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At least 19 recordsLinked to original sources
PubMed1989

[Stable xenon CT-CBF study with measurement of end-tidal xenon concentration--correction by arterial concentration of xenon].

Non-invasive methods with monitoring end-tidal stable xenon (ETXes) are described for estimating local cerebral blood flow (LCBF) and local partition coefficient (L lambda). 30% of Xes in oxygen was inhaled for 240 sec and exhaled for 160 sec during serial CT scannings after denitrogenation with pure oxygen breathing. During the examination, serial samplings of arterial blood and continuous monitoring of ETXes were performed to determine build up range (A) and build up rate constant (K) of artery. Calculated A and K using the arterial sampling (Aa and Ka, respectively) were compared with the calculated A and K using the continuous monitoring of ETXes (Ae and Ke, respectively) in 109 patients with epilepsy, head trauma, or cerebrovascular diseases. Ae and Ke had significantly positive correlation with Aa and Ka, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Inhalation↗
PubMed1992

Discrepancy of xenon concentrations between end-tidal and blood collection methods in xenon-enhanced computed tomographic measurements of cerebral blood flow.

Using xenon-enhanced computed tomography for the study of cerebral blood flow, simultaneous measurements of end-tidal and arterial blood xenon concentrations using the blood collection method were performed to investigate the validity of substituting the end-tidal for the arterial blood xenon concentration. Simultaneous measurement by both methods was performed 68 times in 27 patients. There was no statistical correlation between the arterial blood accumulation rate constant obtained by arterial blood and end-tidal samples, nor between the arterial blood saturation value obtained by the two methods, even when correction was made for age. In brain tissue, all parameters calculated using the end-tidal concentration were lower than those using arterial blood. We therefore suggest that cerebral blood flow values calculated using end-tidal xenon concentration are useful only for qualitative cerebral blood flow mapping, and not applicable to absolute values of cerebral blood flow.

Adolescent↗
PubMed1977

Xenon-127, a comparison with xenon-133 for ventilation studies.

In 133Xe ventilation studies the 81-keV gamma photon emitted is a major disadvantage for imaging. Using a lung model with the same attenuation coefficient as inflated lung, we compared 133Xe with 127Xe to determine the smallest "lesion" that could be imaged at different places within the lung. With the "lung lesion" directly against the collimator, the lesion had to be 10 ml in volume in order to be seen with 127Xe, but with 133Xe "lesion" had to be 30 ml. Xenon-127 gave better resolution, no matter where the lesion was placed within the lung. Xenon-127 was not better than 133Xe in resolving a lead bar phantom. When 133Xe was used with 99mTc in a model of pulmonary embolism, a "ventilation defect" was apparent even though the distribution of xenon was even throughout the model. This artifact was not seen when the 127Xe model was imaged.

Lung Diseases↗
PubMed1992

A comparison of xenon-133 and xenon-127 for the determination of regional cerebral blood flow measured by dynamic SPECT.

Phantom studies and cerebral blood flow (CBF) measurements in 11 normal subjects at rest were performed by single photon emission tomography (SPECT) with Xe-133 (16 mm full-width at half-maximum [FWHM] collimation) and Xe-127 (16 mm, 12 mm, and 9 mm FWHM collimation). The phantom results clearly illustrated the feasibility of Xe-127 studies and the advantage of Xe-127 over Xe-133 for equivalent patient dose exposures. CBF values obtained with Xe-127 were comparable to those of Xe-133 for the 16 mm collimator, although higher flow values were found with the better resolution, probably because of reduced partial volume effects. The correlations between the various groups of examinations were high, except for the Xe-133 and Xe-127 16 mm collimator groups. Xe-127 allows a considerable increase in the resolution of the images, while exposing the patient to a lower radiation dose. Potential limitations because of higher energy penetrating photons from Xe-127 were not observed in this specially shielded equipment.

Adolescent↗
PubMed1991

A minimal-flow system for xenon anesthesia.

We described a minimal-flow system for xenon anesthesia during controlled ventilation. A computer maintained oxygen concentration in the anesthesia circle within +/- 2% of the value set by the anesthesiologist. The ventilator and the circle were connected via a large dead space, through which oxygen from the ventilator entered the circle but which prevented xenon from escaping. This arrangement simplified the computer program. The system was tested on a lung model and in six pigs (37-39 kg). The xenon expenditure and the amount of xenon washed out from the pigs after the anesthetic were measured. Additional experiments with nitrous oxide were made in three pigs. The xenon expenditure during 2 h of xenon anesthesia was 7.6 +/- 0.8 l (mean +/- 1 standard deviation). The corresponding expenditure of nitrous oxide was 16.5 +/- 2.7 l. About 75% of the xenon expenditure was in the 1st h of anesthesia; thereafter 20-40 ml.min-1 was needed to maintain oxygen concentration at 30%. Nitrogen concentration in the circle increased to 12-16% during the xenon anesthetic, although it was preceded by a 20 min denitrogenation period. During the washout phase after the xenon anesthesia, mean expired xenon concentration decreased to below 2% within 4 min. Subsequently, washout was slower and the expired concentration remained above 0.1% for more than 90 min. The estimated total amount of xenon washed out from the lungs and body tissues during 4 h of oxygen breathing was about 4 l. We conclude that xenon anesthesia via a fully automated minimal-flow system is feasible.(ABSTRACT TRUNCATED AT 250 WORDS)

Algorithms↗
PubMedDate not supplied

Effects of inhaled stable xenon on cerebral blood flow velocity.

The effects of inhaled stable xenon gas on cerebral blood flow were studied with 23 transcranial Doppler examinations performed in 13 normal volunteers while breathing, 25, 30, or 35% xenon for 5 min. Doppler velocities from the middle cerebral artery rose significantly during inhalation in 85% of subjects and 78% of studies and decreased significantly in 15% of subjects and 17% of studies. These different velocity responses may represent different responses of pial vasculature to xenon. The mean velocity rise among those studies showing a significant increase was 38 +/- 3.6% (SEM). The velocity rise began 2 min after the start of xenon inhalation and increased rapidly, so that the velocities measured at the four times at which scans were obtained in our xenon CT protocol (0, 1.5, 3, and 5 min after the start of xenon inhalation) were significantly different. A consistent fall in the pulsatility of the Doppler waveform as the velocity increased provided evidence for xenon-induced vasodilation of the small-resistance vessels as the cause of the increase in flow velocity. Most subjects became mildly hyperventilated, so that the observed changes could not be attributed to hypercapnia. Inhalation of 25, 30, or 35% xenon for 5 min induces a delayed but significant rise in cerebral blood velocity. This suggests that cerebral blood flow itself may be rapidly changing during the process of xenon CT scanning. These changes may compromise the ability of the xenon CT technique to provide reliable quantitative measurements of cerebral blood flow.

Administration, Inhalation↗
PubMed1988

Xenon handling in the liver: red cell capacity effect.

Xenon, despite its lack of chemical reactivity, associates preferentially with red cells in blood. To characterize the effect of this and the nature of xenon-tissue interaction in the liver, multiple indicator dilution studies were performed in the anesthetized normal dog through portal vein injection and hepatic vein collection of anaerobic blood samples. Two experimental runs were carried out in each animal, one at the prevailing hematocrit and the other at reduced hematocrit after bleeding and replacement with dextran. For comparison, the injection mixtures contained labeled red blood cells (a vascular reference), sucrose (an interstitial space reference), and labeled water (which freely enters liver cells), as well as labeled xenon. At the higher hematocrit, the labeled xenon curves generally rose earlier, peaked higher, and decayed more quickly than the labeled water curve; at the lower hematocrit, the xenon curve was delayed and diminished in magnitude in relation to the labeled water curves. Analysis of the curve shapes indicated that xenon, like labeled sucrose and water, underwent delayed wave flow-limited distribution. With knowledge of the red cell plasma partition coefficient (2.89 ml/ml), it was possible to both account for the change in form of the xenon curves with hematocrit and to use the data to estimate the liver cell tissue plasma xenon partition coefficient. Values averaged 1.93 ml/ml liver space, or 1.79 ml/g, and did not change significantly from first to second runs. Theoretical analysis indicated that flow cannot be estimated from xenon downslopes.

Animals↗
PubMed1978

Xenon contrast enhancement in computed body tomography.

Xenon has been investigated as a contrast medium for conventional radiography, and in vitro as a contrast medium for computed tomography. The authors evaluated xenon contrast enhancement in vivo for CT body scanning. Nine healthy subjects had CT scans before and during xenon inhalation. Concentrations of xenon used varied from 10--50%. Consistent useful changes in attenuation from inhaled xenon were found in the lung but not in abdominal organs. Lung attenuation varied linearly with the xenon concentration in the inhaled gas. Inhalation of xenon concentrations greater than 30% resulted in side effects. Further studies are required to demonstrate whether xenon contrast enhancement is of diagnostic value in computed tomography.

Clinical Trials as Topic↗
PubMed1991

Effect of stable xenon on regional cerebral blood flow and the electroencephalogram in normal volunteers.

We evaluated the effects of breathing 35% stable xenon in 65% oxygen on regional cerebral blood flow and the electroencephalogram in 20 normal volunteers. We measured blood flow in 32 brain regions over both hemispheres with the xenon-133 intravenous injection technique in two protocols. In the first protocol (n = 10), a baseline study was followed by a second study during 5 minutes of breathing stable xenon; in the other protocol (n = 8), the baseline study was followed by a second study after 5 minutes of breathing stable xenon. Two volunteers were excluded due to excessive movements during the inhalation of stable xenon. Some of the remaining 18 volunteers had varying alterations of consciousness accompanied by electroencephalogram changes. After stable xenon inhalation the electroencephalogram returned to normal within 2-3 minutes. During stable xenon inhalation mean +/- SD PECO2 dropped significantly from 39.4 +/- 4.4 to 33.3 +/- 5.4 mm Hg in the first protocol and from 39.4 +/- 2.6 to 34.8 +/- 4.1 mm Hg in the second protocol due to hyperventilation in 13 volunteers. Mean regional cerebral blood flow increased significantly by 13.5-25.4% without correction for PECO2. In the first protocol regional cerebral blood flow increased by greater than 12% in 11-14 (depending on the flow parameter) of the 20 hemispheres. In the second protocol regional cerebral blood flow increased by greater than 12% in 9-13 of the 16 hemispheres. We conclude that cautious interpretation is necessary in the assessment of regional cerebral blood flow with 35% xenon-enhanced computed tomography.

Adult↗
PubMed1989

Stable xenon versus radiolabeled microsphere cerebral blood flow measurements in baboons.

Regional cerebral blood flow was simultaneously determined using the stable xenon computed tomographic and the radioactive microsphere techniques over a wide range of blood flow rates (less than 10-greater than 300 ml/100 g/min) in 12 baboons under conditions of normocapnia, hypocapnia, and hypercapnia. A total of 31 pairs of determinations were made. After anesthetic and surgical preparation of the baboons, cerebral blood flow was repeatedly determined using the stable xenon technique during saturation with 50% xenon in oxygen. Concurrently, cerebral blood flow was determined before and during xenon administration using 15-microns microspheres. In Group 1 (n = 7), xenon and microsphere determinations were made repeatedly during normocapnia. In Group 2 (n = 5), cerebral blood flow was determined using both techniques in each baboon during hypocapnia (PaCO2 = 20 mm Hg), normocapnia (PaCO2 = 40 mm Hg), and hypercapnia (PaCO2 = 60 mm Hg). Xenon and microsphere values in Group 1 were significantly correlated (r = 0.69, p less than 0.01). In Group 2, values from both techniques also correlated closely across all levels of PaCO2 (r = 0.92, p less than 0.001). No significant differences existed between the slopes or y intercepts of the regression lines for either group and the line of identity. Our data indicate that the stable xenon technique yields cerebral blood flow values that correlate well with values determined using radioactive microspheres across a wide range of cerebral blood flow rates.

Animals↗
PubMed1990

Clinical observations on the effect of carotid artery occlusion on cerebral blood flow mapped by xenon computed tomography and its correlation with carotid artery back pressure.

Xenon computed tomographic cerebral blood flow mapping was correlated with internal carotid artery stump pressures and clinical neurologic assessment during temporary internal carotid artery occlusion. One hundred fourteen patients with skull base tumors or intracranial aneurysms potentially requiring carotid resection or ligation underwent angiography, xenon CT cerebral blood flow mapping, and internal carotid artery blood pressure monitoring. The internal carotid artery was then temporarily occluded with a balloon catheter, stump pressure was measured through the catheter, and the xenon CT cerebral blood flow mapping was repeated. Adequate xenon CT cerebral blood flow was defined as greater than 30 cc/100 gm/min. All patients had normal xenon CT cerebral blood flow before internal carotid artery occlusion. During internal carotid artery occlusion, xenon CT cerebral blood flow was found to be normal (group I, 40 patients), globally reduced but still within the normal range (group II, 50 patients), or low in the distribution of the ipsilateral middle cerebral artery (group III, 13 patients). With balloon occlusion, an immediate neurologic deficit developed in 11 patients (9%) requiring deflation of the balloon preceding xenon CT cerebral blood flow measurement (group IV). In group I internal carotid artery blood pressure was 128 mm Hg. (range 85 to 171 mm Hg) with stump pressure 86 mm Hg (range 46 to 125 mm Hg). In group II internal carotid artery blood pressure was 130 mm Hg. (range 78 to 199 mm Hg), with stump pressure 86 mm Hg (range 31 to 150 mm Hg).(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMedDate not supplied

Xenon inhalation as an adjunct to computerized tomography of the brain: preliminary study.

The purpose of this study is to determine whether computerized tomography can distinguish between brain tissue and brain tissue containing dissolved xenon at physiologic concentrations. Xenon is an inert gas of high atomic number (54), and is highly soluble in tissue, particularly in fat. Its presence in the brain after inhalation is manifested by well known anesthetic effects. Phantom studies using xenon in equilibrium at atomospheric pressure with water, corn oil, and milk samples of varying known fat content, demonstrate that xenon is detectable in all cases with a steep linear increase in change of attenuation factor (EMI number) with increasing fat content. In the rhesus monkey xenon is readily detectable at 20% inhaled gas concentration, with linear detectable at 20% inhaled gas concentration, with linear increase of attenuation factor with increasing concentration. The possible application of our findings to the study of brain pathophysiology is discussed. Since xenon is a potent although safe anesthestic, caution in clinical application is advised.

Animals↗
PubMed1975

Intestinal blood flow. An evaluation by clearance of xenon Xe 133 from the canine jejunum.

Clearance of a parenchymal injection of xenon Xe 133 from the jejunum was used to asses changes in tissue perfusion produced by variations in superiorr mesenteric artery flow resulting from partial aortic occlusion. Disappearance of xenon from submucosa and muscularis was similar and reproducible. The biexponential function of the isotope clearanc exhibited a rapid initial component representing mean flow. Calculated xenon clearance rates, expressed as half-times for isotope disappearance and plotted as a function of decreasing superior mesenteric artery flow, were characteristically rapid for a broad range of superio mesenteric artery flows (90 to 600 ml/min). With reduction of superior mesenteric artery flow beyond 80 plus or minus 10 ml/min, tissue clearance of xenon was markedly prolonged. Adequate perfusion of the vascular compartments of the small bowel as measured by xenon clearance was maintained until 80% reduction of superior mesenteric artery flow.

Animals↗
PubMed1979

A comparison of xenon-133 clearance with electromagnetic flowmeters and an indicator dilution method for the measurement of liver blood flow.

Measurement of liver blood flow has been carried out by three different methods in 14 dogs to assess the accuracy of xenon-133 clearance following portal vein injection. Electromagnetic flowmetry with flow probes on the hepatic artery and portal vein resulted in a mean value of 121.9 +/- 39.3 ml min-1 100 g-1. An indicator dilution study utilizing chromium-51-labelled red cells gave a mean value of 119.4 +/- 31.4 ml min-1 100 g-1 and the xenon-133 clearance following portal vein injection, 120.3 +/- 33.8 ml min-1 100 g-1. One-way analysis of variance showed no statistically significant variation between these three groups. There was a close correlation between xenon-133 clearance and electromagnetic flowmetry and between xenon-133 clearance and the indicator dilution technique. These data suggest that xenon-133 clearance following portal vein injection gives an accurate assessment of liver blood flow and this technique (as well as direct parenchymal injection) can be adapted for clinical use.

Animals↗
PubMed1978

Xenon enhancement in tumours and infarcts.

Computed topography (CT) before and during xenon enhancement and computer subtraction has been performed in 11 patients with intracerebral tumours and 7 with ischaemic lesions. The amount of xenon uptake was expressed where possible as a percentage of that in the corresponding region of the contralateral apparently normal hemisphere. The amount of xenon uptake did not appear to be specific for any particular tumour histology. The margins of tumours were better defined during enhancement, but not to a degree which affected management; large cysts did not enhance and were well demonstrated. Cavities due to mature infarcts did not enhance and the central parts of most large recent infarcts showed markedly diminished enhancement. In recent infarcts delayed xenon uptake at the periphery and sometimes throughout the lesion reflects diminished perfusion of potentially viable tissue. One patient with an ischaemic parietal lesion in which xenon uptake was normal made a complete clinical recovery.

Brain↗