Content uploaded by J. Snel
Author content
All content in this area was uploaded by J. Snel on May 23, 2015
Content may be subject to copyright.
Caffeine and fatigue
... In general, reviews of the literature have treated this short-term task induced fatigue as distinct from the sleep-induced fatigue (e.g. Snel & Lorist, 1999). One key consideration in assessing the size of the caffeine effects in studies employing longer term sleep deprivation, however, has been the potential confound between sleep deprivation and the concurrent caffeine deprivation which is imposed in the design of most of those studies. ...
30 min after ingesting 200 mg of caffeine or a placebo, each of 24 21-26 yr old males drove an automobile simulator for 90 min. Immediately thereafter, the S ingested a supplemental dose of 200 mg of the medication taken initially and then drove for another 90 min. The simulator provided a comprehensive and coherent set of stimulus inputs which produced a degree of realism not usually found in laboratory studies. Both the initial and the supplemental doses of caffeine significantly enhanced performance beyond that found with placebo, on each of 4 measures of alertness. (PsycINFO Database Record (c) 2012 APA, all rights reserved)
Caffeine is the most widely consumed centralnervous-system stimulant. Three main mechanisms of action of caffeine on the central nervous system have been described. Mobilization of intracellular calcium and inhibition of specific phosphodiesterases only occur at high non-physiological concentrations of caffeine. The only likely mechanism of action of the methylxanthine is the antagonism at the level of adenosine receptors. Caffeine increases energy metabolism throughout the brain but decreases at the same time cerebral blood flow, inducing a relative brain hypoperfusion. Caffeine activates noradrenaline neurons and seems to affect the local release of dopamine. Many of the alerting effects of caffeine may be related to the action of the methylxanthine on serotonine neurons. The methylxanthine induces dose-response increases in locomotor activity in animals. Its psychostimulant action on man is, however, often subtle and not very easy to detect. The effects of caffeine on learning, memory, performance and coordination are rather related to the methylxanthine action on arousal, vigilance and fatigue. Caffeine exerts obvious effects on anxiety and sleep which vary according to individual sensitivity to the methylxanthine. However, children in general do not appear more sensitive to methylxanthine effects than adults. The central nervous system does not seem to develop a great tolerance to the effects of caffeine although dependence and withdrawal symptoms are reported.
One of the central themes of this book is the adaptive nature of human response to stress and environmental demands. The basis of adaptive behaviour has not been systematically studied, though it may provide the key to the understanding of individual differences in stress proneness and health-related behaviour. It may also prove fundamental in the development of a general theory of effects of stress on performance and efficiency, for example by focusing attention on the processes which underlie successful and unsuccessful environmental management. The present paper puts forward a model of regulatory activity underlying stress management and coping, based on the “variable state theory” interpretation of stress effects (Hamilton, Hockey & Rejman, 1977). The initial analysis of stress effects leads to a proposal of a broader, more widely — applicable mechanism for adaptive regulation of behaviour. This theory suggests a number of possible sources for the derivation of individual differences. These may arise within the control system itself, or in intrinsic variability in both cognitive and energetical resources.
Die zentrale Wirkung von Coffein wurde in einer kontrollierten Studie an 9 männlichen Versuchspersonen mit Hilfe der Eeg-Spektralanalyse untersucht. Dabei wurden die Effekte von coffeinhaltigem Kaffee, gleichkonzentrierter Coffein-Lösung, coffeinfreiem Kaffee und warmem Wasser aufgrund einer faktoriellen Versuchsanordnung varianzanalytisch untersucht. Die verabfolgte Coffeinmenge betrug 250 mg. Es erfolgte eine Randomisierung sowohl bezüglich der Reihenfolge der Substanzen als auch bezüglich der Untersuchungs-Wochentage. Die hauptsächlichen Ergebnisse sind folgende: coffeinhaltiger Kaffee und gleichkonzentrierte Coffein-Lösung einerseits lassen sich bezüglich ihrer Eeg-Effekte kaum voneinander unterscheiden, ebensowenig andererseits coffeinfreier Kaffee und Wasser. Markante Unterschiede dagegen ergeben sich beim Vergleich beider Substanzgruppen. Die coffeinhaltigen Substanzgruppen bewirken eine bemerkenswerte, signifikante Abnahme der Theta-Amplitude, der Theta-Frequenz und Theta-Frequenzvariabilität, im Alpha-Bereich dagegen eine Zunahme der dominanten Frequenz mit Abnahme der Amplitude, verglichen mit den coffeinfreien Substanzgruppen. Der Befund ist insgesamt als Ausdruck einer deutlichen Aktivierung und Vigilanzsteigerung zu interpretieren. Im übrigen muß darauf hingewiesen werden, daß das elektroenzephalographische Wirkungsprofil des Coffeins, wie das anderer zerebral wirksamer Substanzen auch, beträchtliche interindividuelle Unterschiede aufweist, darüber hinaus aber auch signifikante nicht nur quantitative, sondern teilweise auch qualitative topographische Wirkungsdifferenzen.
SUMMARY Hypnotic medication reliably improves sleep during the day, in terms of increasing total sleep time (TST) and reducing awakenings and light sleep. Middle-aged individuals may benefit more than young adults. In addition, the time of day during which sleep is attempted may influence the efficacious dose of short-acting drugs. Available data suggest that improving sleep during the day may improve alertness/performance at night to a mild degree, but significant circadian-related sleepiness remains. Hypnotic medication may help minimize the cumulative effects of sleep loss associated with daytime sleep. Use for more than one week has not been adequately studied; however, as most night and rotating workers' schedules allow for night-time sleep for two or more nights per week, available evidence indicates that hypnotics can be used effectively on an intermittent basis, e.g. for the first 2–4 day-sleep periods of night shifts. Caffeine has been shown to increase alertness and improve psychomotor performance during usual night-shift hours when taken between 22.30 and 01.20 hours. Available data indicate that at approximate dosages of 250–400 mg, the beneficial effects persist until at least 05.30 hours. For most subjects, caffeine taken at the start of the night-shift does not interfere significantly with daytime sleep beginning at 09.00 hours. There is also some evidence that single doses of caffeine at the beginning of a night shift may be more alerting than divided doses. If caffeine is to be used therapeutically, avoidance of social use may be required to avoid tolerance to CNS stimulant effects. Despite the positive results of laboratory research examining hypnotics or caffeine as shiftwork countermeasures, field trials have not been conducted.
The effect of coffee without and with caffeine (200 mg) on the performance of "awake" respectively "fatigued" subjects was proved. 5 females and 7 males (22 to 32 years) were chosen for the cross-over double-blind study. Motor reaction time, visual-mental processing time, reading-speed and reading-errors were recorded. Further experiments under aggravated conditions were carried out. In the morning ("awake") caffeine increases the efficiency of all parameters excepted the reading errors. At night ("fatigued") the increase by caffeine is insignificant. Even in some subjects caffeine decreases the speed of reading and increases the number of errors. Under test-conditions, which were aggravated by strong acoustical disturbance, caffeine does not improve efficiency, compared with caffeine-free coffee. Overriding into the range of decreasing performance in spite of increasing central activity was not found under any test-condition.
Marked sleepiness occurs during typical night shift work hours and this reduced alertness is associated with marked performance deficits. The effect of caffeine (versus placebo) upon sleepiness at night was studied using objective measures of physiological sleep tendency and ability to sustain wakefulness. Both measures show caffeine to reduce sleepiness at a single dose roughly the equivalent of two to four cups of coffee. Despite impressive objective differences in alertness with caffeine, subjects did not consistently differentiate between drug conditions on subjective alertness assessments. The use of CNS stimulants to promote alertness during night shift hours should be considered, particularly for occupations for which alertness is critical.
Sumario: The primary purpose of the present study was to investigate the effects of caffeine in tasks requiring vigilant performance as well as capacity to hold and process information in memory among persons likely to suffer from a combination of time of day fatigue and sleep-loss related fatigue. One group of subjects was given caffeine and another group was given placebo treatment. Both groups were tested before and after treatment in question
1 The effects of caffeine and cyclizine alone and in combination, on performance tests and subjective ratings have been examined in two groups of twelve volunteer subjects using a balanced design for order of administration of treatments, a lactose control and with double-blind conditions. In the second study the electroencephalograph (EEG) was recorded after subjective ratings. Results were analysed by analysis of variance and values of P < 0.05 taken as significant.2 Caffeine in doses of 75 to 300 mg increased auditory vigilance compared with lactose dummy. Auditory reaction times were shortened, tapping rates increased and subjects felt more alert. No changes occurred in short term memory, arithmetic or digit symbol substitutions. An increase in energy in the delta band (2.3-4Hz) occurred after caffeine 100 mg.3 Cyclizine by contrast, produced few changes. Subjects were more alert after 25 mg and more sedated after 100 mg than after dummy. One test only showed impairment: arithmetic, after the 100 mg dose, which also increased energy in the delta frequency band.4 Combinations of caffeine 100 mg with cyclizine 50 and 100 mg did not produce any subjective changes, or changes in performance tests, differing from lactose. At no time on any test did the performances after combinations of drugs differ from caffeine 100 mg.5 Performance after both combinations of caffeine and cyclizine differed from that after cyclizine 100 mg on the following tests: vigilance, arithmetic and reaction time, thus showing a tendency for the caffeine effect to predominate. Subjective ratings of sedation after combination of the drugs were intermediate between the ratings following caffeine and cyclizine administered alone.