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Biomedical subjects

J Palmer

Publications and source records attributed to J Palmer.

At least 73 records · Page 4Linked to original sources
PubMed2000

A signal detection model predicts the effects of set size on visual search accuracy for feature, conjunction, triple conjunction, and disjunction displays.

Recently, quantitative models based on signal detection theory have been successfully applied to the prediction of human accuracy in visual search for a target that differs from distractors along a single attribute (feature search). The present paper extends these models for visual search accuracy to multidimensional search displays in which the target differs from the distractors along more than one feature dimension (conjunction, disjunction, and triple conjunction displays). The model assumes that each element in the display elicits a noisy representation for each of the relevant feature dimensions. The observer combines the representations across feature dimensions to obtain a single decision variable, and the stimulus with the maximum value determines the response. The model accurately predicts human experimental data on visual search accuracy in conjunctions and disjunctions of contrast and orientation. The model accounts for performance degradation without resorting to a limited-capacity spatially localized and temporally serial mechanism by which to bind information across feature dimensions.

Adult↗
PubMed1999

Charged cyclodextrin-mediated sample stacking in micellar capillary electrophoresis. A simple method for enhancing the detection sensitivity of hydrophobic compounds.

The development of on-line sample stacking techniques for enhancing limits of detection of neutral analytes in micellar capillary electrophoresis (MCE) has recently gained much attention. Utilizing high-conductivity sample matrices to invoke sample stacking is promising, but requires the limited use of sample solubilizing agents such as alcohols in the sample matrix. In this study, we show how simple replacement of the sample solvent (methanol) with a solution of sulfated beta-cyclodextrin (s beta-CD) allows a significant increase in the sensitivity of detection of model hydrophobic analytes. This increase in sensitivity is accompanied by significant peak sharpening. Sulfated CDs in the sample matrix allow for effective solubilization of hydrophobic analytes without the use of organic solvents such as methanol. The testing of various sample matrix s beta-CD concentrations for their effect on peak sharpening identified 3 to 5% as optimal for the estrogen standards. The use of a s beta-CD sample matrix allowed for hydrostatic injections (3.5 kPa) of 297 s, compared with 4 s when the analytes were dissolved in methanol. A mechanism explaining the s beta-CD-induced effect involves an analyte transfer mechanism where the s beta-CDs, despite providing anodic mobility to analytes in the sample zone, are able to transfer analytes to trailing separation buffer micelles for "recycling" back into the sample zone without compromising the stacking process. The overall improvement in sensitivity allows detection of estrogens in the parts-per-billion range and stands to improve the utility of MCE as a bioanalytical technique.

Chromatography, Micellar Electrokinetic Capillary↗
PubMed1999

Adverse effects of mycophenolate mofetil in pediatric renal transplant recipients with presumed chronic rejection.

BACKGROUND: Mycophenolate mofetil (MMF) has been shown to be superior to azathioprine in reducing the incidence of acute rejection in adult renal transplant recipients. Although MMF is also being widely used in pediatric transplant patients, data documenting its safety are limited. METHODS: A retrospective review of the transplant records at St. Christopher's Hospital for Children was conducted to identify patients who had received MMF. RESULTS: Twenty-four children were switched from azathioprine to MMF, 4.8+/-2.9 years after transplantation. After an additional 0.8+/-0.4 years, MMF had been discontinued in 13 patients (54%) because of adverse effects (AE). The only variable that predicted the development of AE was a lower calculated creatinine clearance at the time of initiation of MMF. CONCLUSIONS: In pediatric renal transplant recipients with impaired renal function, the use of MMF at the recommended dose is associated with an unacceptably high incidence of AE; in such patients, the MMF dose may require modification for the level of renal function.

Adolescent↗
PubMed1999

Characterization of the imitation switch subfamily of ATP-dependent chromatin-remodeling factors in Saccharomyces cerevisiae.

We have identified and characterized two Imitation Switch genes in Saccharomyces cerevisiae, ISW1 and ISW2, which are highly related to Drosophila ISWI, encoding the putative ATPase subunit of three ATP-dependent chromatin remodeling factors. Purification of ISW1p reveals a four-subunit complex with nucleosome-stimulated ATPase activity, as well as ATP-dependent nucleosome disruption and spacing activities. Purification of ISW2p reveals a two-subunit complex also with nucleosome-stimulated ATPase and ATP-dependent nucleosome spacing activities but no detectable nucleosome disruption activity. Null mutations of ISW1, ISW2, and CHD1 genes cause synthetic lethality in various stress conditions in yeast cells, revealing the first in vivo functions of the ISWI subfamily of chromatin-remodeling complexes and demonstrating their genetic interactions. A single point mutation within the ATPase domain of both ISW1p and ISW2p inactivated all ATP-dependent biochemical activities of the complexes, as well as the ability of the genes to rescue the mutant phenotypes. This demonstrates that the ATP-dependent chromatin-remodeling activities are essential for the in vivo functions of both ISW1 and ISW2 complexes.

Adenosine Triphosphatases↗
PubMed1999

Determination of a 'GW cocktail' of cytochrome P450 probe substrates and their metabolites in plasma and urine using automated solid phase extraction and fast gradient liquid chromatography tandem mass spectrometry.

A mass spectrometry based method for the simultaneous determination of an in vivo Greenford-Ware or 'GW cocktail' of CYP450 probe substrates and their metabolites in both human plasma and urine is described. The probe substrates, caffeine, diclofenac, mephenytoin, debrisoquine, chlorzoxazone and midazolam, together with their respective metabolites and stable isotope labelled internal standards, are simultaneously extracted from the biological matrix using solid phase extraction in 96-well microtitre plate format, automated by means of a custom built Zymark robotic system. The extracts are analysed by fast gradient high performance liquid chromatography (HPLC) with detection by tandem mass spectrometry (MS/MS) using thermally and pneumatically assisted electrospray ionisation in both positive and negative ion modes and selected reaction monitoring. The methods are specific, accurate and precise with intra- and inter-assay precision (%CV) of less than 15% for all analytes.

Automation↗
PubMed1999

A randomised controlled trial of home-based rehabilitation versus outpatient-based rehabilitation for patients suffering from chronic schizophrenia.

BACKGROUND: Outpatient-based treatments for patients suffering from chronic schizophrenia inadvertently exclude a significant proportion of subjects because they are often too poorly motivated to attend for treatment. In addition there are also concerns about whether the skills that are learnt in a hospital setting will generalize to situations when the individuals are at home. This study attempted to redress some of these potential deficiencies and followed on from an earlier local study which found that a community-based team met more of the needs of patients suffering from chronic schizophrenia. METHOD: Seventy-five patients suffering from chronic schizophrenia were allocated randomly to receive traditional outpatient-based or home-based rehabilitation from a clinical psychologist and an occupational therapist. They were assessed before and after 9 months of treatment on a range of clinical, social and quality of life outcomes. Distress to carers was also assessed. Readmission to hospital was recorded for each subject. RESULTS: There were significant reductions in socially embarrassing behaviour (SBS), increases in interpersonal functioning and recreational activities and a trend for quality of life to improve in the home-based group. There were fewer admissions in the home-based group but the differences, although financially substantial, were not statistically significant. CONCLUSIONS: The home-based rehabilitation service was well received by the majority of patients suffering from chronic schizophrenia and led to some improvement in social behaviour, interpersonal functioning, recreational activities and quality of life.

Adult↗
PubMed1999

Infants code the direction of chromatic quadrature motion.

The present experiment uses a quadrature motion paradigm to investigate the motion correspondence cues used by young infants for coding the direction of motion of red/green isoluminant gratings. Three-month-old infants and adults were tested with 0.25 c/d luminance-modulated or red/green isoluminant gratings, either moving continuously or shifted in spatial quadrature. Both direction-of-motion and detection thresholds were measured, and motion:detection (M:D) threshold ratios were examined. Infants, like adults, could code the direction of motion of red/green quadrature-shifted gratings. In adults, M:D ratios were similar for continuous and quadrature motion. In infants, M:D ratios were higher for quadrature than for continuous motion, but elevations of similar magnitude were seen for both luminance-modulated and red/green gratings. The results suggest that frequency-doubled signals, such as those often seen in the magnocellular (M-cell) pathway, are not necessary for coding the direction of motion of isoluminant gratings in infant subjects. Two other theoretical options--mediation by the scatter of isoluminance points in the M-cell population, and parvocellular (P-cell) mediation--are discussed.

Adult↗
PubMed1999

[Acute myocardial infarct studied by magnetic resonance with gadolinium-DTPA contrast compared to echocardiography].

INTRODUCTION AND OBJECTIVES: Gadolinium-DTPA used as a contrast agent in magnetic resonance imaging allows the detection and quantification of the necrotic area in acute myocardial infarction. The aim of the present study is to assess the value of this method for the diagnosis of myocardial infarction in comparison with clinical and echocardiographic data. METHODS: Contrast magnetic resonance imaging and echocardiographic studies were performed on 16 patients during the first week after admission for acute myocardial infarction. Necrotic and total myocardial mass were calculated from magnetic resonance images and this was compared to the extension of the myocardial infarction assessed by electrocardiography and the peak level of total creatinine-phosphokinase serum enzyme. The number and localization of myocardial segments showing contrast uptake was related to segments with contractile abnormalities at the echocardiographic exam. RESULTS: The mean value of the mass of myocardial necrosis calculated from the total area of gadolinium-DTPA uptake in each patient was 25 g (range: 2-67 g), corresponding to 17% of the total myocardial mass (range: 1-45%). This value correlated with the peak serum level of total creatinine-phosphokinase enzyme (r = 0.714; p < 0.003) and with the number of Q waves present at the electrocardiogram (r = 0.69; p < 0.005). A very good agreement between the location of the myocardial infarction by ECG, echocardiography and magnetic resonance was evidenced, and a satisfactory correlation existed between myocardial segments with gadolinium-DTPA uptake and akinetic echocardiographic segments (kappa = 0.65). CONCLUSIONS: The detection and quantitation of the necrotic area in the acute myocardial infarction with gadolinium-DTPA contrast magnetic resonance shows a good correlation with clinical and echocardiographic data.

Aged↗
PubMed1999

Use of calcium-channel blockers in pediatric renal transplant recipients.

Hypertension (HTN) is a significant problem in pediatric renal transplant (TP) recipients, predisposing the individuals to the development of cardiovascular disease and graft dysfunction. Calcium channel blockers (CCB) are considered excellent agents to treat post-TP HTN. We compared the efficacy and adverse effects of the two most commonly prescribed CCBs in our pediatric renal TP population: nifedipine (Procardia, or P) and amlodipine (Norvasc, or N). All patients (n = 24) had been started on a CCB for systolic (SBP) and/or diastolic BP (DBP) > 95%. There were no other changes in adjunctive antihypertensive medications or doses during the cross-over period. Post-TP, pretreatment (pretx) SBP was 137.6 +/- 10.9 mmHg. The post-treatment SBP were (in mmHg): 128.5 +/- 11.9 (all patients, n = 24) (p = 0.009 vs. pretx); 126.4 +/- 10.0 (P alone, n = 15) (p = 0.007 vs. pretx); 132.8 +/- 14.4 (P + other antihypertensive(s), n = 9) (p = 0.331, NS vs. pretx). The post-TP, pretreatment DBP was 88.2 +/- 11.1 mmHg. The post-treatment DBP were (in mmHg): 78.5 +/- 6.9 (all patients, n = 24) (p = 0.03 vs. pretx); 77.2 +/- 7.4 (P alone, n = 15) (p = 0.008 vs. pretx); 80.7 +/- 6.1 (P + other antihypertensive(s), n = 9) (p = 0.063, NS vs. pretx). P and N were equally effective in reducing SBP (p = 0.843, NS) and DBP (p = 0.612, NS). Cyclosporin A (CyA) dose (p = 0.81) and trough levels (p = 0.19) were similar in P- and N-treated patients. Calculated GFR was virtually identical in P- and N-treated patients (p = 0.89). Patients (or parents of) reported a higher incidence of various side-effects while receiving P, including headache, flushing, dizziness and leg cramps. Furthermore, 22/24 (91.7%) reported some degree of gingival hyperplasia during treatment with P, and all these patients reported a stabilization or reduction of hypertrophy after the switch from P to N. We conclude that CCBs (N) are efficacious drugs for the purpose of BP control and renal protection in pediatric renal TP recipients.

Adolescent↗
PubMed1999

Myocardial SPET: artificial neural networks describe extent and severity of perfusion defects.

Artificial neural networks are computer programs that learn from examples. They have been successfully used to detect coronary artery disease from myocardial perfusion images. The purpose of the present study was to develop neural networks that could classify myocardial scintigrams regarding reversibility, localization, severity and extent of perfusion defects. Rest/exercise technetium-99m sestamibi scintigrams from 338 patients were studied. The classifications of two experts were employed as the gold standard. Artificial neural networks were trained to classify both reversible (ischaemia) and non-reversible (infarct) defects in three vascular territories, corresponding to the main coronary arteries. The extent (small or large) and severity (mild or severe) of the defects were described by the networks. After the training process, separate test sets were used to compare the neural networks with one of the experts who reclassified the scintigrams two months later. The neural networks made correct classifications in 71% of the test cases and the human expert in 70% (P=0.10). It was concluded that artificial neural networks can be trained to make clinical interpretations of myocardial perfusion scintigrams. The results indicate that networks can assist physicians in achieving correct interpretations and thereby improve the diagnostic accuracy of medical imaging.

Adult↗
PubMed1999

Regional VA/Q ratios in man using 133Xe and single photon emission computed tomography (SPECT) corrected for attenuation.

We describe a technique to obtain non-invasively regional pulmonary ventilation-perfusion ratios (VA/Q) using single photon emission computed tomography (SPECT) and continuous infusion of 133Xe. Single photon transmission tomography was used for attenuation correction, for delineation of the lungs and for VA/Q calculations. Data are presented for six normal subjects and compared to those for two patients with moderate chronic obstructive pulmonary disease (COPD). The mean VA/Q for the whole lung of the normal subjects ranged from 0.49 to 0.65, group mean 0.56 +/- 0.07 (1 SD), and there was no significant difference between the right and left lung. The consistently too low VA/Q values are related to the inability to measure regional blood volume and the low resolution of the scintillation camera, giving an under-estimation of tracer input. For the normal subjects, the dispersion of VA/Q, as defined by the standard deviation of the individual distribution functions, ranged from 0.12 to 0.19. One of the patients was characterized by a low mean VA/Q of 0.35, and the other patient had a wide dispersion (SD) of VA/Q of 0.37. In the normal subjects, a consistent VA/Q gradient was found only in the ventrodorsal direction. 133Xe and SPECT can be used to obtain meaningful biological information regarding ventilation/perfusion relationships of potential clinical value.

Adult↗
PubMed1999

High dose intramuscular methylprednisolone in experimental Staphylococcus aureus endophthalmitis.

We attempted to determine whether treatment using intramuscular methylprednisolone plus intravitreal vancomycin decreased ocular inflammation and preserved retinal function better in experimental Staphylococcus aureus (S. aureus) endophthalmitis than treatment with intravitreal vancomycin alone. Sixteen rabbits received intravitreal inoculations in both eyes with S. aureus and the rabbits were divided into two groups (group I and group II) of eight rabbits each. Group I rabbits were treated with one injection of intravitreal vancomycin in each eye at either 24, 36, 48 or 72 hours after bacterial inoculation followed by seven consecutive days of high dose intramuscular methylprednisolone (30 mg/kg per day). Group II rabbits were treated with only one intravitreal injection of vancomycin in each eye at equivalent time intervals as in Group I. Clinical evaluations of ocular inflammation were performed by slit-lamp biomicroscopy and indirect ophthalmoscopy. Electroretinography (ERG) was performed eight days after bacterial inoculation to assess retinal function in all eyes. The combination of intramuscular methylprednisolone and intravitreal vancomycin resulted in a degree of ocular inflammation equal to eyes treated with intravitreal vancomycin alone at all treatment intervals. ERG responses were not significantly different in either group. A single intravitreal injection of vancomycin plus daily intramuscular methylprednisolone for seven days were found neither to decrease ocular inflammation nor preserve retinal function better than a single intravitreal injection of vancomycin in our experimental model of S. aureus endophthalmitis.

Animals↗
PubMed1999

Clinical, haematological and biochemical findings in foals with neonatal Equine herpesvirus-1 infection compared with septic and premature foals.

A retrospective multicentre study comparing historical, clinical, haematological, acid-base and biochemical findings of foals with Equine herpesvirus-1 (EHV-1) infection, septicaemia or prematurity was performed to determine if early diagnosis of EHV-1 foals was possible. Fifty-three foals were studied and were assigned to one of 2 groups: herpes positive (n = 14) or herpes negative (n = 39). The latter group included 20 septic, 11 premature, and 8 premature and septic foals. The presence of herpes antigen was confirmed by immunoperoxidase histochemical staining of tissues from necropsied foals. A nonparametric statistical analysis followed by a backwards elimination logistic regression was performed to establish a model at a P value of <0.05. All herpes positive foals died, while 47% (9/19) of the septic foals survived. Based upon our analysis, herpes positive foals were more likely to have total white blood cell counts less than 3 x 10(9)/l and to be icteric as compared to the septic and premature foals. Despite profound hepatic necrosis in the herpes positive foals, liver enzymes were not elevated and were not significantly different from the controls.

Acid-Base Equilibrium↗
PubMed1999

Surgical management of pediatric tumor-associated epilepsy.

Brain tumors are a common cause of seizures in children. Early surgical treatment can improve seizure outcome, but controversy exists regarding the most appropriate type of surgical intervention. Some studies suggest tumor resection alone is sufficient, while others recommend mapping and resection of the surrounding epileptogenic foci to optimize seizure outcome. To address this issue, we reviewed the charts of 34 pediatric patients aged 18 months to 20 years with medically intractable epilepsy and primary brain tumors. The average age at operation was 12.6 years, and patients had seizures for an average of 6.4 years. The majority of tumors were located in the temporal lobe. Seventeen patients, because of tumor location near an eloquent area, underwent extraoperative mapping using subdural electrode grids prior to definitive tumor resection. Fourteen of these patients had a gross total tumor resection, yet only two had a distinct zone of ictal onset identified and resected. The remaining 17 patients had tumors either in the nondominant hemisphere or far removed from speech-sensitive areas, and therefore did not undergo extraoperative subdural electroencephalograph mapping. Fourteen of these patients also had a gross total tumor resection, while none had intraoperative electrocorticography to guide the resection of additional nontumoral tissue. Overall, of the 28 patients treated with a gross total tumor resection, 24 (86%) are seizure free, while the other four are significantly improved. Of the six patients who had a subtotal tumor removal, five have persistent seizures. The mean follow-up was 3.6 years. We conclude that in children and adolescents, completeness of tumor resection is the most important factor in determining seizure outcome. The routine mapping and resection of epileptogenic foci might not be necessary in the majority of patients. As a corollary, the use of subdural electrode grids in pediatric patients with tumor-associated epilepsy should be limited to cases requiring extraoperative cortical stimulation for localization of nearby eloquent cortex.

Adolescent↗