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Biomedical subjects

T S Chung

Publications and source records attributed to T S Chung.

At least 19 recordsLinked to original sources
PubMed2006

Management of hypertension by private doctors in Hong Kong.

OBJECTIVE: To investigate the management of hypertension by private doctors in Hong Kong. DESIGN: Self-administered questionnaire survey. SETTING: Hong Kong. PARTICIPANTS: Private doctors from all districts in Hong Kong selected by simple random sampling from the website of "The Hong Kong Doctors Homepage" from March to June 2005. MAIN OUTCOME MEASURES: Practice of blood pressure measurement and the treatment prescribed to hypertensive patients. RESULTS: A total of 225 (46%) completed questionnaires were analysed. Only 24.4% of the respondents measured blood pressure in all new patients aged above 18 years. A total of 28.0% of doctors reported that hypertensive status was unknown in over 30% of their patients prior to their first clinic visit when it was consequently diagnosed. Calcium channel blockers (31%), angiotensin-converting enzyme inhibitors (28.5%), diuretics (27.5%), and beta-blockers (21.2%) were the most commonly prescribed antihypertensive medication. Drug efficacy was the reason cited by more than half (56.9%) of doctors for selecting a given drug. Public education about hypertension was considered insufficient by 66.2% of doctors and 32% believed that self-medication would have a very significant effect on drug compliance. CONCLUSIONS: In private clinics, blood pressure measurement should become a routine procedure. There is a need to raise public awareness of hypertension.

Adult↗
PubMed2006

Protective effect of agmatine on a reperfusion model after transient cerebral ischemia: Temporal evolution on perfusion MR imaging and histopathologic findings.

BACKGROUND AND PURPOSE: The goal of thrombolytic therapy in patients with acute ischemic stroke is early recanalization, but this may result in delayed reperfusion injury. The purpose of this study was to evaluate the neuroprotective effect of agmatine in a transient ischemic cat model by using MR perfusion imaging and histopathologic analyses. METHOD: One-hour temporary occlusion of the left middle cerebral artery of cats was performed in the control ischemia group (n = 10), and 100 mg/kg of agmatine was intravenously injected immediately after recanalization in the agmatine-treated group (n = 15). MR imaging was performed at 1, 24, and 48 hours after recanalization, and the perfusion patterns were investigated. Terminal-deoxynucleotidyl transferase mediated nick and end-labeling (TUNEL) and hematoxylin-eosin (H&E) stainings were performed at the corresponding sections. RESULTS: In the control ischemia group, the number of TUNEL-positive cells was significantly increased in the areas with reperfusion hyperemia (P < .05). In the agmatine-treated group, no significant increase in the number of TUNEL-positive cells was noted in the areas of reperfusion hyperemia. The difference in the number of TUNEL-positive cells between the control ischemia and agmatine-treated group in the areas of reperfusion hyperemia was significant (P < .05). The total number of TUNEL-positive cells and the area of severe ischemic neuronal damage on H&E stain were also significantly attenuated in the agmatine-treated cats compared with the control ischemia cats (P < .05). CONCLUSION: Our results suggest that agmatine has neuroprotective effects against reperfusion injury and ischemia.

Agmatine↗
PubMed2004

Surfactant free fabrication of polymeric nanoparticles by combined liquid-liquid phase separation and solvent/nonsolvent mixing technology.

It is generally agreed that, in most cases, surfactants are required to obtain stable polymeric nanoparticle dispersions. Here, we report a method which can be used to produce surfactant free yet stable polymeric nanoparticle dispersions. This method is based on explored mechanism of selective solvation of nanoparticles and EPD (electron pair donor)/EPA (electron pair acceptor) complexes formed among solvent and nonsolvent molecules. Using polyimide P84 (copolyimide 3,3(') 4,4(')-benzophenone tetracarboxylic dianhydride and 80% methylphenylene diamine+20% methylene dianiline) as the model polymer, this mechanism was realized through a combined liquid-liquid phase separation and solvent/nonsolvent mixing technology. Surfactant-free polyimide nanoparticles (<100 nm) were produced. Experimental details and principles of this technology were given based on the ternary diffusion, the liquid-liquid phase separation and the advanced nucleation and growth theory. Two types of methods [denoted as the forward titration method and the backward titration (BT) method] were examined. It was found that the BT method is extremely helpful to prepare polyimide nanoparticles (<100 nm). As another important aspect, explored stabilization mechanism of the resultant nanoparticle dispersions was supported by the comparative experiments, implying that selective solvation of nanoparticles and EPD/EPA complexes may play key roles in stabilization.

Benzophenones↗
PubMed2001

Auto-catalyzed poly(ortho ester) microspheres: a study of their erosion and drug release mechanism.

A study has been carried out to investigate the degradation and protein release mechanisms of BSA-loaded microspheres made with auto-catalyzed poly(ortho esters) (POEs) of varying diol composition and molecular weights. Due to the instability of the POE/dichloromethane primary emulsion, microspheres made using the W/O/W double emulsion solvent extraction/evaporation method showed a multivesicular internal structure. An O/W single emulsion process yielded dense POE microspheres. Using electron scanning microscopy, the microspheres were observed to erode throughout their matrices with increasing internal pore sizes and a steady loss of mass. However, despite a substantial weight loss of almost 80% after an in vitro period of 129 days, the molecular weight of the polymer remained relatively unchanged with loss averaging about 18 and 32% for low- and high-molecular-weight POEs, respectively. Such constancy in molecular weight was similarly reflected in the glass transition temperature of the degrading microspheres. The differences in both the molecular weight loss and polydispersity index changes depended largely on the molecular weight of the polymer. For protein release of POE microspheres, an induction period followed by BSA release for a period of 3 to 10 days was observed. The lag time depended on the hydrophilicity and the molecular weight of the polymer as well as the morphology of the microspheres. Protein release was incomplete, possibly due to the slow degradation of the POE polymers, protein aggregation and protein degradation.

Acetates↗
PubMed2001

POE-PEG-POE triblock copolymeric microspheres containing protein. I. Preparation and characterization.

Poly(ortho ester) (POE)-poly (ethylene glycol) (PEG) triblock copolymers (POE-PEG-POE) with different PEG contents were synthesised as carriers for controlled protein delivery. POE-PEG-POE microspheres containing bovine serum albumin (BSA) were prepared using a double-emulsion (water-in-oil-in-water) process. In this first paper of a two-part series, we report the fundamentals of the fabrication and characterization of POE-PEG-POE microspheres. Because the triblock copolymer is more hydrophilic than neat poly(ortho ester), the triblock copolymer yields a more stable first emulsion (water-in-oil) and a greater BSA encapsulation efficiency (90% vs. 30%). No BSA is found on POE-PEG-POE microsphere surfaces measured by X-ray photoelectron spectroscopy, while uniform BSA distributions are observed within the microspheres by confocal microscopy. SEM pictures show that an increase in PEG content results in microspheres with a denser cross-section because of a more stable first emulsion and better affinity between the copolymer and water. POE-PEG(20%)-POE suffers significant swelling during the fabrication process and yields the biggest microspheres. However, the POE-PEG(30%)-POE microspheres are much smaller since the dissolution loss of POE-PEG(30%)-POE in the external water phase may be much higher than that of POE-PEG(20%)-POE. The salt concentration in the external water phase significantly affects the morphology of the resultant microspheres. Microspheres with a dense wall are produced when using pure water as the external water phase. Polymer concentration has less impact on BSA encapsulation efficiency but has a considerable effect on microsphere size and morphology. Increasing the concentration of the polyvinyl alcohol emulsifier does not cause an obvious decrease in microsphere size. However, increased BSA loading results in bigger microspheres.

Algorithms↗
PubMed2001

POE-PEG-POE triblock copolymeric microspheres containing protein. II. Polymer erosion and protein release mechanism.

The first paper of this series presented the fabrication and characterization of POE-PEG-POE triblock copolymeric microspheres containing protein. In this paper, we focus on the polymer erosion and the mechanism of protein release. Fourteen-week in vitro behaviors of POE-PEG-POE microspheres loaded with bovine serum albumin (BSA) have been monitored. SEM micrographs reveal that after 14-week incubation in PBS buffer, pH 7.4, 37 degrees C, the polymeric particles remain spherical despite mass loss of almost 90%. On the other hand, molecular weight undergoes a high initial loss of 38% and 44% during the first 2-week incubation for POE-PEG(5%)-POE and POE-PEG(10%)-POE, respectively. Then, it keeps relatively unchanged over 12 weeks. However, POE-PEG(20%)-POE copolymer provides a better compatibility between the POE and PEG blocks. Hydrolysis is homogeneous through the polymer backbone. Thus, its molecular weight remains relatively constant and mass loss shows quite sustained over the 14-week in vitro release. The similar phenomena are observed in the polydispersity index of the degrading copolymers. SDS-PAGE of the encapsulated BSA within the POE-PEG(5%)-POE microspheres displays that the structural integrity of BSA is intact for at least 8 weeks due to a mild environment provided by the copolymer. In addition, XPS and FTIR are utilized to investigate protein behaviors in the degrading microspheres. Protein release from the POE-PEG-POE microspheres shows a biphasic pattern, characterized by an initial stage followed by a non-detectable release. The non-release phase is dominated by either slow polymer degradation or dense microsphere matrix structures. The microsphere formulation is optimized and a sustained protein release over 2 weeks is achieved by using POE-PEG(20%)-POE at a high protein loading.

Animals↗
PubMed2001

Morphology, drug distribution, and in vitro release profiles of biodegradable polymeric microspheres containing protein fabricated by double-emulsion solvent extraction/evaporation method.

The surface and internal morphology, drug distribution and release kinetics at 22 degrees C of polyesters such as PCL (polycaprolactone) and PLGA (poly(DL-lactic-co-glycolic acid)) 65:35 microspheres containing BSA (bovine serum albumin) have been investigated in order to understand the relationship amongst morphology, drug distribution and in vitro release profiles and to develop controlled release devices for marine fishes in tropical area. CLSM (confocal laser scanning microscope) micrographs reveal that the polyvinylalcohol (PVA as an emulsifier) concentration in the external water phase strongly influences drug distribution within microspheres and release profiles. The presence of PVA in the internal water phase enhances the stabilization of inner water droplets against coalescence. This results in a more uniform drug distribution and a slower BSA release. Different oil-phase volumes and polymer concentrations yield different solvent exchange and precipitation mechanisms, which lead to different morphologies. A low oil-phase volume yields microspheres with a porous matrix and defective skin surface, which gives a high initial BSA burst as well as a fast release profile. Microspheres fabricated from a low polymer concentration have less defective skin surface, but with a less tortuous inner matrix which results in a more rapid BSA release. A higher BSA loading yields a larger concentration gradient between the emulsion droplet and the continuous water phase as well as between the microspheres and the in vitro medium. The former results in a lower encapsulation efficiency, whereas the latter yields a faster initial burst and a more rapid release profile. High stirring speed can reduce microsphere size, but decreases the yield of microspheres.

Biodegradation, Environmental↗
PubMed2001

Viable myocardium in reperfused acute myocardial infarction: rest and stress first-pass mr imaging.

Feasibility of identifying viable myocardium in rest and stress magnetic resonance imaging (MRI) was evaluated using 3 hr occlusion and 30 min reperfusion model of left anterior descending (LAD) coronary artery in 12 felines. At rest MRI, viable myocardium confirmed by 2,3,5-triphenyl tetrazolium chloride (TTC)-staining showed rapid signal intensity (SI) rise followed by gradual decline not significantly different from normal myocardium that the two hyperperfused regions were distinguishable only from the hypoperfused nonviable myocardium. At stress MRI, hyperemia induced perfusion change was most pronounced in normal myocardium with earlier and greater peak enhancement followed by brisk 'washout' phase while minimally augmented enhancement in viable myocardium was still in 'washin' phase. From these findings, it was concluded that viable myocardium is identified in rest and stress MRI as redistributing hypo- perfusion compared to persistent hyper-perfusion of the normal myocardium and the persistent hypo-perfusion of the nonviable myocardium.

Animals↗
PubMed2000

Effect of preparation temperature on the characteristics and release profiles of PLGA microspheres containing protein fabricated by double-emulsion solvent extraction/evaporation method.

This study describes the influence of preparation temperature on the various characteristics and release profiles of poly(DL-lactide-co-glycolide) (PLGA) microspheres. The bovine serum albumin (BSA)-loaded microspheres were prepared using the water-in-oil-in-water (w/o/w) technique with poly(vinyl alcohol) as surfactant in the external aqueous phase. We have varied the preparation temperature to observe its effect on microsphere characteristics such as the microsphere shrinking rate during formation, particle size, density, surface and internal morphology, BSA encapsulation efficiency, BSA initial release, microsphere degradation and BSA in vitro release behaviour. During fabrication, a low preparation temperature of 5 degrees C gives the fastest initial but the slowest overall shrinking rate. Microspheres formed at high temperatures of 38 degrees C and 42 degrees C on the other hand have the lowest initial yet the highest overall shrinking rate. Subsequently, microsphere mean size increases and the particle size distribution widens with increase in the preparation temperature. Although all the microspheres have a porous surface as well as internal structure, microspheres fabricated at high temperatures have a uniform internal pore distribution and a very thin dense skin layer, while microspheres fabricated at lower temperatures have a thicker but porous skin layer and bigger pores in the middle of the sphere. Microspheres formed at 33 degrees C are found to give the highest initial burst release. In terms of in vitro release, microspheres fabricated at low temperatures (5 degrees C, 15 degrees C and 22 degrees C) exhibit similar, steady rates. Microspheres formed at higher temperatures however give very low release rates after their initial release. The results obtained suggest that preparation temperature significantly affects microsphere formation, resulting in their structural and protein release profile differences. These differences ultimately work together to affect the initial release and overall release patterns of the microspheres.

Algorithms↗
PubMed2000

Hemidystonia and hemichoreoathetosis as an initial manifestation of moyamoya disease.

OBJECTIVE: To describe hemidystonia and hemichoreoathetosis in an adult patient with moyamoya disease without a previous history of cerebrovascular accident. DESIGN: Case report. SETTING: Tertiary care center. PATIENT: A 22-year-old woman suddenly developed dystonic spasms in her left hand and left foot after a severe emotional stress. The dyskinesia gradually subsided over the next 4 months. Five months after the onset, she suddenly developed choreoathetoid movement in her right hand and right foot. MAIN OUTCOME AND RESULTS: The patient had both somatic and cortical sensory deficits in the right hand and right foot. Magnetic resonance imaging of the brain showed an infarction at the right putamen and lesions involving the right frontal lobe and the left frontotemporoparietal lobe. Magnetic resonance cerebral angiography showed severe stenoses of both internal carotid arteries at the supraclinoid portion and numerous collateral vessels, compatible with moyamoya disease. Single photon emission tomography of the brain showed hypoperfused areas at the right frontal and left frontotemporoparietal lobes. The choreoathetosis of the right limbs improved markedly, along with improvement of sensory deficits. CONCLUSIONS: To our knowledge, this is the first report of an adult patient presenting with hemidystonia and hemichoreoathetosis as the initial manifestations of moyamoya disease. Arch Neurol. 2000;57:1510-1512

Adult↗
PubMed1999

Suboptimal contrast-enhanced carotid MR angiography from the left brachiocephalic venous stasis.

The purpose of this study was to evaluate left brachiocephalic venous stasis and its relationship to suboptimal contrast-enhanced carotid magnetic resonance angiography (MRA). Two groups of patients (group 1, 475 patients; group 2, 159 patients) were examined by contrast-enhanced carotid MRA. Dynamic images of four serial phases were obtained by a three-dimensional fast low-angle shot (3D-FLASH) MRA sequence after bolus injection of 20 ml of gadolinium chelate. In group 1, 43 (9.1%) of 475 cases failed in optimal visualization of carotid arteries because of venous stasis. Left-side injection of contrast media was significantly related to venous stasis (42/43) (P < 0.0001). The patients with venous stasis had a higher mean age (54. 8 +/- 1.5 vs. 60.7 +/- 2.9 years) and higher incidence of hypertension (52.8% vs. 72.1%; P < 0.05). Venous stasis was found at the left brachiocephalic vein (42/43). Compression of the left brachiocephalic vein between the sternum and aorta was confirmed in four cases by venography, chest computed tomography, and magnetic resonance imaging. In group 2, right-side injection did not cause venous stasis at all. The results of this study suggest that use of the right arm for contrast media injection is preferable in the absence of contraindications. J. Magn. Reson. Imaging 1999;10:503-509.

Adolescent↗
PubMed1999

Evaluation of reperfusion and recovery of brain function before and after intracarotid arterial urokinase therapy in acute cerebral infarction with brain SPECT.

PURPOSE: Perfusion defects can be demonstrated reliably at an early stage with regional cerebral blood flow studies using SPECT. The administration of thrombolytic therapy in ischemic stroke is targeted at restoring cerebral perfusion immediately, leading to salvage of ischemic penumbra, smaller infarct size, and improved clinical outcome. This study considered the role of brain perfusion SPECT in the evaluation of reperfusion and brain function recovery of the infarcted area after early recanalization (less than 6 hours) of the occluded artery using intracarotid arterial urokinase therapy (ICAU). METHODS: Intracranial artery occlusion was confirmed in seven patients using emergency carotid angiography performed within the initial 6-hour period. Intracarotid arterial urokinase (500,000 to 800,000 units) was administered into the occluded arterial system (the left middle cerebral artery in four and the right middle cerebral artery in three patients). CT scanning was performed when the patients arrived in the emergency department and was repeated 24 to 48 hours after ICAU and at 7 days or earlier if clinically indicated. All patients had two SPECT studies, the first before urokinase administration and the second 24 or 48 hours later. RESULTS: Complete recanalization of the occluded vessels was seen in one patient after ICAU, effective partial recanalization was achieved in four patients, and minimal recanalization occurred in the other two. Before ICAU, Tc-99m HMPAO brain SPECT showed decreased uptake of the infarcted area in all patients, whereas the follow-up brain SPECT performed 24 or 48 hours after ICAU revealed improvement in the uptake of the recanalized area on qualitative and semiquantitative assessments using an asymmetry index, suggestive of brain function recovery and clinical improvement. Hemorrhagic transformation adjacent to the reperfused regions occurred in two patients with partial recanalization of the left middle cerebral artery. CONCLUSIONS: Reperfusion of the recanalized area and brain function recovery could be achieved if the occluded artery is recanalized within the initial 6-hour period using ICAU, and this was documented using brain perfusion SPECT without a delay in the therapeutic time window. Because the number of patients we studied was limited, further study is necessary to evaluate the effect of ICAU and to determine its prognostic significance.

Acute Disease↗
PubMed1999

Idiopathic acquired anhidrosis: reversible generalized anhidrosis after sunstroke.

Idiopathic acquired generalized anhidrosis is a very rare condition in which the pathogenesis is still unknown. Although varied findings have been reported, no consistent abnormal findings in sweat glands have been established by histological study or electronmicroscopic study. An 18-year-old Korean boy suffered from generalized anhidrosis after sunstroke. Physical and neurologic examination could not reveal any abnormal findings. There were no specific changes in the sweat glands, but amorphous vacuole-like structures were seen in the cytoplasm of secretary cells. We reviewed the previous reports about this rare condition and compared them with our patient.

Adolescent↗
PubMed1999

Comparison of Gadomer-17 and Gd-DTPA in image quality of contrast-enhanced MR angiographies using flow phantom model.

The purpose of this study was to compare the image quality of 3D-TOF MR angiography (MRA) using Gadomer-17 with that using Gd-DTPA in a flow phantom model, and to present preliminary data about the proper dose concentration of Gadomer-17. In the visual analysis of vessel conspicuity, we compared the quality of pre- and post-contrast MIP images. For quantitative analysis, the signal intensities were measured in the axial base 3D-TOF images, and then the relative contrast enhancement was calculated. The results of our studies were that: 1. Maximal signal intensities were obtained at 1 mmol/L of Gadomer-17 and 4 mmol/L of Gd-DTPA. 2. Flow-related signal loss was decreased by Gd-DTPA proportional to the concentration, but Gadomer-17 did not show such a dose accumulative effect. In conclusion, after comparing the results of Gd-DTPA, it was clear that improved MRA images and higher signal intensities of vessels were obtained when lower concentrations of Gadomer-17 were used.

Contrast Media↗
PubMed1999

Evaluation of cerebral aneurysms with high-resolution MR angiography using a section-interpolation technique: correlation with digital subtraction angiography.

BACKGROUND AND PURPOSE: The objective was to evaluate the results of high-resolution, fast-speed, section-interpolation MR angiography and digital subtraction angiography (DSA), thereby examining the potential use of a primary noninvasive screening test for intracranial aneurysms. METHODS: The images were obtained in 39 cerebral aneurysmal lesions from 30 patients with a time-of-flight MR angiographic technique using a 1.5-T superconducting MR system. The total image volume was divided into four slabs, with 48 partitions each. To save time, only 24 phase-encoded steps were measured and interpolated to 48. The parameters used included 30/6.4 (TR/TE), a flip angle of 25 degrees , a 160x512 matrix, a field of view of 150x200, 7 minutes 42 seconds of scan time, an effective thickness of 0.7 mm, and an entire thickness of 102.2 mm. Maximum intensity projection was used for the image analysis, and a multiplanar reconstruction technique was used for patients with intracranial aneurysms. RESULTS: Among 39 intracranial aneurysmal lesions in 30 patients, 21 were ruptured and 18 were unruptured. Twelve lesions were less than 2 mm in size, 12 were 3 to 5 mm, 12 were 6 to 9 mm, and three were larger than 10 mm. At initial examinations, 38 of 39 aneurysmal lesions were detected by both MR angiography and DSA, with 97% sensitivity. In confirming aneurysms in neck and parent vessels, multiplanar reconstruction was successful in detecting all 39 aneurysms, whereas MR angiography was successful in detecting 27 (69%) and DSA was successful in detecting 32 (82%) of the lesions. CONCLUSION: High-resolution MR angiography with a section-interpolation technique showed equal results to those of DSA for the detection of intracranial aneurysms and may be used as a primary noninvasive screening test. In the evaluation of aneurysms in neck and parent vessels, the concurrent use of MR angiography and multiplanar reconstruction was far superior to the use of either MR angiography or DSA alone.

Adult↗
PubMed1998

Facial nerve schwannomas: CT and MR findings.

The present study was undertaken to analyze the radiologic findings of intratemporal and extratemporal schwannoma (ITS & ETS). We retrospectively reviewed the CT (9 cases), MR (3 cases) and medical records of 10 facial schwannoma patients. After classifying these into ITS and ETS, radiologic and clinical findings were analyzed. The most common clinical manifestations were facial nerve dysfunction (6/6 cases, 100%) and hearing impairment (5/6 cases, 83.3%) in ITS and parotid mass (4/4 cases, 100%) in ETS. Geniculate ganglion (GG) was the most commonly involved segment of ITS (5/6 cases, 83.5%). On CT, ITS arising in GG (4 cases) showed erosion of the petrous bone (4 cases), cochlea (3 cases), lateral semicircular canal (1 case) and ossicles (3 cases). ITS arising in the mastoid segment (1 case) showed the destruction of the jugular plate and external auditory canal wall. All three ITS in which MRI was performed showed iso- to hypointensity on T1WI, hyperintensity on T2WI and well-enhanced on post-enhanced T1WI. ETS showed various findings, but all four ETS were located in the posterolateral portion of the retromandibular vein and extended toward the stylomastoid foramen. In conclusion, ITS shows the schwannoma on MR. ETS shows various findings. However, if the tumor is located along the extratemporal facial nerve course, then facial schwannoma may be suspected.

Adult↗