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Biomedical subjects

S Choi

Publications and source records attributed to S Choi.

At least 199 records · Page 11Linked to original sources
PubMed1993

CD4+ lymphocytes are an incomplete surrogate marker for clinical progression in persons with asymptomatic HIV infection taking zidovudine.

OBJECTIVE: To determine the extent to which lymphocytes, particularly those with the CD4 surface antigen, are a surrogate marker for the development of the acquired immunodeficiency syndrome (AIDS) in persons with asymptomatic human immunodeficiency virus (HIV) infection. DESIGN: Analysis of data from the AIDS Clinical Trials Group Protocol 019, a placebo-controlled, double-blind, randomized trial. SETTING: University-based referral centers. PATIENTS: Asymptomatic HIV-infected patients with 500 or fewer CD4+ cells/mm3 at baseline who were given placebo (350 patients) or one of two daily doses of zidovudine (725 patients). MEASUREMENTS: Baseline and interim measurements of CD4+ and other leukocytes were assessed. Patients were followed for progression to AIDS. RESULTS: Patients' lymphocyte levels were correlated with progression to AIDS (P < 0.001; relative risk for each depletion of 50 CD4+ cells/mm3, 1.75; 95% CI, 1.53 to 2.01); however, only a small portion (0% to 37%) of the effect of zidovudine on this progression was statistically explained by its effect on CD4+ lymphocyte levels. A substantial portion of zidovudine's effect on delaying progression to AIDS that was independent of the levels of these markers occurred within the first 16 weeks of therapy. In patients who had not progressed to AIDS by week 16, most of the subsequent zidovudine effect in reducing the risk for progression could be explained by its effect on net CD4+ percent (percentage of CD4+ lymphocytes among all leukocytes) for the first 16 weeks of therapy. CONCLUSION: Levels of CD4+ lymphocytes are an incomplete surrogate marker for progression to AIDS, and the association is especially weak during the first 16 weeks of zidovudine therapy.

Acquired Immunodeficiency Syndrome↗
PubMed1993

Effect of THAM upon outcome in severe head injury: a randomized prospective clinical trial.

Although mortality and morbidity rates from head injury have been reduced substantially by improved prehospital interventions, intensive care, and aggressive management of intracranial pressure (ICP), successful treatment of the primary brain injury has been elusive. In experimental models, tromethamine (THAM) has been effective in treating head injury; this drug acts by entering the cerebrospinal fluid compartment, reducing cerebral acidosis and ICP, and reversing the adverse effects of prophylactic hyperventilation on early recovery. In this randomized prospective clinical trial, THAM was studied to determine if it had beneficial effects in the early management of severe head injuries and if the adverse effects of hyperventilation could be prevented. A total of 149 patients with severe head injury (Glasgow Coma Scale scores of < or = 8) were randomly assigned to either a control or a THAM group. Both groups of patients matched in terms of clinical parameters, including age, sex, number of surgical mass lesions, number in each Glasgow Coma Scale stratum, and first ICP measurement. All patients were treated by a standard management protocol, intubated, mechanically ventilated, and maintained in the pCO2 range of 32 to 35 mm Hg for 5 days. Tromethamine was administered as a 0.3-M solution in an initial loading dose (body weight x blood acidity deficit, average 4.27 cc/kg/hr) given over 2 hours, followed by a constant infusion of 1 ml/kg/hr for 5 days. Outcome was measured at 3, 6, and 12 months postinjury. Although analysis indicated no significant difference in outcome between these two groups at 3 months, 6 months, and 1 year, there was a difference regarding ICP. The time that ICP was above 20 mm Hg in the first 48 hours postinjury was less in patients treated with THAM (p < 0.05). Also, the number of patients requiring barbiturate coma was significantly less in the THAM group (5.48% vs. 18.4%, p < 0.05). The authors conclude that THAM ameliorates the deleterious effect of prolonged hyperventilation, may be beneficial in ICP control, and warrants further study as to the dosage and timing of administration.

Adolescent↗
PubMed1993

Incorporating prior biases in network models of conceptual rule learning.

A series of simulations is reported in which extant formal categorization models are applied to human rule-learning data (Salatas & Bourne, 1974). These data show that there are clear differences in the ease with which humans learn rules, with the conjunctive the easiest and the biconditional the hardest. The original ALCOVE model (an exemplar-based model), a configural-cue model, and two-layer backpropagation models did not fit the rule-learning data. ALCOVE successfully fit the data, however, when prior biases observed in human rule learning were implemented into weights of the network. Thus, current empirical learning models may not fare well in situations in which learners enter the concept-formation situation with preconceived biases regarding the kinds of concepts that are possible, but such biases might nevertheless be captured within these models. By incorporating preexperimental biases, ALCOVE may hold promise as a comprehensive category-learning model.

Attention↗
PubMed1992

Biliary obstruction: evaluation with three-dimensional MR cholangiography.

Three-dimensional (3D) magnetic resonance (MR) projection imaging was evaluated as a noninvasive alternative to direct cholangiography in 12 patients with malignancy-related obstructive jaundice. The 3D images of the bile ducts were formed by subjecting consecutive coronal MR images obtained with a fast imaging method to a maximum-intensity projection algorithm. Dilatation and obstruction of the biliary system were well documented in all cases, and good correlation between findings at 3D MR cholangiography and percutaneous transhepatic biliary drainage performed 0-21 days later was observed.

Adult↗
PubMed1992

Norepinephrine utilization in the hypothalamus of the male rat during adolescent development.

This study examined the influence of adolescent development and pubertal changes in gonadal function on the development of norepinephrine (NE) turnover in the hypothalamus and cerebral cortex of rats from late juvenile to young adult ages. In one study, NE utilization was estimated in intact male rats and in male rats castrated at 14 days of age. NE levels were measured 15, 30, 45, 60, 120, and 240 min after inhibition of catecholamine synthesis at 28, 42, and 70 days of age. In a second study, male rats were made precocious by chronic testosterone exposure over days 14-28 and on the 28th day NE utilization was measured in both the hypothalamus and cerebral cortex. Turnover rates were calculated based on steady-state kinetics. The results indicate that in vivo NE levels and turnover rates in both the hypothalamus and cortex significantly increase from a late juvenile age to adulthood. However, when NE levels measured after synthesis inhibition were expressed as a percentage of the mean basal values, there was a significant effect of age only in the hypothalamus. Hence, the age-related increases in hypothalamic NE turnover appear to reflect age-related changes in NE utilization, whereas the increases in cortical turnover rates reflect the increasing basal levels and not age-related changes in NE utilization. During mid-puberty (42 days), NE utilization in the hypothalamus was markedly different from that observed in this region at either 28 or 70 days. At 28 and 70 days, NE levels decreased to 50% of basal levels by 4 h following synthesis inhibition.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Infrared spectroscopic studies on the phosphatidylserine bilayer interacting with calcium ion: effect of cholesterol.

Fourier transform infrared (IR) spectroscopic studies of phosphatidylserine/cholesterol/Ca2+ complexes are reported using the synthetic phosphatidylserines (PS) 1,2-dioleoyl-sn-glycero-3-phospho-L-serine (DOPS), 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-L-serine (POPS), and 1,2-dimyristoyl-sn-glycero-3-phospho-L-serine (DMPS). IR spectra reveal that cholesterol does not significantly alter the binding nature of Ca2+ to PS molecules; Ca2+ binds to the phosphate ester group of PS in the presence of cholesterol up to 50 mol% as in the case of pure PS bilayers. However, the IR data indicate that the presence of cholesterol induces disorder of the acyl chain packing, increases the degree of immobilization of the interfacial and polar regions, and increases the degree of dehydration of the PS/Ca2+ complexes.

Calcium↗
PubMed1991

[MR cholangiography].

A time-reversed gradient echo pulse sequence (PSIF; Siemens), one of the MR imaging methods based on steady-state free precession of excited spins, makes the bile duct quite bright relative to the surrounding tissue. Using this sequence under breath hold combined with a two or three-dimensional data set and maximum intensity projection method provided fair delineation of the dilated bile duct and the site of its obstruction or stricture. Though the clinical experience is limited, this technique is considered to be of value in the non-invasive evaluation of bile duct system in the patient of obstructive jaundice.

Cholestasis↗
PubMed1991

[Stereoscopic MR cisternography].

A time-reversed gradient echo pulse sequence, one of the MR imaging methods based on steady-state free procession of the excited spins, makes the cerebrospinal fluid (CSF) quite bright relative to the normal brain tissue. Using this sequence combined with a three-dimensional data set and maximum intensity projection method, which provided clear delineation of the spatial distribution of the CSF space in the brain. Though the clinical experience is limited, this technique is considered to be of value in the evaluation of CSF pathology.

Cerebrospinal Fluid↗
PubMed1991

Learning to express motion events in English and Korean: the influence of language-specific lexicalization patterns.

English and Korean differ in how they lexicalize the components of motion events. English characteristically conflates Motion with Manner, Cause, or Deixis, and expresses Path separately. Korean, in contrast, conflates Motion with Path and elements of Figure and Ground in transitive clauses for caused Motion, but conflates motion with Deixis and spells out Path and Manner separately in intransitive clauses for spontaneous motion. Children learning English and Korean show sensitivity to language-specific patterns in the way they talk about motion from as early as 17-20 months. For example, learners of English quickly generalize their earliest spatial words--Path particles like up, down, and in--to both spontaneous and caused changes of location and, for up and down, to posture changes, while learners of Korean keep words for spontaneous and caused motion strictly separate and use different words for vertical changes of location and posture changes. These findings challenge the widespread view that children initially map spatial words directly to nonlinguistic spatial concepts, and suggest that they are influenced by the semantic organization of their language virtually from the beginning. We discuss how input and cognition may interact in the early phases of learning to talk about space.

Concept Formation↗
PubMed1990

[Stereoscopic MR angiography of the abdomen].

We have developed a new method of stereoscopic MR angiography of the abdomen using gradient echo images. Consecutive coronal scanning of the abdomen was performed by fast scan during breath hold. These images were overlapped by means of MR angiography. Then two slightly different views that can give a true stereoscopic effect were constructed. The more precise spatial relationship of the abdominal vessels can be visualized with our new method.

Abdomen↗
PubMed1990

Ascorbic acid uptake by young and aged guinea pig lenses.

The dynamics of in vitro uptake of [14C]-ascorbic acid into intact lenses of young (50 days old) and old (730 days old) guinea pigs was evaluated in this study. Two-dimensional protein gel analysis of [35S]-methionine labeled proteins provided evidence that the isolated lenses were viable throughout the culture period. It was found that the in vitro uptake of ascorbate into these lenses follows similar saturation kinetics for lenses from both age groups. Moreover, the linear uptake rate was identical. Ascorbate transport was inhibited by phloretin, p-chloromercuribenzoate, insulin, glucose and ouabain; however, no inhibition was observed with 2,4-dinitrophenol or NaF. These results suggest that the lenticular ascorbate concentration is regulated by a facilitated diffusion process and it not energy-dependent. Data on ascorbate transport into lenses from aged guinea pigs provide strong evidence that the abnormally low ascorbic acid concentrations in lenses of old mammals is not likely the result of a decreased lenticular uptake ability.

Aging↗
PubMed1990

Congenital glioblastoma multiforme--report of an autopsy case.

A congenital neoplasm arising in the central nervous system is rarely encountered, and the majority of case reports that have dealt with intracranial tumors have been divided almost equally between teratomas and various gliomas. We experienced a rare case of congenital glioblastoma multiforme encountered in a three day-old male infant who presented with hydrocephalus since birth. Post-mortem examination revealed that the tumor seemed to have originated from the right thalamic region extending centrifugally to the cerebral cortex and through the brain-stem down to the cerebellum.

Autopsy↗
PubMed1989

The effects of various load paths and different loads on the load transfer characteristics of the wrist.

An experimental model that incorporated a static positioning frame, pressure-sensitive film, and a microcomputer-based videodigitizing system was used to analyze the effects of different loading pathways and various loads on the contact area and pressures within the wrist joint. There was no statistically significant difference in loading the wrist with comparable weights through the second and third metacarpals, through all five metacarpals, or through weights suspended from the wrist flexor and extensor tendons. A nonlinear relation was discovered between increasing loads and greater overall contact areas. The general distribution of the contact between the scaphoid and the lunate contact areas was consistent at all of the loads tested with 60% of the total contact area involving the scaphoid contact area and 40% involving the lunate contact area. Loads greater than 46 pounds were not found to significantly increase the overall contact areas implying that the cartilage of the wrist joint was maximally compressed at loads of this magnitude. At loads higher than 46 pounds it appears that average high pressures increase in a more direct correlation with the increase in weight. The overall contact area even at the highest loads tested were not more than 40% of the available joint surface. The contact areas were not concentric or symmetric as is characteristic of the incongruance of the radio/triangularfibrocartilage (ulna)/carpal joint.

Adult↗
PubMed1988

Subperiosteal orbital hematoma. An unusual complication of sinusitis.

The orbital complications of paranasal sinus infection are well known to otolaryngologists. However, only a few articles have reported subperiosteal orbital hematoma as one of these complications. It is a rare but well-recognized entity in ophthalmology, usually caused by trauma. A case of subperiosteal orbital hematoma secondary to ethmoidal sinusitis is presented. The relevant clinical characteristics, pathophysiology, and differential diagnosis of subperiosteal orbital hematoma, as well as treatment options, are reviewed and presented as they apply to cases associated with sinusitis.

Ethmoid Sinus↗