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Biomedical subjects

R Chiang

Publications and source records attributed to R Chiang.

At least 19 recordsLinked to original sources
PubMed2000

Long-term effect of Nd:YAG laser posterior capsulotomy on intraocular pressure.

OBJECTIVE: To study the long-term effect of Nd:YAG capsulotomy on intraocular pressure (IOP). METHODS: We reviewed the records of patients with bilateral pseudophakia who received Nd:YAG capsulotomy in only 1 eye. Using the Wilcoxon rank sum test, we compared the mean change in IOP in eyes before and after capsulotomy with that of the noncapsulotomy eyes at corresponding time intervals. Using multiple regression tests, we analyzed the factors significantly associated with postcapsulotomy long-term IOP increases. RESULTS: The study included 100 patients who were followed up for a median of 1.5 years after capsulotomy. The mean +/- SD age of the study group was 76+/-7 years, and 37 patients had glaucoma. The changes in IOP in the eyes treated with capsulotomy were significantly higher than those in noncapsulotomy eyes at each time interval following capsulotomy. The long-term IOP increase was significantly associated with the IOP increase measured 1 hour after the capsulotomy (P =. 001). Patients with glaucoma were more likely to require long-term additional glaucoma medication than were nonglaucoma patients to require initial glaucoma therapy after the capsulotomy (P =.002). CONCLUSION: After Nd:YAG capsulotomy, long-term IOP is often elevated above precapsulotomy baselines, especially in glaucoma patients or patients who experience a significant IOP increase within hours after the capsulotomy.

Aged↗
PubMed2000

Generating interactive molecular documentaries using a library of graphical actions.

Paper-based publishing of scientific articles limits the types of presentations that can be used. The emergence of electronic publishing has created opportunities to increase the range of formats available for conveying scientific content. We introduce the Graphical Explanation Markup Language, GEML, implemented as an XML format for defining molecular documentaries which exploit the interactive capabilities of electronic publishing. GEML builds upon existing molecular structure definitions such as the Protein Data Bank (PDB) standard file format. GEML provides a library of gestures (or actions) commonly used for structural explanations, and is extensible. XML allows us to separate explicit statements about how to highlight a molecular structure from the implementation of these instructions. We also present GEIS (Generator of Explanatory Interactive Systems), a program that takes as input a GEML documentary definition file and produces all the files necessary for an interactive, web-based molecular documentary. To demonstrate GEML and GEIS, we constructed a documentary capturing the difficult 3D notions expressed in two selected published reports about human topoisomerase I. We have created a prototype Java application, GEMLBuilder, as an editor of GEML files.

Computer Graphics↗
PubMed1998

Estimation of duration of separation, widowhood, and family life cycle.

This is the second of two reports on a study of the durations related to marriage. Divorce and death of one's spouse, the main causes of dissolution of marriage, are two of the most important events in a person's life. In the United States in 1994, 30.7 million, or 16.2%, of the adult population were either divorced or widowed. Among the widowed, the female to male ratio was 5 to 1! In this paper duration of separation due to divorce and duration of widowhood are the main variables under study. Algebraic formulas are derived and computer programs are written for estimating these durations for husbands and wives, and for living couples of any age. Relations with the duration of marriage, the expectation of life, and the family life cycle are also presented.

Adult↗
PubMed1990

Isolation and molecular genetic characterization of the Bacillus subtilis gene (infB) encoding protein synthesis initiation factor 2.

Western blot (immunoblot) analysis of Bacillus subtilis cell extracts detected two proteins that cross-reacted with monospecific polyclonal antibody raised against Escherichia coli initiation factor 2 alpha (IF2 alpha). Subsequent Southern blot analysis of B. subtilis genomic DNA identified a 1.3-kilobase (kb) HindIII fragment which cross-hybridized with both E. coli and Bacillus stearothermophilus IF2 gene probes. This DNA was cloned from a size-selected B. subtilis plasmid library. The cloned HindIII fragment, which was shown by DNA sequence analysis to encode the N-terminal half of the B. subtilis IF2 protein and 0.2 kb of upstream flanking sequence, was utilized as a homologous probe to clone an overlapping 2.76-kb ClaI chromosomal fragment containing the entire IF2 structural gene. The HindIII fragment was also used as a probe to obtain overlapping clones from a lambda gt11 library which contained additional upstream and downstream flanking sequences. Sequence comparisons between the B. subtilis IF2 gene and the other bacterial homologs from E. coli, B. stearothermophilus, and Streptococcus faecium displayed extensive nucleic acid and protein sequence homologies. The B. subtilis infB gene encodes two proteins, IF2 alpha (78.6 kilodaltons) and IF2 beta (68.2 kilodaltons); both were expressed in B. subtilis and E. coli. These two proteins cross-reacted with antiserum to E. coli IF2 alpha and were able to complement in vivo an E. coli infB gene disruption. Four-factor recombination analysis positioned the infB gene at 145 degrees on the B. subtilis chromosome, between the polC and spcB loci. This location is distinct from those of the other major ribosomal protein and rRNA gene clusters of B. subtilis.

Amino Acid Sequence↗
PubMed1988

Effects of thyroid function on blood pressure. Recognition of hypothyroid hypertension.

Hypothyroidism has been known to be associated, at times, with diastolic hypertension. We have found in 40 thyrotoxic patients that the induction of hypothyroidism by radioiodine therapy significantly increased diastolic blood pressure, raising it above 90 mm Hg in 16 (40%) of the patients. Restoration of euthyroidism with thyroxine administration significantly reduced the systolic and diastolic blood pressures in these patients, with a fall in diastolic pressure below 90 mm Hg in nine of 16 patients. The prevalence of hypothyroidism was determined by measurements of serum thyroxine and thyrotropin concentrations in 688 consecutive hypertensive patients, referred for evaluation and therapy of their hypertension. Hypothyroidism was found in 25 (3.6%) of the patients. Restoration of normal serum thyroxine and thyrotropin levels with thyroid hormone replacement therapy lowered diastolic blood pressure to levels below 90 mm Hg in 32% of these patients who could be followed up after withdrawal of all antihypertensive drug therapy when euthyroidism had been restored (i.e., 1.2% of the 688 patients). It is concluded that diastolic hypertension resulting from hypothyroidism is a relatively common disorder, present in 1.2% of our referred hypertensive patients, that should be sought and treated.

Adult↗
PubMed1985

Elastic jump in male urethra during voiding: clinical observations in male subjects and experimental studies in dogs.

A physical phenomenon known as elastic jump occurs downstream of an elastic constriction applied to a collapsible tube. This flow anomaly is analogous to the hydraulic jump that occurs in surface flows. Some investigators have predicted that an elastic jump could occur in the male urethra (during voiding) in the cavernous segment between constrictions at the membranous and meatal regions. To identify and understand this flow anomaly, and to obtain clinical correlations in human male subjects we have attempted several radiological and urodynamic studies in normal and abnormal subjects. The studies were retrograde urethrography, voiding cystourethrography, static pressure recordings during voiding and uroflowmetry. Retrograde urethrography was believed to delineate accurately the anatomy of the bulbous urethra. Voiding cystourethrography showed the geometry of the functional bulb. Our observations in 43 male subjects suggest that the site and degree of elastic jump depend on the severity of bladder neck or prostatic obstruction, magnitude of detrusor pressure (energy) during voiding, degree of distal constriction and position in which the subject voids. The animal studies (23 dogs) confirmed our clinical urodynamic impression.

Adult↗
PubMed1984

Empty sella turcica in intracranial sarcoidosis. Pituitary insufficiency, primary polydipsia, and changing neuroradiologic findings.

A 37-year-old man with visual loss was found to have hypopituitarism and primary polydipsia associated with sarcoidosis. Neuroradiologic studies demonstrated a dramatic evolution of CNS lesions, including a left thalamic infarct, an enhancing suprasellar mass, and ultimately an empty sella turcica. The patient has been clinically stable in spite of these changes. This case is likely to be the first reported of CNS sarcoidosis with an empty sella turcica documented by computed tomography.

Adult↗
PubMed1979

Resonance Raman investigations of chloroperoxidase, horseradish peroxidase, and cytochrome c using Soret band laser excitation.

Resonance Raman spectra of the heme protein chloroperoxidase in its native and reduced forms and complexed with various small ions are obtained by using laser excitation in the Soret region (350-450 nm). Additionally, Raman spectra of horseradish peroxidase, cytochrome P-450cam, and cytochrome c, taken with Soret excitation, are presented and discussed. The data support previous findings that indicate a strong analogy between the active site environments of chloroperoxidase and cytochrome P-450cam. The Raman spectra of native chloroperoxidase are found to be sensitive to temperature and imply that a high leads to low spin transition of the heme iron atom takes place as the temperature is lowered. Unusual peak positions are also found for native and reduced chloroperoxidase and indicate a weakening of porphyrin ring bond strengths due to the presence of a strongly electron-donating axial ligand. Enormous selective enhancements of vibrational modes at 1360 and 674 cm-1 are also observed in some low-spin ferrous forms of the enzyme. These vibrational frequencies are assigned to primary normal modes of expansion of the prophyrin macrocycle upon electronic excitation.

Binding Sites↗
PubMed1976

Compound X. An intermediate in enzymatic halogenation.

Previous studies have shown that chlorite serves as a halogenation substrate for horseradish peroxidase. In its substrate role, chlorite serves both as a halogen donor and as a source of oxidizing equivalents in the chlorination reaction. We now show that a new spectral intermediate, which we have termed Compound X, can be detected as the initial product of the reaction of chlorite with horseradish peroxidase. The reaction of chlorite with horseradish peroxidase to form Compound X is a relatively fast reaction especially at acidic pH values. The second order rate constant (Kf) for the formation of Compound X at pH 4.5 (optimum pH) is 0.9 X 10(6) M-1 S-1. Compound X, in the absence of a halogen acceptor, decomposes to Compound I and chloride ion. The first order rate constant (Kd) for the decay of Compound X to Compound I is 0.2 s-1 at pH 4.5. The pH optimum for enzymatic chlorination with chlorite compares favorably with the pH profile for the lifetime of Compound X (Kf/Kd). These observations indicate that Compound X is the halogenating intermediate in the chlorite reaction and that the rate of enzymatic chlorination is directly related to the stability of Compound X. We propose an -OCl ligand on a ferric heme as the most likely structure for Compound X.

Binding Sites↗
PubMed1976

Oxidation-reduction potential measurements on chloroperoxidase and its complexes.

The oxidation-reduction potential of chloroperoxidase, an enzyme which catalyzes peroxidative chlorination, bromination, and iodination reactions, has been investigated. In addition to catalyzing biological halogenation reactions, chloroperoxidase is unusual in that the carbon monoxide complex of ferrous chloroperoxidase shows the typical long wavelength Soret absorption associated with P-450 hemoproteins. The pH dependence of the chloroperoxidase oxidation-reduction potential shows a discontinuity around pH 4.7. Similarly, measurements of the affinity of ferrous chloroperoxidase for carbon monoxide monitored both by spectroscopic and potentiometric titration exhibit a discontinuity in the pH 4.7 region. Oxidation-reduction potential measurements on chloroperoxidase in a CO atmosphere also show a discontinuous pH profile. These results suggest that ferrous chloroperoxidase undergoes reversible modification at low pH and that these changes are reflected in the oxidation-reduction potential. The oxidation-reduction potential of chloroperoxidase at pH 6.9 is - 140 mV, close to that measured for cytochrome P-450cam in the presence of substrate. The oxidation-reduction potential of chloroperoxidase at pH 2.7, the pH optimum for enzymatic chlorination, is +150 mV. The oxidation-reduction potentials of the halide complexes of chloroperoxidase (chloride, bromide, and iodide) are essentially identical with the potential measurements on the native enzyme. These observations suggest that, although halide anions bind to the enzyme, they probably do not bind as an axial ligand to the heme ferric iron.

Binding Sites↗
PubMed1976

Diagnostic criteria for computer-aided electrocardiographic 15-lead system. Evaluation using 12 leads and Frank orthogonal leads with vector display.

The criteria for the diagnosis of myocardial infarction and ischaemic heart disease by an automated 15-lead computer-aided electrocardiographic system were examined using electrocardiograms of 543 patients. Errors in the electrocardiographic diagnosis were evaluated for each lead system (Frank orthogonal 3-lead, 12-lead, and hybrid 15-lead) using clinical and catheterization data for definitive diagnosis before review of the electrocardiograms and their reports. The effects of combinations of these diagnoses and additional ventricular conduction defects were also studied. Myocardial infarction and left ventricular hypertrophy were more reliably diagnosed using 3-lead and 12-lead systems together than with either system alone. The most sensitive criteria for anterior infarction were a Q/R ratio in Z less than 0-1 and loss of the first 20 ms of anterior forces in the horizontal and sagittal planes of the vectorcardiogram. However, false positive results were frequent, particularly in association with left ventricular hypertrophy, non-specific intraventricular conduction defects, and left bundle branch system block. Our V lead criteria were more specific whether or not these associated conditions were present. No single criterion with an acceptable false positive rate could be found to be sensitive for inferior infarction in all situations. Our most sensitive criteria were those based on the limb leads, and the presence of superior forces for the first 30 ms in the frontal plane of the vectorcardiogram, but these were better in combination. Limb lead criteria were the most specific. False positive results for inferior infarction were more frequent in the presence of left ventricular hypertrophy or ventricular conduction defects other than left anterior hemiblock. ST and T wave abnormalities were more apparent in the 12 leads than in the orthogonal leads. Specificity and sensitivity of criteria were poor, and specificity was decreased and sensitivity was not significantly improved by combining 3-lead with 12-lead criteria. Because of frequent measurement errors of ST, T, and also Q waves by the computer programme, in practice we have achieved increased sensitivity in the diagnosis of ischaemia and infarction with the combination of 3-lead and 12-lead systems. It is concluded that errors of diagnosis by a computer-aided system can be reduced by using multiple leads and that both 12-lead and orthogonal 3-lead systems are necessary for optimal computer diagnosis of left ventricular hypertrophy, myocardial infarction, and ischaemia.

Adult↗
PubMed1975

Mössbauer investigations of high-spin ferrous heme proteins. II. Chloroperoxidase, horseradish peroxidase, and hemoglobin.

Reduced samples of chloroperoxidase, horseradish peroxidase, and deoxyhemoglobin were studied by Mössbauer spectroscopy in strong magnetic fields. The intricate paramagnetic spectra of chloroperoxidase were evaluated in detail in the framework of a spin Hamiltonian pertinent to high-spin ferrous iron. The studies strongly suggest that, in their reduced states, chloroperoxidase from Caldariomyces fumago and cytochrome P-450 from Pseudomonas putida have similar, if not identical ligand structures of the heme iron. The spectral similarities of these two proteins, noted in an earlier Mössbauer investigation, are further explored and substantiated. Reduced horseradish peroxidase and deoxyhemoglobin, on the other hand, show high-field Mössbauer spectra that differ considerably from each other and, in particular, from those of the P-450 type, suggesting a different ligand arrangement of the heme iron for each case.

Bacterial Proteins↗
PubMed1975

Chloroperoxidase: P-450 type absorption in the absence of sulfhydryl groups.

The oxidation state of the two half-cystine residues in the native ferric form of chloroperoxidase and in the reduced ferrous chloroperoxidase has been examined in order to evaluate the role of sulfhydryl groups as determinants of P-450 type spectra. Mössbauer and optical spectroscopy studies indicate that the ferrous forms of P-450cam and chloroperoxidase have very similar or identical heme environments. Model studies have suggested that sulfhydryl groups may function as axial ligands for developing P-450 character. However, chemical studies involving both sulfhydryl reagents and amperometric titrations show that neither the ferric nor the chemically produced ferrous forms of chloroperoxidase contain a sulfhydryl group. These results rule out the hypothesis that sulfhydryl groups are unique components for P-450 absorption characteristics. The optical and electron paramagnetic resonance (EPR) spectra of the nitric oxide complex of chloroperoxidase have been obtained and compared to those of myoglobin, hemoglobin, and cytochrome c and horseradish peroxidase. The EPR spectrum of the NO-ferrous chloroperoxidase complex, which is similar to that of cytochrome P-450cam, does not show the extra nitrogen hyperfine structure which appears to be characteristic of those hemoproteins which have a nitrogen atom as an axial heme ligand.

Chemical Phenomena↗