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Biomedical subjects

H An

Publications and source records attributed to H An.

At least 73 records · Page 4Linked to original sources
PubMed1994

Utility of high-dose contrast enhancement for detecting recurrent herniated intervertebral disks.

PURPOSE: To study the utility of high-dose contrast enhancement in the detection of recurrent herniated disk fragments. METHODS: Recurrent herniated disks were modeled in nine dogs by placing a fragment of normal autologous disk tissue in the epidural space at laminectomy. MR was performed at 30, 60, and 90 days with 0.3 mmol/kg of gadoteridol and repeated 24 hours later with 0.1 mmol/kg of gadopentetate dimeglumine. Contrast enhancement in the disk and scar tissue was measured and conspicuousness of the disk fragments assessed. RESULTS: In 70% of the animals, disk fragments were more conspicuous with the larger dose of contrast medium than with the smaller dose. In 30% of animals the conspicuousness was approximately equal. Contrast between disk fragment and scar decreased with time elapsed since surgery, with time elapsed since contrast-medium injection, and with decreasing dose of contrast medium. CONCLUSION: In the experimental model, increased conspicuousness of disk fragments was achieved with the larger dose of contrast medium. A clinical study is needed to confirm that a contrast-medium dose of 0.3 mmol/kg improves detection of recurrent herniated disks over a dose of 0.1 mmol/kg.

Animals↗
PubMed1993

Closed reduction of traumatic cervical spine dislocation using traction weights up to 140 pounds.

The purpose of this study was to demonstrate that Gardner-Wells skull tong traction up to 140 lb was both safe and effective in reducing dislocation, without fractures, of facet joints involving the C4-C7 vertebral bodies when applied by experienced practitioners in a spinal cord injury center under close scrutiny. Twenty-four awake patients were selected for the study (age range, 16-82 years). These patients were evaluated for the number of millimeters (7-17 mm) of dislocation as measured from the posterior aspect of the superior vertebral body to the posterior aspect of the inferior vertebral body at the level of injury. The maximum weight required to produce the reduction of the facet joints and the time from the onset of traction were recorded. The patients' neurologic status was monitored before traction, after each increment in weight applied, and after reduction. Careful examination of motor function and sensation was done and recorded at each interval. The 24 patients with cervical spine dislocation of the facet joints underwent successful reduction with traction weights (range, 10-140 lb). Seventeen patients required weights of more than 50 lb. The traction procedures lasted for a period of 8-187 minutes per procedure. Worsening neurologic status did not occur in any of the patients involved in this study.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1992

Prospective comparison of biphasic and monophasic shocks for implantable cardioverter-defibrillators using endocardial leads.

Bidirectional shocks using 2 current pathways have been used in endocardial lead systems for implantable cardioverter-defibrillators, but the optimal shock waveform for endocardial defibrillation is unknown. The clinical efficacy and electrical characteristics of bidirectional monophasic and biphasic shocks for endocardial cardioversion-defibrillation of fast monomorphic or polymorphic ventricular tachycardia (VT), or ventricular fibrillation (VF) were evaluated. Thirty-three patients (mean age 60 +/- 12 years, and mean left ventricular ejection fraction 34 +/- 13%) were studied. Defibrillation catheter electrodes were located in the right ventricular apex and superior vena cava/right atrial junction. A triple-electrode configuration including the 2 catheter electrodes and a left thoracic patch was used to deliver bidirectional shocks from the right ventricular cathode to an atrial anode (pathway 1) and the thoracic patch (pathway 2). The shock waveforms examined were sequential and simultaneous monophasic, and simultaneous biphasic. The efficacy of 580 V (20 J) shocks for fast monomorphic VT were comparable for the 3 waveforms (73% for sequential monophasic, 73% for simultaneous monophasic, and 100% for simultaneous biphasic). However, for polymorphic VT and VF, 580 V sequential monophasic shocks had a significantly lower efficacy (25%) than did simultaneous monophasic (75%; p = 0.01) or biphasic (89%; p less than 0.001) shocks. Single-shock defibrillation thresholds with simultaneous biphasic shocks were significantly lower (9 +/- 5 J) than were those with simultaneous monophasic shocks (15 +/- 4 J; p less than 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)

Electric Countershock↗
PubMed1992

Coordination of expression of Zymomonas mobilis glycolytic and fermentative enzymes: a simple hypothesis based on mRNA stability.

Although Zymomonas mobilis is prototrophic, glycolytic and fermentative enzymes (ethanologenic enzymes) constitute over half of the cytoplasmic protein. In this study, transcript stability, functional message pools, and the abundance of cytoplasmic products were compared for genes encoding eight of these essential enzymes. The transcripts of all were very stable, with half-lives ranging from 8 to 18 min. This transcript stability is proposed as an important feature in Z. mobilis that may distinguish highly expressed genes for energy generation from biosynthetic genes, which are required at much lower levels. The evolution of multiple promoters to enhance transcription from single-copy genes, of structural features that alter translational efficiency, and of differences in protein turnover is hypothesized to serve a subordinate role in the regulation of Z. mobilis gene expression. Among the eight ethanologenic genes examined, differences in transcript stability were found to directly correlate with differences in functional message pools and cytoplasmic protein levels. These differences in transcript stability are hypothesized to have evolved as a primary mechanism to balance the levels of individual enzymes within the glycolytic and fermentative pathways.

Bacterial Proteins↗
PubMed1991

Segmental message stabilization as a mechanism for differential expression from the Zymomonas mobilis gap operon.

In Zymomonas mobilis, three- to fourfold more glyceraldehyde-3-phosphate dehydrogenase protein than phosphoglycerate kinase is needed for glycolysis because of differences in catalytic efficiency. Consistent with this requirement, higher levels of glyceraldehyde-3-phosphate dehydrogenase were observed with two-dimensional polyacrylamide gel electrophoresis. The genes encoding these enzymes (gap and pgk, respectively) form a bicistronic operon, and some form of regulation is required to provide this differential expression. Two transcripts were observed in Northern RNA analyses with segments of gap as a probe: a more abundant 1.2-kb transcript that contained gap alone and a 2.7-kb transcript that contained both genes. Based on the relative amounts of these transcripts, the coding regions for glyceraldehyde-3-phosphate dehydrogenase were calculated to be fivefold more abundant than those for phosphoglycerate kinase. Assuming equal translational efficiency, this is sufficient to provide the observed differences in expression. Operon fusions with lacZ provided no evidence for intercistronic terminators or attenuation mechanisms. Both gap operon messages were very stable, with half-lives of approximately 16 min (1.2-kb transcript) and 7 min (2.7-kb transcript). Transcript mapping and turnover studies indicated that the shorter gap message was a stable degradation product of the full-length message. Thus differential expression of gap and pgk results primarily from increased translation of the more stable 5' segment of the transcript containing gap. The slow turnover of the messages encoding glyceraldehyde-3-phosphate dehydrogenase and phosphoglycerate kinase is proposed as a major feature contributing to the high level of expression of these essential enzymes.

Base Sequence↗
PubMed1991

Gel electrophoretic analysis of Zymomonas mobilis glycolytic and fermentative enzymes: identification of alcohol dehydrogenase II as a stress protein.

The 13 major enzymes which compose the glycolytic and fermentative pathways in Zymomonas mobilis are particularly abundant and represent one-half of the soluble protein in exponential-phase cells. One- and two-dimensional polyacrylamide gel electrophoresis maps were developed for 12 of these enzymes. Assignments were made by comigration with purified proteins, comparison with overexpressed genes in recombinant strains, and Western blots (immunoblots). Although most glycolytic enzymes appeared resistant to turnover and accumulated in stationary-phase cells, the protein levels of pyruvate kinase, alcohol dehydrogenase I, and glucokinase declined. Alcohol dehydrogenase II was identified as a major stress protein and was induced both by exposure to ethanol and by elevated temperature (45 degrees C). This enzyme, encoded by the adhB gene, is expressed from tandem promoters which share partial sequence identity with the Escherichia coli consensus sequence for heat shock proteins.

Alcohol Dehydrogenase↗
PubMed1990

Clinical efficacy of dual electrode systems for endocardial cardioversion of ventricular tachycardia: a prospective randomized crossover trial.

In order to eliminate the need for epicardial electrodes, two large transvenous catheter electrodes or one catheter and one extrathoracic patch electrode have been proposed as alternative electrode configurations for defibrillation and ventricular tachycardia cardioversion by implantable cardioverter/defibrillators. We compared the efficacy and safety of endocardial shocks delivered through these two electrode systems in man in a prospective randomized crossover study. Twelve patients with sustained ventricular tachycardia and heart disease undergoing electrophysiologic study were evaluated. A transvenous tripolar cardioversion electrode catheter with a large distal defibrillation electrode (surface area, 400 mm2) and proximal defibrillation electrode (surface area, 800 mm2) was positioned in the right ventricular apex with a cutaneous patch electrode placed on the cardiac apex. Sustained ventricular tachycardia was induced at electrophysiologic study. Shocks were delivered using two catheter electrodes only (right ventricular cathode and right atrial anode = method I), and one catheter electrode and cutaneous patch (right ventricular cathode and cutaneous apical patch anode = method II). Synchronized monophasic shocks were delivered using three preselected protocols based on ventricular tachycardia cycle length and morphology. Initial shock energies were 25 joules for polymorphic ventricular tachycardia and ventricular fibrillation, 15 joules for monomorphic rapid ventricular tachycardia (cycle length less than or equal to 300 msec), and 5 joules for monomorphic slow ventricular tachycardia (cycle length greater than 300 msec). Ventricular tachycardia was reinduced and shock energies titrated until cardioversion threshold was obtained. Identical ventricular tachycardia episodes were treated with both methods at each energy level.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1990

[Mutagenesis of vitamin B2 producer by using protoplasts].

Studies on preparation, regeneration and ultraviolet-mutagenesis of protoplasts of vitamin B2 producer Eremothecium aohbyii were reported. By using a complex enzyme system (0.5% snial digestase + 0.5% cellulase), a great number of protoplasts were obtained. Ultraviolet-mutagenesising positive mutation ratio is 14.29%. The HPLC analysis indicated that a lot of mutants were screened by using ultraviolet-mutagenesis mutation of protoplasts, Vitamin B2 produced by the mutant E3 increased 116.4%.

Mutation↗
PubMed1989

[An approach to the dental CAD/CAM (Part 4). Fundamental CAD procedure for the data base].

Studies are currently underway to apply the CAD/CAM system to dentistry and to make prosthetic appliances automatically. This paper reports the basic CAD procedure by using the CAD data base in the previous (part 3) report and gives some modified teeth figures. Mathematically, with Affine transformation, extension, contraction, parallel translation, and rotation of the dental figures are done. In the transformation, the origin of the individual tooth is decided from the mean value of the data base points, and X, Y, Z coordinates are the bucco-lingal, mesio-distal, vertical directions, respectively. This basic transforming procedure reduces the time needed for the CAD procedure.

Computer Graphics↗
PubMedDate not supplied

Quantitative measurements of cerebral metabolic rate of oxygen utilization using MRI: a volunteer study.

Quantitative estimates of cerebral metabolic rate of oxygen utilization using magnetic resonance imaging can have profound implications for the understanding of brain metabolic activity as well as the investigation of cerebrovascular disease. In this study, five normal volunteers were studied. All images were acquired on a Siemens 1.5 T scanner (Siemens Medical Systems Inc, Erlangen, Germany). Cerebral blood flow (CBF) was obtained in vivo with a dynamic imaging approach and the acquired images were post-processed with the singular value decomposition method (SVD). In addition, a multi-echo gradient echo/spin echo sequence was employed to provide MR estimates of oxygen extraction fraction (MR_OEF) in vivo. Subsequently, an absolute measure of MR cerebral metabolic rate of oxygen utilization (MR_CMRO(2)) was obtained in all subjects by taking the product of CBF and MR_OEF. A mean MR_CMRO(2) of 28.94 +/- 3.26 ml/min/100 g and 12.57 +/- 3.11 ml/min/100 g was obtained for gray matter and white matter, respectively, suggesting that the gray matter utilizes more oxygen than white matter under normal physiological conditions. These results yield a gray matter to white matter CMRO(2) ratio of 2.37 +/- 0.37, which is comparable to the reported values in the literature. More studies are needed to further improve on the accuracy as well as shortening the required data acquisition time so that the proposed approaches can be utilized in a routine clinical setting.

Brain↗
PubMedDate not supplied

Intervertebral disk appearance correlated with stiffness of lumbar spinal motion segments.

BACKGROUND AND PURPOSE: Because it diminishes the stiffness of the intervertebral disk, disk degeneration results in abnormal motions of the spine. Therefore, disk degeneration associated with back pain may indicate spinal fusion. The purpose of this study was to correlate the MR appearance and stiffness of lumbar intervertebral disks. METHODS: Eighty-two lumbar spinal segments were imaged with MR. The intervertebral disks were classified as: 1) normal, 2) having transverse or concentric tears of the annulus fibrosus if MR imaging showed only these changes, 3) having radial tears of the annulus fibrosus if MR imaging showed high-intensity zones in the annulus fibrosus or reduced signal intensity in the disk characteristic of radial tears, or 4) having advanced degeneration if MR imaging showed markedly reduced height, large osteophytes, or both. The rotation occurring from the application of a 6.6-Newton-meter (Nm) moment of axial rotational torque was measured kinematically. Average stiffness, in Nm/degree, was calculated as the ratio of the torque to the rotation. RESULTS: Stiffness averaged 7.0 Nm/degree for the normal group; 1.9 Nm/degree for the disks with concentric or transverse tears; 1.7 Nm/degree for disks with radial tears; and 3.1 Nm/degree for disks with advanced degeneration. The differences were statistically significant. CONCLUSION: Concentric, transverse, and radial tears of the intervertebral disk indicate reduced stiffness of the intervertebral disk and increased motions for a unit of applied torque. The most severely reduced stiffness was found in disks with radial tears of the annulus fibrosus. With collapse of the disk space, stiffness increases.

Aged↗