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Biomedical subjects

Y K Chan

Publications and source records attributed to Y K Chan.

At least 55 records · Page 3Linked to original sources
PubMed1996

Minimum prostate-specific antigen (PSA) level diagnostic of prostate cancer.

The PSA levels in benign prostatic hyperplasia (BPH) and prostate adenocarcinoma (PA) overlap, both below and above 4 to 10 ng/mL. There is no known PSA level diagnostic of PA. In this study, data were obtained in 160 consecutive men aged 58 to 87. Prebiopsy PSA levels (PSA-1) were obtained prior to "sextant" gun biopsies in 97 cases diagnosed as noncarcinoma, and in 56 cases diagnosed as PA. Multiple hematoxylin and eosin sections were made of each biopsy, and Gleason scores given the PAs. Cases were followed up to 30 months with repeated PSA levels and additional biopsies. The highest PSA level in NPA in this series was 54.6 ng/mL.

Adenocarcinoma↗
PubMed1995

Abnormal sphincter of Oddi response to cholecystokinin in postcholecystectomy syndrome patients with irritable bowel syndrome. The irritable sphincter.

Standard biliary manometry, including cholecystokinin (CCK) provocation, was performed on 42 consecutive patients (36 F, 6 M, median age 45 years) with postcholecystectomy syndrome (PCS) who had no evidence of organic disease but who had objective clinical features suggesting sphincter of Oddi dysfunction (SOD) (classes I and II). Patients were subdivided into those with (N = 14) and without (N = 28) irritable bowel syndrome (IBS) using a validated symptom questionnaire based on the modified Rome criteria. Resting sphincter of Oddi (SO) motor parameters (basal pressure, contractile amplitude and frequency, and proportion of retrograde contractions), the presence of abnormal manometry, and the presence of an abnormal response to CCK were compared in the two groups. No significant differences in resting parameters of SO motor activity between patients with and without IBS were observed, and abnormal biliary manometry as a whole was not more prevalent in either group (8/13 and 18/27, respectively). An abnormal response to CCK (failure of complete inhibition of phasic contractions), however, was demonstrated in five of 12 patients with IBS compared with only one of 23 patients without IBS (P = 0.01). In patients with postcholecystectomy SOD, an abnormal response of the SO to CCK thus appears to be an important feature of the subset of patients with concomitant IBS.

Biliary Dyskinesia↗
PubMed1995

Life satisfaction and associated factors in older Hong Kong Chinese.

OBJECTIVE: To determine life satisfaction and its association with physical, functional, socioeconomic, psychological, and social support characteristics in Hong Kong Chinese aged 70 years and older. DESIGN: Cross-sectional study. SETTING: Territory-wide random sample of persons aged 70 years and older. SUBJECTS: A total of 843 men and 714 women were selected by random sampling, stratified by age and sex, from the Old age and Disability Allowance Register, after exclusion of subjects with cognitive impairment. MEASUREMENTS: Life satisfaction was assessed by the subjects' response to the question "Are you satisfied with life", using a 0 to 10-point linear scale. They were also asked to name the most important factor contributing to life satisfaction. Information was also obtained regarding physical health, functional ability, depressive symptoms, and socioeconomic factors. RESULTS: There was a weak association between score and age. Health, adequate income to meet living expenses, and caring relatives were rated the most important factors (> 65%). Some of these factors were also those associated with a high life satisfaction score. Factors associated with a life satisfaction score greater than 6 points were higher social class and educational attainment, adequate income to meet living expenses, satisfactory living arrangement, Christianity, good social support, participation in social activities, functional independence, good self-perceived health, good hearing and vision, daily exercise, absence of recurrent falls, and low depressive symptom score. Multiple logistic regression identified having two or more relatives and tertiary education as positive associated factors, whereas inadequate income to meet expenses, dissatisfaction with living arrangement, nonparticipation in religious group activities, and a high depressive symptom score were negative associated factors. CONCLUSION: In older Chinese, social factors such as the support provided by family members, as well as adequate income to meet living expenses, play a role equal to that of physical factors in contributing to life satisfaction.

Age Factors↗
PubMed1994

Radiological diagnosis of accidental oesophageal intubation.

Oesophageal intubation is rapidly fatal if not recognised. We report a patient who not only survived an oesophageal intubation but who had chest X-rays taken which showed an oesophageal intubation which was initially recognised by the attending physician.

Accidents↗
PubMed1993

Detection of a nitrous oxide reductase structural gene in Rhizobium meliloti strains and its location on the nod megaplasmid of JJ1c10 and SU47.

The gene encoding a denitrification enzyme, nitrous oxide reductase (EC 1.7.99.6), in Rhizobium meliloti and other gram-negative bacteria was detected by hybridization to an internal 1.2-kb PstI fragment of the structural gene (nosZ) cloned from Pseudomonas stutzeri Zobell (W.G. Zumft, A. Viebrock-Sambale, and C. Braun, Eur. J. Biochem. 192:591-599, 1990). Homology to the probe was detected in the DNAs of two N2-fixing strains of P. stutzeri, two denitrifying Pseudomonas species, one Alcaligenes eutrophus strain, and 36 of 56 R. meliloti isolates tested. Except for two isolates of R. meliloti, all showed nitrous oxide reduction activity (Nos+). Therefore, at least part of the nosZ sequence appears to be conserved and widely distributed among denitrifiers, which include free-living and symbiotic diazotrophs. By using Agrobacterium tumefaciens transconjugants harboring different megaplasmids of R. meliloti JJ1c10 and SU47, sequence homology with the nosZ probe was unequivocally located on the nod megaplasmid. A cosmid clone of JJ1c10 in which nosZ homology was mapped on a 4.2-kb BamHI fragment was selected. This cosmid, which conferred Nos+ activity to the R. meliloti wild-type strains ATCC 9930 and Balsac (Nos- and nondenitrifying, respectively) also restored Nos+ activity in the mutants of JJ1c10 and SU47 in which the 4.2-kb BamHI segment was deleted. Therefore, this segment contains sequences essential for nos gene expression in JJ1c10 and SU47 and thus confirms that the nod megaplasmid in JJ1c10 and SU47 which carries genes essential for symbiotic dinitrogen fixation also carries genes involved in the antagonistic process of denitrification.

Blotting, Southern↗
PubMed1992

Efficient culture of Chlamydia pneumoniae with cell lines derived from the human respiratory tract.

Two established cell lines, H 292 and HEp-2, originating from the human respiratory tract, were found to be significantly more efficient and practical than the currently used HeLa 229 cells for growth of Chlamydia pneumoniae. Six strains of C. pneumoniae recently isolated from patients with respiratory ailments were used as test cultures. The H 292 and HEp-2 cells yielded much higher inclusion counts for all the test strains than did HeLa 229 cells. When they were compared with each other, H 292 cells yielded more inclusions than did HEp-2 cells, and the differences were statistically significant in 10 of 18 test sets. A simple system with these two cell lines appeared to be very efficient for culturing C. pneumoniae. It does not require treatment of tissue cells with DEAE-dextran before infection, and it may eliminate the need for serial subpassages of specimens to increase culture sensitivity. Monolayers of these cells remained intact and viable in the Chlamydia growth medium so that reinfection could take place, resulting in greatly increased inclusion counts for specimens containing few infectious units. This system may make it more practical for laboratories to culture for C. pneumoniae for treatment of infections and outbreak intervention and will facilitate studies on this recently recognized pathogen.

Antibodies, Monoclonal↗
PubMed1992

A comparison of sodium citrate and sodium citrate/ranitidine combination for acid aspiration prophylaxis.

The effectiveness of sodium citrate and sodium citrate/ranitidine were compared in two randomised groups of elective caesarean patients during the various phases of anaesthesia. The mean pH values (3.5, 3.3, 3.6) were lower in the citrate group compared to the citrate/ranitidine group (6.1, 6.3, 5.9). The percentage of patients with pH values less than 2.5 was 40% in the citrate group compared to 7% in the citrate/ranitidine group. Sodium citrate alone is less effective than sodium citrate/ranitidine for acid aspiration prophylaxis.

Adolescent↗
PubMed1992

Xq28: epidemiology and sex-linkage between red-green colour blindness and G6PD deficiency.

Xq28 is the genetic locus of two closely associated conditions of red-green colour blindness and G6PD deficiency. Epidemiologically, both rank among the more frequent sex-linked clinical problems that affect military servicemen in Singapore. This retrospective study is based on the findings of 35714 subjects screened at the Medical Classification Centre--Central Manpower Base (MCC--CMPB) over an eighteen-month period using pseudoisochromatic and fluorescent techniques as well as anomaloscopic and spectrometric methods. The overall prevalence rates of red-green colour blindness, G6PD deficiency and association were determined to be 4.8%, 2.2% and 0.1% respectively. Malays showed the highest prevalence rates among the major races. Statistically significant difference was found with regards to the prevalence rates of G6PD deficiency and its association with red-green colour blindness. Review of literature yielded comparable results with a few local studies of good sample size done over the past twenty years. Sex-linkage analysis was hindered by the lack of pedigree studies.

Adolescent↗
PubMed1991

Persistent liver dysfunction among workers at a vinyl chloride monomer polymerization plant.

Thirteen workers with persistent abnormalities in one or more liver function tests (LFT) at a vinyl chloride monomer (VCM) polymerization plant were investigated. Twelve workers were found to have VCM-induced liver dysfunction based on circumstantial evidence. They were employed between 1971 and 1982 when the VCM levels ranged from 1 to 21 p.p.m. After 1982 when the environmental VCM levels were controlled to below 1 p.p.m., no cases of VCM-induced liver dysfunction were detected. In most cases, glutamic pyruvic transaminase was the earliest parameter to be raised. The second most common parameter is serum gamma glutamyl transpeptidase. The latent period ranged from 1 to 13 years. An improvement in their LFT results was shown by 83.3 per cent of workers within 6 months to 2 years after removal from further VCM exposure. For workers who returned to VCM work, their LFT became abnormal again. Liver scans showed hepato and/or splenomegaly in most cases. Liver biopsies on 9 workers were reported as 'non-specific fatty changes' of varying degrees. These observations highlight the need for continual vigilance with environmental monitoring and medical surveillance of VCM-exposed workers.

Adult↗
PubMed1991

Detection of alternative nitrogenases in aerobic gram-negative nitrogen-fixing bacteria.

Strains of aerobic, microaerobic, nonsymbiotic, and symbiotic dinitrogen-fixing bacteria were screened for the presence of alternative nitrogenase (N2ase) genes by DNA hybridization between genomic DNA and DNA encoding structural genes for components 1 of three different enzymes. A nifDK gene probe was used as a control to test for the presence of the commonly occurring Mo-Fe N2ase, a vnfDGK gene probe was used to show the presence of V-Fe N2ase, and an anfDGK probe was used to detect Fe N2ase. Hitherto, all three enzymes have been identified in Azotobacter vinelandii OP, and all but the Fe N2ase are present in Azotobacter chroococcum ATCC 4412 (MCD1). Mo-Fe N2ase and V-Fe N2ase structural genes only were confirmed in this strain and in two other strains of A. chroococcum (ATCC 480 and ATCC 9043). A similar pattern was observed with Azotobacter beijerinckii ATCC 19360 and Azotobacter nigricans ATCC 35009. Genes for all three systems are apparently present in two strains of Azotobacter paspali (ATCC 23367 and ATCC 23833) and also in Azomonas agilis ATCC 7494. There was no good evidence for the existence of any genes other than Mo-Fe N2ase structural genes in several Rhizobium meliloti strains, cowpea Rhizobium strain 32H1, or Bradyrhizobium japonicum. Nitrogenase and nitrogenase genes in Azorhizobium caulinodans behaved in an intermediate fashion, showing (i) the formation of ethane from acetylene under Mo starvation, a characteristic of alternative nitrogenases, and (ii) a surprising degree of cross-hybridization to the vnfDGK, but not the anfDGK, probe. vnfDGK- and anfDGK-like sequences were not detected in two saccharolytic Pseudomonas species or Azospirillum brasilense Sp7. The occurrence of alternative N2ases seems restricted to members of the family Azotobacteraceae among the aerobic and microaerobic diazotrophs tested, suggesting that an ability to cope with O2 when fixing N2 may be an important factor influencing the distribution of alternative nitrogenases.

Azotobacter↗
PubMed1988

Epinephrine and left ventricular function in humans: effects of beta-1 vs nonselective beta-blockade.

Changes in cardiac performance in response to epinephrine administered by graded infusion were assessed by M-mode echocardiography in normotensive healthy subjects after pretreatment with placebo, the beta 1-selective blocker atenolol, or the nonselective beta-blocker propranolol. Epinephrine alone increased heart rate and left ventricular end diastolic dimension and decreased left ventricular end systolic dimension. Left ventricular performance as assessed by fractional shortening and systolic blood pressure/end-systolic volume (P/V) ratio was also increased. Atenolol pretreatment did not significantly affect the increase in heart rate by epinephrine. However, atenolol did prevent the effects of epinephrine on left ventricular dimensions and left ventricular performance at the lower infusion rates and significantly blunted these effects at the highest infusion rate. After propranolol, epinephrine significantly decreased left ventricular end diastolic dimension despite decreasing heart rate and left ventricular emptying (associated with a high afterload). P/V ratio remained unchanged. These results indicate that beta 2-receptors may play a major role in the increase in heart rate caused by epinephrine. In contrast, epinephrine's positive inotropic effect appears to be mediated primarily via beta 1-receptors and, at higher concentrations, possibly also through beta 2-receptors. The pattern of changes in left ventricular end diastolic dimension suggests that epinephrine increases venous return via both beta 1- and beta 2-receptor stimulation and that alpha-receptor stimulation (epinephrine after propranolol) may actually decrease venous return.

Adrenergic beta-Antagonists↗
PubMed1988

Rhizobium meliloti genes required for C4-dicarboxylate transport and symbiotic nitrogen fixation are located on a megaplasmid.

A mutant of Rhizobium meliloti unable to transport C4 dicarboxylates (dct) was isolated after Tn5 mutagenesis. The mutant, 4F6, could not grow on aspartate or the tricarboxylic acid cycle intermediates succinate, fumarate, or malate. It produced symbiotically ineffective nodules on Medicago sativa in which bacteroids appeared normal, but the symbiotic zone was reduced and the plant cells contained numerous starch granules at their peripheries. Cosmids containing the dct region were obtained by selecting those which restored the ability of 4F6 to grow on succinate. The Tn5 insertion in 4F6 was found to be within a 5.9-kilobase (kb) EcoRI fragment common to the complementing cosmids. Site-specific Tn5-mutagenesis revealed dct genes in a segment of DNA about 4 kb in size extending from within the 5.9-kb EcoRI fragment into an adjacent 2.9-kb EcoRI fragment. The 4F6 mutation was found to be in a complementation group in which mutations yielded a Fix- phenotype, whereas other dct mutations in the region resulted in mutants which produced effective nodules in most, although not all, plant tests (partially Fix-). The dct region was found to be located on a megaplasmid known to carry genes required for exopolysaccharide production.

Cosmids↗
PubMed1987

Comparison of the logistic and Cox regression models when outcome is determined in all patients after a fixed period of time.

This paper presents an evaluation of the logistic and Cox regression models for a prospective study when the outcome is binary and is determined in all patients after a fixed period of time. The similarities and differences between the regression coefficients and test statistics are given for the two-sample case. Extension of results to the multivariate case and under product binomial sampling are discussed. The results are illustrated using data from a clinical trial designed to evaluate the effect of a lipid lowering drug on progression of coronary artery disease.

Coronary Disease↗
PubMed1986

Relationship of staphylococcal tolerance, teichoic acid antibody, and serum bactericidal activity to therapeutic outcome in Staphylococcus aureus bacteremia.

A randomized cooperative study of therapy for Staphylococcus aureus bacteremia was conducted in which nafcillin was given for four or six weeks to patients with clinical endocarditis and for two or four weeks to those without evidence of endocarditis. Eighty-four patients were enrolled, and 32 completed treatment, all of whom had bacteriologic cures. Three patients, treated for two weeks, had complications that were undetectable by assay of serum teichoic acid antibody. Data were insufficient to allow conclusions regarding the optimal duration of therapy for patients with or without endocarditis. However, the results suggest that neither clinical nor immunologic methods can reliably detect complications in patients treated for two weeks only. In addition, patients infected with tolerant organisms remained febrile longer than those infected with nontolerant strains but did not require additional antibiotics for cure. Peak serum bactericidal activity at a dilution of 1:8 or greater was present in all patients. Serum bactericidal activity of 1:8 prior to an antibiotic dose was not necessary for cure.

Antibodies, Bacterial↗
PubMed1986

Veterans Administration cooperative study on hepatitis and dentistry.

Personnel in the VA dental facilities were screened for the detection of viral hepatitis and identification of factors implicating infectivity. A total of 963 personnel from 126 dental facilities throughout the United States voluntarily participated in the study. The rate of seroconversion for any hepatitis B markers was approximately 1% per year. Serial positive tests for antibody to hepatitis B core antigen or antibody to hepatitis B surface antigen (or both) were present in 16.2% of dentists and 13.0% of dental auxiliary personnel. Oral and maxillofacial surgeons composed the highest prevalence occupation (24.0%), and clinical personnel composed the lowest prevalence occupation (8.9%). There was a significant association between years in dental environment and serological positivity for viral B infection. The dentists and dental auxiliary personnel had significant linear trends of increasing serological positivity with years in the dental environment. Although a majority of personnel reported wearing gloves while treating high-risk patients or performing invasive procedures, inadequate prophylactic measures were exercised for most patients undergoing a variety of less invasive procedures. The results of the study show the need for an active immunization program against type B viral infection for dental and dental auxiliary personnel, preferably before the initial exposure to the professional environment.

Dental Auxiliaries↗
PubMed1984

Controlled comparison of hemodialysis and peritoneal dialysis: Veterans Administration multicenter study.

We measured mortality and morbidity among 114 patients assigned randomly to home hemodialysis (HD) and home intermittent peritoneal dialysis (IPD). Data were collected during the time of home training and for 12 months after initiation of home dialysis. Training time was shorter for the IPD than for the HD patients (P less than 0.001) with median time 1.8 months for IPD and 3.9 months for HD. Switching to the alternative mode of treatment was more frequent for the IPD group (29/59 vs. 5/55, P less than 0.001). Survival time was not different, perhaps because of the modality change. More IPD patients were hospitalized in the first 6 months (20 for IPD vs. 9 for HD, P = 0.02), but they had fewer troublesome cardiovascular events in the first year (0 vs. 12, P less than 0.001). The HD patients maintained better nutritional status as reflected in body weight and arm muscle circumference and possibly in urea appearance rate. Thus, these data suggest that for most patients, IPD is a less satisfactory form of therapy than HD, but certain advantages of IPD did emerge. Applications of this information to the currently more popular mode of CAPD await further study.

Clinical Trials as Topic↗