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PubMed1984

[Circadian rhythm of the grip strength of the right and left hands: desynchronization in some shift workers].

38 male shift workers and former shift workers volunteered to self-measure 4 to 8 times/24 hrs. their oral temperature (OT) as well as right and left hand grip strength (HGS) best performance during a 16 to 30 day span. Time series were analyzed individually according to two methods: day by day circadian acrophase drift and power spectrum. Mainly, but not exclusively, subjects with poor tolerance to shift work exhibited an internal desynchronization with a circadian period tau different from 24 hrs. which was the case for OT as well as right and left HGS; each could be different in tau between one another and from 24 hrs. These results suggest that oscillatory systems may be influenced by the neocortex apparently with difference between right and left side.

Adult↗
PubMed1988

Working capacity after myocardial infarction.

The study presents data regarding the functional assessment and prognosis of acute myocardial infarction survivors resident in Prague 4 and an industrial region in north Bohemia. No demonstrable differences between the incidence of myocardial infarction in various professions were found. Acute myocardial infarction occurred in 0.52-0.73% of the total number of workers enrolled in the study. Rehabilitation programmes succeeded in significantly increasing working tolerance, overall performance, and in decreasing the heart rate/blood pressure index within the first six months after acute myocardial infarction. In patients resuming their original jobs, all these parameters were substantially more favourable than in those not seeking re-employment. Prognosis was assessed in 1072 patients. The 10-year mortality was 52.1%. Of the survivors, 30% of patients returned to work, and 24% and 46% remained in partial and full-time retirement, respectively.

Adult↗
PubMed1997

Effects of normobaric hypoxic confinement on visual and motor performance.

INTRODUCTION: The use of reduced oxygen levels has been suggested for fire prevention in closed spaces, such as submarines. However, if humans are to work and live in environments with reduced oxygen levels, the effect of hypoxia on human performance must be further assessed. METHODS: In 3, 11- to 14-d confinements a total of 22 subjects were exposed to different levels of normobaric hypoxia (13, 14, and 15 kPa O2), for up to 10 d, with intervening periods of normoxia. In each experiment eight subjects were divided into two teams, working in 6-h shifts around the clock. Subjects performed tests of spatial orientation, visual reaction time, parallel processing and motor skills. Performance tests and questionnaires were administered once or twice in every 24-h period. RESULTS: All of the subjects appeared to tolerate the acute reduction in oxygen partial pressure well. In many of the tests performance improved with time as a result of learning, despite reductions in the oxygen level. No reduction in performance or decrease in rate of learning was observed at any of the oxygen levels tested. CONCLUSIONS: Oxygen levels down to 14 kPa appear not to impair visual and motor performance during rest.

Adult↗
PubMed1988

The influence of the type of occupation on return to work after myocardial infarction, coronary angioplasty and coronary bypass surgery.

Between January 1980 and December 1983 the medical and social status of 423 patients who were considered candidates for aortocoronary bypass surgery (ACBS) was assessed by a questionnaire, at a mean of 16 months after coronary angiography. Of these patients 54 had refused surgery, 15 were re-operated, 23 had angioplasty and seven had died on the waiting list. After exclusion of these 117 patients, 306 remained, who form the basis of this report. Fifty three patients (17%) had retired before surgery, four (1.3%) had died perioperatively and 19 were on sick-leave for less than three months. Of those who were still employed pre-operatively, 102 (44.3%) went back to work, 85 (37%) had retired and 42 (18%) were on sick-leave for longer than three months. Significant differences were noted between the 102 working and the 85 retired patients as far as medical and social factors are concerned. Of the medical factors, post-operative freedom of symptoms (P less than 0.0001), postoperative exercise tolerance (P less than 0.0001) and completeness of revascularization (P less than 0.05) seemed to have influence on return to work. Of the social factors, age (P less than 0.0001), type of occupation (P less than 0.0002), duration of preoperative absence from work (P less than 0.001) and heavy manual work (P less than 0.05) showed significant differences between the groups. Since duration of preoperative absence from work is the only preoperative factor that can be modified, strategies for improving the return-to-work rate should aim at the shortening of waiting times for coronary angiography and ACBS.

Angioplasty, Balloon↗
PubMed1984

[Effect of work of different types and intensity on changes in work capacity].

Changes in the current effort capacity following 4-hrs' performance of six types of work of different intensity and different muscular system engagement, have been evaluated. The studies involved two groups of women. Group I, consisting of 25 women, performed the dynamic, work on cycle-and manual-ergometers (Rr) and two types of static effort resulting from the shift of the load constituting 20% body weight (N) and maintenance of forced posture during manual weaving (T). Group II, consisting of 9 women, performed the dynamic work on cycle ergometer (R) and dynamic-static work, with an additional load, i.e. holding--in one's hand--2,5 kg (R2,5) and 5.0 kg (R5,0). The effort capacity was determined before and after work, basing on an ergometer test. Whatever the type of the previously performed work, the tolerance of fatigue was found to decrease, which was expressed by lower values of oxygen consumption and heart rate at which the women stopped the test effort. The intensity of the previously performed work (% VO2 max) might be estimated from the difference in the average test effort power, respiratory quotient value and amount of oxygen consumed per one power unit. The static load was evidenced by changes in the blood systolic pressure and increased heart rate during the effort test.

Adult↗
PubMed1992

Alteration of circadian rhythm in shift-working ambulance personnel. Monitoring of salivary cortisol rhythm.

In order to investigate the relationship between internal desynchronization and clinical intolerance to shift work, a set of circadian rhythms including salivary cortisol rhythm were monitored in seven shift-working ambulance personnel. Oral temperature, grip strength of both hands, subjective assessment of drowsiness, fatigue and attention were recorded approximately every four hours except during sleep, for seven days. Self-sampling of salivary cortisol, which was suitable evaluation of endocrine rhythm in field studies, was also tried in this study. cosinor (cosine curve fitting) method and power spectral analysis were used for time series data analysis. The internal desynchronizations between rhythms of physiological variables and sleep-wake cycle were observed in shift-working ambulance personnel. The incidence of internal desynchronization seemed to be higher in intolerant subjects, although the difference between tolerant and intolerant subjects did not reach a statistically significant level. The peak time of salivary cortisol rhythm during a twenty-four hour shift was phase-advanced as intolerant to shift work showed apparently an atypical circadian pattern of salivary cortisol with an abnormal peak at 21.00 h. In this subject, the clinical intolerance to shift work seemed to be associated with internal desynchronization of circadian rhythms. The present study confirmed the internal desynchronization of the circadian rhythm in physiological rhythms like oral temperature and grip strengths, and was in favour of the hypothesis of an internal desynchronization and clinical intolerance to shift work. The clinical implication of impairment of salivary cortisol rhythm remains to be further investigated.

Adult↗
PubMed1988

Predictive markers of occupational activity in 415 post myocardial infarction patients after one-year follow-up.

Predictors of work resumption in 415 patients (372 male and 43 female) one year after myocardial infarction were studied. Clinical data obtained during the hospital phase and during treatment in a specialized rehabilitation centre, and a questionnaire one year after MI were analysed. Significant negative factors for re-employment were complications during the acute phase of illness and post-infarction angina. An increased rate of re-employment was found in patients with a higher work tolerance in an exercise test at discharge from the rehabilitation centre and in patients who climbed to the second floor without symptoms one year after MI (P less than 0.001). Furthermore, patients who perceived their health more positively, and those of higher educational level were more likely to return to work. The motivation to resume work in patients of a higher educational level seems to be more prominent than in patients of a lower educational level. If treatment in a specialized rehabilitation centre started sooner, the rate of re-employment was better (P less than 0.001).

Data Interpretation, Statistical↗
PubMed2001

Effects of supervisor support and coping on shiftwork tolerance.

This study examines the effects of supervisor support and coping on work/non-work conflict and health in shiftwork. It describes a model of shiftwork tolerance that is tested on samples from two populations of shiftworkers. The samples--of nurses and ambulance workers--differed by occupation, gender and shift schedule. Quantitative (survey questionnaire) and qualitative methods (in-depth interviews) were used to triangulate results and to yield richer data on psychosocial variables. Structural equation modelling, using EQS, was used to describe the common path relationships observed within both samples of shiftworkers. The results demonstrated important relationships between social support from supervisors, coping strategies, work/non-work conflict and symptoms that transferred robustly between the two populations of shiftworkers.

Adaptation, Psychological↗
PubMed2001

Is there an association between shift work and having a metabolic syndrome? Results from a population based study of 27,485 people.

OBJECTIVES: To explore how metabolic risk factors for cardiovascular disease (CVD) differ between shift workers and day workers in a defined population. Shift work has been associated with an increased risk of CVD. Risk factors and causal pathways for this association are only partly known. METHODS: A working population of 27,485 people from the Västerbotten intervention program (VIP) has been analysed. Cross sectional data, including blood sampling and questionnaires were collected in a health survey. RESULTS: Obesity was more prevalent among shift workers in all age strata of women, but only in two out of four age groups in men. Increased triglycerides (>1.7 mmol/l) were more common among two age groups of shift working women but not among men. Low concentrations of high density lipoprotein (HDL) cholesterol (men<0.9 and women<1.0 mmol/l) were present in the youngest age group of shift workers in both men and women. Impaired glucose tolerance was more often found among 60 year old women shift workers. Obesity and high triglycerides persisted as risk factors in shift working men and women after adjusting for age and socioeconomic factors, with an OR of 1.4 for obesity and 1.1 for high triglyceride concentrations. The relative risks for women working shifts versus days with one, two, and three metabolic variables were 1.06, 1.20, and 1.71, respectively. The corresponding relative risks for men were 0.99, 1.30, and 1.63, respectively. CONCLUSIONS: In this study, obesity, high triglycerides, and low concentrations of HDL cholesterol seem to cluster together more often in shift workers than in day workers, which might indicate an association between shift work and the metabolic syndrome.

Adult↗
PubMed1990

Pediatricians' attitudes concerning motherhood during residency.

Because half of pediatric residents are women, pregnancy is increasingly common among pediatric house staff. We hypothesized that the heavy work load of pregnant pediatric residents is tolerated because those who have experienced a residency themselves underestimate the strain of residency compared with other work. A questionnaire, designed to survey pediatricians' attitudes concerning the effects of employment on the fetus, mother, and newborn infant, was produced in two formats, which were identical except that one concerned residents, while the other concerned women employed full-time in other jobs. Each type of questionnaire was sent to 1000 randomly selected members of the American Academy of Pediatrics. Respondents in both groups shared many attitudes concerning the effects of maternal employment. Certain subgroups (eg, males, those married to spouses not employed, and those women not pregnant in residency) judged employment as more harmful in general. Contrary to the original hypothesis, however, all subgroups consistently judged residency as more deleterious than other work. Training programs need to adopt humane strategies to integrate motherhood with residency.

Attitude of Health Personnel↗
PubMed1993

Can melatonin improve shift workers' tolerance of the night shift? Some preliminary findings.

The pineal hormone melatonin is potentially useful in the treatment of disorders, especially sleep disorders, associated with circadian rhythm disturbance. We have examined its effects on sleep, mood, and behaviour in a double-blind, placebo-controlled study of a small group of police officers working spans of seven successive night shifts. Compared to placebo, and to no treatment, melatonin (5 mg) taken at the desired bedtime improved problems related to sleep and increased alertness during working hours, especially during the early morning. In letter-target performance tests visual search speed and accuracy were either unchanged or slightly improved. Memory scanning speed and perception of mental load were adversely affected. This preliminary study suggests that melatonin has beneficial effects on sleep and alertness, but that its effects on performance need careful evaluation.

Adult↗
PubMed2006

Extending a model of shift-work tolerance.

The present study contributes to theory and practice through the development of a model of shift-work tolerance with the potential to indicate interventions that reduce nurses' intention toward turnover and increase job satisfaction in hospital-based settings. Survey data from 1257 nurses were used to conduct structural equation modeling that examine the direct and indirect effects of supervisor and colleague support, team identity, team climate, and control over working environment on time-based work/life conflict, psychological well-being, physical symptoms, job satisfaction, and turnover intention. The analysis of the proposed model revealed a good fit The chi-square difference test was non-significant (chi2(26) = 338.56), the fit indices were high (CFI = .923, NFI = .918, and NNFI = .868), the distribution of residuals was symmetric and approached zero, the average standardized residual was low (AASR = .04), and the standardized RMR was .072. In terms of the predictor variable, the final model explained 48% of the variance in turnover intention. The data revealed considerable evidence of both direct effects on adjustment and complex indirect links between levels of adjustment and work-related social support, team identity, team climate, and control. Nurses with high supervisor and coworker support experienced more positive team climates, identified more strongly with their team, and increased their perceptions of control over their work environment. This in turn lowered their appraisals of their time-based work/life conflict, which consequently increased their psychological well-being and job satisfaction and reduced their physical health symptoms and turnover intention. The type of shift schedule worked by the nurses influenced levels of turnover intention, control over work environment, time-based work/life conflict, and physical symptoms.

Adult↗
PubMed1997

Interindividual differences in the flexibility of human temporal organization: pertinence to jet lag and shiftwork.

Interindividual variability in the human temporal structure is seldom taken into account, especially in studies devoted to the effects of shiftwork and jet lag. The understated postulate is that humans can be treated as a pure strain species. This paper reviews some facts and concepts with special reference to interindividual changes in the rhythm period tau and the resulting dyschronism. The following points are addressed. (1) Subjects and methods (importance of longitudinal field studies on shift workers). (2) Criteria for tolerance to shiftwork and jet lag. (3) Interindividual differences and shiftwork problems (subject type; the association between good shiftwork tolerance and stable temporal structure; dychronism with tau s differing from 24h and from variable to variable. (4) The genetic background of circadian dyschronism. The Dian-circadian genetic model of biological rhythms. It allows understanding of one's susceptibility to dyschronism, which was actually observed in approximately equal to 30% of subjects studied longitudinally. (5) Practical implications of interindividual differences (dissociate problems of passengers after a transmeridian flight-who have to adjust their temporal structure to local time-from problems of shiftworkers-who need to prevent alteration of their temporal structure; the advantage for the latter of participating in a rapid rotation system rather than a weekly rotation; emphasis that the suitability of a given subject for a given shiftworking condition is likely to be estimated only after a trial span of time including longitudinal study of a set of rhythms.

Aerospace Medicine↗
PubMed1998

Changes in cortisol secretion during shiftwork: implications for tolerance to shiftwork?

The present study was conducted to determine the size of changes and the time point of those changes in biological rhythms during night-shift and whether they are associated with tolerance to shiftwork. The adrenal hormone cortisol has frequently been investigated in the field of shiftwork since it follows a pronounced circadian variation and has been demonstrated to be affected by night-work. However, studies are restricted with respect to sample size, number of measurements or duration of sampling periods. Therefore, a sample of 24 night-shift workers was investigated in a cardiac emergency unit for seven nights. Saliva samples were collected frequently for determination of cortisol. A total of 28 cortisol measurements in each subject were made in order to decide whether the circadian rhythm changed, and if so at which time point. A clear reversal of circadian function could be observed for the total group (mean cortisol concentrations) after the fifth night. However, inspection of individual patterns revealed that six out of 24 subjects did not change in circadian function. These subjects exhibited lower durations of and less consistency in recovery sleep across the following days after night-work. With respect to personality dimensions a pattern associated with neuroticism can be observed in subjects without appropriate changes in cortisol rhythm. However, owing to the small sample size of non-adapters these results are preliminary and should be replicated with larger samples. The overall relationship between neuroticism and low adaptability has been discussed.

Adaptation, Physiological↗
PubMed1994

Objective assessment for exercise treatment on the B-200 isostation as part of work tolerance rehabilitation. A random prospective blind evaluation with comparison control population.

The purpose of this study was to assess repeated exercise on the B-200 Isostation as part of rehabilitation work tolerance for nonsurgical patients with lumbar spine disorders. For a consecutive 7-month period, treatment subjects were randomly assigned according to birth date for participation in two groups: a standard work tolerance program only or standard work tolerance program plus inclusion of exercise on the B-200 Isostation. Each patient had similar referral diagnosis requiring conservative treatment. Treatment groups were compared with a control population of volunteers who had neither back pain nor known underlying spinal pathology. All study patients had objective measurement of range of motion, isometric strength, and velocity of motion, on the B-200 Isostation before treatment and at follow-up 3 weeks after treatment. The data showed no significant difference of percent improvement when comparing patients in either of the randomized assigned treatment groups. There was a higher percentage of improvement for each treatment group as compared with the control individuals, however. Based on our study using the B-200 Isostation, there is little objective justification for including exercise on the B-200 dynametric Isostation as part of the rehabilitation routine for improvement of functional physical capacity.

Analysis of Variance↗
PubMed1994

Effects on health of a change from a delaying to an advancing shift system.

OBJECTIVES: Shift work can lead to a range of problems for some people that seem to result from the disturbance of the circadian system, and can broadly be classified as: disturbances of sleep, impaired physical and psychological health, and disturbed social and domestic life. The main attempt to try to reduce these problems has focused on the design of the shift system, and the identification of the most problematic features of the shift system. One such feature is believed to be the direction of shift rotation. Systems that advance are thought to be more problematic than those that delay. The present study examines the change in the direction of shift rotation from a delaying to an advancing system on health and wellbeing. METHODS: Self reported measures of tolerance to shift work were taken two months before and six months after the change. These included sleep difficulties, gastrointestinal problems, psychological ill health, chronic fatigue, social and domestic disruption, job satisfaction, and satisfaction with the shift system. RESULTS: The change from a delaying to an advancing system resulted in an increase in sleep difficulties between successive afternoon shifts, but a decrease in social disruption. There was little evidence of impaired health on the advancing compared with the delaying system. CONCLUSIONS: The increase in sleep difficulties was thought to result from the undesired adaptation of the circadian system to night work, as a result of the afternoon shifts now following a series of night shifts, whereas previously they followed a series of morning shifts. The decrease in social disruption was thought to result from the specific sequence of the shifts and the discontinuous nature of the shift system, in particular, the long week-end off every third week. Lack of reported health related differences are explained in terms of the relatively unharmful nature of the shift system in question, and the relatively short time span over which the study was conducted.

Adult↗
PubMed1994

Evaluation of a rapidly rotating shift system for tolerance of nurses to nightwork.

Fifteen female nurses, aged between 21 and 29 years and employed in an intensive care unit, were examined with the aim of evaluating their psychophysical adaptation to one of the most commonly used, rapidly rotating shift systems, the "metropolitan rota" (2-2-2-2), with the length of the shifts modified according to the work load (including night shifts of 10h) and with the start of the morning shift delayed (to 7 a.m.). Subjective evaluations of work load and psycho-physical conditions as well as performance measures (reaction time, search and memory test), blood pressure and heart rate were recorded at the start, middle and end of the work shifts on the last 4 days of the shift cycle, comprising one morning, one afternoon and two consecutive nights. During the shifts, plasma cortisol and urinary excretion rate of 6-sulphatoxymelatonin, adrenaline and noradrenaline were also recorded, as well as oral temperature and activity-sleep logs. The results showed that this rapidly rotating shift system including two consecutive night shifts does not significantly alter the normal circadian rhythms of the body, particularly as concerns performance levels, body temperature and hormone excretion. Moreover, the lengthening of the night shift to 10h can be considered acceptable in terms of work efficiency, provided that work load is reduced and there are sufficient rest pauses available to compensate for tiredness and sleepiness. On the other hand, the shortening of the day shifts to 7h and the delayed start of the morning shift to 7 a.m. appeared convenient in relation to both work load and sleep duration.

Adult↗
PubMed2003

[A study comparing circadian rhythm and sleep quality of athletes and sedentary subjects engaged in night work].

The aim of this study was to show the resistance and persistence of the circadian rhythm of temperature (T degree) and the sleep quality of athletic subjects and sedentary subjects engaged in night work, and attempt to explain the mechanisms that influence these differences. The effects of night work on biological rhythms have been studied extensively in the past few years. The contradictory situations for the night workers irrefutably affect their biological systems. Individuals with high amplitudes in their circadian rhythms have been found to be more tolerant to shift work and this results in a greater stability of circadian rhythms. This seems beneficial in coping with frequent rhythm disturbances. The physical training program seems to improve several mechanisms of the human biological system: amplitudes of circadian rhythms were increased and the circadian rhythm period was more resistant to an environment extreme (night work, shift work, sleep deprivation, or jet lag). To test this hypothesis, athletes and sedentary subjects who were engaged in regular night work were selected in the PSA Peugeot Citroën Automobiles Group in French Normandy country. The circadian rhythm of the T degree for both groups was studied with a specific methodology and with extensive spectral analysis, especially the spectral elliptic inverse method. Study models of the rhythm of the T degree were determined and the characteristic parameters were exposed. A complementary actigraphic study showed the physical training program's effects on the sleep quality. The results revealed a large stability in the rhythm of circadian variation of T degree for the athletes: the amplitude was still large but for the sedentary subjects the amplitude of the T degree decreased and it was difficult to adjust a period on the rhythm of T degree. The stability and persistent quality of the athletes' circadian rhythm was confirmed. We observed that the actigraphic sleep was greater for athletes than for sedentary subjects, and the acrophase time for the athletes was later than for the sedentary subjects during the night shift.

Activity Cycles↗