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Biomedical subjects

D Gur

Publications and source records attributed to D Gur.

At least 109 records · Page 6Linked to original sources
PubMed1987

Effect of low concentration stable xenon on the EEG power spectrum.

The effect on the central nervous system of inhaled stable xenon, at concentrations of 25%, 30% and 35%, was assessed by evaluating changes in power spectra computed on the electroencephalogram. Ten normal adult subjects were studied in a protocol designed as a repeated measures experiment. Synchronous changes in the EEG power spectra were observed with stable xenon inhalation. These changes were equivalent for symmetrical electrode pairs, but the time history of the changes differed depending on the cortical region being measure. This suggests regional effects of stable xenon inhalation on the mechanisms producing the EEG.

Adult↗
PubMed1987

Relief of nonhemispheric symptoms in low flow states by anterior circulation revascularization: a physiologic approach.

Operative intervention remains controversial for patients with transient nonhemispheric symptoms with occlusive disease of both the anterior and posterior cerebral circulations. In addition to the standard evaluation of these patients, we have used stable xenon-enhanced computed tomographic mapping of cerebral blood flow (Xe/CT CBF). This relatively new and potentially widely available CBF methodology, by measuring approximately 30,000 CBF values within each of three CT levels, provides a readily interpretable means of evaluating extremes of hemodynamic compromise within any or all vascular territories. In the past 30 months, Xe/CT CBF studies in 300 patients with occlusive vascular disease have identified nine patients with global low flow and nonhemispheric symptoms (vertigo, lightheadedness, and/or blurred vision). Blood pressures determined by ocular pneumoplethysmography of Gee were markedly abnormal with reduced ocular/brachial ratios. Each patient had a combination of both segmental carotid and vertebrobasilar occlusive disease. Each patient had a flow-augmenting procedure performed on the anterior circulation in an attempt to improve global flow: carotid endarterectomy (two patients), subclavian-external carotid bypass (one patient), and superficial temporal artery-middle cerebral artery bypass (six patients). In each case disabling transient symptoms were relieved. There were no operative deaths, but one stroke occurred, probably as a result of a brief period of postoperative hypotension. Postoperative Xe/CT CBF studies show a long-term improved global CBF in all patients.

Brain↗
PubMed1987

Adverse reactions to xenon-enhanced CT cerebral blood flow determination.

Fourteen institutions performed 1,830 computed tomographic (CT) cerebral blood flow (CBF) examinations with 32% inhaled stable xenon. Respiratory rate delay greater than 10 seconds occurred in 3.6% of patients, with 83% of the delays lasting 10-15 seconds. There was no incident of prolonged respiratory difficulty. Headache (0.4%), seizures (0.2%), nausea and vomiting (0.2%), and change in neurologic status (0.1%) were uncommon, and there were no transient ischemic attacks. The CT CBF method with 32% inhaled stable xenon is thus associated with an acceptably low incidence of adverse reactions.

Brain↗
PubMed1986

Probability of causation tables and their possible implications for the practice of diagnostic radiology.

In compliance with requirements in the Orphan Drug Act (97-414) of 1983, tables were recently constructed by an ad hoc committee of the National Institutes of Health (NIH) in which the probabilities that certain specific cancers are caused by previous radiation exposure are estimated. The reports of the NIH committee and a National Academy of Science oversight committee may have broad implications for the future practice of diagnostic radiology. The basis on which the probability of causation tables were established and some of the possible implications for diagnostic radiology are discussed.

Dose-Response Relationship, Radiation↗
PubMed1986

Xenon/CT cerebral blood flow determination following cranial trauma.

Xenon/CT cerebral blood flow (CBF) analysis has been utilized in the evaluation of 35 patients sustaining severe cranial trauma. The patient population included closed head injury, focal hematoma, and the sequelae of trauma including coma, persistent alteration of consciousness, and brain death. Xe/CT CBF analysis has proven helpful in the determination of appropriate degrees of hyperventilation therapy for the head injured patient. The technique is helpful for determining both local and remote changes of CBF as an aid in deciding upon surgical intervention. Severely decreased flows, compatible with brain death, can be demonstrated. The technique shows promise in the evaluation of physiologic changes accompanying therapy for the injured brain.

Adult↗
PubMed1986

Cerebral blood flow measured by xenon-enhanced computed tomography as a guide to management of patients with cerebrovascular disease.

CT scanning performed before and sequentially during the inhalation of stable xenon (32%), coupled with end-tidal xenon measurements, has made possible the routine construction of regional cerebral blood flow (rCBF) maps with resolution that approximates that of the CT scanner. The capability of obtaining quantitative flow maps with direct anatomic correlation is now available with a commercial package of hardware and software adapted to the General Electric 9800 scanner. The ability to distinguish between normal and reduced rCBF in specific vascular territories has proved useful in the management of cerebrovascular disease. Specific clinical dilemmas that have been addressed with rCBF information from xenon-enhanced CT scanning include the following: In the patient with asymptomatic occlusive disease, is normal rCBF preserved? Is there adequate collateral flow? Are cerebrovascular symptoms a result of emboli or chronic regional low flow? In the patient with complex multivessel occlusive disease, which revascularization procedure is indicated first? Did operation improve rCBF? Should a further procedure be added? May a diffusely diseased but patent artery, which is the source of emboli, be sacrificed safely without compromising rCBF? On the basis of experience with 155 patients, the management and understanding of cerebrovascular disease has been aided substantially by the incorporation of rCBF mapping by xenon-enhanced CT scan in the evaluation of these patients.

Aged↗
PubMed1985

Simultaneous measurements of cerebral blood flow by the xenon/CT method and the microsphere method. A comparison.

Simultaneous measurements of cerebral blood flow have been performed in baboons to assess the correlation between the acute and invasive nondiffusible microsphere technique and the noninvasive xenon-enhanced CT method. Blood flows in small tissue volumes (approximately 1 cm3) were directly compared. The results of these studies demonstrate a statistically significant association between the two methods (P less than .001). Similar correlations were obtained by both the Kendall tau (tau) and the Spearman (r) methods. The problems and limitations of such correlations are discussed.

Animals↗
PubMed1985

Central herniation revealed by focal decrease in blood flow without elevation of intracranial pressure: a case report.

Until recently, in standard hospital settings the tissue blood supply could be inferred only from indirect measures such as assessment of the clinical signs and intracranial pressure (ICP) monitoring. This critical parameter can now be imaged directly with stable xenon-enhanced computed tomographic (CT) imaging. The procedure requires only an additional 10 minutes after a standard head study, yet it provides potentially vital information about tissue perfusion. We describe here a patient in whom a frontal lobe hematoma produced a direct mass effect, causing an element of central herniation with relative sparing of lateral and posterior cortical regions. Although the ICP recordings remained unchanged, symptoms of brain stem compression became apparent. Xenon/CT cerebral blood flow (CBF) mapping demonstrated a flow decrease mainly within the left frontal lobe and throughout central ganglionic structures. After removal of the left frontal hematoma, both clinical status and local and central flow improved. Because the xenon/CT method combines direct anatomical information with blood flow information in one examination, it may be a valuable clinical tool in providing a better understanding of pathophysiology in patients with head injuries and other mass lesions.

Adult↗
PubMed1985

Stable xenon CT blood flow mapping for evaluation of patients with extracranial-intracranial bypass surgery.

Xenon computerized tomography (Xe CT) blood flow studies were conducted in 25 patients referred for a possible extracranial-intracranial bypass procedure for occlusive vascular disease in one or more extra- or intracranial vessels. These studies were helpful in selecting eight candidates for surgery. The Xe CT studies were performed at one or two brain levels using a prototype Xe CT system for measurement of cerebral blood flow which was designed in collaboration with the General Electric Co., and adapted for the GE 9800 scanner. In those patients selected to undergo operation, Xe CT demonstrated compromise of flow reserve regionally, globally, and/or in the watershed area. All eight patients who underwent the procedure showed a favorable clinical response postoperatively, and seven had a dramatic increase in flow. The 17 patients whose baseline CT studies showed no reduction of flow with the Xe CT method were not selected for surgery. All 25 patients have remained neurologically stable to date. Case studies of three of the eight patients undergoing bypass surgery are presented. This limited but consistent experience suggests that Xe CT blood flow mapping makes possible the recognition of brain regions in which flow reserves are compromised. This is due to the relatively high degree of spatial resolution that this technique provides and to the fact that mapping can be correlated directly with the anatomy. Used in combination with a careful clinical examination and an accurate medical history, this study method appears to be a useful guide in the selection of patients who are most at risk from hemodynamic instability and those who are most likely to benefit from flow-augmentation surgery.

Aged↗
PubMed1984

Local lung ventilation in critically ill patients using nonradioactive xenon-enhanced transmission computed tomography.

Nonradioactive xenon is sufficiently radiodense to increase the density of gas-containing lung as seen in a computed tomography (CT) scan. Subtraction of a baseline CT scan from the xenon-enhanced CT scan can accentuate gas space differences by subtracting fixed tissue densities. The baseline scan and the scan obtained during wash-in of xenon (before equilibration) allow circulation of local ventilation. The xenon CT scan, thus, provides more precise information about distribution of ventilation than planar radiogas techniques. The technical aspects of application to a critically ill patient and the mathematical basis of the technique are presented.

Humans↗
PubMed1984

Local cerebral blood flow alterations (Xe-CT method) in an accident victim.

Computed tomography was used before and during inhalation of nonradioactive xenon gas to measure and map local cerebral blood flow noninvasively at two PaCO2 levels in a 19-year-old accident victim. The technique demonstrated normal response to elevated PaCO2 with only a regional loss of autoregulation.

Adult↗
PubMed1984

Xenon/CT blood flow mapping of the kidney and liver.

A noninvasive technique for measuring blood flow by xenon-enhanced X-ray transmission CT has been developed and reported quite extensively in recent years. In this method nonradioactive xenon gas is inhaled, and the temporal changes in radiographic enhancement produced by the inhalation are measured by sequential CT. Time-dependent xenon concentration within various tissue segments is used to derive local blood flow maps. The method has been amply discussed in relation to assessment of local cerebral blood flow. Its application to other body organs is explored in this paper, in which results from six preliminary blood flow studies in the liver and kidneys of nonhuman primates are reported. Blood flow in renal cortex ranged from 150 to 280 ml/100 cc/min and hepatic tissue perfusion from 80 to 120 ml/100 cc/min. The advantages and limitations of the method in such applications are discussed.

Animals↗
PubMed1984

Mapping cerebral blood flow by xenon-enhanced computed tomography: clinical experience.

Local cerebral blood flow was measured and mapped using xenon-enhanced x-ray transmission computed tomography. Studies involving 4-6 minutes of xenon-oxygen inhalation can be performed routinely in awake and anesthetized patients with acceptable patient tolerance and compliance. Several case studies of patients with acute and chronic ischemic injuries and other cerebral abnormalities are presented to illustrate characterization of flow pattern in normal and abnormal tissue, as well as the relevance of this flow information to clinical patient management.

Aged↗
PubMed1982

In vivo mapping of local cerebral blood flow by xenon-enhanced computed tomography.

A noninvasive technique has been developed to measure and display local cerebral blood flow (LCBF) in vivo. In this procedure, nonradioactive xenon gas is inhaled and the temporal changes in radiographic enhancement produced by the inhalation are measured by sequential computerized tomography. The time-dependent xenon concentrations in various anatomical units in the brain are used to derive both the local partition coefficient and the LCBF. Functional mapping of blood flow with excellent anatomical specificity has been obtained in the baboon brain. The response of LCBF to stimuli such as changes in carbon dioxide concentrations as well as the variability in LCBF in normal and diseased tissue can be easily demonstrated. This method is applicable to the study of human physiology and pathologic blood flow alterations.

Animals↗
PubMed1982

Errors associated with single-scan determinations of regional cerebral blood flow by xenon enhanced CT.

Possible errors in the determination of xenon concentrations in arterial blood, and uncertainties in CT tissue enhancements during inhalation of xenon-oxygen mixtures, are used to assess errors in the determination of regional cerebral blood flow by the in vivo autoradiographic (single-scan) technique. The results of this study indicate that errors associated with the determination of xenon concentrations in arterial blood decrease rapidly as the time of scanning after the initiation of xenon inhalation is increased. Analysis of errors caused by statistical uncertainties in image enhancement indicate that time of scanning is optimal between 1.5 and 2.5 min for determination of fast flow, while errors in slow-flow determinations gradually decrease as the time of scanning increases.

Autoradiography↗