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Query: UMLS:C0020440 (hypercapnia)
 7,939 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Previously we have shown that hypercarbia produces a larger decrease in agonal glycolytic rate in 1-month-old swine than in newborns. In an effort to understand the mechanism responsible for this difference, we tested the hypothesis that hypercarbia produces age-related changes in the concentration of one or more effectors of phosphofructokinase activity. Specifically, in vivo 31P and 1H NMR spectroscopy was used to compare changes in lactate levels, intracellular pH, free magnesium concentration, and content of phosphorylated metabolites for these two age groups at three intervals during the first 1.5 min of complete ischemia in the presence or absence of hypercarbia (PaCO2 = 102-106 mm Hg). Hypercarbia produced the same drop in intracellular brain pH for both age groups, but the decrease in phosphocreatine level and increase in inorganic phosphate content were greater in 1-month-olds compared with newborns. During ischemia there was no difference between the magnitude of change in intracellular pH and levels of phosphocreatine and inorganic phosphate in hypercarbic 1-month-olds versus newborns. Under control conditions, i.e., normocarbia and normoxia, the free Mg2+ concentration was lower and the fraction of magnesium-free ATP was higher for newborns than 1-month-olds. However, there was no change in these variables for either age group during hypercarbia and early during ischemia. Thus, age-related differences in the relative decrease in agonal glycolytic rate during hypercarbia could not be explained by differences in intracellular pH, inorganic phosphate content, or free magnesium concentration. The [ADP]free at control was higher in newborns compared with 1-month-olds, and there was no age-related difference in [AMP]free. These variables did not change for newborns when exposed to hypercarbia, but for 1-month-olds [ADP]free and [AMP]free increased during hypercarbia relative to control values. High-energy phosphate utilization during ischemia for hypercarbic 1-month-olds was reduced by 74% compared with normocarbic 1-month-olds during ischemia, whereas the reduction in energy utilization (14%) was not significant for hypercarbic versus normocarbic newborns during ischemia.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Evaluation of potential effectors of agonal glycolytic rate in developing brain measured in vivo by 31P and 1H nuclear magnetic resonance spectroscopy. 779 28

A gradient-echo echo planar imaging (EPI) sequence has been used to generate images of cat brain during respiratory challenges. Direct spectrophotometric measurements have been made simultaneously in order to correlate the changes in oxygen saturation as measured by spectrophotometry with the image intensity changes seen in the gradient-echo images. When blood volume remains approximately constant, as derived from the spectrophotometry data, good correlation is seen between calculated plots made of changes in the transverse relaxation rate, delta R2*, and the oxygen saturation as measured by spectrophotometry for much of the time course of the respiratory challenges of anoxia, apnea and hypercapnia. In some cases, the correlation is poorer during the recovery periods of the apnea and anoxia challenges. Those lower correlations can often be accounted for by changes in blood volume, which also affects the NMR relaxation rate. These results contribute to the understanding of the image intensity changes seen during functional brain imaging studies in humans.
NMR Biomed 1994 Mar
PMID:Comparison of EPI gradient-echo contrast changes in cat brain caused by respiratory challenges with direct simultaneous evaluation of cerebral oxygenation via a cranial window. 806 24

A description is given of the design, construction, and initial use of a polycarbonate resin hyperbaric chamber for in vivo NMR spectroscopy studies of anesthetized, ventilated rats in a horizontal bore 4.7 Tesla magnet. The chamber and its associated equipment, initially used for hyperbaric studies of rats in states of extreme hypercapnia, are also well suited for conventional hyperbaric studies, such as those related to hyperbaric oxygen therapy, oxygen toxicity, and diving. Basic technical challenges that required innovations involved: a) preservation of magnetic field homogeneity; b) avoidance of a metallic chamber body that would overload gradient and RF coils; c) physiological monitoring; and, d) remote control and stabilization of electromagnetic and physiologic factors (especially ventilatory stability) during pressure changes. A small paramagnetic bulk magnetic susceptibility shift from chamber-associated hyperbaric oxygen was observed when chamber oxygen tensions were only one atmosphere. High-quality NMR imaging and spectroscopy were demonstrated during hyperbaric conditions.
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PMID:Nonmagnetic hyperbaric chamber for in vivo NMR spectroscopy studies of small animals. 835 Jul 25

Intracellular pH and ammonium ion concentration are potent modulators of cerebral amino acid metabolism. Furthermore, intracellular acidosis and hyperammonemia accompany conditions such as ischemic encephalopathy and seizures and may contribute to the pathological sequelae observed. In vivo NMR spectroscopy permits multiple, non-destructive measurements of important cerebral metabolic intermediates in the same animal. We describe here the use of 1H, and 31P NMR spectroscopy to investigate the effects of acute changes in intracellular pH and ammonium ions on cerebral glutamate, glutamine, and lactate levels in vivo. We then show how 1H NMR can be used to indirectly follow the flow of 13C label from [1-13C] glucose into the cerebral glutamate pool, allowing us to measure cerebral TCA activity in normal and chronically hyperammonemic rats. Male Sprague-Dawley rats (160-210 gm), fasted 24-hours, were tracheotomized, paralyzed and ventilated on 30% O2/70% N2O. NMR spectroscopy was performed at a field strength of 8.4 Tesla using a Bruker AM-360 wide bore spectrometer. An elliptical surface-coil (8 x 12 mm) was double-tuned to either the 1H and 31P or 1H and 13C frequencies. After retraction of extracranial tissues, the coil was positioned over the skull 2 mm posterior to the bregma. Tail arteries and veins were cannulated allowing periodic measurements of PO2, pCO2, pH and glucose in arterial blood and intravenous infusions. Respiratory acidosis was induced in rats by the addition of CO2 to the ventilation gas mixture. Arterial pCO2 increased within 5 min from a pre-hypercarbic value of 36.4 +/- 6.1 mm Hg to 200-220 mm Hg and was maintained at this level for over 1 hour. Hypercarbia led to rapid cerebral acidification. Intracellular pH decreased from 7.18 +/- 0.08 (pre-hypercarbic period) to 6.68 +/- 0.06 (n = 4) at 10 min and remained stable throughout the NMR observation period. Glutamate decreased to 53 +/- 4% of control after 60 min of hypercarbia, while glutamine increased to 126 +/- 7% of control. Acute hyperammonemia was produced by a programmed intravenous infusion of 250 mM ammonium acetate, which rapidly raised and maintained the concentration of ammonium ions in the blood at approximately 500 microM. Shortly after the start of the infusion (10-20 min), the levels of glutamine and lactate rose continuously throughout the experiment, reaching levels of 170 +/- 25% and 260 +/- 60% of control, respectively (n = 12) after 50 min. Glutamate decreased during the same time interval to 80 +/- 4% of control (n = 12).(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Cerebral metabolic studies in vivo by combined 1H/31P and 1H/13C NMR spectroscopic methods. 842 59

An issue in blood oxygenation level dependent contrast-based functional MRI is the accurate interpretation of the activation-induced signal changes. Hemodynamic factors other than activation-induced changes in blood oxygenation are known to contribute to the signal change magnitudes and dynamics, and therefore need to be accounted for or removed. In this paper, a general method for removal of effects other than activation-induced blood oxygenation changes from fMRI brain activation maps by the use of hypercapnic stress normalization is introduced. First, the effects of resting blood volume distribution across voxels on activation-induced BOLD-based fMRI signal changes are shown to be significant. Second, the effects of hypercapnia and hypoxia on resting and activation-induced signal changes are demonstrated. These results suggest that global hemodynamic stresses may be useful for non-invasive mapping of blood volume. Third, the normalization technique is demonstrated.
NMR Biomed
PMID:A hypercapnia-based normalization method for improved spatial localization of human brain activation with fMRI. 943 Mar 48

A unique method for simultaneously measuring interstitial (pHe) as well as intracellular (pHi) pH in the brains of lightly anesthetized rats is described. A 4-mm microdialysis probe was inserted acutely into the right frontal lobe in the center of the area sampled by a surface coil tuned for the collection of 31P-NMR spectra. 2-Deoxyglucose 6-phosphate (2-DG-6-P) was microdialyzed into the rat until a single NMR peak was detected in the phosphomonoester region of the 31P spectrum. pHe and pHi values were calculated from the chemical shift of 2-DG-6-P and inorganic phosphate, respectively, relative to the phosphocreatine peak. The average in vivo pHe was 7.24+/-0.01, whereas the average pHi was 7.05+/-0.01 (n = 7). The average pHe value and the average CSF bicarbonate value (23.5+/-0.1 mEq/L) were used to calculate an interstitial Pco2 of 55 mm Hg. Rats were then subjected to a 15-min period of either hypercapnia, by addition of CO2 (2.5, 5, or 10%) to the ventilator gases, or hypocapnia (PCO2 < 30 mm Hg), by increasing the ventilation rate and volume. pHe responded inversely to arterial Pco2 and was well described (r2 = 0.91) by the Henderson-Hasselbalch equation, assuming a pKa for the bicarbonate buffer system of 6.1 and a solubility coefficient for CO2 of 0.031. This confirms the view that the bicarbonate buffer system is dominant in the interstitial space. pHi responded inversely and linearly to arterial PCO2. The intracellular effect was muted as compared with pHe (slope = -0.0025, r2 = 0.60). pHe and pHi values were also monitored during the first 12 min of ischemia produced by cardiac arrest. pHe decreases more rapidly than pHi during the first 5 min of ischemia. After 12 min of ischemia, pHe and pHi values were not significantly different (6.44+/-0.02 and 6.44+/-0.03, respectively). The limitations, advantages, and future uses of the combined microdialysis/31P-NMR method for measurement of pHe and pHi are discussed.
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PMID:In vivo microdialysis of 2-deoxyglucose 6-phosphate into brain: a novel method for the measurement of interstitial pH using 31P-NMR. 988 94

Extracellular acidosis has been demonstrated to play a key role in the process of metabolic depression under long-term environmental stress, exemplified in the marine invertebrate Sipunculus nudus. These findings led to the hypothesis that acid-base regulation is associated with a visible cost depending on the rate and mode of H(+)-equivalent ion exchange. To test this hypothesis, the effects of different ion-transport inhibitors on the rate of pH recovery during hypercapnia, on energy turnover and on steady-state acid-base variables were studied in isolated body wall musculature of the marine worm Sipunculus nudus under control conditions (pHe 7.90) and during steady-state extracellular acidosis (pHe 7.50 or 7.20) by in vivo (31)P-NMR and oxygen consumption analyses. During acute hypercapnia (2 % CO(2)), recovery of pHi was delayed at pHe 7.5 compared with pHe 7.9. Inhibition of the Na(+)/H(+)-exchanger by 5-(N,N-dimethyl)-amiloride (DMA) at pHe 7.5 delayed recovery even further. This effect was much smaller at pHe 7.9. Inhibition of anion exchange by the addition of the transport inhibitor 4, 4'-diisothiocyanatostilbene-2,2'-disulphonic acid (DIDS) prevented pH recovery at pHe 7.5 and delayed recovery at pHe 7.9, in accordance with an effect on Na(+)-dependent Cl(-)/HCO(3)(-) exchange. The effects of ouabain, DIDS and DMA on metabolic rate were reduced at low pHe, thereby supporting the conclusion that acidosis caused the ATP demand of Na(+)/K(+)-ATPase to fall. This reduction occurred via an inhibiting effect on both Na(+)/H(+)- and Na(+)-dependent Cl(-)/HCO(3)(-) (i.e. Na(+)/H(+)/Cl(-)/HCO(3)(-)) exchange in accordance with a reduction in the ATP demand for acid-base regulation during metabolic depression. Considering the ATP stoichiometries of the two exchangers, metabolic depression may be supported by the predominant use of Na(+)/H(+)/Cl(-)/HCO(3)(-) exchange under conditions of extracellular acidosis.
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PMID:Modulation of the cost of pHi regulation during metabolic depression: a (31)P-NMR study in invertebrate (Sipunculus nudus) isolated muscle. 1090 56

It has recently been reported in alpha-chloralose anesthetized rats that the hemodynamic response to somatosensory stimulation almost doubled following transient hypercapnia (THC). In principle, this effect could be employed to enhance the sensitivity of perfusion-based fMRI experiments. To investigate whether a comparable effect was detectable in awake normal humans, changes in cerebral blood flow (DeltaCBF) and the effective transverse relaxation time (DeltaT(2)*) induced by a visual search task were measured in 10 healthy volunteers before and after THC. Concerning DeltaT(2)* no significant differences were found, whereas in four subjects DeltaCBF was significantly decreased (p < 0.01) following THC. These results demonstrate no increase in the CBF response following THC for awake humans. We conclude that the most likely explanation for this discrepancy with the earlier results obtained with animals is an as yet unknown mechanism of modulation of the cholinergic system by the anesthesia.
NMR Biomed 2000 Nov
PMID:The effect of transient hypercapnia on task-related changes in cerebral blood flow and blood oxygenation in awake normal humans: a functional magnetic resonance imaging study. 1111 65

The assessment of cerebral interstitial oxygen tension (piO(2)) can provide valuable information regarding cerebrovascular physiology and brain function. Compartment-specific cerebral piO(2) was measured by (19)F NMR following the infusion of an oxygen-sensitive perfluorocarbon directly into the interstitial and ventricular space of the in vivo rat brain. (19)F T(1) measurements were made and cerebral piO(2) were obtained through in vitro calibrations. The effects of graded hyperoxia, hypercapnia, and hypoxia on piO(2) and cerebral blood flow (CBF) were investigated. Under normoxia (arterial pO(2) approximately 120 mm Hg), piO(2) was approximately 30 mm Hg and jugular venous pO(2) was approximately 50 mm Hg. During hyperoxia (arterial pO(2) = 90-300 mm Hg), piO(2) increased linearly with the arterial pO(2). Following hypercapnia (arterial pCO(2) = 20-60 mm Hg), the piO(2) increased sigmoidally with increasing CBF. With hypoxia (arterial pO(2) = 30-40 mm Hg), CBF increased approximately 56% and piO(2) decreased to approximately 15 mm Hg. The hypoxia-induced CBF increase was effective to some extent in compensating for the reduced piO(2). This methodology may prove useful for investigating cerebral piO(2) under pathologically or functionally altered conditions. Magn Reson Med 45:61-70, 2001.
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PMID:Effect of hyperoxia, hypercapnia, and hypoxia on cerebral interstitial oxygen tension and cerebral blood flow. 1114 87

Measurement of cerebral arterial and venous blood volumes during increased cerebral blood flow can provide important information regarding hemodynamic regulation under normal, pathological, and neuronally active conditions. In particular, the change in venous blood volume induced by neural activity is one critical component of the blood oxygenation level-dependent (BOLD) signal because BOLD contrast is dependent only on venous blood, not arterial blood. Thus, relative venous and arterial blood volume (rCBV) and cerebral blood flow (rCBF) in alpha-chlorolase-anesthetized rats under hypercapnia were measured by novel diffusion-weighted (19)F NMR following an i.v. administration of intravascular tracer, perfluorocarbons, and continuous arterial spin labeling methods, respectively. The relationship between rCBF and total rCBV during hypercapnia was rCBV(total) = rCBF(0.40), which is consistent with previous PET measurement in monkeys. This relationship can be linearized in a CBF range of 50-130 ml/100 g/min as DeltarCBV(total)/ DeltarCBF = 0.31 where DeltarCBV and DeltarCBF represent rCBV and rCBF changes. The average arterial volume fraction was 0.25 at a basal condition with CBF of approximately 60 ml/100 g/min and increased up to 0.4 during hypercapnia. The change in venous rCBV was 2-fold smaller than that of total rCBV (DeltarCBV(vein)/DeltarCBF = 0.15), while the arterial rCBV change was 2.5 times larger than that of total rCBV (DeltarCBV(artery)/DeltarCBF = 0.79). These NMR results were confirmed by vessel diameter measurements with in vivo videomicroscopy. The absolute venous blood volume change contributes up to 36% of the total blood volume change during hypercapnia. Our findings provide a quantitative physiological model of BOLD contrast.
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PMID:Relative changes of cerebral arterial and venous blood volumes during increased cerebral blood flow: implications for BOLD fMRI. 1132 5


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