scholarly journals Relation between Cerebral Blood Flow and Metabolism Explained by a Model of Oxygen Exchange

2003 ◽  
Vol 23 (5) ◽  
pp. 536-545 ◽  
Author(s):  
Romain Valabrègue ◽  
Agnès Aubert ◽  
Jacques Burger ◽  
Jacques Bittoun ◽  
Robert Costalat
Keyword(s):  
Blood Flow ◽  
Cerebral Blood Flow ◽  
Experimental Studies ◽  
Tissue Oxygen ◽  
Tight Coupling ◽  
Cerebral Activation ◽  
Temporal Shape ◽  
Physiologic Parameters ◽  
Experimental Works ◽  
Physiologic Model

The cerebral blood flow (CBF) and cerebral metabolic rate of oxygen (CMRO2) are major determinants of the contrast in functional magnetic resonance imaging and optical imaging. However, the coupling between CBF and CMRO2 during cerebral activation remains controversial. Whereas most of the previous models tend to show a nonlinear coupling, experimental studies have led to conflicting conclusions. A physiologic model was developed of oxygen transport through the blood–brain barrier (BBB) for dynamic and stationary states. Common model simplifications are proposed and their implications for the CBF/CMRO2 relation are studied. The tissue oxygen pool, the BBB permeability, and the hemoglobin dissociation curve are physiologic parameters directly involved in the CBF/CMRO2 relation. We have been shown that the hypothesis of a negligible tissue oxygen pool, which was admitted by most of the previous models, implies a tight coupling between CBF and CMRO2. By relaxing this hypothesis, a real uncoupling was allowed that gives a more coherent view of the CBF/CMRO2 relation, in better agreement with the hypercapnia data and with the variability reported in experimental works for the relative changes of those two variables. This also allows a temporal mismatch between CBF and CMRO2, which influences the temporal shape of oxygenation at the capillary end.

scholarly journals Interneurons contribute to the hemodynamic/metabolic response to epileptiform discharges

2016 ◽  
Vol 115 (3) ◽  
pp. 1157-1169 ◽  
Author(s):  
Sandrine Saillet ◽  
Pascale P. Quilichini ◽  
Antoine Ghestem ◽  
Bernard Giusiano ◽  
Anton I. Ivanov ◽  
...  
Keyword(s):  
Blood Flow ◽  
Cerebral Blood Flow ◽  
Metabolic Response ◽  
Metabolic Responses ◽  
Oxygen Level ◽  
Field Potentials ◽  
Tissue Oxygen ◽  
Epileptiform Discharges ◽  
Interneuron Activity ◽  
Partial Oxygen

Interpretation of hemodynamic responses in epilepsy is hampered by an incomplete understanding of the underlying neurovascular coupling, especially the contributions of excitation and inhibition. We made simultaneous multimodal recordings of local field potentials (LFPs), firing of individual neurons, blood flow, and oxygen level in the somatosensory cortex of anesthetized rats. Epileptiform discharges induced by bicuculline injections were used to trigger large local events. LFP and blood flow were robustly coupled, as were LFP and tissue oxygen. In a parametric linear model, LFP and the baseline activities of cerebral blood flow and tissue partial oxygen tension contributed significantly to blood flow and oxygen responses. In an analysis of recordings from 402 neurons, blood flow/tissue oxygen correlated with the discharge of putative interneurons but not of principal cells. Our results show that interneuron activity is important in the vascular and metabolic responses during epileptiform discharges.

scholarly journals Cerebral Blood Flow Response to Functional Activation

2009 ◽  
Vol 30 (1) ◽  
pp. 2-14 ◽  
Author(s):  
Olaf B Paulson ◽  
Steen G Hasselbalch ◽  
Egill Rostrup ◽  
Gitte Moos Knudsen ◽  
Dale Pelligrino
Keyword(s):  
Blood Flow ◽  
Cerebral Blood Flow ◽  
Glucose Metabolism ◽  
Oxidative Metabolism ◽  
Glucose Consumption ◽  
Oxygen Metabolism ◽  
Neural Activation ◽  
Metabolic Demand ◽  
Tight Coupling ◽  
Pronounced Increase

Cerebral blood flow (CBF) and cerebral metabolic rate are normally coupled, that is an increase in metabolic demand will lead to an increase in flow. However, during functional activation, CBF and glucose metabolism remain coupled as they increase in proportion, whereas oxygen metabolism only increases to a minor degree—the so-called uncoupling of CBF and oxidative metabolism. Several studies have dealt with these issues, and theories have been forwarded regarding the underlying mechanisms. Some reports have speculated about the existence of a potentially deficient oxygen supply to the tissue most distant from the capillaries, whereas other studies point to a shift toward a higher degree of non-oxidative glucose consumption during activation. In this review, we argue that the key mechanism responsible for the regional CBF (rCBF) increase during functional activation is a tight coupling between rCBF and glucose metabolism. We assert that uncoupling of rCBF and oxidative metabolism is a consequence of a less pronounced increase in oxygen consumption. On the basis of earlier studies, we take into consideration the functional recruitment of capillaries and attempt to accommodate the cerebral tissue's increased demand for glucose supply during neural activation with recent evidence supporting a key function for astrocytes in rCBF regulation.

scholarly journals Metoprolol Reduces Cerebral Tissue Oxygen Tension after Acute Hemodilution in Rats

2009 ◽  
Vol 111 (5) ◽  
pp. 988-1000 ◽  
Author(s):  
Tenille E. Ragoonanan ◽  
W Scott Beattie ◽  
C David Mazer ◽  
Albert K.Y. Tsui ◽  
Howard Leong-Poi ◽  
...  
Keyword(s):  
Heart Rate ◽  
Blood Flow ◽  
Cardiac Output ◽  
Cerebral Blood Flow ◽  
Oxygen Tension ◽  
Tissue Oxygen Tension ◽  
Beta Blockade ◽  
Tissue Oxygen ◽  
Cerebral Tissue ◽  
Protein Levels

Background Perioperative beta-blockade and anemia are independent predictors of increased stroke and mortality by undefined mechanisms. This study investigated the effect of beta-blockade on cerebral tissue oxygen delivery in an experimental model of blood loss and fluid resuscitation (hemodilution). Methods Anesthetized rats were treated with metoprolol (3 mg x kg) or saline before undergoing hemodilution with pentastarch (1:1 blood volume exchange, 30 ml x kg). Outcomes included cardiac output, cerebral blood flow, and brain (PBrO2) and kidney (PKO2) tissue oxygen tension. Hypoxia inducible factor-1alpha (HIF-1alpha) protein levels were assessed by Western blot. Systemic catecholamines, erythropoietin, and angiotensin II levels were measured. Results Hemodilution increased heart rate, stroke volume, cardiac output (60%), and cerebral blood flow (50%), thereby maintaining PBrO2 despite an approximately 50% reduction in blood oxygen content (P < 0.05 for all). By contrast, PKO2 decreased (50%) under the same conditions (P < 0.05). Beta-blockade reduced baseline heart rate (20%) and abolished the compensatory increase in cardiac output after hemodilution (P < 0.05). This attenuated the cerebral blood flow response and reduced PBrO2 (50%), without further decreasing PKO2. Cerebral HIF-1alpha protein levels were increased in beta-blocked hemodiluted rats relative to hemodiluted controls (P < 0.05). Systemic catecholamine and erythropoietin levels increased comparably after hemodilution in both groups, whereas angiotensin II levels increased only after beta-blockade and hemodilution. Conclusions Cerebral tissue oxygen tension is preferentially maintained during hemodilution, relative to the kidney, despite elevated systemic catecholamines. Acute beta-blockade impaired the compensatory cardiac output response to hemodilution, resulting in a reduction in cerebral tissue oxygen tension and increased expression of HIF-1alpha.

scholarly journals A Model for the Coupling between Cerebral Blood Flow and Oxygen Metabolism during Neural Stimulation

1997 ◽  
Vol 17 (1) ◽  
pp. 64-72 ◽  
Author(s):  
Richard B. Buxton ◽  
Lawrence R. Frank
Keyword(s):  
Blood Flow ◽  
Cerebral Blood Flow ◽  
Metabolic Rate ◽  
Oxygen Metabolism ◽  
Neural Stimulation ◽  
Brain Capillaries ◽  
Tight Coupling ◽  
Positron Emission ◽  
General Mathematical Model ◽  
The Brain

A general mathematical model for the delivery of O2 to the brain is presented, based on the assumptions that all of the brain capillaries are perfused at rest and that all of the oxygen extracted from the capillaries is metabolized. The model predicts that disproportionately large changes in blood flow are required in order to support small changes in the O2 metabolic rate. Interpreted in terms of this model, previous positron emission tomography (PET) studies of the human brain during neural stimulation demonstrating that cerebral blood flow (CBF) increases much more than the oxygen metabolic rate are consistent with tight coupling of flow and oxidative metabolism. The model provides a basis for the quantitative interpretation of functional magnetic resonance imaging (fMRI) studies in terms of changes in local CBF.

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