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Biomedical subjects

C L Lim

Publications and source records attributed to C L Lim.

At least 19 recordsLinked to original sources
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↗
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↗
PubMed1999

Electrodermal activity in schizophrenia: a quantitative study using a short interstimulus paradigm.

BACKGROUND: Electrodermal activity in response to short interstimulus interval (ISI) stimulation allows aspects of information processing to be examined, but such paradigms cause skin conductance responses (SCRs) to overlap. A signal decomposition method was developed and employed to score the overlapped SCRs. This is the first application of the method to the study of schizophrenia. METHODS: Electrodermal activity of 30 medicated patients with schizophrenia and 50 normal controls was obtained using a conventional auditory oddball paradigm with an ISI of 1.3 sec. Tonic skin conductance level (SCL), phasic SCRs, SCR temporal dynamics, and a range of SCR variables in response to target tones were examined. RESULTS: The schizophrenic group showed reduced response rate, proportion of responders, SCR amplitude, rise time, peak latency, and steady-state response amplitude, over the trial compared with controls. There were no between-group differences in SCL or SCR onset time. CONCLUSIONS: The combined use of a conventional short ISI paradigm and the new SCR scoring method demonstrated new facets of electrodermal hyporeactivity in medicated patients with schizophrenia. The hyporeactivity could not be attributed to changes in tonic arousal or dysfunctions in peripheral sympathetic nerve conductance.

Acoustic Stimulation↗
PubMed1999

Simultaneous EEG and EDA measures in adolescent attention deficit hyperactivity disorder.

Adolescent unmedicated ADHD males and age- and sex-matched normal control subjects were examined simultaneously using EEG and EDA measures in a resting eyes-open condition. ADHD adolescents showed increased absolute and relative Theta and Alpha1 activity, reduced relative Beta activity, reduced skin conductance level (SCL) and a reduced number of non-specific skin conductance responses (NS.SCRs) compared with the control subjects. Our findings indicate the continuation of increased slow wave activity in ADHD adolescents and the presence of a state of autonomic hypoarousal in this clinical group.

Adolescent↗
PubMed1999

Cytokine levels in patients with previous heatstroke under heat stress.

We attempted to determine whether persons susceptible to heatstroke produced higher serum concentrations of interleukin-6, tumor necrosis factor-alpha, and interleukin-10 when subjected to heat stress. Nine patients with previous heatstroke and 21 matched controls were subjected to a heat-stress test (at 32 degrees C, 67% humidity, 900 W/m2 solar radiation, and wind speed of 2.5 m/s) for 60 minutes and rested at 24 degrees C for another 60 minutes in full battle gear. During the heat-stress test, blood was drawn at intervals of 0, 30, 60, and 120 minutes, and serum lipopolysaccharide, interleukin-6, tumor necrosis factor-alpha, and interleukin-10 concentrations were measured. Patients with previous heatstroke had a higher mean core temperature (0.6 degree C; p < 0.05) and sweated less (0.3 liters; p < 0.05). During the heat-stress test, the lipopolysaccharide levels were not increased and there was no difference in the serum cytokine concentrations between patients with previous heatstroke and controls. However, patients with previous heatstroke had higher absolute serum cytokine concentrations and poorer thermoregulatory response to heat stress in terms of core temperature and sweat loss.

Adult↗
PubMed1999

Dynamics of SCR, EEG, and ERP activity in an oddball paradigm with short interstimulus intervals.

Studies of concurrent central, and autonomic activity using a conventional event-related potential (ERP) oddball paradigms, are considered useful in elucidating the relationship between central and autonomic responses, but the autonomic response tends to overlap. A new method was used to decompose and score overlapping skin conductance responses (SCR). This method enabled examination of dynamic relationships of phasic SCR, prestimulus electroencephalogram (EEG), and ERP to auditory target stimuli in 50 normal adults. SCR amplitude was negatively correlated to EEG and N200 amplitude. The SCR amplitude changes over time exhibited an exponential decline opposite to those of N200, alpha, and beta. All the fitted exponential functions had a time constant of 1-2 min. The findings suggest that a N200 component, active in the auditory sensory discrimination, is concomitant with the SCR. The narrow range of the time constant may provide a clue to the conjoint processes underlying central and autonomic adaptive functions.

Adult↗
PubMed1998

Dysfunctions of automatic (P300a) and controlled (P300b) processing in Parkinson's disease.

P300 Event Related Potentials components (P300a and P300b) were investigated using an auditory oddball paradigm (with a button press response to target stimuli) in 15 Parkinson's disease patients and 50 normal controls whilst simultaneously measuring electrodermal activity. Cluster analysis showed that the first 10 target stimuli generated the largest skin conductance responses. The first 10 single-trial ERP epochs were therefore analysed as an ERP sub-average for each individual. The P300a component (associated with the automatic 'Orienting Reflex') was expected to be most prevalent in this sub-average (compared with sub-averages of subsequent blocks of 10 target stimuli). Twenty-nine out of 50 normal controls (58%) elicited a P300a in the first 10 target sub-average, compared with only 2 out of 15 Parkinson's disease subjects (13%). The conventional P300b component (associated with controlled processing) was found to be significantly delayed for all sub-averages for the Parkinson's disease group when compared with controls. These preliminary findings suggest a possible dysfunction in both automatic and controlled processing in this disorder.

Adult↗
PubMed1998

A comparison of maximum oxygen consumption, aerobic performance, and endurance in young and active male smokers and nonsmokers.

The purpose of this study was to compare 2.4-km running performance in 2,639 smoking (SM) and nonsmoking (NS) male conscripts aged 18 to 26 years. Maximum oxygen consumption (VO2max) and aerobic exercise endurance were also compared between SM and NS subjects (N = 156) stratified into various running performance bands. SM subjects ran significantly slower (10.59 +/- 1.17 minutes) than NS subjects (10.32 +/- 1.03 minutes) in the 2.4-km run test (p < 0.001). The mean VO2max of SM subjects (53.38 +/- 8.58 ml kg-1 min-1) was not significantly different from that of the NS subjects (54.42 +/- 7.82 ml kg-1 min-1) (p > 0.05). Exercise endurance time on the treadmill protocol (EXtm) was significantly longer in the NS group only among those who completed the 2.4-km run in < 9.01 minutes (p < 0.05). Maximum minute ventilation (VEmax) was also significantly higher in the NS group in the < 9.01-minute performance band. No other significant differences were found between SM and NS subjects in EXtm and VEmax. Mean maximum heart rate achieved during the tread-mill test ranged from 180 +/- 4 to 191 +/- 12 beats per minute in the SM group and from 183 +/- 5 to 188 +/- 19 beats per minute in the NS group. These were not significantly different (p > 0.05). In conclusion, smoking habit was shown to influence aerobic performance in the 2.4-km run, VEmax, and EXtm only during high-intensity aerobic exercise. VO2max was not influenced by smoking habit when aerobic performance was held constant.

Adolescent↗
PubMed1997

Evoked related potentials associated with and without an orienting reflex.

Late component event related potentials (ERP) and concomitant electrodermal activity (EDA) measures of the orienting reflex (OR) were undertaken in 50 normal subjects. Our group recently developed a model to quantify electrodermal activity in conventional ERP paradigms (auditory oddball) with short interstimulus intervals (ISI). The method was used to classify the presence or absence of skin conductance response following each auditory target stimulus. Using a conventional paradigm in which data is traditionally averaged, single-trial target ERPs were sorted into those with a skin conductance response OR (ERP[+OR]) and those without (ERP[-OR]) an OR, and ERP sub-averages of the two groups were derived. The ERP(+OR) showed significantly larger P300 amplitudes and relatively earlier N200 and P300 latency than those of the ERP(-OR). These findings suggest that using concomitant SCR-ERP measures, separate ERP related processes can be determined, that are complementary to the traditional average measure.

Adolescent↗
PubMed1997

Decomposing skin conductance into tonic and phasic components.

Overlapping phasic skin conductance responses (SCRs) obtained using short interstimulus interval (ISI) paradigms such as those employed in cognitive research, confound measurement of each discrete phasic SCR as well as the tonic skin conductance level (SCL). We report a method of resolving this problem using a modelling technique that takes advantage of the stereotyped nature of the within-subject SCR waveform. A four-parameter sigmoid-exponential SCR model that describes the entire response, was developed and extended to five-, six- and eight-parameter skin conductance (SC) models. These SC models were successfully curve-fitted to more than 60 SC segments, each containing one SCR or two overlapping SCRs on a sloping baseline obtained from 20 normal subjects. The SC segments were consequently decomposed into their components: the tail of the previous response, one or two SCRs and the SCL. The SCRs free of the complication of overlap were then quantified. The raw SCRs of the same data set were also measured using a standard method. The standard measurement showed a significant reduction of 15% in amplitude and 140 ms in peak latency compared to our method. The basic four SCR model parameters--onset time, rise time, decay time constant and gain--showed increasing inter-subject variability in that order. These SCR model parameters may be studied as variables in normal and patient groups and as indices of treatment response. This quantitative method also provides a means to assess the relationships between central and autonomic psychophysiologic measures.

Adult↗
PubMed1997

Automatic processing dysfunction in Parkinson's disease.

Simultaneous measures of Event Related Potentials (ERP) and electrodermal activity (EDA) allow the delineation of ERPs that did, and did not, evoke an electrodermal 'Orienting Reflex' (OR). The OR is an automatic reflex invoked by novel or significant stimuli. Our group have developed a model to quantify electrodermal OR activity acquired in conventional late component ERP paradigms with short interstimulus intervals. Target late component (N100, P200, N200, P300) ERPs (acquired in an auditory oddball paradigm) and EDA was examined in 15 Parkinson's disease (PD) subjects and 50 normal controls. Single-trial target ERPs were averaged according to whether or not they elicited an electrodermal OR. Compared with controls, the PD group showed significantly decreased N100 and N200 amplitudes in the OR related ERPs ('Orienting ERPs'). These preliminary findings suggest that conventional late component ERPs can be delineated according to whether or not they evoked an OR. The 'orienting ERPs' in PD showed more significant disturbances compared with controls, than ERPs that did not evoke an OR.

Acoustic Stimulation↗
PubMed1997

Effects of a pre-training conditioning programme on basic military training attrition rates.

The medical attrition rates of 4 cohorts of recruits undergoing basic military training (BMT) were studied. They were grouped as follows: Group A (n = 3475), a mixture of fit and unfit recruits; Group B (n = 2081), consisting only of fit recruits; Group C (n = 940) comprising only unfit recruits who underwent a 4 to 6 weeks conditioning programme prior to being subjected to a similar 3-month BMT for all 3 groups and Group D (n = 2613) comprising unfit recruits who underwent an extended 4-month BMT. It was found that Group B [Relative risk (RR) = 0.26 95% confidence interval (CI) = 0.21, 0.33] and Group C (RR = 0.45 95% CI = 0.38, 0.62) had significantly lower medical attrition rates compared with Group A (RR = 1). Group D, however, did not show significantly lower attrition rates in spite of a more gradual training pace. When the unfit cohorts were compared, Group C (RR = 0.52 95% CI = 0.40, 0.67) had significantly lower attrition rates than Group D (RR = 1). The major cause of medical attrition in all groups was musculo-skeletal injuries sustained during training. Our results showed that a formal pre-training conditioning programme resulted in lower attrition during BMT and this reduction was more effective than training the recruits at a slower pace by extending the BMT by one month.

Adult↗
PubMed1997

The effects of prolonged passive heat exposure and basic military training on thermoregulatory and cardiovascular responses in recruits from a tropical country.

This study investigates the effects of long-term passive heat exposure and a 16-week basic military training program on heat acclimatization. Thirty recruits were tested on the zero (T1), 2nd (T2), 6th (T3), and 16th (T4) weeks of the basic military training program. The trials involved 1 hour of marching on a treadmill at 5.5 km h-1, with a 5% gradient. The subjects wore their camouflage uniforms during the trials, with simulated combat loads. The trials were conducted in a climatic chamber programmed at 32 degrees C, 60% relative humidity, 900 Wm-2 of simulated solar radiation, and wind speed of 3 m s-1. There was no fluid replacement during the trials. Because only 9 subjects attended all the trials, the results presented are based on these subjects. No significant difference was found in mean skin temperature in all the four trials. Tympanic temperature was significantly reduced (p < 0.05) only at 20 minutes. Pairwise analysis was significant (p < 0.05) only between T1 (37.18 +/- 0.38 degrees C) and T4 (36.48 +/- 0.53 degrees C). Average body temperature was significantly different only at 10 and 60 minutes (p < 0.05). A significant pairwise difference (p < 0.05) was found only between T1 (36.61 +/- 0.33 degrees C) and T4 (36.07 +/- 0.46 degrees C) in 10 minutes. No pairwise difference was found at 60 minutes. Mean heart rate (HR) was significantly reduced during the 16 weeks at 10, 20, and 30 minutes. Mean HR at 10 minutes was reduced from 152.11 +/- 14.18 beats min-1 in T1 to 130.78 +/- 10.43 beats min-1 in T4 (p < 0.001). Mean HR at 20 and 30 minutes was reduced from 156.11 +/- 17.74 beats min-1 (T1) to 137.25 +/- 11.42 beats min-1 (T4) (p < 0.001), and from 157.14 +/- 15.77 beats min-1 (T1) to 146.11 +/- 12.64 beats min-1 (T4) (p < 0.05). There was no significant difference in sweat loss and mean sweat rate during the 16 weeks. This study concluded that long-term passive heat exposure was effective at inducing heat acclimatization in terms of tympanic temperature, average body temperature, mean skin temperature, sweat loss, and mean sweat rate, but not in terms of HR. Physical training was still necessary to induce further adaptation in HR. The limiting factor to task completion during the trials was physical fitness rather than beat fitness.

Analysis of Variance↗
PubMed1996

Brainstem myoclonus in a patient with non-dopa-responsive parkinsonism.

In the few reports where electrophysiologic techniques have been used to characterise stimulus-sensitive myoclonus in the setting of a parkinsonian syndrome, the origin of the myoclonus has usually been found to be cortical. We describe a patient with parkinsonism unresponsive to levodopa who had myoclonus that was both spontaneous and induced by somatosensory stimuli. In addition, autonomic symptoms and a marked sleep disturbance were present early in his illness. Results of electrophysiologic investigations including electromyography (EMG) studies, routine electroencephalography (EEG) recording, jerked locked back-averaging of EEG, and somatosensory evoked potentials were consistent with a brainstem origin for the myoclonic jerks. Following ipsilateral digital and supraorbital electrical stimulation, the earliest muscle activation occurred in the trapezius. An all-night sleep study showed frequent myoclonic jerks during sleep and markedly abnormal sleep architecture. We believe that this patient's myoclonus was related to pathologic changes in brainstem reticular nuclei that occurred as part of his disease process. To our knowledge, brainstem myoclonus has not been described as a feature of parkinsonian syndromes.

Brain Stem↗
PubMed1996

Apomorphine can increase cutaneous inhibition of motor activity in Parkinson's disease.

We studied the effect of non-nociceptive ipsilateral digital stimulation on EMG recorded from a small hand muscle before and after the administration of subcutaneous apomorphine in 6 patients with Parkinson's disease. All were receiving the drug to control ¿on-off¿ fluctuations in motor performance. Averaged rectified EMG was recorded from tonically contracted abductor pollicis brevis (APB) following index finger stimulation using a brief stimulus train. In 5 patients motor evoked potentials (MEPs) were also recorded from APB during tonic contraction. A conditioning stimulus train was applied to the index finger at intervals between 15 and 65 msec prior to the transcranial magnetic stimulus. After apomorphine administration the patient group showed a significant increase in both EMG and MEP inhibition induced by digital stimulation. In patients with Parkinson's disease who have marked motor fluctuations, the inhibitory response of upper limb motor neurones to low level digital cutaneous stimulation can be altered by dopamine agonists.

Aged↗