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Biomedical subjects

L S Ong

Publications and source records attributed to L S Ong.

At least 19 recordsLinked to original sources
PubMed2005

An intelligent tutoring system for trauma management (Trauma-Teach): a preliminary report.

Trauma-Teach is an interactive software for tutoring surgical trainees on medical trauma management procedures. Users of the system interact with a virtual patient suffering from trauma injuries. The task of the user is to stabilise the virtual patient, discover the underlying injuries and decide on an appropriate management plan. Artificial intelligence techniques are used to simulate the patient's pulmonary and cardiovascular systems in real time, determine the responses and results of treatments and diagnostics accordingly, model the patient deterioration if wrong actions are taken, and give a measure of reality to the system by selecting actual trauma cases from the hospital's database.

Artificial Intelligence↗
PubMed1999

Successful transluminal coronary angioplasty facilitated only by guidewire support.

We describe a case where extreme tortuosity in the patient's iliac arterial system precluded the manipulation and therefore engagement of 8 Fr guiding catheters with our target vessel. After diagnostic coronary angiography was performed with 6 Fr catheters, successful balloon angioplasty was negotiated over a stiff guidewire without guiding catheter support. Balloon dilatation of the ostial stenosis enabled subsequent engagement with 8 Fr guiding catheter and successful stent delivery.

Aged↗
PubMed1999

Asymmetry in optic disc parameters: the Blue Mountains Eye Study.

PURPOSE: To examine asymmetry in vertical optic disc parameters among subjects classified as normal, as having ocular hypertension (OH), and as having open-angle glaucoma (OAG) in a population-based sample. METHODS: The Blue Mountains Eye Study examined 3654 people aged 49 to 97 years, including 2929 normal subjects, 118 with OH, and 79 with OAG in the groups of interest for the asymmetry study. Optic disc parameters were measured in a masked manner from stereo optic disc photographs. RESULTS: Vertical disc diameter asymmetry (the absolute value of left minus right disc diameters) was similar among normal, OH, and OAG groups (median, 0.07-0.08 mm). Vertical cup- disc ratio asymmetry was higher in patients with OAG (median, 0.11) than in normal subjects (median, 0.06; P < 0.0001) and in those with OH (median, 0.05; P < 0.0001) but was similar between normal subjects and patients with OH (P = 0.17). A cup- disc ratio asymmetry of 0.2 or more was found in 24% of patients with OAG, compared with 1% of patients with OH and 6% of normal subjects. Corresponding rates for cup- disc ratio asymmetry of 0.3 or more in these three groups were 10%, 0%, and 1%, respectively. Using multiple linear regression, cup-disc ratio asymmetry was associated with disc diameter asymmetry and intraocular pressure asymmetry. However, these two factors explained only 3% of the variability of cup- disc ratio asymmetry and 20% of cup diameter asymmetry. CONCLUSIONS: Despite differences between the OAG group and either the OH or normal groups, asymmetry alone was not useful in identifying patients with OAG. At all levels of asymmetry, subjects were more likely to be classified as normal than with OH or OAG.

Aged↗
PubMed1997

Pharmacokinetics of intrapericardial administration of 5-fluorouracil.

UNLABELLED: A 30-year-old patient with metastatic breast adenocarcinoma was diagnosed as having a malignant pericardial effusion. METHODS: The patient was treated with two courses of 200 mg 5-fluorouracil (5-FU) followed by 20 mg cisplatin 5 h later directly infused into the pericardial space through a catheter. The drug levels of the 5-FU were monitored during the second treatment. The half-life of 5-FU in the pericardial space was 168.6 min with a concentration of 0.113 mg/ml still detected at 5 h. The area under the curve (AUC) was estimated to be 4.739 mg h/ml. The plasma concentrations of 5-FU ranged from 0.022 to 0.04 mg/ml throughout the infusion. RESULTS: There was no significant change in the patient's blood counts or chemistry profile. She did not experience any side effects during the treatment. A pericardial window was performed 2 days later when balloon pericardiectomy was unsuccessful. The patient eventually succumbed to her disease 4 months later, but without evidence of pericardial effusion. CONCLUSIONS: We conclude that pericardial infusion of 5-FU allowed a high concentration of 5-FU to be achieved within the pericardial sac with a greatly increased half-life over that of systemic 5-FU treatment (168 min vs 6-20 min), and with little systemic toxicity.

Adenocarcinoma↗
PubMed1997

The Colorectal Cancer Recurrence Support (CARES) System.

Colorectal cancer has risen in incidence to become the second commonest form of cancer in Singapore. The primary treatment is surgery but up to 50% of patients still suffer from recurrence of the cancer after surgery. Early identification of recurrence will increase the effectiveness of therapy and the survival of patients. This paper describes the CARES (Cancer Recurrence Support) System, whose objective is to predict the recurrence of colorectal cancer, using Case-based Reasoning (CBR), and supported by other techniques such as data mining and natural language processing. The CARES System employs CBR to compare and contrast between the new and past colorectal cancer patient cases, and makes inferences based on those comparisons to determine the high risk patient groups. The features and functionality of the system are described.

Artificial Intelligence↗
PubMed1996

Safety and effectiveness of the Arani curve guiding catheters in Palmaz-Schatz stenting of right coronary artery stenosis.

The purpose of this study was to evaluate the safety and efficacy of Arani curve guiding catheters in Palmaz-Schatz stenting of right coronary artery (RCA) stenosis. A total of 15 stents was implanted in 13 right coronary arteries. For stenting of the RCA with marked superior orientation and shepherd's crook configuration of the proximal segment, a catheter with a 75 degrees primary curve was used. A catheter with a 90 degrees primary curve was usually the best choice for stenting of the RCA with slight superior, horizontal, or interior orientation of the proximal segment. These catheters provided excellent support in 12 of 13 cases (93%) and resulted in successful stent deployment in these patients. There was one dissection which occurred distal to the stent following poststent balloon dilatation, and which required emergency coronary artery bypass graft surgery. There were no complications attributed to these guiding catheters. An extraordinary formation of pseudostenosis occurred in one patient. We conclude that Arani curve guiding catheters provide strong support and are safe and effective in stenting of RCA stenosis.

Aged↗
PubMed1994

Long-term patency of a Cook stent without anticoagulation.

In recent years intracoronary stenting has been proven to be an effective bail out for acute and threatened closure during and after coronary angioplasty. Initial enthusiasm has been hampered by significant anticoagulation related vascular and bleeding problems. We report a patient with intracoronary stent whose stent remained patent despite lack of any anticoagulation.

Angioplasty, Balloon, Coronary↗
PubMed1992

Evaluation of coronary flow reserve using myocardial contrast echocardiography in humans.

To evaluate the applicability of myocardial contrast echocardiography for the assessment of coronary blood flow reserve, 21 consecutive patients undergoing coronary angiography were studied. Only patients with a single left anterior descending lesion or normal coronary angiogram were included. Intracoronary injections of sonicated albumin were performed before and after the administration of intracoronary papaverine. Good quality studies at baseline and after the administration of papaverine were obtained in 14 of 21 patients. Ten patients had a significant (greater than 75%) single left anterior descending lesion and four had normal or insignificant lesions (70% or less stenosis) in the left anterior descending coronary artery. Time-intensity curves for the left anterior descending coronary artery region of interest were generated and then the peak contrast intensity (PCI), washout half-time (T1/2) and the area under the curve (AUC) were calculated. The post-papaverine increases in PCI and in the AUC, compared to baseline, were 55 +/- 22% and 102 +/- 14% in the four patients with 70% or less left anterior descending diameter stenosis serving as a control group and 3 +/- 25% and 40 +/- 10%, respectively, in the 10 patients with significant left anterior descending coronary artery disease (mean +/- 1 SD, P less than 0.01). In patients with normal coronary arteriography T1/2 increased after intracoronary injection of papaverine. In patients with severe lesions, either an increase or a decrease in T1/2 was observed. Significant left anterior descending coronary artery stenosis associated with impaired coronary blood flow reserve can be detected by failure of myocardial contrast echocardiographic parameters to increase after injection of papaverine. Mild and transient side effects were noted in three patients.

Aged↗
PubMed1989

Quantitative assessment of the immediate results of coronary angioplasty by myocardial contrast echocardiography.

A low pressure gradient across the residual lesion and a minimal percent residual stenosis are markers of a successful coronary angioplasty. A more physiologic method of assessing the results of coronary angioplasty would involve assessment of myocardial perfusion in the affected coronary bed. Contrast two-dimensional echocardiography provides information about regional myocardial perfusion. To assess the correlation between pre- to postcoronary angioplasty changes in gradient or percent stenosis and the increase in peak contrast intensity, 23 consecutive patients were studied during coronary angioplasty. In 19 of the 23 patients, the coronary angioplasty was successful and in 15 (79%) of the 19, an adequate echocardiographic study was obtained. Mild and transient side effects of echo contrast were observed in 3 of the 15 patients. The gradient across the residual lesions decreased from 52 +/- 12 to 11 +/- 4 mm Hg (mean +/- SD), the diameter of the stenotic lesion decreased from 89 +/- 10 to 25 +/- 16% and corrected peak contrast intensity (peak contrast - baseline contrast in gray level U/pixel) increased from 15 +/- 16 to 50 +/- 26. All these differences were significant at the p less than 0.001 level. Corrected peak contrast intensity correlated exponentially with the decrease in pressure gradient (r = 0.82, p less than 0.001). The correlation curve had a greater increase in peak contrast intensity at gradient decreases greater than 45 mm Hg. Corrected peak contrast intensity did not correlate with decrease in diameter of the stenotic lesion (r = 0.19).

Adult↗
PubMed1989

Myocardial perfusion imaging by contrast echocardiography with use of intracoronary sonicated albumin in humans.

Sonicated albumin has been proposed as a near ideal echocardiographic contrast agent with little myocardial toxicity or hemodynamic effect. Its use has not yet been reported in humans, partly because of difficulties in preparation. With use of the newly modified sonication method, 10 ml of 5% albumin was sonicated for 75 s with a 5.0 ml slow infusion of air. This resulted in microbubbles with a mean diameter (+/- SD) of 5 +/- microns). Fourteen patients undergoing routine coronary angiography were studied. One patient had normal coronary arteries; the other 13 had significant coronary artery disease. In a subgroup of nine patients, sonicated albumin and sonicated diatrizoate meglumine sodium (microbubble diameter 9 +/- 3 microns) were injected several minutes apart, using the same technique. Videodensity-time curves were obtained from a region of interest in the myocardium. Corrected peak contrast intensity (baseline contrast intensity subtracted from peak contrast intensity, gray scale U/pixel) for sonicated albumin and for sonicated diatrizoate meglumine sodium was 51 +/- 26 and 52 +/- 19, respectively (p = 0.89). Washout half-time (T1/2) for the two agents was 5.5 +/- 4.5 and 16.0 +/- 12.2 s, respectively (p = 0.01). One patient with unstable angina experienced transient chest pain after repeated albumin injections. No electrocardiographic changes, blood pressure changes or wall motion abnormalities were observed. Administered by intracoronary injection, sonicated 5% albumin is a safe and effective echocardiographic contrast agent for myocardial perfusion imaging, yielding excellent myocardial contrast with physiologic washout time.

Adult↗
PubMed1988

Magnet unresponsive pacemaker endless loop tachycardia.

Endless loop tachycardia is a well-known complication of DDD pacing and is almost invariably terminated by conversion to the asynchronous DOO mode upon application of a magnet over the pulse generator. Occasionally magnet application is ineffectual because the ventriculoatrial (VA) synchrony of endless loop tachycardia is converted directly or indirectly to an atrioventricular (AV) desynchronization arrhythmia, another form of VA synchrony. This occurs when a paced ventricular beat engenders an unsensed retrograde P wave and the continual delivery of an ineffectual atrial stimulus during the atrial myocardial refractory period creates self-perpetuating VA synchrony. Upon magnet removal, AV desynchronization arrhythmia reverts immediately to endless loop tachycardia. In the absence of access to programmers, magnet unresponsive endless loop tachycardia can be easily and reliably terminated by chest wall stimulation through inhibition of the ventricular channel of the DDD pulse generator.

Cardiac Pacing, Artificial↗
PubMed1988

Termination of ventricular tachycardia by chest wall stimulation during DDD pacing. A report of two cases.

This report describes the use of chest wall stimulation (CWS) for the termination of ventricular tachycardia in two patients with dual chamber pulse generators functioning in the DDD mode. Rapid CWS induced burst ventricular pacing when CWS was selectively sensed by the atrial channel, whereupon the pulse generator triggered its ventricular output. In this way, by programming the pulse generators to the maximum upper rate, this CWS technique produced burst ventricular pacing at a rate of 175 to 180/minute that successfully terminated ventricular tachycardia in both patients. The same CWS technique also initiated ventricular tachycardia by burst ventricular pacing. This CWS technique may be useful for the termination of relatively slow ventricular tachycardia in patients with DDD pulse generators when the maximum rate of ventricular pacing cannot be otherwise increased.

Aged↗
PubMed1988

Pacemaker endless loop tachycardia: termination by simple techniques other than magnet application.

PURPOSE: Pacemaker endless loop (or reentrant) tachycardia (ELT) is often terminated by conversion to the asynchronous mode of pacing by simply placing a magnet over the implanted atrial tracking (DDD or VDD) pacemaker. We investigated three other simple methods of ELT termination--chest wall stimulation (CWS), provocation of myopotential oversensing, and chest thumping--that may be useful when the arrhythmia is unresponsive to magnet application or a magnet is unavailable. PATIENTS AND METHODS: A modified CWS technique using an external pulse generator (pulse width = 40 msec) ordinarily used for transcutaneous cardiac pacing was tested in 74 patients (40 with unipolar and 34 with bipolar DDD devices). CWS inhibited the ventricular channel of all DDD pacemakers easily and reliably. CWS was then applied during ELT in 20 patients (10 with unipolar and 10 with bipolar DDD devices). Provocation of myopotential oversensing by the ventricular channel was attempted during ELT in 10 patients with unipolar DDD pacemakers. Chest thumping was tried during ELT in six patients. RESULTS: CWS by the modified technique terminated ELT in all patients in whom the arrhythmia was induced. Myopotential oversensing resulted in successful ELT termination in six of the 10 patients. ELT was successfully terminated by chest thumping in four of six patients. CONCLUSION: These simple techniques provide effective ways of ELT termination other than magnet application, and may be easily applied by physicians unfamiliar with the complexities of contemporary DDD pacemakers and their programmers.

Cardiac Pacing, Artificial↗