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Biomedical subjects

A Cheng

Publications and source records attributed to A Cheng.

At least 109 records · Page 6Linked to original sources
PubMed1995

Scrub typhus pneumonitis with delayed resolution.

A 35-year-old lady was admitted to hospital with fever and dry cough. Chest radiograph showed bilateral basal infiltrate. Her Weil-Felix test was strongly positive (OX-K > 1:160) and her fever came down with intravenous tetracycline. There was no improvement in the lung shadow and spirometry showed a severe restrictive defect. Open lung biopsy confirmed the diagnosis of interstitial pneumonitis. CT of thorax 6 months after presentation showed partial resolution of the interstitial shadow.

Adult↗
PubMed1994

Is weekly port filming adequate for verifying patient position in modern radiation therapy?

PURPOSE: The objective of this study is to use daily electronic portal imaging to evaluate weekly port filming in detecting patient set-up position. METHODS AND MATERIALS: A computer-based portal alignment method was used to quantify the field displacements on 191 digitized weekly port films and 848 daily electronic portal images in 21 radiation therapy patients. An electronic portal image data set as a control for actual daily treatment position was used to evaluate weekly port films with respect to same-day field displacement, rate of field placement error detection, and prediction of subsequent daily field displacements. RESULTS: The field displacements measured on a port film frequently deviated from the corresponding field displacements on the electronic portal image obtained in the same treatment set-up. A linear regression analysis showed that the curves fitted to the same-day field displacements had slopes that differed significantly from unity (p < 0.001). Overall, the respective frequencies of field placement error, beyond clinical tolerance limits of 5, 7, and 10 mm (corresponding to head and neck, thoracic, and pelvic sites) for port filming and electronic portal imaging were 11% and 14% (p = 0.4) in the X-direction (lateral or anteroposterior) and 24% and 13% (p = .0001) in the Y-direction (caphalad-caudad). When the data were broken down by anatomical region, this discrepancy was found to be mainly due to the differences in the thorax, and head and neck image data sets. For thoracic fields, error in Y-shifts was 28% by port filming, but only 9% by portal imaging (p = 0.01). In the head and neck region, 18% of the port films exceeded tolerance, whereas only 6% of the electronic portal images did (p = 0.0001). Field displacements on the treatment set-ups between the acquisition of port films were not predicted by those films. CONCLUSION: There are discrepancies between the field displacements and field placement errors detected by weekly port films and daily electronic portal images. This study suggests that improved methods of treatment verification may be necessary in modern radiation therapy.

Diagnostic Imaging↗
PubMed1994

Kinetics and mechanism of the barotropic lamellar gel/lamellar liquid crystal phase transition in fully hydrated dihexadecylphosphatidylethanolamine: a time-resolved x-ray diffraction study using pressure jump.

The kinetics and mechanism of the barotropic lamellar gel (L beta')/lamellar liquid crystal (L alpha) phase transition in fully hydrated 1,2-dihexadecyl-sn-glycero-3-phosphoethanolamine (DHPE) has been studied using time-resolved x-ray diffraction (TRXRD). The phase transition was induced by pressure jumps of varying amplitudes in both the pressurization and depressurization directions at controlled temperature (78 degrees C). Both low- and wide-angle diffracted x rays were recorded simultaneously in live time using an x-ray-sensitive image intensifier coupled to a CCD camera and Super-VHS videotape recorder. Such an arrangement allowed for the direct and quantitative characterization of the long- (lamellar repeat spacing) and short-range order (chain packing) during a kinetic experiment. The image-processed live-time x-ray diffraction data were fitted using a nonlinear least-squares model, and the parameters of the fits were monitored continuously throughout the transition. The pressure-induced transitions from the L alpha to the L beta' phase and from the L beta' to the L alpha phase was two-state (no formation of intermediates apparent during the transition) to within the sensitivity limits of the method. The corresponding transit time (the time during which both phases coexist) associated with the long- and short-range order of the pressurization-induced L alpha-to-L beta' phase transition decreased to a limiting value of approximately 50 ms with increasing pressure jump amplitude. This limiting value was close to the response time of the detector/recording system. Thus, the intrinsic transit time of this transition in fully hydrated DHPE at 78 degrees C was less than or equal to 50 ms. In contrast, the depressurization-induced L beta'-to-L alpha phase transition was slower, taking approximately 1 s to complete, and occurred with no obvious dependence of the transit time on pressure jump amplitude. In the depressurization jump experiment, the lipid responded rapidly to the pressure jump in the L beta' phase up to the rate-determining L beta'-to-L alpha transition. Such behavior was examined carefully, as it could complicate the interpretation of phase transition kinetic measurements.

Crystallization↗
PubMed1994

Sperm-egg recognition in the mouse: characterization of sp56, a sperm protein having specific affinity for ZP3.

Recognition between mammalian gametes occurs when the plasma membrane of the sperm head binds to the zona pellucida (ZP), an extracellular coat surrounding eggs. ZP3, one of three glycoproteins in the ZP, is the egg protein recognized by sperm. A mouse sperm surface protein, sp56 (M(r) = 56,000), has been identified on the basis of its specific affinity for ZP3 (Bleil, J. D., and P. M. Wassarman. 1990. Proc. Natl. Acad. Sci. USA. 87:5563-5567). Studies presented here were designed to characterize mouse sperm sp56 and to further test whether or not this protein specifically recognizes ZP3. sp56 was purified by both ZP3 affinity chromatography and by ion exchange chromatography followed by size-exclusion chromatography. The purified native protein eluted from size-exclusion columns as a homomultimer (M(r) approximately 110,000). Each monomer of the protein contains intramolecular disulfide bonds, consistent with its extracellular location. Immunohistochemical and immunoblotting studies, using monoclonal antibodies, demonstrated that sp56 is a peripheral membrane protein located on the outer surface of the sperm head plasma membrane, precisely where sperm bind ZP3. Results of crosslinking experiments demonstrated that the ZP3 oligosaccharide recognized by sperm has specific affinity for sp56. Collectively, these results suggest that sp56 may be the sperm protein responsible for sperm-egg recognition in the mouse.

Amino Acid Sequence↗
PubMed1994

The incidence of ophthalmopathy after radioiodine therapy for Graves' disease: prognostic factors and the role of methimazole.

Radioactive iodine-131 (RAI) has been reported to be associated with a high incidence of development or exacerbation of Graves' ophthalmopathy (GO). This is thought to be associated with a surge of autoantibodies after RAI therapy. The role of methimazole (MMI), which possesses immunomodulatory action, in the prevention of GO was explored by studying 114 patients with Graves' disease. They were assigned randomly to receive either RAI alone or adjunctive antithyroid drugs, which consisted of MMI and L-T4 as a block-replacement therapy for 12 months and were followed for 2 yr. Thirty-five patients (30.7%) had GO at presentation. Twenty-one (18%) patients developed new GO, and six had worsening of preexisting GO. The development of hypothyroidism (P < 0.01) and an elevation of TSH (P < 0.05) were associated with increased risk of development or exacerbation of GO. The chance of development or exacerbation of GO is higher in those with no ophthalmopathy than in those with preexisting GO at presentation (P = 0.002). The incidence of development or exacerbation of GO was similar in the two treatment groups (RAI, 22.8%; adjunctive antithyroid drugs, 23.7%; P = NS). MMI was able to suppress the surge of TSH receptor antibody (TRAB) after RAI, but a surge in TRAB was not of prognostic significance for the development of GO after RAI. Patients who developed or had exacerbation of GO actually had lower TRAB at presentation (P = 0.02). We conclude that hypothyroidism with elevated TSH is an important adverse factor for the development or exacerbation of GO, and MMI was unable to prevent the development or exacerbation of GO after RAI.

Adult↗
PubMed1993

An evaluation of two methods of anatomical alignment of radiotherapy portal images.

PURPOSE: Two techniques have been developed at our institution to allow anatomical registration of digitized portal images to a simulation film. Accuracy of the portal image alignment methods is tested and single intrauser and multiple interuser variation is examined using each technique. METHODS AND MATERIALS: Method one requires the identification of anatomical fiducial points on a simulation image and its corresponding portal image. The parameters required to align the corresponding points are calculated by a least squares fit algorithm. Method two uses an anatomical template generated from the simulation image and superimposing it upon a portal image. The template is then adjusted by a computer mouse to obtain the best subjective anatomical fit on the portal image. Megavoltage portal images of a skull phantom with various known shifts and eight clinical image files were aligned by each method. Each data set was aligned several times by both a single user and multiple users. RESULTS: Alignment of the anatomical phantom portal images demonstrates an accuracy of less than 0.8 +/- 0.9 mm and 0.7 +/- 1.0 degrees with either method. As out of plane rotation increased from 0 to 5 degrees, simulating out of plane malpositioning, alignment orthogonal to the plane of rotation worsened to 1.5 +/- 1.1 mm with the point method and 2.4 +/- 1.6 mm with the template method. Alignment parallel to the axis of the gantry rotation was insensitive to this change and remained constant as did the rotational alignment parameters. For the clinical image files the magnitude of variation for a single user is typically less than +/- 1 mm or +/- 1 degree. The magnitude of variation of alignment increased when multiple users aligned the same image files. The variation was dependent upon anatomical site and to a lesser degree the method of alignment used. The root mean square deviation of translational shifts range from +/- 0.68 mm when using the template method in the pelvis to as high as +/- 2.94 mm with the template method to align abdominal portal images. In the thorax and pelvis translational alignments along the horizontal axis were more precise than along the vertical axis. Multiple user variability was in part due to poor image quality, user experience, non rigidity of the anatomical features, and the difficulty in locating an exact point on a continuous anatomical structure. CONCLUSION: In well controlled phantom studies both the fiducial point and template method provide similar and adequate results. The phantom studies show that alignment error and variance increase with distortion in anatomical features secondary to out of plane rotations. In clinical situations intrauser variation is small, however, multiple interuser variation is larger. The magnitude of variation is dependent upon the anatomical site aligned.

Computer Simulation↗
PubMed1993

The use of on-line image verification to estimate the variation in radiation therapy dose delivery.

PURPOSE: On-line radiotherapy imaging systems provide data that allow us to study the geometric nature of treatment variation. It is more clinically relevant to examine the resultant dosimetric variation. In this work, daily beam position as recorded by the on-line images is used to recalculate the treatment plan to show the effect geometric variation has on dose. METHODS AND MATERIALS: Daily 6 MV or 18 MV x-ray portal images were acquired using a fiberoptic on-line imaging system for 12 patients with cancers in the head and neck, thoracic, and pelvic regions. Each daily on-line portal image was aligned with the prescription simulation image using a template of anatomical structures defined on the latter. The outline of the actual block position was then superimposed on the prescription image. Daily block positions were cumulated to give a summary image represented by the block overlap isofrequency distribution. The summary data were used to analyze the amount of genometric variation relative to the prescription boundary on a histogram distribution plot. Treatment plans were recalculated by considering each aligned portal image as an individual beam. RESULTS: On-Line Image Verification (OLIV) data can differentiate between systematic and random errors in a course of daily radiation therapy. The data emphasize that the type and magnitude of patient set-up errors are unique for individual patients and different clinical situations. Head and neck sites had the least random variation (average 0-100% block overlap isofrequency distribution width = 7 mm) compared to thoracic (average 0-100% block overlap isofrequency distribution width = 12 mm) or pelvic sites (average 0-100% block overlap isofrequency distribution width = 14 mm). When treatment delivery is analyzed case by case, systematic as well as random errors are represented. When the data are pooled by anatomical site, individuality of variations is lost and variation appears random. Recalculated plans demonstrated dosimetric deviations from the original plans. The differences between the two dosimetric distributions were emphasized using a technique of plan subtraction. This allowed quick identification of relative "hot and cold spots" in the recalculated plans. The magnitude and clinical significance of dosimetric variation was unique for each patient. CONCLUSIONS: OLIV data are used to study geometric uncertainties because of the unique nature for individual patients. Dose recalculation is helpful to illustrate the dosimetric consequences of set-up errors.

Humans↗
PubMed1993

A rate turbidimetric immunoassay for theophylline using biotin-avidin system.

We describe a biotin-avidin based rate turbidimetric homogeneous immunoassay for the determination of serum theophylline with a measuring range of 0-40 micrograms/ml. The assay features an avidin-biotin-labeled theophylline conjugate and a monoclonal antibody. The rate of change of turbidity caused by the antibody-conjugate complexing was monitored on the Beckman Synchron CX 4 System at 340 nm and 37 degrees C. Theophylline in a sample inhibited the complexation, and the extent of inhibition allowed the quantitation of theophylline in the sample. The within-run coefficient of variation (CV) was < 3.7% and the between-run CV was 5.2-9.2% depending on the theophylline concentration. Linear regression analysis showed a good correlation with an established fluorescence polarization immunoassay (r = 0.9866, n = 94).

Avidin↗
PubMed1993

Vasovagal reactions may occur after orthotopic heart transplantation.

OBJECTIVES: This study evaluated the ability of patients to manifest vasovagal reactions after orthotopic heart transplantation. BACKGROUND: Paradoxic stimulation of left ventricular baroreceptors may be the afferent limb of the vasovagal reflex in humans. Orthotopic heart transplantation causes surgical denervation of these receptors and would therefore be expected to abolish the vasovagal reflex. METHODS: To attempt to confirm this hypothesis, 10 patients with orthotopic heart transplantation underwent both head-up tilt testing while resting on a saddle support and testing for parasympathetic innervation of the donor heart before and after atropine infusion. Native and donor heart sinus rates were monitored by using an esophageal pill electrode throughout tilting and during parasympathetic testing. RESULTS: Unexpectedly, seven patients had vasovagal responses at saddle support tilt testing, during which native heart rate decreased by 25 +/- 7 beats/min and mean arterial blood pressure decreased by 55 +/- 9 mm Hg. In three of these patients, there was also a decrease in donor heart rate of 23 +/- 26 beats/min. Parasympathetic testing showed possible evidence of donor heart vagal reinnervation in these patients with donor heart bradycardia during tilt but not in those with vasovagal reactions to tilt without slowing of the donor heart rate. CONCLUSIONS: Vagal efferent reinnervation can occur after orthotopic heart transplantation in humans. However, the absence of such reinnervation in some patients with vasovagal responses to tilt calls into question the role of left ventricular receptors in inducing the vasovagal reaction.

Adolescent↗
PubMed1993

The study of relationships between the damage of visual function and hemorrheology, ocular rheography, as well as other related factors in patients with primary open angle glaucoma (POAG).

Researches of glaucoma visual function damage, hemorheology, ocular rheography and other related multiplex factors, with computed multifactorial stepwise regression analysis, indicate that the elevation of intraocular pressure (IOP) is not the only factor to induce visual impairment. POAG patients are shown to have markedly reduced diastolic perfusion pressure in ophthalmic artery, besides prolonged filling time of the retinal artery and vein, diminished erythrocyte deformability and increased platelet adhesion rate. The characteristic of ocular rheographic changes in POAG patients of controlled IOP suggest that the abnormal changes of hemorheology be responsible for the damage of visual function. The abnormal changes of plasma viscosity, blood apparent viscosity, blood viscoelasticity, hematocrit, mean red cell volume etc could be found in addition to the reduction of PO2, SO2% and trace elements (Cr, Zn, Mg, Fe) in patients with POAG. Computed multiply stepwise regression analysis and Bayes discrimination were made among the deteriorate rate of quantitative visual field and 28 factors from the combined investigation. Only the hemorrheological index could be introduced into the multiply regression equations. The more the damage of visual function in POAG patients, the more accurate the discriminatory effect. Based upon the results, and the reports of articles published as well as the search of 1982-1989 Compact Combridge MEDLINE Medical data base, the new clinical concept could be presented that POAG might belong to the scope of blood hyperviscosity syndromes. When IOP elevation and the decrease of ocular artery pressure existed, the damage of visual function in POAG patients should be deteriorated.

Adult↗
PubMed1992

Shc proteins are phosphorylated and regulated by the v-Src and v-Fps protein-tyrosine kinases.

The mammalian shc gene encodes two overlapping proteins of 46 and 52 kDa, each with a C-terminal Src homology 2 (SH2) domain and an N-terminal glycine/proline-rich sequence, that induce malignant transformation when overexpressed in mouse fibroblasts. p46shc, p52shc, and an additional 66-kDa shc gene product become highly tyrosine phosphorylated in Rat-2 cells transformed by the v-src or v-fps oncogene. Experiments using temperature-sensitive v-src and v-fps mutants indicate that Shc tyrosine phosphorylation is rapidly induced upon activation of the v-Src or v-Fps tyrosine kinases. These results suggest that Shc proteins may be directly phosphorylated by the v-Src and v-Fps oncoproteins in vivo. In cells transformed by v-src or v-fps, or in normal cells stimulated with epidermal growth factor, Shc proteins complex with a poorly phosphorylated 23-kDa polypeptide (p23). Activated tyrosine kinases therefore regulate the association of Shc proteins with p23 and may thereby control the stimulation of an Shc-mediated signal transduction pathway. The efficient phosphorylation of Shc proteins and the apparent induction of their p23-binding activity in v-src- and v-fps-transformed cells are consistent with the proposition that the SH2-containing Shc polypeptides are biologically relevant substrates of the oncogenic v-Src and v-Fps tyrosine kinases.

Animals↗
PubMed1992

Randomised controlled trial of short term treatment to eradicate Helicobacter pylori in patients with duodenal ulcer.

OBJECTIVE: To determine whether one week's drug treatment is sufficient to eradicate Helicobacter pylori in patients with duodenal ulcer. DESIGN: Single blind, randomised controlled trial. SETTING: Specialised ulcer clinic in a teaching hospital. PATIENTS: 155 patients with H pylori and a duodenal ulcer verified endoscopically which had either bled within the previous 24 hours or was causing dyspepsia. INTERVENTIONS: Patients were allocated randomly to receive either omeprazole for four weeks plus bismuth 120 mg, tetracycline 500 mg, and metronidazole 400 mg (all four times a day) for the first week (n = 78), or omeprazole alone for four weeks (n = 77). Further endoscopy was performed four weeks after cessation of all drugs. MAIN OUTCOME MEASURES: Presence or absence of H pylori (by urease testing, microscopy, and culture of antral biopsy specimens), duodenal ulcer, and side effects. RESULTS: Eradication of H pylori occurred in 70 (95%) patients taking the four drugs (95% confidence interval 86% to 97%) compared with three (4%) patients taking omeprazole alone (1% to 11%). Duodenal ulcers were found in four (5%) patients taking the four drugs (2% to 12%) and in 16 (22%) patients taking omeprazole alone (14% to 32%). Mild dizziness was the only reported side effect (six patients in each group) and did not affect compliance. CONCLUSIONS: A one week regimen of bismuth, tetracycline, and metronidazole is safe and effective in eradicating H pylori and reduces the number of duodenal ulcers four weeks after completing treatment.

Bismuth↗
PubMed1992

Multicenter evaluation of a new enzyme immunoassay for detection of Clostridium difficile enterotoxin A.

The Premier Clostridium difficile toxin A enzyme immunoassay (PTA EIA) (Meridian Diagnostics, Inc., Cincinnati, Ohio) for rapid diagnosis of antibiotic-associated colitis (AAC) was evaluated in a multicenter study. Stool samples from 421 patients suspected of having AAC were tested for toxin A by the PTA EIA and for toxin B by three tissue culture assays (TCA) employing WI-38 cells (New England Deaconess Hospital) in conventional tubes or foreskin fibroblasts (Children's Hospital) or Vero cells (Beth Israel Hospital) in microwells. The tubes and plates were examined at 24 and 48 h for cytotoxicity. Clinical criteria, repeat testing at another site, and culture of frozen stool samples for C. difficile were used to evaluate discrepant results. Of 504 samples, 66 were positive and 409 were negative by both tests. Eight samples had indeterminate PTA EIA results and were excluded from this analysis. Of 21 discrepancies, 9 were PTA EIA positive and TCA negative and 12 were PTA EIA negative TCA positive. Following resolution of the discrepancies, 11 of 12 PTA EIA-negative-TCA-positive and 5 of 9 PTA EIA-positive-TCA-negative samples were considered true positive for AAC. The sensitivity and specificity were, respectively, 86.6 and 99.0% for the PTA EIA and 93.9 and 99.8% for TCA. The predictive values of positive and negative tests were, respectively, 94.7 and 97.4% for the PTA EIA and 98.7 and 98.8% for TCA. We conclude that the PTA EIA is a rapid, simple EIA technique whose accuracy in detecting enterotoxin A approaches that of reference TCA methods for detection of cytotoxin B.

Bacterial Proteins↗