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Biomedical subjects

W K Cheng

Publications and source records attributed to W K Cheng.

12 recordsLinked to original sources
PubMed1992

Hydrocarbon exposures at petroleum bulk terminals and agencies.

Occupational exposures to the 55 hydrocarbon components of gasoline and petroleum products were measured at the bulk terminals and agencies of six Ontario petroleum companies during the summer of 1986. A total of 82 long-term (full-shift) and 111 short-term personal samples were taken over 3 months. The data, expressed as concentrations in milligrams per cubic meter, were highly variable and appeared to fit the lognormal distribution well. Full-shift exposures of bulk terminal drivers, agency drivers, and plantmen to total hydrocarbons (THC), computed as an n-hexane equivalent, and other hydrocarbon components for which exposure limits exist can be expected to exceed their respective 1986-1987 threshold limit value-time-weighted average (TLV-TWA) no greater than 1% of the time on the basis of the lognormal model. The short-term THC exposures of agency truck drivers can be expected to exceed the 1986-1987 TLV-short-term exposure limits about 7% of the time while top-loading and more than 17% while off-loading. For benzene, the short-term exceedance percentages are 1% and 4% for top- and off-loading operations, respectively. For long-term benzene exposures, up to 69% of the assessments can be expected to exceed the 1990-1991 proposed TLV-TWA of 0.3 mg/m3 (0.1 ppm). The full-shift hydrocarbon exposures of agency drivers were significantly higher than those for bulk terminal drivers. At the bulk terminals, the short-term hydrocarbon exposures during top-loading were significantly higher than during bottom-loading.

Dose-Response Relationship, Drug↗
PubMed1989

Urgent biliary decompression after endoscopic retrograde cholangiopancreatography.

Acute cholangitis complicating diagnostic endoscopic retrograde cholangiopancreatography (ERCP) is potentially fatal. Among 323 consecutive patients with proved biliary obstruction, 21 (7 percent) developed acute cholangitis after examination. Four patients underwent emergency surgery for the control of sepsis with two deaths. Of the 21 parameters chosen for evaluation, malignant obstruction, fever (higher than 37.5 degrees C) within 72 hours before the procedure or when afebrile, and an increased aspartate transaminase level of 70 IU or more were the independent predictive factors identified by multivariate analysis. An increased temperature should be regarded as an absolute contraindication to examination unless followed by immediate ductal drainage. Since the risk of septic complications is minimal when none of the risk factors are present, routine urgent biliary decompression after ERCP is probably unnecessary for these selected patients. For patients with malignant obstruction or other risk factors, early elective surgical drainage is advisable. When surgery is not feasible, nonoperative drainage of the obstructed biliary system as a preventive measure might be considered.

Acute Disease↗
PubMed1988

Structural EEG analysis: an explorative study.

A method is described to detect (subtle) changes in an EEG (electroencephalogram) by means of a Markovian modeling approach. This method, termed structural EEG analysis, treats the non-stationary EEG as a sequence of a finite number of short elementary patterns. Subtle changes in an EEG may be detected by studying the transition probabilities between the different patterns. By viewing the patterns as states in a Markov chain, a representation of the EEG structure based on a state transition probability matrix emerges. Various techniques to estimate the state transition probability matrices have been investigated. A number of experiments were performed with artificially generated data to determine the data length required to obtain a reliable estimate of the transition matrices. It appeared that a data length of approximately five to eight times the number of entries in the matrices is needed to accurately estimate the matrices. It was determined that the data length required to reliably estimate the transition probability matrix is dependent on the number of states and the number of non-zero entries of the matrix. Also, the data length appears independent of the values of the probabilities. The structural analysis approach was applied to actual EEG data, recorded from normal volunteers and epileptic subjects. It was demonstrated that visually confirmable changes in the EEG could be detected by the structural analysis method more accurately than by a more conventional approach.

Adult↗
PubMed1986

Changes in composition of the porcine zona pellucida during development of the oocyte to the 2- to 4-cell embryo.

Our objective was to identify any changes that occur in the composition of the porcine zona pellucida during development of the 2- to 4-cell embryo from the oocyte. Oocytes, unfertilized eggs and single and 2- to 4-cell embryos have been recovered surgically and their zonae pellucidae 125I-labelled and analysed individually by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). The zonae from ovulated eggs possessed two major glycoproteins Mr250 000 and 90 000 which were absent from follicular oocytes but present in the fluid from the oestrus, but not luteal, oviduct. The glycoproteins remained on the zona pellucida of 2- to 4-cell embryos whose analysis showed the presence of additional polypeptides of Mr 150 000, 57 000, 50 000 and 25 000. It is concluded (i) that shortly after ovulation, and in spite of the presence around the egg of cumulus oophorus and corona radiata cells, significant amounts of oviducal glycoproteins are able to bind firmly to the zona pellucida, and (ii) that after contact with spermatozoa there is evidence of a limited hydrolysis of the structure by the sperm protease acrosin.

Animals↗