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Biomedical subjects

M C Chan

Publications and source records attributed to M C Chan.

At least 19 recordsLinked to original sources
PubMed2006

Nasal CPAP reduces systemic blood pressure in patients with obstructive sleep apnoea and mild sleepiness.

BACKGROUND: A randomised controlled study was undertaken to examine the effect of nasal continuous positive airway pressure (CPAP) on 24 hour systemic blood pressure (BP) in patients with obstructive sleep apnoea (OSA). METHODS: Patients were fitted with an ambulatory BP measuring device as outpatients during normal activities and recorded for 24 hours before starting therapeutic or subtherapeutic (4 cm H(2)O) CPAP treatment. BP monitoring was repeated before completion of 12 weeks of treatment. The primary end point was the change in 24 hour mean BP. RESULTS: Twenty three of 28 participants in each treatment arm completed the study. There was no significant difference between the two groups in age, body mass index, Epworth Sleepiness Score, apnoea-hypopnoea index, arousal index, and minimum Sao(2). Twenty four patients were hypertensive. The pressure in the therapeutic CPAP group was 10.7 (0.4) cm H(2)O. CPAP usage was 5.1 (0.4) and 2.6 (0.4) hours/night for the therapeutic and subtherapeutic CPAP groups, respectively (p<0.001). After 12 weeks of treatment there were significant differences between the two CPAP groups in mean (SE) changes in 24 hour diastolic BP (-2.4 (1.2) v 1.1 (1.0) mm Hg (95% CI -6.6 to -0.5), p = 0.025); 24 hour mean BP (-2.5 (1.3) v 1.3 (1.1) mm Hg (95% CI -7.2 to -0.2), p = 0.037); sleep time systolic BP (-4.1 (2.1) v 2.2 (1.8) mm Hg (95% CI -11.8 to -0.7), p = 0.028); and sleep time mean BP (-3.6 (1.7) v 1.3 (1.4) mm Hg (95% CI -9.2 to -0.4), p = 0.033). CONCLUSIONS: Compared with subtherapeutic CPAP, 12 weeks of treatment with therapeutic CPAP leads to reductions in 24 hour mean and diastolic BP by 3.8 mm Hg and 3.5 mm Hg, respectively, in mildly sleepy patients with OSA.

Antihypertensive Agents↗
PubMed2006

Radiology curriculum for medical students: clinicians' perspectives.

This study was conducted to establish clinicians' perspectives of a set of radiology curriculum topics for medical student teaching, which were held to be important by radiologists. A questionnaire was sent to clinicians in all specialties. Forty-six clinicians (51.1%) out of 90 returned the questionnaires. All curriculum topics were scored above an average of 4 (agree). The five highest ranking curriculum topics in order of importance were: developing a system for viewing chest radiographs (5.59), developing a system for viewing abdominal radiographs (5.56), developing a system for viewing bone and joint radiographs (5.33), distinguishing normal structures from abnormal in chest and abdominal radiographs (5.33) and identifying gross bone or joint abnormalities in skeletal radiographs (5.22). Correlative analysis between speciality groups showed surgical and medical specialities were significantly different in their responses of two learning outcomes: basic knowledge about the contrast media benefits and risks (P= 0.01) and ability to select the most appropriate and the most cost-effective methods of radiological investigations for clinical situations (P= 0.03). Acute specialities were not significantly different from the other two groups for these two learning outcomes. There was no statistically significant difference for other learning outcomes between the three speciality groups.

Curriculum↗
PubMed2005

Impact of severe acute respiratory syndrome (SARS) on pulmonary function, functional capacity and quality of life in a cohort of survivors.

OBJECTIVE: To examine the impact of severe acute respiratory syndrome (SARS) on pulmonary function, exercise capacity, and health-related quality of life (HRQoL) among survivors. METHODS: 110 survivors with confirmed SARS were evaluated at the Prince of Wales Hospital, HK at the end of 3 and 6 months after symptom onset. The assessment included lung volumes (TLC, VC, RV, FRC), spirometry (FVC, FEV1), carbon monoxide transfer factor (TLCO adjusted for haemoglobin), inspiratory and expiratory respiratory muscle strength (Pimax and Pemax), 6 minute walk distance (6MWD), chest radiographs, and HRQoL by SF-36 questionnaire. RESULTS: There were 44 men and 66 women with a mean (SD) age of 35.6 (9.8) years and body mass index of 23.1 (4.8) kg/m2. Seventy (64%) were healthcare workers. At 6 months 33 subjects (30%) had abnormal chest radiographs; four (3.6%), eight (7.4%), and 17 (15.5%) patients had FVC, TLC, and TLCO below 80% of predicted values; and 15 (13.9%) and 24 (22.2%) had Pimax and Pemax values below 80 cm H2O, respectively. The 6MWD increased from a mean (SD) of 464 (83) m at 3 months to 502 (95) m (95% CI 22 to 54 m, p<0.001), but the results were lower than normal controls in the same age groups. There was impairment of HRQoL at 6 months. Patients who required ICU admission (n = 31) had significantly lower FVC, TLC, and TLCO than those who did not. CONCLUSION: The exercise capacity and health status of SARS survivors was considerably lower than that of a normal population at 6 months. Significant impairment in surface area for gas exchange was noted in 15.5% of survivors. The functional disability appears out of proportion to the degree of lung function impairment and may be related to additional factors such as muscle deconditioning and steroid myopathy.

Adult↗
PubMed2001

Palladium(II) and platinum(II) analogues of luminescent diimine Triangulo complexes supported by triply bridging sulfide ligands: structural and spectroscopic comparisons.

Reaction of [M(L-L)Cl(2)] [M = Pd, Pt; L-L = 4,4'-di-tert-butyl-2,2'-bipyridine ((t)Bu(2)bpy), 4,4'-dimethylcarboxylate-2,2'-bipyridine ((CO(2)Me)(2)bpy), bis(diphenylphosphino)methane (dppm)] with Na(2)S in refluxing methanol afforded [M(3)((t)Bu(2)bpy)(3)(mu(3)-S)(2)](2+) [M = Pd (1a), Pt (2a)], [M(3)((CO(2)Me)(2)bpy)(3)(mu(3)-S)(2)](2+) [M = Pd (1b), Pt (2b)], and [Pt(3)(dppm)(3)(mu(3)-S)(2)](2+) (3) as perchlorate salts. X-ray crystal analysis revealed that 1a, 1b, 2a, and 3 have triangular M(3)S(2) core structures. The three metal atoms in 1a, 2a, and 3 form virtual equilateral triangles with intramolecular Pd-Pd and Pt-Pt separations of 3.027(1)-3.065(1) and 3.104(1)-3.154(1) A, respectively. An isosceles triangle of Pd(3) atoms is observed in the molecular structure of 1b. The (1)MLCT absorption of 2a and 2b appears at 415 and 448 nm, respectively, in dichloromethane and is significantly red-shifted from the lowest energy absorption band of the Pd(3) analogues. Complex 1a exhibits weak photoluminescence in the solid state at 77 and 298 K (uncorrected lambda(max) 760 and 730 nm, respectively) while the 77 K solid-state emission of 1b (uncorrected lambda(max) 760 nm) is also weak. At 77 K, complexes 2a, 2b, and 3 display broad unstructured emissions at lambda(max) 616-630 nm in the solid state. Ligand-field excited states are tentatively assigned for these emissions.

Journal Article↗
PubMed2001

Organic light-emitting materials based on bis(arylacetylide)platinum(II) complexes bearing substituted bipyridine and phenanthroline ligands: photo- and electroluminescence from 3MLCT excited states.

We present the synthesis and photophysical and electroluminescent properties for a series of platinum(II) alpha-diimine bis(arylacetylide) complexes. The molecular structures of five derivatives have been elucidated by X-ray crystallography. Intermolecular pi-pi interactions (between aromatic diimine and phenylacetylide moieties) are apparent in the crystal lattices of two of these. All bis(phenylacetylide) derivatives exhibit intense triplet metal-to-ligand charge transfer (MLCT) photoluminescence in the solid state and in fluid solutions at room temperature. The impact of different solvents, substituents on the diimine ligands, and complex concentrations upon their emissive behavior have been examined and demonstrates that their emission energies can be systematically modified. Application of the 3MLCT excited state of the [Pt(alpha-diimine) (C(triple bond)CPh)2] materials in single- and double-layer organic light-emitting devices are described. The bis(butadiynyl) complex [Pt(4,4'-dtbpy)(C(triple bond)C-C(triple bond)CPh)2] (dtbpy = 4,4'-di-tert-butyl-2,2'-bipyridine) displays strong solid-state and solution phosphorescence at 77 and 298 K; the associated excited state is proposed to arise from both acetylenic 3pi pi*(C(triple bond)C-C(triple bond)CPh) and 3MLCT [Pt --> pi*(diimine)] transitions.

Journal Article↗
PubMed2001

Severe tricuspid regurgitation after heart transplantation.

BACKGROUND: Tricuspid regurgitation (TR) is common after heart transplantation. However, the incidence of severe TR and the incidence of symptoms after echocardiographic diagnosis of severe TR have not been documented. The purpose of this study is to determine the incidence of severe TR and its clinical significance in the heart transplant population. METHODS: We reviewed echocardiograms (echo) of all heart transplant patients coming for regular echocardiographic follow-up between 1990 and 1995. We reviewed the charts of all patients who had echo diagnosis of severe TR. RESULTS: A total of 336 patients had echo follow-up during this time period. The number of months post-heart transplant to last echo was 54 +/- 50 (range, 1 to 265 months). Ninety patients had moderate TR and 23 patients had severe TR. Mean time from heart transplantation to diagnosis of severe TR was 43 +/- 38 months (range, 1 to 132). Using Cutler-Ederer analysis, at 5 years, 92.2% of surviving patients were free from severe TR. At 10 years, 85.8% of surviving patients were free from severe TR. Of the 23 patients with severe TR, 17 had charts available for review. The mean number of prior endomyocardial biopsies was 28 +/- 21 (range, 3 to 88). These patients were followed for 35 +/- 18 months after diagnosis. During this period, they developed significant heart failure and peripheral edema. Six patients eventually underwent tricuspid valve replacement. CONCLUSIONS: Moderate to severe TR commonly occurs following heart transplantation. Severe TR is associated with significant morbidity.

Adult↗
PubMed2000

Luminescent mononuclear and binuclear cyclometalated palladium(II) complexes of 6-phenyl-2,2 bipyridines: spectroscopic and structural comparisons with platinum(II) analogues.

The mononuclear cyclometalated Pd(II) complexes [Pd(L1)X] (HL1 = 6-phenyl-2,2'-bipyridine; X = Cl, la; Br, 1b; I, 1c), [Pd(L1)PPh3]+ (1d), [Pd(L2-5)Cl] [2a-5a, HL2-5 = 4-(aryl)-6-phenyl-2,2'-bipyridine; aryl = phenyl (2), 4-chlorophenyl (3), 4-tolyl (4), 4-methoxyphenyl (5)] and the binuclear derivatives [Pd2(L1-5)2(mu-dppm)]2+ (1e-5e, dppm = bis(diphenylphosphino)methane) and [Pd2(L1)2(mu-dppCs)]2+, (1f, dppC5 = 1,5-bis(diphenylphosphino)pentane) were prepared. The crystal structures of 1d(ClO4), 1e(ClO4)2 x DMF, and 2e(ClO4)2 have been determined by X-ray crystallography. The magnitude of the Pd-Pd distances in le and 2e (3.230(1) and 3.320(2) A, respectively) suggest minimal metal-metal interaction, although pi-stacking of the aromatic ligands (interplanar separations 3.34 and 3.35 A, respectively) is evident. All complexes display low-energy UV absorptions at lambda approximately 390 nm, which are tentatively assigned to 1MLCT transitions; red shifts resulting from Pd-Pd interactions in the binuclear species are not apparent. The complexes in this work are non-emissive at 298 K, but the cationic derivatives exhibit intense luminescence at 77 K. The structured emissions of 1d and 1f in MeOH/EtOH glass (lambdamax 467-586 nm) and all cationic species in the solid state (lambdamax 493-578 nm) are assigned to intraligand excited states. Complexes le-5e display dual emissions in MeOH/EtOH glass at 77 K, and the broad structureless bands at lambdamax 626-658 nm are attributed to pi-pi excimeric IL transitions. A comparison between the photophysical properties of Pd(II) and Pt(II) congeners is presented.

Journal Article↗
PubMed1999

Kinetics of cellular trafficking and cytotoxicity of 9.2.27-gelonin immunotoxins targeted against the high-molecular-weight melanoma-associated antigen.

The high-molecular-weight melanoma-associated antigen (HMW-MAA) is expressed on a large majority of melanoma tissues but not on most normal or other neoplastic tissues. Monoclonal antibody 9.2.27 binds with high affinity and specificity to the HMW-MAA, making it an attractive choice as an agent for targeting toxins or chemotherapeutic agents specifically towards melanomas. To characterize the interactions between 9.2.27 and melanoma cells more carefully, data on the kinetics of binding, internalization, and degradation of 9.2.27 by SK-MEL-2 cells were collected. Binding of 9.2.27 to SK-MEL-2 cells was rapid, and followed by slow loss of surface-bound antibody, probably because of loss of surface antigen caused by degradation and/or shedding. A small fraction (approx. 5%) of surface-bound 9.2.27 was internalized and degraded. A mathematical model describing these interactions was developed, and equilibrium and kinetic constants were fitted to the data. To evaluate the utility of 9.2.27 as a toxin-targeting agent, 9.2.27-gelonin immunotoxins were constructed and tested in protein synthesis inhibition assays. The dependence of the toxicity data for 9.2.27-gelonin on time and concentration was quantitatively related to the accumulated intracellular exposure to 9.2.27-gelonin by a relatively simple equation. This equation had been previously validated for immunotoxins targeted against the transferrin receptor, for which the trafficking kinetics are quite dissimilar from those of the HMW-MAA. The success of the approach here suggests that this method may be widely applicable for analysis of immunotoxin efficacy.

Animals↗
PubMed1999

Use of physical restraints on elderly patients: an exploratory study of the perceptions of nurses in Hong Kong.

A qualitative study was designed to explore nurses' perceptions of the use of physical restraints on elderly patients in Hong Kong. Content analysis of semi-structured interviews with 20 registered nurses working in medical and geriatric settings of two regional hospitals revealed that although nurses generally had mixed feelings about the use of physical restraints on elderly patients, they did not question this 'routine' practice and their knowledge about the consequences and alternatives to the use of restraint was limited. It was found that nurses had an overriding concern in ensuring elderly patients' physical safety and using restraints therefore provided them with a sense of security. The deleterious impact of restraint on the care received by elderly patients was largely unrecognized. Implications for practice and future studies are discussed in the light of these findings.

Adult↗
PubMed1997

Effects of diet on measurement of nitric oxide metabolites.

1. The present study investigated whether a low nitrate/nitrite diet could minimize variability in the measurement of endogenous plasma and urine nitric oxide (NO) metabolites, nitrate and nitrite (NOx) in normal subjects. 2. Nitrate and nitrite concentrations were measured in plasma and urine as indicators of NO production in six subjects during a free diet and then during a low nitrate/nitrite diet for 6 days. 3. The plasma concentration and 24 h urine NOx/creatinine ratio were significantly lower on the low nitrate/nitrite diet than on the free diet (P < 0.01). Nitric oxide production appeared to vary greatly within and between subjects, but these variations were substantially decreased by the fourth day of a low nitrate/nitrite diet. 4. Human plasma and urine NOx measurements should be determined after a low nitrate/nitrite diet for at least 4 days.

Adult↗
PubMed1996

Linear epitopes of sperm whale myoglobin identified by polyclonal antibody screening of random peptide library.

Distinct enhancement of antibody-specific clones was apparent during the screening against random peptide libraries with antigen-specific polyclonal antibodies. Several sequence motifs obtained from these screenings were homologous with the primary sequence of myoglobin. Two of these motifs have been confirmed as antigenic determinants by competitive inhibition tests using eight-branched synthetic peptides. One of the peptides has a sequence that corresponds to amino acid residues 42-50, KFDRFKHLK, of the myoglobin sequence. This is a new epitope of myoglobin that is reported for the first time. The epitope is located precisely in the "turn' or "loop' region between helices C and D of the crystal structure of myoglobin. The second antibody binding site has a sequence of DIAAKYKELGYQG, and this is located between residues 141-153, which is the C-terminus of myoglobin. This epitope encompassed two linear epitopes of myoglobin, amino acid residues 145-151 and 147-153, that have been reported earlier based on immunochemical characterisation of cleavage fragments of the protein. These results clearly indicate that epitope mapping using polyclonal antibodies against random peptide libraries can identify new epitopes precisely, as well as confirm epitopes of myoglobin obtained earlier using established methodologies.

Animals↗
PubMed1996

Stereotactic fine needle aspiration in the management of mammographic abnormalities detected in breast screening.

BACKGROUND: Fine needle aspiration (FNA) is used routinely in the management of palpable breast lumps; with the implementation of the stereotactic technique its use has been extended to the investigation of mammographic abnormalities. The advent of breast screening means that many mammographic abnormalities will be detected; because routine open biopsy is impractical and undesirable, stereotactic fine needle aspiration becomes the method of choice for investigation. METHOD: Within a 28 month interval, 81 Chinese women underwent stereotactic FNA in Kwong Wah Hospital, Hong Kong. RESULTS: Fifty-one women (62.9%) had a benign cytology result and no further investigations were required. Inconclusive results were obtained in 18.6% of the aspirates. Open biopsy was required in 16 women (19.8%). CONCLUSION: Stereotactic FNA is very useful in the exclusion of malignancy and the avoidance of open biopsy in asymptomatic women who have mammographic abnormalities.

Adult↗
PubMed1995

Neonatal jaundice, aflatoxins and naphthols: report of a study in Ibadan, Nigeria.

This study set out to investigate the prevalence of naphthols and aflatoxins in the sera of babies with neonatal jaundice and their mothers in order to determine whether they contribute to the occurrence of unexplained neonatal jaundice in Ibadan. Blood was obtained from 327 jaundiced neonates and 80 of their mothers, and 60 non-jaundiced controls and seven of their mothers admitted to hospital between April 1989 and April 1991. Blood group, bilirubin concentration, erythrocyte G6PD status, aflatoxin and naphthol concentrations in blood were measured. Altogether, 30.9% of the jaundiced neonates were G6PD-deficient, compared with 13.3% of controls (chi 2 = 6.88; p = 0.009). Aflatoxins were detected in 27.4% of jaundiced neonates, 17% of their mothers, 16.6% of controls and 14.4% of control mothers. Naphthols were detected in 7.2% of jaundiced babies, 6.3% of their mothers, 6.25% of control babies and 14.4% of their mothers. Analysis of the data revealed that either G6PD deficiency or the presence of any serum aflatoxin is a risk factor for neonatal jaundice; odds ratio were 2.97 (95%) confidence intervals (CI): 1.31-6.74) and 2.68 (CI: 1.18-6.10), respectively. This study demonstrates that G6PD deficiency and/or the presence of serum aflatoxins are risk factors for neonatal jaundice in Nigeria. Aflatoxins are an additional risk factor not previously reported.

Aflatoxins↗
PubMed1994

Detection of naphthols and aflatoxins in Nigerian cord blood.

Widespread use of napthol-containing compounds and frequent contamination of foods by aflatoxins occurs in Nigeria. Napthols cause haemolysis and aflatoxins are hepatotoxic. A study was carried out to determine the extent of fetal exposure to these compounds and their influence on birthweight. Cord blood samples were collected at delivery from 625 babies and their sera were analysed for aflatoxins and naphthols. Mothers' histories and babies' weights were recorded. Naphthols were detected in 6.9% and aflatoxins in 14.6% of serum samples. No correlation was found between the presence of either compound and birthweight. Reported exposure to naphthalene-containing compounds was not related to detection of serum naphthol. Results show considerable fetal exposure to these potentially toxic compounds in Ibadan, Nigeria.

Aflatoxins↗
PubMed1994

Placental transfer of tetanus toxoid antibodies in Nigerian mothers.

The aim of this study was to assess the efficacy of the tetanus toxoid immunization programme in Nigeria, specifically the placental transfer of antibody to newborn Nigerian babies. Tetanus toxoid antibody levels were measured in 39 mother-baby pairs in Ibadan, Nigeria and compared with 78 British mother-baby pairs. Geometric means of the ratios of cord/mother (sequestration index SI) were 0.776 for Nigerian pairs and 1.306 for British pairs, indicating a limitation in the placental transfer of tetanus toxoid in the Nigerian population. These findings confirm that there is a block in the placental transfer of anti-tetanus toxoid antibodies in African populations which will affect current immunization programmes and requires further investigation.

Antibodies, Bacterial↗