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Biomedical subjects

L K Tan

Publications and source records attributed to L K Tan.

At least 19 recordsLinked to original sources
PubMed1995

Glycerol versus radiofrequency rhizotomy--a comparison of their efficacy in the treatment of trigeminal neuralgia.

Ever since the anatomical basis of trigeminal neuralgia has been postulated to be vascular compression, microvascular decompression has been gaining acceptance as the definitive treatment of the condition. However, the majority of patients are over 50 years of age, and posterior fossa procedures carry significant risk in terms of morbidity and mortality. Radiofrequency and glycerol rhizotomy are the two procedures commonly performed in patients considered unsuitable for posterior fossa craniectomy. This study attempts to assess the relative merits and demerits of these two procedures and seeks to establish indications for each. It is felt that glycerol rhizotomy is better as the first line treatment.

Adult↗
PubMed1995

Imaging patterns in melioidosis.

Melioidosis is an infectious disease caused by Pseudomonas pseudomallei. It is seldom diagnosed promptly and, if untreated, can lead to an 80-100% mortality rate. Twenty-eight patients with melioidosis were identified over a 6 year period, and their imaging patterns were analysed. Respiratory infections were the commonest form of presentation, frequently shown as diffuse airspace consolidation, and accounted for the highest mortality. Visceral and musculoskeletal infections were associated with chronicity and a high relapse rate. Multifocal splenic abscesses were a common occurrence. Septic arthritis of the knee was frequently seen. The majority of patients had diabetes mellitus and chronic ill-health. An increased awareness of the disease can contribute to its early detection and appropriate treatment.

Abscess↗
PubMed1991

Signal transduction by the T cell antigen receptor.

The T cell antigen receptor (TCR) must recognize antigen, and translate this recognition event into intracellular signal transduction events. Two signal transduction events are regulated by the TCR: the activation of a protein tyrosine kinase (PTK) and phospholipase C (PLC). Recent studies suggest that the TCR-activated PTK regulates PLC activation by the phosphorylation of tyrosine residues of PLC gamma 1. The complex structure of the TCR is now being related to its signal transduction function. Studies with chimeric receptors reveal that the antigen binding Ti heterodimer communicates with the subunits involved with signal transduction, the CD3 chains and zeta dimers, through the carboxy-terminal regions of the Ti chains that surround and include the transmembrane domains. Other chimeras have helped demonstrate that the zeta chain family of dimers function to couple the TCR to intracellular signal transduction mechanisms. The signal transduction function of the TCR can be regulated in a number of ways and by other T cell surface molecules. The plasma membrane tyrosine phosphatase CD45, plays a critical role to specifically regulate TCR-mediated activation of PTK's and PLC. Thus, an understanding of the complex structure of the TCR and the intricacies of its signal transduction function is rapidly emerging.

Animals↗
PubMed1991

Colorectal smooth-muscle tumors. A pathobiologic study with immunohistochemistry and histomorphometry.

Smooth-muscle tumors are an interesting group of tumors that show considerable site specificity in their pathobiology. Recent work has also shown that some previously so-called smooth-muscle tumors were not, in fact, truly leiomyogenic, hence the origin of the more embracing term stromal tumors. The purpose of this retrospective study was to delineate the tumor subsets constituting colorectal stromal tumors, and to determine the histopathologic correlates for biologic aggressiveness for these tumors. The cohort was constituted of 12 patients; the mean follow-up was 6.6 years with a median of 5.0 years. Immunohistochemical evaluations showed tumoral positivity for muscle-specific actin (12 of 12), vimentin (11 of 12), desmin (two of 12), and S100 protein (zero of 12). Electron microscopic examinations corroborated this leiomyogenicity profile (five of five). Semiquantitative histomorphometric analysis showed that tumor size, cellularity, mitoses, and necrosis, in that order, correlated with biologic aggressiveness. The immunohistochemistry results for this cohort of colorectal stromal tumors vindicated the traditional histochemical evaluations in that all tumors showed features of leiomyogenicity. For colorectal smooth-muscle tumors, tumor size appears to be the best predictor for biologic aggressiveness. This study reinforces the concept of site-specificity for smooth-muscle tumors.

Adult↗
PubMed1990

Influence of the hinge region on complement activation, C1q binding, and segmental flexibility in chimeric human immunoglobulins.

We have characterized a series of genetically engineered chimeric human IgG3 and IgG4 anti-dansyl (DNS) antibodies with identical antibody-combining sites but different hinge region amino acid compositions to determine how the hinge region influences Fab fragment segmental flexibility, C1q binding, and complement activation. Our data support the correlation between "upper hinge" length and Fab segmental flexibility; moreover, we confirm that a hinge region is essential for C1q binding and complement activation. However, the hinge length by itself is not sufficient for complement activity in IgG molecules. We have demonstrated that the IgG4 hinge, which imparts restricted segmental flexibility, reduces the ability of IgG3 molecules to activate complement. We also find that the IgG3 hinge region, which imparts greater segmental motion, is not sufficient to create complement activation activity in IgG4 anti-DNS antibodies. Finally, we conclude that (i) segmental motion is correlated with "upper hinge" length, (ii) hinge length and segmental flexibility is not enough to alter complement binding and activation, and (iii) segmental flexibility does not correlate with proficiency to activate the complement cascade.

Amino Acid Sequence↗
PubMed1990

Herpes labialis in parturients receiving epidural morphine following cesarean section.

A significant association exists between the use of epidural morphine (EM), reactivation of herpes labialis (HL) commonly known as coldsores, and pruritus in the obstetric population. A randomized prospective study was designed to eliminate previously identified confounding variables. Immediately following delivery, parturients having undergone cesarean section with epidural anesthesia with carbonated lidocaine (Xylocaine CO2, Astra, Mississauga, Ontario, Canada) with 1:200,000 epinephrine were sequentially randomized to receive either EM or im opioids for postoperative analgesia. One blood sample was collected for viral serology and two mouthwashes (day 0 and 2) were collected to determine oral viral shedding. The patients were observed daily for 5 days. Coldsores were cultured for herpes simplex virus (HSV). Of 187 patients, 96 received EM and 91 im opioids; herpes labialis occurred in 14 of 96 (14.6%) of the former but in 0 of 91 of the latter (P = 0.0004). All 14 experienced facial pruritus. The two groups were at equal risk for reactivation (seropositivity 64.6% and 62.6%, respectively). Analysis of data for those with positive HSV serology reveals 14 of 62 (22.5%) had EM and herpes labialis compared with 0 of 57 in the im group (P less than 0.0001). The incidence of oral viral shedding was low. Surgical stress, the local anesthetic solution, and epinephrine addition to the local anesthetic were eliminated as confounders. Stepwise logistic regression analysis revealed that EM and a history of herpes labialis in these patients were predictive for reactivating oral HSV.

Adult↗
PubMed1990

Diaphragmatic and external intercostal muscle control during vomiting: behavior of inspiratory bulbospinal neurons.

1. The role of dorsal and ventral respiratory group (DRG and VRG) bulbospinal inspiratory (I) neurons in the control of diaphragmatic and external intercostal (inspiratory) muscle activity during vomiting was examined by recording from these neurons during fictive vomiting in decerebrate, paralyzed cats. Fictive vomiting was defined by a characteristic series of bursts of coactivation of phrenic and abdominal muscle nerves, elicited either by electrical stimulation of abdominal vagal afferents or by emetic drugs, which would be expected to produce vomiting if the animals were not paralyzed. 2. Data were recorded from 22 DRG and 29 VRG I neurons that were antidromically activated from the fourth cervical spinal segment (C4). Only 10% (5/51) of these neurons started to fire near the beginning of phrenic discharge during fictive vomiting and thus had the appropriate discharge pattern to contribute to the initial activation of the diaphragm and coactive external intercostal muscles during vomiting. The frequency of occurrence of these Active neurons was not significantly different in the DRG (3/22) and VRG (2/29) (chi 2 test). Most remaining neurons were either totally silent (n = 7) or had only sporadic, infrequent firing (n = 16) (Silent neurons, 23/51 = 45%), or else fired near the end of phrenic discharge during fictive vomiting (End neurons, 21/51 = 41%). Two neurons were categorized as having miscellaneous (Misc) behavior. 3. No differences were found among neurons having different response patterns during fictive vomiting in regard to the following: the manner in which fictive vomiting was elicited: cell location: conduction velocity; and neuronal firing onset, rate, and pattern during respiration.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Brainstem projections to cats' upper lumbar spinal cord: implications for abdominal muscle control.

Unilateral L1-L2 gray matter HRP injections labeled neurons bilaterally in nucleus retroambiguus (expiratory neuron region of caudal ventral respiratory group) and ventromedial reticular formation. Minor labeling occurred in raphe, vestibular, and medial parabrachial nuclei, lateral reticular formation, and C1-C2. Midsagittal lesions between C1 and obex prevented nucleus retroambiguus labeling (except 1 contralateral cell adjacent an incomplete lesion), indicating that these neurons decussate between C1 and obex and have collaterals that recross the spinal cord.

Abdominal Muscles↗
PubMed1989

Treatment of primary liver cancer in Singapore. A review of 3200 cases seen between January 1, 1977, and July 31, 1987.

Between January 1977 and July 1987, 3200 patients with hepatocellular carcinoma (HCC) were studied in Singapore. HCC formed 90% of primary liver cancers seen in Singapore and is the second most common fatal malignancy seen in men in the country. Extensive clinical and basic research has defined certain treatment strategies. Of importance is the prompt detection of early nodular tumours, which can be resected. Resection, 'targetting' with anticancer drugs and, in selected cases, synchronised direct hepatic irradiation with adriamycin, used as a radiosensitiser, have been promising treatment methods. Biological modifiers, such as interferons and interleukins, offer potential for the future. Preliminary pilot studies suggest that interferons may prevent the development of HCC, but more studies are required. Similarly, selective localisation of anticancer agents with radio-isotopical agents opens opportunities for treatment.

Antineoplastic Agents↗
PubMed1989

The role of fine needle aspiration for breast cancer in the climacteric--a preliminary report.

Fine needle biopsy has been used with great accuracy in the diagnosis of breast tumours. There have been few reports on its efficacy as an adjunct to other breast screening techniques like x-ray mammography. Abnormal mammograms in the absence of a palpable breast lump are sometimes detected in the climacteric and these pose a problem of tissue sampling for pathologic diagnosis. We have tried to evaluate the technique of radiologically guided fine needle aspiration in such patients. Our report is of an initial series of 13 cases of non-palpable, mammographically abnormal breast lesions. Eight cases were fibroadenoma, 4 cases mammary dysplasia and 1 a benign breast lesion. Representative cytologic samples were obtained in 11 of our 13 cases. Cytologic diagnosis should be correlated with mammographic findings.

Adenofibroma↗
PubMed1988

Central motor program for relaxation of periesophageal diaphragm during the expulsive phase of vomiting.

Relaxation of the periesophageal diaphragm during expulsion in decerebrate cats was found to arise from central mechanisms rather than a reflex of peripheral origin. Reductions in periesophageal EMG activity during expulsion were similar before and after cervical vagotomy, which abolishes reflex relaxation of the periesophageal diaphragm following esophageal distension. Reduced activity was also observed in a phrenic nerve branch to the periesophageal region during 'fictive vomiting' in a paralyzed animal.

Animals↗
PubMed1988

Bacteriologic surveillance of indwelling urinary catheters in pediatric intensive care unit patients.

Daily cultures were obtained from the proximal tubing port on 108 indwelling urinary catheters in 100 pediatric ICU (PICU) patients aged 1 month to 17 yr to establish the risk of acquiring bacteriuria. Group 1 patients (58 catheters) were catheterized in the PICU and group 2 patients (50 catheters) were catheterized in the operating room. Group 1 patients had a significantly (p less than .03) greater risk of bacteriuria than group 2 during the early days of surveillance, but the final cumulative risk in both groups was similar (27% in group 1 and 37% in group 2). Combined, the overall cumulative risk was 29.1%. The risk of acquiring a urinary tract infection was not related to sex or prior antibiotic use. There was a significantly greater risk (p less than .025) in children under 1 yr of age.

Adolescent↗
PubMed1988

Production and characterization of genetically engineered antibody molecules.

Expression of antibody heavy- and light-chain genes by transfection permits the production of monoclonal antibodies with improved biological and antigen-binding properties. The immunoglobulin genes are placed in vectors containing a gene for encoding a protein that provides a biochemically selectable function in eukaryotic cells; these vectors are transfected into myeloma and hybridoma cells. Selection of drug-resistant cells permits the efficient isolation of the rare cells that express the transfected DNA. By placing heavy and light chains on plasmids with different selectable markers, one can deliver heavy- and light-chain genes simultaneously to the same cell. The transfected immunoglobulin genes are efficiently expressed and the proteins produced are a faithful mirror of the genes that were introduced. Using the standard techniques of genetic engineering and gene transfection, we can now produce antibodies of widely varying structures, including chimeric antibodies with segments derived from different species. These antibodies provide useful reagents to study structure-function relationships within the antibody molecule. Ultimately it will be possible to produce a new generation of antibody molecules with improved antigen-binding properties and effector functions.

Animals↗
PubMed1988

Recurrent herpes simplex virus labialis and the use of epidural morphine in obstetric patients.

A retrospective study of sequential obstetric patients delivering at University Hospital and receiving epidural anesthesia was conducted to determine if a suggested association exists between the recurrence of oral herpes simplex lesions and the use of epidural morphine. In a retrospective study of 291 patients, 13 of 134 (9.7%) receiving epidural morphine developed recurrent oral herpes lesions in contrast to 1 of 157 (0.6%) not receiving the drug (P less than 0.001). In a prospective hospital-based study of 729 consecutive obstetric patients, 146 patients received epidural opioids (morphine, fentanyl, or both) and 583 did not. Recurrent HSVL lesions occurred in 13 of 140 (9.3%) patients given epidural morphine but in only 6 of 583 (1.0%) not given epidural opioids (P less than 0.001). Three of the 13 patients with HSVL received both epidural morphine and fentanyl and 10 received only epidural morphine. Because of the small numbers of patients receiving only fentanyl, no relation between HSVL reactivation and epidural fentanyl could be established. In patients having caesarean sections, the association of recurrent HSVL and the use of epidural morphine was significant (P = 0.04), suggesting cesarean delivery was not a confounder. A hitherto undescribed triggering agent, epidural morphine, appears to be associated with reactivation of HSVL in obstetric patients in the postpartum period.

Adult↗
PubMed1987

Control of abdominal and expiratory intercostal muscle activity during vomiting: role of ventral respiratory group expiratory neurons.

The role of ventral respiratory group (VRG) expiratory (E) neurons in the control of abdominal and internal intercostal (expiratory) muscle activity during vomiting was examined in decerebrate cats by recording from these neurons during fictive vomiting in paralyzed animals and comparing abdominal muscle activity during vomiting before and after sectioning the axons of these descending neurons. Fictive vomiting was defined by a series of bursts of coactivation of abdominal and phrenic nerves elicited by either subdiaphragmatic vagus nerve stimulation or emetic drugs. Such coordinated activity would be expected to produce vomiting if the animals were not paralyzed. Data were recorded from 27 VRG E neurons that were antidromically activated from the lower thoracic (T13) or lumbar spinal cord. During fictive vomiting, almost two-thirds of these neurons (17/27) were mainly active in between periods of abdominal and phrenic nerve coactivation, when the internal intercostal motoneurons are known to be active. This group of neurons was termed INT neurons. INT neurons were subdivided according to whether they were active between every burst of phrenic and abdominal nerve coactivation (INTa neurons, n = 10) or only between some bursts (INTb neurons, n = 7). Another one-third of the VRG E neurons had normal or increased levels of activity when the abdominal nerves were active during fictive vomiting (ABD neurons). The one remaining neuron was mainly silent throughout fictive vomiting. ABD neurons were indistinguishable from INT neurons on the basis of their location in the VRG, type of firing pattern (ramp versus step ramp), conduction velocity, or extent of projection in the lumbar cord. However, INTa neurons had a significantly higher discharge rate during respiration than either ABD or INTb neurons. Abdominal muscle EMG and nerve activity were recorded from six unparalyzed cats before and after cutting the axons of VRG E neurons as they cross the midline between C1 and the obex. The lesions abolished or almost eliminated expiratory modulation of abdominal muscle activity. In contrast, the abdominal muscles were always active during vomiting; however, the amplitude of postlesion abdominal activity varied from approximately 70-100% of prelesion values in three cats to 60-70% of normal in a fourth animal to only approximately 20% of prelesion values in two other cats.(ABSTRACT TRUNCATED AT 400 WORDS)

Abdominal Muscles↗