Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Krypton”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,657 records · Page 92Linked to original sources
PubMed1984

Unstable rest angina with ST-segment depression. Pathophysiologic considerations and therapeutic implications.

Because of recent findings, a reassessment is needed of the concept that rest angina associated with ST-segment depression is due to a spontaneous, transient increase of blood pressure or heart rate, or both, in the presence of critical coronary artery stenosis. Continuous hemodynamic and electrocardiographic recordings done before and during attacks of rest angina and thallium-201 scintigrams done during pain indicate that a transient reduction of flow is the immediate cause of ischemia in most, but not all, instances. Flow reduction, in turn, appears to be due to coronary arterial spasm or platelet aggregation, or both, acting at a site of atherosclerotic narrowing. Therapy for unstable rest angina should include measures to prevent both transient reductions of flow and increases of myocardial oxygen consumption. A combination of long-acting nitrates, a beta-blocker, a calcium-channel blocker, and aspirin or heparin is suggested for this purpose. Intravenous nitroglycerin is useful when angina occurs despite this therapy or when frequent attacks of ischemia are occurring at the time of admission.

Angina Pectoris↗
PubMed1986

Positional effects on distribution of ventilation in chronic obstructive pulmonary disease.

Ventilation is distributed predominantly to the dependent lung in normal persons in the decubitus position. We evaluated the distribution of ventilation in four patients with mild-to-moderate chronic obstructive pulmonary disease using 81mKr gas. Patients were tested in the sitting and right and left decubitus positions with and without the application of positive end expiratory pressure (PEEP). In contrast to findings in controls, ventilation was predominantly distributed to the nondependent lung in patients in the decubitus position. Mean ventilation in the right lung decreased from 51% of the total in the sitting position to 31% in the right decubitus position; it increased with the application of 10 cm PEEP. Reduced ventilation in the dependent lung most likely is caused by closure of the airways after a decrease in volume. Application of PEEP resulted in increased lung volume and preferential distribution of ventilation to the dependent lung.

Aged↗
PubMed1975

Evaluation of intracardiac shunts.

This article will review the qualitative and quantitative methods of radionuclide evaluation of intracardiac shunts. Radionuclide angiocardiography of the cardiopulmonary system has proven adequate, with few exceptions, for qualitative detection of left-to-right and right-to-left intracardiac shunts. Numerous authors have reported on the detection of intracardiac shunts using qualitative methods such as rapid sequential visualization of nuclide angiocardiography using the scintillation camera with Polaroid, 35mm or 70mm film. Recent development of videotape storage systems and computers offers a quantitative technique of permanently recording the nuclide angiocardiogram and thus the capability for replay and analysis of the study. Quantitative analysis of the nuclide angiogram in the form of heart chamber dilution curves or pulmonary dilution curves permits 1) determination of the presence or absence of left-to-right, right-to-left, or bi-directional intracardiac shunts, including shunts which might go undetected using the qualitative techniques, 2) shunt location at the atrial or ventricular level, 3) determination of the functional status of a corrective left-to-right shunt, and 4) shunt quantitation. By quantitative analysis of the isotope dilution curves, it is possible to calculate the size of left-to-right or right-to-left intracardiac shunts (Qp/Qs ratio) to within 10% of the values obtained at cardiac catheterization.

Adolescent↗
PubMed1975

Production and characteristics of 125Xe: a new noble gas for in vivo studies.

Radionuclides of the noble gases are extensively used to assess ventilation and blood flow in clinical and investigative studies. Xenon-133 is most commonly used but is not optimal for these in vivo studies. Xenon-125 has better physical characteristics and can be produced with a cyclotron by a 127I(p,3n)125Xe reaction; this reaction results in a maximum of 25 mCi/gm/cm2/muA-hr for 31-MeV protons. Under actual production conditions, 11 mCi/muA-hr were collected. Xenon-125 decays by electron capture with a 17.2-hr half-life and contributes less radiation per dose of radioactivity than 133Xe. The radiation dose to the lungs from 133Xe and 125Xe is 5.0 and 1.8 mrads/mCi-min, respectively. The radiation dose per usable photon for 125Xe is only 0.3 of 133Xe. The principal photons of 125Xe, 188 keV (55%) and 243 keV (29%), are more intense and are in an energy range that is more advantageous for imaging than the 81 keV (35%) of 133Xe. These physical properties of 125Xe result in better spatial resolution at the same information density and with less radioactivity administered to the patient. Phantom studies showed that 12.7-, 9.5-, and 6.4-mm lead bars were resolved with 125Xe using a 410- keV diverging collimator wheras only the 12.7- and 9.k-mm lead bars were resolved using 133Xe and either a 410-keV or 140keV diverging collimator.

Krypton↗
PubMed2001

Technegas versus (81m)Kr ventilation-perfusion scintigraphy: a comparative study in patients with suspected acute pulmonary embolism.

UNLABELLED: 81mKr is widely used as a ventilation agent to diagnose pulmonary embolism (PE). However, (81m)Kr is expensive, which limits its continuous availability. Technegas can be an alternative ventilation agent with the advantage of being less expensive and available daily. The aim of this study was to compare the value of technegas with that of (81m)Kr in the detection of PE. METHODS: Ninety-two consecutive patients (29 men; mean +/- SD, 53 +/- 17 y old) with at least one segmental perfusion defect (Hull criteria) were studied prospectively. Perfusion and ventilation (V/Q) lung scintigraphy with both technegas and (81m)Kr were performed within 24 h on all patients. V/Q lung scan results were classified as high probability for PE (normal ventilation study) or nondiagnostic (abnormal ventilation study). All V/Q lung scans were read by two experienced nuclear physicians in consensus. For the intra- and interobserver variabilities, two experienced observers independently read the V/Q lung scans. RESULTS: (81m)Kr and technegas showed a good agreement (kappa, 0.68; 95% confidence interval [CI], 0.53-0.82). However, technegas significantly increased the number of nondiagnostic V/Q lung scans (P: = 0.035). In 15 patients, a discrepancy was found between (81m)Kr and technegas. False-positive V/Q lung scan results occurred in 4 of 12 patients (33%) with (81m)Kr and in 2 of 3 patients (66%) with technegas. The intra- and interobserver variabilities were 0.71-0.88 (95% CI, 0.56-1.0) for perfusion/(81m)Kr and 0.74-0.96 (95% CI, 0.58-1.0) for perfusion/technegas. CONCLUSION: In comparison with (81m)Kr, technegas does not result in more false-positive V/Q lung scan results. The use of technegas, however, increases the number of nondiagnostic V/Q lung scan results, which would increase the demand for further additional testing to confirm or refute PE.

Acute Disease↗
PubMed1975

Factors affecting the cerebrovascular response to noradrenaline in the dog.

1 Noradrenaline infused into the internal carotid artery of the dog (0.01-1 mug kg(-1) min(-1)) constricts the blood vessels of the cortex. This constriction is mediated by the action of noradrenaline on alpha-adrenoceptors of the cerebral arteries.2 Intravenous (1 mug kg(-1) min(-1)) or intra common carotid arterial (0.01-1 mug kg(-1) min(-1)) infusions of noradrenaline cause an increase in cortical blood flow that can be dissociated from changes in blood pressure.3 The effect of intravenous noradrenaline on the cortical blood vessels and metabolism is blocked by high PaCO(2) levels, or by the prior administration of (+/-)-propranolol. (+)-Propranolol is without such effect.4 Following section of both vagi and both sinus nerves, intravenous noradrenaline fails to cause an increase in cortical blood flow.5 In another series of animals the area of the carotid bifurcation was vascularly isolated and perfused with blood from a second dog. Chemoreceptor and baroreceptor activity was shown to be intact.6 Administration of 5% CO(2) to the donor dog caused an increase in cerebral blood flow in the recipient dog.7 Administration of intravenous noradrenaline (1.0 mug kg(-1) min(-1)) to the donor animal caused an increase in cerebral blood flow, cerebral O(2) and glucose utilization of the recipient.8 Administration of 5% CO(2) and intravenous (-)-noradrenaline (1.0 mug kg(-1) min(-1)) caused a further increase in flow and metabolism.9 This evidence suggests that the cerebrovasodilatation observed following intravenous noradrenaline is reflex and is triggered by chemoreceptor activity.10 The evidence also suggests that the antagonism of the cortical dilatory effects of intravenous noradrenaline by raised PaCO(2) in the intact animal must be at a site different from the peripheral chemoreceptors.

Animals↗
PubMed1975

Autoregulatory responses of cerebral blood vessels in hypercapnia.

Simultaneous determinations of cerebral blood flow, measured by 85Kr clearance, and of intracranial pressure, measured in the cisterna magna, were made in anesthetized normocapnic and hypercapnic vagotomized cats. All animals were tested at their normal arterial pressure and at elevated arterial pressure induced by angiotensin infusion. Autoregulatory responses of cerebral blood vessels to the elevation of blood pressure were quantitatively characterized by a pressure-flow function. In 10 of 12 animals, hypercapnia interfered with the autoregulatory responses of the cerebral vasculature. Analysis of the simultaneous behavior of intracranial pressure and cerebral vascular resistance did not indicate that changes in intracranial pressure affected the autoregulatory responses. The results of this study support the view that CO2 interferes with the basic reaction of vascular smooth muscle to contract after distension by increased transmural pressure.

Air↗
PubMed2002

How to use a gestalt interpretation for ventilation-perfusion lung scintigraphy.

UNLABELLED: The use of a so-called gestalt interpretation, an integration of different sets of criteria and the physician's own experience, has been advocated in the interpretation of lung scintigraphs of patients with clinically suspected pulmonary embolism. However, data on the reliability of this approach are limited. The aim of this study was to investigate the observer variability and accuracy of the gestalt interpretation of perfusion scintigraphy (combined with chest radiography) as well as the impact of adding ventilation scintigraphy and clinical pretest information. METHODS: Three experienced observers independently reviewed the chest radiograph and ventilation-perfusion scans of 101 consecutive patients with clinically suspected pulmonary embolism. All datasets were reviewed twice by each observer, using a visual analog scale to indicate the estimated probability of pulmonary embolism. The results of the gestalt interpretations were analyzed against the presence or absence of pulmonary embolism. RESULTS: All 3 gestalt interpretations had a good-to-excellent interobserver variability (intraclass correlation coefficient [ICC], 0.73-0.89), with similar intraobserver agreement (ICC, 0.76-0.95). The performance of all 3 readers was comparable. The areas under the curve (AUCs) of all 3 observers were high and similar (for observer 1, the AUCs were 0.96 [95% confidence interval (CI)], 0.93-1.00), 0.96 (95% CI, 0.93-1.00), and 0.95 (95% CI, 0.90-1.00), respectively, for the 3 gestalt interpretations). CONCLUSION: A gestalt interpretation is a useful classification scheme with good-to-excellent intra- and interobserver variability. However, the interpretation and the consequences of this result are dependent on the observer. Unexpectedly, the addition of information on ventilation scintigraphy and clinical information did not affect the overall assessment.

Female↗
PubMed2002

Distribution of ventilation/perfusion ratios in pulmonary embolism: an adjunct to the interpretation of ventilation/perfusion lung scans.

UNLABELLED: Diagnosis of pulmonary embolism (PE) by visual interpretation of ventilation/perfusion (V/Q) scans is limited by the high percentages of patients classified in the intermediate- and low-probability categories. This study proposes a quantitative analysis of the distribution of V/Q ratios to better identify patients with PE. METHODS: We studied 99 consecutive patients who underwent dual-isotope (81m)Kr/(99m)Tc-macroaggregate V/Q scanning and arterial blood gas analysis within 48 h. The 8-view V/Q scans were visually analyzed by 2 observers according to the revised criteria of the Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED) (normal scan or low, intermediate, or high probability of PE). Quantitative analysis of the posterior-view distribution histogram of V/Q ratios was performed using dedicated software. Briefly, regions of interest were drawn around the lungs on the matched V/Q images, smooth filtering was applied, normalized regional V/Q ratios were calculated within each pixel, and a distribution histogram was built. RESULTS: Patients with normal scans (n = 16) had a predominance of V/Q ratios (63.3% +/- 13.0%) between 0.8 and 1.2. They had only 9.8% +/- 5.8% of ratios > 1.2, and the remaining 26.9% +/- 7.5% of ratios were <0.8. By contrast, patients with PE (n = 34) were characterized by a significant increase (15.5 +/- 10.0%, P = 0.04) in high V/Q ratios (>1.2) and a significant increase (34.5% +/- 8.2%, P = 0.003) in low V/Q ratios (<0.8). Interestingly, a similar pattern was found in patients with a high PIOPED probability of PE, 21.3% +/- 11.0% and 37.5% +/- 9.2%, respectively. Within the nondiagnostic group (intermediate- + low-probability scans, n = 58), 17 patients were finally diagnosed with PE. Analysis of the distribution histogram in this group allowed the identification of 5 patients with PE (specificity, 78%). CONCLUSION: A quantitative approach to lung scan interpretation, based on the distribution histogram of V/Q ratios, may be helpful for categorizing patients with suspected PE.

Adult↗