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Biomedical subjects

J W King

Publications and source records attributed to J W King.

At least 19 recordsLinked to original sources
PubMed2002

Variability in AC amplifier distortions: estimation and correction.

AC amplifiers can introduce significant distortions into the low frequency and DC components of recorded electrophysiological data such as event-related potentials (ERPs). Methods for correcting such distortions (i.e., estimating the waveform of the original data) after the data have been amplified and recorded rely on an accurate estimate of the amplifier's time constant (TC). We show that the filter characteristics of AC amplifiers in at least some commercially available ERP recording instruments may vary considerably across individual channels, even when each houses an identical AC amplifier circuit. Clearly, distortion correction methods must take this variability into account. We propose an empirical means of estimating the correct TC value. This approach yields more accurate correction than those based on TCs calculated analytically.

Algorithms↗
PubMed2001

Supercritical fluid extraction and chromatography for fat-soluble vitamin analysis.

Extraction and chromatographic separation of fat-soluble vitamins is a challenging task, due to the sensitivity of these compounds towards light, oxygen, heat and pH. In light of this, supercritical fluid extraction (SFE) and supercritical fluid chromatography (SFC) are attractive techniques as they function at considerably milder conditions than conventional solvent-based analytical techniques. Moreover, supercritical techniques consume much less amounts of organic solvents than conventional ones. This review gives a brief description of suitable supercritical media as well as basic theory on SFE and SFC processes. Furthermore, guidelines are provided for optimizing the important extraction and separation parameters to facilitate a successful method development. Finally, applications employing SFE and/or SFC for fat-soluble vitamin enrichment and final determination are reviewed.

Chromatography, Supercritical Fluid↗
PubMed2001

Solubility of triazine pesticides in pure and modified subcritical water.

Solubility measurements in pure and modified water serve as a basis for optimizing the subcritical water extraction of target analytes such as food contaminants. The solvent strength of the water is affected by both the system's temperature and the amount and type of cosolvent modifier that is added to the water, which causes a reduction in the dielectric constant of water. In the present work, the solubilities of the triazine pesticides atrazine, cyanazine, and simazine were measured in pure and modified water at temperatures ranging from 50 to 125 degrees C and at a pressure of 50 atm. The solubility data were obtained using a static solubility apparatus with on-line liquid chromatographic (LC) detection. By increasing the temperature of the water, the solubilities of the triazine pesticides increased approximately 3-fold in pure water for each 25 degrees C temperature increment. Cyanazine was 5 times more soluble than atrazine and an order of magnitude more soluble than simazine at 100 degrees C. The solubility of atrazine was also measured in ambient and hot water modified with ethanol and urea. At 100 degrees C, the solubility of atrazine is doubled when the water is modified with urea, and is increased over an order of magnitude when ethanol is used as modifier. The data, therefore, indicate that adding a cosolvent to water in addition to increasing the system temperature increases the solubilities of triazine pesticides in subcritical water. It was further determined that the solutes do not thermally degrade or hydrolyze at the temperatures reported in this study.

Atrazine↗
PubMed2001

On-line supercritical fluid extraction/enzymatic hydrolysis of vitamin a esters: a new simplified approach for the determination of vitamins a and e in food.

An on-line supercritical fluid extraction (SFE)/enzymatic hydrolysis procedure using immobilized lipase has been developed for the determination of vitamin A in dairy and meat products. Several lipases were tried, of which Novozyme 435 (Candida antarctica type B) showed the highest activity toward retinyl palmitate. There was no observed activity with alpha-tocopheryl acetate. When pressure, temperature, modifiers, flow rate, extraction time, and water content were varied, high vitamin A recovery was obtained in milk powder. Collected extracts were analyzed by reversed-phase high-performance liquid chromatography with ultraviolet and fluorescence detection without additional sample cleanup. The procedure gave reliable values of vitamin A as well as of vitamin E in other food items such as infant formula, minced pork and beef meat, and low- and high-fat liver paste. The described method is faster and more automated than conventional methods based on liquid-liquid extraction, or SFE using off-line saponification, for vitamin A and E determination. Results obtained with the new method did not differ significantly from those obtained with the other two methods mentioned above.

Animals↗
PubMed2001

Ethanol-modified subcritical water extraction combined with solid-phase microextraction for determining atrazine in beef kidney.

The determination of the levels of pesticides in food products has prompted the development of sensitive and rapid methods of analysis that are solvent-free or utilize solvents that are benign to the environment and laboratory worker. In this study we have developed a novel extraction method that utilizes ethanol-modified subcritical water in combination with solid-phase microextraction (SPME) for the removal of atrazine from beef kidney. In situ sample cleanup was achieved using the technique of matrix solid-phase dispersion. A cross-linked polymer, XAD-7 HP, was utilized as a dispersing material for kidney samples. Subcritical water extractions were performed with a pressurized solvent extraction unit at 100 degrees C and 50 atm. Experimental parameters investigated were the volume of solvent and amount of modifier required for the complete extraction of atrazine and optimization of the extraction time. It was determined that 30% ethanol in water (v/v) is adequate for the complete extraction of atrazine. A Carbowax-divinylbenzene SPME fiber was used to sample the aqueous extracts. Analysis of the fiber contents was by ion-trap GC/MS utilizing the single ion mode. The total time of analysis for a single kidney sample is 90 min. The average percent recoveries from samples spiked to the concentrations of 2 and 0.2 microg/g were 104 and 111, respectively. The average relative standard deviations were 10 and 9, respectively. The method limit of detection for beef kidney spiked with atrazine was found to be 20 ng/g of sample.

Animals↗
PubMed2001

Supercritical fluid extraction of fat from ground beef: effects of water on gravimetric and GC-FAME fat determinations.

This study investigated the supercritical carbon dioxide (SC-CO(2)) extraction of fat from ground beef and the effects of several factors on the gravimetric determination of fat. The use of ethanol modifier with the SC-CO(2) was not necessary for efficient fat extraction; however, the ethanol did increase the coextraction of water. This coextraction of water caused a significant overestimation of gravimetric fat. Oven-drying ground beef samples prior to extraction inhibited the subsequent extraction of fat, whereas oven-drying the extract after collection decreased the subsequent gas chromatographic fatty acid methyl ester (GC-FAME) fat determination. None of the drying agents tested were able to completely prevent the coextraction of water, and silica gel and molecular sieves inhibited the complete extraction of fat. Measurements of collection vial mass indicated that CO(2) extraction/collection causes an initial increase in mass due to the density of CO(2) (relative to displaced air) followed by a decrease in vial mass due to the removal of adsorbed water from the collection vial. Microwave-drying of the empty collection vials removes approximately 3 mg of adsorbed water, approximately 15-20 min is required for readsorption of the displaced water. For collection vials containing collected fat, microwave-drying effectively removed coextracted water, and the vials reached equilibration after approximately 10-15 min. Silanizing collection vials did not significantly affect weight loss during microwave-drying. SC-CO(2) can be used to accurately determine fat gravimetrically for ground beef, and the presented method can also be followed by GC-FAME analysis to provide specific fatty acid information as well.

Animals↗
PubMed2001

Possible clinically significant interaction of itraconazole plus rifampin.

We report two patients treated with the combination of itraconazole plus rifampin for more than 4 months. While on itraconazole plus rifampin, patient 1 lost weight at a rate of 30 g/d. After stopping rifampin, he gained 14 g/d. While on itraconazole plus rifampin, patient 2 lost 41 grams/day. After stopping rifampin, he gained 33 g/d. Weight loss while taking the combination of itraconazole plus rifampin, followed by weight gain after stopping rifampin, suggests the possibility of a clinically significant drug interaction between itraconazole and rifampin.

AIDS-Related Opportunistic Infections↗
PubMed2001

Fatty and resin acid analysis in tall oil products via supercritical fluid extraction-supercritical fluid reaction using enzymatic catalysis.

Supercritical fluid extraction (SFE) is combined with supercritical fluid reaction (SFR) in an analytical mode to assess tall oil products for their fatty or resin acid content or both. The SFR consists of an inline enzymatically catalyzed reaction in which a lipase transesterifies specific lipids with methanol. The SFE-SFR sequence is conducted employing commercially available extractors using supported lipases in the extraction cell to form methyl esters. In this study, six different commercially available lipases are screened for activity. The SFE-SFR extracts are analyzed by capillary gas chromatography and supercritical fluid chromatography and then compared with tall oil products derivatized by conventional chemical derivatization techniques.

Journal Article↗
PubMed2001

Comparison of hepatitis C viral loads in patients with or without human immunodeficiency virus.

A better understanding of how human immunodeficiency virus (HIV) coinfection affects the course of hepatitis C virus (HCV) infection is required to select patients with HIV who would benefit from current HCV therapy. Between June 1996 and March 2000, HCV RNA levels were quantified for 1,279 patients at the Louisiana State University Health Sciences Center; 28 of these patients were coinfected with HIV. HCV loads were quantified by the Bayer branched-DNA assay with a lower limit of detection of 0.2 Meq/ml. We compared the median HCV RNA levels of for patients coinfected with HIV and HCV and patients infected only with HCV who were in the same age range (23 to 55 years). The median HCV load for the 28 patients coinfected with HCV and HIV (17.8 Meq/ml) was significantly greater (P < 0.05) than that for similarly aged patients infected only with HCV (6.1 Meq/ml). The HCV load did not correlate with age or sex for either group of patients. A significant (R = -0.4; P < 0.05) negative correlation was observed between HCV load and CD4 count in the coinfected group, for whom the CD4 counts at the time of HCV load analysis ranged from 6 to 1,773/mm(3). The increased HCV load in patients coinfected with HCV and HIV compared to that in patients infected only with HCV and the inverse relationship of the HCV load to the CD4 count indicate that immunosuppression results in decreased control of HCV replication. In addition, we report significantly higher HCV loads among coinfected African Americans than Caucasians.

AIDS-Related Opportunistic Infections↗
PubMed2000

Optimization of the extraction and fractionation of corn bran oil using analytical supercritical fluid instrumentation.

Supercritical fluid extraction (SFE) is combined with supercritical fluid chromatography (SFC) in an analytical mode to develop a system for fractionating and enriching high value ferulate-phytosterol esters (FPE) contained in corn bran oil. Corn bran is initially extracted with neat supercritical carbon dioxide (SC-CO2) at various pressures (13.8, 34.5, and 69 MPa) and temperatures (40, 60, and 80 degrees C) to see if the FPE can be enriched in the extracts. These initial studies show the greatest percentage of FPE could be extracted under two sets of conditions: 69 MPa at 80 degrees C and 34.5 MPa at 40 degrees C. Both sets of parameters yield an extract containing approximately 1.25% FPE. A stock supply of corn bran oil is then produced by scaled-up SFE at 34.5 MPa and 40 degrees C for subsequent chromatographic fractionation. The SFE-obtained corn bran oil is then applied to the head of a minichromatographic column containing an amino-propyl sorbent. SFC is than commenced using neat SC-CO2 at 69 MPa and 80 degrees C to remove the majority of the triglyceride-based oil. Pressure and temperature are then lowered to 34.5 MPa and 40 degrees C, respectively, and ethanol is added as a modifier. The modifier is added in an increasing stepwise gradient program, and fractions are collected at equal volume intervals. The resultant fractions are analyzed by analytical high-performance liquid chromatography with evaporative light-scattering detection and show that FPE could be enriched to a 14.5% (w) level.

Carbon Dioxide↗
PubMed1998

Neural plasticity in the dynamics of human visual word recognition.

Repeated exposure to words leads to plastic changes in the nervous system throughout the lifespan, with the consequence that common words are processed more rapidly and accurately than rare words. Most behavior time measures correlate highly with the logarithm of a stimulus word's experiential frequency. Here, we demonstrate similar but earlier changes in the latency of a brain-generated evoked potential recorded over the left anterior scalp as individuals silently read sentences. We conclude that experience can speed the processing of some words by at least 50 ms within the first 335 ms of visual processing.

Brain↗
PubMed1997

Event-related potentials elicited by spoken relative clauses.

Sentence-length event-related potential (ERP) waveforms were obtained from 23 scalp sites as 24 subjects listened to normally spoken sentences of various syntactic structures. The critical materials consisted of 36 sentences each containing one of two types of relative clauses that differ in processing difficulty, namely Subject Object (SO) and Subject Subject (SS) relative clauses. Sentence-length ERPs showed several differences in the slow scalp potentials elicited by SO and SS sentences that were similar in their temporal dynamics to those elicited by the same stimuli in a word-by-word reading experiment, although the effects in the two modalities have non-identical distributions. Just as for written sentences, there was a large, fronto-central negativity beginning at the linguistically defined "gap" in the SO sentences; this effect was largest for listeners with above-median comprehension rates and is hypothesized to index changes in on-line processing demands during comprehension.

Adolescent↗
PubMed1996

Fat content for nutritional labeling by supercritical fluid extraction and an on-line lipase catalyzed reaction.

A method using sequential supercritical fluid extraction (SFE) and enzymatic transesterification has been developed for the rapid determination of total nutritional fat content in meat samples. SFE conditions of 12.16 MPa and 50 degrees C were utilized to extract lipid species from the sample matrix. The enzymatic transesterification of the lipids by methanol was catalyzed by an immobilized lipase isolated from Candida antarctica. Conversion of the triglycerides to fatty acid methyl esters was monitored by supercritical fluid chromatography, while the fatty acid content of the extract was determined by capillary gas chromatography (GC). Total fat, saturated fat and monounsaturated fat contents were calculated from the GC data and compared to values from traditional extraction and lipid determination methods. Both off-line SFE and automated SFE followed by on-line GC analysis using two different instruments were utilized in this study. The enzymatic-based SFE method gave comparable results to the organic solvent extraction-based method followed by conventional BF3-catalyzed esterification.

Animals↗
PubMed1996

Disparate prognosis of thrombotic microangiopathy in HIV-infected patients with and without AIDS.

Thrombotic microangiopathy (TMA) is more common in HIV-infected individuals than in the normal population. In idiopathic TMA, plasmapheresis with or without prednisone decreases the mortality rate from almost 100 to 10%. Patients with HIV-associated TMA, who do not have AIDS, have a similar favorable outcome when treated with plasmapheresis. However, all 12 patients previously reported with AIDS-associated TMA have died. We report another patient with AIDS-associated TMA, who had a fulminant hospital course and died despite plasmapheresis. None of the reported AIDS-associated TMA patients had evidence of opportunistic infections, sepsis or disseminated malignancies at the time of their death. Since many infections and malignancies can be associated with TMA, it is possible that TMA can be an association of the terminal illness rather than an independent cause of death in AIDS patients. To examine this possibility, we reviewed the charts of all the patients who were hospitalized and died of AIDS at our medical centers from 1987 to 1994. Of the 214 patients reviewed, 15 patients (7%) had evidence of TMA at the time of their death. Seven of the 15 patients (47%) had no direct cause of death other than TMA. The remaining 8 patients had evidence of sepsis and other overwhelming infections. In conclusion, TMA is common in AIDS patients. While HIV-associated TMA has a good prognosis similar to that of idiopathic TMA, AIDS-associated TMA has a grave prognosis. The etiology of the higher mortality in AIDS-associated TMA as compared to HIV-associated TMA remains unclear.

Acquired Immunodeficiency Syndrome↗
PubMed1995

Cardiopulmonary arrest after retrobulbar anesthesia in a patient with an orbital roof defect.

PURPOSE: Cardiopulmonary arrest developed after injection of bupivacaine hydrochloride, lidocaine, and hyaluronidase in a 78-year-old woman who had previously undergone ipsilateral transcranial orbital surgery with removal of the bone of the orbital roof. METHODS: The patient required immediate cardiopulmonary resuscitation and intubation. Mechanical ventilation was necessary for 18 hours before spontaneous respirations resumed. RESULTS: The patient improved and was discharged on the fifth postanesthetic day. CONCLUSIONS: There were several possible mechanisms by which the local anesthetic could have entered the central nervous system. In patients with orbital roof defects, we recommend that retrobulbar anesthetic agents be used with caution.

Aged↗
PubMed1993

Ribavirin and intravenous immune globulin therapy for measles pneumonia in HIV infection.

We have described a patient, immunocompromised from an infection with the human immunodeficiency virus, who had rapidly progressive measles complicated by measles pneumonia and respiratory failure. Rapid improvement in the patient's condition followed therapy with inhaled ribavirin and intravenous immune globulin. Patients who have measles pneumonia associated with respiratory failure may benefit from combination therapy with ribavirin and IV immune globulin.

Adult↗
PubMed1993

Do topical antibiotics help corneal epithelial trauma?

Topical antibiotics are routinely used in emergency rooms to treat corneal trauma, although no published evidence supports this treatment. In a noncomparative clinical trial, 351 patients with corneal epithelial injuries were treated without antibiotics. The infection rate was 0.7%, suggesting that such injuries can be safely and effectively managed without antibiotics. A comparative clinical trial is neither warranted nor feasible.

Administration, Topical↗