Biomedical subjects

M C Lim

Publications and source records attributed to M C Lim.

At least 19 recordsLinked to original sources

PubMed2001

Late onset lens particle glaucoma as a consequence of spontaneous dislocation of an intraocular lens in pseudoexfoliation syndrome.

PURPOSE: To report acute onset lens particle glaucoma associated with pseudoexfoliation-related dislocation of an intraocular lens implant 12 years after cataract surgery. METHODS: Case report. RESULTS: An 80-year-old woman presented with acute onset of left eye pain that was associated with white fleck-like particles circulating in the anterior chamber and an intraocular pressure of 48 mm Hg. The posterior chamber intraocular lens within the capsular bag was positioned more posteriorly to the iris plane than usual, and pseudoexfoliative material was present on the lens capsule and the zonules. Anterior chamber aspirate confirmed the presence of lens cortical fibers. CONCLUSION: Spontaneous dislocation of the posterior chamber intraocular lens in patients with pseudoexfoliation syndrome several years after cataract surgery may liberate lens cortical material, causing lens particle glaucoma.

Acute Disease↗

PubMed2001

Decreased macular leukocyte velocity in human immunodeficiency virus-infected individuals.

PURPOSE: To determine whether human immunodeficiency virus (HIV)-infected individuals have decreased macular capillary blood flow in vivo. DESIGN: Case control study. METHODS: Macular leukocyte velocity and perceived leukocyte density were determined in 41 HIV-infected individuals without cytomegalovirus retinitis and 31 HIV-negative control subjects using the blue field simulation technique (BFS-2000, Oculix, Inc., Jenkintown, PA). Velocity and density measurements for HIV-infected individuals were compared to current and lowest previous CD4+ T-lymphocyte counts, HIV RNA blood levels, and blood leukocyte counts. RESULTS: Mean macular leukocyte velocity was lower in HIV-infected individuals than in controls (P = 0.0006). No correlations were identified between velocity measurements and the following factors in HIV-infected individuals: current or lowest previous CD4+ T-lymphocyte count; or HIV RNA blood level. Mean perceived leukocyte density in HIV-infected individuals was lower than in controls (P = 0.003), but was not correlated with blood leukocyte count in HIV-infected individuals. No relationships were identified between macular leukocyte velocity and duration of medication use or duration of elevated CD4+ T-lymphocyte count in patients receiving potent antiretroviral therapy. CONCLUSIONS: Reduced macular leukocyte velocity may have important implications for understanding the retinal microvasculopathy of HIV disease, the pathogenesis of opportunistic retinal infections, and visual dysfunction in HIV-infected individuals who do not have opportunistic retinal infections. We found no evidence that macular leukocyte velocity increased with immune reconstitution.

Adult↗

PubMed1998

Depolarization counteracts glucocorticoid inhibition of adenohypophysical corticotroph cells.

In AtT20 mouse corticotroph tumour cells large conductance Ca2+-activated K+-channels (BK-channels) have an essential role in the early glucocorticoid inhibition of adrenocorticotrophin (ACTH) secretion evoked by corticotrophin-releasing factor. The present study examined whether or not BK-channels are also pivotal to glucocorticoid inhibition of normal rat anterior pituitary cells. A membrane-permeant, non-metabolizable cyclic AMP analogue, 8-(4-Chlorophenylthio)adenosine-3',5'-cyclic-monophosphate (CPT-cAMP) was used as the primary secretagogue stimulus, as this mimics the increase of intracellular cyclic AMP caused by corticotrophin-releasing factor, but is not subject to the complex Ca2+-dependent regulation of cyclic AMP metabolism that is evident in corticotroph cells. Experiments in AtT20 cells showed that ACTH secretion stimulated by 1 mM CPT-cAMP was suppressed to 34+/-1.5% (n = 12) of the control stimulus by a maximal dose of 100 nM dexamethasone. The ACTH secretion evoked by the combination of 1 mM CPT-cAMP with either 5 microm (-)BayK8644 (L-type Ca2+-channel activator) or 5 mM TEA (K+-channel blocker) was respectively 69.1+/-7.6% and 69.3+/-11.8% of control after 2 h preincubation with 100 nM dexamethasone (P<0.05 vs CPT-cAMP). The ACTH response elicited by 5 microM (-)BayK8644 and 5 mM TEA given together was completely resistant to inhibition by 100 nM dexamethasone. Furthermore, TEA and (-)BayK8644 given together synergistically stimulated ACTH release in combination with 0.1 mM or 1 mM CPT-cAMP, and these ACTH responses were not inhibited by 100 nM dexamethasone. In primary cultures of rat anterior pituitary cells, TEA (up to 20 mM), charybdotoxin (30 nM) or apamin (100 nM) failed to modify the glucocorticoid inhibition of 0.1 mM CPT-cAMP-induced ACTH release. The combination of 5 mM TEA and 5 microM (-)BayK8644 elicited a small but significant increase in ACTH secretion but did not modify the inhibition of 0.3 mM CPT-cAMP-induced ACTH secretion by 100 nM dexamethasone. In primary cultures of rat anterior pituitary cells, depolarization of the membrane potential with 40 mM KCl enhanced the ACTH response to CPT-cAMP and markedly reduced the maximal inhibitory effect of dexamethasone to 55+/-1.2% as well as that of corticosterone to 33+/-2.1% vs 100+/-2.5% and 100+/-1.9% inhibition respectively, when 0.1 mM CPT-cAMP was used alone. Introduction of 5 microM (-)BayK8644 with 40 mM KCl in this system had no additional effect on glucocorticoid inhibition. No glucocorticoid inhibition of ACTH release to any of the stimuli applied was observed in cells pretreated with the mRNA synthesis inhibitor, 5,6-dichloro-furanosyl-benzimidazole riboside (DRB) (0.1 mM) or the protein synthesis blocker, puromycin (0.1 mM). In summary, early glucocorticoid inhibition of stimulated ACTH release by cultured rat anterior pituitary cells was dependent on the synthesis of new mRNA and protein. Depolarization of the membrane potential potentiated CPT-cAMP-induced ACTH secretion in AtT20 cells as well as cultured rat corticotrophs and this was associated with a resistance to the early inhibitory effect of glucocorticoids. Glucocorticoid inhibition in rat anterior pituitary corticotrophs was unaltered by TEA, charybdotoxin as well as apamin, and hence it is unlikely to involve predominantly BK-or SK-type Ca2+-activated K+-channels. These results support the thesis that a prime target of glucocorticoid feedback inhibition in anterior pituitary corticotrophs is the membrane potential and indicate that glucocorticoid-induced proteins regulate the activities of several distinct plasma membrane ion channels.

Adrenocorticotropic Hormone↗

PubMed1996

Effects of loratadine and terfenadine on the induced nasal allergic reaction.

OBJECTIVE: To evaluate the effect of terfenadine and loratadine on the early nasal allergic response to challenge and the subsequent cellular influx and hyperresponsiveness. DESIGN: Double-blind, placebo-controlled, triple-crossover study. SUBJECTS: Fourteen, asymptomatic, allergic volunteers. INTERVENTIONS: After an initial challenge with methacholine chloride, subjects received treatment with placebo, loratadine (10 mg by mouth daily), or terfenadine (60 mg by mouth twice daily) for 1 week, followed by a nasal allergen challenge with lavages; 24 hours later, while the subjects were still receiving medication, the quantity of cells in the nasal lavage was determined, and another challenge with methacholine was done. Mediator levels were quantified in the nasal lavages after the allergen c hallenge, and the weight of the methacholine-induced nasal secretions was measured. RESULTS: Both loratadine and terfenadine treatment resulted in significant reductions in allergen-induced sneezing and the levels of histamine, kinins, albumin, and N-alpha-tosyl-L-arginine methyl ester-esterase activity in recovered nasal lavages compared with the reductions that resulted from placebo treatment, with no significant difference among the treatments. Treatment had no effect on the levels of tryptase, prostaglandin D2 or leukotriene C4. A significant eosinophil influx into nasal secretions 24 hours after the allergen challenge in patients who were receiving placebo (P=.006) was not affected by loratidine or terfenadine treatment. Comparing methacholine-induced secretions between screening challenges and challenges with the patients who were being treated with either loratadine or terfenadine, there was a significant decrease in secretions after the use of these antihistamines (P<.05). CONCLUSION: Both loratadine and terfenadine partially inhibit the early nasal response to allergen challenge and the subsequent reactivity to a challenge with methacholine without affecting the influx of eosinophils into nasal secretions.

Adult↗

PubMed1996

Clinical and echocardiographic features of mitral valve prolapse patients in a local population.

Mitral valve prolapse (MVP) is a commonly diagnosed condition with varied clinical presentations but local data is lacking. In our study, we reviewed 98 patients (54 males, 44 females) with echocardiographic mitral valve prolapse diagnosed between 1991 and 1993 to study the clinical profile and echocardiographic features of patients with this condition in our local population. The mean and median age at presentation/detection were 42 years and 38 years respectively. The majority of the patients were asymptomatic (59%); the rest presented with palpitations (21%), congestive heart failure (4%) and infective endocarditis (5%). On clinical examination, 64 patients had mitral regurgitation (13 patients had both mitral regurgitation murmur and a systolic click), while one or more systolic clicks were heard in another 32 patients. Six patients also had associated Marfan syndrome. 2D echo revealed isolated anterior and posterior leaflet involvement in 55 and 19 patients respectively. Another 24 patients had involvement of both leaflets. Mitral regurgitation was detected on colour Doppler study in 78 patients. Nine patients had associated tricuspid valve prolapse. Of the 98 patients, 8 patients developed flail mitral valve. Four were detected at presentation/diagnosis, while the other 4 were diagnosed incidentally on routine follow-up 2D echo. Of these 8 patients, one developed cardiac failure. The patients had been on follow-up for a mean period of 9 months. During this period, mitral regurgitation progressed in 3 patients resulting in valve surgery. Only 20 patients had arrhythmias detected on ambulatory ECG monitoring, most of them were frequent atrial and ventricular premature beats. No patient was found to have haemodynamically significant arrhythmia. In summary, most patients with MVP had anterior mitral valve leaflet prolapse and mitral regurgitation. Although most patients with MVP are asymptomatic or have minor symptoms, it is associated with significant morbidity.

Adult↗

PubMed1995

Implicating adhesion molecules in nasal allergic inflammation.

Allergic rhinitis is now considered an inflammatory disorder where many leukocyte types, including eosinophils and T-lymphocytes, accumulate in increased numbers. Along with mast cells and other cells, they release a wide variety of mediators, cytokines, and granule constituents that can directly cause inflammation or activate the local vascular endothelium to further enhance the recruitment of leukocytes through the expression and function of adhesion molecules. While the understanding of the importance of leukocyte and endothelial adhesion molecules is still at a very early stage, recent evidence has already begun to implicate these cell surface molecules in the pathogenesis of allergic diseases such as rhinitis and asthma. Additional studies, including the use of adhesion molecule antagonists when available, will clarify the importance of these structures in the pathophysiology of these disorders.

Cell Adhesion Molecules↗

PubMed1995

Vortex vein exit sites. Scleral coordinates.

PURPOSE: The authors determined the frequency and scleral coordinates of vortex vein exit sites in 46 autopsy eyes to provide topographic data that will enable surgeons to locate these vessels more precisely. METHODS: Forty-six autopsy eyes were examined under a dissecting microscope to measure the frequency of vortex veins and the cord lengths between the vortex vein scleral exit sites and the limbus, rectus muscle insertions, and oblique muscle insertions. RESULTS: Data from this study showed that 32 (70%) of the 46 individual eyes studied had more than four vortex veins. The number of second or third vortex veins found in the nasal quadrants was significantly higher than the number found in the temporal quadrants (P < 0.01). Statistical analyses of the measurements provided mean values for distances between vortex vein scleral exit sites and the three nearest extraocular muscle insertions; these positions among eyes were found to be relatively uniform (standard deviation, 0.7-2.5 mm). CONCLUSION: The authors suggest that the majority of adult eyes encountered by a surgeon will have more than four vortex vein exit sites and that more vortex veins may be expected in the nasal quadrants than in the temporal quadrants. This study delineates the locations of vortex vein exit sites so that surgeons can reliably predict their surface positions to avoid vessel laceration and its ensuing complications.

Anthropometry↗

PubMed1995

The histology of allergic rhinitis and its comparison to cellular changes in nasal lavage.

To better understand how changes in cells in nasal secretions reflect changes in the nasal mucosa occurring during allergic reactions, we obtained nasal lavage and biopsy specimens from normal (n = 11) asymptomatic, seasonally allergic (n = 18), and perennially allergic (n = 18) subjects. Initial baseline lavages showed that perennially, and seasonally allergic subjects, out of their allergy seasons, had significantly higher numbers of eosinophils (p < 0.01) and neutrophils (p < 0.01) and total cell counts (p < 0.05) than normal subjects. Biopsy results showed that at baseline, seasonally allergic subjects had thicker mucosa (p < 0.01), greater numbers of intraepithelial mononuclear cells and total cells (p < 0.01), and greater numbers of subepithelial neutrophils (p < 0.001) than perennially allergic subjects. Twenty-four hours after antigen provocation, nasal lavage of allergic subjects showed an increase in the number of eosinophils (p < 0.05). Seasonally allergic subjects also had significant increases in numbers of intraepithelial mononuclear cells (p < 0.05) and total cells (p < 0.01), and in subepithelial eosinophils (p < 0.001) and mononuclear cells (p < 0.05), which were localized to the side challenged. Despite an influx in eosinophils, the epithelial layer was not changed from baseline. The data provide evidence that nasal secretions and the nasal mucosa represent two distinct cellular compartments.

Adult↗

PubMed1995

Diagnosis of deep vein thrombosis using duplex ultrasonography.

Duplex ultrasonography is a safe, accurate, efficient, inexpensive, noninvasive diagnostic test for deep vein thrombosis (DVT). The sensitivity and specificity of this technique is comparable to venography in symptomatic patients in many studies. The diagnostic accuracy of this test can be further enhanced by serial studies. We report our experience with the use of this technique for study of 180 patients with clinically suspected DVT. Only 55 (30.6%) patients were confirmed to have DVT on duplex ultrasonography which illustrates the inaccuracy of bedside diagnosis of this potentially life-threatening condition. Almost all our DVT patients have proximal vein involvement, indicating that venous thrombosis usually do not cause signs or symptoms until they become large, occlusive and extend into the proximal veins. It is also observed in our study cohort that half of the patients with proximal vein thrombosis has incomplete recanalisation on follow-up study. None of them with normal study developed significant sequelae of untreated DVT, suggesting that it is safe to withhold treatment based on result of this non-invasive test. Duplex ultrasonography is the diagnostic modality of choice for suspected DVT in symptomatic patients and is an excellent substitute for conventional contrast venography.

Adult↗

PubMed1995

Stenting of stenosis of the abdominal aorta.

Isolated abdominal aortic stenosis resulting in bilateral lower limb claudication is uncommon in Asians. We report a 75-year-old Oriental man with isolated abdominal aortic stenosis who underwent intraluminal stenting, resulting in the abolishment of a 76 mmHg gradient. As the stenotic segment was local, only the mid-segment of the Palmaz stent was apposed to the aortic wall. Follow-up ultrasound scans showed that the partially apposed stent was potent, with no thrombosis in the free space between the stent and the wall. Hence, although aortic stenting in this patient resulted in partial apposition of the stent to the aortic wall, there was no thrombosis or migration of the stent. The patient remained symptom-free one year post-stenting. Stenting in this patient with failed balloon angioplasty was a safe and efficacious method of treating significant isolated abdominal aortic stenosis.

Aged↗

PubMed1994

Nasal challenge with allergen upregulates the local expression of vascular endothelial adhesion molecules.

To understand the events involved in selective eosinophil migration into allergic inflammatory sites, we studied the expression of vascular endothelial adhesion molecules in the nasal mucosa. Ten subjects with asymptomatic seasonal allergic rhinitis and 13 nonallergic subjects underwent localized allergen challenge of one inferior turbinate. Twenty-four hours later, biopsy specimens were obtained from the inferior turbinates, bilaterally in the seasonally allergic subjects and unilaterally in the nonallergic control subjects. The specimens were divided, sectioned, and either stained for identification of eosinophils or analyzed immunohistochemically for intercellular adhesion molecule-1, E-selectin, vascular cell adhesion molecule-1 (VCAM-1), and von Willebrand's factor. Intercellular adhesion molecule-1 expression was observed in all mucosal specimens, with no significant difference among groups. E-selectin showed minimal baseline expression, and low levels were significantly induced on the challenged mucosa of the allergic compared with nonallergic subjects (p < 0.05). VCAM-1 was expressed basally and was significantly upregulated by allergen challenge, compared with the nonchallenged side and nonallergic control subjects (p < 0.05). Submucosal eosinophils increased significantly in allergic subjects 24 hours after antigen challenge, compared with nonallergic control subjects and weakly correlated with VCAM-1 expression (rs = 0.33, p = 0.06). Our results suggest that endothelial activation accompanies allergic inflammation. Furthermore, because the counterligand for VCAM-1, very late activation antigen-4, is present on eosinophils, VCAM-1 upregulation may contribute to the selective recruitment of these cells to the nasal mucosa.

Adult↗

PubMed1994

Pregnancy outcome and mitral valve prolapse.

Mitral valve prolapse (MVP) comprises a large proportion of obstetric cardiac problems and has a general prevalence of 4%. We examined the obstetric outcome of patients with MVP delivered between 1988-1991 at the National University Hospital, Singapore. During this interval, deliveries totalled 16,755 of which 85 (0.51%) had maternal cardiac disease. Of these, 28 (32.9%) had echocardiographic evidence of non-myxomatous MVP. Ten patients (37.5%) had demonstrable mitral regurgitation and 4 (14.3%) had benign ventricular ectopics. All patients remained well throughout pregnancy. Gestation at delivery and use of analgesia did not differ significantly from non-cardiac patients. However, the labour induction rate was twice the department average at 17.9%. Twenty-four (85.7%) patients achieved vaginal delivery and 4 (14.3%) patients were delivered abdominally. All babies were liveborn. Eight patients (28.6%) did not receive antibiotic prophylaxis during labour and postpartum period and remained afebrile. The role of antibiotics in this category of patients is discussed. Patients with MVP without myxomatous valve changes may expect excellent pregnancy outcome.

Adult↗

PubMed1994

The new titanium Greenfield vena cava filter: initial experience and review.

The Greenfield vena cava filter is an established therapeutic option in the prevention of pulmonary embolism. The development of a 12 French modified titanium Greenfield filter (TGF) has made it possible to insert the filter percutaneously and to have a low complication rate. We report our initial experience with percutaneous insertion of the 12-French titanium Greenfield vena cava filter for 6 patients who all had major extensive deep venous thrombosis (DVT) and contraindications to anticoagulation. The inferior vena cava (IVC) filters were inserted in all the 6 patients via the internal jugular route without difficulty. There was no bruising, haematoma or bleeding complications despite the use of the 12 French system. The IVC filter was opened without cross-snaring of the filter legs in all 6 patients. This was confirmed with cranio-caudal, left anterior oblique and right anterior oblique views of the deployed filter. There was however some asymmetry of the filter leg positions but it did not cause any significant angulation of the filter in relation to the IVC. The IVC filters were firmly secured with no filter migration immediately post-procedure. The 12-French titanium Greenfield vena cava filter was safely deployed percutaneously with no complications in our small series of patients. With the use of titanium in the design of Greenfield filter, the clinical effectiveness and performance is maintained while providing for easier insertion and reduction of patient discomfort.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1994

Severe aortic regurgitation due to Neisseria mucosa endocarditis.

A rare occurrence of Neisseria mucosa endocarditis on a native aortic valve not known to be diseased is reported. Despite vigorous antibiotic therapy, severe aortic regurgitation developed necessitating aortic valve replacement. At operation, the right coronary cusp was retracted with two small nodules attached to its edge and the non-coronary cusp was perforated. Neisseria mucosa endocarditis is very rare, and involves abnormal mitral or prosthetic valves predominantly. Infection of a native aortic valve, with no known history of disease, is exceptional.

Adult↗

PubMed1993

Prevalence of peripheral artery disease in patients with coronary artery disease.

The incidence of coronary artery disease in Singapore has shown a rapid rise in recent years, however, there is a subjective impression that the prevalence of atherosclerotic peripheral artery diseases, although sharing common aetiological factors with coronary artery disease, has not shown a similar rise. We set out to determine the incidence of occlusive peripheral artery diseases of the lower limb in a selected population of Asian patients using a non-invasive test and we analysed the risk factors. The overall prevalence of peripheral artery disease of the subjects as determined by an abnormal ankle brachial index less than 0.9 in at least one limb was 19.1%. Increasing age, hypercholesterolemia and smoking were risk factors. In patients with proven coronary artery disease, abnormal ankle brachial indices were present in 21.3% of patients with angiographic evidence of coronary artery disease but in only 13.0% of those without. In this study, the incidence of peripheral artery disease in this selected Asian population was high. With the increasing availability of vascular laboratories and awareness of the diseases, we can expect to see increasing numbers of patients presenting with these problems.

Adult↗

PubMed1993

Review of patients with infective endocarditis of native valves over a five-year period.

The clinical characteristics, echocardiographic features, bacteriologic data, morbidity and mortality of patients who were admitted to our hospital with infective endocarditis of their native valves over a five-year period were reviewed. There were 32 patients with a mean age of 38.2 +/- 16.2 years (range: 17 to 71 years) in our study population; 24 patients had underlying valvular abnormalities, six patients had congenital heart disease and two patients had no structural cardiac abnormality. Echocardiography was performed for all patients. Vegetations were absent in three (9.4%) patients, single in 19 (59.4%) patients and multiple in ten (31.3%) patients. Of the 24 (75%) patients who had left-sided endocarditis, mitral valve disease was the commonest valvular abnormality (16 patients). Ventricular septal defect was the commonest underlying abnormality in patients with right-sided endocarditis. Blood cultures were positive in 26 (81.3%) patients; the commonest organism was streptococcal (16 or 50% patients). Complications were present in 13 (40.6%) patients, of which eight patients had evidence of embolism, four patients had cardiac failure and one patient had a paravalvular abscess. Four (12.5%) patients died, two as a result of refractory heart failure and two as a consequence of septic embolism. Advances in medicine have resulted in a better outcome for patients with infective endocarditis, however, it remains an important disease with significant morbidity and mortality.

Adolescent↗

PubMed1992

Early experiences of intra-operative trans-oesophageal echocardiography (TEE) in mitral valve repair.

Whenever possible Mitral valve repair should be performed instead of Mitral valve replacement. It is important to assess the adequacy of the repair during the operation so that any corrective steps may be taken immediately. We present three cases of Mitral valve repair in which the intraoperative TEE was used to assess the adequacy of the repair. There was good correlation of the immediate post bypass TEE findings and early post operative transthoracic echocardiographic findings. Intraoperative TEE is a useful tool in the early assessment of Mitral Valve Repair.

Adult↗

PubMed1992

Efficacy and cost-effectiveness of simvastatin and gemfibrozil in the treatment of hyperlipidaemia.

The aim of this study is to compare the efficacy and cost-effectiveness of simvastatin with gemfibrozil in regulating the serum lipid profiles in the local population. In this study, we reviewed the effect of medication on 75 patients with hypercholesterolaemia with or without hypertriglyceridaemia; 26 patients were on simvastatin 10 mg nightly, 24 patients were on gemfibrozil 300 mg twice daily and 25 patients were on gemfibrozil 600 mg twice daily. The average follow-up period was 10.8 weeks, 19.0 weeks and 16.2 weeks for simvastatin 10 mg, gemfibrozil 300 mg and gemfibrozil 600 mg groups respectively. Prior to drug therapy, patients were put on dietary control. The pre-treatment and post-treatment serum lipid profiles were monitored. The mean changes in the lipid profiles of the patients on gemfibrozil 600 mg twice daily were a 21.6% reduction in total cholesterol, a 21.8% reduction in low-density lipoprotein cholesterol (LDL-C), a 46.3% reduction in serum triglyceride and an 11.2% increase in high density lipoprotein cholesterol (HDL-C). The patients in all three groups had raised HDL-C and lowered triglyceride levels post-treatment but patients on gemfibrozil had a greater increase in HDL-C and a greater decrease in triglycerides as compared to the simvastatin group. In comparison to gemfibrozil, simvastatin was more efficacious in the reduction of LDL-C. The mean reduction in the LDL-C was 21.8% for gemfibrozil 600 mg twice daily group as compared to 28.0% for simvastatin 10 mg nightly group.(ABSTRACT TRUNCATED AT 250 WORDS)

Cost-Benefit Analysis↗