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Biomedical subjects

T T Nguyen

Publications and source records attributed to T T Nguyen.

At least 55 records · Page 3Linked to original sources
PubMed2001

Contrast microbubbles improve diagnostic yield in ICU patients with poor echocardiographic windows.

OBJECTIVE: To determine the value of contrast echocardiographic studies in patients admitted to ICUs who have poor echocardiographic windows secondary to COPD, ventilator use, or inability to obtain optimal positioning for the echocardiogram. DESIGN: A prospective comparison study of technically difficult patients in the ICU. OUTCOME MEASURE: The total scores for the left ventricle (LV) in the two-chamber and four-chamber views were calculated at baseline and following injection of 1 to 2 mL of a contrast agent. The mean numbers of segments visualized in all patients at baseline and after injection of contrast agent were compared to assess the effect on improved visualization. RESULTS: Forty consecutive patients underwent echocardiography in the ICU for evaluation of LV function. Of these, 25 patients (63%) had poor visualization of the endocardium and required IV contrast agent. In these 25 patients, the average baseline segmental score was 4.5, compared to 11.6 in patients who received an IV contrast agent. Nineteen patients had an average baseline segmental score of 3.9 and were deemed to have a nondiagnostic study. After administration of IV contrast, all patients converted to a diagnostic study, with an average score of 11.6 segments visualized. CONCLUSIONS: Use of echocardiographic contrast agents in selected patients with poor baseline echocardiographic windows in the ICU setting significantly enhances segmental LV visualization and yielded 100% conversion from nondiagnostic to diagnostic studies.

Adult↗
PubMed2001

Comparison of quality of care by specialist and generalist physicians as usual source of asthma care for children.

OBJECTIVE: To determine whether care for children was more consistent with national asthma guidelines when a specialist rather than a generalist was the usual source of asthma care. DESIGN: Cross-sectional survey. SETTING: Two large managed care organizations in the United States. PARTICIPANTS: A total of 260 parents of children with asthma. INTERVENTIONS: None. MAIN OUTCOME MEASURES: Parent reports of the physician primarily responsible for asthma care (specialist, generalist, or both equally) and whom they would call (specialist or generalist) for questions about asthma care were used to define usual source of care. We assessed consistency of care with 1997 National Asthma Education and Prevention Program guidelines using 11 indicators in 4 domains of asthma care: patient education, control of factors contributing to asthma symptoms, periodic physiologic assessment and monitoring, and proper use of medications. RESULTS: In all 4 domains, care was more likely to be consistent with guidelines when specialists were the usual source of care. These differences remained after adjustment for symptom severity, recent care encounters, and parent demographics. Greatest differences for specialist versus generalist management were for use of controller medications (odds ratio [OR] 6.7; 95% confidence interval [CI]: 1.5-30.4), ever having a pulmonary function test (OR 6.5; 95% CI: 2.4-18.1), and having been told about asthma triggers and how to avoid them (OR 5.9; 95% CI: 1.3-26.2). CONCLUSIONS: In these managed care organizations, asthma care in children was more likely to be consistent with national guidelines when a specialist was the primary provider. Greater use of specialists or altering generalist physicians' care may improve the degree to which the care of children with asthma is consistent with national guidelines.

Adolescent↗
PubMed2001

Effect of vitamin B6 deficiency on the synthesis and accumulation of S-adenosylhomocysteine and S-adenosylmethionine in rat tissues.

The effect of vitamin B6-deficiency on the B6-vitamer concentrations, level of S-adenosylhomocysteine (SAH) and S-adenosylmethionine (SAM) were studied in rat tissues. The plasma pyridoxal 5'-phosphate (PLP) and, pyridoxal (PL) levels were lower in the B6-deficient group compared to the control group. After 5 weeks of feeding the experimental diets, tissue PLP, pyridoxamine 5'-phosphate (PMP) and PL concentrations were significantly lower in the B6-deficient group compared to the control and the pair-fed control groups. Thymus PLP and PL levels were lower in the B6-deficient group. The concentration of SAM in the B6-deficient group decreased to approximately 50% and 25% in liver and thymus, respectively. However SAH concentration was 3.5 and 2 fold higher compared to the control and the pair-fed control groups. Thus, the ratio of SAM/SAH was significantly decreased in the B6-deficient group compared to the control or the pair fed-control group. In addition, the S-adenosylhomocysteine hydrolase (EC 3.3.1.1) activity increased by 45% and 15% in liver and thymus, respectively, in the B6-deficient group compared to the pair-fed control and the control groups. However, the activity of L-methionine S-adenosyltransferase (EC 2.5.1.6) was also unaffected. Concentrations of SAH and SAM, SAM/SAH ratio and activities of S-adenosylhomocysteine hydrolase and L-methionine S-adenosyltrasferase in rat brain were not affected by the B6-deficiency. We infer that the alteration of B6 metabolism, especially the reduction of PLP contents in liver and thymus, caused by the B6 deficiency, resulted in accumulation of SAH as well as reduction of SAM and the SAM/SAH ratio. The reduction of the SAM/SAH ratio was due to a block in the catabolism of methionine via the trans-sulfuration pathway. These may lead to inhibition of transmethylation reaction of DNA, RNA and protein, the synthesis and function of thymic lymphocyte and result in damage to tissues.

Animals↗
PubMed2001

Hyperhomocysteinemia in patients with cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL).

OBJECTIVE: To determine whether patients with cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) had evidence of increased homocysteine levels compared with non-CADASIL patients with ischemic stroke or transient ischemic attack. PATIENTS AND METHODS: We compared fasting plasma homocysteine levels and levels 6 hours after oral loading with methionine, 100 mg/kg, in non-CADASIL patients with ischemic stroke or transient ischemic attack and in patients with CADASIL. Prechallenge, postchallenge, and change in homocysteine levels between the 2 groups were compared with use of the Wilcoxon rank sum test. RESULTS: CADASIL and non-CADASIL groups were similar in age (mean, 48.8 vs. 46.5 years, respectively; 2-tailed t test, P=.56) and sex (men, 86% vs 59%; Fisher exact test, P=.12). The 59 patients in the CADASIL group had higher median plasma homocysteine levels compared with the 14 patients in the non-CADASIL group, both in the fasting state (12.0 vs 9.0 micromol/L; P=.03) and after methionine challenge (51.0 vs 34.0 micromol/L; P=.007). Median difference between homocysteine levels before and after methionine challenge was greater in the CADASIL group than in the non-CADASIL group (34.5 vs. 24.0 micromol/ L; P = .02). CONCLUSION: Our findings raise the possibility that increased homocysteine levels or abnormalities of homocysteine metabolism may have a role in the pathogenesis of CADASIL.

Adult↗
PubMed2001

Predictors of macrovascular disease in patients with type 2 diabetes mellitus.

OBJECTIVE: To assess the importance of classic and nonclassic risk factors in the development of coronary artery disease (CAD) or cerebrovascular disease (CVD) in patients with type 2 diabetes mellitus (DM). PATIENTS AND METHODS: In this community-based, prospective cohort study, quantitative measurements for cholesterol, triglycerides (TGs), glucose, and lipoprotein(a) detected as a sinking pre-beta-lipoprotein band on electrophoresis were obtained from 1968 through 1982 from 449 patients who were free of CAD and CVD but had type 2 DM. Demographic data and covariables obtained were age, body mass index, duration of diabetes, sex, smoking, and hypertension. The relationship of individual continuous factors to the development of CAD and CVD as well as multivariate models were evaluated with use of the Cox proportional hazards model. The primary outcome was to determine which risk factors are associated with development of CAD or CVD in patients with type 2 DM. RESULTS: After a mean follow-up of 13 years, 216 CAD and 115 CVD events had developed. The hazard ratio estimates with 95% confidence intervals (CIs) for CAD after multivariate analysis were significant for age, 1.45 (95% CI, 1.27-1.67); fasting glucose levels at enrollment, 1.63 (95% CI, 1.17-2.25); smoking, 1.45 (95% CI, 1.10-1.91); and TGs, 1.49 (95% CI, 1.15-1.92). The hazard ratio estimates for CVD were significant for age, 1.95 (95% CI, 1.59-2.38); hypertension, 1.89 (95% CI, 1.30-2.74); fasting glucose levels at enrollment, 1.69 (95% CI, 1.06-2.70); and smoking, 1.57 (95% CI, 1.07-2.30). CONCLUSION: In diabetic patients, age, fasting glucose levels, smoking, and TG levels are independent risk factors for development of CAD events. Age, hypertension, glucose, and smoking predicted development of CVD events.

Age Distribution↗
PubMed2000

Cloning and sequence analysis of the rat norepinephrine transporter promoter.

We isolated a 2.5-kb fragment of the promoter for the rat norepinephrine transporter (NET) gene. The transcription start site was identified approximately 200 base pairs upstream from the translation start site. Several potential regulatory elements were identified by sequence analysis. The structure of the rat NET promoter was compared to mouse and human. Expression studies in placental and neuroblastoma cells suggested the presence of a 'repressor' element more than 500 base pairs upstream from the transcription start site. These studies provide the basis for examination of transcriptional regulation of this gene and for understanding its temporal and tissue-specific modes of regulation.

5' Untranslated Regions↗
PubMed2000

Reorganization of adult rat barrel cortex intrinsic signals following kainic acid induced central lesion.

A plasticity model studying the adult rat barrel cortex intrinsic signal after a central lesion was developed. Repeated optical imaging studies of the barrel cortex of five rats were performed over variable periods of time (2 days to 6 weeks) after intracortical injection of kainic acid. The signal of the elicited principal whisker corresponding to the injected barrel in the repeat studies relocated to the perimeter of the lesion. The area of the signals of this principal whisker and of surrounding whiskers were larger in the first two weeks studies than those obtained before injection (P<0.01) resulting in increase overlapping of adjacent signals (P=0.01). Even though the signal of the PW remains relocated in the later studies (>2 weeks), all the signals returned to normal size. These findings demonstrate recovery and reorganization of sensory representation in the somatosensory cortex following a central lesion.

Age Factors↗
PubMed2000

Increase of GAP-43 expression following kainic acid injection into whisker barrel cortex.

Plasticity after microinjection of kainic acid (KA) into the adult rat whisker barrel cortex was investigated with immunohistochemical staining of phosphorylated growth-associated protein (GAP)-43. After mapping the barrel cortex with the technique of intrinsic signal optical imaging, a small volume of KA was injected into one barrel. Rats were sacrificed at 2 days, 3 days, 1 week, and 6 weeks after lesioning. GAP-43 staining demonstrated intense immunoreactivity (IR) at the injected barrel which spread to the inter-barrel septa and the surrounding barrels. Elevated IR of GAP-43 was visible 2 days after KA injection, and increased gradually at least 6 weeks following the lesion. This model has the possibility of offering a simple and reliable tool for studying cortical plasticity.

Animals↗
PubMed2000

Analysis of cyclin-dependent kinase inhibitor expression and methylation patterns in human prostate cancers.

BACKGROUND: Downregulation of genes which negatively control cell cycle progression represents a possible mechanism for prostate tumorigenesis. We examined the expression levels of the p16, p15, p14, and retinoblastoma-susceptibility (RB) genes in primary prostate cancers and human prostate cancer cell lines, and correlated this with the DNA methylation levels of two loci in p16. METHODS: The mRNA levels of p16, p15, and p14 were examined by reverse transcriptase-PCR (RT-PCR). DNA methylation of the p16 5' CpG island was determined by bisulfite genomic sequencing, while methylation of exon 2 shared by the p16 and p14 genes was measured by a quantitative bisulfite-based technique, methylation-sensitive single-nucleotide primer extension (Ms-SNuPE). RB protein levels were assessed by immunohistochemical staining of histologic sections of normal and tumor prostate tissues, using a monoclonal antibody (mAB). RESULTS: Overexpression of p16 mRNA was found in 6/9 (67) of prostate tumors compared to the adjacent normal prostate, whereas elevated p14 and p15 levels were only observed in 2/9 (22) and 1/6 (17) of prostate cases, respectively. There was no statistically significant association of grade (P = 0.18) and stage (P = 1.00) of prostate cancer to the elevated p16 levels in the tumors. The p16 5' CpG island was completely unmethylated in these tissues. In contrast, exon 2 of p16/p14 was methylated in both the tumor and normal adjacent prostates, and was increased in 8/11 (73) of tumors relative to normal tissues. There was no association between p16 overexpression and increased p16/p14 exon 2 methylation in these tumors (P = 1.00). Diminished RB levels in prostate tumors that had upregulated p16 mRNA were found, although absent RB was also detected in tumors without elevated p16 levels. The expression levels of the two genes, RB and p16, were not correlated statistically (P = 0.16). CONCLUSIONS: Our studies show that although the levels of the cell cycle regulators p16, p15, p14, and Rb are altered in prostate cancers, there is no apparent correlation to grade, stage, or any pattern of regulation between the related genes. Exon 2 of p16/p14 is methylated in a majority of prostate tumors compared to the unmethylated upstream 5' region, and may be a potential tumor marker for human prostate cancer.

CpG Islands↗
PubMed2000

Quantitative measure of c-abl and p15 methylation in chronic myelogenous leukemia: biological implications.

We used a sensitive, quantitative bisulfite PCR assay, methylation sensitive single nucleotide primer extension (Ms-SNuPE), to measure methylation of the 5' CpG islands of c-abl and p15 in chronic myelogenous leukemia (CML) patients during progression. We found that the Pa promoter of c-abl was methylated in 81% (17/21) of the white blood cells (WBCs) of CML patients, which correlates with previous reports. In contrast, WBCs from healthy donors, acute myelogenous leukemias, acute lymphocytic leukemias, and myelodysplastic syndromes were unmethylated at the c-abl Pa promoter locus. We also observed p15 hypermethylation in 24% (8/34) of CML cases. Methylation of the p15 but not c-abl Pa promoters was associated with CML progression (P = 0.047 vs 0.46), and the two events were independently acquired. We conclude that de novo methylation of c-abl and p15 both occur in CML, and analysis of DNA methylation changes using the bisulfite-based MS-SNuPE assay allows both a sensitive and quantitative assessment of these molecular events compared to other methods currently utilized. (Blood. 2000;95:2990-2992)

Blast Crisis↗
PubMed2000

Two critical cysteine residues implicated in disulfide bond formation and proper folding of Kir2.1.

Inwardly rectifying potassium channels are important in cellular repolarization of many excitable tissues. Amino acid sequence alignment of different mammalian inward rectifier K(+) channels revealed two absolutely conserved cysteine residues in the putative extracellular face, suggesting a possible disulfide bond. Replacement of these cysteine residues in the Kir2.1 channel (i.e., C122 and C154) with either alanine or serine abolished current in Xenopus laevis oocytes although Western blotting established that the channels were fully expressed. The digestion pattern of channels treated with V8 protease combined with Western blotting under reducing and nonreducing conditions confirmed intrasubunit cross-linking of C122 and C154. Whole-cell and single channel current recordings of oocytes expressing tandem tetrameric constructs with one or two of the mutant subunits suggested that insertion of one mutant subunit is sufficient to eliminate channel function. Coexpression studies confirmed that the cysteine mutant channels eliminate wild-type Kir2.1 currents in a dominant-negative manner. Despite these results, sulfhydryl reduction did not alter the functional properties of Kir2.1 currents. Molecular modeling of Kir2.1 with the two cysteines cross-linked predicted that the extracellular loop between the first transmembrane domain and the pore helix contains a beta-hairpin structure. Distinct from the KcsA structure, the disulfide bond together with the beta-hairpin structure is expected to constrain and stabilize the P-loop and selectivity filter. Taken together, these results suggest that intramolecular disulfide bond exists between C122 and C154 of Kir2.1 channel and this cross-link might be required for proper channel folding.

Amino Acid Sequence↗
PubMed2000

A prospective study of holiday weight gain.

BACKGROUND: It is commonly asserted that the average American gains 5 lb (2.3 kg) or more over the holiday period between Thanksgiving and New Year's Day, yet few data support this statement. METHODS: To estimate actual holiday-related weight variation, we measured body weight in a convenience sample of 195 adults. The subjects were weighed four times at intervals of six to eight weeks, so that weight change was determined for three periods: preholiday (from late September or early October to mid-November), holiday (from mid-November to early or mid-January), and postholiday (from early or mid-January to late February or early March). A final measurement of body weight was obtained in 165 subjects the following September or October. Data on other vital signs and self-reported health measures were obtained from the patients in order to mask the main outcome of interest. RESULTS: The mean (+/-SD) weight increased significantly during the holiday period (gain, 0.37+/-1.52 kg; P<0.001), but not during the preholiday period (gain, 0.18+/-1.49 kg; P=0.09) or the postholiday period (loss, 0.07+/-1.14 kg; P=0.36). As compared with their weight in late September or early October, the study subjects had an average net weight gain of 0.48+/-2.22 kg in late February or March (P=0.003). Between February or March and the next September or early October, there was no significant additional change in weight (gain, 0.21 kg+/-2.3 kg; P=0.13) for the 165 participants who returned for follow-up. CONCLUSIONS: The average holiday weight gain is less than commonly asserted. Since this gain is not reversed during the spring or summer months, the net 0.48-kg weight gain in the fall and winter probably contributes to the increase in body weight that frequently occurs during adulthood.

Adult↗
PubMed2000

Nocturnal asthma in children affects school attendance, school performance, and parents' work attendance.

CONTEXT: Asthma symptoms that occur at night may signal worse asthma control, but the nighttime occurrence may have additional clinical significance. To date, however, there have been few studies of the impact of nocturnal awakening from asthma on children with the disease, including problems with daytime functioning. OBJECTIVE: To determine if school absenteeism and school performance in children and work absenteeism in their parents are associated with nocturnal awakenings from asthma. DESIGN: Cross-sectional survey during the winter of 1997 through 1998. SETTING: Three managed care organizations in the United States. PARTICIPANTS: Parents of 438 children with asthma, aged 5 to 17 years, who were enrolled in managed care organizations. INTERVENTION: None. MAIN OUTCOME MEASURES: Parent's reports of number of days their child missed school and parent missed work and how often the child's education suffered because of asthma in the past 4 weeks. RESULTS: Overall, more than 40% of children had nocturnal awakenings from asthma in the past 4 weeks. Multivariate analyses were performed that adjusted for child age, race, overall symptom severity, and use of reliever medications. Compared with children who did not awaken from asthma, there were greater odds of missed school days in children who awakened 1 to 3 nights (odds ratio [OR], 3.6; 95% confidence interval [CI], 2.1-6.2), 4 to 7 nights (OR, 4.4; 95% CI, 2.0-10.0), and more than 7 nights (OR, 14.7; 95% CI, 5.9-37.0). Similarly, there were greater odds of education suffering in children who awakened 1 to 3 nights (OR, 2.3; 95% CI, 1.4-3.7), 4 to 7 nights (OR, 2.1; 95% CI, 0.9-4.6), and more than 7 nights (OR, 2.3; 95% CI, 1. 0-5.4), and parents missing work in children who awakened 1 to 3 nights (OR, 4.0; 95% CI, 2.2-7.1), 4 to 7 nights (OR, 6.5; 95% CI, 2.7-16), and more than 7 nights (OR, 3.2; 95% CI, 1.3-7.9). Greater overall symptom severity and high use of reliever mediation were also associated with missed school, education suffering, and parent absenteeism. CONCLUSIONS: Nighttime awakenings in children with asthma may affect school attendance and performance, as well as work attendance by parents. Nighttime symptoms have independent prognostic value, even when overall asthma symptom severity is accounted for. By addressing whether there are nighttime awakenings in children with asthma, clinicians may be able to tailor the therapeutic regimen to counter these symptoms.

Absenteeism↗
PubMed2000

Incidence and significance of profound hypotension during dobutamine stress echocardiography.

BACKGROUND: Mild hypotension (drops of systolic blood pressure of > or = 20 mmHg) occurs in 14-38% of dobutamine stress echo (DSE) and carries a good prognosis for subsequent cardiac events. The incidence and significance of more profound hypotension (PH) (> or = 50 mmHg) is unknown. HYPOTHESIS: The aim of the study was to determine the incidence of PH during DSE and its prognosis for subsequent cardiac events. METHODS: We reviewed 617 DSE performed at our institution between 1992 and 1996 and identified two DSE subgroups. The first group (PH group) consisted of all patients with PH during DSE. A second group was selected with baseline characteristics similar to the PH group but without PH during DSE (non-PH group). Follow-up was by a physician chart review and direct telephone contact. Cardiac event rates were determined for hard [myocardial infarction (MI), or cardiac death] and soft (angina, congestive heart failure, coronary angioplasty, or coronary bypass surgery) events occurring after the DSE. RESULTS: Of the 617 DSE performed, 16 (3%) patients developed PH (PH group) during DSE, with 13 showing no inducible ischemia. The hard and soft cardiac event rate in this 13 PH group was 46% (mean follow-up of 28.7 +/- 18 months). Of the non-PH group, 32 patients had a negative DSE with a coronary event rate of 12.5%. Profound hypotension correlated with a significantly higher cardiac event rate (p < 0.02). CONCLUSIONS: The incidence of PH during DSE is low (3%) and appears to predict a worse prognosis for subsequent cardiac events.

California↗
PubMed2000

Microarthropod community structures (Oribatei and Collembola) in Tam Dao National Park, Vietnam.

A study on the microarthropod community with special reference to species diversity of Oribatid and Collembola communities (Microarthropoda: Oribatei and Collembola) in Tam Dao National Park of Vietnam, a subtropical evergreen broad leaf alpine forest, was undertaken with the aim to explain how they are related to forest decline, and whether they can be used as bioindicators of forest plant succession. The results have shown that microarthropod community structures, particularly species diversity of oribatid and collembolan communities, are related to forest decline. Therefore they can be used as bioindicators of forest plant succession. In Tam Dao National Park, there was an inverse relation between species diversity of the oribatid and Collembola communities. The species diversity of the oribatid community gradually decreased with forest decline whereas the species diversity of the Collembola community gradually increased.

Animals↗
PubMed2000

Toluene degradation in the recycle liquid of biotrickling filters for air pollution control.

Pollutant degradation in biotrickling filters for waste air treatment is generally thought to occur only in the biofilm. In two experiments with toluene degrading biotrickling filters, we show that suspended microorganisms in the recycle liquid may substantially contribute to the overall pollutant removal. Two days after reactor start up, the overall toluene elimination capacity reached a maximum of 125 g m(-3) h(-1), which was twice that found during prolonged operation. High biodegradation activity in the recycle liquid fully accounted for this short-term peak of pollutant elimination. During steady-state operation, the toluene degradation in the recycle liquid was 21% of the overall elimination capacity, although the amount of suspended biomass was only 1% of the amount of immobilized biomass. The results suggest that biotrickling filter performance may be improved by selecting operating conditions allowing for the development of an actively growing suspended culture.

Air Pollutants↗