Biomedical subjects

C Feng

Publications and source records attributed to C Feng.

At least 19 recordsLinked to original sources

PubMed2007

Power analyses for longitudinal study designs with missing data.

Existing methods for power analysis for longitudinal study designs are limited in that they do not adequately address random missing data patterns. Although the pattern of missing data can be assessed during data analysis, it is unknown during the design phase of a study. The random nature of the missing data pattern adds another layer of complexity in addressing missing data for power analysis. In this paper, we model the occurrence of missing data with a two-state, first-order Markov process and integrate the modelling information into the power function to account for random missing data patterns. The Markov model is easily specified to accommodate different anticipated missing data processes. We develop this approach for the two most popular longitudinal models: the generalized estimating equations (GEE) and the linear mixed-effects model under the missing completely at random (MCAR) assumption. For GEE, we also limit our consideration to the working independence correlation model. The proposed methodology is illustrated with numerous examples that are motivated by real study designs.

Adolescent↗

PubMed2004

Prevalence of multiple sclerosis in a residential area bordering an oil refinery.

BACKGROUND: Community concerns about a potential excess of multiple sclerosis (MS) prompted this study. OBJECTIVE: To determine the period prevalence of MS in a community bordering a closed oil refinery and a control community. METHODS: Cases seen by a neurologist during 1998 to 2001 were obtained from area neurologists and hospital discharge data. Population data were obtained from the year 2000 US Census. Patient data were abstracted by a trained abstractor onto a standardized report form. A consulting neurologist reviewed the form and made a final diagnosis using the Poser criteria plus the category of presumed. Age-adjusted prevalence rates and rates of agreement were calculated. RESULTS: The direct age-adjusted period prevalence for both sexes and all races for the entire study area was 113 per 100,000 (95% CI = 93 to 136). For white subjects only, the prevalence was 123 per 100,000 (95% CI = 102 to 147). With use of an indirect method of age adjustment, the number of observed cases in the community bordering the refinery was similar to the number of cases expected (standardized morbidity ratio = 130.8, 95% CI = 62.3 to 199.3), based on rates from the comparison area. The agreement between the treating neurologist (for definite plus probable cases) and the consulting neurologist (for definite plus probable plus presumed cases) was good (kappa = 0.5733). CONCLUSIONS: The prevalence of multiple sclerosis (MS) for this area was generally consistent with prevalence estimates calculated in previous studies in other areas. No significant excess was seen in the exposed area. MS was more prevalent in females than in males. The overall agreement between the consulting and treating neurologist was good.

Adult↗

PubMed2003

Rapid manufacturing techniques in the development of an axial blood pump impeller.

This paper presents a comparison of manufacturing techniques used in the development of an axial blood pump impeller. In this development process the impeller was designed and its performance was evaluated with the aid of computational fluid dynamics (CFD). Prototypes of those designs where the CFD results show promise were needed in sufficient quantities at a low cost for experimental validation of the CFD results. As the impeller is less than 16 mm in diameter with a maximum blade thickness of about 1.5 mm, innovative manufacturing techniques are explored in this paper to determine the best process for quick fabrication of prototypes that are dimensionally accurate, structurally robust and low in cost. Four rapid prototyping techniques were explored. The completed parts were compared on the basis of manufacturing time, quality and strength of parts obtained, manufacturing cost and also in vitro performances. Based on these studies, it was concluded that selective laser sintering (SLS) is the most appropriate method for the quick production of prototype parts for evaluation of pump performance.

Blood Flow Velocity↗

PubMed2001

Down-regulation of IL-12 p40 gene in Plasmodium berghei-infected mice.

We analyzed the mechanism that causes suppression of IL-12 p40 gene induction during Plasmodium berghei infection. Although IL-12 together with IFN-gamma plays an important role in protection against pathogenic infection, the IL-12 p70 protein production of infected macrophages is lower than that by the uninfected macrophages. We showed in the present study that the induction of IL-12 p40 gene but not IL-12 p35 gene in macrophages of P. berghei-infected mice was profoundly inhibited. The inhibition was induced by interaction with macrophages that had contacted with P. berghei-infected erythrocytes and was mediated by a soluble factor, IL-10. There was comparable activation of NF-kappaB in uninfected and infected cells. The induction of IFN-regulatory factor-1 gene was comparable in transcription level in uninfected and infected cells, while the unidentified complex formation of IFN-regulatory factor-1 was observed in infected cells. Therefore, the inhibition of the IL-12 p40 gene induction appeared to be regulated at transcriptional regulation level of the gene.

Animals↗

PubMed2001

Preoperative combined modality therapy for clinically resectable uT3 rectal adenocarcinoma.

PURPOSE: To determine the acute toxicity, outcome, and sphincter preservation rates in patients with clinically resectable uT3 adenocarcinoma of the rectum treated with preoperative combined modality therapy. METHODS AND MATERIALS: A total of 72 patients were treated from 12/90-7/98 with preoperative 50.4 Gy plus 2 cycles of concurrent 5-fluorouracil (5-FU) and leucovorin (LV) bolus daily x 5 followed by sharp or total mesorectal excision and 4 cycles of postoperative 5-FU and LV. RESULTS: Individual Grade 3+ toxicities during preoperative therapy included diarrhea, 11%; bowel movements, 9%; leukopenia, 18%; tenesmus, 1%; and thrombocytopenia, 1%. Total Grade 3+ toxicity was 28%. The pathologic complete response (CR) rate was 13%, and an additional 9% had a clinical CR for a total CR rate of 22%. Of the 35 patients who were judged clinically by their operating surgeon to require an abdominoperineal resection (APR) and were therefore treated with the goal of sphincter preservation, 89% were able to undergo sphincter-preserving surgery. Of the 21 patients eligible for analysis, 81% had good to excellent sphincter function. The 3-year actuarial patterns of failure were 2% local, 8% abdominal, and 13% distant. The 3-year actuarial survival was 95%. CONCLUSIONS: Our data confirm our preliminary reports of encouraging rates of acute toxicity, local control, survival, sphincter preservation and function with preoperative combined modality therapy. It is an alternative approach for the treatment of uT3 clinically resectable rectal cancer.

Adenocarcinoma↗

PubMed2001

Serological and epidemiological effects and influence factors of primary immunization with current live attenuated measles vaccine (Hu191) among infants aged 6-15 months.

A study of the serological and epidemiological effects of primary immunization with current live attenuated measles vaccine (Hu191) among 503 children aged 6-15 months, was conducted in Jingzhou, Hubei province, China from 1991 to 1998. The results showed that the positive conversion rate of measles IgG was 91.65%, geometric mean titer (GMT) was 1:266.74 and its ratio reaching protective titer was 46.52% at 1 month after first immunization. As time goes on, the above-mentioned indexes reduced rapidly. Short-term and long-term efficacy of 0.2, 0.3 and 0.5 ml measles vaccine was similar. The positive conversion rate, GMT and ratio of protective titer of IgG of different potency measles vaccine were not significantly different, however, latter two indexes showed a tendency to increase gradually with the rise of vaccine potency. The age for primary immunization was a main factor influencing immune response to measles vaccine. Immune efficacy of 6 months old group by primary vaccination was significantly lower than those of > or = 8 months old group. The result indicated it is practicable that infant aged 8 months be vaccinated with measles vaccine in China. Twenty-nine suspected measles cases were reported, out of them, 26 cases were negated in time from December 1991 to November 1998. The study showed that the short-term positive conversion rate of the enzyme immune assay IgG antibody of the Hu191 is higher, but its serological endurance isn't ideal, and its epidemiological effect should be evaluated further.

Age Factors↗

PubMed2001

On the stability analysis of delayed neural networks systems.

In this paper, the problems of stability of delayed neural networks are investigated, including the stability of discrete and distributed delayed neural networks. Under the generalization of dropping the Lipschitzian hypotheses for output functions, some stability criteria are obtained by using the Liapunov functional method. We do not assume the symmetry of the connection matrix and we establish that the system admits a unique equilibrium point in which the output functions do not satisfy the Lipschitz conditions and do not require them to be differential or strictly monotonously increasing. These criteria can be used to analyze the dynamics of biological neural systems or to design globally stable artificial neural networks.

Action Potentials↗

PubMed2001

Application and field validation of a continuous nonmethane organic carbon analyzer.

Nonmethane organic carbon (NMOC) is a measure of total organic carbon except for that from CH4. We recently reported the development of online instrumentation for continuous NMOC monitoring. This instrument, referred to as C-NMOC, uses a microsorbent trap in combination with a gas-sampling valve as the sampling interface. A conventional oxidation/reduction NMOC detector is used for quantitation. In addition to being an online concentrator and an injector, the microtrap serves as a separator that isolates NMOC from H2O, CO, CO2, CH4, and other background gases. Therefore, the C-NMOC is able to handle high concentrations of background gases commonly found in stack emissions and has detection limits in the ppb levels. This paper reports the results of field validation and testing of a C-NMOC analyzer at a coatings facility in the eastern United States. The instrument was able to monitor the process transients in real time, based on which corrective actions could be taken. It demonstrated good accuracy, high precision, and long-term stability.

Air Pollution↗

PubMed2001

PPARalpha deficiency reduces insulin resistance and atherosclerosis in apoE-null mice.

PPARalpha is a ligand-dependent transcription factor expressed at high levels in the liver. Its activation by the drug gemfibrozil reduces clinical events in humans with established atherosclerosis, but the underlying mechanisms are incompletely defined. To clarify the role of PPARalpha in vascular disease, we crossed PPARalpha-null mice with apoE-null mice to determine if the genetic absence of PPARalpha affects vascular disease in a robust atherosclerosis model. On a high-fat diet, concentrations of atherogenic lipoproteins were higher in PPARalpha(-/-)apoE(-/-) than in PPARalpha(+/+)apoE(-/-) mice, due to increased VLDL production. However, en face atherosclerotic lesion areas at the aortic arch, thoracic aorta, and abdominal aorta were less in PPARalpha-null animals of both sexes after 6 and 10 weeks of high-fat feeding. Despite gaining as much or more weight than their PPARalpha(+/+)apoE(-/-) littermates, PPARalpha(-/-)apoE(-/-) mice had lower fasting levels of glucose and insulin. PPARalpha-null animals had greater suppression of endogenous glucose production in hyperinsulinemic clamp experiments, reflecting less insulin resistance in the absence of PPARalpha. PPARalpha(-/-)apoE(-/-) mice also had lower blood pressures than their PPARalpha(+/+)apoE(-/-) littermates after high-fat feeding. These results suggest that PPARalpha may participate in the pathogenesis of diet-induced insulin resistance and atherosclerosis.

Animals↗

PubMed2001

[Stress response of Nilaparvata lugens at high temperature and activities of its protective enzyme systems].

The nymphae and different wing-form adults of Brown Planthopper (BPH) were treated intermittently at 34 degrees C, 36 degrees C and 38 degrees C. During the process of heat shock treatment, the variation of the activities of the endogenous enzymes of protective system and the content of lipid peroxides (LPO) in BPH were researched. The results showed that the effect of heat shock treatments on CAT activity in 4th instar of nymphae was higher than that in 3rd and 5th instar. The CAT activity in BPH adults increased with the day-age, and 36 degrees C was the suitable temperature at which H2O2 was scavenged by CAT. The GSH-px activity was higher in old than that in young nymphae, and the ability of GSH-px to scavenge H2O2 was higher in old adults than in those adults emerged early. The activity of SOD had a positive correlation with the treated temperatures, and decreased with the increase of nymphae instar and the day-age of adults after emergence at the same temperature. The activities of CAT, GSH-px, and SOD in macropterous adults were higher than those in brachypterous adults. There were no significant difference for the activities of CAT, GSH-px and SOD between female and male adults (alpha > 0.05). The content of LPO in BPH increased with the rise of treated temperature, and also increased with the increase of instars in nymphae and day-age after emergence in adults at the same temperature. The LPO content was higher in brachypterous than in macropterous adults.

Animals↗

PubMed2000

The major cyclic trimeric product of indole-3-carbinol is a strong agonist of the estrogen receptor signaling pathway.

Indole-3-carbinol (I3C), a component of Brassica vegetables, is under study as a preventive agent of cancers of the breast and other organs. Following ingestion, I3C is converted to a series of oligomeric products that presumably are responsible for the in vivo effects of I3C. We report the effects of the major trimeric product, 5,6,11,12,17,18-hexahydrocyclonona[1,2-b:4,5-b':7,8-b' ']triindole (CTr), on the estrogen receptor (ER) signaling pathways. Tumor-promoting effects of high doses of I3C may be due to activation of aryl hydrocarbon receptor (AhR)-mediated pathways; therefore, we also examined the effects of CTr on AhR activated processes. We observed that CTr is a strong agonist of ER function. CTr stimulated the proliferation of estrogen-responsive MCF-7 cells to a level similar to that produced by estradiol (E(2)) but did not affect the growth of the estrogen-independent cell line, MDA-MD-231. CTr displaced E(2) in competitive-binding studies and activated ER-binding to an estrogen responsive DNA element in gel mobility shift assays with EC(50)s of about 0.1 microM. CTr activated transcription of an E(2)-responsive endogenous gene and exogenous reporter genes in transfected MCF-7 cells, also with high potency. CTr failed to activate AhR-mediated pathways, consistent with the low-binding affinity of CTr for the AhR reported previously. Comparisons of the conformational characteristics of CTr with other ER ligands indicated a remarkable similarity with tamoxifen, a selective ER antagonist used as a breast cancer therapeutic agent and suggest an excellent fit of CTr into the ligand-binding site of the ER.

Animals↗

PubMed2000

An emergent mechanism of selective visual attention in Drosophila.

Due to the limited computational capacity of visual systems and the limited capacity to perform several mental operations at once, animals only select a small proportion of the stimuli available at any one time. It remains to be clarified how this process is related to the spatio-temporal dynamics of cell assemblies in the brain. By employing the flight simulator, selective visual attention behavior is studied in Drosophila. It has been found that for the visual objects presented, the tethered fruitflies display various attention patterns. Specifically, the learning memory mutants dunce and amnesiac possess attention patterns totally different from that of the wild-type fly. To explain these results from the viewpoint of dynamic cell assemblies, a neural network has been developed in which a possible link between the activity of cell assemblies, encoding of sensory information, and selective attention in Drosophila is proposed.

Animals↗

PubMed2000

Differential interleukin-10 expression in interferon regulatory factor-1 deficient mice during Plasmodium berghei blood-stage infection.

Mice deficient of functional interferon regulatory factor-1 (IRF-1-/-) by targeted gene disruption infected with a lethal murine malaria strain, Plasmodium berghei ANKA survived longer than its wild-type littermates despite the inability to induce appreciable amounts of interferon-gamma (IFN-gamma) and nitric oxide. In addition, infected IRF-1-/- mice displayed less organ injury with reduced necrosis and inflammation. Both wild-type and IRF-1-/- mice treated with exogenous interleukin-12 (IL-12) suffered extensive organ damage with corresponding up regulation of IFN-gamma, suggesting the pathogenic potential of IL-12 and IFN-gamma. IL-10 is a cytokine produced by CD4+ T lymphocytes belonging to the Th2 subset. Expression of IL-10 in the wild-type mice correlated with the severity of the infection, with higher mRNA expression towards the later stage of infection. In contrast to the wild-type mice, IL-10 levels in the IRF-1-/- mice were induced early in the infection and decreased gradually as the infection progressed. Both untreated and IL-12 treated wild-type mice appeared to follow a Th1-like immune response early in the infection and a Th2-like immune response later in the infection. However, the IRF-1-/- mice were able to launch an altered immune response with a Th2-like immune response early in the infection. These findings suggest that IL-10 expression in the IRF-1-/- mice during the early stage of P. berghei ANKA infection could play an important role in suppressing pathogenic effects of a cell mediated immune response and promoting protective immunity against the parasite.

Animals↗

PubMed2000

Consumption of eicosapentaenoic acid and docosahexaenoic acid impair murine interleukin-12 and interferon-gamma production in vivo.

In mice, individual dietary omega-3 polyunsaturated fatty acids n-3 (PUFA) were found to be sufficient to effect the changes in circulating interleukin (IL)-12 and interferon (IFN)-gamma levels that were previously seen in fish oil-fed mice. Weanling female C3H mice were fed one of five experimental diets. All five diets met all known nutritional requirements for mice and differed only in the fat source. After 4 weeks, mice were challenged with live Listeria monocytogenes or sterile PBS. Twenty-four hours after infection, n-3 PUFA-fed mice had significantly lower circulating IL-12 p70 and IFN-gamma than mice fed the control diet (P<.01). In addition, splenic cytokine mRNA for IL-12 p40, tumor necrosis factor-alpha, and IL-1beta were lower in infected mice fed n-3 PUFA-containing diets than in mice fed the olive oil ethyl esters control diet. The reduction of IL-12 and IFN-gamma production by n-3 PUFA may have important implications for host infectious disease resistance.

Animals↗

PubMed2000

[Electron spin resonance studies on inhibiting methemoglobin in erythrocyte with exogenous ascorbic acid].

Research on inhibiting the methemoglobin (MetHb) in erythrocyte by means of exogenous ascorbic acid is helpful to elucidating whether exogenous antioxidant inhibits the oxidative denaturation of hemoglobin when the erythrocyte does not inhibit such denaturation with its own antioxidation system. Using electron spin resonance (ESR) technique, we have studied the oxidative denaturation of hemoglobin and the inhibition of MetHb in erythrocyte with the exogenous ascorbic acid. The results indicate that there is the ESR absorption of high spin MetHb (g = 6) at the 5th, 35th and 90th min after the blood was mixed with NaNO2. The ESR absorption of high spin MetHb increases with time. Yet, in the case where the blood was mixed with exogenous ascorbic acid in advance, the ESR absortpion of high spin MetHb (g = 6) only appears at the 35th min among the ESR measures at the 5th, 35th, and 90th min after the blood was mixed with NaNO2. These findings suggest that exogenous antioxidant can inhibit the oxidative denaturation of hemoglobin when the erythrocyte does not inhibit such dematuration with its own antioxidation system.

Adult↗

PubMed2000

[Experimental study of biologic effects of tumour necrosis factor-alpha on scar-derived fibroblasts].

OBJECTIVE: To investigate the biologic effects of tumour necrosis factor-alpha(TNF-alpha) on scar-derived fibroblasts and to evaluate the role of TNF-alpha in genesis, prevention and treatment of scar. METHODS: Cell strains were established by tissue culture technique. To study the fibroblasts derived from hypertrophic scar and normal dermis, cytoactivity and expression of fibronectin (FN) were determined by MTT, FCM and immunofluorescence. RESULTS: 1. When TNF-alpha is at a high concentration (1,000 U/ml increases), the cytoactivity of hypertrophic scar fibroblasts was decreased significantly, and the positive rate of FN expression was decreased by 11.7%. 2. Cytoactivity of normal dermis fibroblasts was increased with TNF-alpha while the positive rate of FN expression was increased by 9.6%. CONCLUSIONS: TNF-alpha has different biological effects on fibroblasts derived from hypertrophic scar or normal dermis. Studying the regulative mechanisms of TNF on abnormal scar will probably provide a new way to prevent and cure it.

Adult↗

PubMed2000

[Electron spin resonance studies on the oxidative denaturation of hemoglobin of blood preserved at 20 degrees C].

In order to further understand the injurious change of erythrocytes during blood preservation at room temperature, we studied the denaturation of oxidative hemoglobin of blood preserved at 20 degrees C using electron spin resonance (ESR) technique. The results showed: when blood was preserved at 20 degrees C, there was ESR absorption of low spin hemichrome (g = 2) during the 204-hour preservation period; when the blood was preserved at 4 degrees C after it had been preserved at 20 degrees C for 24 hours, there were ESR absorption of the high spin methemoglobin (g = 6) and ESR absorption of low spin hemichrome (g = 2) during the 40-day preservation period. This study demonstrates that ESR absorption will increase when preservation time increases. When blood is preserved at 4 degrees C, no ESR absorption will emerge during 40 days' preservation.

Adult↗

PubMed2000

Microsurgical treatment of Mooren's ulcer.

OBJECTIVE: To evaluate effect of microsurgery of lamellar keratoplasty (LKP) on Mooren's corneal ulcer. METHODS: The effect, postoperative astigmatism, postoperative vision, ulcer recurrence of postoperation, and surgical complications of two groups of consecutive Mooren's ulcer inpatients treated respectively by non-microsurgery of LKP and microsurgery of LKP were analyzed. RESULTS: There were significant differences of the effect, postoperative astigmatism, postoperative vision, ulcer recurrence of postoperation, and surgical complications between the two groups. The effect and postoperative vision of the microsurgery-treated group were better than those of the non-microsurgery-treated group. The postoperative astigmatism, ulcer recurrence of postoperation, and surgical complications of the microsurgery-treated group were less than those of the nonmicrosurgery-treated group. CONCLUSION: Microsurgery of LKP of Mooren's corneal ulcer can greatly improve the ulcer healing and postoperative vision, and reduce the surgical complication and the ulcer recurrence of postoperation.

Adolescent↗