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Biomedical subjects

A S Ng

Publications and source records attributed to A S Ng.

At least 19 recordsLinked to original sources
PubMed2001

Long-term survivor mixture model with random effects: application to a multi-centre clinical trial of carcinoma.

A mixture model incorporating long-term survivors has been adopted in the field of biostatistics where some individuals may never experience the failure event under study. The surviving fractions may be considered as cured. In most applications, the survival times are assumed to be independent. However, when the survival data are obtained from a multi-centre clinical trial, it is conceived that the environmental conditions and facilities shared within clinic affects the proportion cured as well as the failure risk for the uncured individuals. It necessitates a long-term survivor mixture model with random effects. In this paper, the long-term survivor mixture model is extended for the analysis of multivariate failure time data using the generalized linear mixed model (GLMM) approach. The proposed model is applied to analyse a numerical data set from a multi-centre clinical trial of carcinoma as an illustration. Some simulation experiments are performed to assess the applicability of the model based on the average biases of the estimates formed.

Carcinoma, Squamous Cell↗
PubMed2001

Determinants of maternity length of stay: a Gamma mixture risk-adjusted model.

With obstetrical delivery being the most frequent cause for hospital admissions, it is important to determine health- and patient-related characteristics affecting maternity length of stay (LOS). Although the average inpatient LOS has decreased steadily over the years, the issue of the appropriate LOS after delivery is complex and hotly debated, especially since the introduction of the mandatory minimum-stay legislation in the USA. The purpose of this paper is to identity factors associated with maternity LOS and to model variations in LOS. A Gamma mixture risk-adjusted model is proposed in order to analyze heterogeneity of maternity LOS within obstetrical Diagnosis Related Groups (DRGs). The determination of pertinent factors would benefit hospital administrators and clinicians to manage LOS and expenditures efficiently.

Diagnosis-Related Groups↗
PubMed2001

Laryngeal mask airway insertion in paediatric anaesthesia: comparison between the reverse and standard techniques.

Sixty-seven children between one and 15 years of age were randomized to have Laryngeal Mask Airway (LMA) insertion using either the standard technique (Group A) as described by Brain or the "reverse technique" (involving a 180 degree turn after insertion with the cuff facing the palate) (Group B). A blinded observer using a fibreoptic bronchoscope assessed the final position of the LMA. The LMA had to be placed within 15 seconds for the procedure to be considered "successful". The success rate using the standard technique was 90.3% (28/31) and 100% (36/36) using the reverse technique (P value 0.06). The 95% confidence interval for the difference in success rates between Group B and A (B-A) was -0.73% to 20.1%. It is our opinion that the reverse technique of insertion of the LMA is an acceptable alternative to the standard technique.

Adolescent↗
PubMed2001

Argpyrimidine, a blue fluorophore in human lens proteins: high levels in brunescent cataractous lenses.

PURPOSE: To determine whether the human lens contains argpyrimidine, a modification of arginine by methylglyoxal, to establish how argpyrimidine content relates to lens aging and cataract formation. METHODS: A monoclonal antibody was used to measure argpyrimidine by a competitive ELISA in water soluble (WS) and insoluble (WI) lens fractions from young, aged, nuclear cataractous, and brunescent cataractous lenses. Brunescent cataractous lens proteins were digested by enzymes, the digest was subjected to HPLC, and the eluate was analyzed for argpyrimidine. Lens proteins from aged lenses (from donors 65 to 80 years of age) were fractionated on a Sephadex G-200 column, and the crystallins were tested for argpyrimidine. RESULTS: The competitive ELISA showed two to three times as much argpyrimidine in water-insoluble proteins as in water-soluble proteins. Although no clear cut increase with the age of the lens donors in either the water-soluble or the insoluble protein fractions was found, the argpyrimidine levels in brunescent cataractous lenses were significantly higher (254.0 +/- 155 pmol/mg protein, P < 0.005) than in age-matched, aged (16.1 +/- 8 pmol/mg) or nuclear cataractous lenses (49.0 +/- 26 pmol/mg). Lenses from diabetic individuals showed a modest increase (50.3 pmol/mg) compared with age-matched normal lenses. HPLC results provided additional evidence that human lenses contain argpyrimidine. Western blotting experiments showed consistently stronger reactions with cataractous lens proteins than those from noncataractous lenses, and argpyrimidine was found in both crystallin monomers and polymers. All crystallins and several cross-linked high-molecular-weight aggregates reacted with the antibody to argpyrimidine, but a protein of approximately 28 kDa in the alpha-crystallin fraction displayed the greatest immunoreactivity. CONCLUSIONS: Methylglyoxal modifies arginine within the human lens, and the changes occur at a much higher rate in brunescent lens proteins than in either nuclear cataractous or normal lenses. All crystallins contained argpyrimidine and covalently cross-linked aggregates. This is the first report of immunologic evidence for an arginine modification in the human lens by a physiologically important alpha-dicarbonyl compound.

Adolescent↗
PubMed2001

A ten-year review of ruptured sinus of valsalva: clinico-pathological and echo-Doppler features.

Rupture of the sinus of valsalva (RSOV) is an uncommon condition with a variety of manifestations ranging from an asymptomatic murmur to cardiogenic shock. This retrospective 10-year review (1985-1995) of 18 patients from a single institution revealed that 6 (33%) were female and 12 (67%) were male with a mean age of 37.6 +/- 13.4 years and that 72% were Chinese by ethnic descent with the remaining 28% being Malay. Eight patients (44.4%) presented with an asymptomatic murmur, 4 (22.2%) with acute chest pain, 4 (22.2%) with mild heart failure, 2 (11.1%) with severe heart failure, and 2 (11.1%) with cardiogenic shock. Rupture of the right aneurysmal coronary cusp (RCC) made up 15 (83.3%) while those of the non-coronary cusp (NCC) made up the remaining. Most of the RCC ruptures were directed into the right ventricle and all of the NCC ruptures were into the right atrium. Ventricular septal defects (VSDs) were found in 9 (50%) of the patients, (although detected by echocardiography in only one third of those patients), aortic regurgitation in 6 (33.3%) and aortic valve vegetations in 2 (11.1%). Echocardiography was found to be accurate in diagnosing RSOVs with 100% diagnostic accuracy after 1990 with four misdiagnoses before 1990. Of these four patients, two were misdiagnosed as having VSDs, one as having a coronary arteriovenous fistula and one as having a patent ductus arteriosus. The anatomical structure of the "windsock" was seen in 64% of the patients who were correctly diagnosed. The pattern of colour flow and spectral Doppler was seen in all patients and helped to localise the site of rupture and the direction of flow. In summary, echocardiography is a simple and accurate way of diagnosing and defining RSOVs and is the imaging modality of choice.

Adult↗
PubMed1999

Postoperative vomiting (POV) in the paediatric outpatient general surgical population.

AIM: To determine the incidence of postoperative vomiting (POV) in the paediatric outpatient general surgical population, the factors affecting POV and the incidence of unplanned admissions contributed by POV. METHOD: One hundred and ninety-nine children below 13 yeas of age undergoing elective outpatient general surgical procedures were enrolled into this prospective study. Anaesthesia was induced either intravenously or via the inhalational route. It was then maintained with nitrous oxide, oxygen and isoflurane or halothane. The age, sex, body weight, duration of fasting, administration of trimeprazine, type of general surgical procedure, maintenance technique for general anaesthesia, duration of general anaesthesia, the administration of opiods or local anaesthetics and the incidence of POV were noted. The results were analysed initially with chi-squared test and subsequently subjected to multivariate logistic regression analysis and stepwise variable selection method. RESULTS: The incidence of POV was 8.5%. Duration of general anaesthesia greater than one hour was associated with a significantly higher incidence of POV. Postoperative emesis did not contribute to unplanned admissions in these day surgical patients.

Adolescent↗
PubMed1998

Caudal morphine in paediatric patients: a comparison of two different doses in children after major urogenital surgery.

We compared the duration of postoperative analgesia and the occurrence of side-effects of two different doses of caudal morphine in children undergoing major urogenital surgery. Fifty-two children aged between 1 and 12 years were randomly selected to receive caudal morphine, either 25 micrograms.kg-1 (Group A) or 50 micrograms.kg-1 (Group B) with 0.5 ml kg-1 of 0.25% plain bupivacaine immediately before surgery. They were monitored for 24 hours in a high dependency area for known complications of epidural morphine. There was no significant difference in postoperative analgesia between the two doses of caudal morphine. Clinically significant respiratory depression or sedation was not detected in either group. The occurrence of vomiting and pruritus was similar in both groups. Urinary retention was not recorded as all children had an indwelling catheter as required by the surgical procedure. We concluded that 25 micrograms.kg-1 of caudal morphine is as effective as 50 micrograms.kg-1 for providing postoperative analgesia in children undergoing urogenital surgery.

Analgesics, Opioid↗
PubMed1996

Oral premedications in paediatric day surgery.

The degree of sedation in 191 day-stay children after oral premedication were compared. One hundred and forty-six were 1-5 years old (Group 1) and were randomised to receive either chloral 40 mg/kg, midazolam 0.2 mg/kg, promethazine 1 mg/kg, trimeprazine 3 mg/kg or placebo. Forty-five were 5-12 years old and were randomised to receive either trimeprazine 3 mg/kg, midazolam 0.2 mg/kg or placebo (Group 2). The children were assessed using four categories: asleep or drowsy, awake but calm, crying or anxious and oversedated or obstructed airway. They were assessed on leaving the ward, at separation from the parents, at induction, in the recovery room and one and two hours after returning to the ward. In Group 1, it was found that chloral and trimeprazine gave the best degree of sedation but the sedative effect of trimeprazine lasted longer into the post operative period. In Group 2, it was found that the children did not require deep sedation and the anxiolysis obtained with midazolam was adequate.

Administration, Oral↗
PubMed1996

A questionnaire survey on practice of chest tube management.

AIM: With the aim towards better education of junior medical staff on chest tube management, we designed a questionnaire to survey their practice and at the same time to assess their level of understanding of the physical principles of chest tube and its drainage system. METHODS: The questionnaire was distributed to 130 junior medical staff (house officers, medical officers, trainee medical officers and specialist medical officers) from 7 Medical and Surgical Departments in Singapore General Hospital. Eighty-seven (66.9%) candidates responded. The mean age of the respondents was 27 +/- 2.1. They had an average of 3.2 +/- 1.9 years after basic medical qualification and 5 hospital postings. Nine respondents had obtained higher medical qualifications. RESULTS: About a quarter of the respondents, and 40% of those with higher medical qualifications gave appropriate answers. Ninety percent indicated that they received no lectures on chest tube management. Incomplete response ranged from 0% to 6%. CONCLUSION: To improve education on chest tube management, our results and the feedback we obtained from the respondents, suggest that lectures on important physical principles of chest tube and its drainage system should be delivered to all junior medical staff.

Chest Tubes↗
PubMed1995

Amide and alpha-keto carbonyl inhibitors of thrombin based on arginine and lysine: synthesis, stability and biological characterization.

We report structure-activity investigations in a series of tripeptide amide inhibitors of thrombin, and the development of a series of highly potent active site directed alpha-keto carbonyl inhibitors having the side chain of lysine at P1. Compounds of this class are unstable by virtue of reactivity at the electrophilic carbonyl and racemization at the adjacent carbon (CH). Modifications of prototype alpha-keto-ester 8a have afforded analogs retaining nanomolar Ki. Optimal potency and stability have been realized in alpha-keto-amides 11b (Ki = 2.8 nM) and 11c (Ki = 0.25 nM).

Amides↗
PubMed1995

Pharmacokinetics of propofol infusion in Asian patients undergoing coronary artery bypass grafting.

The pharmacokinetics of propofol was studied in 11 Asian patients with fentanyl-isoflurane anaesthesia during cardiopulmonary bypass (CPB) and undergoing elective coronary artery bypass grafting (CABG). Instead of the usual increments of morphine and a benzodiazepine, propofol (4 mg/kg/h) was initiated at the start of CPB and ceased at CPB separation. Whole blood propofol concentrations were determined during and postinfusion using high-performance liquid chromatography with fluorescence detection. Data from four patients seemed to fit a two-compartment model, whereas those from seven patients were significantly (F test, p < 0.05) better fitted to a three-compartment model. The pharmacokinetic parameters were as follows: The mean (SD) of the initial distribution phase t1/2 pi, intermediate distribution phase t1/2 alpha, and elimination phase t1/2 beta were 2.22 (1.04) min, 42.9 (16.4) min, and 370 (138) min, respectively. The mean clearance of 1.31 (0.50) L/min was lower than those reported from other studies, whereas the mean blood concentration of 2.2 (1.0) mg/L at the 1-h infusion period was higher. The mean calculated apparent Css was 3.9 (1.5) mg/L. The low clearance is likely to be due to hemodynamic changes during CPB and CABG, thereby affecting drug distribution and blood flow to the liver.

Aged↗
PubMed1995

Inhibition of thrombin by peptides containing Lysyl-alpha-keto carbonyl derivatives.

Several H-N-Me-D-Phe-Pro-Lysyl-alpha-keto carbonyl derivatives were shown to be potent thrombin inhibitors (Ki 0.2 to 27 nM). The inhibitory potencies of these compounds toward tissue plasminogen activator, plasmin and factor Xa were minimal; however, substantial cross-reactivity versus trypsin was observed (Ki values from 0.5 to 1500 nM). Inhibition of thrombin by alpha-keto carbonyl compounds appeared to occur via a one-step reversible reaction. The alpha-keto carbonyl inhibitors bound thrombin with a second order rate constant (k1 1-4 microM-1s-1) that was 10-100-fold slower than that expected for a diffusion-controlled reaction. Certain alpha-keto carbonyl inhibitors were as potent (on a weight basis) as hirudin when evaluated in a rat arterial thrombosis model. The modest oral bioavailability (10-19%) in rats demonstrated for three of the alpha-keto carbonyl thrombin inhibitors suggests the possibility that alpha-keto amide containing thrombin inhibitors may have utility as orally-active antithrombotic agents.

Amino Acid Sequence↗
PubMed1993

Inhibition of thrombin and other trypsin-like serine proteinases by cyclotheonamide A.

Cyclotheonamide A (CA), a cyclic peptide isolated from the marine sponge of the genus Theonella was shown to be a slow-binding inhibitor of several trypsin-like serine proteinases. Values of 4.6 x 10(4), 4.8 x 10(4), 9.3 x 10(3), 2.1 x 10(3) and 2.7 x 10(2) M-1 s-1 were determined for the second-order rate constants for formation of CA complexes with thrombin, trypsin, plasmin, 2-chain t-PA and factor Xa, respectively. The equilibrium constant (Ki) was measured for dissociation of CA from the CA complex with human thrombin (Ki = 1.0 nM), bovine trypsin (Ki = 0.2 nM), human plasmin (Ki = 12 nM), human factor Xa (Ki = 50 nM) and human 2-chain tissue plasminogen activator (t-PA) (Ki = 40 nM). CA produces dose dependent increases in clotting time assays. The clotting time in the thrombin time, activated partial thromboplastin time and prothrombin time assays, were doubled by 1.5, 0.9 and 48 microM CA, respectively. A model for the binding of CA to the active site of thrombin is proposed.

Binding Sites↗
PubMed1992

Lipid screening in a volunteer population in Singapore.

Coronary risk profile screening was performed in 1065 volunteers during the National Heart Week 1988 as part of the National Heart Association's campaign against the increasing incidence of ischaemic heart disease. Of particular importance was the use of a desktop analyser for lipid screening of total cholesterol and high density lipoprotein (HDL) cholesterol. It was found that the mean serum cholesterol was 211 +/- 39.5 mg/dl, with 62% of the participants having a total cholesterol greater than 200 mg/dl and 23.1% having a total cholesterol greater than 240 mg/dl. For HDL cholesterol, the mean was 48.4 +/- 17 mg/dl, with 18.7% of the participants having a low HDL cholesterol of less than 35 mg/dl. The male Indians had a significantly lower HDL cholesterol compared to male Malays. Three or more risk factors for coronary artery disease was present in 21.7% of Chinese, 41.2% of Malays and 50% of Indians. We conclude therefore that a proportion of this volunteer population, the majority of which have no overt heart disease, is at risk from coronary artery disease from an elevated cholesterol or low HDL cholesterol level. A follow-up of 90 participants who were initially detected to have an elevated cholesterol in 1986, however, showed that only 54.4% still had an elevated cholesterol of greater than 240 mg/dl, thus suggesting that early detection may help to reduce this risk.

Age Factors↗
PubMed1990

beta-Endorphin-like and adrenocorticotropin-like hormones in the pituitary of the snake Ptyas mucosa.

Snake (Ptyas mucosa) pituitaries were heated, extracted with an acidic medium, and the extract subsequently chromatographed on carboxymethyl cellulose (CMC). Fractions were assayed for their abilities to displace D-ala2-D-leu5-[tyrosyl, 3,53H] enkephalin from binding to rat brain membranes and 125I-beta-endorphin from binding to its antibody, and to stimulate corticosterone production by isolated rat adrenal cells. The fraction unadsorbed on CMC (having the least basic character) had the lowest opiate receptor binding activity and beta-endorphin-like immunoreactivity. The highest steroidogenic activity, opiate receptor binding activity and beta-endorphin-like immunoreactivity were concentrated in a strongly adsorbed fraction. Snake pituitaries were also extracted with Tris-HCl buffer (pH 7.8). The extract from the second procedure was subsequently chromatographed on ConA-Sepharose, ultrafiltered and dialyzed to obtain a nonglycopeptide fraction with a molecular weight between 1,000 and 10,000. This fraction also exhibited steroidogenic and opiate receptor binding activities.

Adrenocorticotropic Hormone↗