Biomedical subjects

R Chua

Publications and source records attributed to R Chua.

At least 37 records · Page 2Linked to original sources

PubMed2000

The cost-effectiveness of teleneurology consultations for patients admitted to hospitals without neurologists on site. 1: A retrospective comparison of the case-mix and management at two rural hospitals.

We are currently evaluating the use of telemedicine for improving the care of patients admitted with neurological symptoms to hospitals that do not have specialist neurologists on site. To do this we have been comparing the outcome of patients admitted to two small hospitals. In one hospital all patients with neurological symptoms are seen by a neurologist at a distance using an interactive video-link transmitting at 384 kbit/s; in the other patients with neurological problems are managed as per usual practices. For the results of this study to be valid, it is essential that the case-mix and process of management for neurological patients are similar at the two hospitals. We therefore compared the case-mix, process of management, and outcome for all patients admitted over a four-month period to either hospital who had been coded using ICD-10 as having a final diagnosis of a neurological condition. No appreciable differences were noted between the two hospitals for measures of case-mix or outcome. Likewise, most measures of process were similar, although there was a significant difference for the overall length of hospital episode between the two hospitals. When patients with prolonged hospital episodes were excluded, or only patients with a diagnosis of headache, epilepsy or transient ischaemic attack were considered (who as a group made up the bulk of neurological admissions), the difference in the length of hospital episode was not significant. It should therefore be possible for us to estimate the effect of telemedicine on the management of patients with neurological problems.

Cohort Studies↗

PubMed2000

A pilot study of telemedicine for new neurological outpatient referrals.

We investigated whether new patients attending a neurological outpatient clinic could be safely managed by neurologists at a distance, using a video-link. In Northern Ireland, a video-link, transmitting at 384 kbit/s, was set up between a neurological centre and a small rural hospital 140 km away. Twenty-five unselected patients who had been referred by their family doctor were assessed by a neurologist using the telemedicine link and then immediately by another neurologist face to face. Examiners were blinded to the results of each other's assessment. In 24 cases the diagnoses made after the telemedicine and face-to-face examinations were identical. There were minor differences between the type and number of investigations requested, and the requirements for treatment and follow-up between the two groups. Disposal method was the same in 21 of the cases. No major organizational difficulties were encountered during the study. The study showed that neurologists can deliver outpatient neurological care to distant patients using telemedicine. This has the potential to allow access to assessment for the large number of neurological outpatients who might otherwise be denied it.

Adult↗

PubMed1999

Changes in posture alter the attentional demands of voluntary movement.

Two simple experiments reveal that the ease with which an action is performed by the neuromuscular-skeletal system determines the attentional resources devoted to the movement. Participants were required to perform a primary task, consisting of rhythmic flexion and extension movements of the index finger, while being paced by an auditory metronome, in one of two modes of coordination: flex on the beat or extend on the beat. Using a classical dual-task methodology, we demonstrated that the time taken to react to an unpredictable visual probe stimulus (the secondary task) by means of a pedal response was greater when the extension phase of the finger movement sequence was made on the beat of the metronome than when the flexion phase was coordinated with the beat. In a second experiment, the posture of the wrist was manipulated in order to alter the operating lengths of muscles that flex and extend the index finger. The attentional demands of maintaining the extend-on-the-beat pattern of coordination were altered in a systematic fashion by changes in wrist posture, even though the effector used to respond to the visual probe stimulus was unaffected.

Acoustic Stimulation↗

PubMed1999

The utilization of visual information in the control of rapid sequential aiming movements.

Two experiments were conducted to examine the role of vision in the execution of a movement sequence. Experiment 1 investigated whether individual components of a sequential movement are controlled together or separately. Participants executed a rapid aiming movement to two targets in sequence. A full vision condition was compared to a condition in which vision was eliminated while in contact with the first target. The size of the first target was constant, while the second target size was varied. Target size had an influence on movement time and peak velocity to the first target. Vision condition and target size did not affect the time spent on the first target. These results suggest that preparation of the second movement is completed before the first movement is terminated. Experiment 2 examined when this preparation occurred. A full vision condition was compared to a condition in which vision was occluded during the flight phase of the first movement. Movement initiation times were shorter when vision was continually available. Total movement time was reduced with vision in two-target condition, but not in a control one-target condition. The time spent on the first target was greater when vision was not available during the first movement component. The results indicate that vision prior to movement onset can be used to formulate a movement plan to both targets in the sequence [Fischman & Reeve (1992).

Adolescent↗

PubMed1999

The clinical utility of CMV surveillance cultures and antigenemia following bone marrow transplantation.

At our institution, the cytomegalovirus (CMV) prophylaxis protocol for allogeneic bone marrow transplant (BMT) recipients who are CMV-seropositive or receive marrow from a CMV-seropositive donor consists of a surveillance bronchoscopy approximately 35 days posttransplant. Patients with a positive surveillance bronchoscopy for CMV receive pre-emptive ganciclovir. In order to determine the utility of other screening methods for CMV, we prospectively performed weekly CMV antigenemia, and blood, urine and throat cultures from time of engraftment to day 120 post-BMT in 126 consecutive patients. Pre-emptive ganciclovir was given to 11/81 patients (13.6%) because of a positive surveillance bronchoscopy for CMV. Results of CMV blood, urine and throat cultures and the antigenemia assay done prior to or at the time of the surveillance bronchoscopy were analyzed for their ability to predict the bronchoscopy result. The antigenemia test had the highest positive and negative predictive values (72% and 96%, respectively). The ability of these tests to predict CMV disease was evaluated in the 70 patients with a negative surveillance bronchoscopy who did not receive pre-emptive ganciclovir. Of 19 cases of active CMV disease, CMV antigenemia was positive in 15 patients (79%) a mean of 34 days preceding symptoms. Blood cultures were positive in 14/19 patients (74%) a mean of 31 days before onset of disease. CMV antigenemia is useful for predicting the surveillance bronchoscopy result, and also predicts the development of CMV disease in the majority of patients missed by the surveillance bronchoscopy.

Adolescent↗

PubMed1999

Molecular characterization of a nosocomial outbreak of human respiratory syncytial virus on an adult leukemia/lymphoma ward.

Although nosocomial transmission of human respiratory syncytial virus (HRSV) and its effect on morbidity and mortality among immunocompromised adults are well recognized, few studies have applied molecular techniques to differentiate nosocomial from community-acquired infections. Between January and April 1997, an outbreak of HRSV occurred among adult patients in a leukemia/lymphoma ward. Among 45 hospitalized patients undergoing bronchoscopy for investigation of acute respiratory illness, 8 were identified with HRSV infection. One infected patient developed symptoms before admission and was thought to be the index case. However, subsequent sequencing of 7 HRSV isolates identified 2 distinct genotypes, GA5 (1 case) and GB3 (6 cases). The 6 GB3 isolates could be further differentiated into 2 strains with identical nucleotide sequences that differed from each other and from 14 community HRSV isolates. Instead of a single nosocomial outbreak of HRSV, multiple introductions of HRSV likely occurred with distinct lines of nosocomial transmission.

Adult↗

PubMed1999

Multicenter comparison of the digene hybrid capture CMV DNA assay (version 2.0), the pp65 antigenemia assay, and cell culture for detection of cytomegalovirus viremia.

We compared the Digene Hybrid Capture CMV DNA Assay version 2.0, the pp65 antigenemia assay, traditional tube culture, and shell vial culture for the detection of cytomegalovirus (CMV) viremia in several patient populations at three centers. Of 561 blood specimens collected from 402 patients, complete clinical and laboratory data were available for 489. Using consensus definitions for true positives and true negatives, the sensitivities of the Hybrid Capture assay, antigenemia, shell vial, and tube culture were 95, 94, 43, and 46%, respectively. The specificities of the Hybrid Capture assay and antigenemia were 95 and 94%, respectively. At all three study sites, the detected level of CMV viremia was significantly higher with the Hybrid Capture assay or antigenemia than with shell vial and tube culture. In a group of 131 healthy nonimmunosuppressed volunteers, the Hybrid Capture assay demonstrated a specificity of over 99%. The Hybrid Capture assay is a standardized assay that is simple to perform and can utilize whole blood specimens that have been stored for up to 48 h. The high sensitivity and specificity of the Hybrid Capture assay along with its simplicity and flexibility make it a clinically useful assay for the detection of CMV viremia in immunocompromised or immunosuppressed patients. Further evaluation to determine its role in predicting CMV disease and for monitoring the therapeutic response to anti-CMV therapy is needed.

Adolescent↗

PubMed1996

Retro-retinoids in regulated cell growth and death.

Vitamin A serves as a prohormone from which three classes of active metabolites are derived: the aldehydes, the carboxylic acids, and the retro-retinoids. Although these three classes are united under the rubric of signal transduction, they act by different molecular mechanisms: the 11-cis-retinaldehydes combine with opsin to form the universal visual pigments and the retinoic acids form ligands for transcription factors, whereas the retro-retinoids, as shown here, intersect with signal transduction at a cytoplasmic or membrane site. The retro-retinoid, anhydroretinol (AR), has long been known to act as a growth inhibitor in lymphocytes, whereas 14-hydroxy-4,14-retro-retinol (14-HRR) is required for normal lymphocyte proliferation. A mutually reversible relationship exists between these two retro-retinoids as one can reverse the effects of the other when given in pharmacological doses. The common explanation for reversible inhibition is competition for a shared receptor. We now provide evidence that when AR is given to T cells unmitigated by 14-HRR, rapid cell death can occur. The circumstances are closely related to nonclassical forms of apoptosis: within 2 h of AR administration the T cells undergo widespread morphological changes, notably surface blebbing and ballooning and, inevitably, bursting. In contrast, nuclear changes are comparatively mild, as indicated by absence of chromatin condensation and overt DNA cleavage to discrete nucleosomal fragments, although DNA nicks are readily discernible by terminal deoxynucleotidyl transferase assay. What further distinguishes the AR-induced form of apoptosis from classical ones is a lack of requirements of messenger RNA and protein synthesis, suggesting that the events leading to cell death are primarily initiated and play themselves out in the cytoplasm. This view is further reinforced by the finding that herbimycin A can prevent the onset of programmed cell death. The importance of our findings is that they strongly suggest a second messenger role for vitamin A metabolites in the cytoplasmic realm that has not been seen previously. These findings are entirely compatible with a general notion that in a cell requiring multiple coordinated signals for survival, the provision of an unbalanced signal can initiate programmed cell death. Collectively, our data also challenge the paradigm that retinoids (outside vision) solely mediate their function via the steroid/ retinoic acid receptor family of nuclear transcription factors. Instead, a mode of action in the cytoplasmic realm akin to one attributed to other small lipophilic second messenger molecules, such as diacyl glycerol or ceramide, may apply to retro-retinoids.

Animals↗

PubMed1996

A mucopyocele of the clivus: case report.

OBJECTIVE AND IMPORTANCE: There are increasing reports of nasal sinus mucopyoceles eroding the base of the cranium and causing the rapid onset of neurological complications. Uncommon presentations can mimic tumors, but the infectious nature mandates an urgent surgical decompression. It is important to document these uncommon presentations. CLINICIAL PRESENTATION: A mucopyocele of the clivus is reported in a patient with a frequent history of sinusitis. Diplopia caused by an acute sixth nerve palsy prompted the radiological diagnosis with computed tomography and magnetic resonance imaging. INTERVENTION: Transsphenoidal drainage of the lesion lead to marked improvement in the patient. CONCLUSION: This is the third reported case of a clival mucocele. Mucoceles of nasal sinuses can erode intracranially, causing neurological sequalae, and clival involvement is extremely rare. Early drainage leads to marked improvement.

Adult↗

PubMed1996

Evaluation of the Digene Hybrid Capture System for detection and quantitation of human cytomegalovirus viremia in human immunodeficiency virus-infected patients.

The Digene Hybrid Capture System (DHCS) is a solution hybridization antibody capture assay for the chemiluminescent detection and quantitation of cytomegalovirus (CMV) DNA in leukocytes. This assay was compared with the CMV antigenemia assay and shell vial and tube cultures for the detection of CMV in 234 blood specimens from 72 patients with human immunodeficiency virus. Intra- and interrun precision of the DHCS assay gave coefficients of variation of 17.8 and 16.3%, respectively. The correlation coefficient for the quantitative results obtained by the DHCS assay and the antigenemia assay was 0.911 (95% confidence interval, 0.885 to 0.930). Agreement between the DHCS assay and the other three assays ranged from 83 to 86%. The DHCS assay detected 71, 87, and 84% of specimens that were positive by antigenemia, shell vial cultures, and tube culture, respectively. A total of 92% of specimens that were positive by the DHCS assay were also positive by at least one of the other assays. Evaluation of the usefulness of quantitation of CMV DNA by using the DHCS assay and its correlation with clinical disease demonstrated that, with some exceptions, patients with clinical CMV disease tended to have high levels of DNA whereas asymptomatic patients tended to have low or undetectable levels. Overall, the DHCS assay provided a rapid, quantitative, and objective measure of CMV activity in leukocytes, but results did not always correlate with clinical disease.

AIDS-Related Opportunistic Infections↗

PubMed1995

13,14-Dihydroxy-retinol, a new bioactive retinol metabolite.

Deprivation of vitamin A (retinol) leads to reduced potential of B cell proliferation and nearly complete block of T cell activation in vitro. Retinol, which is thought to function as a pro-hormone, is enzymatically converted into intracellular messenger molecules. Thus, 14-hydroxy-retro-retinol (14-HRR) is an intracellular messenger molecule linked to activation and growth regulation of lymphocytes; whereas, anhydroretinol, another natural retro-retinoid, is an antagonist of 14-HRR effects. In this article, we describe the isolation, structure determination, synthesis, and biological properties of a new intracellular retinol derivative, 13,14-dihydroxy-retinol (DHR), which also supports the viability of retinol-deprived lymphocytes. DHR is found in numerous cell lines representing a large cross-section of tissues and animals from insects to mammals. In T lymphocytes the production of DHR and 14-HRR is up-regulated by phorbol ester. DHR is converted to 14-HRR by mild acid treatment, but not by cells; therefore DHR is not a biosynthetic intermediate in the conversion of retinol to 14-HRR. DHR is a distinct end point of retinol metabolism. Although it is linked to cell proliferation, its biological role remains to be determined.

Cell Line↗

PubMed1995

Contributions of experience to the development of musical processing in infancy.

Full-term infants' performance in detection of melodic alterations appeared to be influenced by perceptual experience from 6 months to 1 year of age, and an experiment with infants born prematurely supported the hypothesis that experience affects music processing in infancy. These findings suggest parallel developmental tendencies in the perception of music and speech that may reflect general acquisition of perceptual abilities for processing of complex auditory patterns. This acquisition may contribute to the cultural enfranchisement of infants through perceptual experience.

Attention↗

PubMed1995

The preparation of aiming movements.

Three experiments are reported in which subjects made rapid aiming movements to visual targets with their left and right hands. In Experiments 1 and 3, a precue protocol was employed. In the "simple" reaction time condition, subjects were precued with complete information concerning the target position. In the four-choice condition, subjects were precued with partial information, indicating a subset of four possible target positions. In the eight-choice condition, advance information regarding the target position was entirely ambiguous. Results indicated that when subjects were provided with unspecific advance information concerning the position of the target, and thus were unable to partially prepare movements prior to the imperative stimulus, a left hand advantage for speed of initiation was obtained. When complete advance information was available, reaction times for the left and right hands were equivalent. The left hand advantage in choice conditions was eliminated when the accuracy of response execution was emphasized and subjects were afforded the opportunity for "on-line" preparation (Experiment 3). These data are discussed in relation to the role of the right hemisphere in the preparation of movement.

Adult↗

PubMed1995

The influence of target perturbation on manual aiming asymmetries in right-handers.

Ten right-handed subjects performed 100 target-aiming movements with each hand. These movements were directed toward a small target on the midline. On 60% of the trials, the target remained stationary. On other randomly placed trials, the target "jumped" to a location 3 cm to the right (20%) or left (20%) of its original position when the cursor had travelled 6.5 cm. Although no hand differences were evident in the control condition, the right hand acquired the new target location more quickly than the left hand when the target was perturbed in either direction. Kinematic data revealed that this advantage was not due to initiating an adjustment to the initial movement more rapidly, but rather less time decelerating the corrective movement. Movement adjustments on perturbed trials were implemented more rapidly in left space than right space independent of the hand doing the aiming. These asymmetries may reflect the differential role of the two cerebral hemispheres in the control of goal-directed movements.

Female↗

PubMed1995

Evaluation of the automated vitek immunodiagnostic assay system (VIDAS) for the detection of measles (rubeola) IgG antibodies.

BACKGROUND: The VIDAS MSG assay is a rapid, automated assay system for the detection of measles antibodies which has not yet been fully evaluated. OBJECTIVES: To compare the VIDAS MSG assay with hemagglutination inhibition (HAI) and a commercial enzyme immunoassay (EIA) for the determination of measles immune status. STUDY DESIGN: Four hundred and seventy-seven serum samples collected from hospital employees for pre-employment screening were tested for measles antibodies using the VIDAS MSG assay and the results compared with those obtained by HAI and EIA. Intra-and inter-assay precision runs of the VIDAS instrument were evaluated using the positive standard provided by the manufacturer. RESULTS: The sensitivity of the VIDAS assay compared to HAI and EIA was 96.4% and 96.7%, respectively. The specificity of the VIDAS assay, when grouping equivocal with negative results was 77.6% and 100% compared to HAI and EIA respectively. The co-efficient of variation for both precision runs was less than 10%, indicating good reproducibility. CONCLUSIONS: The VIDAS MSG assay system is rapid and less labour intensive than HAI and manual EIA for the detection of measles antibody. The significance of equivocal results is not known, but may represent low, non-protective antibody levels. Testing of equivocal samples using another test may provide a definitive (positive or negative) result, but the degree of protection afforded by a positive result is not known. Alternatively, equivocals may be grouped with negatives for exposure or vaccination purposes. This may result in overuse of vaccine if the VIDAS MSG assay is used to determine immune status in screening programs such as pre-employment of hospital staff.

Journal Article↗

PubMed1995

Optimizing the use of vision in manual aiming: the role of practice.

The purpose of this study was to determine how subjects learn to adjust the characteristics of their manual aiming movements in order to make optimal use of the visual information and reduce movement error. Subjects practised aiming (120 trials) with visual information available for either 400 msec or 600 msec. Following acquisition, they were transferred to conditions in which visual information was available for either more or less time. Over acquisition, subjects appeared to reduce target-aiming error by moving to the target area more quickly in order to make greater use of vision when in the vicinity of the target. With practice, there was also a reduction in the number of modifications in the movement. After transfer, both performance and kinematic data indicated that the time for which visual information was available was a more important predictor of aiming error than the similarity between training and transfer conditions. These findings are not consistent with a strong "specificity of learning" position. They also suggest that, if some sort of general representation or motor programme develops with practice, that representation includes rules or procedures for the utilization of visual feedback to allow for the on-line adjustment of the goal-directed movement.

Adult↗

PubMed1995

Intermittent vision and discrete manual aiming.

This study was designed to assess how the precision requirements of discrete aiming movements affect the utility of brief visual samples provided during execution of movement. Subjects pointed with a hand-held stylus to targets with indices of difficulty of 3, 4, 5, and 6 bits with full vision, no vision, and in conditions in which 20-msec. visual samples were provided every 80, 140, or 200 msec. While intermittent vision required slightly longer movement times for targets with a high index of difficulty, subjects' accuracy was similar to the full-vision situation. Moreover, with intermittent vision, the movement trajectories resembled the full-vision and not the no-vision situation. It would appear that brief visual samples of the movement environment are sufficient for reasonably precise closed-loop control.

Adult↗

PubMed1995

Cerebral specialization for spatial processing in adults with Down syndrome.

Cerebral specialization for spatial processing in adults with Down syndrome was examined. In the first experiment, both control and right-handed subjects with Down syndrome exhibited no lateral advantage in a dihaptic shape-matching task, whereas left-handed subjects with Down syndrome displayed an expected left-hand advantage. In a visual field dot enumeration task in the second experiment, all groups exhibited left-field superiority. Thus, atypical cerebral organization of function in adults with Down syndrome appears to be confined to speech perception (Elliott & Weeks, 1993).

Brain↗