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Query: UMLS:C0242706 (hyperoxia)
 5,219 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

An animal model of oxygen-induced pulmonary injury was used to assess the potential of contrast-enhanced MRI to identify and quantify abnormal capillary permeability. Sprague-Dawley rats were exposed to 100% oxygen for 48 h (n = 5) or 60 h (n = 9). Axial spin-echo MR images were acquired in intubated, anesthetized rats with ECG-gating (TR 400; TE 6) immediately or 7 days after the cessation of oxygen exposure. Polylysine-Gd-DTPA, a macromolecular paramagnetic blood-pool marker, was then given intravenously and the lungs were serially imaged for 42 to 47 min to monitor changes in signal intensity. Pulmonary enhancement was stable in rats exposed to 48 h of oxygen, and in rats exposed to 60 h of oxygen and given 7 days to recover. However, animals exposed to 100% oxygen for 60 h without a period of recovery showed a progressive increase in lung signal intensity for 15 min after polylysine-Gd-DTPA. Pleural effusions also showed progressively increasing signal, reflecting a capillary endothelial leak. A two compartment model describing the kinetics of polylysine-Gd-DTPA in the plasma and interstitial water of the lung was consistent with the dynamic MRI data and allowed estimation of the fractional leak rate (0.235 min-1) of the contrast agent from plasma to interstitial water. Given the assumption of our kinetic model, MRI following intravenous administration of polylysine-Gd-DTPA can be used to quantitate changes in capillary integrity induced by hyperoxia, including acute capillary leakiness and return to normal endothelial integrity with recovery from hyperoxic injury.
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PMID:Pulmonary oxygen toxicity: demonstration of abnormal capillary permeability using contrast-enhanced MRI. 830 47

The authors report a patient with migraine in whom they measured brain oxygenation indirectly during a visual aura by means of T2-weighted MRI. An aura of left homonomous quadrantanopia was accompanied by increased T2-weighted contrast intensity of bilateral regions in the occipital cortex, and the red nucleus and substantia nigra bilaterally. The mechanisms of these changes remain to be determined, but in this patient the migraine aura was associated with probable hyperoxia and not cerebral ischemia.
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PMID:MRI of the occipital cortex, red nucleus, and substantia nigra during visual aura of migraine. 981 84

Bold contrast MRI was applied for mapping vascular maturation in tumor- and wound-induced skin angiogenesis using the response of mature vessels to hypercapnia (inhalation of air vs. air 5% CO(2)) and the response of all vessels to hyperoxia (air 5% CO(2) vs. oxygen 5% CO(2) (carbogen)). MRI signal enhancement with hypercapnia was reduced in centered vs. linear phase encoding, suggesting increased blood flow. However, intravital microscopy demonstrated constriction of arterioles and reduced flux and density of red blood cells in mature capillaries with hypercapnia, with no change in the diameter of wound-induced neovasculature. The discrepancy in flow between MRI and intravital microscopy is consistent with increased plasma flow and reduced hematocrit. Hyperoxia resulted in increased blood oxygenation and constriction of all vessels. These results provide a hemodynamic explanation for the selective registration of MRI response to hypercapnia with mature vessels and the response to hyperoxia with total vascular function.
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PMID:In vivo BOLD contrast MRI mapping of subcutaneous vascular function and maturation: validation by intravital microscopy. 1132 16

The hypercapnia induced by carbogen (95% O(2)/5% CO(2)) breathing, which is being re-evaluated as a clinical radiosensitiser, causes patient discomfort and hence poor compliance. Recent preclinical and clinical studies have indicated that the CO(2) content might be lowered without compromising increased tumour oxygenation and radiosensitisation. This preclinical study was designed to see if lower levels of hypercapnia could evoke similar decreases in the transverse relaxation rate R(2)* of rodent tumours to those seen with carbogen breathing. The response of rat GH3 prolactinomas to 1%, 212% and 5% CO(2) in oxygen, and 100% O(2) breathing, was monitored by non-invasive multi-gradient echo MRI to quantify R(2)*. As the oxygenation of haemoglobin is proportional to the blood p(a)O(2) and therefore in equilibrium with tissue pO(2), R(2)* is a sensitive indicator of tissue oxygenation. Hyperoxia alone decreased R(2)* by 13%, whilst all three hypercapnic hyperoxic gases decreased R(2)* by 29%. Breathing 1% CO(2) in oxygen evoked the same decrease in R(2)* as carbogen. The DeltaR(2)* response is primarily consistent with an increase in blood oxygenation, though localised increases in tumour blood flow were also identified in response to hypercapnia. The data support the concept that levels of hypercapnia can be reduced without loss of enhanced oxygenation and hence potential radiotherapeutic benefit.
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PMID:Effects of different levels of hypercapnic hyperoxia on tumour R(2)* and arterial blood gases. 1135 53

Blood oxygenation level-dependent (BOLD) contrast MRI is a potential method for a physiological characterization of tissue beyond mere morphological representation. The purpose of this study was to develop evaluation techniques for such examinations using a hyperoxia challenge. Administration of pure oxygen was applied to test these techniques, as pure oxygen can be expected to induce relatively small signal intensity (SI) changes compared to CO(2)-containing gases and thus requires very sensitive evaluation methods. Fourteen volunteers were investigated by alternating between breathing 100% O(2) and normal air, using two different paradigms of administration. Changes ranged from >30% in large veins to 1.71% +/- 0.14% in basal ganglia and 0.82% +/- 0.08% in white matter. To account for a slow physiological response function, a reference for correlation analysis was derived from the venous reaction. An objective method is presented that allows the adaptation of the significance threshold to the complexity of the paradigm used. Reference signal characteristics in representative brain tissue regions were established. As the presented evaluation scheme proved its applicability to small SI changes induced by pure oxygen, it can readily be used for similar experiments with other gases.
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PMID:Oxygen-enhanced MRI of the brain. 1221 Sep 35

The hypothesis of an oxygen-limited thermal tolerance was tested in the Antarctic teleost Pachycara brachycephalum. With the use of flow-through respirometry, in vivo (31)P-NMR spectroscopy, and MRI, we studied energy metabolism, intracellular pH (pH(i)), blood flow, and oxygenation between 0 and 13 degrees C under normoxia (PO(2): 20.3 to 21.3 kPa) and hyperoxia (PO(2): 45 kPa). Hyperoxia reduced the metabolic increment and the rise in arterial blood flow observed under normoxia. The normoxic increase of blood flow leveled off beyond 7 degrees C, indicating a cardiovascular capacity limitation. Ventilatory effort displayed an exponential rise in both groups. In the liver, blood oxygenation increased, whereas in white muscle it remained unaltered (normoxia) or declined (hyperoxia). In both groups, the slope of pH(i) changes followed the alpha-stat pattern below 6 degrees C, whereas it decreased above. In conclusion, aerobic scope declines around 6 degrees C under normoxia, marking the pejus temperature. By reducing circulatory costs, hyperoxia improves aerobic scope but is unable to shift the breakpoint in pH regulation or lethal limits. Hyperoxia appears beneficial at sublethal temperatures, but no longer beyond when cellular or molecular functions become disturbed.
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PMID:Oxygen-limited thermal tolerance in Antarctic fish investigated by MRI and (31)P-MRS. 1237 20

The purpose of this study was to compare the results from oxygen-induced MR-signal intensity changes with polarographic pO2 measurements in tumors. Balb-c mice with an intramuscular transplanted osteosarcoma were examined. To study the response of tumors to changes in oxygen supply, hyperoxia was induced by breathing pure oxygen for a short period. The examination of each animal started with T2* weighted MRI followed by the pO2 measurements (Eppendorf Histograph). During oxygen inhalation in all tumors, when the hypoxic tumor fraction drops, both areas of significant MR-signal intensity increase and decrease were observed in each animal.
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PMID:Comparison study of oxygen-induced MRI-signal changes and pO2 changes in murine tumors. 1456 41

Neurological complications such as stroke are known consequences of sickle cell disease (SCD). In order to improve methods for the evaluation of stroke risk in SCD, MRI was used to evaluate cerebrovascular function in transgenic mouse models of human SCD. It is hypothesized that oxygen-sensitive imaging in the brain will reveal areas of excess deoxygenation that are either at risk of or the result of vaso-occlusion. Arterial spin labeling (ASL) perfusion was performed in order to correlate BOLD results with microvascular cerebral blood flow. Upon comparison with control animals, there was a relative increase in BOLD hyperoxia response of 42-67% (P < 0.001) in the transgenic mice while cerebral blood flow during normoxia was reduced by 30-40% (P < 0.02). Hyperoxia caused cerebral blood flow to decrease in control mice, whereas blood flow increased in the sickle transgenic mice. These results indicate impairment in brain autoregulation in the sickle cell transgenic mice leading to increased cerebral deoxyhemoglobin. Increased deoxyhemoglobin coupled with reduced perfusion may further increase the risk of vaso-occlusion and stroke. This may reflect polymer reduction or reduced cell adhesion during hyperoxia. The MRI protocol is noninvasive and thus directly applicable to a clinical population.
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PMID:Decreased cerebral perfusion correlates with increased BOLD hyperoxia response in transgenic mouse models of sickle cell disease. 1500 94

Indirect qualitative MRI of pulmonary function is feasible using the paramagnetic effects of oxygen physically dissolved in blood. In this study, a more quantitative oxygen-enhanced pulmonary function test based on the slope of a plot of R(1) vs. oxygen concentration-the oxygen transfer function (OTF)-was developed and tested in a pool of five healthy volunteers and five patients with cystic fibrosis (CF). The lung T(1) relaxation rate, R(1), under normoxic conditions (room air, 21% O(2)), and the response to various hyperoxic conditions (40%-100% O(2)) were studied. Lung T(1) in healthy volunteers showed a relatively homogeneous distribution while they breathed room air, and a homogeneous decrease under hyperoxic conditions. Lung T(1) in CF patients showed an inhomogeneous distribution while they breathed room air, and the observed lung T(1) decrease under hyperoxia depended on the actual state of the diseased lung tissue. In the selected group of CF patients, areas with reduced OTF also showed reduced perfusion, as confirmed by qualitative contrast-enhanced MR pulmonary perfusion imaging. The results demonstrate that this completely noninvasive oxygen-enhanced pulmonary function test has potential for clinical applications in the serial diagnosis of lung diseases such as CF. .
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PMID:Assessment of human pulmonary function using oxygen-enhanced T(1) imaging in patients with cystic fibrosis. 1512 84

Because meningiomas tend to recur after (partial) surgical resection, radiotherapy is increasingly being applied for the treatment of these tumors. Radiation dose levels are limited, however, to avoid radiation damage to the surrounding normal tissue. The radiosensitivity of tumors can be improved by increasing tumor oxygen levels. The aim of this study was to investigate if breathing a hyperoxic hypercapnic gas mixture could improve the oxygenation of meningiomas. Blood oxygen level-dependent magnetic resonance imaging and dynamic Gadolinium (Gd)-DTPA contrast-enhanced MRI were used to assess changes in tumor blood oxygenation and vascularity, respectively. Ten meningioma patients were each studied twice; without and with breathing a gas mixture consisting of 2% CO(2) and 98% O(2). Values of T(2)* and the Gd-DTPA uptake rate k(ep) were calculated under both conditions. In six tumors a significant increase in the value of T(2)* in the tumor was found, suggesting an improved tumor blood oxygenation, which exceeded the effect in normal brain tissue. Contrarily, two tumors showed a significant T(2)* decrease. The change in T(2)* was found to correlate with both k(ep) and with the change in k(ep). The presence of both vascular effects and oxygenation effects and the heterogeneous response to hypercapnic hyperoxia necessitates individual assessment of the effects of breathing a hyperoxic hypercapnic gas mixture on meningiomas. Thus, the current MRI protocol may assist in radiation treatment selection for patients with meningiomas.
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PMID:BOLD MRI response to hypercapnic hyperoxia in patients with meningiomas: correlation with Gadolinium-DTPA uptake rate. 1523 44


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