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Biomedical subjects

R C Chan

Publications and source records attributed to R C Chan.

At least 19 recordsLinked to original sources
PubMed1999

Angiotensin-converting enzyme inhibition as antiatherosclerotic therapy: no answer yet. QUIET Investigators. QUinapril Ischemic Event Trial.

Angiotensin-converting enzyme inhibitors have proven to be of clinical benefit in congestive heart failure. Whether they also provide benefit to patients with coronary artery disease in the absence of congestive heart failure via an antiatherosclerotic mechanism is a question the QUinapril Ischemic Event Trial quantitative coronary angiography (QCA) study attempted to answer: 1,750 patients with normal left ventricular function who were undergoing coronary angiography and angioplasty were randomized to 20 mg/day of quinapril versus placebo and followed for 3 years for cardiac end points. A randomly selected subgroup of the total cohort underwent follow-up angiography. The primary QCA end point was the categorical designation of progression versus nonprogression, defined either by QCA or by a cardiac event in patients selected for the QCA trial who had no usable follow-up x-ray film. Secondary end points in patients with 2 angiograms were: new stenosis development, change in minimum lumen diameter index, and change in percent diameter stenosis index. There were 119 progressors among 243 placebo-treated patients (49%) and 111 progressors among 234 quinapril-treated patients (47%) (p = NS). There were 44 patients with new stenosis development in the placebo group (19%) and 50 (22%) in the quinapril group (p = NS). Change in minimum lumen diameter index was -0.21+/-0.03 mm in the placebo group and -0.18+/-0.03 mm in the quinapril group (p = NS). Finally, change in percent diameter stenosis index was +5.1+/-1.0 in the placebo group and +3.5+/-1.0 in the quinapril group (p = NS). Potential confounders of this trial are presented and discussed.

Adult↗
PubMed1999

Increased CD4+ T-lymphocyte senescence fraction in advanced human immunodeficiency virus type 1 infection.

Human immunodeficiency virus type 1 (HIV-1) infection is accompanied by peripheral CD4+ T-cell losses. CD4+ T-cell numbers often increase during antiviral treatment of acquired immune deficiency syndrome (AIDS), however, alterations in the CD4+ T-cell repertoire have not been completely corrected for these patients. Such individuals remain at increased risk of infection. Although senescence of the CD4+ T cells has not been adequately evaluated for advanced HIV-1 infection, hypothetically, replicative senescence could complicate therapeutic reconstitution of the CD4+ T cells in AIDS. In this study, correlates of replicative senescence, terminal restriction fragment (TRF) length and percentage short (< 5.0 kb) telomeric DNA (senescence fraction), were measured for the CD4+ T cells of HIV-1-infected patients with peripheral CD4+ T-cell counts of < 200/mm3. The results show that for advanced HIV-1 infection the TRF length of the CD4+ T cells is decreased (P < 0.01), and the senescence fraction increased (P < 0.05), when compared with uninfected controls. These findings suggest that cellular senescence may contribute to disruption of CD4+ T-cell diversity observed following the therapeutic, immunologic reconstitution of AIDS.

Adult↗
PubMed1998

Cubital tunnel syndrome: diagnosis by high-resolution ultrasonography.

The purpose of this study was to evaluate the morphologic changes in the ulnar nerve in cubital tunnel syndrome with high-resolution ultrasonography. The mean values of the short axis (cm) x long axis (cm) at the arm, epicondyle, and forearm levels were 0.057 +/- 0.01, 0.068 +/- 0.019, and 0.062 +/- 0.01 in control group; 0.069 +/- 0.04, 0.139 +/- 0.06, and 0.066 +/- 0.023 in the symptomatic side in patients with cubital tunnel syndrome; and 0.063 +/- 0.029, 0.068 +/- 0.029, and 0.057 +/- 0.012 in the normal side in patients with cubital tunnel syndrome. No significant difference was found in the area (short axis x long axis) of the ulnar nerve at the arm, epicondyle and forearm levels between the left and right ulnar nerve in the control group and between the control group and the normal side in symptomatic patients. However, the mean value of the area of the ulnar nerve at the epicondyle level in symptomatic patients was significantly larger than that of the control group and that of the contralateral side in patients, and the P value was less than 0.001. High resolution ultrasonography can detect morphologic changes in the ulnar nerve accurately, and it could therefore be useful as a screening and even follow-up modality in patients with cubital tunnel syndrome.

Adult↗
PubMed1998

Heart rate variability as an assessment of acute rejection after heart transplantation.

BACKGROUND: Orthotopic heart transplantation is currently a widely accepted treatment for end-stage heart disease. Early detection and adequate therapy of acute rejection increases the survival rate. Currently, the most reliable technique for the detection of acute cardiac rejection (ACR) is endomyocardial biopsy (EMB), which is an invasive procedure with some intrinsic problems. The purpose of this study was to assess heart rate variability (HRV) as a noninvasive procedure for frequent monitoring of ACR. METHODS: Six consecutive orthotopic cardiac transplant recipients were prospectively recruited into this study. The follow-up periods ranged from seven to 359 days (median; 146 days). A precordial electrocardiograph (ECG) of 288 seconds was recorded at 5:00 PM before the patient underwent EMB. The results from the frequency domain analysis of the ECG signals were evaluated to correlate with the findings from EMB. RESULTS: Of 48 EMBs, 42 (87.5%) showed no evidence of rejection, four showed mild focal ACR (EMB grade 1A), one mild diffuse ACR (1B) and one moderate plurifocal ACR (3A). There was no moderate focal ACR (2), severe diffuse ACR (3B) or severe ACR (4). Correlation between ACR (3A) and a significant increase in HRV with a corresponding 'broad-band' or bell-shaped pattern on the power spectrum was noted. CONCLUSIONS: Our study in consecutive cardiac transplant recipients indicates that the changes in HRV provide clinicians with a new concept for heart transplant monitoring. Further study is needed to verify clinical utility.

Acute Disease↗
PubMed1997

Intraoperative monitoring of skin temperature changes of hands before, during, and after endoscopic thoracic sympathectomy: using infrared thermograph and thermometer for measurement.

OBJECTIVE: To investigate the roles of the second and third thoracic spinal segments in the preganglionic sympathetic innervation of the hand, and to compare skin temperature changes between thenar and other parts of palm before, during, and after endoscopic thoracic sympathectomy. DESIGN: Twelve patients, four women and eight men, with severe palmar hyperhydrosis underwent endoscopic thoracic sympathectomy. The T3 segment was identified and dissected first, followed by T2 segment extirpation. Skin temperature changes of the hand were assessed by thermograph and thermometer simultaneously before, during, and after sympathectomy. Sympathetic skin responses were undertaken 1 day preoperatively and followed up 6 months postoperatively. SETTING: An electrophysiological laboratory and operating room in a national medical center. SUBJECTS: Twelve patients who sustained a profound degree of palmar hyperhydrosis. INTERVENTIONS: Skin temperature differences of the hands were measured by infrared thermograph and thermometer before, during, and after endoscopic thoracic sympathectomy. MAIN OUTCOME MEASURES: Group's average temperature differences, and sympathetic skin response (all or none response). RESULTS: The T2 spinal segment is thought to be the main source of sympathetic outflow to the sweat glands of the hand. The group's average temperature changes were significantly higher at the 2nd through 5th fingers' tips than at the thenar after completion of T2 extirpation (p < .005). CONCLUSIONS: Intraoperative monitoring of palmar skin temperature, as judiciously measured by infrared thermograph, yields useful information about the locations of the sympathetic segments and confirmation of their entire ablation by endoscopic thoracic sympathectomy.

Adolescent↗
PubMed1997

The polypyrimidine tract binding protein binds upstream of neural cell-specific c-src exon N1 to repress the splicing of the intron downstream.

The neural cell-specific N1 exon of the c-src pre-mRNA is both negatively regulated in nonneural cells and positively regulated in neurons. We previously identified conserved intronic elements flanking N1 that direct the repression of N1 splicing in a nonneural HeLa cell extract. The upstream repressor elements are located within the polypyrimidine tract of the N1 exon 3' splice site. A short RNA containing this 3' splice site sequence can sequester trans-acting factors in the HeLa extract to allow splicing of N1. We now show that these upstream repressor elements specifically interact with the polypyrimidine tract binding protein (PTB). Mutations in the polypyrimidine tract reduce both PTB binding and the ability of the competitor RNA to derepress splicing. Moreover, purified PTB protein restores the repression of N1 splicing in an extract derepressed by a competitor RNA. In this system, the PTB protein is acting across the N1 exon to regulate the splicing of N1 to the downstream exon 4. This mechanism is in contrast to other cases of splicing regulation by PTB, in which the protein represses the splice site to which it binds.

Animals↗
PubMed1996

Baseline clinical and angiographic data in the Quinapril Ischemic Event (QUIET) Trial.

The QUinapril Ischemic Event Trial (QUIET) is the first prospective, double-blind, placebo-controlled trial to investigate the long-term antiatherosclerotic effects of angiotensin-converting enzyme inhibition. Normotensive, nonhyperlipidemic subjects (1,750) with normal left ventricular systolic function were randomly assigned to treatment or placebo at percutaneous transluminal coronary angioplasty (PTCA). The primary end point is time to first cardiac ischemic event. Baseline clinical characteristics are (mean +/- SD): age 58 +/- 9 years; blood pressure 123 +/- 15/74 +/- 10 mm Hg; low density lipoprotein cholesterol 124 +/- 27 mg/dL; high density lipoprotein cholesterol 37 +/- 10 mg/dL; and triglycerides 167 +/- 91 mg/dL. In addition, 81% are men; 22% are current smokers; 49% give a history of myocardial infarction. Baseline angiographic characteristics are (mean +/- SD): left ventricular ejection fraction 59% +/- 11%; per patient diameter stenosis (excluding the PTCA segment) 49% +/- 31%; 8.9 +/- 3.5 analyzable segments per patient (excluding the PTCA segment), 3.8 +/- 2.3 of which have visible stenosis. Including the PTCA segment, 52% have single vessel disease and 48% have multivessel disease. Baseline angiographic data for non-PTCA segments will be correlated with cardiac ischemic events which occur after 6 months. Up to 500 subjects will undergo follow-up angiography with quantitative coronary angiographic analysis (QCA) of baseline and follow-up films. The primary QCA end point will be per-patient categorical designation as progressor or nonprogressor based on the presence or absence of > or = 400 microns narrowing in > or = 1 vessels that did not undergo PTCA.

Adult↗
PubMed1996

Guillain-Barré syndrome: an unusual complication after snake bite.

The mortality rate of the Formosan krait bite has been reported to be 23%; death is from respiratory paralysis caused by neuromuscular junctions being blocked by bungarotoxin. This article presents the first case report of Guillain-Barré syndrome after snake envenomization. The patient presented with symmetric paresis and sensory signs in the upper and lower limbs, autonomic dysfunction, facial nerve involvement, and mild elevated cerebrospinal fluid protein at about 4 weeks after the bite. Electrodiagnostic studies revealed profound sensory and motor polyneuropathy. Repeated electrophysiologic findings confirmed nerve regeneration. The patient reached satisfactory functional outcome after a short-term intensive rehabilitation program despite severe axonal degeneration. This article also discusses the possible mechanism of immunopathogenesis of Guillain-Barré syndrome after krait bite.

Activities of Daily Living↗
PubMed1996

Ultrasound cardioscopy: embarking on a new journey.

OBJECTIVE: To present the results of investigation of a new application of invasive ultrasonography-ultrasound cardioscopy, a procedure in which a self-contained ultrasound device is capable not only of producing an under-blood field of view but also of delivering diagnostic and therapeutic tools. DESIGN: Twenty adult mongrel dogs were studied with the ultrasound cardioscopy device during experimental catheter ablation procedures. MATERIAL AND METHODS: A rigid prototype probe, 34 cm long and 8 mm in diameter with a 7-MHz side-viewing transducer at the tip and an 8-F diameter tool delivery port, was introduced through the right external jugular vein into the right heart chambers. Remote and device-directed ablation procedures were monitored. Subsequently, the canine hearts were excised and examined. RESULTS: The self-contained cardioscopy device with a contained ablation catheter could both direct and visualize a specified ablation injury. Under-blood observation of the details of the ablation procedure was possible. Although a learning curve existed for appropriate manipulation of the device, inspection of the excised hearts showed that the size of the injury was accurately predicted with use of ultrasound cardioscopy. CONCLUSION: Ultrasound cardioscopy is a promising means of performing precise under-blood diagnostic and therapeutic maneuvers.

Animals↗
PubMed1996

Hepatitis C virus is not recoverable from liver tissue in cryptogenic cirrhosis: failure to identify hepatitis C virus-RNA using reverse transcription-mediated polymerase chain reaction.

Polymerase chain reaction (PCR) has been used to study liver biopsy tissue in patients with known or suspected hepatitis C virus (HCV). Recent studies of cryptogenic cirrhosis using PCR have been based on study of sera, and HCV has not been shown. The failure to show HCV in patients so studied has left unanswered the question of whether or not patients with cryptogenic cirrhosis could still harbor the virus in the liver. The authors studied liver tissue, obtained at the time of orthopic liver transplantation from 10 patients clinically diagnosed as having end-stage liver disease without demonstrable origin, so-called cryptogenic cirrhosis, using reverse transcription (RT)-PCR to try to recover HCV-RNA. Formalin-fixed, paraffin-embedded tissue was used. For comparison, the authors also studied similarly obtained samples from 10 patients with typical hepatitis C-associated cirrhosis and 10 patients with end-stage liver disease resulting from autoimmune hepatitis. The authors recovered HCV-RNA from 9 of 10 livers from patients with cirrhosis resulting from HCV, and 3 of 10 livers from patients with autoimmune hepatitis. HCV-RNA was not recovered from any of the livers of the 10 patients designated as having cryptogenic cirrhosis.

Adolescent↗
PubMed1996

Rapid high performance liquid chromatographic assay for antifungal agents in human sera.

Serum concentration of seven antifungal agents, amphotericin B, 5-flucytosine, ketoconazole, fluconazole, itraconazole, miconazole and econazole were assayed using a single step sample preparation and an isocratic High Performance Liquid Chromatography (HPLC) procedure based on three mobile phases of similar components. Our method was simple, flexible and rapid, the assays being completed within half an hour. The method showed high reproducibility, good sensitivity with detection limits of 0.078 to 0.625 mg/L except for miconazole and econazole, and high recovery rates of 86-l05%. Out of 24 therapeutic agents tested only aztreonam and trimethoprim were found to interfere with the assay of 5-flucytosine and fluconazole respectively, using this protocol. HPLC assay should be useful in the clinical laboratory for monitoring patients on antifungal therapy.

Amphotericin B↗
PubMed1996

Power spectrum analysis of EMG at different voluntary efforts in normal subjects.

BACKGROUND: In the previous studies, the results from power spectrum frequency changes at different sustained forces have been quite conflicting. This was the result of enormous changing in firing rate and motor units recruited; these were deciding factors of electromyographic power spectrum. The aim of this study was to investigate the characteristics of rate coding and electromyograph (EMG) interference pattern in two EMG-computer sets. METHODS: Thirty-nine healthy subjects were included in our study. Each was in a relaxed sitting position with forearm, wrist, and metacarpophalangeal joints fixed by straps. Two surface electrodes were attached to the muscle belly of extensor digitorum communis. EMG signals were processed at 10%, 25%, 50% and 100% of maximal voluntary contraction (MVC) using visual feedback from a dynamometer. RESULTS: The amplitude in dB remained constant at different isometric forces. The rate-coding parameters showed non-significant decrease as the percentage of MVC increased, ashereas the time-domain parameters revealed significant increase with stepwise increase in force. CONCLUSIONS: EMG power spectrum analysis provides an easy, painless way of assessing global recruitment/rate descriptions of motor units.

Adult↗
PubMed1995

The generally expressed hnRNP F is involved in a neural-specific pre-mRNA splicing event.

The proteins and RNA regulatory elements that control tissue-specific pre-mRNA splicing in mammalian cells are mostly unknown. In this study, a set of proteins is identified that binds to a splicing regulatory element downstream of the neuron specific c-src N1 exon. This complex of proteins bound specifically to a short RNA containing the regulatory sequence in neuronal extracts that splice the N1 exon. It was not seen in non-neuronal cell extracts that fail to splice this exon. UV-cross-linking experiments identified a neuron-specific 75-kD protein and several nontissue-specific proteins, including the 53-kD heterogeneous nuclear ribonucleoprotein F (hnRNP F), as components of this complex. Although present in both extracts, hnRNP F binds tightly to the RNA only in the neuronal extracts. A mutation in the regulatory RNA sequence, that inhibits N1 splicing in vivo, abolished formation of the neuron-specific complex and the binding of the neuron-specific 75-kD protein. Competition experiments in the two extracts show that the binding of the neuronal protein complex to the src pre-mRNA is required to activate N1 exon splicing in vitro. Antibody inhibition experiments indicate that the hnRNP F protein is a functional part of this complex. The assembly of regulatory complexes from both constitutive and specific proteins is likely to be a general feature of tissue-specific splicing regulation.

Animals↗
PubMed1995

Neuromuscular injury during limb lengthening: a longitudinal follow-up by rabbit tibial model.

Limb lengthening has been used for many years to correct congenital anomalies and unequal leg length. Some surgeons focus on bone genesis and anatomical alignment, and pay less attention to potential damage to muscles, nerves, and vessels during the gradual stretching. In an attempt to identify the presence and extent of neuromuscular abnormalities during leg elongation, a rabbit tibial osteotomy model was used for 17 male rabbits, and fixation-distraction apparatuses were applied at a rate of 1 mm lengthening per day. Electrophysiological test was used to investigate both hindlegs every 2 weeks for 8 weeks after surgery. Needle electromyography (EMG) showed denervation in the elongated legs with 14 limbs having peroneal nerve damage and 12 limbs having damage to the posterior tibial nerve. Nerve regeneration signs were found in ankle extensors and flexors beginning 2 weeks postoperatively. The results of nerve conduction studies revealed significant differences (P < .05) in CMAP amplitude (mV) and area (mV.mS) in ankle extensors and flexors between elongated and nonelongated legs. There was no significant side-to-side difference with respect to distal latency. The incidence of neuromuscular injury was common in these rabbits. These findings suggest that early detection of neuromuscular involvement by electrophysiological test is a practical way to assess neuromuscular function during limb lengthening.

Animals↗
PubMed1995

The effect of age on the presentation of patients with tuberculosis.

OBJECTIVE: To study the differences in presentation of young and elderly patients with tuberculosis (TB). DESIGN: Between January 1991 and December 1992 all patients with TB diagnosed at the Department of Medicine, Prince of Wales Hospital, were recruited into the study. The following data were collected: body weight, coexisting medical problems, presenting symptoms, radiographic appearance, sputum results for acid-fast bacilli and peripheral blood biochemistry. The patients were divided into young ( < 65 years) and elderly ( > or = 65 years) age groups and differences in presentation of the 2 groups were analysed. RESULTS: There were 78 young and 94 elderly patients with TB. The elderly patients had lower body weight, less haemoptysis but more non-specific complaints (25% vs 1%, P = 0.001). The chest radiographs in the elderly patients were less likely to have upper lobe infiltration (9% vs 37%, P = 0.0002) but more commonly had extensive infiltration of both lungs (17% vs 2%, P = 0.014). The only biochemical abnormality that was more common in the elderly was a low serum albumin level (64% vs 45%, P < 0.05). CONCLUSION: Elderly patients with TB are more likely to present with non-specific complaints and atypical radiographic appearance. A high index of suspicion and prompt investigations in elderly patients may allow for earlier diagnosis and treatment of TB.

Adolescent↗
PubMed1995

The constituent structure of subjective memory questionnaires: evidence from multiple sclerosis.

A number of different instruments have been devised for investigating individual differences in memory on the basis of subjective reports. One such questionnaire was mailed to individuals on a register of patients with multiple sclerosis, a condition that is known to be associated with objective impairments in cognition and memory. A similar questionnaire was enclosed to be completed about each patient by a close relative. The patients' and relatives' responses were found to share a factor structure identifying memory problems in five areas: receptive communication, route finding, absent-mindedness, face recognition, and expressive communication. These were dominated by a single second-order factor representing a global subjective memory impairment. There were some minor differences between the patients and relatives in their factor scores, but there was generally a high degree of concordance in their responses.

Adult↗
PubMed1995

Conserved intron elements repress splicing of a neuron-specific c-src exon in vitro.

The neuron-specific N1 exon of the mouse c-src transcript is normally skipped in nonneuronal cells. In this study, we examined the sequence requirements for the exclusion of this exon in nonneuronal HeLa cell nuclear extracts. We found that the repression of the N1 exon is mediated by specific intron sequences that flank the N1 exon. Mutagenesis experiments identified conserved CUCUCU elements within these intron regions that are required for the repression of N1 splicing. The addition of an RNA competitor containing the upstream regulatory sequence to the HeLa extract induced splicing of the intron downstream of N1, indicating that the competitor sequence binds to splicing repressor proteins. The similarities between this mechanism for src splicing repression and the repression of other regulated exons point to a common role of exon-spanning interactions in splicing repression.

Alternative Splicing↗