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Biomedical subjects

H Y Chan

Publications and source records attributed to H Y Chan.

At least 19 recordsLinked to original sources
PubMed2006

The effects on maternal anxiety of two-dimensional versus two- plus three-/four-dimensional ultrasound in pregnancies at risk of fetal abnormalities: A randomized study.

OBJECTIVE: To test the hypothesis that the use of two-dimensional (2D) ultrasonography with three-dimensional/four-dimensional (3D/4D) ultrasonography can reduce anxiety to a greater extent in women at risk of having a fetus with congenital abnormalities than the use of 2D ultrasonography alone. METHODS: A total of 124 women attending the prenatal diagnostic clinic of a teaching hospital were randomized into the intervention group (2D ultrasonography followed by 3D/4D ultrasonography) or control group (2D ultrasonography alone). The primary outcome was maternal anxiety levels, which were assessed by the Spielberger state-trait anxiety inventory. We measured the anxiety levels in all women at the first visit, at around 18 weeks' gestation (immediately after ultrasound examinations) and at 28 weeks' gestation. RESULTS: A short-term reduction of the state-anxiety score (by around 2 points) from the first visit to after ultrasound examinations was observed in both the intervention group and the control group. Unexpectedly, a small increase in the state-anxiety score from the first visit to 28 weeks' gestation was observed in the intervention group but not in the control group, though there was no significant difference in the changes between the two groups. Repeated measures ANOVA (analysis of variance) also showed that there was no significant interaction effect between groups and time of assessment on the state-anxiety scores (F = 1.072 and P = 0.344). About 80% of women reported a better understanding that their baby was normal after viewing 3D rather than 2D images. CONCLUSION: This randomized study indicates that the addition of 3D/4D ultrasound does not cause a significant reduction in maternal anxiety in pregnancies at risk of fetal abnormalities compared with conventional 2D ultrasound alone.

Adult↗
PubMed2006

A treatable case of dementia--intracranial dural arteriovenous fistula.

Dementia is a common medical problem that affects elderly patients. We report on a 77-year-old man with an intracranial dural arteriovenous fistula who presented with dementia that was initially thought to be irreversible and degenerative. Subsequent neuroendovascular intervention resulted in significant functional and cognitive improvement.

Aged↗
PubMed2004

Theory of networked minority games based on strategy pattern dynamics.

We formulate a theory of agent-based models in which agents compete to be in a winning group. The agents may be part of a network or not, and the winning group may be a minority group or not. An important feature of the present formalism is its focus on the dynamical pattern of strategy rankings, and its careful treatment of the strategy ties which arise during the system's temporal evolution. We apply it to the minority game with connected populations. Expressions for the mean success rate among the agents and for the mean success rate for agents with k neighbors are derived. We also use the theory to estimate the value of connectivity p above which the binary-agent-resource system with high resource levels makes the transition into the high-connectivity state.

Adaptation, Physiological↗
PubMed2004

Scale-free networks with tunable degree-distribution exponents.

We propose and study a model of scale-free growing networks that gives a degree distribution dominated by a power-law behavior with a model-dependent, hence tunable, exponent. The model represents a hybrid of the growing networks based on popularity-driven and fitness-driven preferential attachments. As the network grows, a newly added node establishes m new links to existing nodes with a probability p based on popularity of the existing nodes and a probability 1-p based on fitness of the existing nodes. An explicit form of the degree distribution P(p,k) is derived within a mean field approach. For reasonably large k, P(p,k) approximately k(-gamma(p)) F(k,p), where the function F is dominated by the behavior of 1/ln (k/m) for small values of p and becomes k independent as p-->1, and gamma(p) is a model-dependent exponent. The degree distribution and the exponent gamma(p) are found to be in good agreement with results obtained by extensive numerical simulations.

Journal Article↗
PubMed2004

Cost-effectiveness of prenatal screening for thalassaemia in Hong Kong.

OBJECTIVES: To determine the cost effectiveness of a universal prenatal screening program for alpha- and beta-thalassaemia. METHODS: We retrospectively reviewed our program from 1998 to 2002, and calculated the direct and indirect costs of various components. RESULTS: 18,936 women were screened at our prenatal clinic and 153 couples were subsequently referred to our Prenatal Diagnostic Centre for counselling and further investigations. In addition, there were 238 tertiary referrals and 157 self-referrals. After investigations, 84 fetuses were at risk of beta-thalassaemia major/beta-E thalassaemia, 19 of them were affected and 18 were aborted. The total expenditure on our program (HK 10.0 million dollars) would be less than the postnatal service costs (HK 40.4 million dollars) for 18beta-thalassaemia major fetuses if they were born. Of 361 women at risk of carrying a homozygous alpha0-thalassaemia fetus, 311 (86.2%) opted for the indirect approach (using serial ultrasound examinations to exclude Hb Bart's disease), and 76 (24.5%) subsequently underwent an invasive test for a definitive diagnosis. The sensitivity and false positive rate of this indirect approach was 100.0% and 2.9% respectively. CONCLUSION: It is cost effective to run a universal prenatal screening program in an area where both beta-thalassaemia and alpha-thalassaemia are prevalent. The indirect approach can effectively avoid an invasive test in unaffected pregnancies.

Cost-Benefit Analysis↗
PubMed2004

Randomised trial comparing an interactive multimedia decision aid with a leaflet and a video to give information about prenatal screening for Down syndrome.

OBJECTIVES: (1)To compare an interactive multimedia decision aid (IMDA) with a leaflet and a video to give information about prenatal screening for Down syndrome and (2) to determine the women's acceptance of IMDA. METHODS: Two hundred and one women were recruited from the prenatal clinic of a university teaching hospital and randomised into the intervention group (IMDA, video, and information leaflet) or the control group (video and information leaflet). RESULTS: There were no significant differences in the initial decision for and the final uptake of the prenatal screening test between the control and intervention groups. The proportion of women who were undecided was less than 10% in both groups. Of the women in the intervention group, 86.6% and 78.9% agreed that IMDA was user-friendly and acceptable, respectively. Significantly more women aged < 35 (88.1%) accepted IMDA than women aged > or = 35 (68.3%) (P = 0.030), but the logistic regression analysis did not confirm this finding after adjusting for other factors (computer knowledge and usage of computer). CONCLUSION: The use of IMDA did not affect the women's overall uptake rate of the prenatal screening test for Down syndrome. More women less than 35 years accepted IMDA probably because they used computer more frequently and had more computer knowledge.

Adult↗
PubMed2002

Perceptions of sex-role stereotypes, self-concept, and nursing role ideal in Chinese nursing students.

AIM: This study examined the relationship between sex-role stereotypes, self-concept and the requisite personality characteristics of an ideal nurse in a cohort of Hong Kong nursing students. METHODS: To rate these concepts a measure of eight comprehensive dimensions of personality perception was administered to 177 nursing students, studying on preregistration and postregistration programs at a Hong Kong tertiary institution. Both male and female nursing students perceived an ideal nurse to possess a profile of traits including being high on the dimensions of emotional stability, application, intellect, helpfulness and restraint. RESULTS: No significant difference between the self-ratings of the male and female students was found, indicating that male students had undergone a highly self-selective process when choosing nursing education under the influence of Chinese cultural stereotypical attitudes towards nursing. A typical Chinese nurse was rated as similar to the typical female in Chinese society by both male and female nursing students. A typical Chinese nurse was rated relatively low on the masculine dimensions of openness, extroversion and assertiveness. The self-ratings of male nursing students more closely approximated the ideal nurse than did the self-ratings of female nursing students. CONCLUSION: The conclusions highlight implications for the recruitment and education of both male and female nursing students in Hong Kong society.

Cohort Studies↗
PubMed2002

Effect of 17beta-estradiol exposure on vasorelaxation induced by K(+) channel openers and Ca(2+) channel blockers.

17beta-Estradiol has been shown to relax blood vessels partly through inhibition of Ca(2+) channels at supraphysiological concentrations; however, it is unknown whether acute exposure of the isolated artery rings to near physiological concentrations of sex steroid hormones could modulate the ionic channels that are involved in regulation of vascular tone. Brief incubation (20 min) with 17beta-estradiol (1-3 nmol/l) did not alter the relaxant response to three blocking agents of L-type voltage-sensitive Ca(2+) channels, nifedipine, diltiazem and verapamil in either endothelium-intact or endothelium-denuded rat mesenteric artery rings. In contrast, 17beta-estradiol at 3 nmol/l significantly attenuated the relaxation induced by K(+) channel openers, cromakalim and pinacidil in endothelium-denuded rings. Similarly, preincubation with progesterone (3 nmol/l) inhibited pinacidil-induced relaxation with much less effect on cromakalim-induced relaxation. It appears that 17beta-estradiol and progesterone attenuated the cromakalim- and pinacidil-induced relaxation in a different manner. These results suggest that acute exposure to female sex steroid hormones at near physiological levels may reduce the activity of ATP-sensitive K(+) channels in the rat arteries.

Animals↗
PubMed2001

Different role of endothelium/nitric oxide in 17beta-estradiol- and progesterone-induced relaxation in rat arteries.

The present study was aimed to examine the different role of endothelium/nitric oxide in relaxation induced by two female sex hormones, 17beta-estradiol and progesterone in rat isolated aortas and mesenteric arteries. The isometric force of each ring was measured with Grass force-displacement transducers in the organ bathes. 17beta-Estradiol induced both endothelium-dependent and -independent relaxation in the rat aortas but only the endothelium-independent relaxation in the rat mesenteric arteries. In contrast. progesterone induced both endothelium-dependent and -independent relaxation in the rat mesenteric arteries but only endothelium-independent relaxation in rat aortas. N(G)-Nitro-L-arginine methyl ester and methylene blue attenuated the relaxant response to 17beta-estradiol in the aortic rings or to progesterone in the mesenteric arteries. Pretreatment with L-arginine antagonized the effect of N(G)-nitro-L-arginine methyl ester on sex hormone-induced relaxation. The endothelium contribution to relaxation seems to only relate to lower concentrations of 17beta-estradiol and progesterone. In summary, the present results clearly demonstrate a different role of the functional endothelium in the relaxant response to 17beta-estradiol or progesterone in the conduit vessel (aorta) and the resistance vessels (mesenteric artery). Nitric oxide contributes largely to the endothelium-dependent relaxation induced by 17beta-estradiol in the isolated aortas or by progesterone in the mesenteric arteries.

Animals↗
PubMed2001

Inhibitory effect of tetrabutylammonium ions on endothelium/nitric oxide-mediated vasorelaxation.

Apart from the well-described K+ channel blocking effects in vascular smooth muscle cells, monovalent quaternary ammonium ions may also interact with endothelial cells in the endothelium-intact mammalian arteries. The present study was aimed to examine the effect of tetrabutylammonium ions on endothelium-dependent and -independent relaxation in the rat isolated aortic rings. Pretreatment with tetrabutylammonium concentration dependently reduced the endothelium-dependent relaxation induced by acetylcholine, cyclopiazonic acid and ionomycin. Tetrabutylammonium also inhibited endothelium-independent relaxation induced by hydroxylamine or nitroprusside. Pretreatment of endothelium-denuded rings with tetrabutylammonium did not affect relaxation induced by NS1619 or by diltiazem. In contrast, tetrabutylammonium significantly reduced the pinacidil- or cromakalim-induced relaxation. Tetrabutylammonium also inhibited the acetylcholine- but not nitroprusside-induced increase of tissue content of cyclic GMP in the aortic rings. The present study indicates that tetrabutylammonium ions could inhibit endothelial and exogenous nitric oxide-mediated aortic relaxation while it had no effect on relaxation induced by activation of Ca2+-activated K+ channels (by NS1619) or by inhibition of voltage-gated Ca2+ channels (by diltiazem). The inhibitory effect on pinacidil- and cromakalim-induced relaxation suggests that tetrabutylammonium ions also inhibit ATP-sensitive K+ channels in aortic smooth muscle cells.

Animals↗
PubMed2001

Axillary lymph node scarring and the association with tumour response following neoadjuvant chemoendocrine therapy for breast cancer.

We observed that the axillary lymph nodes of some of our breast cancer patients who received neoadjuvant chemoendocrine therapy (NCT) showed evidence of scarring. The purpose of this study is to determine whether such scarring exists and, if so, whether it is confined to neoadjuvant patients and may be related to response to therapy of the primary tumour. We examined the axillary lymph nodes of a consecutive series of 255 breast cancer patients, all of whom had undergone radical axillary dissection. Fifty-three had received NCT; the remainder formed the control group. A scar was defined as an area of cellular fibrous tissue >0.25 mm in diameter and for each patient scar count, median size and score were recorded. Nodes with scars were stained immunohistochemically (IHC) with 2 epithelial markers for the presence of occult micrometastases. The nodes of 20.7% of patients who had received NCT contained scars compared with 13.4% of controls. The median scar size was significantly greater in neoadjuvant patients (P<0.001) and within this group scar count and score were significantly higher (P=0.026 and 0.020) in those with no or minimal evidence of residual primary tumour. Scars which were IHC-positive for micrometastases were almost exclusively confined to neoadjuvant patients. Our results suggest that axillary lymph node scarring does exist, but is not a common phenomenon. It is more significant in neoadjuvant patients and within this group is most marked in those with the greatest primary tumour response to therapy. We believe that scarring is likely to represent downstaging of axillary disease. A prospective study involving a larger group of patients receiving NCT is indicated, to confirm these preliminary findings and establish whether scarring has prognostic or predictive potential.

Journal Article↗
PubMed2001

Dribble, the Drosophila KRR1p homologue, is involved in rRNA processing.

The Drosophila dribble (dbe) gene encodes a KH domain protein, homologous to yeast KRR1p. Expression of dbe transcripts is ubiquitous during embryogenesis. Overexpressed Dribble protein is localized in the nucleus and in some cell types in a subregion of the nucleolus. Homozygous dbe mutants die at first instar larval stage. Clonal analyses suggest that dbe(+) is required for survival of dividing cells. In dbe mutants, a novel rRNA-processing defect is found and accumulation of an abnormal rRNA precursor is detected.

Amino Acid Sequence↗
PubMed2001

Vascular endothelial growth factor transgenic mice exhibit reduced male fertility and placental rejection.

Recent evidence points to the involvement of vascular endothelial growth factor (VEGF) in mammalian reproductive physiology. Transgenic mice expressing VEGF (121 isoform) under the control of the polyepithelial mucin-1 (muc-1) promoter showed a reduction in male fertility due to impaired spermiogenesis, and aberrant placentation leading to preferential rejection of male embryos. A skew in the sex ratio of the litters was seen (three females to two males), independently of whether the transgene was carried by the male or female parent. In-situ hybridization permitted distinction of expression of the human VEGF transgene from endogenous mouse VEGF, and confirmed expression of the transgene in a wide range of epithelial tissues. Expression of the transgene in spermatocytes and in the embryonic portion of placenta is thought to be responsible for the reduced fertility and embryonic resorptions respectively. Males showed either complete sperm maturation arrest or various gradations of partial fertility. Abnormally high or low VEGF in human semen has been reported to be correlated with a lack of pregnancy success following IVF. The muc1-VEGF (121 isoform) transgenic mouse provides an animal model with which to further study this VEGF-induced pathology.

Animals↗
PubMed2001

[Fast SEP measurement applied to intraoperative spinal cord monitoring].

Spinal cord monitoring techniques based on measuring somatosensory evoked potential (SEP) are presented. The principles and the experimental system for spinal cord monitoring are described in detail in the paper. The fast SEP measurement algorithm using pseudo-random sequence technique is also given. Experimental results show that our techniques can greatly improve the monitoring as compared to the traditional method, and further research in this connection is worth doing.

Algorithms↗
PubMed2000

Mechanisms of chaperone suppression of polyglutamine disease: selectivity, synergy and modulation of protein solubility in Drosophila.

At least eight dominant human neurodegenerative diseases are due to the expansion of a polyglutamine within the disease proteins. This confers toxicity on the proteins and is associated with nuclear inclusion formation. Recent findings indicate that molecular chaperones can modulate polyglutamine pathogenesis, but the basis of polyglutamine toxicity and the mechanism by which chaperones suppress neurodegeneration remains unknown. In a Drosophila: disease model, we demonstrate that chaperones show substrate specificity for polyglutamine protein, as well as synergy in suppression of neurotoxicity. Our analysis also reveals that chaperones alter the solubility properties of the protein, indicating that chaperone modulation of neurodegeneration in vivo is associated with altered biochemical properties of the mutant polyglutamine protein. These findings have implications for these and other human neurodegenerative diseases associated with abnormal protein aggregation.

Animals↗