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G Barr

Publications and source records attributed to G Barr.

At least 19 recordsLinked to original sources
PubMed2006

Observation of muon neutrino disappearance with the MINOS detectors in the NuMI neutrino beam.

This Letter reports results from the MINOS experiment based on its initial exposure to neutrinos from the Fermilab NuMI beam. The rates and energy spectra of charged current nu(mu) interactions are compared in two detectors located along the beam axis at distances of 1 and 735 km. With 1.27 x 10(20) 120 GeV protons incident on the NuMI target, 215 events with energies below 30 GeV are observed at the Far Detector, compared to an expectation of 336+/-14 events. The data are consistent with nu(mu) disappearance via oscillations with |Delta(m)2/32|=2.74 +0.44/-0.26 x10(-3)eV(2) and sin(2)(2theta(23))>0.87 (68% C.L.).

Journal Article↗
PubMed2005

Are even impaired fasting blood glucose levels preoperatively associated with increased mortality after CABG surgery?

AIMS: Impaired fasting glucose (IFG) below the diagnostic threshold for diabetes mellitus (DM) is associated with macrovascular pathology and increased mortality after percutaneous coronary interventions. The study goal was to determine whether pre-operative fasting blood glucose (fB-glu) is associated with an increased mortality after coronary artery bypass grafting (CABG). METHODS AND RESULTS: During 2001-03, 1895 patients underwent primary CABG [clinical DM (CDM) in 440/1895; complete data on fB-glu for n=1375/1455]. Using pre-operative fB-glu, non-diabetics were categorized as having normal fB-glu (<5.6 mmol/L), IFG (5.6< or =fB-glu<6.1 mmol/L), or suspected DM (SDM) (> or =6.1 mmol/L). fB-glu was normal in 59%. The relative risks of 30 day and 1 year mortality compared with patients with normal fB-glu was 1.7 [95% confidence interval (CI): 0.5-5.5] and 2.9 (CI: 0.8-11.2) with IFG, 2.8 (CI: 1.1-7.2) and 1.9 (CI: 0.5-6.3) with SDM vs. 1.8 (CI: 0.8-4.0) and 1.6 (CI: 0.6-4.3) if CDM, respectively. The receiver operator characteristic area for the continuous variable fB-glu and 1 year mortality was 0.65 (P=0.002). CONCLUSION: The elevated risk of death after CABG surgery known previously to be associated with CDM seems also to be shared by a group of similar size that includes patients with IFG and undiagnosed DM.

Aged↗
PubMed2005

Effects of thoracic epidural analgesia on glucose homeostasis after cardiac surgery in patients with and without diabetes mellitus.

BACKGROUND AND OBJECTIVE: Even moderate hyperglycaemia increases mortality/morbidity after coronary artery bypass grafting, stroke and myocardial infarction. The goal of this prospective study was to determine if using thoracic epidural analgesia from start of surgery until the end of the third postoperative day would blunt postoperative hyperglycaemia. METHODS: Forty-four patients had diabetes mellitus, 60 did not; half of each group had an epidural with continuous local anaesthetics. All patients received continuous insulin infusions during the initial 24 h period beginning with surgery. Blood glucose was measured four times daily (fasting or 2-3 h post-prandial) until end of the third postoperative day. RESULTS: For patients without diabetes, the epidural group had lower mean blood glucose and insulin requirements (P < 0.02) than controls during the initial 24 h period beginning with surgery. For patients with diabetes mellitus, thoracic epidural analgesia reduced mean blood glucose (P = 0.017) with unchanged insulin requirements. Epidural did not diminish the increase (vs. preoperative) in fasting blood glucose on the third postoperative day (32% vs. 22%, P < 0.001) for non-diabetics. Epidural analgesia was not able to attenuate hyperglycaemia during the first 3 postoperative days. CONCLUSIONS: Epidural analgesia improved glucose homeostasis minimally during the initial 24 postoperative hours but did not attenuate hyperglycaemia during the subsequent 3 postoperative days.

Aged↗
PubMed2005

Clinical comparison of three different anaesthetic depth monitors during cardiopulmonary bypass.

The lack of a gold standard complicates the evaluation and comparison of anaesthetic depth monitors. This randomised study compares three different depth-of-anaesthesia monitors during cardiopulmonary bypass (CPB) at 34 degrees C with fentanyl/propofol anaesthesia adjusted clinically and blinded to the monitors. Coronary artery bypass grafting patients (n = 21) were randomly assigned to all three possible paired combinations of three monitors: Bispectral Index (Aspect Medical), AAI auditory evoked potential (Danmeter), Entropy (Datex-Ohmeda). Indices were manually recorded every 5 min during CPB. Agreement between paired indices was classified as good, non-, or disagreement. Anaesthesia was classed as adequate, inadequate, or excessive according to recommended index values. Of the 255 paired indices recorded, 62% showed good agreement, 33% showed non-agreement, and 5% showed disagreement. Using good agreement between two monitors as a gold standard, a quarter of the measurements indicate inappropriate anaesthetic depth monitoring during CPB with clinically titrated anaesthetic depth.

Adult↗
PubMed2005

Cerebral state index during anaesthetic induction: a comparative study with propofol or nitrous oxide.

BACKGROUND: Confidently predicting the depth of anaesthesia for the individual patient and independently of drug(s) type using EEG-based monitors has proven difficult. This open, randomized, explorative study of day surgical patients evaluates the ability of the Cerebral State Monitor (Danmeter AB, Odense, Denmark) of anaesthetic depth to identify loss of response (LOR) using either propofol or N(2)0 for induction. METHODS: In this open, randomized study, day surgical patients (n=10 in each group) were studied using the Cerebral State Index Monitor. After baseline measurements, induction to LOR was achieved with either repeated 30-mg boluses of propofol every second minute or with N(2)0 (after premedication 5 min before with 30 mg propofol) increased every other minute in 15% increments (max. 75%). Sedation level was evaluated every other minute using the Observer's Assessment of Alertness/Sedation scale. RESULTS: Baseline values were 91 (82-98) and 94 (82-100) for N(2)0 and propofol patients, respectively. During induction CSI decreased with increasing sedation in patients given propofol (P<0.001) but not in patients given nitrous oxide. Median value at LOR was 56 (40-76) and 95 (87-100) for the propofol and nitrous oxide group of patients, respectively. CONCLUSION: The Cerebral State Index(trade mark) behaves as other depth of anaesthesia monitors with a progressive decrease during propofol induction but loss of consciousness with N(2)0 results in no change in CSI.

Adolescent↗
PubMed2004

A membrane-mimetic barrier for islet encapsulation.

BACKGROUND: Enhanced control of both transport properties and surface physiochemical characteristics will be important steps in the development of an effective immunoisolation barrier critical to the success of pancreatic islet cell transplantation. We hypothesize that the cell membrane establishes an important paradigm for the design of a biomimetic immunoisolation barrier with improved performance characteristics because of its capacity to control interfacial mass transport, as well as its ability to act as a template for more complex structures with other immunoregulatory macromolecules. METHODS: Islets were isolated from Wistar rats using collagenase digestion and a discontinuous Ficoll-Histopaque gradient and subsequently encapsulated in 2% alginate. After coating with a polyelectrolyte multilayer of polylysine and alginate, a polymeric membrane-mimetic coating was applied to the capsule surface. Individual islet viability was evaluated at each stage of the encapsulation procedure by use of a two-color live/dead cell assay. Preservation of islet function was determined by transplanting 1000 encapsulated islets into the peritoneal cavity of streptozotocin-induced diabetic nonobese diabetic NOD/Scid mice. RESULTS: At the end of the coating procedure, the proportion of viable cells within each islet was >50% in 88% of encapsulated rat islets and >75% in over half of the encapsulated cohort. Nonfasting blood glucose levels normalized within 24 hours after transplantation (n = 8). Normoglycemia has been maintained in all mice with the longest time course being 73 days thus far. CONCLUSIONS: We have demonstrated that microencapsulated islets coated with a membrane-mimetic thin film can be generated with high viability in vitro and persistent function in vivo.

Animals↗
PubMed2004

Entropy during propofol hypnosis, including an episode of wakefulness.

Depth of anaesthesia has proved to be a complex process to quantify. Monitors based on bispectral analysis of the electroencephalogram and auditory evoked potential have been available, but only recently has a monitor based on entropy become available. This study determined state entropy and response entropy in nine healthy volunteers during propofol hypnosis with a brief intervening period of wakefulness. Both the calculated entropy indices decreased with increasing levels of sedation (r2 = 0.58 and 0.61, respectively) and they showed a high correlation with each other (r2 = 0.94). However, an overlap was observed in real time indices between different stages of the Observer's Assessment of Alertness/Sedation Scale. Only three of the nine volunteers had explicit memories from the episode of wakefulness. Electroencephalographic entropy monitors seem to have potential for staging clinical hypnotic effects.

Adolescent↗
PubMed2003

The AAI index, the BIS index and end-tidal concentration during wash in and wash out of sevoflurane.

The bispectral index (BIS), auditory evoked potential index (AAI) and the end-tidal sevoflurane concentration were studied during induction and emergence in 10 ASA I-II patients. Both during 'wash-in' and 'wash-out' of sevoflurane, the AAI and BIS indices show huge variability and an overlap of indices between awake and not responding to command. This was the most pronounced during induction and the range of values was larger for the AAI index as compared with the BIS index. Mean (range) BIS was 85 (73-98) and 48 (10-83) awake and unconscious, respectively, and mean AAI index was 71 (43-99) and 21 (4-85), respectively. This study demonstrates the difficulties of using processed EEG variables in real time in a clinical situation of non-steady state pharmacodynamics.

Anesthetics, Inhalation↗
PubMed2002

The effects of nitrous oxide on the auditory evoked potential index during sevoflurane anaesthesia.

We have studied the effects of nitrous oxide on the auditory evoked response index (AAI-index) derived from the A-line monitoring device during sevoflurane anaesthesia in 21 patients undergoing minor ambulatory surgery. During sevoflurane anaesthesia with an AAI-index < 30, the addition or withdrawal of nitrous oxide in a concentration of 66% end tidal did not show any linear dose dependent change in AAI-index . However, comparing nitrous oxide > 40% to nitrous oxide < 10% end tidal concentration the AAI-index did decrease, p < 0.05. The AAI-index is either non-linear at deeper anaesthetic levels or is insensitive to the anaesthetic effects of nitrous oxide in terms of MAC-multiples.

Adult↗
PubMed2001

Being awake intermittently during propofol-induced hypnosis: a study of BIS, explicit and implicit memory.

BACKGROUND: Being awake during anaesthesia is a serious complication. An anaesthetic depth monitor must discriminate in real time between wakefulness and unconsciousness. The present study created a period of wakefulness during propofol-induced hypnosis. Bispectral index (BIS), explicit and implicit memories of the awake period were investigated. METHODS: Ten volunteers were studied. The calculated brain concentration of a target controlled infusion of propofol was increased until loss of response (LOR) to verbal command and then propofol was stopped. When fully awake, volunteers were presented with a picture, sound and smell. Propofol infusion was restarted until LOR and then ceased. BIS and the calculated brain concentration of propofol were recorded every minute. A structured interview was conducted for explicit memories after awakening and for explicit as well as implicit memories the day after. RESULTS: Median BIS-index for the transition between awake and asleep and vice versa differed significantly. It was not possible, however, to establish any threshold value or zone for discriminating between wakefulness and LOR due to the large inter-individual variations in BIS-index. No volunteer could explicitly recall any of the stimuli presented during the period of wakefulness. CONCLUSION: The BIS-index decreases with increasing sedation but because of the large individual variations, the real-time BIS-index for the individual subject cannot reliably discriminate wakefulness from unconsciousness during propofol infusion. Propofol causes such profound amnesia that lack of postoperative recall does not assure that episodes of awareness have not occurred during propofol-induced hypnosis.

Acoustic Stimulation↗
PubMed2001

A study of bispectral analysis and auditory evoked potential indices during propofol-induced hypnosis in volunteers: the effect of an episode of wakefulness on explicit and implicit memory.

The bispectral index (BIS) and the auditory evoked potential (AEP) index as calculated by the new A-line monitor were measured during hypnosis with propofol, which included an episode of wakefulness. Both indices followed a similar pattern during sedation, with values decreasing with sedation and increasing when awake. Baseline AEP values varied between 60 and 98, and BIS values were between 96 and 98. The AEP-index value was at all times 10-20 points lower than the BIS-index. The transition to loss of response occurred at a mean AEP value of 46 and BIS value of 58. The transition to just responding following a period of unconsciousness occurred at a mean AEP value of 46 and BIS 65. Both monitoring techniques, however, displayed large interindividual variations making it impossible to discriminate in real time between subtle changes of clinical state. The new neurophysiological monitors A-line AEP and BIS are interesting tools for creating a better understanding of the anaesthetic effects of drugs; however, further refinements are required before their relative roles can be fully established in the clinical setting.

Adult↗
PubMed2000

Charge densities from high-resolution synchrotron X-ray diffraction experiments.

The combination of intense X-ray sources, especially synchrotron radiation, with area-detector technology has accomplished an enormous advance in the experimental conditions available for charge-density analysis by single-crystal high-resolution X-ray diffraction. Such experiments can now be carried out in a time measured in hours rather than weeks. Some features of these experiments are examined and preliminary results are reported for charge-density studies of 2-hydroxy-5-nitrobenzaldehyde N-cyclohexylimine (1), octakis(m-tolylthio)naphthalene (2), and 7-fluoro-4-styrylcoumarin (3). Weak interactions in crystals of (1) and (3) are found to have similar charge-density characteristics. Cages in the crystal lattice of (2) have a complex charge distribution.

Journal Article↗
PubMed2000

Effects on the bispectral index during medium-high dose fentanyl induction with or without propofol supplement.

BACKGROUND: The search for a drug-independent monitor to determine depth of anaesthesia and hypnosis continues. The bispectral analysis (BIS) of the EEG correlates well with the clinical dose-response of hypnotic drugs during induction, but the effect on BIS of an opiate induction, as for coronary bypass surgery, is not known. METHODS: Fourteen patients scheduled for elective coronary bypass surgery were studied. BIS was recorded during induction in 7 patients receiving 10 microg/kg fentanyl without any hypnotic agent and in 7 patients receiving 0.5 mg/kg propofol before the fentanyl dose. RESULTS: The effect of fentanyl was very variable both regarding BIS and clinical response. Five of the 7 patients that received only fentanyl lost their response to verbal command within 8 min. BIS values at loss of response varied between 45 and 94. One patient remained awake with BIS 43. All 7 patients receiving propofol before the fentanyl dose lost their response to verbal command within 5 min. BIS values at the time for loss of response varied between 78 and 98. CONCLUSION: Loss of response to verbal command when a medium-high dose of fentanyl is used for induction cannot be distinguished from wakefulness with adequate sensitivity by BIS. The current BIS algorithm seems not to accurately reflect the hypnotic effects of fentanyl.

Aged↗
PubMed2000

Fentanyl and midazolam anaesthesia for coronary bypass surgery: a clinical study of bispectral electroencephalogram analysis, drug concentrations and recall.

Bispectral index (BIS) was assessed as a monitor of depth of anaesthesia during fentanyl and midazolam anaesthesia for coronary bypass surgery. In 10 patients given morphine premedication, anaesthesia was induced with a combination of midazolam and fentanyl and thereafter maintained with a continuous infusion of a mixture of midazolam and fentanyl 5 and 50 micrograms kg-1 h-1, respectively. BIS was recorded continuously but not shown to the attending anaesthetist. Plasma concentrations of midazolam and fentanyl were measured five times during the procedure. An auditory stimulus was given during bypass. All patients were interviewed twice after operation for explicit and implicit recall. No patient had any anaesthetic complications. BIS decreased during anaesthesia, but varied considerably during surgery (range 36-91) with eight patients having values > 60. Midazolam and fentanyl drug concentrations did not correlate with BIS. No patient reported explicit or implicit recall. During clinically adequate anaesthesia with midazolam and fentanyl BIS varies considerably. The most likely reason is that BIS is not an accurate measure of the depth of anaesthesia when using this combination of agents.

Acoustic Stimulation↗
PubMed1999

Nitrous oxide does not alter bispectral index: study with nitrous oxide as sole agent and as an adjunct to i.v. anaesthesia.

We have studied the effect of nitrous oxide on bispectral index (BIS), calculated from a bipolar encephalogram. Inhalation of 70% nitrous oxide resulted in loss of consciousness in all healthy volunteers (n = 10) but no change in BIS. Brief inhalation up to 1.2% sevoflurane also resulted in loss of consciousness in volunteers (n = 5), but with sevoflurane, BIS decreased. BIS and the haemodynamic effects of adding nitrous oxide were also measured during coronary artery bypass surgery in patients (n = 10) receiving midazolam and fentanyl infusions. Measurements were made after 0%, 33%, 66% and 0% nitrous oxide, just before skin incision and after sternotomy. Nitrous oxide caused no change in BIS. BIS may indicate a sufficient hypnotic depth to prevent awareness during surgery, but our study demonstrated that pharmacological unconsciousness-hypnosis can also be reached by mechanisms to which BIS is not sensitive. Thus BIS is a sufficient but not a necessary criterion for adequate depth of anaesthesia or prevention of awareness.

Adult↗
PubMed1995

Is endothelin-1 release at reperfusion of the ischaemic human heart due to cold-induced displacement of endothelin from binding sites?

Following reperfusion of ischaemic human hearts subjected to cold (4 degrees C) cardioplegia during coronary bypass surgery, there was an increase in cardiac outflow of endothelin-1 but not the pro-peptide big endothelin-1. Furthermore, specific endothelin-1 binding in human lung membrane preparations was displaced by incubation in buffer medium at 4 degrees C. The present results thus indicate that cold-induced displacement of endothelin-1 binding, rather than increased synthesis, may explain the cardiac release of endothelium-1 following ischaemia during heart surgery in which cold cardioplegia has been used.

Aged↗