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Biomedical subjects

R Sun

Publications and source records attributed to R Sun.

At least 55 records · Page 3Linked to original sources
PubMed2000

Sexual and fertility behaviors of American females aged 15-19 years: 1985, 1990, and 1995.

OBJECTIVES: This study characterized changes in sexual and reproductive behaviors from 1985 through 1995 among American females aged 15 to 19 years and related these changes to family factors. METHODS: Nationally representative sample survey data from the 1995 National Survey of Family Growth were analyzed with Weibull hazards models of age at first intercourse and first pregnancy and with logistic regression models of contraceptive use at first intercourse and pregnancy outcome. RESULTS: Improvements in the family socioeconomic situations of young women have lessened the risk of teen motherhood, while changes in family structure have increased the risk. Young women whose parents have more than a high school education, who live with both parents, and who attend church delay the timing of first sexual intercourse and are more likely to use a contraceptive. CONCLUSIONS: The trend of increases in teenage motherhood has ended owing to a halt in increases in the proportion of sexually active young women and substantial improvement in contraception, with the greatest improvements among those from advantageous family situations.

Adolescent↗
PubMed2000

Effects of growth hormone and prolactin on hematopoiesis.

The use of the neuroendocrine hormones growth hormone (GH) and prolactin (PRL) in preclinical models, demonstrating promotion of hematopoietic recovery and immune function, offers promise for several clinical situations. These hormones do not appear to produce the same extent of immune/hematopoietic effects when compared to conventional hematopoietic and immune stimulating cytokines (i.e. G-CSF or interleukin-2). However, their pleiotropic effects and limited toxicity after systemic administration makes them attractive to test in myeloablative situations. More work needs to be performed to understand the mechanism(s) of GH and PRL action, particularly with regard to hematopoietic progenitor cell expansion and differentiation both in normal and pathologic situations.

Animals↗
PubMed2000

Experience with PCR screening.

The COBAS AmpliScreen Hepatitis C (HCV) Test, Version 2.0, which is designed for screening pools composed of samples from individual units of blood or plasma, employs a MultiPrep sample processing procedure that simultaneously extracts and concentrates HCV, HIV-1 and Hepatitis B virus particles from plasma. An HCV Internal Control (IC) RNA serves as an extraction and amplification control for each independently processed sample. Processed samples are amplified by RT-PCR using HCV-specific complementary primers and detected by hybridization of the amplified products to HCV- and IC-specific oligonucleotide probes. The analytical sensitivity of the test is 25 International Units (IU) of HCV per mL of pooled plasma; all HCV genotypes are detected with similar efficiency. The test detected HCV RNA 23 to 32 days prior to anti-HCV antibody seroconversion for four of the five seroconversion panels tested. The test had sufficient sensitivity to reproducibly detect a single infected unit containing 2.4 x 10(3) copies of HCV per mL in a pool with 23 uninfected units. COBAS AmpliScreen tests for HIV-1 and HBV now being validated by Roche Molecular Systems also incorporate the MultiPrep specimen processing method, thereby making it possible to use a single processed specimen to screen for all three viruses.

Genotype↗
PubMed2000

[Vascular anastomoses in free jejunal reconstruction to the neck vessels: an experience of consecutive 20 cases without using surgical microscope].

Twenty consecutive cases of pharyngoesophageal cancer who underwent free jejunal reconstruction were reported. The common carotid or external carotid artery was used for a feeder of the free graft. The internal jugular vein were served as a drainage vein. All anastomoses were performed in an end-to-side fashion without using surgical microscopes. Mean carotid artery clamping time was 16 minutes and no neurological complications were noticed postoperatively. Graft failure was occurred in 1 patient. The presenting technique, showing 95% success rate, is recommended as a simple option for vascular anastomosis in free jejunal reconstructive surgery.

Anastomosis, Surgical↗
PubMed1999

Performance characteristics of the AmpliScreen HIV-1 test, an assay designed for screening plasma mini-pools.

This study evaluated the performance characteristics of the AmpliScreen(TM)Human Immunodeficiency Virus-Type 1 (HIV-1) Test, Version 1.5, a test designed for screening pools composed of samples from individual units of blood or plasma. HIV-1, hepatitis C (HCV) and hepatitis B (HBV) virus particles were simultaneously extracted and concentrated from plasma by a multi-prep sample processing procedure. An HIV-1 Internal Control (IC) RNA was added to each sample to serve as an extraction and amplification control. Processed samples were amplified by RT-PCR using HIV-1-specific complementary primers and detected by hybridization of the amplified products to HIV-1- and IC-specific oligonucleotide probes. The analytical sensitivity of the test (concentration that yields >/=95% positive results in a set of replicate tests) was 25 copies of HIV-1 RNA per mL of pooled plasma. Representative strains from all HIV-1 group M subtypes were reproducibly detected (>95% positive results among 22 replicate tests) at concentrations of 30 to 75 viral particles per ml. The test exhibited excellent specificity; it did not cross-react with a set of 30 viral and five bacterial isolates and yielded negative results on a panel of 500 blood samples from HIV-1 seronegative donors. Samples containing abnormally high levels of haemoglobin, albumin, triglycerides or bilirubin in plasma samples did not interfere with the detection of HIV-1 RNA at a concentration of 100 copies of per ml. The test detected HIV-1 RNA 7-17 days prior to anti-HIV-1 antibody seroconversion for all 10 seroconversion panels tested. A fully automated COBAS AmpliScreen(TM)version of this test is being validated. COBAS AmpliScreen tests for HCV and HBV also incorporate the multi-prep specimen processing method, thereby making it possible to use a single processed specimen to screen for all three viruses.

Evaluation Studies as Topic↗
PubMed1999

Accounting for the computational basis of consciousness: a connectionist approach.

This paper argues for an explanation of the mechanistic (computational) basis of consciousness that is based on the distinction between localist (symbolic) representation and distributed representation, the ideas of which have been put forth in the connectionist literature. A model is developed to substantiate and test this approach. The paper also explores the issue of the functional roles of consciousness, in relation to the proposed mechanistic explanation of consciousness. The model, embodying the representational difference, is able to account for the functional role of consciousness, in the form of the synergy between the conscious and the unconscious. The fit between the model and various cognitive phenomena and data (documented in the psychological literatures) is discussed to accentuate the plausibility of the model and its explanation of consciousness. Comparisons with existing models of consciousness are made in the end.

Cognition↗
PubMed1999

Effects of temperature and photoperiod on thermogenesis in plateau pikas (Ochotona curzoniae) and root voles (Microtus oeconomus).

We examined the effects of temperature and photoperiod on metabolic thermogenesis and the thermogenic characteristics of brown adipose tissue in plateau pikas (Ochotona curzoniae) and root voles (Microtus oeconomus), the dominant species of small mammals in the alpine meadow ecosystems on the Qinghai-Tibetan Plateau. Pikas and voles were acclimated in the following groups: (1) Long day-warm temperature (16L:8D, 23 degrees C) (2) Long day-cold temperature (16L:8D, 5 degrees C), (3) short day-warm temperature (8L:16D, 23 degrees C), and (4) short day-cold temperature (8L:16D, 5 degrees C). Both temperature and photoperiod were important environmental cues for changes in thermogenesis for both species. Low temperature and short photoperiod induced increases in metabolic rate, nonshivering thermogenesis (NST), mitochondrial protein contents of brown adipose tissue, and cytochrome C oxidase activity of brown adipose tissue mitochondria in both species. Plateau pikas were more sensitive to cold (79% of the total NST response) than to short photoperiod (21%), while root voles were more sensitive to short photoperiod (60% of the total NST response) than to cold (40%), although cold clearly enhanced thermogenesis. Their thermogenic characteristics correlated with their preferred habitats: plateau pikas are found mainly in more exposed microhabitats in open sunny meadow, while root voles live in more sheltered microhabitats in relatively closed shrub. Our results also showed that temperature and photoperiod combined induce thermogenic adjustments in both species in seasonal acclimatization in their alpine meadow macrohabitat.

Acclimatization↗
PubMed1999

Prolactin exerts hematopoietic growth-promoting effects in vivo and partially counteracts myelosuppression by azidothymidine.

Prolactin (PRL) is a neuroendocrine hormone that influences immune and hematopoietic development. The mechanism of action of this hormone in vivo remains unclear; therefore, we assessed the effects of PRL on hematopoiesis in vivo and in vitro. Normal resting mice were treated with 0, 1, 10, or 100 microg of recombinant human prolactin (rhPRL) for 4 consecutive days and euthanized on the fifth day for analysis of myeloid and erythroid progenitors in the bone marrow and spleen. Both frequencies and absolute numbers of splenic colony-forming unit granulocyte-macrophage (CFU-GM) and burst-forming unit-erythroid (BFU-e) were significantly increased in mice receiving rhPRL compared to the controls that had received saline only. Bone marrow cellularities were not significantly affected by any dose of rhPRL, but the absolute numbers and frequencies of bone marrow CFU-GM and BFU-e were augmented by rhPRL. These results suggest that rhPRL can promote hematopoiesis in vivo. Because rhPRL augments myeloid development in vivo, we examined the potential of the hormone to reverse the anemia and myelosuppression induced by azidothymidine (AZT). Mice were given rhPRL injections concurrent with 2.5 mg/mL AZT in drinking water. rhPRL partially restored hematocrits in the animals after 2 weeks of treatment and increased CFU-GM and BFU-e in both spleens and bone marrow. The experiments with AZT and rhPRL support the conclusion that the hormone increases myeloid and erythroid progenitor numbers in vivo, and they suggest that the hormone is clinically useful in reversing myelosuppression induced by AZT or other myeloablative therapies.

Animals↗
PubMed1999

Comparison of 4 topical anesthetic agents for effect and corneal toxicity in rabbits.

PURPOSE: To compare the onset time, duration of action, corneal toxicity, and corneal epithelial healing time of 4 topical anesthetic agents in rabbits. SETTING: Faculty of Medicine, University of Calgary, Calgary, Alberta, Canada. METHOD: Fifty-six rabbits were treated with 4 topical anesthetics (bupivacaine, lidocaine, procaine, and benzocaine) at different concentrations and different pH of solutions. Corneal sensation, corneal toxicity, and corneal epithelial healing time were measured. RESULTS: The onset time of all 4 anesthetic agents was within 1 minute; however, bupivacaine and lidocaine produced significantly longer action than procaine or benzocaine (P < .05). Buffered bupivacaine and lidocaine had a significantly longer anesthetic effect than that of the nonbuffered solutions (P < .05). No significant effect on corneal epithelial healing time or corneal toxicity was observed. CONCLUSION: Topical bupivacaine and lidocaine had a longer anesthetic effect, particularly in buffered solutions. No significant corneal toxicity was observed.

Anesthetics, Local↗
PubMed1999

Photorefractive keratectomy in keratoconus suspects.

PURPOSE: To compare the refractive outcome after photorefractive keratectomy (PRK) in keratoconus-suspect patients with that in patients with normal corneal topography. SETTING: Gimbel Eye Centre, Calgary, Alberta, Canada. METHOD: In a retrospective study, 3 patients (5 eyes) with unusually shaped corneal topography before surgery were selected as keratoconus suspects. Corneal topography (inferior-superior [I-S] value, central corneal power, and central power difference between both eyes), preoperative and 1 year postoperative refraction, and visual acuity in the keratoconus suspects were compared with those in a control group. RESULTS: The mean preoperative I-S value was 1.79 diopters (D) in the keratoconus-suspect eyes and 0.35 D in the control group eyes (P = .0001). The I-S value of individual corneas in the keratoconus suspects was more than 2 standard deviations above the mean in the control group except in 1 eye in which the steepened area was located in the central cornea. The central power difference between the eyes of this patient was 3.60 D, which was significantly higher than that in the control group. The refractive outcomes in the keratoconus suspects were comparable to those in the control group. CONCLUSION: In this study, the refractive outcomes after PRK in the keratoconus suspects and controls were comparable. However, further investigation with a larger sample and longer follow-up is needed.

Adult↗
PubMed1999

Multi-agent reinforcement learning: weighting and partitioning.

This article addresses weighting and partitioning, in complex reinforcement learning tasks, with the aim of facilitating learning. The article presents some ideas regarding weighting of multiple agents and extends them into partitioning an input/state space into multiple regions with differential weighting in these regions, to exploit differential characteristics of regions and differential characteristics of agents to reduce the learning complexity of agents (and their function approximators) and thus to facilitate the learning overall. It analyzes, in reinforcement learning tasks, different ways of partitioning a task and using agents selectively based on partitioning. Based on the analysis, some heuristic methods are described and experimentally tested. We find that some off-line heuristic methods perform the best, significantly better than single-agent models.

Journal Article↗
PubMed1999

Physicochemical and structural characterization of alkali soluble lignins from oil palm trunk and empty fruit-bunch fibers.

Six alkali soluble lignin fractions were extracted from the cell wall materials of oil palm trunk and empty fruit-bunch (EFB) fibers with 5% NaOH, 10% NaOH, and 24% KOH/2% H(3)BO(3). All of the lignin fractions contained rather low amounts of associated neutral sugars (0.8-1.2%) and uronic acids (1.1-2.0%). The lignin fractions isolated with 5% NaOH from the lignified palm trunk and EFB fibers gave a relatively higher degree of polymerization as shown by weight-average molecular weights ranging between 2620 and 2840, whereas the lignin fractions isolated with 10% NaOH and 24% KOH/2% H(3)BO(3) from the partially delignified palm trunk and EFB fibers showed a relatively lower degree of polymerization, as shown by weight-average molecular weights ranging between 1750 and 1980. The results obtained by alkaline nitrobenzene oxidation showed that all of the lignin preparations contained a high proportion of noncondensed syringyl units with small amounts of noncondensed guaiacyl and fewer p-hydroxyphenyl units. The lignin fraction extracted with 5% NaOH from the lignified EFB fiber was mainly composed of beta-O-4 ether-linked units. Small amounts of 5-5', beta-5, and beta-beta' carbon-carbon linkages were also found to be present between the lignin structural units. Further studies showed that uronic, p-hydroxybenzoic, and ferulic acids in the cell walls of palm fibers were esterified to lignin.

Alkalies↗
PubMed1999

Stabilized plasmid-lipid particles for regional gene therapy: formulation and transfection properties.

Previous work (Wheeler et al, Gene Therapy 1999; 6: 271-281) has shown that plasmid DNA can be entrapped in 'stabilized plasmid-lipid particles' (SPLP) containing the fusogenic lipid dioleoylphosphatidylethanolamine (DOPE), low levels (5-10 mol%) of cationic lipid, and stabilized by a polyethyleneglycol (PEG) coating. The PEG moieties are attached to a ceramide anchor containing an arachidoyl acyl group (PEG-CerC20). These SPLP exhibit low transfection potencies in vitro, due in part to the long residence time of the PEG-CerC20 on the SPLP surface. In this work we employed SPLP stabilized by PEG attached to ceramide containing an octanoyl acyl group (PEG-CerC8), which is able to quickly exchange out of the SPLP, to develop systems that give rise to optimized in vitro and in vivo (regional) transfection. A particular objective was to achieve cationic lipid contents that give rise to maximum transfection levels. It is shown that by performing the dialysis procedure in the presence of increasing concentrations of citrate, SPLP containing up to 30 mol% of the cationic lipid dioleoydimethylammonium chloride (DODAC) could be generated. The SPLP produced could be isolated from empty vesicles by sucrose density gradient centrifugation, and exhibited a narrow size distribution (62 +/- 8 nm, as determined by freeze-fracture electron microscopy) and a high plasmid-to-lipid ratio of 65 microg/micromol (corresponding to one plasmid per particle) regardless of the DODAC content. It was found that isolated SPLP containing 20-24 mol% DODAC resulted in optimum transfection of COS-7 and HepG2 cells in vitro, with luciferase expression levels comparable to those achieved for plasmid DNA-cationic lipid complexes. In vivo studies employing an intraperitoneal B16 tumor model and intraperitoneal administration of SPLP also demonstrated maximum luciferase expression for DODAC contents of 20-24 mol% and significantly improved gene expression in tumor tissue as compared with complexes. We conclude that SPLP stabilized by PEG-CerC8 and containing 20-24 mol% cationic lipid are attractive alternatives to plasmid DNA-cationic lipid complexes for regional gene therapy applications.

Animals↗
PubMed1999

Simultaneous extraction of hepatitis C virus (HCV), hepatitis B virus, and HIV-1 from plasma and detection of HCV RNA by a reverse transcriptase-polymerase chain reaction assay designed for screening pooled units of donated blood.

BACKGROUND: Testing for viral nucleic acids should reduce the residual risk of transmitting viral infections by transfusion of blood components. The AmpliScreen Hepatitis C (HCV) Test, Version 2.0, was designed for screening pools composed of samples from individual units of blood or plasma. STUDY DESIGN AND METHODS: An ultracentrifugation step during sample processing simultaneously extracts and concentrates HCV, HIV type 1, and hepatitis B virus particles from plasma. An HCV internal control RNA serves as an extraction and amplification control for each processed sample. Processed samples are amplified by reverse transcriptase polymerase chain reaction and detected by hybridization of the amplified products to HCV- and internal-control-specific oligonucleotide probes. Plasma samples containing known quantities of HCV were used to evaluate analytical sensitivity and precision. RESULTS: The analytical sensitivity of the test was 25 IU of HCV per mL of pooled plasma; all HCV genotypes were detected with similar efficiency. The test did not react with other blood-borne viruses. The within-run and total coefficients of variation were 1.3-13.0 percent and 1.7-22.0 percent, respectively, with low copy samples producing the more variable results. The test performed well using plasma collected in either EDTA, ACD, or PPT Vacutainer tubes. Plasma samples containing elevated levels of hemoglobin, albumin, triglycerides, or bilirubin did not interfere with the test. The test detected HCV RNA 23 to 32 days prior to seroconversion for four of the five seroconversion panels tested. CONCLUSION: The AmpliScreen HCV Test, Version 2.0 provides a reproducible and specific method for screening pooled blood units for HCV. Theoretically, this test has sufficient sensitivity to detect a single infected unit containing 2.4 x 10(3) IU of HCV per mL in a pool with 95 uninfected units and should reduce the window period by at least 20 to 30 days.

Blood↗
PubMed1999

A cost comparison of methohexital and propofol for ambulatory anesthesia.

UNLABELLED: Methohexital is eliminated more rapidly than thiopental, and early recovery compares favorably with propofol. We designed this study to evaluate the recovery profile when methohexital was used as an alternative to propofol for the induction of anesthesia before either sevoflurane or desflurane in combination with nitrous oxide. One hundred twenty patients were assigned randomly to one of four anesthetic groups: (I) methohexital-desflurane, (II) methohexital-sevoflurane, (III) propofol-desflurane, or (IV) propofol-sevoflurane. Recovery times after the anesthetic drugs, as well as the perioperative side effect profiles, were similar in all four groups. A cost-minimization analysis revealed that methohexital was less costly for the induction of anesthesia. At the fresh gas flow rates used during this study, the costs of the volatile anesthetics for maintenance of anesthesia did not differ among the four groups. However, at low flow rates (< or = 1 L/min), the methohexital-desflurane group would have been the least expensive anesthetic technique. In conclusion, methohexital is a cost-effective alternative to propofol for the induction of anesthesia in the ambulatory setting. At low fresh gas flow rates, the methohexital-desflurane combination was the most cost-effective for the induction and maintenance of general anesthesia. IMPLICATIONS: Using methohexital as an alternative to propofol for the induction of anesthesia for ambulatory surgery seems to reduce drug costs. When fresh gas flow rates < or = 1 L/min are used, the combination of methohexital for the induction and desflurane for maintenance may be the most cost-effective general anesthetic technique for ambulatory surgery.

Adult↗
PubMed1999

Kinetics of Kaposi's sarcoma-associated herpesvirus gene expression.

Herpesvirus gene expression can be classified into four distinct kinetic stages: latent, immediate early, early, and late. Here we characterize the kinetic class of a group of 16 Kaposi's sarcoma-associated herpesvirus (KSHV)/human herpesvirus 8 genes in a cultured primary effusion cell line and examine the expression of a subset of these genes in KS biopsies. Expression of two latent genes, LANA and vFLIP, was constitutive and was not induced by chemicals that induce the lytic cycle in primary effusion lymphoma (PEL) cell lines. An immediate-early gene, Rta (open reading frame 50 [ORF50]), was induced within 4 h of the addition of n-butyrate, and its 3.6-kb mRNA was resistant to inhibition by cycloheximide. Early genes, including K3 and K5 that are homologues of the "immediate-early" gene of bovine herpesvirus 4, K8 that is a positional homologue of Epstein-Barr virus BZLF1, vMIP II, vIL-6, and polyadenylated nuclear (PAN) RNA, appeared 8 to 13 h after chemical induction. A second group of early genes that were slightly delayed in their appearance included viral DHFR, thymidylate synthase, vMIP I, G protein-coupled receptor, K12, vBcl2, and a lytic transcript that overlapped LANA. The transcript of sVCA (ORF65), a late gene whose expression was abolished by Phosphonoacetic acid, an inhibitor of KSHV DNA replication, did not appear until 30 h after induction. Single-cell assays indicated that the induction of lytic cycle transcripts resulted from the recruitment of additional cells into the lytic cycle. In situ hybridization of KS biopsies showed that about 3% of spindle-shaped tumor cells expressed Rta, ORF K8, vIL-6, vMIP I, vBcl-2, PAN RNA, and sVCA. Our study shows that several KSHV-encoded homologues of cellular cytokines, chemokines, and antiapoptotic factors are expressed during the viral lytic cycle in PEL cell lines and in KS biopsies. The lytic cycle of KSHV, probably under the initial control of the KSHV/Rta gene, may directly contribute to tumor pathogenesis.

Chemokines↗