Search PubMed⌕ Search

Biomedical subjects

T Nguyen

Publications and source records attributed to T Nguyen.

At least 271 records · Page 15Linked to original sources
PubMed1995

Thiazide diuretics and fractures: can meta-analysis help?

Published observational estimates of the effect of thiazide diuretics on osteoporotic fracture risk vary from a 70% reduction to a 60% increase but there have been no randomized controlled trials. The aims of this study were to use the technique of meta-analysis to attempt to resolve this conflict and to explore whether duration and/or dose of therapy has an effect on osteoporotic fracture risk. The data sources utilized were Medline and Excerpta Medica databases supplemented by reviews and back references. A total of 18 observational studies that looked at the relationship between diuretics and fracture were located, of which 13, involving 29,600 subjects, had extractable data on thiazides and fracture occurrence. Current thiazide users were protected against hip fracture (OR 0.82, 95% CI 0.73-0.91). Thiazide use of long duration may be protective (OR 0.82, 95% CI 0.62-1.08) but not short duration (OR 1.23, 95% CI 0.99-1.54). The size of this effect, which compares favorably to other interventions, indicates that a randomized controlled trial to resolve the problem of potential confounders and safety profile would require a minimum of 7000 person-years of observation in those at highest risk of fracture (women aged 80 or over) which is unlikely to be pursued at the present time. The results of this meta-analysis indicate that current thiazide users have a 20% reduction in fracture risk and that long-term use may reduce fractures by a similar amount.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1995

Calcium-activated proteolysis of neurofilament proteins in goldfish Mauthner axons.

We have examined the proteolytic breakdown of neurofilament proteins (NFPs) in isolated Mauthner axoplasm (M-axoplasm). Documentation of proteolytic breakdown of NFPs in M-axoplasm is important because NFPs are not degraded in distal segments of severed Mauthner axons (M-axons) maintained in vivo for up to 62 days at 20 degrees C. By incubating M-axoplasm with 2 mM calcium in vitro, we have demonstrated that M-axoplasm contains an endogenous calcium-activated neutral protease that degrades NFPs. This calcium-activated proteolysis of M-axoplasm NFPs produced novel bands on silver-stained gels. These novel bands were presumed to be NFP breakdown products because they reacted with antibodies to the alpha-intermediate filament antigen (anti-IFA) on immunoblots from these gels. Incubations of M-axoplasm with 2 mM calcium plus exogenous calpain produced novel bands similar to those observed for M-axoplasm incubated with 2 mM calcium. Incubations of M-axoplasm with 2mM calcium plus calpain inhibitors did not produce these novel bands. These in vitro data indicate that M-axoplasm contains calpain that degrades NFPs and produces novel bands similar to those observed from distal segments of severed M-axons maintained in vivo longer than 62 days postseverance. Factors that affect the activity of calpain or affect the ability of calpain to degrade NFPs could account for the delayed degradation of NFPs in distal segments of severed M-axons maintained in vivo.

Animals↗
PubMed1995

Laparoscopic cholecystectomy for gallbladder volvulus.

Torsion of the gallbladder is a rare entity. Approximately 300 cases have been reported since it was first described in 1898 by Wendel (Ann. Surg. 1898; 27:199). The condition occurs most often in the elderly. Although the etiology is unknown, a constant finding is the presence of the gallbladder on a mobile mesentery ("floating" gallbladder). Torsion, or volvulus, of the gallbladder occurs when this gallbladder twists axially, with subsequent occlusion of bile and/or blood flow. We present a case of gallbladder volvulus diagnosed and treated laparoscopically. This is the first reported laparoscopic cholecystectomy for volvulus of the gallbladder.

Aged↗
PubMed1995

Instruction by retinoic acid of incisor morphology in the mouse embryonic mandible.

Endogenous retinoids are present in the embryonic mouse mandible and reach a peak in concentration at the time of the formation of the dental lamina. All-trans retinoic acid is present in a 10-fold higher concentration in the future incisor region of the mouse embryonic mandible at day 11.5. It was found here that exogenous all-trans retinoic acid has pleiotropic effects on the pattern of odontogenesis when applied before the formation of the dental lamina. These effects include a change in the pattern of the dental lamina, supernumerary buds and incisors in the diastema region, and replacement of molars with incisors in the molar region. Thus retinoic acid appears to instruct incisor morphology in the mouse embryonic mandible.

Animals↗
PubMed1995

Blockade of the initiation of murine odontogenesis in vitro by citral, an inhibitor of endogenous retinoic acid synthesis.

Endogenous retinoids are present in the embryonic mouse mandible and reach a concentration peak immediately before the formation of the dental lamina. Because exogenous retinoids alter the pattern of the dental lamina and the expression of epidermal growth factor mRNA (a transcript necessary for initiation of odontogenesis), the role of retinoic acid in the initiation of odontogenesis was studied here. Citral (3,7-dimethyl-2,6-octadienal), a known inhibitor of retinoic acid synthesis, was used to block the endogenous synthesis of retinoic acid in the mouse embryonic mandible before the formation of the dental lamina (gestational day 9). A 24-h exposure to citral totally blocked tooth formation in 7/10 mandibles. Reductions of endogenous retinoic acid concentrations were confirmed by high-performance liquid chromatography. Tooth formation was restored by simultaneous treatment with all-trans retinoic acid or 9-cis retinoic acid during the citral exposures (first 24 h of culture). Endogenous retinoic acid is necessary for the initiation of odontogenesis.

Acyclic Monoterpenes↗
PubMed1995

Spatial and temporal distribution of sonic hedgehog mRNA in the embryonic mouse mandible by reverse transcription/polymerase chain reaction and in situ hybridization analysis.

Hedgehog genes have recently been implicated in the control of pattern formation in many developing organ system. Vertebrate homologues of the Drosophila hedgehog have been identified in mouse and rate embryos. The temporal regulation of sonic hedgehog (mouse homologue) has previously been studied by Northern analysis of whole embryos with varying results. Sonic hedgehog transcript expression in the mouse mandibular process was now characterized using polymerase chain reaction (PCR) an in situ hybridization techniques. PCR analysis revealed transcripts at gestational days 10 and 11, before the formation of the dental lamina, but not at days 12-14, after tooth buds have formed. Transcripts were localized to, primarily, the epithelium in the presumptive incisor region of the mandibular midline at gestational day 10. No mRNA was detected by in situ hybridization techniques in the presumptive molar regions of odontogenic epithelium. Sonic hedgehog expression may be involved in the regulation of pattern formation through establishment of an incisor-molar axis of polarity.

Actins↗
PubMed1995

The effect of tray material and surface condition on the shear bond strength of impression materials.

This study compared the adhesive shear bond strength of three selected impression materials with that of thermoplastic and acrylic resin tray materials as a function of surface preparation. Polyether (Impregum), polyvinylsiloxane (Reprosil), and polysulfide (Permlastic) impression materials were evaluated on smooth, rough, and contaminated tray surfaces. Smooth surface samples were formed against glass and served as the control groups. Experimental groups consisted of samples contaminated with artificial saliva and rough surface samples that were abraded with 110 microns of Al203. A total of 126 samples were subdivided into 18 groups of seven specimens each. Each sample consisted of a 1 inch square, 3 mm thick mass of an impression material sandwiched between the prepared surfaces of a pair of resin plates. Each specimen was tested in a universal testing machine for adhesive shear bond strength. Data were analyzed with three-way analysis of variance and Scheffe's test. The results indicated that the thermoplastic resin material had better adhesive properties than the acrylic resin. For both tray materials mean adhesive shear bond strengths for Impregum and Reprosil were significantly greater than those of Permlastic. Tray surface contaminated with saliva decreased the adhesive shear strength at the tray adhesive impression interface.

Acrylic Resins↗
PubMed1995

A model for estimating spinal cord injury prevalence in the United States.

A model was developed to provide a tool to forecast demographic trends in populations of people with traumatic spinal cord injury at the national and state level. This information is critical to planning for the allocation and distribution of resources to care for people with spinal cord injury. The literature on incidence, mortality, and prevalence of spinal cord injury in the United States was reviewed and reported values were evaluated for incorporation into the model. A linear relationship between age specific survival rates of the spinal cord injury population, and expected survival rates in the absence of spinal cord injury was established and this provided the basis for projections using age cohort survival methodology. The model's projections indicate a need for future expansion of capacity to treat traumatic spinal cord injury in the private sector, and a need to prepare for an aging disabled population. The annual number of traumatic spinal cord injury cases admitted to hospitals is projected to increase from approximately 11,500 in 1994 to almost 13,400 in 2010. Age adjusted post-hospitalization incidence rate in 1994 is estimated at approximately 38 per million (23 per million for females and 55 per million for males). A 20% increase in the US spinal cord injury prevalence can be expected over the next 10 years, going from approximately 207,000 estimated in 1994, to 247,000. During this time, the veteran segment, which currently comprises 22% of the spinal cord injury population, is projected to decline.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1995

Isolation of three novel human genes encoding G protein-coupled receptors.

We have cloned and mapped the chromosomal location of three novel human genes encoding G protein-coupled receptors that we have named GPR6, GPR5, and GPR4. The entire coding region for each of these genes was contained on single exons. Gene GPR6 encoded a receptor that shared closest identity (71% in the transmembrane regions) with the human orphan receptor GPR3 and was localized to chromosome 6 (q21-q22.1). Northern blot analysis revealed that GPR6 transcripts were abundant in the human putamen and to a lesser extent in the frontal cortex, hippocampus, and hypothalamus. Gene GPR5 encoded a receptor that most closely resembled the orphan receptor RBS11 (48% in the transmembrane regions) and the MIP 1 alpha/RANTES receptor (45% in the transmembrane regions) and was localized to chromosome 3 (p21.3-p21.1). Gene GPR4 shared identity (40% in the transmembrane regions) with the human platelet-activating factor receptor and was localized to chromosome 19 (q13.2-q13.3).

Amino Acid Sequence↗
PubMed1995

Distributed representations of semantic knowledge in the brain.

Category-specific language impairments have been postulated to require the existence of an explicit category organization within semantic memory. However, it may be possible to demonstrate analytically that this is not necessary. We hypothesize that category-specific organization can emerge from perceptual, functional, and associative feature information about objects that is maintained in order to process language. In this paper, we conduct several experiments to test the computational validity of this hypothesis. Physical objects were encoded in terms of semantic features, based on basic perceptual and motor modalities and higher level knowledge of function, for use in artificial neural networks. Mathematical methods were used to analyse the encodings and the neural networks. The results demonstrate the emergence of semantic categories in the networks, although such information was not preprogrammed. We conclude that category-specific language organization can emerge from the inherent nature of semantic features themselves, and does not require special internal categorical organization of semantic memory.

Brain↗
PubMed1995

Mixed venous oxygen saturation during cardiopulmonary bypass poorly predicts regional venous saturation.

Mixed venous oxygen saturation is generally accepted as an indicator of adequacy of systemic oxygen delivery; however, cardiopulmonary bypass (CPB) may alter this relationship. Major postoperative complications potentially secondary to inadequate oxygen delivery during CPB indicate that mixed venous oxygen saturation may not detect regional venous desaturation during CPB. We therefore tested the hypothesis that mixed venous oxygen saturation and pH did not predict regional venous oxygen saturations and pH during 2 h of bypass in a swine model. Six immature swine (27-34 kg) received standard normothermic CPB. Sagittal sinus and portal vein oxygen saturations and blood gases were measured at 30, 60, 90, and 120 min of bypass. Although the venous reservoir oxygen saturation remained unchanged during 2 h of bypass, sagittal sinus saturation and pH decreased significantly (66% +/- 3.3% to 33% +/- 2.2% and 7.38 +/- 0.04 to 7.23 +/- 0.05, respectively). Likewise in the portal vein, oxygen saturation and pH also decreased (82% +/- 2.4% to 59.3% +/- 3.9% and 7.39 +/- 0.03 to 7.27 +/- 0.06, respectively). We conclude that profound regional venous desaturation and progressive regional acidemia may go undetected even when a standard pump flow rate of 100 mL.kg-1.min-1 is used and mixed venous oxygen saturation is normal.

Animals↗
PubMed1995

Genetic influences on bone density: physiological correlates of vitamin D receptor gene alleles in premenopausal women.

Common vitamin D receptor (VDR) gene alleles have recently been shown to contribute to the genetic variability in bone mass and bone turnover, however, the physiological mechanisms involved are unknown. To examine this, the response to 7 days of 2 micrograms oral 1,25-dihydroxyvitamin D[1,25-(OH)2D] (calcitriol) stimulation was assessed in 21 premenopausal women, homozygous for one or other of the common VDR alleles (bb, n = 11; BB, n = 10). Indices of bone turnover and calcium homeostasis were measured during 2 weeks. Baseline osteocalcin, 1,25-(OH)2D, type I collagen carboxyterminal telopeptide, and inorganic phosphate levels were significantly higher and spinal bone mineral density was significantly lower in the BB allelic group. After calcitriol administration, similar levels of 1,25-(OH)2D were attained throughout the study in both genotypic groups. The increase in serum osteocalcin levels in the BB group was significantly less than that in the bb group (11% vs. 32%, P = 0.01). The genotype-related baseline difference in osteocalcin levels was not apparent at the similar serum 1,25-(OH)2D levels. By contrast, the baseline differences in phosphate and type I collagen carboxyterminal telopeptide persisted throughout the study. Serum ionized calcium levels did not differ between genotypes, nor did it move out of normal range values. However, parathyroid hormone was less suppressed in the low bone density group (38% vs. 11%, P = 0.01). These data indicate that the VDR alleles are associated with differences in the vitamin D endocrine system and may have important implications in relation to the pathophysiology of osteoporosis.

Adult↗
PubMed1995

Intrauterine repair of surgically created defects in mice (lip incision model) with a microclip: preamble to endoscopic intrauterine surgery.

We compared the difference between a nonpenetrating silver microclip and suture on wound healing, inflammatory response, and application time in the repair of surgically created standardized unilateral cleft lip type defects in fetal mice. Excellent lip continuity and dermal reconstitution were achieved by both methods of repair. Furthermore, collagen accumulation did not occur. Occasional mononuclear cells were seen around sutured repairs in contrast to microclipped repairs. The most significant difference, however, was in application time with the microclip requiring an average of 7 seconds (+/- 2) compared to 90 seconds (+/- 15) for suture. We conclude that the microclip offers distinct advantages for intrauterine cleft lip repair: (1) nonpenetrating tissue approximation; (2) less inflammatory response than suture; (3) technically more rapid and less difficult to apply than suture; and (4) can be utilized more readily than suture for endoscopic approaches limiting the risks of fetal surgery for both the mother and the fetus.

Animals↗
PubMed1995

Orotracheal intubation of rats by transillumination.

We described a new technique of orotracheal intubation in the rat. This technique is performed under direct vision by transillumination to obtain a better view of the rat's small and distant vocal cords. We also emphasize overextension of the neck to allow for a more direct path to the animal's trachea. This technique is easily learned, is atraumatic, and does not depend on expensive equipment.

Animals↗
PubMed1995

[Evaluation of an ELISA technique for the serodiagnosis of legionnaires' disease].

The presence of anti-Legionella antibodies was studied comparatively in 81 sera with a commercially available ELISA kit (containing serogroups 1 to 6 as antigens) and the indirect immunofluorescence assay (IFA) with serogroup 1. The values obtained with the ELISA method were converted into immunofluorescence titers by using standard sera. Results of both methods were concordant in 83% of the sera when a cutoff value of 1/128 was used, and in 88% of the sera when the cutoff value was 1/128 for IFA and 1/256 for ELISA. In 6 other patients infected by serogroups other than 1, antibodies were detected in 5 cases with ELISA and in none with IFA.

Enzyme-Linked Immunosorbent Assay↗
PubMed1995

Osteoarthritis, bone density, postural stability, and osteoporotic fractures: a population based study.

OBJECTIVE: Osteoarthritis (OA) is associated with an increase in bone density both locally and at distant sites. Prospective data are limited on the relationship between OA and fracture. We studied the possible relationship between self-reported OA, bone density, postural stability measures, and atraumatic fractures as part of a study of men and women over 60 years of age. METHODS: Subjects were part of the Dubbo Osteoporosis Epidemiology Study (a longitudinal population based study of fracture risk factors). Bone density was measured by dual energy x-ray absorptiometry. Postural stability was assessed by the validated measures of quadriceps strength and sway. Medication use and self-reported arthritis were assessed by a structured personal interview. Fractures were ascertained retrospectively by interview and prospectively by viewing radiographic reports for fracture. RESULTS: Among a study population of 1101 women and 720 men (mean age 69) there were 462 subjects (25%) who reported a diagnosis of OA. In both sexes, subjects with OA had higher bone density (adjusted for age and body mass index) at both the femoral neck (men, p = 0.026; women, p = 0.048) and lumbar spine (men, p = 0.0007; women, p = 0.0007). However, in both sexes, those with self-reported OA also had higher body sway and lower quadriceps strength. The combination of these observed differences in fracture risk factors led to no predicted change in fracture risk overall when using established nomograms for this population [men, OR = 1.11 (95% CI 0.83-1.45); women, OR = 1.08 (95% CI 0.83-1.39)]. This paralleled our observational finding that self-reported OA was not associated with a decrease in fracture incidence compared to those not reporting OA in both men (RR 0.64, 95% CI 0.29-1.39) and women (RR 1.00, 95% CI 0.66-1.51). CONCLUSION: Individuals with self-reported OA, despite higher bone density, are not protected against nonvertebral osteoporotic fracture, apparently due to worsened postural stability and thus an increased tendency to fall.

Aged↗