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Biomedical subjects

P K Lam

Publications and source records attributed to P K Lam.

At least 19 recordsLinked to original sources
PubMed2003

Experimental investigation of criteria for continuous variable entanglement.

We generate a pair of entangled beams from the interference of two amplitude squeezed beams. The entanglement is quantified in terms of EPR paradox and inseparability criteria, with both results clearly beating the standard quantum limit. We experimentally analyze the effect of decoherence on each criterion and demonstrate qualitative differences. We also characterize the number of required and excess photons present in the entangled beams and provide contour plots of the efficacy of quantum information protocols in terms of these variables.

Journal Article↗
PubMed2002

Surpassing the standard quantum limit for optical imaging using nonclassical multimode light.

Using continuous wave superposition of spatial modes, we demonstrate experimentally displacement measurement of a light beam below the standard quantum limit. Multimode squeezed light is obtained by mixing a vacuum squeezed beam and a coherent beam that are spatially orthogonal. Although the resultant beam is not squeezed, it is shown to have strong internal spatial correlations. We show that the position of such a light beam can be measured using a split detector with an increased precision compared to a classical beam. This method can be used to improve the sensitivity of small displacement measurements.

Journal Article↗
PubMed2002

Allogenic skin: transplant or dressing?

The use of biological dressings is an established aspect of contemporary burns care. The type and source of these biological materials can give rise to both legal and ethical issues. This paper looks at these issues in relation to allogenic skin. It is argued, from a medical perspective, that non-viable allogenic skin, cannot be transplanted and so should therefore be classified both medically and legally as a dressing.

Animals↗
PubMed2001

Generation of continuous variable Einstein-Podolsky-Rosen entanglement via the Kerr nonlinearity in an optical fiber.

We report on the generation of a continuous variable Einstein-Podolsky-Rosen (EPR) entanglement using an optical fiber interferometer. The Kerr nonlinearity in the fiber is exploited for the generation of two independent squeezed beams. These interfere at a beam splitter and EPR entanglement is obtained between the output beams. The correlation of the amplitude (phase) quadratures is measured to be 4.0+/-0.2 (4.0+/-0.4) dB below the quantum noise limit. The sum criterion for these squeezing variances 0.80+/-0.03<2 verifies the nonseparability of the state. The product of the inferred uncertainties for one beam (0.64+/-0.08) is well below the EPR limit of unity.

Journal Article↗
PubMed2001

Bioenergetics and RNA/DNA ratios in the common carp (Cyprinus carpio) under hypoxia.

Hypoxia caused by eutrophication occurs over large areas in aquatic systems worldwide. Common carp (Cyprinus carpio) exposed to hypoxia (1 mg.O2.l(-1) and 2 mg.O2.l(-1)) for 1 week showed a significant reduction in feeding rate, respiration rate, faecal production and nitrogenous excretion compared to those maintained at normoxia (7 mg.O2.l(-1)). Fish exposed to hypoxia showed negative scope for growth (SfG), but no significant difference in the specific growth rate was revealed after 1 week in both hypoxic groups. A significant reduction in RNA/DNA ratio was, however, clearly evident in the white muscle of the 1 mg.O2.l(-1) treatment group, but not in the 2 mg.O2.l(-1) treatment group. Both specific growth rate and RNA/DNA ratio were significantly reduced when fish were exposed to severe hypoxia (0.5 mg.O2.l(-1)) for 4 weeks. At all levels of hypoxia, growth reduction was accompanied by a significant decrease in RNA/DNA ratio in white muscle. Covariance analysis showed no significant difference between the slope of RNA/DNA ratio and growth rate under normoxic conditions and 0.5 mg. O2.l(-1) for 4 weeks (F= 1.036, P > 0.326), as well as 1.0 mg.O2.l(-1) and 2.0 mg.O2.l(-1) for 1 week (F = 0.457, P > 0.5), indicating that the RNA/DNA ratio serves as a biomarker of growth under all oxygen levels, at least under controlled experimental conditions. SfG also appears to be more sensitive than the RNA/DNA ratio in responding to hypoxia in fish.

Animals↗
PubMed2001

Predicting effects of toxic chemicals in the marine environment.

Ecological risks are typically characterized in risk assessment procedures by considering the ratio between exposure concentrations and critical effect concentrations. In OECD countries, critical effect concentrations are typically derived from laboratory-based ecotoxicity tests using well-defined protocols on a limited number of species. More and more countries in the tropics are adopting this approach in environmental assessment, protection, and management. In this article we consider a number of issues associated with such an approach, and in particular potential problems with extrapolating effects on individuals observed in laboratory-based ecotoxicological investigations to effects on ecosystems. It is hoped that by making explicit some of the assumptions made in the potential limitations of these tests, we can better target our limited resources to protect valuable and vulnerable systems.

Environmental Monitoring↗
PubMed2001

DNA adduct formation and DNA strand breaks in green-lipped mussels (Perna viridis) exposed to benzo[a]pyrene: dose- and time-dependent relationships.

Green-lipped mussels, Perna viridis, were exposed to 0, 0.3, 3 and 30 micrograms l-1 (nominal concentrations) B[a]P under laboratory conditions over a period of 24 days. Mussels were collected on day 0, 1, 3, 6, 12, 18 and 24, and the levels of DNA adducts and DNA strand breaks in their hepatopancreas tissues monitored. Mussels exposed to 0.3 and 3 micrograms l-1 B[a]P showed marked increases in strand breaks after 1 day of exposure. DNA strand break levels in these mussels remained high and significantly different from the control values until day 3 for the 0.3 microgram l-1 treatment group, and day 6 for the 3 micrograms l-1 treatment group. This was followed by a gradual reduction in strand breaks. After 12 days, the levels of both groups had returned to the same level as that of the control. No increase in DNA strand breaks was observable in mussels exposed to 30 micrograms l-1 B[a]P in the first 12 days of exposure, but a significant increase was observed from day 12 to day 24. Increasing B[a]P concentrations resulted in elevated DNA adduct levels after 3-6 days of exposure, but this pattern of dose-related increase disappeared after 12 days. These results indicate that a better understanding of the complex interactions between exposure levels and durations is crucially important before DNA adduct levels and DNA strand breaks in P. viridis can be used as effective biomarkers for monitoring genotoxicants in marine waters.

Animals↗
PubMed2001

A comparison of mussels (Perna viridis) and semi-permeable membrane devices (SPMDs) for monitoring chlorinated trace organic contaminants in Hong Kong coastal waters.

A comparison of mussels (Perna viridis) and semi-permeable membrane devices (SPMDs) was carried out at five sites, representing a gradient of contaminant concentrations, in Hong Kong coastal waters. Mussels, originally collected from a "clean" location, were deployed along with SPMDs at each site for 30 days. Analyses for chlorinated pesticides and polychlorinated biphenyls (PCBs) indicated that SPMDs have potential as monitoring tools, and to some extent can overcome the problems associated with mussels, such as natural variability, differing age, sex, and physical condition. However, in most cases, SPMDs failed to rank the sites in the same order as mussels in terms of contaminant concentrations. Nonetheless, in localities where mussels cannot survive--as shown at Kwun Tong in the present experiment--SPMDs may be valuable in providing an indication of potentially bio-available lipophilic pollutants.

Animals↗
PubMed2001

Relationships between tissue concentrations of polycyclic aromatic hydrocarbons and antioxidative responses of marine mussels, Perna viridis.

Local mussels, Perna viridis, were transplanted from a relatively clean site to various polluted sites in Hong Kong. After a 30-day field exposure, different antioxidant parameters including glutathione S transferase (GST), superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GR), NADPH DT-diaphorase (DT-d), glutathione (GSH) and lipid peroxidation were quantified, and tissue concentrations of benzo[a]pyrene (B[a]P) as well as a total of five polycyclic aromatic hydrocarbons (PAHs) with potential carcinogenicity were determined for individual mussels. Results indicated that: (1) tissue concentrations of B[a]P and total PAHs from the same site were highly variable; (2) gill SOD, DT-d and lipid peroxidation showed no response to tissue pollutants; (3) the majority of the antioxidant parameters were induced by increasing tissue pollutant concentrations; and (4) amongst the various parameters, oxyradical scavenger GSH best correlated with tissue concentrations of pollutants.

Animals↗
PubMed2001

Review of effects of water pollution on the breeding success of waterbirds, with particular reference to ardeids in Hong Kong.

Predatory waterbirds, such as ardeids, are susceptible to bioaccumulation of pollutants through the ingestion of contaminated food sources. High body burdens of contaminants, including PCBs, PAHs, cadmium, mercury, lead, copper, zinc and arsenic have been detected in many bird species worldwide. There is a paucity of literature, however, linking contaminant body burden and effects on reproductive success in waterbirds. This review is a synthesis of pertinent literature on this topic, with specific reference to contaminant residues in various tissue types, relationship between body burden and reproductive success, and the use of biomarkers to predict more serious adverse affects. The impetus for this review was the development of a conservation strategy and management plan (commissioned by the Agriculture, Fisheries and Conservation Department of Hong Kong Special Administrative Region (SAR)) for an important wetland in Hong Kong that supports many threatened waterbirds, including ardeids.

Animals↗
PubMed2001

Recurrent IgA nephropathy in renal transplant allografts.

Previous reports of renal transplantation for patients with underlying immunoglobulin A (IgA) nephropathy suggested a recurrence rate greater than 50% for transplant IgA nephropathy. Initially regarded as a benign condition, more recent data showed that recurrent transplant IgA nephropathy may be a significant contributor to graft loss. We performed a retrospective analysis in a single center of 48 kidney transplant recipients, all of Chinese origin, with biopsy-proven IgA nephropathy as the cause of end-stage renal failure to determine the recurrence rate of IgA nephropathy in the transplant allograft and subsequent clinical course in Chinese patients. Median duration of follow-up was 52 months (range, 18 to 155 months). Fourteen patients (29%) had biopsy-confirmed recurrent transplant IgA nephropathy after a median of 52 months (interquartile range, 23 to 82 months) posttransplantation. Recurrent transplant IgA nephropathy was associated with greater serum IgA levels (P = 0.01). The presence of HLA-A2 in transplant recipients (P = 0.002) appeared to protect them from developing recurrent IgA nephropathy in the transplant allograft. Twenty-nine percent of patients with recurrent transplant IgA nephropathy had progressive deterioration of graft function. The progressive graft dysfunction (GD) rate was greater in patients with a transplant from a living related donor (LRD; 21%) compared with those with a transplant from a cadaveric or living unrelated donor (URD; 3%; P = 0.062). Although the cumulative graft survival rate was 100% at 5 years for transplants from both LRDs and URDs, the 10-year graft survival rate was only 63% for a graft from an LRD versus 93% for a URD (log-rank test, P = 0.19). A review of other reported series of recurrent transplant IgA nephropathy also showed an apparently greater incidence of GD for a graft from an LRD (28%) compared with a URD (15%). Our data suggest that although recurrent transplant IgA nephropathy is highly prevalent among the Chinese population, the risk for disease recurrence is not particularly increased compared with other ethnic groups. The trend toward a greater risk for GD for living related compared with unrelated allografts in patients with IgA nephropathy needs to be confirmed with further prospective study.

Adult↗
PubMed2001

Dermal fibroblasts do not enhance the graft take rate of autologous, cultured keratinocyte suspension on full-thickness wounds in rats.

Dermal fibroblasts are known to play an important role in wound healing. In this study, cultured autologous keratinocyte suspension was applied with fibrin glue to the full-thickness wounds in rats (N = 20). Histological analysis on day 14 showed regenerated epithelium in 10 wounds (50%). Keratinocytes were also premixed with allogeneic dermal fibroblasts in a ratio of 3:1 and 5:1 before application to other full-thickness wounds (N = 20) with fibrin glue. Regeneration of epithelium was observed in 10 (50%) and 9 (45%) wounds respectively. Acute inflammatory reaction and mild to moderate proliferation of fibroblasts in the subepithelial layer of the allogeneic fibroblasts were noted. The addition of dermal fibroblasts to keratinocytes/fibrin glue does not enhance the take rate of the cultured keratinocyte suspension.

Animals↗
PubMed2001

A new technique to resurface wounds with composite biocompatible epidermal graft and artificial skin.

BACKGROUND: The incorporation of cultured epidermal autograft on the neodermis of artificial skin (Integra, Integra LifeSciences, Plainsboro, NJ) has been met with some difficulties. A new engraftment technique to resurface the wounds with Integra and composite biocompatible epidermal graft (CBEG) has been successfully applied on three patients for elective reconstructive procedures. METHODS: A small skin biopsy was taken from the normal edge of the lesion for keratinocytes and dermal fibroblast cultures 2 weeks before surgery. When sufficient cells were grown, the patient was admitted for the excision of the lesions or scars. The wounds of the patients, ranging from 125 to 250 cm2, were covered with Integra. When the neodermis of the Integra was fully vascularized, the silicone membrane of the Integra was removed and replaced with the CBEG, which consisted of autologous keratinocytes cultivated on a hyaluronate-derived membrane (Laserskin; Fidia Advanced Biopolymers, Abano Terme, Italy)) using human dermal fibroblasts as a feeder layer. RESULTS: Clinically, there was good initial "take" of the CBEGs in these three patients, ranging from 50% to 100%. Biopsy specimens of the grafted wounds were taken 1 to 3 weeks after the application of the CBEGs. Epithelialization was noted in all patients. CONCLUSION: This engraftment technique has several advantages. The CBEG is much easier to handle than the conventional cultured epidermal autograft. It eliminates the invasive second procedure for skin harvesting, with resulting pain and scarring. The application of the CBEG can be easily performed at the bedside.

Adolescent↗
PubMed2001

Rate of rise in maternal plasma corticotrophin-releasing hormone and its relation to gestational length.

OBJECTIVE: To assess the relationship between rate of increase in maternal plasma corticotrophin-releasing hormone and gestational length. DESIGN: A prospective observational study. SETTING: Department of Obstetrics and Gynaecology, Prince of Wales Hospital, Hong Kong. METHODS: Serial venous samples taken at four to six week intervals from 81 pregnant Chinese subjects were assayed for corticotrophin-releasing hormone concentrations. The investigators responsible for the laboratory assay were blinded to the obstetric outcome. RESULTS: A total of 380 blood samples were taken. Each subject provided three to seven samples (median = 5). Seven of the 81 subjects had preterm delivery. Maternal corticotrophin-releasing hormone levels increased exponentially as gestation advanced. A negative correlation between the rate of rise of logarithmic equivalence of corticotrophin-releasing hormone concentrations (Ln-corticotrophin releasing hormone) per week and the gestational age at delivery was demonstrated (r = -0.45, P < 0.001). The rate of increase of Ln-corticotrophin releasing hormone concentrations per week was also significantly greater for those who delivered preterm before 37 weeks compared with those with uncomplicated term deliveries (0.27 Vs 0.22, P = 0.018). CONCLUSIONS: The rate of increase in maternal plasma corticotrophin-releasing hormone is inversely proportional to gestational length. Results in a Chinese population confirm and extend results from previous caucasian populations. This study provides another piece of evidence on the close link between maternal plasma corticotrophin-releasing hormone and the timing of human parturition. As the hormone is synthesized by the placenta, it supports the suggestion that the human placenta has an important role in determining gestational length.

Adult↗
PubMed2001

Measurement of body fat using leg to leg bioimpedance.

AIMS: (1) To validate a leg to leg bioimpedance analysis (BIA) device in the measurement of body composition in children by assessment of its agreement with dual energy x ray absorptiometry (DXA) and its repeatability. (2) To establish a reference range of percentage body fat in Hong Kong Chinese children. METHODS: Sequential BIA and DXA methods were used to determine body composition in 49 children aged 7-18 years; agreement between the two methods was calculated. Repeatability for the BIA method was established from duplicate measurements. Body composition was then determined by BIA in 1139 girls and 1243 boys aged 7-16 years, who were randomly sampled in eight local primary and secondary schools to establish reference ranges. RESULTS: The 95% limits of agreement between BIA and DXA methods were considered acceptable (-3.3 kg to -0.5 kg fat mass and -3.9 to 0.6% body fat). The percentage body fat increased with increasing age. Compared to the 1993 Hong Kong growth survey, these children had higher body mass index. Mean (SD) percentage body fat at 7 years of age was 17.2% (4.4%) and 14.0% (3.4%) respectively for boys and girls, which increased to 19.3% (4.8%) and 27.8% (6.3%) at age 16. CONCLUSION: Leg to leg BIA is a valid alternative method to DXA for the measurement of body fat. Provisional reference ranges for percentage body fat for Hong Kong Chinese children aged 7-16 years are provided.

Absorptiometry, Photon↗
PubMed2001

Benign and malignant breast masses and axillary nodes: evaluation with echo-enhanced color power Doppler US.

PURPOSE: To evaluate microbubble contrast enhancement in distinguishing malignant from benign breast masses and malignant from benign axillary nodes in patients with breast cancer. MATERIALS AND METHODS: Eighty-six patients with 86 breast masses and 32 patients with breast cancer (subgroup of 86 patients) with 32 axillary nodes underwent color power Doppler ultrasonography with and without contrast material. Vascular features and contrast material transit times were recorded. Nodal enhancement was compared with corresponding primary breast cancer enhancement in the subset of 32 patients. RESULTS: Pathologic analysis revealed 58 breast carcinomas and 28 benign breast lesions and 20 malignant and 12 benign axillary nodes in the 32 patients with breast cancer. Breast cancers had a greater total number and greater number of peripheral vessels than did benign lesions before and after contrast material administration (P <.001). Malignant nodes had a greater total number and greater number of peripheral vessels at baseline and after contrast enhancement (P <.05), and a longer enhancement duration (P =.004) compared with benign nodes. Malignant nodes enhanced more than did corresponding primary breast cancers. Postcontrast number of peripheral vessels was an independent predictor of primary breast cancer (P <.05), and increased number of peripheral vessels after contrast enhancement and enhancement duration were independent predictors of nodal malignancy (P <.05). CONCLUSION: Primary breast cancers and malignant axillary nodes had a greater total number and greater number of peripheral vessels compared with benign breast masses and axillary nodes, respectively.

Adult↗