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Biomedical subjects

L K Lee

Publications and source records attributed to L K Lee.

At least 19 recordsLinked to original sources
PubMed2006

Premarital sexual intercourse among adolescents in Malaysia: a cross-sectional Malaysian school survey.

INTRODUCTION: Sexual intercourse among Malaysian adolescents is a major concern, especially with the worry of HIV/AIDS. This study was done to determine the prevalence of sexual intercourse among secondary school students aged 12 to 19 years in Negeri Sembilan, Malaysia. METHODS: This is a cross-sectional school survey conducted on 4,500 adolescent students based on a structured questionnaire. Data were collected using the self-administered questionnaire (translated version of the Youth Risk Behaviour Surveillance in Bahasa Malaysia). RESULTS: The study showed that 5.4 percent of the total sample were reported to have had sexual intercourse. The proportion among male students who had had sex was higher (8.3 percent) compared with female students (2.9 percent). The mean age at first sexual intercourse was 15 years. One percent of students reported that they had been pregnant or had made someone else pregnant. Adolescent sexual intercourse was significantly associated with (1) socio-demographical factors (age, gender); (2) environmental factors (staying with parents); and (3) substance use (alcohol use, cigarette smoking, drug use), even after adjustment for demographical factors. The survey showed that 20.8 percent of respondents had taken alcohol, 14.0 percent had smoked cigarettes, 2.5 percent had tried marijuana, 1.2 percent had tried ecstasy pills, 2.6 percent had tried glue sniffing, 0.7 percent had tried heroin, and 0.7 percent had intravenous drugs. CONCLUSION: Prevalence of sexual intercourse among Malaysian adolescents was relatively low compared to developed countries. However, certain groups of adolescents tend to be at higher risk of engaging in sexual intercourse. This problem should be addressed early by targeting these groups of high-risk adolescents.

Adolescent↗
PubMed2006

Menstruation among adolescent girls in Malaysia: a cross-sectional school survey.

INTRODUCTION: The onset of menstruation is part of the maturation process. However, variability in menstrual cycle characteristics and menstrual disorders are common. The purpose of this study was to determine the menstrual characteristics of adolescent females and factors associated with it. METHODS: This is a cross-sectional descriptive study carried out on 2,411 secondary school adolescent females in Negeri Sembilan, Malaysia. Data were collected using a self-administered structured questionnaire on menstruation in Bahasa Malaysia. RESULTS: Abnormal cycle length (menstrual cycle longer than 35 days or cycle length between 14 to 20 days or irregular pattern) was common and affected 37.2 percent of subjects. The majority (74.6 percent) experienced premenstrual syndrome and 69.4 percent had dysmenorrhoea. About 18 percent reported excessive menstrual loss (use two pads at a time to prevent blood from soaking through or confirmed by doctor to be anaemic due to heavy menstrual flow). Only 11.1 percent of schoolgirls seeked medical consultation for their menstrual disorders. Mothers remained the most important source of information (80 percent). Menstrual disorders were significantly more common in female adolescents who smoke and have suicidal behaviours (p-value is less than 0.05). CONCLUSION: Menstrual problems among adolescent female are common. They are influenced by certain modifiable factors.

Adolescent↗
PubMed2005

Smoking among secondary school students in Negeri Sembilan, Malaysia.

This study was done to determine the prevalence of smoking and factors influencing cigarette smoking among secondary school students in Negeri Sembilan, Malaysia. This is a cross-sectional school survey conducted on 4500 adolescent students based on a structured questionnaire. Data was collected using the supervised self-administered questionnaire the Youth Risk Behaviour Surveillance in the Malaysian National Language Bahasa Malaysia. The prevalence of smoking among the students was 14.0%. About a third of the students (37.8%) started smoking at 13 to 14 years of age. The prevalence of smoking among the male students was higher (26.6%) compared to the female students (3.1%). Adolescent smoking was associated with (1) sociodemographic factors (age, ethnicity, rural/urban status); (2) environmental factors (parental smoking, staying with parents); (3) behavioural factors (playing truant and risk-taking behaviours such as physical fighting, drug use, alcohol use, sexual activity, lack of seatbelt use, riding with a drunk driver); (4) lifestyle behaviours (being on diet and lack of exercise); (5) personal factors (feeling sad and suicidal behaviours). In conclusion, smoking is a major problem among Malaysian adolescents. Certain groups of adolescents tend to be at higher risk of smoking. This problem should be curbed early by targeting these groups of high risk adolescents.

Adolescent↗
PubMed2005

Portfolio as a learning tool: students' perspective.

Portfolio writing is a method of encouraging reflective learning among professionals. Although portfolio-based learning is popular among educators, not many studies have been done to determine students' perceptions of portfolio as a learning tool. A questionnaire survey was conducted among 143 medical students to find out their perceptions of the portfolio as a learning tool. A majority of the students felt that the portfolio is a good learning tool. However, they also perceived that it is stressful and time-consuming to develop a proper portfolio. The study indicates that students need appropriate guidance from the academic staff for the system to succeed.

Documentation↗
PubMed2003

Formation of LID vector complexes in water alters physicochemical properties and enhances pulmonary gene expression in vivo.

There is currently an urgent need to develop efficient gene-delivery systems for the lung that are free of inflammatory effects. The LID vector is a synthetic gene delivery system, comprised of lipofectin (L), an integrin-targeting peptide (I) and DNA (D) that has previously been shown to have high transfection efficiency in the lung. We have assessed the effect of alternative methods of complex preparation on structural features of the complex, levels and duration of reporter gene expression and the host response to the LID vector. We have demonstrated that making the complex in water affects the structure of the LID complexes making them smaller and more stable with a more cationic surface charge than complexes prepared in phosphate-buffered saline (PBS). When the LID vector was constituted in water and instilled intratracheally into the lungs of mice there was a 10-fold increase in luciferase activity compared with preparation in PBS. Furthermore, luciferase activity was still evident 1 week following vector instillation. This enhancement may be because of altered complex structure, although effects of the hypotonic vector solution on the lung cannot be excluded. The inflammatory effects of instilling the LID vector in water were minimal, even after three administrations of the LID vector, with only mild alterations in cytokine and broncho-alveolar lavage fluid (BALF) cell profiles. These results demonstrate that the LID vector can generate high, and prolonged, levels of gene expression in the lung from small quantities of DNA and that careful attention to synthetic polyplex structure may be important to optimize efficiency of gene expression in vivo.

Animals↗
PubMed2002

A study on the use of car occupant restraint in Selangor.

A survey was conducted in December 1995 to study car occupant restraint usage in Selangor. A total of 1082 car occupants were observed in 536 cars. The results of the study shows that only 57.3% of the car occupants observed were protected by any form of restraints. Most of the cars (99.8%) examined had front seat belts but only 44.2% had rear seat belts. Only 0.6% of the cars were found to have child restraints in the cars. 80.2% of drivers used restraints and only 65.4% of front seat passengers used any forms of restraints. In the case of the rear seat passengers, only 0.42% used an available restraint. More people in the urban areas (84.42%) than in the rural areas (66.51%) used seat belts. Usage of seat belts by car drivers influenced the use of seat belts by front seat passengers. Type of seat belts fitted was associated with usage rate. It is sad to note that 21.9% of the drivers used seat belts incorrectly.

Adolescent↗
PubMed2001

Ultrastructure of acetylcholine receptor aggregates parallels mechanisms of aggregation.

BACKGROUND: Acetylcholine receptors become aggregated at the developing neuromuscular synapse shortly after contact by a motorneuron in one of the earliest manifestations of synaptic development. While a major physiological signal for receptor aggregation (agrin) is known, the mechanism(s) by which muscle cells respond to this and other stimuli have yet to be worked out in detail. The question of mechanism is addressed in the present study via a quantitative examination of ultrastructural receptor arrangement within aggregates. RESULTS: In receptor rich cell membranes resulting from stimulation by agrin or laminin, or in control membrane showing spontaneous receptor aggregation, receptors were found to be closer to neighboring receptors than would be expected at random. This indicates that aggregation proceeds heterogeneously: nanoaggregates, too small for detection in the light microscope, underlie developing microaggregates of receptors in all three cases. In contrast, the structural arrangement of receptors within nanoaggregates was found to depend on the aggregation stimulus. In laminin induced nanoaggregates receptors were found to be arranged in an unstructured manner, in contrast to the hexagonal array of about 10 nm spacing found for agrin induced nanoaggregates. Spontaneous aggregates displayed an intermediate amount of order, and this was found to be due to two distinct population of nanoaggregates. CONCLUSIONS: The observations support earlier studies indicating that mechanisms by which agrin and laminin-1 induced receptor aggregates form are distinct and, for the first time, relate mechanisms underlying spontaneous aggregate formation to aggregate structure.

Animals↗
PubMed2001

Effects of one night of sleep deprivation on hormone profiles and performance efficiency.

This study examined the effects of one night of sleep deprivation on melatonin and cortisol profiles, as well as performance efficiency of military service members. Sleep intervention consisted of total lack of sleep (N = 7) or 8 hours of sleep (control group; N = 7) during the night. All parameters were measured at selected time intervals before (day 1), during (only in sleep-deprived individuals), and after (day 2) sleep intervention. Rotary pursuit scores and handgrip strength data were used as indices of psychomotor and physical performance, respectively. In sleep-deprived individuals, more salivary melatonin, but not cortisol, was secreted than in subjects who slept adequately. Significant increases in melatonin and cortisol were noted, especially at 1:30 p.m. on the day after nighttime sleep deprivation. In contrast, the tracking scores for rotary pursuit and grip strength among sleep-deprived and rested individuals were comparable. Across a normal working day (day 1), all parameters studied revealed time-specific fluctuations in both control and sleep-deprived groups. Irrespective of nighttime sleep schedule, the patterns of performance on day 2 differed from those on day 1. The tracking performance improved on day 2, whereas grip strength worsened, which may reflect inherent learning and muscle fatigue, respectively. During the night of sleep deprivation, performance declined. In conclusion, the present study showed that one night of sleep deprivation (8 hours) resulted in significant hormonal changes on the next afternoon but did not modify tracking and muscular strength performance.

Adult↗
PubMed2001

The rotary pursuit test is not an index of normal psychomotor function in humans.

OBJECTIVE: This study sought to assess whether the rotary pursuit test is a good indication of the psychomotor performance of human subjects during normal working hours. Circadian hormonal profiles of salivary melatonin and cortisol were also established for correlation with performance. METHODS: Ten healthy individuals working in the Department of Obstetrics and Gynecology laboratory participated in this study. The experiment was conducted during a normal 8.5-hour working day in which routine laboratory tasks such as running radioimmunoassays were performed. Saliva samples were collected every 2 hours starting at 8:00 a.m. Simultaneously, self-rated questionnaires on mood states, sleepiness, stress, and types of food and drinks consumed were also recorded. At 10:00 a.m., 12:00 noon, 2:00 p.m., and 4:00 p.m., the subjects' were tested on the rotary pursuit machine, on which their ability to track a rotating target with a stylus was tested by means of measuring the time the stylus stays on target. RESULTS: The circadian profiles of salivary melatonin and cortisol were similar to what previous studies have shown. Increases in cortisol levels were associated with food intake, work stress, or spontaneous awakening. Tracking performance (time on target) improved significantly from 10:00 a.m. to 2:00 p.m. and then decreased nonsignificantly at 4:00 p.m. only at the speed setting of 60 rpm. There was no correlation between the three parameters measured. SUMMARY: Variation of psychomotor performance during a normal working day and in noncircadian disrupted individuals cannot be measured by the rotary pursuit test. Furthermore, a learning effect could mask any variation in performance.

Adult↗
PubMed2000

Circadian disturbances after night-shift work onboard a naval ship.

The aim of the present study was to investigate how night duties can affect the circadian rhythms of military personnel working onboard a naval ship. Twenty individuals on a regular day-work schedule from 9:00 a.m. to 6:00 p.m. (serving as controls) and 40 individuals on night-shift duties participated in the study. Salivary melatonin and cortisol profiles were established within two 24-hour periods from 2-hour saliva samplings. Under the condition of abrupt shift in work/rest schedule, the majority of the navy officers (52%) retained their normal melatonin profiles. Twelve percent displayed a right phase shift in melatonin rhythm after night work. Nineteen percent exhibited distortions in the form of abnormal peaks or troughs, and 17% showed signs of disrupted rhythm in the form of low daytime levels of melatonin throughout the sampling period. No consistent relationship was found between the melatonin changes and various work stations of the ship. Prominent changes in the cortisol profile included unexpected peaks or troughs that may be related to the conditions that individuals were exposed to, i.e., high noise level in the engine room, as well as to performing intense tracking operations. The findings of this study (1) show the possible detrimental effects of shift duties on circadian rhythms, (2) highlight a wide interindividual variation in the manner in which the circadian systems respond to an abrupt phase shift in work/rest schedules, and (3) form the basis for further investigations into effective strategies to help military personnel cope with shift work, thereby maintaining health and high working standards while on duty.

Adult↗
PubMed2000

Sleep/wake cycle and circadian disturbances in shift work: strategies for their management--a review.

INTRODUCTION: There has been a growing concern about the ability of individuals to maintain adequate levels of performance over long work shifts, particularly when those shifts span night-time hours. It has, therefore, become expeditious to understand and apply principles of circadian rhythms in order to establish simple, rational and appropriate strategies to help our shift workers maximise their performance and minimise their health problems under the various shift work regimes. This review sought to outline several principles of circadian rhythms and the sleep/wake cycle and some possible strategies to manage disturbances in the sleep and performance arising from shift works. METHODS: Many studies in this field had been carried out. The present review concerns studies which elucidate the general circadian principles as well as those which may provide helpful information applicable for us in the work environment we are living in. RESULTS: It has been found that shift workers invariably suffer from a constellation of symptoms, which can sometime severely compromise their ability to perform optimally during their shift work. There are many factors that influence the sleep/wake cycle and thus, the performance of shift work. These include 1) circadian factors, 2) type of shift work, 3) how a person adapt to circadian disruption, 4) ageing, 5) sleep factors and 6) social and domestic factors. CONCLUSIONS: Several possible strategies could be adopted to improve sleep and performance. These include 1) appropriate scheduling of shift work, 2) proper consideration of the speed of shift rotation, 3) strategies for sleep and napping, 4) installing appropriate lighting at the workplace, 5) the use of sleeping pills/hypnotics such as melatonin and melatonin agonists.

Humans↗
PubMed1999

Backbone dynamics of a short PU.1 ETS domain.

The resonance assignments, secondary structure and backbone dynamics of the ETS domain of the transcription factor PU.1 have been determined for the free protein in solution by NMR spectroscopy. The secondary structure for the free ETS domain is similar to that observed in the crystal structure of the PU.1 protein complexed with DNA, except that helix alpha2 and recognition helix alpha3 are shorter for the free protein in solution. Backbone dynamics of the protein have been examined using amide hydrogen-deuterium exchange and (15)N laboratory-frame spin relaxation measurements. A significant probability of local unfolding of helix alpha2, which precedes the loop-helix-loop DNA recognition domain, is inferred from the very fast hydrogen-deuterium exchange for amide protons in this helix. The (15)N relaxation measurements indicate that the protein is partially oligomerized at a concentration of 2.5 mM, but monomeric at a concentration of 0.3 mM. The (15)N relaxation data for the low concentration sample were interpreted, using the model-free formalism, to provide insight into protein dynamics on picosecond-nanosecond and microsecond-millisecond time scales. High flexibility of the protein backbone is observed for the residues in the loop between alpha2 and alpha3. This loop is variable in length and in structure within the class of winged helix proteins and is partially responsible for binding to DNA. The dynamic properties observed for alpha2, alpha3 and the intervening loop may indicate a correlation between protein plasticity in particular structural elements and recognition of specific DNA sequences.

Amino Acid Motifs↗
PubMed1999

An interstitial light assembly for photodynamic therapy in prostatic carcinoma.

OBJECTIVE: To develop an interstitial laser light delivery system using multiple optical fibres for photodynamic therapy (PDT) in the treatment of prostate cancer. PATIENTS AND METHODS: A laser beam was divided equally with a 1 x 4 fibre splitter to deliver PDT simultaneously through four 2-cm long, flexible cylindrical optical diffusers. Biplanar transrectal ultrasonography (TRUS) and a template were used to position the optical fibres percutaneously. In vivo measurements of light penetration depth (1/micro[eff] ) in prostate tissue were made in seven patients, using a sheathed isoprobe to measure light fluence rates at varying radial distances from the diffuser. The prostate was fixed with stabilization needles to minimize displacement during needle placement. RESULTS: The mean (sd, range) micro(eff) in the prostates of the seven patients was 0.35 (0.07, 0.22-0.44) mm-1, which produced closely parallel slopes of light attenuation. However, there was up to a 10-fold variation in absolute light levels at the same diffuser-detector separation distances amongst the seven patients, probably caused by blood pooling around the diffuser light source. A similar problem around the isoprobe detector was overcome by sheathing the probe in clear plastic tubing. By stabilizing the prostate, the optical fibre positioning was precise to within 2 mm. CONCLUSION: Although this light delivery and TRUS assembly were developed for clinical PDT in the prostate, the same instrumentation can be used reliably for in vivo light-penetration studies. Haemorrhage was unpredictable and highlighted one of the main problems which needs to be overcome.

Aged↗
PubMed1999

The roles of multileaf collimators and micro-multileaf collimators in conformal and conventional nasopharyngeal carcinoma radiotherapy treatments.

The purpose of this work is to study the efficacy and limitations of using standard multileaf collimators (MLCs) and micro-multileaf collimators (mMLCs) in the treatment of nasopharyngeal carcinoma (NPC) by conventional and conformal radiotherapy techniques. The penumbra characteristics of MLC, mMLC, and customized block collimated beams are measured with respect to leaf edge angle, beam energy, treatment depth, and field size and compared with those generated by a commercial three-dimensional planning computer system. Upon verification of the planning system, it is used to evaluate the treatment plans generated with these beam shapers for conventional and conformal NPC treatments. The effective penumbra of a MLC beam is strongly influenced by its edge angle, leaf width, and treatment depth. The suitability of standard MLCs in conventional NPC treatments is determined mainly by the edge angle to be used. For conformal NPC treatments involving six or more fields, dose volume histograms comparable to those of customized beam blocks are obtained with a standard MLC. The mMLC does not have the same restrictions as those on standard MLC but is limited to phase II treatment by its small usable field size. Both standard MLCs and mMLCs can be used to replace customized divergent beam blocks in both conventional and conformal NPC treatments. However, a MLC, due to its larger effective penumbra, may be unsuitable for use in cases when the tumor volumes extend very close to the critical normal structures. A mMLC, on the other hand, is limited by its small maximum field size and can only be used for collimating the facial portals in the second phase treatment.

Humans↗
PubMed1997

Rotational diffusion anisotropy of proteins from simultaneous analysis of 15N and 13C alpha nuclear spin relaxation.

Current methods of determining the rotational diffusion tensors of proteins in solution by NMR spectroscopy exclusively utilize relaxation rate constants for backbone amide 15N spins. However, the distributions of orientations of N-H bond vectors are not isotropic in many proteins, and correlations between bond vector orientations reduce the accuracy and precision of rotational diffusion tensors extracted from 15N spin relaxation data. The inclusion of both 13C alpha and 15N spin relaxation rate constants increases the robustness of the diffusion tensor analysis because the orientations of the C alpha-H alpha bond vectors differ from the orientations of the N-H bond vectors. Theoretical and experimental results for calbindin D9k, granulocyte colony stimulating factor, and ubiquitin, three proteins with different distributions of N-H and C alpha-H alpha bond vectors, are used to illustrate the advantages of the simultaneous utilization of 13C alpha and 15N relaxation data.

Amino Acid Sequence↗
PubMed1997

Interstitial photodynamic therapy in the canine prostate.

OBJECTIVE: To determine the depth of tissue destruction and the minimum light dose required for necrosis in interstitial photodynamic therapy (PDT), as a prerequisite for the investigational therapy of patients. MATERIALS AND METHODS: Seven adult beagle dogs were given 2 mg/kg of the photosensitizer Photofrin intravenously and two controls received none. After 24 h, 450 J/cm of 630 nm wavelength laser light was delivered interstitially to the prostate via a 2 cm long diffuser fibre. Seven single-fibre treatments were performed in five sensitized dogs and two single-fibre treatments in the controls. The two remaining sensitized dogs had two fibres placed 10 mm apart within the prostate to determine the coalescence of PDT lesions. The penetration depth of light was measured in all prostates, and after PDT the extent of necrosis was assessed histologically. RESULTS: The mean (standard deviation, SD) radius of PDT destruction around each diffuser was 5.3 (1.4) mm and PDT lesions overlapped in prostates treated with two fibres placed 10 mm apart. There was no observable tissue damage in the controls. The mean (SD) minimum light dose required for PDT necrosis was 84 (64) J/cm2. Differences among animals in the light penetration depth were small, with a mean of 2.14 (0.2) mm, and did not correlate with the depth of necrosis (P = 0.07). Bleeding around the optical diffuser fibre impeded light penetration. CONCLUSION: Interstitial PDT in the canine prostate using Photofrin produced modest volumes of tissue necrosis. The minimum light dose required to induce necrosis was variable because bleeding was unpredictable in relation to the optical fibre.

Animals↗