Spontaneous haemothorax caused by an internal mammary artery aneurysm.
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Adult↗
Biomedical subjects
L W Chan
Publications and source records attributed to L W Chan.
Attraction basin of bidirectional association memories.
In this paper, we investigate the attraction basin of the bidirectional associative memory (BAM) model. The BAM is a two-layer heteroassociator that stores a prescribed set of bipolar library pairs. It consists of two layers of neurons. One layer has n neurons and the other has p neurons. We will first point out why the conventional energy approach cannot tell us about the attraction basin of each library pair. We then rigorously derive the statistical dynamics of the BAM, which shows how the upper bound on the number of errors changes during recalling for an arbitrary error pattern in the initial state. From the dynamics, we can estimate the attraction basin for the worst case errors, as well as the memory capacity and the number of errors in the retrieved pairs. The memory capacity is alpha rn, where alpha r (0 < alpha r < 1) depends on the ratio [formula: see text]. The number of errors in the retrieved pairs is [formula: see text] when the number of library pairs is alpha n. When r = 1, the lower bound on the attraction basin for the worst case errors is about 0.0068n.
Algorithms↗
Existence of iodine deficiency in Hong Kong--a coastal city in southern China.
OBJECTIVE: Iodine deficiency is a serious public health problem worldwide which is associated with mental retardation and cretinism. In view of a high incidence of transient neonatal hypothyroidism and a relatively high mean cord blood thyrotropin (TSH) concentration, a pilot study was carried out to analyse the urine iodine excretion in Hong Kong, a coastal city in the southern part of China. DESIGN: Early morning urine was collected from healthy volunteers including children (n = 104), adults (n = 112) and elderly subjects (n = 349). A semi-quantitative questionnaire survey on the pattern of food intake was conducted in the adults and elderly. RESULTS: 45.3% of the children, 51.7% of the adults and 55.3% of the elderly had urine iodine concentration below the criteria for iodine sufficiency (< 0.79 mumol/l). Iodine content in the drinking water and salt was low. A dietary survey revealed that seafood was not commonly consumed. 50-80% of the subjects never consumed high-iodine containing food such as seaweed, kelp or laver, and only 50% consumed seawater fish daily. CONCLUSION: We confirmed that although Hong Kong is a non-goitrous area, iodine insufficiency exists. It is unsafe to assume that iodine deficiency does not exist in coastal urban areas.
Adolescent↗
Aggressive fibromatosis of the spermatic cord. A typical lesion in a "new" location.
The authors describe a 31-year-old man with a 7 cm aggressive fibromatosis (desmoid tumor) of the spermatic cord presenting as a swelling in the left inguinal area that was excised along with the testis and cord. The desmoid tumor is histologically typical, but such tumors arising primarily from the paratesticular structures have apparently not been previously reported and the diagnosis would not be questioned if it not for the unusual site. This tumor is histologically and immunohistochemically indistinguishable from abdominal wall desmoid tumor, with or without Gardner's syndrome. Desmoid tumors at this location should be distinguished from reactive processes, such as pseudosarcomatous myofibroblastic proliferation (so-called "proliferative funiculitis") and inflammatory fibrous pseudotumor, all of which exhibit fibroblastic/myofibroblastic differentiation. Paratesticular fibrosarcoma and leiomyosarcoma should also be differentiated from desmoid tumor that does not have the metastatic potential of sarcomas. Thirty-four months post-operatively, an 8 cm local recurrence in the remaining portion of the left vas deferens causing left hydroureter and hydronephrosis was detected.
Adult↗
Uterine prolapse and acute renal failure in a Chinese patient.
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Acute Kidney Injury↗
Interaction of preservatives with macromolecules: Part I--Natural hydrocolloids.
Antibacterial activity of methyl-p-hydroxybenzoate against Ps. aeruginosa was evaluated in the presence of varying concentrations of acacia, tragacanth, sodium alginate, guar gum and carrageenin. All these hydrocolloids reduced the antibacterial activity to varying degrees. Tragacanth and guar gum inhibited the activity to a greater extent than acacia, sodium alginate and carrageenin. Hydrocolloids reduce the antibacterial activity of preservatives in two ways. Interaction of the preservative with hydrophilic macromolecules and subsequent reduction in the availability of preservative appears to be the predominant mechanism by which tragacanth and guar gum reduce the activity of methyl-p-hydroxybenzoate. Acacia, sodium alginate and carrageenin apparently act by offering physical protection to microbial cells from the action of the preservative. It is also probable that these hydrocolloids provide more favourable media for microbial growth thereby increasing the preservative requirement for adequate preservation.
Colloids↗
Effect of surfactants on the antibacterial activity of preservatives.
Antibacterial activities of methyl-p-hydroxybenzoate, phenoxyethanol and chlorocresol against Pseudomonas aeruginosa were evaluated in the presence of varying concentrations of Tween 80. Below cmc level, the bactericidal activities increased with decrease in the surface tension values of Tween 80 solutions and with interfacial tension values of Tween 80 solution/liquid paraffin systems. Linear relationships were found to exist between the concentrations of each preservative required to reduce the microbial population by a factor 10(3) within 48 hours and the values of surface tension and interfacial tension respectively. Reduction in surface tension and interfacial tension would have increased the adsorption and uptake of preservatives by bacterial cells thereby killing the cells at a faster rate. Concentrations of Tween 80 above cmc also enhanced the antibacterial activities of these preservatives. This was attributed to the increase in the permeability of bacterial membranes to preservatives.
Microbial Sensitivity Tests↗
Availability and activity of preservatives in emulsified systems.
Availability and activity of methyl-p-hydroxybenzoate, phenoxyethanol and chlorocresol in emulsions were studied by equilibrium dialysis and microbiological methods. Equation proposed by Bean and coworkers for calculating the availability of free preservatives in the aqueous phase of simple emulsion was also found to be applicable to modern emulsions composed of more than one oil and surfactant. The antimicrobial activity varied with the type of preservative and microorganism. Among the four test organisms, Pseudomonas aeruginosa and Staphylococcus aureus were more resistant to the various preservatives than Candida albicans and Aspergillus niger. The concentration of free preservative in the aqueous phase of the emulsion required to reduce the microbial population to the level specified in BP was found to be less than the concentration needed in distilled water indicating that the antimicrobial activity of the preservatives in emulsions is not entirely dependent on the concentration of their free form in the aqueous phase of emulsions.
Bacteria↗
Absorption of intranasal salmon calcitonin in normal subjects and hypogonadic men.
The absorption kinetics of intranasal salmon calcitonin were assessed in 4 normal subjects and 9 patients with Klinefelter's syndrome. After administration, absorption occurred within 5 minutes. There was a highly significant correlation between the amount administered and the amount absorbed (r = -0.83, P less than 0.0005).
Administration, Intranasal↗
Partition of preservatives in oil/water systems.
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Chemistry, Pharmaceutical↗
Labelled leucine uptake in the visual cells and pigment epithelium of young albino rats in response to different light-dark cycles.
The leucine uptake in the visual cells and pigment epithelium were studied in the young albino rats after exposing to different light-dark cycles. Some form a cycle pattern was found in the visual cell layer and two peaks were recorded. The pattern on the uptake in the pigment epithelium was less distinct but at least a peak in the morning was recognized. The peaks could be shifted by manipulating the light-dark environment.
Age Factors↗
Effect of tabletting compaction pressure on alginate microspheres.
Alginate and alginate-hydroxypropylmethylcellulose (HPMC) microspheres were prepared by the emulsification method. The compaction of microspheres for producing tablet dosage forms raises concerns about possible damage to microsphere walls with subsequent unpredictable dissolution rates. The effect of different compaction pressures on the integrity of the microspheres was investigated. The addition of a diluent, microcrystalline cellulose (MCC), was required to make compacts containing alginate and alginate-HPMC microspheres. Compacts containing alginate-HPMC (7:3) microspheres had the highest crushing strength followed by compacts containing alginate-HPMC (9:1) microspheres and alginate microspheres. However, compact crushing strength did not vary significantly with increased compaction pressures over the range of compaction pressures investigated. Differences in the drug release profiles of the original non-compacted and compacted alginate and alginate-HPMC microspheres were slight and not marked. Although dentation and distortion of the microspheres were observed with increasing compaction pressures, the microspheres generally remained intact, with minimal rupture/fracture.
Alginates↗
Microencapsulation of oils using sodium alginate.
The feasibility of encapsulating wheatgerm oil and evening primrose oil using sodium alginate by the emulsification method was explored in this study. It is based on the chemical reaction between the water-soluble sodium alginate and polyvalent cation, calcium, to form the water-insoluble alginate. The factors investigated were the physical appearance of the microspheres, the amount of oil that could be encapsulated, the flow property, size distribution and mean size of the microspheres produced. Encapsulation efficiency and oil content of wheatgerm oil increased with an increase in oil load. The mean size of the microspheres increased sharply at a high oil load of 250% w/w. Photographs of microspheres taken showed that the microspheres were larger, spherical and had more vesicles within, as oil load increased. Encapsulation efficiency of evening primrose oil microspheres was similar to wheatgerm oil microspheres at the respective oil loads of 50, 250 and 350% w/w. The emulsification method developed was successfully applied to wheatgerm oil, a fixed oil, with a maximum encapsulation efficiency of approximately 88%. It was satisfactory for evening primrose oil, which also belongs to the family of fixed oils.
Alginates↗
Release characteristics of pectin microspheres prepared by an emulsification technique.
The potential application of pectin as a matrix polymer for making microspheres by an emulsification technique was explored, and the drug release property of these pectinate microspheres containing drug cores of varying aqueous solubilities: sulphanilamide, sulphaguanidine and sulphathiazole, was investigated using different dissolution media. The size and size distribution, specific surface area, drug content and drug release property of the pectinate microspheres were determined. The solubility and solution pH of drugs and their propensity to interact with pectin were characterized. Pectinate microspheres were successfully prepared by external gelation, using a modified emulsification technique. The kinetics of drug release from the microspheres best fitted Higuchi's model. Interestingly, the lowest percentage of drug released was produced by microspheres which were smallest in size and, therefore, largest in specific surface area, and containing sulphanilamide, the most aqueous soluble and the lowest molecular weight drug. Mathematical correlation study indicated that the drug release profile of pectinate microspheres was notably affected by the drug content and the extent of drug-pectin interaction in the microspheres. Generally, a higher percentage of drug was released from the microspheres with a higher drug content and/or lower extent of drug-pectin interaction. The extent of drug-pectin interaction was highest in microspheres containing sulphanilamide, followed by sulphaguanidine and sulphathiazole, opposite to that of drug content.
Delayed-Action Preparations↗
Formation of alginate microspheres produced using emulsification technique.
This study investigated the formative process of alginate microspheres produced using an emulsification technique. The alginate microspheres were produced by cross-linking alginate globules dispersed in a continuous organic phase using various calcium salts: calcium chloride, calcium acetate, calcium lactate and calcium gluconate. The size, shape, drug content and Ca2+ content of the microspheres were evaluated. The tack, viscosity and pH of the calcium salt solution and percentage of Ca2+ partitioned into the organic phase were determined. Microscopic examination of the test emulsion at various stages of the emulsification process was also carried out. The propensity of cross-linking reaction was found to be dependent on successful collision between alginate and calcium salt globules. Examination of the characteristics of microspheres indicated that the formed microsphere was a resultant product of alginate globule clustering. The growth propensity of microspheres was promoted by the higher rate and extent of cross-linkage which was governed by the pH, tack and/or Ca2+ content of the cross-linking solution, as well as the dissociation constant and diffusivity of the calcium salt. Overall, the amount of free Ca2+ cross-linked with alginate in the formed microspheres was in the following order: calcium acetate > calcium chloride + calcium acetate > calcium chloride + calcium gluconate; calcium chloride + calcium lactate > calcium chloride. In microencapsulation by emulsification, the mean size of the microspheres produced can be modified by varying the tack, pH and Ca2+ content of the cross-linking solution and through the use of a combination of calcium salts. The shape of the microspheres produced was, nonetheless, unaffected by the physicochemical properties of the cross-linking solution.
Alginates↗
Prediction of differential creatinine clearance in chronically obstructed kidneys by non-contrast helical computerized tomography.
PURPOSE: We investigate the use of non-contrast helical computerized tomography (NCHCT) in the measurement of differential renal parenchymal volume as a surrogate for differential creatinine clearance (CrCl) for unilateral chronically obstructed kidney. MATERIALS AND METHODS: Patients with unilateral chronically obstructed kidneys with normal contralateral kidneys were enrolled. Ultrasonography (USG) of the kidneys was first done with the cortical thickness of the site with the most renal substance in the upper pole, mid-kidney, and lower pole of both kidneys were measured, and the mean cortical thickness of each kidney was calculated. NCHCT was subsequently performed for each patient. The CT images were individually reviewed with the area of renal parenchyma measured for each kidney. Then the volume of the slices was summated to give the renal parenchymal volume of both the obstructed and normal kidneys. Finally, a percutaneous nephrostomy (PCN) was inserted to the obstructed kidney, and CrCl of both the obstructed kidney (PCN urine) and the normal side (voided urine) were measured two 2 after the relief of obstruction. RESULTS: From March 1999 to February 2001, thirty patients were enrolled into the study. Ninety percent of them had ureteral calculi. The differential CrCl of the obstructed kidney (%CrCl) was defined as the percentage of CrCl of the obstructed kidney as of the total CrCl, measured 2 weeks after relief of obstruction. The differential renal parenchymal volume of the obstructed kidney (%CTvol) was the percentage of renal parenchymal volume as of the total parenchymal volume. The differential USG cortical thickness of the obstructed kidney (%USGcort) was the percentage of mean cortical thickness as of the total mean cortical thickness. The Pearson's correlation coefficient (r) between %CTvol and %CrCl and that between %USGcort and %CrCl were 0.756 and 0.543 respectively. The regression line was %CrCl = (1.00) x %CTvol - 14.27. The %CTvol overestimated the differential creatinine clearance by about 14%, but the correlation is good. CONCLUSION: The differential renal parenchymal volume measured by NCHCT provided a reasonable prediction of differential creatinine clearance in chronically obstructed kidneys.
Adult↗
17-year follow-up of a randomized prospective controlled trial of adjuvant intravesical doxorubicin in the treatment of superficial bladder cancer.
PURPOSE: To evaluate the efficacy of adjuvant intravesical doxorubicin in superficial transitional cell carcinoma of the urinary bladder on long-term follow-up. MATERIALS AND METHODS: Between July 1986 and November 1991, all patients harboring superficial bladder cancers (Ta or T1) with one or more of these criteria (stage>a, grade>1, size>1 cm, multiple or recurrent tumors) were randomized to receive either 50 mg doxorubicin or no adjuvant therapy. Patients with recurrences were allowed to receive doxorubicin or other intravesical agents. Recurrence, progression and survival were analyzed. RESULTS: There were 82 patients included (64 males and 18 females). The mean age was 64 years. Forty-six patients were randomized to the doxorubicin group and 36 to the control group. Final analysis was made at median follow-up of 45, 128 and 131.5 months for recurrence, progression and survival, respectively. Recurrence free, progression free and disease specific survival did not differ significantly between groups. The 10-year Kaplan-Meier estimates for recurrence free, progression free and disease specific survival were 67%, 84% and 92%, respectively for the doxorubicin group, and were 50%, 89% and 97%, respectively for the control group. Tumor size predicted recurrence (p=0.013) and grade predicted progression (p=0.004) with multivariate analysis. CONCLUSIONS: Adjuvant intravesical doxorubicin could not be shown to improve recurrence, progression and survival of superficial bladder cancer, compared with control on long-term follow-up. Tumor size and grade were shown to be prognostic factors for recurrence and progression, respectively.
Administration, Intravesical↗
Drug encapsulation in alginate microspheres by emulsification.
A method based on an emulsification process was developed for the production of calcium alginate microspheres. Isopropyl alcohol and acetone, which are strong dehydrating agents, were used to aid in the hardening and drying of the microspheres. However, the amount of drug encapsulated was very low. This was due to the drug being soluble in the dehydrating solvents. In the absence of the solvents a high percentage of drug was encapsulated, and this was further increased by forming the microspheres by phase inversion. It was also found that a suspension of the drug particles was required for effective microencapsulation. The efficiency of drug encapsulation generally increased with the ratio of drug to encapsulating material. The microspheres produced were free-flowing and most of them were smaller than 150 microns.
1-Propanol↗