Biomedical subjects

W S Tan

Publications and source records attributed to W S Tan.

At least 37 records · Page 2Linked to original sources

PubMed1999

Two distinct segments of the hepatitis B virus surface antigen contribute synergistically to its association with the viral core particles.

The long surface antigen polypeptide (L-HBsAg) of hepatitis B virus (HBV) is believed to mediate contact between the virus envelope and nucleocapsid protein (HBcAg). The N and C termini of L-HBsAg were shortened progressively in order to define the minimum contiguous sequence of amino acids that contains the residues necessary for association with HBcAg. The resulting mutants were expressed in rabbit reticulocyte lysates and their interaction with HBcAg was examined with an immunoprecipitation assay and an equilibrium binding assay in solution to give relative dissociation constants. Binding of HBcAg particles by L-HBsAg displayed two widely differing dissociation constants, indicating two distinct binding sites between the molecules. The two distinct sites, one located between residues 24 and 191 and the other between residues 191 and 322 of L-HBsAg, contribute synergistically to high-affinity binding to HBcAg, but disruption of either of these segments resulted in a much weaker interaction showing only one dissociation constant. Inhibition of the interaction by peptides that bind to the tips of the nucleocapsid spikes differentiated contacts in HBcAg for the two binding domains in L-HBsAg and implied that the amino-terminal binding domain contacts the tips of the HBcAg spikes. Analysis of specific single amino acid mutants of L-HBsAg showed that Arg92 played an important role in the interaction.

Animals↗

PubMed1995

Nucleotide sequence of the haemagglutinin-neuraminidase (HN) gene of a Malaysian heat resistant viscerotropic-velogenic Newcastle disease virus (NDV) strain AF2240.

The nucleotide sequence of the haemagglutinin-neuraminidase (HN) gene of Newcastle disease virus (NDV) viscerotropic-velogenic strain AF2240 was determined by direct RNA sequencing and by sequencing RT-PCR products. It encodes a single open reading frame of 581 amino acids with a calculated Mr of 63.8 kDa. The predicted sequence contains five asparagine glycosylation sites. Comparison of the AF2240 HN protein sequence with 13 other previously published sequences showed 88% homology. This HN protein is unique because it lacked the Arg 403 residue which is present in all of the other strains and cannot be grouped under the proposed three size classes of HN proteins in NDV.

Amino Acid Sequence↗

PubMed1994

Quantitative investigations of cell-bubble interactions using a foam fractionation technique.

Previous work by the authors and others has shown that suspended animal cell damage in bioreactors is caused by cell-bubble interactions, regardless whether the bubbles are from bubble entrainment or direct gas sparging. As approach to measure the adsorptivity of animal cells to bubbles, a modified batch foam fractionation technique has been developed in this work and proven to be applicable. By using this technique, the number of cells absorbed per unit bubble surface area and the adsorption coefficients have been measured to quantify hybridoma cell-bubble interactions, and the preventive effects of serum and Pluronic F68 on these interactions. It was demonstrated quantitatively that the hybridoma cells adhere to bubbles spontaneously and significant numbers exist in the foam, and that both the serum and Pluronic F68 provide strong prevention to these cell-bubble interactions. The results obtained provide criteria for bioreactor operation and medium formulation to prevent cell-bubble interactions and cell damage in the culture processes.

Adsorption↗

PubMed1993

Duplex scanning of the inferior epigastric artery.

PURPOSE: The inferior epigastric artery (IEGA) has been used as a conduit for coronary artery bypass grafting. Because of varying lengths, diameters, and depths, a method of determining vessel adequacy before operation was needed. METHOD: A BioSound Phase II scanner (BioSound, Indianapolis, Ind.) with a 10 MHz probe was used to image the IEGA in 40 patients. Beginning at the common femoral artery and moving superiorly, the external iliac artery is identified with its first branch, which is the IEGA. The IEGA is located deep in the rectus muscle, along the posterior rectus sheath. Frequent measurements of the diameter and depth are taken along the length of the IEGA. RESULTS: When comparing the group of patients in whom there was operative confirmation of the ultrasound findings, we found, on the right side, a mean length of 9.0 cm and mean diameter of 2.4 mm by ultrasonography and 10.5 mm and 2.4 mm at operation. On the left side the findings were 9.6 cm and 2.6 mm by ultrasonography and 11 cm and 2.6 mm at operation. There was one wound complication in an IEGA harvest site that had a body wall thickness of less than 4 cm (1/23; 4.2%), but all four sites with a body wall thickness of 4 cm or greater developed wound complications (4/4; 100%). CONCLUSION: The use of duplex scanning of the IEGA before operation provided excellent information about the length, diameter, depth, and patency of the vessel. Preoperative scanning prevented unnecessary dissection when the IEGA was not of adequate length or diameter. It was also very useful in providing information regarding risk of wound complications in obese patients.

Abdominal Muscles↗

PubMed1991

Tissue plasminogen activator thrombolysis of a middle cerebral artery embolus in a patient with an arteriovenous malformation. Case report.

A patient harboring a cerebral arteriovenous malformation (AVM) underwent angiography in an attempt to embolize the AVM. During catheterization (and prior to embolization) he became hemiplegic and aphasic. Angiography revealed a complete middle cerebral artery (MCA) occlusion by an embolus. The patient was treated with recombinant tissue plasminogen activator (t-PA), a thrombolytic agent. Restoration of MCA flow was achieved, and the patient recovered. Immediately after MCA embolus, t-PA infusion may lead to thrombolysis and neurological recovery. The decision-making process as well as the risks associated with the use of t-PA are discussed.

Adult↗

PubMed1990

Acute hypertensive encephalopathy in minimal change nephrotic syndrome.

A 3-year-old child with minimal change nephrotic syndrome (MCNS) developed an acute hypertensive encephalopathy characterized by coma, focal seizures, right hemiparesis, global aphasia and cortical blindness. Episodic hypertension and seizures persisted for 24 h despite intervention with antihypertensive and anticonvulsant therapy. Clinical suspicion of cortical blindness was confirmed by visual-evoked potential studies. CT scans performed 14 and 21 days after the acute episode demonstrated symmetric occipital white matter lucencies compatible with ischemia and/or associated edema. Hypertensive encephalopathy with cortical blindness and symmetric white matter hypodense lesions visualized on CT scan have recently also been described in eclampsia of pregnancy. This report documents an unusual acute hypertensive encephalopathy in childhood MCNS, unassociated with membranoproliferative glomerulonephritis, or progressive focal glomerulosclerosis.

Blindness↗

PubMed1987

Pitfalls in diagnosing brain death in infancy.

A 3-year-old child with phenotypic trisomy 18 syndrome survived 26 days after a cardiopulmonary arrest, secondary to an acute viral illness. The child was deeply comatose. No barbiturates, other sedatives, or aminoglycoside antibiotics had been recently administered. The child was normothermic with adequate cardiovascular function. Brain stem function was absent, as assessed by testing of brain stem reflexes. Serial cerebral radionuclide angiograms (CRAG) documented intact cerebral blood flow while electrocerebral silence (ECS) was present on two consecutive EEG recordings within 24 hours. Preservation of intracranial circulation was confirmed by rapid rotational computed tomographic (CT) scans. Cranial CT scans also revealed communicating hydrocephalus, and bilateral basal ganglia hemorrhages. This unusual case illustrates discordance between apparent irreversible loss of cortical function as indicated by electrocerebral silence with preserved cerebral blood flow. The implications of these apparent paradoxical events will be discussed in the context of defining brain death in children.

Brain Death↗

PubMed1987

The role of the neuroradiologist in vascular disorders involving the orbit.

CT and MRI have become imaging techniques of great value in the diagnosis of vascular orbital lesions. Intraorbital vascular lesions, vascular tumors, intracranial aneurysms, carotid cavernous fistulas, and Tolosa-Hunt syndrome are discussed in detail. They illustrate how the accuracy of CT and MRI in evaluating orbital and intracranial masses has focused the role of angiography in exophthalmos and ophthalmoplegia on detection and assessment of those vascular lesions that may require surgical intervention.

Arteriovenous Fistula↗

PubMed1987

Cardiac tumors in 19 years of private practice.

Since 1966 the authors have encountered nine cardiac tumors: eight myxomas and one tumor initially thought to be a sarcoma but histologically a squamous carcinoma. Seven myxomas were left atrial and the other were right atrial in location. The carcinoma was predominantly located in the right ventricle. Eight of the nine patients were female; ages ranged from 32 to 85 years. Of the myxomas, five displayed fever and dyspnea, two congestive heart failure and one transient ischemic episodes. The patient with carcinoma was in right heart failure. All patients underwent cardiac catheterization as well as echocardiography when it became available. Five myxomas were correctly diagnosed preoperatively while three were thought to have mitral stenosis. The patient with carcinoma showed a large right ventricular filling defect and a picture of constriction. All myxoma patients underwent surgery--three via left thoracotomy and five via sternotomy. Seven patients survived; however, the patient with right atrial myxoma was explored via the left chest for mitral stenosis and the myxoma was not discovered. She died of a pulmonary embolism pathologically confirmed as myxoma. All survivors have been followed by yearly echocardiograms and are free of recurrence. The patient with carcinoma died before surgery could be performed. Autopsy revealed almost complete replacement of the right ventricle by tumor and constrictive pericarditis. The terminal event was pulmonary embolus of squamous carcinoma. Although cardiac tumors are a rare entity, a high incidence of suspicion plus modern diagnostic methods can yield the diagnosis and allow a curative operation.

Adult↗

PubMed1986

Sciatic nerve block under fluoroscopic guidance.

Sciatic nerve block under fluoroscopic guidance was performed in 17 patients. This anesthetic technique along with femoral nerve block was found to be effective in patients having unilateral femoral arteriography or occlusive arteriography of their extremities. No complication was encountered in this group of patients.

Bupivacaine↗

PubMed1986

Subclavian aneurysm producing the subclavian steal syndrome.

An atherosclerotic aneurysm of the right subclavian artery causing subclavian steal syndrome is described. Complementary information obtained from digital subtraction angiography and computed tomography helped to establish a correct preoperative diagnosis.

Aneurysm↗

PubMed1986

Normal cerebral radionuclide angiogram in a child with electrocerebral silence.

Pediatric neurologists agree that the determination of brain death in children, and especially retarded children, is difficult and that the criteria used in adult brain death may not be sufficient in pediatric cases. An unusual case of sustained electrocerebral silence on electroencephalogram (EEG) in a three-year-old retarded comatosed child with preserved intracerebral perfusion documented by a series of cerebral radionuclide angiograms (CRAG) is presented. The EEG showing electrocerebral silence represents loss of cerebrum (cortex) function (Barlow 1976). This absence of cortical function is demonstrated even though intracranial circulation is shown to be intact. We believe that the correlative studies presented accurately document a discordance between apparent loss of cortical function in a child as indicated by electrocerebral silence in the face of preserved cerebral blood flow. It is suggested that when evaluating brain death in retarded children with known cerebral atrophy, special emphasis should be placed on the CRAG and that the EEG should be read with caution.

Brain↗

PubMed1986

Arterial digital angiography in the evaluation of potential renal donors.

Twenty-two potential renal donors were examined by both arterial digital and conventional aortography. The digital studies accurately identified all of the renal arteries. Digital subtraction angiography may be a suitable alternative to conventional aortographic evaluation of the renal arterial supply of potential renal donors.

Adult↗

PubMed1986

Regional cerebral blood flow assessment prior to balloon detachment in the treatment of intracranial giant aneurysms.

Three patients with giant aneurysms (2 internal carotid and 1 anterior communicating) were treated by internal carotid occlusion with a detachable balloon. 133Xe regional cerebral blood flow (rCBF) was performed on each patient on admission. Due to low CBF, one patient received a superficial temporal artery--middle cerebral artery (STA-MCA) bypass. The rCBF was repeated when the balloon was inflated in the internal carotid prior to detachment of the balloon. All three patients were discharged within one week with no neurologic deficit. The rCBF assessment appears useful to decide which patient will tolerate acute balloon occlusion of the internal carotid and to help select patients who will need an extra-cranial-intracranial (EC-IC) bypass to avoid ischemic complication.

Aged↗

PubMed1986

Magnetic resonance imaging and computed tomography of choroidal detachment.

The magnetic resonance imaging (MRI) and computed tomography (CT) findings in 9 patients with hemorrhagic choroidal detachment, serous choroidal detachment and/or ocular hypotony, choroidal effusion and 6 patients with exudative retinal detachment are described. Subacute hemorrhagic choroidal detachment appeared as moderately hyperintense image in T1 weighted MR scans and as hypointense in T2 weighted scans. Chronic hemorrhagic choroidal detachment was seen as hyperintense image in T1 and T2 weighted scans. Serous choroidal detachment and choroidal effusion appeared as moderately hyperintense image in T1 and T2 weighted scans. The exudative retinal detachment characteristically appeared on MR scans as a dependent hyperintense object in T1 and T2 weighted scans.

Choroid Diseases↗

PubMed1986

Clinical assessment of the St. Jude medical cardiac prosthesis. A 5-year experience.

Mechanical prosthetic valves have established their long-term durability, but the incidence of thromboembolism has been less satisfying. Therefore, the search for the perfect valve continues. The choice of replacing a cardiac valve with a prosthetic valve is based upon its hemodynamics, durability, thromboembolic and hemolytic characteristics. The hemodynamic assessment of the St. Jude Valve demonstrates that it performs well in the aortic, mitral, and tricuspid positions. The central bileaflet flow design leads to minimal gradients, even in the small valves which make it ideal for its use in children. The purpose of its all-pyrolite construction is to decrease the incidence of thromboembolism. Replacement of heart valves with the St. Jude Medical prosthesis was initiated in April, 1979. An analysis of all patients undergoing valve replacement between April 1, 1979, and June 1, 1984, was carried out to assess the durability, incidence of thrombosis, and thromboembolic as well as other complications.

Adolescent↗

PubMed1985

Dynamic computed tomography of the head and neck: differential diagnostic value.

A retrospective review of the dynamic CT studies performed in our institution on head and neck lesions, excluding the brain, was carried out. Five basic types of density vs. time curves were obtained. Dynamic CT scanning is valuable in the differential diagnosis, management, and followup of such cases; its usefulness as an imaging modality in diagnosis and followup of hemangiomas is stressed.

Adult↗

PubMed1984

Cystic mural nodule in cerebellar hemangioblastoma: CT demonstration.

An example of a form of cystic hemangioblastoma of the cerebellum in which the mural nodule itself showed a central cystic area is presented. Although the precise etiology of the cystic component within hemangioblastoma tumor nodules is not known, it probably results from tumor degeneration. Computed tomography is valuable in identifying this feature, which, if present, is very suggestive of the diagnosis of hemangioblastoma. Other diagnostically useful CT features of hemangioblastoma that were present in this case included location of the mural nodule adjacent to the nearest pial surface, isodensity of the nodule on the preinfusion scan, and very rapid circulation of contrast material through the wall of the nodule, demonstrated by dynamic CT technique.

Adult↗