The effects of graded hypoxia upon transient cerebral blood flow and oxygen consumption

Shimojyo, S.; Scheinberg, Peritz; Kogure, Kimitaka; Reinmuth, Oscar M.

doi:10.1212/wnl.18.2.127

Cited by 89 publications

(32 citation statements)

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“…We have determined Y sat with a noninvasive devise, but have no direct data from partial pressure for arterial carbon dioxide content (PaCO 2 ). Studies exposing healthy volunteers to similar levels of hypoxia have shown that PaCO 2 decreases by 2 to 3 mm Hg (Mintun et al, 2001;Shimojyo et al, 1968). The relevance of hypocapnia to the fMRI data interpretation is that previous human BOLD studies have indicated that PaCO 2 o30 mm Hg alone may decrease the BOLD response in the visual cortex Weckesser et al, 1999).…”

Section: Discussionmentioning

confidence: 98%

Heterogeneous Oxygen Extraction in the Visual Cortex during Activation in Mild Hypoxic Hypoxia Revealed by Quantitative Functional Magnetic Resonance Imaging

Tuunanen

Murray

Parry

et al. 2006

J Cereb Blood Flow Metab

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Functional magnetic resonance imaging (fMRI) techniques were used to study haemodynamic and metabolic responses in human visual cortex during varying arterial blood oxygen saturation levels (Y sat , determined by pulse-oximeter) and stimulation with contrast-reversing checkerboards. The visual-evoked potential amplitude remained constant at lowered Y sat of 0.8270.03. Similarly, fMRI cerebral blood flow (CBF) responses were unchanged during reduced Y sat . In contrast, visual cortex volume displaying blood oxygen level-dependent (BOLD) fMRI response decreased as a function of Y sat , but the BOLD signal change of 3.6%71.4% was constant. Oxygen extraction ratio (OER) during visual activation showed values of 0.2670.03 for normal Y sat . At lowered Y sat , two OER patterns were observed. Firstly, a reduced OER of 0.1470.03 in the visual cortex structures showing BOLD in hypoxia was observed. Secondly, signs of much higher OER in other parts of visual cortex were obtained. T 2 *-weighted magnetic resonance imaging revealed signal increases by 0.8%70.4% with visual activation during lowered Y sat in the visual cortex structures, which showed BOLD of 3.6% in magnitude under normoxia. Because the CBF response in the visual cortex was quantitatively similar during stimulation in normoxia and hypoxia, attenuated T 2 *-weighted signal increase in parts of visual cortex indicated high OER during visual activation in hypoxia, which was close to that encountered in the resting brain. These spatially localised regions of tissue oxygen extraction and metabolism argue for dissociation between CBF and BOLD fMRI signals in mild hypoxia. The findings point to heterogeneity with regard to oxygen requirement and its coupling to the haemodynamic response in the brain.

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Section: Discussionmentioning

confidence: 98%

Heterogeneous Oxygen Extraction in the Visual Cortex during Activation in Mild Hypoxic Hypoxia Revealed by Quantitative Functional Magnetic Resonance Imaging

Tuunanen

Murray

Parry

et al. 2006

J Cereb Blood Flow Metab

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“…A compensatory increase in cerebral blood flow also takes place during hypoxemia. These changes all aim at restoring tissue pH (10,16,22,27).…”

Section: Discussionmentioning

confidence: 99%

Effect of Hypoxia on Monoamine Synthesis in Brains of Developing Rats

Hedner¹,

Lundborg²,

Engel³

1977

Neonatology

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Tyrosine and tryptophan hydroxylase activity was studied in vivo in the postnatal rat brain by measuring the accumulation of dihydroxyphenylalanine (DOPA) and 5-hydroxytryptophan (5-HTP) respectively after inhibition of Z-aromatic amino acid decarboxylase with NSD 1015. 1-, 4-, 14- and 28-day-old rats were exposed to a 12% oxygen environment for a period of 30 min, 2 and 6 h. After 30 min in the 12% oxygen environment the tryptophan hydroxylase activity decreased significantly in all age groups studied, but increased significantly after 6h hypoxia compared to controls in 1- and 4-day-old rats. Tyrosine hydroxylase activity in 1-day-old rats was significantly decreased only after 30 min hypoxia as it returned to normal after 2 and 6 h. In the 4-day-old rats a decrease was noted after 30 min and 6 h. In the 14- and 28-day-old rats a significant reduction of tyrosine hydroxylase activity was found after all the time intervals studied. It is concluded that the oxygen dependent, first, rate-limiting step in the synthesis of the neurotransmitters dopamine, noradrenaline and 5-hydroxytryptamine seems to be less vulnerable in the brains of early postnatal rats. Decreases and increases of the levels of tryptophan correlated well to the found changes in 5-HTP levels. This correlation did not seem to be present in the case of tyrosine and DOPA accumulation. It is thus suggested that the observed changes in tryptophan hydroxylation may in part depend on the changes in tryptophan availability. This did not seem to be the case concerning tyrosine hydroxylation and tyrosine availability.

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“…However, recent observational studies and post hoc analysis of other trials link liberal use of RBCT with medical complications, infection, vasospasm, poor cognitive performance, and poor outcome [29, 44, 55-57, 60, 68]. It is conceivable that avoiding hypoxia, rather than anemia alone, may prevent neuron damage [106]. RBCT, however, does not always increase PbtO 2 , and in 20-25% of patients, PbtO 2 may decrease [44,46].…”

Section: Rbct In Sahmentioning

confidence: 99%

Anemia and Transfusion After Subarachnoid Hemorrhage

Roux

2011

Neurocrit Care

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Delayed cerebral ischemia after subarachnoid hemorrhage (SAH) may be affected by a number of factors, including cerebral blood flow and oxygen delivery. Anemia affects about half of patients with SAH and is associated with worse outcome. Anemia also may contribute to the development of or exacerbate delayed cerebral ischemia. This review was designed to examine the prevalence and impact of anemia in patients with SAH and to evaluate the effects of transfusion. A literature search was made to identify original research on anemia and transfusion in SAH patients. A total of 27 articles were identified that addressed the effects of red blood cell transfusion (RBCT) on brain physiology, anemia in SAH, and clinical management with RBCT or erythropoietin. Most studies provided retrospectively analyzed data of very low-quality according to the GRADE criteria. While RBCT can have beneficial effects on brain physiology, RBCT may be associated with medical complications, infection, vasospasm, and poor outcome after SAH. The effects may vary with disease severity or the presence of vasospasm, but it remains unclear whether RBCTs are a marker of disease severity or a cause of worse outcome. Erythropoietin data are limited. The literature review further suggests that the results of the Transfusion Requirements in Critical Care Trial and subsequent observational studies on RBCT in general critical care do not apply to SAH patients and that randomized trials to address the role of RBCT in SAH are required.

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The effects of graded hypoxia upon transient cerebral blood flow and oxygen consumption

Cited by 89 publications

References 0 publications

Heterogeneous Oxygen Extraction in the Visual Cortex during Activation in Mild Hypoxic Hypoxia Revealed by Quantitative Functional Magnetic Resonance Imaging

Heterogeneous Oxygen Extraction in the Visual Cortex during Activation in Mild Hypoxic Hypoxia Revealed by Quantitative Functional Magnetic Resonance Imaging

Effect of Hypoxia on Monoamine Synthesis in Brains of Developing Rats

Anemia and Transfusion After Subarachnoid Hemorrhage

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