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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
PubMed2006

Quantum study of information delay in electromagnetically induced transparency.

Using electromagnetically induced transparency (EIT), it is possible to delay and store light in atomic ensembles. Theoretical modeling and recent experiments have suggested that the EIT storage mechanism can be used as a memory for quantum information. We present experiments that quantify the noise performance of an EIT system for conjugate amplitude and phase quadratures. It is shown that our EIT system adds excess noise to the delayed light that has not hitherto been predicted by published theoretical modeling. In analogy with other continuous-variable quantum information systems, the performance of our EIT system is characterized in terms of conditional variance and signal transfer.

Journal Article↗
PubMed2005

Outdoor carbon monoxide, nitrogen dioxide, and sudden infant death syndrome.

AIMS: To investigate whether infants who died of SIDS were more likely to have higher acute and lifetime average exposures to outdoor carbon monoxide (CO) and nitrogen dioxide (NO2) than comparison healthy infants. METHODS: A total of 169 case and 169 matched control infants born between 1988 and 1992, were studied. CO and NO2 concentrations, averaged for all days within the infant's lifespan, and the last 30 days, 7 days, 3 days, and 1 day of life were obtained from air pollutant data provided by the California Air Resources Board. RESULTS: Based on monthly aggregated data, average CO and particularly NO2 were associated with SIDS count, even after adjustment for seasonal trends. SIDS outcome was not significantly associated with high average outdoor CO levels for any time period. However, high average outdoor NO2 levels on the last day of the infant's exposure period were significantly associated with SIDS; the adjusted odds ratio was 2.34 (95% CI 1.13 to 4.87). CONCLUSIONS: SIDS may be related to high levels of acute outdoor NO2 exposure during the last day of life. Further studies are needed to replicate this finding.

Air Pollutants↗
PubMed2005

Integration of microscopy and serodiagnostic tests to screen for active tuberculosis.

SETTING: University of California San Diego Medical Center, USA. OBJECTIVE: To create a simple screening strategy for tuberculosis (TB) that includes antibody detection assays to improve the accuracy of microscopic examination of sputum for acid-fast bacilli (AFB smear). METHODS: Serum samples were obtained from 190 patients suspected of having active TB. TB diagnosis was established by Mycobacterium tuberculosis culture. HIV status was determined by commercial serologic tests. IgG antibody levels were measured by ELISA using purified M. tuberculosis antigens. Data from 130 randomly selected patients were used to develop a screening strategy; data from the remaining 60 patients were used for validation. RESULTS: AFB smear had 70% sensitivity and 88% specificity. In algorithms integrating single or multi-antigen ELISA with AFB smear and HIV results, the sensitivity improved over each test alone. The algorithm that included a four-antigen ELISA (38 kDa antigen, lipoarabinomannan, MPT-64 and glutamine synthase) had a sensitivity of 93% and a specificity of 76%. Compared to AFB smear, the sensitivity of the algorithm was significantly higher, while the specificity was not statistically different. CONCLUSION: This study demonstrates that a screening strategy can be created by integrating multi-antigen ELISA with AFB smear and HIV testing.

Adult↗
PubMed2004

In vitro cytotoxicity testing of a nanocrystalline silver dressing (Acticoat) on cultured keratinocytes.

Acticoat is a polyethylene mesh coated with nanocrystalline silver. It has been used widely as a dressing for chronic wounds, acute partial-thickness burn wounds and donor sites. In this study, the in vitro cytotoxicity of Acticoat on cultured keratinocytes is tested. Human keratinocytes are cultivated on a pliable hyaluronate-derived membrane (Laserskin) using dermal fibroblasts as the feeder layer. When the cultured Laserskin (CLS) is subconfluent it is covered by Acticoat, which is exposed to water (Group 1), phosphate-buffered saline (Group 2) or culture medium (Group 3). The control group is not exposed to the Acticoat. After 30 minutes incubation at 37 degrees C, the inhibitory effect of the nanocrystalline silver on keratinocyte growth is measured by an MTT assay. Compared with the control, the relative viability of the CLS dropped to 0%, 0% and 9.3%, respectively. Thus, Acticoat is cytotoxic to cultured keratinocytes and should not be applied as a topical dressing on cultured skin grafts.

Bandages↗
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↗