Circadian rhythm amplitude--is it related to rhythm adjustment and/or worker motivation?

Present Mood States in Brazilian Night Nurses

Variations in the state of momentary emotions of Brazilian hospital nurses on day and night shifts were recorded. Ten graduate nurses working on day and night shifts in the clinical ward of hospitals completed the Present Mood States List of Engelmann at the beginning and end of the first and last days of each shift. Analysis indicated (a) nurses had a stable emotional profile, present at the working shift, and (b) variations in present mood states related to specific effects of shift work were observed when comparisons were made between the present mood states at the beginning and end of each shift duty.

Circadian rhythms, sleep deprivation, and human performance

Much of the current science on, and mathematical modeling of, dynamic changes in human performance within and between days is dominated by the two-process model of sleep-wake regulation, which posits a neurobiological drive for sleep that varies homeostatically (increasing as a saturating exponential during wakefulness and decreasing in a like manner during sleep), and a circadian process that neurobiologically modulates both the homeostatic drive for sleep and waking alertness and performance. Endogenous circadian rhythms in neurobehavioral functions, including physiological alertness and cognitive performance, have been demonstrated using special laboratory protocols that reveal the interaction of the biological clock with the sleep homeostatic drive. Individual differences in circadian rhythms and genetic and other components underlying such differences also influence waking neurobehavioral functions. Both acute total sleep deprivation and chronic sleep restriction increase homeostatic sleep drive and degrade waking neurobehavioral functions as reflected in sleepiness, attention, cognitive speed, and memory. Recent evidence indicating a high degree of stability in neurobehavioral responses to sleep loss suggests that these trait-like individual differences are phenotypic and likely involve genetic components, including circadian genes. Recent experiments have revealed both sleep homeostatic and circadian effects on brain metabolism and neural activation. Investigation of the neural and genetic mechanisms underlying the dynamically complex interaction between sleep homeostasis and circadian systems is beginning. A key goal of this work is to identify biomarkers that accurately predict human performance in situations in which the circadian and sleep homeostatic systems are perturbed.

Stress, geomagnetic disturbance, infradian and circadian sampling for circulating corticosterone and models of human depression?

While certain circadian hormonal changes are prominent, their predictable assessment requires a standardization of conditions of sampling. The 24-hour rhythm in circulating corticosterone of rodents, known since the 1950s, was studied as a presumed proxy for stress on 108 rats divided into 9 groups of 6 male and 9 groups of 6 female animals sampled every 4 hours for 24 hours. In a first stress study, the "no-rhythm" (zero-amplitude) assumption failed to be rejected at the 5% probability level in the two control groups and in 16 out of the 18 groups considered. A circadian rhythm could be detected with statistical significance, however, in three separate follow-up studies in the same laboratory, each on 168 rats kept on two antiphasic lighting regimens, with 4-hourly sampling for 7 or 14 days. In the first stress study, pooling of certain groups helped the detection and assessment of the circadian corticosterone rhythm. Without extrapolating to hormones other than corticosterone, which may shift more slowly or adjust differently and in response to different synchronizers, the three follow-up studies yielded uncertainty measures (95% confidence intervals) for the point estimate of its circadian period, of possible use in any future study as a reference standard. The happenstance of a magnetic disturbance at the start of two follow-up studies was associated with the detection of a circasemiseptan component, raising the question whether a geomagnetic disturbance could be considered as a "load". Far beyond the limitations of sample size, the methodological requirements for standardization in the experimental laboratory concerning designs of studies are considered in the context of models of depression. Lessons from nature's unforeseen geomagnetic contribution and from human studies are noted, all to support the advocacy, in the study of loads, of sampling schedules covering more than 24 hours.

A saúde do trabalhador na sociedade 24 horas

Este artigo trata, em um primeiro momento, de fatores subjacentes às diferenças individuais quanto à tolerância ao trabalho em turnos e noturno. Associadas a esses fatores, também são apresentadas características do trabalho que podem ou não favorecer a tolerância ao trabalho em turnos. Em um segundo momento, apresenta-se medidas de intervenção que visam minimizar as dificuldades enfrentadas pelos trabalhadores quanto à saúde e ao bem-estar orgânico e social.

The lights are bright? Debating the future of the permanent night shift

Debates a controversial issue in healthcare management, that is, whether internal rotation (day-night) or permanent night shifts is an appropriate shift system for nursing staff. A multidisciplinary approach draws together international research from the fields of occupational psychology, management, ergonomics and medicine. Explores evidence on sleep, physical and mental health, job satisfaction, performance, absenteeism, and social and domestic disruption, all important factors in considering appropriate shift patterns. Suggests that both nurse choice (or non-choice) of shift and adjustment, or otherwise, of circadian rhythms are important causal factors influencing the debate. As no unequivocal picture emerges, recognizes some of the real and potential limitations of a paper of this kind; however, the balance of argument tends to favour the maintenance of permanent night shift nurses as opposed to the further extension of internal rotation systems. This is especially the case as many nurses will still be given a choice of shift pattern which may, in itself, negate some of the potential ill-effects of night working. Decisions further to extend internal rotation may, in the light of the complex, ambiguous and equivocal evidence, be informed by partial knowledge and influenced by a managerial perspective.

Effects of nocturnal shiftwork on mood states of student nurses

Daily mood changes were monitored over successive 24-h periods using the Profile of Mood States (POMS) (3) to assess the effect of nocturnal shiftwork on mood. Twenty-three student nurses, age range 19-24 years, were studied throughout their first experience of nocturnal shiftwork. The POMS was administered over four complete solar days during a 12-week period that included an 8-week block of night work. Five POMS dimensions displayed circadian rhythmicity: vigor-activity; fatigue-inertia; confusion-bewilderment; friendliness; and total-mood-disturbance. These five dimensions were sensitive to changes in living patterns, showing phase shifts in their circadian rhythms when subjects alternated between diurnal and nocturnal living patterns. The dimensions were also observed to be sensitive to adjustment to two different nocturnal shiftwork schedules. The subjects who worked "four on, three off" showed similar phase shifts to the subjects who worked "eight on, seven off," suggesting that mood adjustment takes place by the fourth night of a rotation of nights. The "commitment" of the students to the nocturnal living pattern was thought to have a bearing on the adaptation of the students to the nocturnal shifts, as regards mood.

Sleepiness and shiftwork: individual differences

On-site studies of shiftwork show considerable differences in sleepiness between workers. Variation between individuals depends on different sleeping, coping and living habits of the workers, on possible sleep disorders, but also on more 'permanent' inter-individual factors that may influence sleepiness by changing either the circadian or homeostatic factors of sleep. The effects of circadian phase, age, sex, physical fitness, domestic and personality factors on shiftworkers' sleepiness and work-related accidents are reviewed. It is concluded that only a minor part of the variation in sleepiness between individuals can be explained. The present knowledge is not sufficient to carry out reliable 'selection' of individuals suitable for shiftwork. However, preventive advice and medical surveillance focusing on individual differences in sleepiness are recommended.

An evaluation of the Circadian Type Questionnaire

This study evaluates the psychometric properties and assesses the test-retest reliability and longer-term stability of scores on the Circadian Type Questionnaire (CTQ) of Folkard et al. (1979) in a sample of 445 students. The scales were found to lack internal consistency and the factor structure originally proposed was not replicated. Cultural variation in CTQ scores was suggested. Test-retest reliability, over three months in a subgroup of 36, was poor for the V and M scales. Longer-term stability, over nine months in a subgroup of 36 who were exposed to shiftwork, was better but significant decreases were found in rigidity of sleeping habits (R_s) and morningness (M) scores. A factor analysis suggested that the scales should be constructed differently; however, the properties of such scales were still not optimal. The CTQ has psychometric flaws and needs to be improved before it could be expected to reliably function as a predictive test of adaptation to shiftwork.

The prediction of the adaptation of circadian rhythms to rapid time zone changes

The aim of the study was to find out which factors could explain individual differences in the resynchronization speed of circadian rhythms of salivary melatonin and subjective alertness after transmeridian flights over 10 time zones. The mean age of the 40 female subjects was 33.0 +/- 6.9 years. The data were gathered by measurements of the circadian rhythms of melatonin excretion and altertness at 2 h intervals in Helsinki (Finland) two days before westward flight to Los Angeles (USA), where the measurements were repeated on the 2nd day after the flights and on the 2nd day in Finland after return flight. This shift in the acrophases of the two circadian rhythms were used as dependent variables in regression analyses. The predictors used were length of day, marital status, amount of physical exercise, age, neuroticism, extroversion, and eveningness. Age, day length, marital status, and physical exercise explained the acrophase adaptation of the melatonin rhythm after westward flight, and day length, neuroticism, and extroversion after eastward flight. Marital status, neuroticism, and physical exercise explained the variation of the acrophase adjustment of the alertness rhythm after westward flight, and age and eveningness after eastward flight. It is concluded that the amount of daylight and personality are the best predictors of the circadian rhythm adaptation after transmeridian flights.

Individual differences in tolerance to shiftwork: a review

Individual differences in the subjective health effects of shiftwork are reviewed. Circadian regulation and brain restitution (sleep) are the crucial mechanisms by which inter-individual factors can affect tolerance to shiftwork. On the other hand, shiftworkers can use different coping mechanisms by trying to schedule their lives and especially their sleeping habits to work at unusual hours. Individual factors related to shiftwork tolerance are discussed in two groups; first, the factors which affect primarily the circadian adjustment; and, second, the factors which mainly relate to the ability to sleep at unusual hours. The significance of circadian adjustment in shiftwork tolerance is outlined.

The relation of shift work tolerance to the circadian adjustment

The amplitude and phasing of circadian rhythms are under discussion as possible predictors of tolerance to night work. In a field study, subjective sleepiness and oral temperature of 147 female nurses were measured at 2-hour intervals during a period with one morning shift and two consecutive night shifts. The nurses also filled out a questionnaire. Two types of tolerance indices were constructed: The "health index" was based on questions referring to general fatigue, gastrointestinal symptoms, and sleep disturbances, and the "sleepiness index" on the actual subjective ratings of sleepiness. According to the health index, the group with good tolerance had a larger circadian amplitude of the oral temperature rhythm on the day of the morning shift than the group with poor tolerance. However, with regard to the sleepiness index, the corresponding difference between the groups with good or poor tolerance was not significant. The data did not confirm the hypothesis that predicts a quick adjustment of the circadian rhythm when the circadian amplitude is small before the change to night work. The contradictory results found in this and in other studies do not yet permit prediction of tolerance to night work.

Does 'anchor sleep' entrain circadian rhythms? Evidence from constant routine studies

Experiments have been performed in an isolation unit to investigate the effects of abnormal sleep-waking schedules upon circadian rhythms of renal excretion and deep-body temperature. In confirmation of previous work, nychthemeral rhythms appeared to be 'anchored' to a 24 h period if 4 h sleep was taken regularly each day, even though another 4 h was taken irregularly. The endogenous components were investigated by assessing circadian rhythmicity under constant routine conditions, that is, when rhythmic influences in the environment and sleep-waking pattern had been minimized. Analysis of the constant routine data indicated the presence of a rhythmic component which had been stabilized to a period of 24 h by the 'anchor sleep'. In addition, a delayed component was also present. The starting time of the constant routines produced a direct effect upon the rhythms, which was presumed to result from removing the 'masking' effect that sleep normally exerts upon rhythms. There was some evidence that the relative importance of the masking effect and the delayed component depended upon the variable under consideration. The implications of these findings, in terms of the effects of anchor sleep, the presence of more than one internal clock and the usefulness of constant routines, are discussed.