Ljiljana Kaliterna

Personality differences in the phase of circadian rhythms: a comparison of morningness and extraversion

Abstract Individual differences in the phase of circadian (around 24 h) rhythms are thought to be important in determining adjustment to shift work and rapid time-zone transitions. Attempts to predict such phase differences on the basis of paper and pencil ‘personality’ tests have concentrated on extraversion and morningness, of which Kerkhof (1985), in a recent review of this literature, concluded morningness was the more important. However, the literature on which this conclusion was based suffers from a number of problems. The present study attempted to overcome these problems by examining the trends over a complete 24 h cycle for a range of performance and psychophysiological measures in students with extreme scores for both extraversion and morningness. In general, the results support KerkhoFs conclusion. However, reliable phase differences associated with morningness were confined to subjective ratings of alertness, oral temperature, and, in combination with extraversion, choice reaction time. Two a...

Productivity on a weekly rotating shift system: circadian adjustment and sleep deprivation effects?

Abstract There is little doubt that productivity and safety can be impaired on the night shift. Two main factors have been identified that may be responsible for this. On the one hand, the circadian rhythm in performance on at least simple tasks is at a low ebb at night, and adjusts only slowly over a span of night shifts. On the other, the day sleeps of shift workers taken between night shifts are of a reduced duration, and thus a cumulative sleep debt may accrue over successive night shifts. The former thus predicts that productivity should improve over a span of night duty, while the latter predicts that it should decline. We have examined the productivity of 53 female shift workers, and the sleeping habits of a sub-sample of 30 of them, on a weekly rotating shift system in order to assess the relative contribution of these two factors. Our results suggest that circadian adjustment to night work is the dominant factor for the first three or four successive nights shifts, but that sleep deprivation effe...

Is tolerance to shiftwork predictable from individual difference measures

Abstract This study was aimed at evaluating the most important relations between individual characteristics of shiftworkers and their subjective health complaints, obtained by cross-sectional and longitudinal procedures. A total of 604 shiftworkers and 185 young subjects who were going to enter shiftwork were examined by means of individual difference and subjective health questionnaires. The questionnaires were administered concurrently to the group of workers already involved in shiftwork. In the other group studied, the questionnaires were administered before they entered shiftwork, and subjective health was re-examined after the first and third year of work on shifts. More health complaints were reported by the group of older workers and those with longer shiftwork experience, with higher scores of neuroticism, hard-driving and competitiveness, speed and impatience, and rigidity of sleeping habits, and lower scores on relaxedness, efficiency and vigorousness. However, the correlations between these di...

Individual differences in circadian rhythm parameters and short-term tolerance to shiftwork: a follow-up study

The relationship between individual differences in the phase and amplitude of circadian rhythms and tolerance to shiftwork has been the subject of several studies. Those studies recorded circadian rhythms and shiftwork tolerance at approximately the same time. The present study aimed to examine the predictive relationships between the amplitude, phase, and mesor of 24 h rhythms obtained before exposure to shiftwork, and subsequent indices of tolerance measured after one and three years of shiftwork. The results revealed some stable relations between the various rhythm parameters and subsequent tolerance measures. Workers who had a higher mesor of positive moods, and a lower mesor of negative moods and fatigue, before entering shiftwork tended to tolerate shiftwork better. Further, those whose heart rate rhythm showed an earlier acrophase had better subsequent sleep quality scores, while those with a smaller amplitude of their temperature, negative mood and fatigue rhythms showed better night-shift tolerance.

Evaluation of the Survey of Shiftworkers (SOS)- short version of the Standard Shiftwork Index

Abstract The objective of the study was to evaluate the psychometric properties of a translated SOS version and to compare the results obtained on groups of shiftworkers of different gender, working in different shift schedules. The subjects: (a) 61 women working 12-hour shifts (day-night-two days off), (b) 78 men working 12-hour shifts (day-night-two days off) and (c) 69 men working 8-hour shifts (2 : 2 : 2; morning-afternoon-night) were administered the SOS which consists of questions and rating scales covering description of the shift system worked, individual difference and tolerance to shiftwork measures. The scales used as tolerance to shiftwork measures showed satisfactory psychometric properties. The discriminant analysis performed showed that the ‘social’, ‘domestic’ and ‘non-domestic’ disruption scores were the most potent discriminant factors to differentiate between different shift systems. Irrespective of gender, workers in 12-hour shift system reported less disturbed domestic, non-domestic and social life than workers in 8-hour shift system. Relevance to industry As a relatively short and easy to administer, the Survey on Shiftworkers could be used to identify problems of industrial shiftworkers associated with different types of shift systems and to evaluate possible interventions.

Sleep and napping in young shiftworkers : A 5-year follow-up

Abstract The present study examined sleep characteristics in young workers who entered rapidly rotating shiftwork for the first time and stayed on shifts for 5 years. Data were collected when the subjects had shiftwork experience of approximately 1.5, 3.5 and 5.5 years and a mean age of 22, 24 and 26 years. Data are presented showing significant differences in the main sleep durations between situations within the shift cycle and a small reduction in overall sleep over the observed period, primarily due to a sleep reduction on afternoon shift days. Data on sleep quality did not show any change over this early period of shiftwork exposure. In addition, napping strategies did not change, with the exception of a small increase in those taking naps on night-shift days between 1.5 years and 3.5 years of shiftwork exposure. At all the observed phases there were more young shiftworkers taking a nap on the morning shift days than on the night-shift days. The data suggested that reduced sleeps on morning and night...

Shiftwork tolerance and circadian rhythms in oral temperature and heart rate

Abstract The study aimed at establishing differences in the circadian rhythm parameters of oral temperature and heart rate between three groups of workers matched by age: tolerant shiftworkers with good sleep quality and few psychosomatic and digestive complaints, intolerant shiftworkers with poor sleep quality and more psychosomatic and digestive complaints, and workers who had never worked in shifts. The study was performed at an oil refinery recreation centre where the subjects were isolated for three days. During that period they lived under constant conditions, i.e. their activities, timing and content of meals, ambient temperature and light were controlled. Hourly measurements of oral temperature and heart rate were performed over a 24-h period. The parameters of the physiological rhythms were estimated by means of the COSINA method. Generally, the differences between the groups were low and not statistically significant. The authors could find no difference in the amplitude and phase position betwe...

Shiftwork tolerance and 24-h variations in moods

Abstract The objective of the study was to identify the differences in 24-h variations in moods between three groups of oil-refinery workers: tolerant shiftworkers, intolerant shiftworkers and workers who had never worked in shifts. Each group comprised 29 workers matched by age. The mood measurements were taken during a 24-h period every 2 h starting from 08:00 h. Results were scored for three scales: positive moods, negative moods and fatigue. The two-factor ANOVA revealed the significant main effect of groups for all three moods indicating differences at the average level of 24-h variations in all moods between workers who differed in the degree of tolerance to shiftwork. The significant main effect of time of day was also found for all moods while the reliable interaction between groups and time of day was observed for negative moods only, indicating a different shape of 24-h variations for non-shiftworkers in comparison to shiftworkers.