
Human Visual Cortex

scholarly journals APOE4 genotype increases neuronal calcium signals and decreases pial arteriole responsivity and vasomotion in visual cortex of awake mice

2021 ◽  
Author(s):  
Orla Bonnar ◽  
Kira Shaw ◽  
Dori M Grijseels ◽  
Devin Clarke ◽  
Laura Bell ◽  
...  
Keyword(s):  
Blood Flow ◽  
Visual Stimulation ◽  
Late Onset ◽  
Vascular Dysfunction ◽  
Beta Amyloid ◽  
Blood Oxygenation ◽  
Vascular Density ◽  
Calcium Signals ◽  
Doppler Flowmetry ◽  
Acute Surgery

Vascular dysfunction is an early feature of late onset Alzheimer's disease (AD), preceding classic AD pathology such as beta amyloid accumulation and formation of hyperphosphorylated tau. Such vascular dysfunction may promote classic AD pathology by decreasing blood flow, impairing brain oxygenation and clearance of molecules such as beta amyloid. The main genetic risk factor for AD is the ϵ4 allele of APOE, which has been found to increase blood brain barrier permeability and decrease vascular density, as well as decrease blood flow and functional hyperaemia in anaesthetised mice undergoing acute surgery. These results suggest that APOE4 may confer AD risk via its effects on the vasculature. However, the responses of neurons and individual vessels have not been studied, so neurovascular relationships are unknown, and no previous studies have looked at awake mice. We therefore measured neurovascular responses at rest and in response to visual stimulation using 2 photon imaging of awake APOE3 and APOE4 targeted-replacement (APOE TR) mice that expressed the calcium indicator GCaMP6f in excitatory neurons, while labelling the vascular lumen with Texas Red dextran. In parallel, we measured cerebral blood flow, blood oxygenation and cerebral blood volume using combined laser Doppler flowmetry and haemoglobin spectrometry. Measurements were performed in mice aged between 3-4 months to 12-13 months. We found a milder vascular deficit in awake mice than previous studies that used an acute surgical preparation: capillary responses to visual stimulation were the same in APOE3 and APOE4 TR mice, leading to unimpaired functional hyperaemia. However, neuronal calcium signals during visual stimulation were significantly enhanced in APOE4 mice, while there was a marked decrease in pial arteriole responsiveness and vasomotion. This pattern of results was unaffected by age, suggesting that APOE4 expression creates a stable, but mildly altered neurovascular state that does not itself cause degeneration. However, these changes likely make the system more sensitive to subsequent insults; for example, weaker vasomotion could impair clearance of beta amyloid as it starts to accumulate, and therefore may help explain how APOE4 expression increases risk of developing AD.

scholarly journals Body mass scaling of passive oxygen diffusion in endotherms and ectotherms

2016 ◽  
Vol 113 (19) ◽  
pp. 5340-5345 ◽  
Author(s):  
James F. Gillooly ◽  
Juan Pablo Gomez ◽  
Evgeny V. Mavrodiev ◽  
Yue Rong ◽  
Eric S. McLamore
Keyword(s):  
Oxygen Consumption ◽  
Body Mass ◽  
Oxygen Diffusion ◽  
The Body ◽  
Activity Levels ◽  
Mass Dependence ◽  
Diffusion Capacity ◽  
Aerobic Activity ◽  
Mass Scaling ◽  
Consumption Rates

The area and thickness of respiratory surfaces, and the constraints they impose on passive oxygen diffusion, have been linked to differences in oxygen consumption rates and/or aerobic activity levels in vertebrates. However, it remains unclear how respiratory surfaces and associated diffusion rates vary with body mass across vertebrates, particularly in relation to the body mass scaling of oxygen consumption rates. Here we address these issues by first quantifying the body mass dependence of respiratory surface area and respiratory barrier thickness for a diversity of endotherms (birds and mammals) and ectotherms (fishes, amphibians, and reptiles). Based on these findings, we then use Fick’s law to predict the body mass scaling of oxygen diffusion for each group. Finally, we compare the predicted body mass dependence of oxygen diffusion to that of oxygen consumption in endotherms and ectotherms. We find that the slopes and intercepts of the relationships describing the body mass dependence of passive oxygen diffusion in these two groups are statistically indistinguishable from those describing the body mass dependence of oxygen consumption. Thus, the area and thickness of respiratory surfaces combine to match oxygen diffusion capacity to oxygen consumption rates in both air- and water-breathing vertebrates. In particular, the substantially lower oxygen consumption rates of ectotherms of a given body mass relative to those of endotherms correspond to differences in oxygen diffusion capacity. These results provide insights into the long-standing effort to understand the structural attributes of organisms that underlie the body mass scaling of oxygen consumption.

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