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Biomedical subjects

M Wong

Publications and source records attributed to M Wong.

At least 271 records · Page 15Linked to original sources
PubMed1989

Assessment of Doppler color flow mapping in quantification of aortic regurgitation--correlations and influencing factors.

Real-time two-dimensional Doppler echocardiography (Doppler color flow mapping) offers useful information on valvular regurgitation. In order to quantify aortic regurgitation by Doppler color flow mapping, this study determined the relationships between regurgitant jet dimensions and angiographic grades in 100 patients, and between regurgitant jet dimensions and regurgitant fractions or regurgitant volumes in 47. Doppler data were obtained using 4 different echo windows, parasternal long and short axes, and apical two- and four-chamber views. Maximum jet area, length and diameter taken from all available views were examined in relation to angiographic grades, regurgitant fractions and regurgitant volumes. Moreover, we analyzed the technical, biological and hemodynamic factors influencing these relationships. Significant correlations were found between all maximum jet dimensions and angiographic grade (diameter, r = 0.641; length, r = 0.549; area, r = 0.611; p less than 0.01). Means and standard deviations for maximum jet dimensions according to angiographic grading revealed significant differences between all grades except in jet length between grades 3 and 4. However, these relations tended to be influenced by various factors: equipment, echo window, shape of jet, coexistence with mitral stenosis or aortic stenosis, left ventricular size, left ventricular stroke volume, and diastolic blood pressure. On the other hand, with regurgitant fractions and regurgitant volumes, maximum jet dimensions correlated well (diameter, r = 0.614 and 0.567; length, r = 0.769 and 0.767; area, r = 0.791 and 0.773; p less than 0.01) when data associated with atrial fibrillation were excluded. Thus significant correlations between regurgitant jet dimensions in Doppler color flow mapping and angiographic grades can be obtained in all patients despite various factors influencing jet dimensions. Better correlations with regurgitant fractions or regurgitant volumes may be expected in patients with normal sinus rhythm.

Adult↗
PubMed1989

The glomerular basement membrane defect in Alport-type hereditary nephritis: absence of cationic antigenic components.

Alport-type hereditary nephritis is a familial disorder which results in progressive renal insufficiency and sensorineural hearing loss. It is thought to result from a biochemical defect affecting basement membranes. To study this further, non-collagenous components of type IV collagen were prepared from the glomerular basement membrane (GBM) by collagenase digestion from three male patients with hereditary nephritis. The normal Goodpasture antigenicity of the 28 and 26 kD monomers and 54 and 50 kD dimers which may be isolated from the GBM was absent on one-dimensional immunoblots. Two-dimensional electrophoresis and immunoblotting studies showed absence of Goodpasture antigenicity of these molecular weight components as well as all cationic monomeric and dimeric spots. It is concluded that the expression of the Goodpasture antigen is altered in basement membranes of hereditary nephritis patients. The altered antigenicity thus acts as a marker for the underlying abnormality.

Anti-Glomerular Basement Membrane Disease↗
PubMed1989

Frequency analysis of accommodation: single sinusoids.

We present an experimental frequency analysis of a neurological control system, the accommodation system, using single sinusoids. Also, by means of continual experimental calibration full coverage of one subject's dynamic range, we demonstrate an AC nonlinearity saturation, which probably lies in the motor-response portion of the system; in contrast to the switching-mode nonlinearity, which probably lies in the sensory-processing portion. We offer our findings as a basis for further models. In addition, our results can be compared with studies using multiple sinusoids and transients to document how the different aspects of the accommodation system are realized given their different input conditions.

Accommodation, Ocular↗
PubMed1989

Are Texas dentists burned out?

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 occupation often requires intense interaction with fearful, demanding patients on a daily basis. The purpose of this study was to assess the prevalence of burnout among Texas dentists using a standardized measurement device, the Maslach Burnout Inventory (MBI). Dentists attending the 1989 Texas Dental Association Annual Session were surveyed using the MBI. The respondents' results were analyzed and compared to each other as well as to the norms of medicine and to society (human service workers nationwide). Among the Texas sample, male dentists scored significantly higher for emotional exhaustion and depersonalization than did female dentists. When compared to the norms of medical workers, Texas dentists scored higher burnout in the depersonalization subscale, but lower burnout for personal accomplishment. The Texas sample again scored lower for burnout in the personal accomplishment subscale when compared to societal norms. At no time did the Texas sample fall into the high range of experienced burnout as defined by the survey instrument. Texas dentists did not appear "burned out" as a group and actually demonstrated an increased sense of personal accomplishment in their profession.

Adult↗
PubMed1989

Preoperative identification of patients likely to have left ventricular dysfunction after aortic valve replacement. Participants in the Veterans Administration Cooperative Study on Valvular Heart Disease.

The purpose of this study was to identify preoperative and intraoperative variables predictive of left ventricular dysfunction 6 months after aortic valve replacement. Patients were considered to have postoperative left ventricular dysfunction if the end-diastolic-volume index was greater than or equal to 101 ml/m2 or if the ejection fraction was less than or equal to 0.50. Data from 180 patients entered into the Veterans Administration Cooperative Study on Valvular Heart Disease who had technically satisfactory cardiac catheterizations 6 months postoperatively were analyzed by a series of univariate and multivariate analyses. For the 88 patients with preoperative aortic stenosis, the most powerful predictor of postoperative left ventricular dysfunction in the final multivariate model was preoperative left ventricular ejection fraction (p = 0.0001), followed by preoperative myocardial infarction (p = 0.012), aortic valve gradient (p = 0.020), and incomplete coronary revascularization (p = 0.059). Abnormal preoperative left ventricular ejection fraction had a sensitivity of 72% and a specificity of 82% in identifying patients with postoperative left ventricular dysfunction. Preoperative left ventricular systolic-volume index greater than or equal to 40 ml/m2 had a similar sensitivity and specificity (79% and 84%, respectively). For the 36 patients with aortic regurgitation, preoperative left ventricular ejection fraction was again the most powerful predictor of postoperative left ventricular dysfunction (p = 0.013), followed by left ventricular systolic pressure (p = 0.038) and arteriovenous oxygen difference (p = 0.054). For the 56 patients with mixed aortic stenosis and regurgitation, left ventricular systolic pressure (p = 0.007) and preoperative myocardial infarction (p = 0.022) were the variables predictive of postoperative left ventricular dysfunction. Although many patients with preoperative left ventricular dysfunction experience improved left ventricular performance after aortic valve replacement, performance does not always return to normal. For patients with either aortic stenosis or regurgitation, the strongest predictor of postoperative left ventricular dysfunction is preoperative dysfunction. These data support the concept that patients with moderate or severe aortic stenosis or regurgitation should be operated on before the onset of significant left ventricular dysfunction.

Aortic Valve↗
PubMed1989

Clinical experience with the Tangent Streak RGP bifocal contact lens.

Eighty-one screened presbyopic subjects were fitted with the Tangent Streak Bifocal (TSB) rigid gas permeable contact lens. Sixty subjects received lenses, and of this group, 42 (70%) have worn the lens successfully for 6 months or longer. Failures mainly resulted from discomfort and occasionally, reduced visual quality. Successful subjects were particularly pleased with their crisp vision at distance and near. The TSB may be the lens of choice for those presbyopic patients who require high definition visual quality at distance and near.

Adult↗
PubMed1989

Modulation of embryonic glutathione reductase and phenytoin teratogenicity by 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU).

The teratogenicity of phenytoin may be mediated through a reactive electrophilic and/or free radical intermediate which, if not detoxified, may interact with fetal cellular macromolecules and initiate teratologic effects. Glutathione (GSH) maintains cellular physiological processes and detoxifies xenobiotic reactive intermediates. The role of GSH in protection against phenytoin embryopathy was studied by altering GSH homeostasis using 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU), an inhibitor of glutathione reductase. BCNU was administered to pregnant CD-1 mice on gestational day 12, in doses ranging from 10 to 50 mg/kg i.p., with or without phenytoin, 55 or 65 mg/kg i.p., given 4 and 24 hr after BCNU. BCNU alone in doses of 10, 25 or 50 mg/kg resulted in a dose-related increase in the incidence of resorptions, cleft palates and postpartum death (P less than .05), and in lowered fetal weight (P less than .05). Fetuses exposed to 50 mg/kg of BCNU had an array of gross abnormalities, and this dose was not used in subsequent studies. BCNU, 25 mg/kg, inhibited GSH reductase activity by 23% in the placenta (P less than .05) and by 30% in the embryo (P less than .05) at 4 hr after treatment. Embryonic, but not placental GSH reductase activity remained significantly inhibited at 24 hr after BCNU. A BCNU dose-related increase in the incidence of resorptions (P less than .0001) and postpartum death (P less than .05) was seen in groups treated with both BCNU and 65 mg/kg of phenytoin, compared to controls treated with either chemical alone.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

The fragmentation of 670A MeV neon-20 as a function of depth in water. I. Experiment.

We present the final analysis of an experiment to study the interaction of a beam of 670A MeV neon ions incident on a water column set to different thicknesses. The atomic number Z (and, in some cases, the isotopic mass A) of primary beam particles and of the products of nuclear interactions emerging from the water column close to the central axis of the beam was obtained for nuclei between Be (Z = 4) and Ne (Z = 10) using a time-of-flight telescope to measure the velocity and a set of silicon detectors to measure the energy loss of each particle. The fluence of particles of a given charge was obtained and normalized to the incident beam intensity. Corrections were made for accidental coincidences between multiple particles triggering the TOF telescope and for interactions in the detector. The background due to beam particles interacting in beam line elements upstream of the detector was calculated. Sources of experimental artifacts and background in particle identification experiments designed to characterize heavy ion beams for radiobiological research are summarized, and some of the difficulties inherent in this work are discussed. Complete tables of absolutely normalized fluence spectra as a function of LET are included for reference purposes.

Ions↗
PubMed1988

Mechanical stresses and endochondral ossification in the chondroepiphysis.

In 1911, Gebhardt used a photoelastic model to relate mechanical stresses to the ossification pattern of the chondroepiphysis. Pauwels later conducted a photoelastic study using the same model geometry to develop a theory that the secondary ossific nucleus originates at a position of high-magnitude hydrostatic pressure where the shear stresses are zero. We conducted two-dimensional finite element analyses of the model used by Gebhardt and Pauwels. We demonstrate that Pauwels's photoelastic results are correct but are based on the imposition of incorrect boundary conditions. When more realistic boundary conditions were used, the finite element results changed dramatically. These results suggest that (a) the ossific nucleus appears in an area of high shear (deviatoric) stresses; (b) the edge of the advancing ossification front (zone of Ranvier or ossification grove) also experiences high shear stresses; and (c) the joint surface, where articular cartilage forms, is exposed to high-magnitude hydrostatic compression. These findings support the theory proposed by Carter and associates that intermittently applied shear stresses (or strain energy) promote endochondral ossification and that intermittently applied hydrostatic compression inhibits or prevents cartilage degeneration and ossification.

Growth Plate↗
PubMed1988

The role of mechanical loading histories in the development of diarthrodial joints.

The possible role of mechanical loading history in chondroosseous development at the ends of long bones is explored using two-dimensional finite element models of chondroepiphyses. Loading histories are characterized in terms of discrete loading cases defined by joint contact pressure distributions and an associated number of loading cycles. An osteogenic stimulus throughout the chondroepiphyses is calculated following the theory that cyclic octahedral shear stresses promote endochondral ossification and cyclic compressive dilatational stresses inhibit ossification. The resulting distributions for the osteogenic stimulus predict the appearance of the secondary ossific nucleus and the shape of the developing bony epiphysis. The zone of Ranvier and the formation of articular cartilage and the growth plate are also predicted by the models. These findings are consistent with the hypothesis that tissue stress histories constitute an important influence during skeletal morphogenesis. Further study and testing of the concepts introduced in this study are appropriate.

Biomechanical Phenomena↗
PubMed1988

Effects of N-acetylcysteine on fetal development and on phenytoin teratogenicity in mice.

The teratogenicity of phenytoin may result from its enzymatic bioactivation to a reactive intermediate, which interacts irreversibly with fetal tissues. Since glutathione (GSH) is involved in the detoxification of many reactive intermediates, N-acetylcysteine (NAC), a glutathione precursor, was evaluated for its effects on murine fetal development and phenytoin teratogenicity. NAC, 100 to 275 mg/kg, was given intraperitoneally (ip) or per os (po), or as 266 to 410 mg/kg in the drinking water, at various times before or after phenytoin, 65 to 75 mg/kg ip, on gestational days 12 and 13. Dams were killed on gestational day 19, fetal resorptions were noted, and fetuses were examined for anomalies. Significant reductions in phenytoin-induced fetal weight loss and cleft palates were observed when NAC was given by gavage 6 hours after phenytoin or in the drinking water with the lower dose of phenytoin. NAC administered in the drinking water also reduced the incidence of resorptions produced by the higher dose of phenytoin and enhanced postpartum survival in fetuses exposed to 65 or 75 mg/kg phenytoin (P less than .05). Conversely, the incidence of resorptions increased when NAC was given by gavage at other times before or after phenytoin, by single or repetitive ip injections, or in high concentrations in the drinking water (P less than .05). When given with the higher dose of phenytoin, NAC administered via the drinking water significantly increased the incidence of phenytoin-induced cleft palates and fetal weight loss (P less than .05). Similar results were obtained with a single ip injection of NAC and a lower dose of phenytoin. Thus, when given orally, NAC can partially reduce phenytoin teratogenicity and embryopathy. However, altering the route of NAC administration, or increasing the dose of phenytoin and/or NAC, enhanced phenytoin embryotoxicity, and NAC alone at higher doses had embryopathic effects.

Acetylcysteine↗
PubMed1988

Doppler evaluation of bioprosthetic and mechanical aortic valves: data from four models in 107 stable, ambulatory patients.

To test the applicability of Doppler ultrasound in the evaluation of prosthetic valve function, 107 patients with normal ejection fractions in whom Starr-Edwards, Björk-Shiley, Carpentier-Edwards, and Hancock models had been implanted in the aortic position were examined. Maximal transvalvular velocity was recorded by non-imaging continuous wave Doppler ultrasound. Means of maximal velocities by model and size ranged from less than 2 to 4 m/sec. The Starr-Edwards valve showed the highest velocities, the Björk-Shiley the lowest, and the bioprosthetic models showed velocities in between. A significant inverse relation between velocity and size, and standard deviations averaging +/- 14% enabled the technique to measure differences between sizes of the same model. Aortic regurgitation was detected in 24% of the patients. This study, conducted in well and stable patients, established values for maximal velocity across normally functioning aortic mechanical and tissue prostheses of different models and sizes. The intersubject variability was relatively small which, together with a previously shown minimal intrasubject variability, was testimony to a methodology that should prove useful in longitudinal postoperative evaluations.

Aged↗
PubMed1988

Six month postoperative hemodynamics of the Hancock heterograft and the Björk-Shiley prosthesis: results of a Veterans Administration cooperative prospective randomized trial.

In a Veterans Administration Cooperative Study involving 13 medical centers, 575 patients undergoing single valve replacement were prospectively randomized to receive either the standard Björk-Shiley prosthesis or the Hancock porcine heterograft (with a modified orifice for sizes 23 and smaller). The hemodynamic data in the 268 patients who underwent cardiac catheterization an average of 6 months (range 3 to 12) postoperatively are reported. Statistical analyses were performed on valve sizes 23, 25 and 27 in the aortic position, and 29, 31 and 33 in the mitral position. A wide variation was observed in mean pressure gradient and calculated orifice area in both valve types within all sizes in both the aortic and the mitral positions. In the aortic position, the Björk-Shiley prosthesis tended to have a lower pressure gradient and larger calculated orifice area than the Hancock heterograft, but the differences in gradient between the two valve types were significant only in the larger-sized valves. The difference in calculated area between the two valve types was not significant within each valve size. In the mitral position, there were no differences in gradient and calculated orifice area between the two types of prostheses. The postoperative cardiac index, regurgitant volume, pulmonary artery systolic and mean pressures, left ventricular end-diastolic pressure, left ventricular ejection fraction and left ventricular end-diastolic volume index did not differ in patients receiving the Björk-Shiley prosthesis from values in patients receiving the Hancock heterograft. Hence, the overall hemodynamic performance of both types of valves is remarkably similar. The choice between these two prostheses should, therefore, be governed not by the hemodynamic performance, but by other factors such as valve durability, risk of anticoagulation and incidence of valve-related complications.

Aortic Valve↗
PubMed1988

The curvilinear relationship between aortic regurgitant volumes and color flow jets. Intraoperative two-dimensional Doppler and electromagnetic flowmeter correlation.

The potential usefulness of two-dimensional Doppler to quantitate valvular regurgitation depends on the relationship between the dimensions of the velocity maps and the regurgitant volumes. We previously found a significant linear regression between aortic regurgitant fraction and jet area, but because of a shallow slope, postulated an exponential or curvilinear relationship. A retrospective analysis of intraoperative electromagnetic flowmeter measurements of aortic flow and epicardial color flow maps of regurgitant jets gave us a more direct examination of the relationship over a wider range of lower flows. Regurgitant volume was calculated from reverse aortic flow and was compared to jet length, area (by planimetry) and volume (from Simpson's rule). Both linear and curvilinear regressions were determined. Correlation coefficients were similar but consistently closer to unity with the exponential equations, and data points were more closely distributed along a curved rather than a straight line. Length regressions were flatter and the volume regressions were steeper than the slopes of the area equations. Thus, the relationship of the gradual slope of the color flow jet area to the regurgitant volume is geometrically determined and limits quantitative application.

Aortic Valve↗
PubMed1988

Microdosimetry near the trajectory of high-energy heavy ions.

Single-event energy distributions were measured in a 1.3-micron-diameter site as a function of radial distance from the trajectory of high-energy iron ions having an energy of about 600 MeV/amu. It was found that beyond distances of a few micrometers the average lineal energy of the (mostly single) secondary electrons (delta rays) is of the order of 3 keV/micron. This is similar to the value found in a medium irradiated by 170-keV photons. The frequency-mean specific energy for delta rays occurring at large distances from the path of the primary ion exceeds the calculated (radial) absorbed dose by two orders of magnitude.

Ions↗
PubMed1988

Mechanical stress and morphogenetic endochondral ossification of the sternum.

The possible role of mechanical stress in determining the patterns of endochondral ossification in skeletal anlages was explored using stress-analysis computer models of developing human sterna. It has been hypothesized previously that the normal sequence of proliferation, maturation, degeneration, and ossification of cartilage is accelerated in regions of high cyclic octahedral shear stress and inhibited in regions of intermittent compressive-hydrostatic (dilatational) stress. This hypothesis was investigated using two-dimensional, all-cartilage, plane-stress finite-element models of the three basic shapes of human sterna that were identified by Ashley. A mathematical criterion, which combined the opposing influences of the shear and dilatational stresses into a single net stimulus for ossification, was used successfully to simulate the three basic patterns of sternal endochondral ossification that were previously documented. Our findings support the view that mechanical forces may strongly influence skeletal morphogenesis, growth, and development, beginning at a very early stage.

Computer Simulation↗
PubMed1987

Technical and biologic sources of variability in the mapping of aortic, mitral and tricuspid color flow jets.

The quantification of valvular regurgitation by 2-dimensional Doppler imaging depends on identifying and minimizing variability. Aortic, mitral and tricuspid regurgitant jet areas were measured in 50 patients with sinus rhythm or atrial fibrillation to analyze the variables of reading error, valve site, jet size, rhythm and frame rate. One technician recorded jet velocities at 1 frame/cycle at a triggered interval after the electrocardiographic R wave and at frame rates of 7.5 and 15 frames/s. Jet areas from 5 consecutive beats were measured by planimetry by 1 observer. Coefficients of variation between and among groups were compared by analysis of variance; mean values were 14 to 22%. Jets grouped less than 2.5, 2.5 to 5 and greater than 5 cm2 showed the variance of small jets exceeding that of medium and large jets. Aortic regurgitant jets were largest and had smaller variance than mitral tricuspid jets. Variability due to atrial fibrillation and the slower frame rate was marginal. Intraobserver error was 4.3% and interobserver 15.4%. Thus, reproducing jet areas carries a minimum variability of 15% or higher, depending on jet size. Valve site could not be excluded as a separate variable. Comparative quantification is best limited to 1 observer.

Adolescent↗