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Biomedical subjects

M Wong

Publications and source records attributed to M Wong.

At least 235 records · Page 13Linked to original sources
PubMed1991

Estimating left ventricular ejection fraction from two-dimensional echocardiograms: visual and computer-processed interpretations.

Digital echocardiography makes computer-processed estimates of ejection fraction feasible for clinical use but increases physician reading time. The practicabilities were examined by three novice fellows and four experienced attendings. Ejection fraction was visually estimated from playback of videotape or cine-loop displays. Ejection fraction was also estimated from single tracings of endocardium, digitized and applied to biplane Simpson's rule, and expressed in whole units. Differences between fellows' and attendings' visual estimates were close to 0 +/- 6.4 median standard deviation. The 95% confidence intervals for reproducing visual and computer-processed ejection fractions ranged from 15% to 46% of mean ejection fraction; for comparing the two methods, from 7% to 36%. Intraobserver reading errors varied widely and with one observer, systematically, and were independent of experience, but dependent on the quality of signals. Computer-processed readings of ejection fraction should be reserved for images of reasonable quality and for confirming visually estimated ejection fractions between the lower limits of normal (45%-50%) to moderately severely depressed (25%-30%), when accuracy is clinically relevant or when a serial change is at the confidence limits of the reader and needs verification.

Aged↗
PubMed1991

In vitro study of placental trophoblast calcium uptake using JEG-3 human choriocarcinoma cells.

During human fetal development, placental syncytiotrophoblasts actively transport calcium from the maternal to the fetal circulation. Two functional components, a cytosolic Ca2(+)-binding protein (CaBP) and a Ca2(+)-ATPase have been identified in the syncytiotrophoblasts of the chorionic villi. We report here the calcium uptake properties of a human choriocarcinoma cell line, JEG-3, which was used as an in vitro model cell system for the syncytiotrophoblasts. In culture, JEG-3 proliferated as large syncytial aggregates expressing typical syncytiotrophoblast markers. 45Ca uptake by JEG-3 was a substrate- and temperature-dependent, membrane-mediated active process that exhibited linear kinetics for up to 7 min. Both the CaBP and the Ca2(+)-ATPase were expressed by JEG-3, on the basis of biochemical, histochemical, immunochemical and or mRNA assays. Immunohistochemistry and in situ hybridization revealed that JEG-3 cells were heterogeneous with respect to the expression of the CaBP. The Ca2(+)-ATPase activity of JEG-3 was similar to the placental enzyme in terms of sensitivity to specific inhibitors, and was detected histochemically along the cell membrane. Fura-2 Ca2+ imaging revealed that calcium uptake by JEG-3 was not accompanied by a concomitant increase in cytosolic [Ca2+], suggesting a specific Ca2+ sequestration mechanism. The involvement of calciotropic hormonal regulation was evaluated by studying the response of JEG-3 to 1,25-dihydroxy vitamin D3. Calcium uptake was significantly stimulated in a dose-dependent manner by a 24-h treatment of the cells with 1,25-dihydroxy vitamin D3 (optimal dose approximately 0.5 nM); the CaBP level doubled whereas steady-state CaBP mRNA did not, suggesting that CaBP expression was regulated by 1,25-dihydroxy vitamin D3. These observations strongly suggest that the JEG-3 human choriocarcinoma cells should serve as a convenient in vitro model system for studying the cellular mechanism and regulation of transplacental calcium transport.

Biological Transport, Active↗
PubMed1991

Perceptions of dentists' chairside behavior in a military dental care system.

A dental questionnaire was developed to assess patients' perceptions of dentists' chairside behavior in the military dental care system at Fort Carson, CO. Patients' perceptions of military and civilian dentists were found to be generally positive. No significant difference was found on the perceptions of civilian and military dentists in six of eight categories of personal behaviors involved in the chairside dentist-patient relationship. However, patients felt more rushed with civilian dentists and questioned more the necessity of dental work by civilian dentists. Nevertheless, patients appear to make minimal distinctions between these two groups, simply perceiving them as "the dentist."

Adult↗
PubMed1991

Prevalence of burnout among military dentists.

Burnout is a syndrome of emotional exhaustion, depersonalization, and reduced personal accomplishment that can occur among individuals who do "people work" of some kind. Health care providers, including dentists, are at high risk for burnout because their occupations often require intense interactions between themselves and fearful, demanding patients on a daily basis. The purpose of this study was to assess the prevalence of burnout among military dentists practicing at a large installation using a standardized measurement device, the Maslach Burnout Inventory. Results indicate that the military dentists surveyed experience low to moderate levels of burnout. The military dentists sampled, in general, scored lower for burnout when compared to the norms of society and medicine.

Burnout, Professional↗
PubMed1990

Elevated substance P and accelerated cartilage degradation in rabbit knees injected with interleukin-1 and tumor necrosis factor.

Cytokines, interleukin-1 (IL-1), tumor necrosis factor alpha, and the neurotransmitter, substance P, have been implicated in the pathogenesis of arthritis because they stimulate synovial cells to secrete prostaglandin E2 and collagenase in vitro. We investigated in vivo changes in intraarticular substance P and the degradation of cartilage proteoglycan in response to intraarticular cytokine injections in rabbits. Twenty-four hours after a single injection of 10 ng, 30 ng, or 100 ng of recombinant human IL-1 alpha (rHuIL-1 alpha) per joint, the mean +/- SEM levels of substance P detected in the cell-free joint lavage fluid were 250 +/- 67 fmoles, 480 +/- 60 fmoles, and 530 +/- 130 fmoles (n = 4-5), respectively. The level of substance P in the contralateral knees injected with diluent was 58 +/- 8 fmoles (n = 12). The level of substance P had increased by 2 hours after IL-1 injection and remained elevated in the joint 48 hours after injection. Cytokine-induced proteoglycan depletion was also time- and dose-dependent. Proteoglycan concentrations in articular cartilage dissected from the weight-bearing condyles were calculated as the ratio of sulfated glycosaminoglycan measured using 1,9-dimethylmethylene blue: hydroxyproline. After 48 hours, 10 ng, 30 ng, or 100 ng of rHuIL-1 alpha per joint decreased proteoglycan levels by 9 +/- 4%, 14 +/- 4%, and 21 +/- 3% (n = 8), respectively. Likewise, the injection of recombinant human tumor necrosis factor alpha induced depletion of intraarticular substance P and cartilage proteoglycan.

Animals↗
PubMed1990

Electrophysiological actions of luteinizing hormone-releasing hormone: intracellular studies in the rat hippocampal slice preparation.

The electrophysiological effects of luteinizing hormone-releasing hormone (LHRH) on CA1 pyramidal cells were investigated utilizing intracellular recordings from the in vitro rat hippocampal slice preparation. Bath application of LHRH (10(-7) - 10(-12) M) resulted in several changes in the electrophysiological properties of CA1 neurons. LHRH induced a long-lasting depolarization associated with increased input resistance, a decrease in the afterhyperpolarization (AHP) following a train of action potentials, and a reduction in accommodation of repetitive cell discharge. These effects were blocked by the synthetic LHRH antagonist [Ac-delta-Pro1,pCl-D-Phe2,D-Trp3,6]-LHRH. These findings provide electrophysiological evidence for the role of LHRH as a neurotransmitter/neuromodulator in the hippocampus.

Action Potentials↗
PubMed1990

Identification of occupational cancer risks using a population-based cancer registry.

The study of Xuan Wei fuel use and lung cancer mortality and also the interim case-control study suggested an association between domestic smoky coal use and Xuan Wei lung cancer. The collaborative studies of physical characterization, chemical analysis, and toxicology further substantiated this linkage. The Xuan Wei residents who used smoky coal inhaled extremely high concentrations of mostly submicron-sized particles, which can be inhaled and deposited effectively deep in the lung. These fine particles were composed mostly of organic compounds (72%), including mutagenic and carcinogenic organic compounds, especially in the aromatic and polar fractions. These residents were exposed to polycyclic aromatic compounds, such as benzo[a]pyrene, at comparable or higher levels than those measured in coke oven plants and other occupational environments (International Agency for Research on Cancer 1984). In comparison with wood and smokeless coal combustion emissions, the organic extracts of smoky coal emission particles showed much higher activity of genotoxicity and carcinogenicity. These results all point to a strong etiological link between the complex organic mixtures from smoky coal emissions and Xuan Wei lung cancer. This study and studies reported by other investigators (de Koning et al. 1984) suggested little association between indoor open-fire wood smoke and lung cancer. The less efficient lung deposition of the larger particles from wood combustion, as well as the lower concentrations of biologically active organic compounds, may contribute to the low rate of lung cancer in the wood-burning communes. As to the smokeless coal emissions, the lower particulate concentration and the lower organic content of the particles emitted may also contribute to the low lung cancer rate in the commune using this fuel. In conclusion, the complex organic mixtures from combustion emissions are genotoxic and carcinogenic in animal and in vitro assays. The magnitude of the cancer risks from the complex organic mixtures in man depends on the degree of the exposure, the types of the compounds contained in the mixtures, and the concentrations of these biologically active compounds present in the combustion emissions.

Air Pollutants↗
PubMed1990

A theoretical model of endochondral ossification and bone architectural construction in long bone ontogeny.

The role of mechanical stresses in the formation of endochondral ossification patterns and the construction of basic bone architecture in human long bones is investigated using a three-dimensional generalized model of long bone development. The distribution of mechanical stress which is created in developing bones as a result of intermittent mechanical loading is calculated using a computer model that mathematically represents the bone's geometry, material properties and loading conditions. The process of endochondral ossification is simulated by iteratively converting cartilaginous regions of the computer model to bone, based on the calculated intermittent hydrostatic and shear stress distributions. Once local regions of mineralized bone have formed, these regions are remodeled according to an algorithm which relates bone density to a mechanical stress stimulus. The results simulated the correct sequence of the appearance of morphological structures which are common to long bones in the human appendicular skeleton. These developmental structures include the site of the first endochondral bone and the secondary ossification center and the tubular nature of long bones. Our results suggest that mechanical loading histories may influence bone morphogenesis beginning from the early stages of endochondral ossification and continuing throughout life. The stress-based algorithms may be part of the 'rules of construction' or 'developmental constraints' which guide limb ontogeny.

Algorithms↗
PubMed1990

A radioimmunoassay for measuring alpha-amidating enzyme activity.

A sensitive alpha-amidating enzyme (alpha AE) assay using C-terminal glycine-extended substance P (SP-Gly) as a substrate was developed. The product, substance P (SP), was measured by a radioimmunoassay with specific polyclonal antibodies which recognize SP with an affinity 10,000-fold higher than that of SP-Gly. The sensitivity of the radioimmunoassay was 5 fmol. Enzyme activity could be readily detected with 25 ng alpha AE partially purified from the conditioned medium of rat medullary thyroid carcinoma CA-77 cells. The Km and Vmax values were 2.0 +/- 0.2 microM and 1.7 +/- 0.1 nmol/mg/min (mean +/- SE, n = 3), respectively. The assay enabled the kinetic characterization of alpha AE from a single rat pituitary homogenate. Optimal Cu2+ required was 30 microM and greater than 3 mM of ascorbate was needed for maximal enzyme activity. The sensitivity of this assay will aid efforts to examine the regulation of in vivo alpha AE activity.

Animals↗
PubMed1990

Left atrial dimension and risk of systemic embolism in patients with a prosthetic heart valve. Department of Veterans Affairs Cooperative Study on Valvular Heart Disease.

The relation between left atrial dimension measured by M-mode echocardiography and systemic embolization after valve replacement was examined prospectively among 397 patients with a prosthetic valve enrolled in the Department of Veterans Affairs Cooperative Study on Valvular Heart Disease. Baseline characteristics including several measures of left atrial enlargement were compared for 31 patients who developed systemic embolism and 366 who did not develop embolism during a 5 year follow-up period. Variables that were significantly related to left atrial dimension or systemic embolization in univariate analyses were included with several others in a multiple logistic regression model. The incidence rate of systemic embolism was more than three times higher after mitral valve replacement than after aortic valve replacement (4.4 and 1.3 per 100 patient-years, respectively); this difference persisted after adjustment for other factors. Univariate analysis indicated a threefold higher incidence of systemic embolism in patients with a left atrial dimension greater than or equal to 4 cm compared with that in patients with a dimension less than 4 cm (3 versus 1 per 100 patient-years, respectively). However, when the effect of valve location (mitral versus aortic) was taken into account using either univariate or multivariate techniques, left atrial dimension was found not to be associated with systemic embolism. In multivariate analysis, atrial fibrillation, age, ejection fraction and location of the prosthetic valve were significantly associated with embolism. Results of this multicenter study suggest that left atrial dimension is not independently related to the development of systemic embolism in patients undergoing valve replacement.

Aortic Valve↗
PubMed1990

Theoretical stress analysis of organ culture osteogenesis.

In a series of in vitro organ culture experiments by Klein-Nulend et al., intermittent ambient hydrostatic pressure was found to significantly increase the rate of calcification in the diaphysis of mouse rudiments while proteoglycan production was increased in the noncalcified epiphyses. In this study, we have conducted finite element stress analyses of this organ culture system in an effort to better understand the distribution of local tissue stresses which were created. Furthermore, we sought to clarify how these experimental results relate to our theory for skeletal morphogenesis which postulates that endochondral ossification is accelerated in regions of octahedral shear (deviatoric) stress and inhibited in areas of compressive hydrostatic (dilatational) stress. The results of the stress analyses show that externally applied hydrostatic pressure produces significant shear stresses at the cartilage/calcified cartilage interface and pure hydrostatic pressure at the rudiment ends. The accelerated osteogenesis in regions of high shear and the increased synthesis of proteoglycans in regions of high compressive hydrostatic stress are therefore consistent with our theory which predicts the regulation of cartilage maintenance and endochrondral ossification by intermittent tissue stresses.

Animals↗
PubMed1990

Comparison of the sealing ability of four obturation techniques.

This study compared the apical seal produced by four obturation techniques. The Canal Finder system was compared with lateral condensation, the Ultrafil system, and the sectional warm gutta-percha techniques. Forty-two anterior single-rooted teeth were instrumented. Ten teeth were not obturated and served as positive and negative controls. The apical seal was tested for leakage with 0.25% methylene blue dye. The teeth were shaved horizontally and dye penetration was measured with a Boley gauge. Results revealed there was no statistically significant difference among the four obturation techniques.

Analysis of Variance↗
PubMed1990

In vitro comparison of bleaching agents on the crowns and roots of discolored teeth.

Sixty teeth were stained in vitro to compare the decolorizing effect of three bleaching agents on the crowns and on the roots of teeth containing an intracoronal isolating base. With an intracoronal isolating base placed either at the cementoenamel junction (CEJ) or 2-mm below the CEJ, bleaching agents of Superoxol, sodium perborate, and a combination of the two were placed in the pulp chamber of teeth and the accesses sealed with IRM. Customized shade guides were used to evaluate the color changes of the crowns and roots. After three treatments, the combination technique was found to be more effective in decolorizing the crowns and roots of teeth than Superoxol or sodium perborate alone (p less than 0.05). No difference was found between the Superoxol group and the sodium perborate group. There was no difference in color shades of crowns in which the IRM base was placed either at the CEJ or 2-mm below the CEJ. The roots of all groups showed some degree of decoloration. Based on the bleaching effects on discolored roots, the effectiveness of this seal is questionable.

Borates↗
PubMed1990

Comparison of endodontic file tip quality.

Tip angulation and four visual characteristics denoting manufacturing quality of endodontic files were studied. One-hundred eighty K-type, Hedstrom, and Flex-type files from two manufacturers (Kerr and Mallefer) were evaluated. Photomicrographs (x 115) were made of each file. Two evaluators examined the photomicrographs. Tip angulation was studied to determine if files were compliant with ANSI/ADA Specification Nos. 28 and 58. The four visual characteristics compared in the study were symmetry versus asymmetry, smooth versus irregular, tip configuration, and shoulder configuration. Statistical analysis was made using the chi-square method. Mallefer files appear to be more in conformity with specifications for tip angle and more meticulously manufactured than Kerr files. Kerr Hedstrom files appear to conform less often to tip angle specifications than Kerr K-type or K-Flex files. K-type and Flex-type file tips appear to be better manufactured than Hedstrom file tips. Certification status of a file manufacturer did not correlate with a higher level of compliance with tip angulation specifications or with a better machined file tip.

Chi-Square Distribution↗
PubMed1990

Growth of Plasmodium falciparum in human erythrocytes containing abnormal membrane proteins.

To evaluate the role of erythrocyte (RBC) membrane proteins in the invasion and maturation of Plasmodium falciparum, we have studied, in culture, abnormal RBCs containing quantitative or qualitative membrane protein defects. These defects included hereditary spherocytosis (HS) due to decreases in the content of spectrin [HS(Sp+)], hereditary elliptocytosis (HE) due to protein 4.1 deficiency [HE(4.1(0))], HE due to a spectrin alpha I domain structural variant that results in increased content of spectrin dimers [HE(Sp alpha I/65)], and band 3 structural variants. Parasite invasion, measured by the initial uptake of [3H]hypoxanthine 18 hr after inoculation with merozoites, was normal in all of the pathologic RBCs. In contrast, RBCs from six HS(Sp+) subjects showed marked growth inhibition that became apparent after the first or second growth cycle. Preincubation of HS(Sp+) RBCs in culture for 3 days did not alter these results. Normal parasite growth was observed in RBCs from one HS subject with normal membrane spectrin content. The extent of decreased parasite growth in HS(Sp+) RBCs closely correlated with the extent of RBC spectrin deficiency (r = 0.90). Homogeneous subpopulations of dense HS RBCs exhibited decreased parasite growth to the same extent as did HS whole blood. RBCs from four HE subjects showed marked parasite growth inhibition, the extent of which correlated with the content of spectrin dimers (r = 0.94). RBCs from two unrelated subjects with structural variants of band 3 sustained normal parasite growth. Decreased growth in the pathologic RBCs was not the result of decreased ATP or glutathione levels or of increased RBC hemolysis. We conclude that abnormal parasite growth in these RBCs is not the consequence of metabolic or secondary defects. Instead, we suggest that a functionally and structurally normal host membrane is indispensable for parasite growth and development.

Animals↗
PubMed1990

Visualization of mitral valve aneurysm by transesophageal echocardiography.

This article describes the transesophageal echocardiographic findings in a patient with pathologically proven mitral valve aneurysm. This aneurysm probably occurred as a complication of aortic valve endocarditis. Transesophageal echocardiography showed a saccular structure attached to the left atrial side of the anterior mitral leaflet with systolic expansion and diastolic collapse, and its orifice was visualized with excellent resolution. Transesophageal echocardiography is a useful diagnostic tool for evaluation of mitral valve aneurysm.

Aortic Valve↗