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Biomedical subjects

J Wong

Publications and source records attributed to J Wong.

At least 487 records · Page 27Linked to original sources
PubMed1992

Self-setting hydroxyapatite cement: a novel skeletal drug-delivery system for antibiotics.

A novel approach using a self-setting hydroxyapatite (HAP) cement as a skeletal drug-delivery system has been proposed to solve the problem of delivering drugs to skeletal tissue at sufficiently high local concentrations for desirable therapeutic effects. HAP cements loaded with antibiotics can be formed in situ and can be used as bonding materials between bone and prostheses, as well as drug-release devices. The cement also possesses sufficient mechanical strength to be a potential bone grafting material. Using cephalexin and norfloxacin as model drugs, we observed continuous in vitro release profiles of these compounds from cement pellets loaded 0.9-4.8% by weight with one of the drugs. This drug-release pattern correlated well with the Higuchi model. This hydroxyapatite cement drug-delivery system can be applied in the treatment of osteomyelitis and infected compound fractures.

Anti-Bacterial Agents↗
PubMed1992

Gross and histological abnormalities of the foregut in familial adenomatous polyposis: a study from a South East Asian Registry.

Polyps in the stomach and duodenum are frequently found in familial adenomatous polyposis. Cancer arising from some of these polyps may be an important cause of death in patients who have had large bowel resections. This study aims to determine the nature and distribution of foregut polyps in Chinese patients. Twenty-five patients with familial adenomatous polyposis were gastroscoped by a single operator using the end viewing video-endoscopy system. Representative biopsies of normal mucosa or polyps where appropriate were taken from the gastric fundus, antrum and the duodenum. Twenty-five patients were studied. Male = 17, female = 8. Median age was 32 years (range = 17-63 yrs). Nineteen patients were found to have macroscopically visible polyps in the foregut. Ten patients had gastric polyps alone, three patients had duodenal polyps alone whilst six patients had both gastric and duodenal polyps. Twelve, one and three patients had more than 20 polyps in the gastric fundus, antrum and duodenum respectively. Only one patient had polyps which were larger than 10 mm. The commonest polyp in the gastric fundus was the fundic gland polyp whilst hyperplastic and adenomatous polyps were the commonest polyps in the gastric antrum and duodenum respectively. Five patients had adenomatous polyps of which four had duodenal adenomas alone whilst one patient had adenomas in the duodenum, gastric antrum and fundus. Seventy-six per cent of our patients with familial adenomatous polyposis had foregut polyposis. Adenomatous polyps were found in 56% of patients with duodenal polyps or 20% of patients with foregut polyps but hyperplastic and hamartomatous polyps occur commonly in patients with familial adenomatous polyposis as well.

Adenomatous Polyposis Coli↗
PubMed1992

Choice of palliation for malignant hilar biliary obstruction.

Clinical data from 50 consecutive patients with unresectable hilar tumors situated at or proximal to the common hepatic duct were retrospectively analyzed to aid in the selection of appropriate palliative measures. Thirty-four patients had cholangioenteric bypass (CEB) to either left (28 patients), right (3 patients), or both (3 patients) intrahepatic ductal systems. Sixteen patients had nonoperative drainage (NOD) established either endoscopically (4 patients), percutaneously (9 patients), or using a combined endoscopic-percutaneous approach (3 patients). When compared with patients with CEB, patients with NOD had more frequent medical problems (p less than 0.03) and lower serum albumin levels on admission (p less than 0.03). While comparable postprocedural complications (13 CEB patients versus 4 NOD patients) were observed, patients with NOD had a significantly higher hospital mortality (9 CEB patients versus 9 NOD patients, p less than 0.05). Excluding the 12 patients (6 CEB patients versus 6 NOD patients) who died within 30 days after drainage, the quality of survival of the remaining 38 patients was analyzed with reference to 6 objective parameters. Although patients with NOD had significantly more frequent admissions relating to their catheters (p less than 0.02), there was no qualitative difference in the survival rate between the two groups of patients. For selected high-risk patients with limited life expectancy, NOD should be offered. However, additional prospective studies are required to decide the best choice of palliation for patients who are not at such high risk.

Aged↗
PubMed1992

Immediate and long-term results of percutaneous balloon aortic valvuloplasty: a report of 33 procedures.

The purpose of this study was to evaluate the immediate and long-term clinical and haemodynamic effects of Percutaneous Balloon Aortic Valvuloplasty (PBAV). Thirty-three procedures were performed in 27 patients, 11 males and 16 females with a mean age of 72 years. The peak to peak systolic gradient across the aortic valve decreased by 52%, from 67 +/- 24 mmHg to 31 +/- 15 mmHg (p < 0.0001) and the aortic valve area increased by 35%, from 0.48 +/- 0.16 to 0.67 +/- 0.21 cm2 (p < 0.001) after PBAV. There were no procedural deaths. Minor complications occurred in seven patients. Eighty-one per cent of patients (27 procedures) showed immediate symptomatic improvement, five remained symptomatic and one died in hospital before discharge. In a mean follow-up of 17 +/- 12 months (range six to 38 months), eight patients died due to congestive cardiac failure, six underwent repeat PBAV, three died due to noncardiac causes and three had recurrent symptoms controlled on medical therapy. Event free survival at 15 months was 43%. In conclusion PBAV produces a satisfactory immediate clinical and haemodynamic result, however, considering the high rate of symptom recurrence, this procedure has a beneficial role only in short-term palliation of severely symptomatic patients who are unable to undergo aortic valve replacement.

Actuarial Analysis↗
PubMed1992

Combined effects of laser irradiation and chemical inhibitors on the dissolution of dental enamel.

It has previously been shown that the susceptibility of human teeth to acid dissolution can be reduced by the presence of various chemical agents in the dissolution medium or by pretreatment of the teeth with laser irradiation. Now synergism between these two approaches to improving acid resistance has been demonstrated. Extracted human teeth were irradiated with a continuous-wave carbon dioxide laser at a wavelength of 10.6 microns. Energy doses of either 65 or 130 J/cm2 given over periods of 2 or 4 s, respectively, were applied and the teeth subjected to a severe acid challenge (0.1 M acetate buffer, pH 4.5, no calcium or phosphate common ion present) for 24 h. Mineral loss was assessed by measurement of mineral density profiles with quantitative microradiography. Experiments were carried out in the presence or absence of three chemical inhibitors with distinctly different mechanisms of action: ethane-1-hydroxy-1, 1-diphosphonic acid, fluoride, and dodecylamine HCl. Laser irradiation alone was found to lead to increased resistance of the teeth to acid challenge, with the higher energy dose being more effective than the lower dose. Each of the chemical inhibitors was effective on both lased and unlased teeth, with the percent reduction of dissolution greater when the inhibitors were applied to teeth lased with an energy dose of 130 J/cm2 which were already more resistant to acid challenge than were unlased teeth or teeth lased with a dose of 65 J/cm2.(ABSTRACT TRUNCATED AT 250 WORDS)

Absorptiometry, Photon↗
PubMed1992

Initial dissolution rate studies on dental enamel after CO2 laser irradiation.

The influence of CO2 laser irradiation on the dissolution behavior of human dental enamel has been investigated. Human enamel was irradiated by a continuous-wave CO2 laser at 10.6 microns and initial dissolution rates (IDRs) were measured in 0.1 mol/L acetate buffer, pH = 4.5, both with and without calcium and/or phosphate common ion, by means of a rotating disk assembly. The effects of (1-hydroxyethylidene) bisphosphonic acid (EHDP), fluoride (F), and dodecylamine HCl (DAC) at various levels upon the IDR were also determined. All of the findings were consistent with the hypothesis that CO2 laser irradiation converts dental enamel to hydroxyapatite (HAP) possessing site #2 character (Yamamoto et al., 1986). The dissolution driving force function, KHAP = aCa10aPO4(6)aOH2, was found to have a value of 10(-129.9) after being lased, as compared with 10(-121.4) before being lased. The IDR values for EHDP (3 mmol/L) and DAC (3 mmol/L) were essentially zero as expected for site #2 HAP. For solution F, the deduced dissolution driving force function, KFAP = aCa10aPO4(6)aF2 was 10(-128.6) after being lased as compared with 10(-116.3) before being lased. These results all support the hypotheses (1) that laser irradiation may convert the surface of human dental enamel to an apatite of significantly lower effective solubility (i.e., site #2 HAP) than that of unlased enamel; and (2) that there is significant synergism between laser treatment and these chemical dissolution rate inhibitors (again consistent with site #2 HAP). Simple model calculations indicate that, in both the presence and absence of fluoride, these laser-induced changes in the driving force for dissolution should dramatically lessen the susceptibility of enamel to the types of acid challenge that might be encountered in the mouth.

Amines↗
PubMed1992

Interferon alfa-2a and fluorouracil in the treatment of patients with advanced esophageal cancer.

PURPOSE: The trial was undertaken to determine the response rate to and toxicities from the combination of interferon alfa-2a (IFN) and fluorouracil (FU) in patients with advanced esophageal cancer. MATERIALS AND METHODS: In this prospective phase II trial conducted at a large tertiary referral cancer center and university hospital, 40 patients with advanced locoregional, metastatic epidermoid, or adenocarcinoma of the esophagus were given FU 750 mg/m2 by 24-hour continuous intravenous infusion days 1 to 5, followed by weekly outpatient bolus FU 750 mg/m2 and IFN 9 x 10(6) U three times per week from day 1. Dose was attenuated for fatigue, neurotoxicity, gastrointestinal toxicity, and myelosuppression. RESULTS: Complete and partial responses were seen in 10 of 37 assessable patients with esophageal cancer (27%; 95% confidence interval, 0.13 to 0.41). Although substantial, toxicity was tolerable and primarily involved fatigue and mild myelosuppression. The median duration of response was 6.4 months (range, 2.8 to 14+ months). CONCLUSION: The combination of IFN and FU is an active regimen in the treatment of advanced esophageal cancer with a response rate similar to that reported for cisplatin-containing combinations in similar patient populations. Further studies based on this combination are indicated.

Adenocarcinoma↗
PubMed1992

The Singapore Polyposis Registry.

The Singapore Polyposis Registry was established in 1989 in Singapore General Hospital. The aim is to provide a central registry service to all doctors in Singapore to facilitate in identification, surveillance and management of families and individuals at high risk of getting colorectal cancer from FAP (Familial Adenomatous Polyposis) and HNPCC (Hereditary Non-polyposis Colorectal Cancer). Both have an autosomal dominant inheritance that gives rise to colorectal cancer at any early age if untreated. They account for 5-6% of all colorectal cancers. Sixteen FAP families with 139 members have been evaluated. Fifty-eight members are affected and 81 are at risk or unaffected. Those who have been screened positive have a much lower risk of cancer (13%) compared with those who presented with the disease (89%) and death from colorectal cancer in the corresponding groups were nil and 58%. Eight HNPCC families with 36 affected and 170 at-risk members have been registered. Colonoscopic surveillance have just started: one case of Dukes' A cancer in a 26 year-old patient, and two cases with polyps have been diagnosed. Advances in molecular genetics and the identification of APC (Adenomatous Polyposis Coli) gene in the FAP locus of Chromosome 5 have made it possible to diagnose FAP genetically. This has important impact on management in terms of prenatal diagnosis and dietary and chemoprevention programmes in addition to surgical intervention.

Adenomatous Polyposis Coli↗
PubMed1992

Surgery for malignant obstructive jaundice: analysis of mortality.

Surgery on patients with malignant obstructive jaundice carries formidable morbidity and mortality rates. Clinical records of 120 consecutive patients who had a serum total bilirubin levels of 100 mumol/L or greater before exploration were analyzed retrospectively to provide guidelines for better management. Although most patients underwent bilienteric bypass to either the extrahepatic (n = 45) or intrahepatic ductal system (n = 28), resection was possible in 32 (26.7%). Complications developed in 42 patients (35%), among whome 12 (10%) required reexploration and 32 (26.7%) died within the same hospitalization. Identification of risk factors associated with hospital deaths after surgery was conducted on 84 of the 120 (group A) patients randomly selected from the entire study period. Based on multivariate analysis, age greater than 65 years, a raised serum aspartate transaminase value greater than 90 IU, and serum urea level greater than 7 mmol/L before surgery were the risk factors selected from 39 different clinical (n = 6), laboratory (n = 26), and operative (n = 7) parameters studied. The predictive value was validated in the remaining 36 patients (group B), and a high-risk patient population had been isolated. Because both serum urea and aspartate transaminase values correlated significantly with the necessity of urgent exploration, aggressive nonoperative treatment should be used to control the emergency. Alternative therapeutic options or perioperative management should be considered for the selected high-risk patients before definitive surgical biliary decompression.

Adult↗
PubMed1992

Anastomotic complications after esophagectomy for cancer. A comparison of neck and chest anastomoses.

Leakage, tumor recurrence, and stricture formation at the anastomosis are serious problems after esophagectomy for cancer of the esophagus or cardia. Because the prevalence of these postoperative complications may be affected by whether an anastomosis is made in the neck or in the chest, a comparison was made between anastomoses made at these two sites. During a period of some 7 years, we studied prospectively 411 patients who underwent resection for cancer of the esophagus or cardia and, after immediate reconstruction, had an anastomosis made in the neck or chest. The anastomotic leak rate for the neck anastomosis group was 4.3% and for the chest anastomosis group, 3.7% (p = not significant). The difference between leak rates of anastomoses fashioned by hand-sewn (5.0%) or stapled (3.0%) techniques was also not significant. The median upper resection margins in the neck and chest anastomosis groups were 4.5 cm and 3.5 cm, respectively. The corresponding rates of anastomotic tumor recurrence were 6.1% and 8.1% (p = not significant). The prevalence of benign stricture formation was significantly higher in the chest anastomosis group (19.2%) than in the neck anastomosis group (9.0%) (p = 0.002). This difference was a reflection of a significantly increased prevalence of stricture formation when an anastomosis was made by the stapler technique than with the hand-sewn method, and whereas most of the anastomoses in the neck were hand sewn (90%) the majority of those in the chest were stapled (80%). There were thus no statistically significant differences between the sites in terms of anastomotic leak and tumor recurrence rates, and the higher stricture rate in the chest anastomosis group was the result of more stapled anastomoses.

Anastomosis, Surgical↗
PubMed1992

Single lung transplantation: replacement therapy for end-stage lung disease.

Advances in immunosuppression and operative techniques have allowed single lung transplantation to become a viable treatment option at selected medical centers. We describe eight patients, all from the southeastern United States, who had single lung transplantation at Vanderbilt University Medical Center from March 1990 to June 1991. Their diagnoses represent a diverse set of diseases including idiopathic pulmonary fibrosis, primary pulmonary hypertension, emphysema, and pulmonary veno-occlusive disease. After thorough evaluation, the average waiting period to transplantation was 165 days. The posttransplantation periods were conspicuous for rejection, infection, and other complications. All of these recipients have either returned to an active life or are actively recuperating; this center's first single lung recipient has now survived 15 months. Our initial experience with single lung transplantation is encouraging, yet broader application requires that the paucity of donor organ availability be rectified.

Adult↗
PubMed1992

A comparison of outcome after resection for squamous cell carcinomas and adenocarcinomas of the esophagus and cardia.

Among 625 patients with squamous cell carcinoma and 134 patients with adenocarcinoma of the esophagus and cardia, a one stage resection was performed upon 375 patients of the squamous carcinoma group (excluding pharyngolaryngoesophagectomy) and 92 patients in the adenocarcinoma group. The patients formed the basis of the current analysis. Male to female ratio was 7:1 for those with squamous carcinoma compared with 3.6:1.0 for those with adenocarcinoma (p = 0.037). Most squamous carcinomas were located in the middle one-third (56.3 percent) and lower one-third (33.0 percent) of the esophagus. Adenocarcinomas were predominantly found at the cardia (91.3 percent) and lower one-third (6.5 percent). Postoperatively, respiratory complications occurred in 34.4 percent of patients in the group with squamous carcinoma and in 19.6 percent of patients in the group with adenocarcinoma (p = 0.01). Cardiac complications occurred in 28.3 percent of patients in the group with squamous carcinoma and in 16.3 percent of patients in the group with adenocarcinoma (p = 0.03). Anastomotic leaks were uncommon for both groups (4.3 and 5.4 percent, respectively). Anastomotic recurrence occurred in 6.1 and 7.6 percent of patients, respectively. Respiratory complications, malignant cachexia and sepsis accounted for most of the deaths in the hospital. The 30 day mortality rates for patients with squamous carcinoma and adenocarcinoma were comparable (4.8 and 6.5 percent, respectively) (p = 0.33). After 30 days, mortality rates differed significantly (11.7 and 3.3 percent, respectively) (p = 0.026). The overall hospital mortality rates, however, were comparable (16.5 and 9.8 percent, respectively) (p = 0.14). The overall five year survival rate for both groups was 15 percent. For patients with squamous carcinomas, the five year survival rate after curative resection was 31 percent compared with 5 percent for palliative resection. For patients with adenocarcinomas, the respective five year survival rates were 35 and zero percent. It was concluded that the two types of tumor differ significantly in the incidence of postoperative morbidity, but mortality and the long term survival rates were similar.

Adenocarcinoma↗
PubMed1991

Mammographically guided fine-needle aspiration biopsy of nonpalpable breast lesions. Can it replace open biopsy?

The authors report the accuracy of mammographically guided fine-needle aspiration (FNA) for the diagnosis of nonpalpable breast lesions in a series of 71 patients. Each mammographically guided FNA was immediately followed by hookwire localization and open biopsy. Seven malignancies were identified cytologically, but three cancers were not detected in aspirates judged to be sufficient for diagnosis. In addition, 19 aspirates were reported to be insufficient, and 4 of these were obtained from lesions histologically proven to be adenocarcinoma. Although no false-positive diagnoses were encountered, the technique demonstrated a sensitivity of 78% and a diagnostic accuracy of 94% for adequate specimens. In this study, mammographically guided FNA was insufficiently sensitive to replace open biopsy for the diagnosis of nonpalpable breast lesions.

Biopsy↗
PubMed1991

A broad-spectrum human lung fibroblast-derived mitogen is a variant of hepatocyte growth factor.

A heparin-binding mitogen was isolated from conditioned medium of human embryonic lung fibroblasts. It exhibited broad target-cell specificity whose pattern was distinct from that of any known growth factor. It rapidly stimulated tyrosine phosphorylation of a 145-kDa protein in responsive cells, suggesting that its signaling pathways involved activation of a tyrosine kinase. Purification identified a major polypeptide with an apparent molecular mass of 87 kDa under reducing conditions. Partial amino acid sequence analysis and cDNA cloning revealed that it was a variant of hepatocyte growth factor, a mitogen thought to be specific for hepatic cells and structurally related to plasminogen. Recombinant expression of the cDNA in COS-1 cells established that it encoded the purified growth factor. Its site of synthesis and spectrum of targets imply that this growth factor may play an important role as a paracrine mediator of the proliferation of melanocytes and endothelial cells, as well as cells of epithelial origin.

Amino Acid Sequence↗
PubMed1991

Acute cholangitis secondary to hepatolithiasis.

In a series of 88 patients with acute cholangitis secondary to hepatolithiasis, 26 (30%) required emergency therapeutic intervention because of septicemic shock (n = 15), persistent fever (n = 8), or spreading peritonitis (n = 3). Analysis was made to define factors that predisposed to failure of conservative treatment and characteristics that could predict the need for emergency biliary decompression. The age, incidence of concomitant medical diseases, previous biliary surgery, positive blood culture, bacterial strains resistant to antibiotics used, and multiplicity of bacterial strains in bile cultures in patients who required emergency intervention were similar to these factors in patients who had elective operations after successful conservative management. The incidence of intrahepatic segmental obstruction by stones or strictures was similar, but many more patients who required emergency intervention had concomitant extrahepatic obstruction due to impacted common ductal stones or strictures. Logistic regression analysis of clinical, hematological, and biochemical data showed that maximum pulse rate within 24 hours of presentation (greater than 100 beats per minute, relative risk, 2.8) and platelet count at the time of admission (less than 150 x 10(9)/L, relative risk, 5.2) were the factors with independent significance in predicting the need for emergency therapeutic procedures. This finding may serve as a guideline for identifying high-risk patients for early intervention.

Adolescent↗