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Query: UMLS:C0015672 (fatigue)
 51,768 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

When visual evoked potentials (VEPs) are tested patients are often expected to focus on a pattern screen for prolonged periods of time. This may lead to fatigue, failure of concentration and drowsiness, and consequently to a deterioration in the recorded VEP. To determine whether there may be time-dependent changes in the VEP of normal subjects independent of the degree of alertness, attention and altertness were controlled using a reaction time (RT) task in which the subjects were required to re-illuminate the fixation point in the middle of the stimulating screen for the VEP. It was first established that the switching of the fixation point produced little contamination of the background VEP to pattern reversal and that the latency and amplitude of P100 to pattern reversal were identical whether or not the subject was engaged in the RT task. A sequence of 16 averages of the VEP to 256 pattern reversals was recorded, alternately with or without the RT task. The measured RTs decreased during the sequence, presumably due to practice. There was a progressive decrease in the amplitude N70-P100, accompanied by an increase in the variability of the latency of P100. These changes cannot be attributed to lack of alertness, given the improvement in RT. Clinicians should be aware of the possibility of a deterioration in the VEP due to physiological mechanisms when the testing protocol involves multiple averages.
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PMID:Sequence-dependent deterioration in the visual evoked potential in the absence of drowsiness. 137 Apr

To assess central nervous system effects and visual fatigue induced by work with visual display terminals (VDT), symptom frequency was assessed and visual evoked potential (VEP), critical flicker fusion (CFF) and near-point distance were measured in 24 female keypunchers before and after 2.5 h of VDT work and in 6 non-VDT-exposed subjects at the same intervals. Each keypuncher had been engaged in data entry for 1-7 (mean, 4) years. After VDT work, the number of complaints of subjective fatigue as well as an objective measure of near-point distance were significantly increased as compared with those before work; also, the N75, P100 and N145 latencies of VEP were significantly prolonged. The change of P100 latency during VDT work was inversely correlated with the number of years worked in data entry. No significant change was seen in any of these tests in the non-VDT-exposed subjects. The changes in N75 latency and subjective fatigue related to drowsiness and dullness in the keypunchers were significantly larger than those in the non-VDT-exposed subjects. The CFF was significantly lower in keypunchers than in non-VDT-exposed subjects in both the first and the second tests. These data suggest that VDT work is associated with impairment of the visual nervous system function, that VEP latencies appear to be a sensitive indicator of visual fatigue, at least transiently, and that CFF appears to be a good parameter for estimations of chronic visual fatigue.
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PMID:Central nervous system effects and visual fatigue in VDT workers. 188 79

A new provocative test for early diagnosis of Multiple Sclerosis (MS) is presented. It is based on the recording of pattern visual evoked responses (VER) before and after exposing patients to a high luminance background. All 13 patients tested showed a biphasic enlargement of the P100 wave after bleaching even in the absence of an increased P100 latency. This biphasic enlargement can be interpreted as a fatigue or a saturation-like phenomenon as can be seen psychophysically. The saturation-like effect involves probably only affected fibers. No change in the VER was observed in 20 Normal observers examined in the same way. This test can be usefully employed in dubious cases of MS where routine VER do not provide reliable results.
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PMID:Provocative test for early diagnosis of multiple sclerosis. 407 57

A 39 year-old severely disabled woman with a 19 year history of chronic relapsing-remitting multiple sclerosis (MS) began to experience improvement in symptoms within 24 hours after she received experimental treatment with picotesla electromagnetic fields (EMFs). Pattern reversal visual evoked potential (VEP) study obtained three weeks after the initiation of the first magnetic treatment showed a return to normal of the P100 latencies in each eye. The patient continued to receive 1-2 EMFs treatments per week and during the following 32 months she made a dramatic recovery with resolution of diplopia, blurring of vision, dysarthria, ataxia of gait, and bladder dysfunction as well as improvement in fatigue, heat tolerance, mood, sleep, libido, and cognitive functions. VEP studies, which were repeated in April of 1995 more than 2 1/2 years after the initiation of magnetic treatment, showed that P100 latencies remained normal in each eye providing objective documentation that continued application of these EMFs may sustain normal conduction in the damaged optic pathways over a long period of time. This is the first case report documenting the dramatic long term beneficial effects of treatment with picotesla range EMFs in a patient with MS.
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PMID:Long term beneficial effects of weak electromagnetic fields in multiple sclerosis. 874 48

Pethidine (meperidine) is a compound with both local anaesthetic and opioid agonist properties. We have in a recent study demonstrated that pethidine could be an interesting alternative to prilocaine in arthroscopy with local anaesthetic technique. Therefore, we investigated, in a controlled randomized double-blind study, the effect of three doses of pethidine compared with a standard local anaesthetic, in patients subjected to arthroscopic knee joint surgery. Ten patients in each group received 50 mg (P50), 100 mg (P100), 200 mg (P200) of pethidine or prilocaine (5 mg/ml) + adrenaline (4 mg/ml) (PC), injected intra-articularly (i.a.) before surgery. We measured pain intensity and discomfort during arthroscopy and pain intensity at rest and at movement, nausea and tiredness for 3 days post-operatively at regular intervals using the VAS-technique. We also measured the concentration of pethidine and its demethylated metabolite, norpethidine, in plasma by collecting blood samples at 20, 40, 60, 80, 140 and 200 min following injection, and in synovial fluid which was collected through the arthroscope at the start and the end of the surgery. It was found that significantly more patients in the P50 group (n = 6) needed general anaesthesia due to intense pain than those in the P100 group (n = 1), P200 group (n = 0) or the PC group (n = 1). The PC group required significantly more analgesics and had a significantly higher calculated total sum of pain scores at movement post-operatively, than the other three groups. The P200 group more often reported tiredness post-operatively than the other three groups. We conclude that 100 or 200 mg pethidine i.a. produces satisfactory anaesthesia for surgery. There was a rapid transfer of pethidine from synovial fluid to plasma, resulting in plasma levels earlier reported to produce centrally mediated effects, such as analgesia and tiredness. We found much higher concentrations of norpethidine in the synovial fluid than in plasma, suggesting a local demethylation in the knee joint tissues. This site of drug oxidation has not earlier been demonstrated neither in vitro nor in vivo. The results suggest that pethidine given i.a. in the dose range of 50 to 200 mg results in analgesia due to both peripheral and central mechanisms. The significant systemic uptake of pethidine can cause unwanted side-effects.
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PMID:A comparison of 50, 100 and 200 mg of intra-articular pethidine during knee joint surgery, a controlled study with evidence for local demethylation to norpethidine. 1020 35

Visual evoked potentials (VEPs) were recorded in a group of 20 operators aged 25-45 years during two sessions, before and after a 5-hour work at computer terminals, in order to assess visual system fatigue. The outcomes were referred to the norms established for the age-matched population of 30 subjects not exposed to professional contact with computers. Most of the examined operators suffered various complaints concerning not only the organ of vision but the central nervous system as well. VEPs were elicited by means of monocular stimulation using the reversal checkerboard pattern and recorded simultaneously from the scalp electrodes placed over the right and the left cerebral hemisphere. Only recording acquired after finishing of a working day demonstrated significant statistically abnormalities of the VEPs waveforms, which suggests their transient character. The changes mentioned above included prolongation of peaks P100 and N2 latency with concomitant attenuation of their amplitudes and a decrease of the correlation coefficient values for the recordings from the hemispheres. The preliminary findings presented in this paper seem to justify a conclusion that the non-invasive VEPs method can be considered as the objective indicator of the central visual fatigue induced by the workload at computer terminals.
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PMID:[The evaluation of central visual fatigue in computer terminal users by visual evoked potentials]. 1035 27

This study evaluated the ability of a qualitative fit-test method (irritant smoke) to detect known exhalation valve leakage. The OSHA protocol for the irritant smoke test mandates the use of a low flow air pump at 200 mL/minute or an aspirator squeeze bulb. Many commercial test kits include an aspirator bulb, which is subject to variation in frequency, depth of squeeze, fatigue rate, and individual hand strength. Previous studies on irritant smoke used a handheld squeeze bulb. This study evaluated the effectiveness of a low flow pump for irritant smoke fit-testing. Twenty subjects wearing North 7600 series full-face respirators equipped with P100 filters were fit-tested with a Portacount Plus to ensure adequate fit. After successful fit was demonstrated, the exhalation valve was replaced with a damaged valve and/or rotated approximately 90 degrees to produce a fit factor below 100. Having induced an exhalation valve leak, the irritant smoke fit-test was performed using the OSHA irritant smoke protocol. To avoid introducing additional unknown leakage, all head movement exercises were replaced with the head straight, normal breathing maneuver. Irritant smoke did not detect 40 percent of respirators with leaking exhalation valves. Sixty percent of the subjects were able to detect the irritant smoke. Test sensitivity was 60 percent, well below the recommended 95 percent criterion. Of the 12 subjects that detected irritant smoke, none detected the smoke in less than a minute; the average detection time was 3 min 5 s. Some subjects were able to suppress the cough reflex. These findings suggest that qualitative fit-testing using irritant smoke with a 200 ml/min continuous flow pump does not have adequate sensitivity to detect fit factors less than 100.
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PMID:An evaluation of irritant smoke to detect exhalation valve leakage in respirators. 1290 38

In order to evaluate the effects of dietary taurine supplementation on visual fatigue induced by visual display terminals (VDT) work, 25 male college students aged from 20 to 24 years who were not engaged in VDT work were selected to participate in the study. Volunteers were randomly assigned to either the taurine supplementation (n=13) or the placebo supplementation control group (n=12). Before and after 12 days of taurine (3 g/day) or placebo supplementation, two identical 2.5-hr VDT work tests were performed while recording the P100, N75 and N145 latencies and P100 amplitude of pattern visual evoked potential (PVEP) and the frequency of critical flicker fusion (CFF). Following 2.5-hr of VDT work, the P100 and N75 latencies of PVEP increased ( P<0.01) while the P100 amplitude decreased significantly ( P<0.01). The frequency of CFF also reduced significantly ( P<0.01). After 12 days of taurine supplementation, the reduction in P100 amplitude after VDT work alleviated significantly ( P<0.05). The results suggest that taurine supplementation alleviates visual fatigue induced by VDT work.
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PMID:Effects of taurine supplementation on VDT work induced visual stress. 1475 17

The aim of the study was to evaluate visual and brainstem auditory evoked potentials (VEP, BAEP) in multiple sclerosis (MS) patients with regards to fatigue and disease-related variables. The study comprised 86 MS patients and 40 controls. Fatigue was assessed using the Fatigue Severity Scale (FSS/FSS-5) and the Modified Fatigue Impact Scale (MFIS). Latencies and amplitudes of the P100 component of VEP and the I-V components of BAEP were analyzed. The results of EP were compared between non-fatigued, moderately and severely fatigued MS patients and controls. P100 latency was increased and amplitude decreased in moderately and severely fatigued MS subjects. The latency of the V component of BAEP and interlatencies I-III-V were increased in severely fatigued patients. The amplitude of the V component was lowered in fatigued patients. VEP and BAEP abnormalities were usually one-sided. Interocular P100 latency difference tended to correlate with FSS/FSS-5. The parameters of VEP and BAEP correlated with functional system scores but not with MS duration, overall degree of disability or its progression over time. Significant, usually asymmetrical VEP and BAEP abnormalities were found in fatigued MS patients, with no relationships to disease-related variables. EP may be considered an electrophysiological marker of fatigue in MS patients.
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PMID:Assessment of visual and auditory evoked potentials in multiple sclerosis patients with and without fatigue. 2524 Feb 78

A single-trial extraction of a visual evoked potential (VEP) signal based on the partial least-squares (PLS) regression method has been proposed in this paper. This paper has focused on the extraction and estimation of the latencies of P100, P200, P300, N75, and N135 in the artificial electroencephalograph (EEG) signal. The real EEG signal obtained from the hospital was only concentrated on the P100. The performance of the PLS has been evaluated mainly on the basis of latency error rate of the peaks for the artificial EEG signal, and the mean peak detection and standard deviation for the real EEG signal. The simulation results show that the proposed PLS algorithm is capable of reconstructing the EEG signal into its desired shape of the ideal VEP. For P100, the proposed PLS algorithm is able to provide comparable results to the generalized eigenvalue decomposition (GEVD) algorithm, which alters (prewhitens) the EEG input signal using the prestimulation EEG signal. It has also shown better performance for later peaks (P200 and P300). The PLS outperformed not only in positive peaks but also in N75. In P100, the PLS was comparable with the GEVD although N135 was better estimated by GEVD. The proposed PLS algorithm is comparable to GEVD given that PLS does not alter the EEG input signal. The PLS algorithm gives the best estimate to multitrial ensemble averaging. This research offers benefits such as avoiding patient's fatigue during VEP test measurement in the hospital, in BCI applications and in EEG-fMRI integration.
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PMID:Single-Trial Visual Evoked Potential Extraction Using Partial Least-Squares-Based Approach. 2537 49


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