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Biomedical subjects

M K Lim

Publications and source records attributed to M K Lim.

At least 55 records · Page 3Linked to original sources
PubMed1995

The response of neurons and microglia to blast injury in the rat brain.

Rats subjected to a single non-penetrative blast were examined for possible neuronal damage and glial reaction by immunohistochemistry and electron microscopy. The most dramatic feature in rats killed between 1 and 14 days after the blast was the widespread response of microglial cells in various parts of the brain in which the cells were hypertrophied and their surface antigens, like complement type three receptors (CR3), were upregulated. The blast wave also induced the vigorous expression of major histocompatibility complex (MHC) class I and II (Ia) antigen. In rats killed 21 days after the blast, the elevated immunoreactivity of microglia had subsided and at 28 days both the microglial external morphology and immunoreactivity were comparable to those of normal animals. In rats killed 4-7 days after the blast, the neurons in the cerebral and cerebellar cortex appeared normal except for the occurrence of some 'darkened' dendrites. The incidence of 'darkened' dendrites was most common in rats killed at day 14 but they were absent at 21 and 28 days. Microglial cells were closely associated with some of the 'darkened' dendrites. Results in this study show that a non-penetrative blast in rats provokes a widespread microglial activation suggesting increased endocytosis and immunological responses. However, it remains uncertain whether such a drastic response was a direct activation of the cells by the blast wave or elicited indirectly by some chemical factors released from the damaged brain tissues.

Animals↗
PubMed1995

Oral acyclovir in the treatment of adult varicella.

An open study was conducted to evaluate the efficacy of oral acyclovir in a group of 295 Singapore Armed Forces male servicemen. The 148 patients who were willing to take acyclovir were given 800 mg orally five times per day for seven days. The other 147 who refused to take acyclovir were monitored as a control group. Each of these groups was further classified into two groups. Group A patients presented with rash within 24 hours of rash onset and Group B presented between 24 and 72 hours. Daily lesion counts, temperature, pruritus scores and laboratory tests were used to monitor disease progression. Early acyclovir intervention (Group A) reduced the time to 100% crusting from 7.19 to 5.71 days (P = 0.0001), decreased the maximum number of all lesions by 26% (P = 0.03) and the maximum number of vesicular lesions by 45% (P = 0.0004). Late therapy (Group B) was effective in reducing the maximum number of vesicular lesions by 38% (P = 0.003). The number of patients requiring antibiotics for suspected secondary skin infection, the duration of fever and paracetamol consumption were significantly reduced in both the early and late intervention groups. However, there were no effects in minimizing pruritus in either group. Serious complications such as pneumonia, encephalitis or death were not observed in this study. The most common adverse effect of acyclovir was mild diarrhoea occurring in 35% of patients treated with the drug. We conclude that early treatment with acyclovir was beneficial whereas late therapy had limited effect in reducing the severity of cutaneous lesions in patients with varicella.

Acyclovir↗
PubMed1995

Prevalence of G6PD deficiency among recruits in the Singapore Armed Forces.

Between 1986 and 1990, 107,397 National Servicemen between the ages of 17 to 18 years were screened on enlistment for Glucose-6-Phosphate Dehydrogenase (G6PD) enzyme activity by fluorescent spot test. The overall prevalence rate was 1.6% with ethnic differences as follows: 1.62% for Chinese, 1.80% for Malay, 0.76% for Indian and 0.68% for other races. The majority had no prior knowledge of their G6PD deficiency status (89.9%), or of any significant haemolytic episode (93.3%). The rest gave a history of neonatal jaundice, non-neonatal jaundice, anaemia and haemoglobinuria. Maloprim, fava beans, sulphur drugs and aspirin were cited as triggering factors.

Adolescent↗
PubMed1994

Treatment with flecainide for symptomatic and refractory tachyarrhythmias in children.

Nine children, aged 2.5 months to 16 years, presenting with tachyarrhythmias were treated with intravenous (i.v.) flecainide, a type 1C antiarrhythmic drug. There were four boys and five girls; seven were supraventricular and two ventricular tachycardias and three had structural cardiac abnormalities. The i.v. dose required to terminate the arrhythmias ranged from 1.0 to 2.4 mg/kg (mean 1.55 mg/kg) although a mean of 1.94 mg/kg per dose was required to maintain sustained sinus rhythm after a single i.v. dose. Eight of the patients--six supraventricular and two ventricular tachyarrhythmias, required maintenance oral flecainide. Oral dosages of 6.7-9.5 mg/kg per day (mean of 7.97 mg/kg per day in three divided doses) were required to effectively prevent the tachyarrhythmias. Intravenous and oral flecainide are safe and effective in terminating supraventricular and ventricular tachyarrhythmias. No evidence of proarrhythmia was found in the patients during follow up of between 5 and 9 months. The present limitation of performing radiofrequency ablation on infants and small children justifies the important place of medical therapy for re-entrant supraventricular tachyarrhythmias.

Administration, Oral↗
PubMed1994

Occupational heat stress.

Heat stress is an occupational health problem affecting Man in diverse, hostile environments ranging from deep mining to outer space. Healthy, young military recruits and industrial workers exposed to hot, humid environments are typically at risk. The International Classification of Diseases classifies heat disorders into 10 separate entities, of which the most clinically significant are heat cramps, heat exhaustion and heat stroke. The latter is a medical emergency of the first order. Clinical management hinges upon early treatment based on a high index of suspicion. Effective preventive measures and adequate education of those at risk form the basis for its control.

Emergencies↗
PubMed1994

Twenty-five years of national service--changes in height, weight and body mass index.

The height and weight of 18-year-old Singapore National Service enlistees were extracted from computer records spanning 25 years (1967-1991). These were analysed for mean height, weight and body mass index (BMI) which overall show increases of 4.12 cm, 10.13 kg and 2.60 kg/m2 respectively. All ethnic groups (Chinese, Malay, Indian and Others) show a similar rising trend. While mean height appears to have stabilised in recent years, mean weight continues to rise. This is reflected in an increasing mean BMI. The proportion of 18-year-old male recruits with a BMI in the overweight range (> or = 25 kg/m2) increased from 1.37% in 1967 to 12.07% in 1991.

Adolescent↗
PubMed1994

Absent pulmonary valve syndrome--a case report.

A 7-year old female child was admitted for recurrent bronchopulmonary since one week of life. She was diagnosed to have ventricular septal defect and was treated conservatively. At seven years of life, repeat echocardiogram revealed a large perimembranous ventricular septal defect, absent pulmonary valve with overriding of aorta, narrow pulmonary artery annulus, and dilated main pulmonary artery and its branches. She was treated conservatively, discharged and follow-up at the National Heart Institute Kuala Lumpur, for corrective surgery.

Child↗
PubMed1993

Education and myopia in 110,236 young Singaporean males.

Computerised data of 110,236 Singaporean males aged 15 to 25 (mean 17.75) years who underwent compulsory medical examination from April 1987 to January 1992 were used to estimate the prevalence and severity of myopia among young Chinese, Malay, Indian and Eurasian Singaporean males with different educational levels. The prevalence and severity of myopia amongst the groups with different educational levels were compared. These groups were fairly well-matched for important known confounding factors such as age, sex, race and degree of urbanisation of place of residence. Our data showed a positive association between educational attainment and both the prevalence and severity of myopia. Both the prevalence of myopia and the proportion of myopes with severe myopia were in general higher among those with more years of formal education.

Adolescent↗
PubMed1993

Race, culture and Myopia in 110,236 young Singaporean males.

Computerised data of 110,236 Singaporean males aged 15 to 25 (mean 17.75) years who underwent compulsory medical examination from April 1987 to January 1992 was used to estimate the prevalence of myopia among young Chinese, Malay, Indian and Eurasian Singaporean males. The prevalence of myopia amongst the different racial groups was compared after they had been matched for important known confounding factors such as age, sex, educational attainment and degree of urbanization of place of residence. The estimated myopia prevalence was 48.5% in Chinese, 34.7% in Eurasians, 30.4% in Indians and 24.5% in Malays. The overall myopia prevalence rate for all races combined was 44.2%. Within each educational group, the Chinese generally had the highest myopia prevalence whilst the Malays generally had the lowest. Myopia prevalence among the Indians tended to be between that of the Chinese and the Malays. Having matched the various racial groups for age, sex, educational attainment and degree of residential urbanization, it would appear that racial and cultural differences are major influences responsible for the difference in myopia prevalence observed amongst the different races.

Adolescent↗
PubMed1992

Intermittent ductal patency in healthy newborn infants: demonstration by colour Doppler flow mapping.

Colour Doppler flow mapping was used to determine the time of closure of the arterial duct in 51 healthy newborn infants. Initial time of closure corresponded with previous reports: 20% on the first day, 82% by the second day, 96% by the third day, and 100% by the fourth day. Twenty infants were delivered by caesarean section and followed up for seven days even if the duct had apparently closed; in six intermittent patency was demonstrated with flow in the third, fourth or fifth day, although earlier functional closure had been observed. All were found to be closed on the sixth and seventh days. It is necessary to be aware of the phenomenon of intermittent closure in any study determining or assessing the effect of any intervention on ductal patency.

Ductus Arteriosus↗
PubMed1992

Myopia and educational attainment in 421,116 young Singaporean males.

Data of 421,116 Singaporean males aged 15 to 25 (mean 17.75) years who underwent compulsory medical examination in 1974-84 and 1987-91 were used to estimate the prevalence of myopia and to study the correlation between the prevalence and severity of myopia and educational attainment. The estimated myopia prevalence rate was 26.3% in 1974-84 and 43.3% in 1987-91. This rise in the rate was accompanied by an increase in the proportion of males who achieved higher levels of education over the same period. The overall myopia prevalence rate was 30.4%. Both the prevalence and severity of myopia were higher as the level of education attained increased. The myopia prevalence rate was 15.4% in males with no formal education and increased steadily through groups with intermediate education to 65.2% among those with GCE 'A' level education, 57.5% among diploma holders and 65.1% among university graduates in 1987-91. Seventy out of 173 (40%) myopes with no formal education compared to 1035 out of 1612 (64%) myopes with university degrees had unaided visual acuity worse than 6/60 in 1987-91. Our findings confirm indications from other sources that the association between the prevalence and severity of myopia and education attainment is real. A combination of genetic and environmental factors may be the cause of this association.

Adolescent↗
PubMed1992

Xq28: epidemiology and sex-linkage between red-green colour blindness and G6PD deficiency.

Xq28 is the genetic locus of two closely associated conditions of red-green colour blindness and G6PD deficiency. Epidemiologically, both rank among the more frequent sex-linked clinical problems that affect military servicemen in Singapore. This retrospective study is based on the findings of 35714 subjects screened at the Medical Classification Centre--Central Manpower Base (MCC--CMPB) over an eighteen-month period using pseudoisochromatic and fluorescent techniques as well as anomaloscopic and spectrometric methods. The overall prevalence rates of red-green colour blindness, G6PD deficiency and association were determined to be 4.8%, 2.2% and 0.1% respectively. Malays showed the highest prevalence rates among the major races. Statistically significant difference was found with regards to the prevalence rates of G6PD deficiency and its association with red-green colour blindness. Review of literature yielded comparable results with a few local studies of good sample size done over the past twenty years. Sex-linkage analysis was hindered by the lack of pedigree studies.

Adolescent↗
PubMed1991

Doppler ultrasound and the silent ductus arteriosus.

A clinically undetectable, small ductus arteriosus was identified by Doppler ultrasonography in 21 individuals. Infants were excluded from the study and no patient had pulmonary hypertension. Persistence of the ductus arteriosus is likely to be more common than shown by less sensitive diagnostic methods. Some patients considered to have infective endocarditis with a normal heart may have a silent ductus arteriosus. Evidence of such an association would justify ligation or antibiotic cover as prophylactic measures.

Adolescent↗
PubMed1989

Effect of swollen soft tissue on the impedance of bone for fracture healing diagnosis.

A prominent resonance frequency, due to swollen soft tissue, was observed below the first mode resonance frequency of the bone in the mechanical impedance measurement of the limb. Distinction should be made between these two frequencies in the diagnosis of fracture healing. A two-port network analogy is used to explain the existence of the resonance frequency.

Biomechanical Phenomena↗
PubMed1989

Variability of the Doppler gradient in pulmonary valve stenosis before and after balloon dilatation.

The variability of the valve gradient measured by Doppler in pulmonary stenosis was compared with the variability of the gradient measured at catheterisation in 42 infants and children undergoing catheterisation with a view to balloon dilatation of the pulmonary valve. The maximum value measured by Doppler when the patient was unsedated was significantly higher than that measured when the patient was sedated for catheterisation, and the maximum gradient was significantly higher shortly after than several days later. In a patient with pronounced infundibular obstruction after dilatation the Doppler signal clearly showed that the obstruction was dynamic, with a superimposed lower fixed signal that correctly predicted the final low gradient. The Doppler gradient in an alert and unsedated patient may be a better measure of the true physiological value. The highest Doppler value so obtained is a more appropriate indicator of the need for balloon dilatation than a single catheter measurement. The result of dilatation is best assessed by Doppler measurement at least a day after the procedure.

Adolescent↗
PubMed1989

Doppler flow characteristics in the assessment of pulmonary artery pressure in ductus arteriosus.

The Doppler spectral pattern of flow through the ductus arteriosus was studied in 117 patients. In 37 who underwent catheterisation, Doppler records and aortic and pulmonary artery pressure were available (21 simultaneously with two catheters) for review while the others had surgical ligation of the duct on the basis of the results of non-invasive tests. Four flow patterns were obtained: (a) continuous flow, maximum velocity in late systole with gradual fall throughout diastole; (b) continuous flow, high systolic flow with rapid fall to a very low early diastolic velocity maintained throughout diastole; (c) continuous low velocity, maximum in late diastole; and (d) bidirectional flow. Flow pattern (a) was associated with normal or slightly raised pulmonary artery pressure; (b) with raised pulmonary artery pressure; and (c) and (d) with pulmonary artery pressure at systemic values. Comparison of the Doppler and measured pressure differences between the great arteries was reasonably good for peak values but poor for the trough readings. Doppler ultrasound clearly showed ductal flow; the flow pattern gave an indication of the pulmonary artery pressure, but pressure measurement by application of the Bernoulli equation to the flow velocities cannot yet be regarded as reliable.

Adolescent↗