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Biomedical subjects

W H Wong

Publications and source records attributed to W H Wong.

At least 19 recordsLinked to original sources
PubMed2006

A comparison study of cerebral protection using Ginkgo biloba extract and Losartan on stroked rats.

It has been well documented that oxidative stress is involved in stroke. Currently, many neuroprotective strategies have been targeted at molecules that are able to act as an oxidant to intervene with free-radical mediated apoptosis in the ischemic penumbra. In particular, natural products which contain antioxidant properties have undoubtedly efficacious for stroke treatment. In the current study, therapeutic effects of Ginkgo biloba extract (EGb) against cerebral protection in Wistar rats underwent middle cerebral artery occlusion (MCAO) was evaluated. A comparison study was conducted by using Losartan, an antihypertensive drug. Gene expression levels of pro-apoptotic genes (AT2 receptor, Fas, Bax and Bcl-xS) have shown to have significant reduction by EGb- and Losartan-treated groups as compared to vehicle group. Significant reduction of immunoreactivity of protein production of these genes, together with least nuclear green fluorescence observed in TUNEL, EGb, as an antioxidant drug, is concluded to have potent and promising therapeutic effect for stroke treatment.

Angiotensin II Type 1 Receptor Blockers↗
PubMed2006

Nonspecular effects on reflection from absorbing media at and around Brewster's dip.

We show that, for a TM (or p-state) Gaussian beam incident onto an absorbing medium at and around Brewster's dip, the reflected beam always remains Gaussian and undergoes a Goos-Hänchen-like (GH) shift, an angular shift, a focal shift, and a beam-waist modification, provided that the beam is sufficiently collimated that the third-order change of the (logarithmic) reflection coefficient can be ignored in the angular range of beam divergence. For weak absorption, not only are a large negative GH shift and an odd-functioned-like focal shift with greater magnitude found but also the angular shift, though small by itself, is shown to give an even larger lateral net shift at a distance beyond the Rayleigh range.

Journal Article↗
PubMed2005

Evaluation of Streptomyces sp. strain g10 for suppression of Fusarium wilt and rhizosphere colonization in pot-grown banana plantlets.

Streptomyces sp. strain g10 exhibited strong antagonism towards Fusarium oxysporum f.sp. cubense (Foc) races 1, 2 and 4 in plate assays by producing extracellular antifungal metabolites. Treating the planting hole and roots of 4-week-old tissue-culture-derived 'Novaria' banana plantlets with strain g10 suspension (10(8) cfu/ml), significantly (P < 0.05) reduced wilt severity when the plantlets were inoculated with 10(4) spores/ml Foc race 4. The final disease severity index for leaf symptom (LSI) and rhizome discoloration (RDI) was reduced about 47 and 53%, respectively, in strain g10-treated plantlets compared to untreated plantlets. Reduction in disease incidence was not significant (P < 0.05) when plantlets were inoculated with a higher concentration (10(6) spores/ml) of Foc race 4. Rhizosphere population of strain g10 showed significant (P = 0.05) increase of more than 2-fold at the end of the 3rd week compared to the 2nd week after soil amendment with the antagonist. Although the level dropped, the rhizosphere population at the end of the 6th week was still nearly 2-fold higher than the level detected after 2 weeks. In contrast, the root-free population declined significantly (P = 0.05), nearly 4-fold after 6 weeks when compared to the level detected after 2 weeks. Neither growth-inhibiting nor growth-stimulating effects were observed in plantlets grown in strain g10-amended soil.

Fusarium↗
PubMed2005

Anaesthesia for a patient with long QT syndrome undergoing renal transplantation.

Anaesthetizing patients with Long QT Syndrome is a major challenge, as the potential for sudden catastrophic cardiovascular collapse is well known. We present a 15-year-old boy with Long QT Syndrome who presented for an elective renal transplant. All electrolyte concentration abnormalities were corrected preoperative and adequate beta-blockade was maintained. The patient was given a target controlled infusion of propofol, together with opioids and atracurium. Anaesthesia was uneventful and the patient was extubated at the end of the surgical procedure.

Adolescent↗
PubMed2005

Perceived skill and utilisation of information technology in medical education among final year medical students, Universiti Putra Malaysia.

The objective of this survey was to obtain a self-reported assessment of the use of information technology (IT) by final year medical students. Two hundred and sixty five students responded to a questionnaire survey. 81.5% of students considered their computer skills adequate, while 87.9% had access to computers outside the campus. Most students reported adequate skills at word processing, e-mailing and surfing the Internet. Fifty three percent of students spent three hours or more each week on the computer. While students indicated a general willingness to access Internet-based materials, further steps need to be taken to increase the use of this method of instruction.

Computer Literacy↗
PubMed2004

Extinction paradox and actual power scattered in light beam scattering: a two-dimensional study.

The extinction paradox is examined by applying partial-wave analysis to a two-dimensional light beam interacting with a long transverse cylinder without absorption, assuming always short wavelengths. We show that the (conventional) power scattered, Psca, except for a very narrow beam hitting a transparent cylinder on axis, is always double the power directly intercepted by the scatterer, Pitc, including a zero result for Psca when the incident beam is basically off the material surface. This contradicts the interpretation that attributes one half of Psca to edge diffraction by the scatterer. Furthermore, we identify the shadow-forming wave (SFW) from the partial-wave sum in the forward direction and show that the actual power scattered or, equivalently, the power depleted from the incident beam is equal to one unit of Pitc for a narrow beam, gets larger for a broader beam, and approaches 2Pitc for a very broad beam. The larger value in the latter cases is due to the extent of divergence of the SFW beam out of the incident beam at distances well beyond the Rayleigh range.

Journal Article↗
PubMed2001

Issues in cDNA microarray analysis: quality filtering, channel normalization, models of variations and assessment of gene effects.

We consider the problem of comparing the gene expression levels of cells grown under two different conditions using cDNA microarray data. We use a quality index, computed from duplicate spots on the same slide, to filter out outlying spots, poor quality genes and problematical slides. We also perform calibration experiments to show that normalization between fluorescent labels is needed and that the normalization is slide dependent and non-linear. A rank invariant method is suggested to select non-differentially expressed genes and to construct normalization curves in comparative experiments. After normalization the residuals from the calibration data are used to provide prior information on variance components in the analysis of comparative experiments. Based on a hierarchical model that incorporates several levels of variations, a method for assessing the significance of gene effects in comparative experiments is presented. The analysis is demonstrated via two groups of experiments with 125 and 4129 genes, respectively, in Escherichia coli grown in glucose and acetate.

Acetic Acid↗
PubMed2001

Genome-wide expression analysis reveals dysregulation of myelination-related genes in chronic schizophrenia.

Neuropathological and brain imaging studies suggest that schizophrenia may result from neurodevelopmental defects. Cytoarchitectural studies indicate cellular abnormalities suggestive of a disruption in neuronal connectivity in schizophrenia, particularly in the dorsolateral prefrontal cortex. Yet, the molecular mechanisms underlying these findings remain unclear. To identify molecular substrates associated with schizophrenia, DNA microarray analysis was used to assay gene expression levels in postmortem dorsolateral prefrontal cortex of schizophrenic and control patients. Genes determined to have altered expression levels in schizophrenics relative to controls are involved in a number of biological processes, including synaptic plasticity, neuronal development, neurotransmission, and signal transduction. Most notable was the differential expression of myelination-related genes suggesting a disruption in oligodendrocyte function in schizophrenia.

Chronic Disease↗
PubMed2001

Model-based analysis of oligonucleotide arrays: expression index computation and outlier detection.

Recent advances in cDNA and oligonucleotide DNA arrays have made it possible to measure the abundance of mRNA transcripts for many genes simultaneously. The analysis of such experiments is nontrivial because of large data size and many levels of variation introduced at different stages of the experiments. The analysis is further complicated by the large differences that may exist among different probes used to interrogate the same gene. However, an attractive feature of high-density oligonucleotide arrays such as those produced by photolithography and inkjet technology is the standardization of chip manufacturing and hybridization process. As a result, probe-specific biases, although significant, are highly reproducible and predictable, and their adverse effect can be reduced by proper modeling and analysis methods. Here, we propose a statistical model for the probe-level data, and develop model-based estimates for gene expression indexes. We also present model-based methods for identifying and handling cross-hybridizing probes and contaminating array regions. Applications of these results will be presented elsewhere.

Animals↗
PubMed2001

Feature extraction and normalization algorithms for high-density oligonucleotide gene expression array data.

Algorithms for performing feature extraction and normalization on high-density oligonucleotide gene expression arrays, have not been fully explored, and the impact these algorithms have on the downstream analysis is not well understood. Advances in such low-level analysis methods are essential to increase the sensitivity and specificity of detecting whether genes are present and/or differentially expressed. We have developed and implemented a number of algorithms for the analysis of expression array data in a software application, the DNA-Chip Analyzer (dChip). In this report, we describe the algorithms for feature extraction and normalization, and present validation data and comparison results with some of the algorithms currently in use.

Algorithms↗
PubMed2001

Dynamic locomotor function in normals and patients with vertigo.

Gait analysis was performed in patients with various vestibular systems using a tactile sensor. There were 4 patients with vestibular neuronitis, 6 patients with large acoustic neuroma and 6 patients with spino-cerebellar degeneration (SCD). Gait phase related parameters such as stance, swing and double support were studied to assess gait stability. Also the area ratio of trajectories of center of force during stance and progression of foot pressure were checked. The calculated value of each variable became high in pathological cases compared with normal controls, and the highest value was obtained in the SCD group. As regards the effect of visual deprivation on stability of gait, the most striking change was found in the large acoustic neuroma group. In a case with a unilateral lesion such as vestibular neuronitis and large acoustic neuroma, foot pressure was greater on the lesion side, especially during gait with eyes closed. As for the foot pressure progression curve, the SCD group showed the most irregular pattern in general, although there were some individual variations. Those results could reflect a functional disorder of the gait control system caused by each disease. Significance of gait analysis is also discussed.

Adult↗
PubMed2001

Feasibility of a high-speed gamma-camera design using the high-yield-pileup-event-recovery method.

UNLABELLED: Higher count-rate gamma cameras than are currently used are needed if the technology is to fulfill its promise in positron coincidence imaging, radionuclide therapy dosimetry imaging, and cardiac first-pass imaging. The present single-crystal design coupled with conventional detector electronics and the traditional Anger-positioning algorithm hinder higher count-rate imaging because of the pileup of gamma-ray signals in the detector and electronics. At an interaction rate of 2 million events per second, the fraction of nonpileup events is < 20% of the total incident events. Hence, the recovery of pileup events can significantly increase the count-rate capability, increase the yield of imaging photons, and minimize image artifacts associated with pileups. A new technology to significantly enhance the performance of gamma cameras in this area is introduced. METHODS: We introduce a new electronic design called high-yield-pileup-event-recovery (HYPER) electronics for processing the detector signal in gamma cameras so that the individual gamma energies and positions of pileup events, including multiple pileups, can be resolved and recovered despite the mixing of signals. To illustrate the feasibility of the design concept, we have developed a small gamma-camera prototype with the HYPER-Anger electronics. The camera has a 10 x 10 x 1 cm NaI(Tl) crystal with four photomultipliers. Hot-spot and line sources with very high 99mTc activities were imaged. The phantoms were imaged continuously from 60,000 to 3,500,000 counts per second to illustrate the efficacy of the method as a function of counting rates. RESULTS: At 2-3 million events per second, all phantoms were imaged with little distortion, pileup, and dead-time loss. At these counting rates, multiple pileup events (> or = 3 events piling together) were the predominate occurrences, and the HYPER circuit functioned well to resolve and recover these events. The full width at half maximum of the line-spread function at 3,000,000 counts per second was 1.6 times that at 60,000 counts per second. CONCLUSION: This feasibility study showed that the HYPER electronic concept works; it can significantly increase the count-rate capability and dose efficiency of gamma cameras. In a larger clinical camera, multiple HYPER-Anger circuits may be implemented to further improve the imaging counting rates that we have shown by multiple times. This technology would facilitate the use of gamma cameras for radionuclide therapy dosimetry imaging, cardiac first-pass imaging, and positron coincidence imaging and the simultaneous acquisition of transmission and emission data using different isotopes with less cross-contamination between transmission and emission data.

Equipment Design↗
PubMed2001

Role of tramadol in reducing pain on propofol injection.

Propofol is frequently associated with pain on injection. We evaluated the effect of tramadol in a randomised, double-blind study using a tourniquet venous retention technique. Normal saline placebo was given intravenously to patients in Group 1 (n = 30),tramadol 50 mg to Group 2 (n = 30), and lignocaine 50 mg to Group 3 (n = 30). The venous retention of drugs was maintained for 1 minute, followed by tourniquet release and intravenous administration of propofol. Pain assessment was made immediately after propofol injection. There was a significant reduction in the incidence of pain associated with propofol administration in patients pretreated with lignocaine and tramadol (P < 0.05). In addition, pretreatment with tramadol was as effective as lignocaine in reducing pain on propofol injection.

Adolescent↗
PubMed2000

Analyzing high-density oligonucleotide gene expression array data.

We have developed methods and identified problems associated with the analysis of data generated by high-density, oligonuceotide gene expression arrays. Our methods are aimed at accounting for many of the sources of variation that make it difficult, at times, to realize consistent results. We present here descriptions of some of these methods and how they impact the analysis of oligonucleotide gene expression array data. We will discuss the process of recognizing the "spots" (or features) on the Affymetrix GeneChip(R) probe arrays, correcting for background and intensity gradients in the resulting images, scaling/normalizing an array to allow array-to-array comparisons, monitoring probe performance with respect to hybridization efficiency, and assessing whether a gene is present or differentially expressed. Examples from the analyses of gene expression validation data are presented to contrast the different methods applied to these types of data.

Base Sequence↗
PubMed2000

The coevolution of cell senescence and diploid sexual reproduction in unicellular organisms.

In this paper, we investigate the coevolution of diploid sexual reproduction and cell senescence (i.e., cell aging). We use probability analysis, computer simulation, and exact numerical computation to analyze the impacts of deleterious recessive mutations on sexual and asexual reproduction. The main conclusion is that, without cell senescence, the evolutionary advantages of sexual reproduction cannot be realized in unicellular organisms that reproduce both sexually and asexually. Also, cell senescence is found to be useful in the maintenance of sexual reproduction. This result suggests that diploid sexual reproduction was unlikely to establish itself as a widespread reproduction mechanism without the complementary process of cell senescence.

Biological Evolution↗
PubMed2000

Pain on injection of rocuronium: influence of two doses of lidocaine pretreatment.

We have assessed the incidence of pain on injection of rocuronium and evaluated if pretreatment with lidocaine i.v. reduced it, in a randomized, controlled study in 90 patients. We found that 37% of patients who received lidocaine 10 mg pretreatment had pain on injection of rocuronium compared with 77% of patients who received saline pretreatment and 7% of patients who were pretreated with lidocaine 30 mg (P < 0.05 in each instance compared with control). In addition, patients pretreated with lidocaine were less likely to suffer moderate or severe pain. Both lidocaine 10 mg and 30 mg i.v. given before administration of rocuronium significantly reduced the incidence and severity of pain on injection of rocuronium, and the higher dose was more effective.

Adolescent↗
PubMed1999

Determination of domoic acid in phytoplankton by high-performance liquid chromatography of the 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate derivative.

Domoic acid is the toxin that can cause amnesic shellfish poisoning. In this work, a new precolumn derivatization reagent, 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate, was used to react with domoic acid to form a stable unsymmetrical urea derivative, which was readily analyzed by reversed-phase HPLC with fluorescence detection. The one-step derivatizing method is rapid and straightforward. The method was applied to detect domoic acid in phytoplankton using a 3.9 x 150 mm Nova-Pak, 4 microm, C(18) column.

Aminoquinolines↗