Industrial Health

SPECIAL ISSUE
SLEEP HEALTH AT WORK

Review Articles

Epidemiology

An Epidemiologic Review on Occupational Sleep Research among Japanese Workers

Yuriko DOI

2005 Volume 43 Issue 1 Pages 3-10
Published: 2005
Released on J-STAGE: March 17, 2006

DOIhttps://doi.org/10.2486/indhealth.43.3

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Epidemiologic sleep research on Japanese workers has been increasing in recent years. It is timely to give an overview of the sleep issues facing the Japanese working population by reviewing the accumulated epidemiological evidence, which will contribute to the promotion of a sound occupational health policy and the development of occupational sleep research in epidemiology. This paper reviews 24 studies, 13 for non-shift and 11 for shift Japanese workers, identified by using MEDLINE and Japan Cetra Revuo Medicina. The results reviewed are as follows: 1) the prevalence of insomnia and other sleep problems is substantially varied, 5 to 45% for non-shift and 29 to 38% for shift workers, 2) poor sleep quality is related to health, occupational activities and personal relations, 3) the risk or associated factors are identified in pathophysiology (e.g., hypertension), lifestyle behaviors (e.g., diet, alcohol, tobacco), job-related conditions (e.g., job stress, social support, job dissatisfaction, workload, shift schedules) and psychopathology (e.g., depressed mood). The methodological limitations found in the studies and the strategies of future epidemiologic sleep research in workers are discussed.

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Socioeconomic Impact of Insomnia in Working Populations

Arnaud METLAINE, Damien LEGER, Dominique CHOUDAT

2005 Volume 43 Issue 1 Pages 11-19
Published: 2005
Released on J-STAGE: March 17, 2006

DOIhttps://doi.org/10.2486/indhealth.43.11

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To determine whether insomnia impact the professional life of patients and have an economical weight, this review article focused on the socioeconomic impacts of sleep related problems in working populations. The goal is to summarise the work that has been accomplished in that field. Several occupational factors have an impact on insomnia: the work schedules (shift work and night work), the physical environment at work and the occupational stressors. Insomnia is also a common problem in daytime workers. The daytime functioning of insomniacs is a key point to understand the impact of insomnia on workers. Absenteeism is one major target in the evaluation of severe insomnia at the workplace. Most of the studies find a higher rate of work accidents in insomniacs. The economic impact is severe in term of direct and indirect costs. Insomnia is a common problem at the workplace. The negative impact is not only on individual but also at the societal levels. More epidemiological studies appear warranted to demonstrate a reciprocal link between work conditions and sleep disorders.

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Shiftwork: Safety, Sleepiness and Sleep

Simon FOLKARD, David A. LOMBARDI, Philip T. TUCKER

2005 Volume 43 Issue 1 Pages 20-23
Published: 2005
Released on J-STAGE: March 17, 2006

DOIhttps://doi.org/10.2486/indhealth.43.20

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This brief paper reviews the available published literature on shiftwork and safety that allows the relative risk of “accidents” or injuries associated with specific features of shift systems to be estimated. Three main trends in risk are discussed, namely that (i) risk is higher on the night shift, and to a lesser extent the afternoon shift, than on the morning shift, (ii) risk increases over a span of shifts, especially so if they are night shifts, and (iii) risk increases with increasing shift length over eight hours. We discuss that some of these trends are not entirely consistent with predictions derived from considerations of the circadian variations in sleep propensity or rated sleepiness, and consider factors relating to sleep that may underlie the observed trends in risk. Finally, the practical implications of the trends in risk for the design of safer shift systems are discussed.

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The Nighttime Nap Strategies for Improving Night Shift Work in Workplace

Hidemaro TAKEYAMA, Tomohide KUBO, Toru ITANI

2005 Volume 43 Issue 1 Pages 24-29
Published: 2005
Released on J-STAGE: March 17, 2006

DOIhttps://doi.org/10.2486/indhealth.43.24

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Nighttime napping is an effective measure to prevent adverse effects due to night shift work. A characteristic of nighttime nap is that it can result in considerably deeper sleep. Several studies have shown that taking nighttime naps suppressed increasing sleepiness, decreasing alertness during the period following awaking from a nap, and prevented disturbance of circadian rhythm (“anchor sleep”). The length of daytime sleep after night shift, when combined with a nighttime nap, is shorter than that without nap. This finding might be interpreted as a beneficial effect rather than a negative feature because workers can then spend time engaged in other activities rather than sleeping. Nevertheless, the introduction of nighttime sleep break in the workplace has not been widely accepted. To promote nighttime napping strategy in the workplace, consensus building while acting on conflicting interest is essential. Recently, participatory method for improvement of working condition has expanded worldwide. A characteristic of the activity is using action checklist and group work, and heightening motivation to improvement working condition between worker and manager. Through the activities, nighttime napping strategy would be spread more in the workplaces and play a role as one of the effective tools for improving working conditions, work performance and safety in the future.

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Sleepiness of Occupational Drivers

Pierre PHILIP

2005 Volume 43 Issue 1 Pages 30-33
Published: 2005
Released on J-STAGE: March 17, 2006

DOIhttps://doi.org/10.2486/indhealth.43.30

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Drowsiness and sleeping at the wheel are now identified as the reasons behind fatal crashes and highway accidents caused by occupational drivers. For many years, fatigue has been associated to risk of accidents but the causes of this symptom were unclear. Extensive or nocturnal driving was associated to accidents but few reports differentiated fatigue from sleepiness. In the early nineties, epidemiological data started investigating sleepiness and sleep deprivation as cause of accidents. Sleepiness at the wheel, sleep restriction and nocturnal driving have been incriminated in 20% of traffic accidents. Drugs affecting the central nervous system (i.e., narcotic analgesics, anti histamine drugs), nocturnal breathing disorders and narcolepsy have been also associated with an increasing risk of accidents. Treatments improving daytime vigilance (i.e., nasal Continuous Positive Airway Pressure) reduce significantly the risk of traffic accidents for a reasonable economical cost. Sleep disorders among occupational drivers need to be systematically investigated. Chronic daytime sleepiness is still under diagnosed and sleep disorders (i.e. obstructive sleep apnea syndrome) are not enough explored and treated in this exposed population of sedentary males. Drivers education and work schedules integrating notions of sleep hygiene as well as promotion of sleep medicine could significantly improve road safety.

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Human Experiments

Light Treatment and Circadian Adaptation to Shift Work

Diane B. BOIVIN, Francine O. JAMES

2005 Volume 43 Issue 1 Pages 34-48
Published: 2005
Released on J-STAGE: March 17, 2006

DOIhttps://doi.org/10.2486/indhealth.43.34

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Work at unconventional hours can have both long and short term consequences. Shift workers are often required to perform their duties at times that are not favoured by the body's endogenous clock, or circadian pacemaker. A typical night shift worker, for example, may report reductions in alertness and performance during shifts, or significant difficulty attaining sleep of recuperative value in the day, all the while being more likely to develop health complications. The study of circadian physiology has significantly contributed to our current ability to aid the shift worker deal with atypical schedules. We discuss the usefulness of light treatment as a countermeasure for maladaptation to atypical work schedules.

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Health Management

Imbalance between the Reality of Sleep Specialists and the Demands of Society in Japan

Naoko TACHIBANA

2005 Volume 43 Issue 1 Pages 49-52
Published: 2005
Released on J-STAGE: March 17, 2006

DOIhttps://doi.org/10.2486/indhealth.43.49

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In contrast to the fruitful achievements of sleep research, sleep medicine has never been properly defined and recognized in Japan. Therefore, it is difficult for any clinician to have a united view as to what constitutes a sleep specialist. The United States (US) has set up sleep medicine as a comprehensive clinical specialty connected with various medical, psychological, scientific and social fields, having sleep physiology that is methodologically represented by polysomnography as a common language. The US system around a core of sleep disorders centers and sleep specialists armed with a comprehensive knowledge of sleep and sleep disorders can not only diagnose and treat patients with sleep disorders, but are also sensitive to the various sleep-related problems at the work place such as circadian related safety issues and productivity. Daytime sleepiness is dangerous in some situations for the individual as well as society. Although this safety issue is an urgent demand in every workplace, sleep medicine has not matured nor established enough to respond to it in Japan. Together with advancement of sleep research, the sleep medicine community should do everything in its power to establish sleep medicine as a practical patient-based clinical field.

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Screening for Sleep-Disordered Breathing at Workplaces

Takeshi TANIGAWA, Seichi HORIE, Susumu SAKURAI, Hiroyasu ISO

2005 Volume 43 Issue 1 Pages 53-57
Published: 2005
Released on J-STAGE: March 17, 2006

DOIhttps://doi.org/10.2486/indhealth.43.53

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Sleep-disordered breathing (SDB) is a condition of repetitive episodes of decreased or arrested respiratory airflow during sleep. Many workers over the world remain undiagnosed and untreated for SDB, and leaving themselves at the high risk for accidents and cardiovascular disease. Since, the Japanese Ministry of Land, Infrastructure and Transport distributed the sleep apnea syndrome manual together with sending an official notice to relevant bodies in all over Japan in March, 2003, employees and employers are expected to co-operate to prevent SDB-related accidents at work. We have conducted several surveys using the pulse-oximetry to detect SDB in working populations and found the high prevalence of SDB among workers in Japan, as many as in the US and EU countries. The proper use of the result from the screening for SDB seems to be beneficial both to workers and employers by maintaining occupational safety and by preventing future development of cardiovascular disease.

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An Occupational Health Physician's Report on the Improvement in the Sleeping Conditions of Night Shift Workers

Toshio HIROSE

2005 Volume 43 Issue 1 Pages 58-62
Published: 2005
Released on J-STAGE: March 17, 2006

DOIhttps://doi.org/10.2486/indhealth.43.58

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This paper reviews briefly our research findings on sleep and health for shift workers at a bakery and a dish factory and aims to give some information on health protection with improved sleep. Our medical examinations revealed that rises in blood pressure (BP) were frequently observed in male bakery workers on the fixed night shift. They took a two-hour nap from 1:00 to 3:00 during the night shifts according to our advice. As a result, their diastolic BP significantly decreased in subsequent years. Women working shifts before 3:00 at a dish factory seemed to show more sleep disturbance, higher daytime sleepiness, and more fatigue than those working shits from 3:00. Total sleep hours taken during the daytime was similar between two groups. Among the dish factory workers who switched to midnight or night shifts, 70% reported slow recovery from fatigue and 30% felt deteriorated health. These women also reported increased efforts to obtain a deep sleep, probably making up for shortened sleep. Occupational physicians can act to improve shift work conditions through monitoring the health of workers, applying naps, and designing possible schedules to secure deep, sufficient sleep.

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Law

Fatigue and the Criminal Law

Christopher B. JONES, Jillian DORRIAN, Shanthakumar M.W. RAJARATNAM

2005 Volume 43 Issue 1 Pages 63-70
Published: 2005
Released on J-STAGE: March 17, 2006

DOIhttps://doi.org/10.2486/indhealth.43.63

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Fatigue is an increasingly recognised risk factor for transportation accidents. In light of this, there is the question of whether driving whilst fatigued should be a criminal offence. This paper discusses the current legal position, including the problems of voluntary conduct and self awareness. Three models for reform are proposed. The manner in which scientific research can inform legal consideration and future directions for research are discussed.

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Research Needs

International Research Needs for Improving Sleep and Health of Workers

Kazutaka KOGI

2005 Volume 43 Issue 1 Pages 71-79
Published: 2005
Released on J-STAGE: March 17, 2006

DOIhttps://doi.org/10.2486/indhealth.43.71

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Research needs in identifying preventive measures dealing with working time arrangements and associated sleep problems are reviewed. These needs are based on the recognition of a range of risk factors for health involving disturbed circadian rhythms leading to various levels of sleep deficits. The review takes account of recent joint change approaches that address both working time arrangements and various relevant intervening factors. As examples of such approaches, voluntary industry-based guidelines for improving shift work are examined. Also reviewed is evidence indicating the effects of improved working time arrangements and sleep hygiene on the tolerance of workers working irregular shifts. Trends in action-oriented risk assessment are further discussed as the effects on health and sleep of these workers may be modified by complex aspects related to working situations, family and social conditions, personal characteristics and social support. Generally relevant are not only the relationships between sleep-affecting factors and health, but also advances in taking the various support measures. The effective use of participatory steps is found important in dealing with working time arrangements and associated health and sleep problems together. It is thus considered important to study (a) the efficacy of joint change approaches addressing complex sleep and health factors, (b) effective procedures for action-oriented health risk assessment in various work life situations, and (c) the relevance of innovative participatory steps to improving health and tolerance of workers. Future research topics mentioned by the participants of the international symposium on night and shift work held in Santos in 2003 are presented, and international efforts to promote research into these aspects in field conditions are discussed. Interactive research involving local people appears crucial.

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The Future of Work Hours—the European View

Torbjörn ÅKERSTEDT, Göran KECKLUND

2005 Volume 43 Issue 1 Pages 80-84
Published: 2005
Released on J-STAGE: March 17, 2006

DOIhttps://doi.org/10.2486/indhealth.43.80

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In Europe the way work hours are handled varies between different countries. However, there are some issues that dominate the discussion in Europe and seem representative for what is happening. One such is the reduction of working hours—which was attempted in several countries but which now seems to be backfiring—probably related to the competition from countries outside Europe. Another area is compressed work hours—the drive towards maximizing the hours per work day in order to increase the number of days off. The health effects are debated—some find clear positive effects. A third area is company oriented flexible work hours, permitting the employer to make moderate changes in work hours when needed. The health impacts have not been evaluated but the loss of individual influence at work is obvious. In some parts of Europe self-determined work hours have been tried with very positive effects. The EU work hour directive is intended to provide uniformity but permits a counterproductive “opting out”, creating problems of imbalance.

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Toward Better Sleep for Workers: Impressions of Some Needs

Roger R. ROSA

2005 Volume 43 Issue 1 Pages 85-87
Published: 2005
Released on J-STAGE: March 17, 2006

DOIhttps://doi.org/10.2486/indhealth.43.85

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We know there are persons exposed demanding work schedules and sleep loss in almost every occupation or industry, but we still need better population-based information on how many sleepy or inattentive workers there are, where they are, and to what extent they are a risk to themselves or others. The absence of such information, however, does not prevent us from continuing to conduct worksite interventions and demonstrations that will produce good, evidence-based guidelines to help workers and workplace administrators make informed choices about sleep and provide optimal conditions for sleep. In addition, systematic study and publication of how managers and policy-makers accept our research to make worksite changes, and what factors beside our research influence their decisions, would contribute techniques to the greater public health community aiming to translate research results into good practice.

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Original Articles

Epidemiology

Sleep-related Risk of Occupational Injuries in Japanese Small and Medium-scale Enterprises

Akinori NAKATA, Tomoko IKEDA, Masaya TAKAHASHI, Takashi HARATANI, Yose ...

2005 Volume 43 Issue 1 Pages 89-97
Published: 2005
Released on J-STAGE: March 17, 2006

DOIhttps://doi.org/10.2486/indhealth.43.89

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A cross-sectional study evaluated the contribution of daily sleep habits to occupational injuries. A self-administered questionnaire solicited answers about sleep, symptoms of depression, occupational injury, demographics, presence of diseases and lifestyle factors from 2,903 workers between the ages of 16-83 (mean 45) yr in small and medium-scale enterprises. Eight sleep habits were queried and dichotomized: 1) less or more than 6 hr of daily sleep, 2) taking more or less than 30 min to fall asleep (Difficulty initiating sleep; DIS), 3) awakening during sleep more or less than 3 times/wk (Difficulty maintaining sleep; DMS), 4) early morning awakening more or less than 3 times/wk (EMA), 5) definitely/somewhat difficulty waking up or not, 6) sleeping very poorly/not so well at night or not, 7) definitely/somewhat insufficient nightly sleep or not, and 8) difficulty in breathing during sleep more than once/week or less. Occupational injury was assessed by asking subjects ‘Have you ever been injured during your work, including minor scratches and cuts (Yes/No)?’ Both sleep and injury were assessed over the previous one year period. One-third of workers answered that they had experienced injury. Workers with sleep features of DIS, sleeping poorly at night, insufficient sleep, and insomnia had a significantly higher prevalence for injury after adjusting for multiple confounders. The findings suggest that poor nocturnal sleep habits are associated with self-reported occupational injury.

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How Well Do Train Driver's Sleep in Relay Vans?

Nicole LAMOND, David DARWENT, Drew DAWSON

2005 Volume 43 Issue 1 Pages 98-104
Published: 2005
Released on J-STAGE: March 17, 2006

DOIhttps://doi.org/10.2486/indhealth.43.98

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Relay working operations typically require two crews of train drivers to work a rotating 8-h schedule for two or more days. While one crew is driving, the other has the opportunity to sleep onboard the train. The current study investigated the impact of relay work on drivers sleep quantity and quality. Fourteen drivers wore wrist activity monitors and completed sleep/wake diaries for 3 d prior to and during short (<48 h) relay trips. Drivers obtained an average of 7.8 h sleep per night while at home, and an average of 4 h sleep per opportunity during the relay trip. Sleep obtained in the relay van was associated with longer sleep onset latencies, lower efficiency and poorer subjective quality than sleep at home. During the relay trip, drivers obtained significantly more sleep during opportunities that occurred in the evening, than those that occurred early morning or during the day. These findings suggest that while drivers are able to obtain sleep during short relay operations, it is of poorer quality than sleep obtained at home. Further, the timing of the sleep opportunities during the relay trip impacts on the quantity and quality of sleep obtained.

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The Impact of Extended Leave on Sleep and Alertness in the Australian Rail Industry

Katie J. KANDELAARS, Nicole LAMOND, Gregory D. ROACH, Drew DAWSON

2005 Volume 43 Issue 1 Pages 105-113
Published: 2005
Released on J-STAGE: March 17, 2006

DOIhttps://doi.org/10.2486/indhealth.43.105

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In the past, scientific studies have investigated the effects of shift timing and duration on sleep and alertness in the rail industry. To our knowledge no research has been conducted to determine the effects of extended break lengths (>48 h) on these factors. Hence, this study analyses the work and rest schedules of 304 Australian rail employees (mean age 41.3 yr, standard deviation 7.4 yr) to determine the effect of prior break lengths (12-169 h) on sleep and subjective alertness at work after periods of leave. Extended break periods (>48 h) were found to increase the length of the sleep prior to returning to work and reduce the total wake time to the end of the first shift, but did not influence levels of subjective alertness immediately prior to the commencement of the first shift. Research into the influence of longer break periods (>169 h) is needed in order to make definitive conclusions regarding sensible return to work policies after extended leave within the Australian rail industry.

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Sleepiness in Various Shift Combinations of Irregular Shift Systems

Mikael SALLINEN, Mikko HÄRMÄ, Pertti MUTANEN, Riikka RANTA, ...

2005 Volume 43 Issue 1 Pages 114-122
Published: 2005
Released on J-STAGE: March 17, 2006

DOIhttps://doi.org/10.2486/indhealth.43.114

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The present study examined the occurrence of sleepiness in various shift combinations ending with a night or morning shift. Three weeks' sleep/work shift diary data, collected from 126 randomly selected train drivers and 104 traffic controllers, were used in statistical analyses. The occurrence of sleepiness at work (i.e., Karolinska Sleepiness Scale 7 or higher) was tested with a generalised linear model with repeated measurements including explanatory factors related to shifts, sleep, and individual characteristics. The prevalence of severe sleepiness varied between 25% and 62% in the combinations ending with a night shift and between 12% and 27% in the combinations ending with a morning shift. The occurrence of sleepiness did not, however, systematically vary between the shift combinations in either case. An increased risk for sleepiness was associated with high sleep need and long shift duration in the night shift and with high sleep need, short main sleep period, long shift duration and an early shift starting time in the morning shift. Also having a child was associated with an increased risk for sleepiness in the night shift. The results suggest that the shift history of 24-36 h prior to the night and the morning shift is not strongly associated with the occurrence of sleepiness at work, but there are other factors, such as shift length and starting time and sleep need, that affect a risk for sleepiness at work.

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Self-Report Naps in Irregular Work Schedules

June J. PILCHER, Stephen M. POPKIN, Karen ADKINS, Lindsay ROETHER

2005 Volume 43 Issue 1 Pages 123-128
Published: 2005
Released on J-STAGE: March 17, 2006

DOIhttps://doi.org/10.2486/indhealth.43.123

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Few studies have examined napping in irregular work schedules such as those experienced by freight locomotive engineers. The current study examined the effect of napping in irregular work schedules on sleep length and three subjective measures: ability to go to sleep, ability to stay asleep, and a feeling of being well-rested upon awakening. One hundred and seventy-nine freight engineers completed a 14-d activity log, providing information on sleep times and subjective evaluations of sleep. The results indicated that days with naps resulted in significantly more total sleep but less sleep in the main sleep period of the day. The days with naps also resulted in somewhat more difficulty with going to sleep, staying asleep and with feeling well-rested upon awakening. It is important to note, however, that when examining the days with naps, nap length was not significantly correlated with main sleep time, ability to go to sleep, ability to stay asleep, or feeling well-rested upon awakening. These results suggest that napping may be useful when working irregular work schedules if the engineer is willing to accept a slight decrease in ability to go to sleep, stay asleep, and feeling rested.

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Sleep Deprivation in Junior Doctors—House Officers in Singapore

K. PUVANENDRAN, Jayant VENKATRAMANI, Amit JAIN, Mohamad FARID

2005 Volume 43 Issue 1 Pages 129-132
Published: 2005
Released on J-STAGE: March 17, 2006

DOIhttps://doi.org/10.2486/indhealth.43.129

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House officers are known to endure marked levels of sleep deprivation in administration of their duties. We aim to establish sleep patterns of local house officers while on the job and the impact it might have on their mood and sleepiness state. We also studied their sleep during their final year of medical school and pre-university for identification of any prior sleep deprivation. Questionnaires were used to assess sleep and mood change. Sleepiness levels on the day after call were assessed using the Stamford Sleepiness Scale. Subjects were found to sleep a median of only 1.0 (±2.0) h per night on call and 6.0 h (±1.0) per non-call night. They suffered median of 5 interruptions (±5) during sleep on one night call. Night call was found to adversely affect mood in 89.5% of the subjects while daytime sleepiness levels following call were found to increase the more the time spent at work after call. Subjects were found to have had 6.5 h (±1.0) of sleep per night during final year of medical school and 8.0 h (±1.0) in final year of pre-university. House officers enter the profession chronically sleep-deprived. The call schedule and general work regime further add to the existent sleep deprivation and may have adverse consequences on patient care and doctor's health. This calls for measures to be instituted for provision of proper sleep and work hours for them.

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Associations of Sleep Problems and Recent Life Events with Smoking Behaviors among Female Staff Nurses in Japanese Hospitals

Takayuki KAGEYAMA, Toshio KOBAYASHI, Noriko NISHIKIDO, Junko OGA, Miek ...

2005 Volume 43 Issue 1 Pages 133-141
Published: 2005
Released on J-STAGE: March 17, 2006

DOIhttps://doi.org/10.2486/indhealth.43.133

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For the purpose of examining the relation of sleep problems and other possible correlates with smoking among staff nurses in hospitals, the cross-sectional data of a self-administered questionnaire survey for 522 Japanese female staff nurses were reanalyzed. Registered nurses or licensed practical nurses were 82%, while nursing assistants were 18%. The prevalence of current smoking (PCS) was 29%, being higher than that in the general population of Japanese women. The current smokers exhibited a high tendency toward tobacco dependence. Multivariate analyses revealed that PCS was associated with recent frequent night shifts and a large amount of support from coworkers, while the association of a large amount of job control and a feeling of light overnight sleep with PCS was also suggested. The tobacco-dependent tendency was associated with recent life events and the presence of insomnia. It is possible that smoking is a countermeasure against sleepiness caused by the disadaptation to shift-work, or that tobacco-intake pharmacologically disturbs sleep. For decreasing PCS in staff nurses, further research should focus on the relation of smoking with their sleepiness and shift-working system, and also on the process in which major life events develop smoking behaviors.

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Actual Conditions of Work, Fatigue and Sleep in Non-Employed, Home-Based Female Information Technology Workers with Preschool Children

Tsukasa SASAKI, Shun MATSUMOTO

2005 Volume 43 Issue 1 Pages 142-150
Published: 2005
Released on J-STAGE: March 17, 2006

DOIhttps://doi.org/10.2486/indhealth.43.142

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We conducted a study on time budget and fatigue feelings over a two-month period of 12 non-employed, home-based female workers using computers (mean age 35.2 yr). All of them had at least one preschool child. The actual amount of work done by these women and the related effects on the fatigue feelings and sleep were investigated. The results showed that the work done was characterized by involving many night hours, irrespective of the day of the week. The degree of subjective fatigue was not dependent on the number of hours worked, but affected by the time at which the work of the day was completed. This tendency was notable after one o'clock in the morning when the work was completed. Those who followed such a work pattern took daytime naps, although a quality of the subsequent nighttime sleep taken might be poor. They took a nap around 14:00 but not around 19:00. The sleep strategies were thus shown to be affected by home-based work. A need is suggested to support these workers in adjusting work time distribution and taking sleep patterns adapted to individual conditions.

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Shiftwork Locus of Control, Situational and Behavioural Effects on Sleepiness and Fatigue in Shiftworkers

Lawrence SMITH, Takeshi TANIGAWA, Masaya TAKAHASHI, Keiko MUTOU, Naoko ...

2005 Volume 43 Issue 1 Pages 151-170
Published: 2005
Released on J-STAGE: March 17, 2006

DOIhttps://doi.org/10.2486/indhealth.43.151

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A number of situational and behavioural individual differences moderate the impact of shift and night work. The aims of this study were to identify individual differences correlates of sleep and fatigue-related shiftwork outcomes and examine their potential relative causal impact. Power company shiftworkers completed a questionnaire that measured age/experience, number of dependents, shiftwork locus of control, morningness-eveningness, workload and sleep/health-related behaviours. Shiftwork sleep and fatigue outcome variables were also measured. Hierarchical multiple regression was used to examine predictive contributions of the individual difference variables and to generate path coefficients from situational and psychological predictors through behavioural variables to the outcome variables. Shiftwork-specific internality showed the most systematic significant causal relationships with sleep and fatigue outcomes. While not having as strong a direct causal influence on sleep and fatigue outcomes as internality, the other predictors did show more significant causal effects upon sleep-related behaviours than did internality. Behavioural variables made little contribution to the total causal effects of the predictors on the outcome variables. The results suggest control beliefs to be a moderating factor in shiftwork exposure and the potential utility of this construct in aiding more effective targeting of interventions.

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Modifying Effects of Perceived Adaptation to Shift Work on Health, Wellbeing, and Alertness on the Job among Nuclear Power Plant Operators

Masaya TAKAHASHI, Takeshi TANIGAWA, Naoko TACHIBANA, Keiko MUTOU, Yosh ...

2005 Volume 43 Issue 1 Pages 171-178
Published: 2005
Released on J-STAGE: March 17, 2006

DOIhttps://doi.org/10.2486/indhealth.43.171

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This study examined the relationship between perceived adaptation to shift work and shift-related problems. A total of 608 male operators at nuclear power plants completed a set of validated questionnaires including a modified version of the Standard Shiftwork Index, which covered adaptation to shift work, fit to job content, chronotypes, chronic fatigue, sleep, naps, shift work locus of control (SHLOC), psychological health, social/family life, daytime sleepiness, workload, alertness on the job, and lifestyle factors. Participants were divided into two groups according to their perceived level of adaptation to shift work. The good adaptation group showed better outcomes than the poor adaptation group in terms of fit to job content, chronic fatigue, daytime sleep before night shifts, social and family disruption, SHLOC, psychological health, and alertness during night shifts (ps<0.001). Operators who reported good adaptation also took a more frequent, longer nap and more cigarettes during night shifts (ps<0.05). The cross-sectional study design cannot determine a causal relationship between perceived adaptation and shift work problems, yet the present results suggest that the effects of working shifts may be modified by perceptions of shift work adaptation.

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Human Experiments

Self-Awakening Prevents Acute Rise in Blood Pressure and Heart Rate at the Time of Awakening in Elderly People

Kosuke KAIDA, Keiko OGAWA, Mitsuo HAYASHI, Tadao HORI

2005 Volume 43 Issue 1 Pages 179-185
Published: 2005
Released on J-STAGE: March 17, 2006

DOIhttps://doi.org/10.2486/indhealth.43.179

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Self-awakening, waking up at a designated time decided before sleeping, could prevent failure in the blood circulation vessel system such as heart attack, acute increases in heart rate or blood pressure upon waking. Previous research showed that anticipatory changes occurred in heart rate prior to awakening from a short nap by means of self-awakening for young participants. However, the effects of self-awakening remained unclear for elderly people. The present study examined the effects of self-awakening on heart rate and blood pressure in a short afternoon nap (20 min) among the elderly. Nine participants [74.1 (SD = 5.01) years old] underwent both self-awakening and forced-awakening conditions. In the self-awakening condition, it was revealed that blood pressure gradually increased before the scheduled time of awakening, and that heart rate did not show a rapid increase at arousal. In contrast, forced-awakening induced acute increases in both heart rate and blood pressure. These results suggest that self-awakening facilitates a more smooth transition from sleep to wakefulness via autonomic activation before the time of self-awakening.

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The Impact of Sustained Wakefulness and Time-of-day on OSPAT Performance

Renée M. PETRILLI, Sarah M. JAY, Drew DAWSON, Nicole LAMOND

2005 Volume 43 Issue 1 Pages 186-192
Published: 2005
Released on J-STAGE: March 17, 2006

DOIhttps://doi.org/10.2486/indhealth.43.186

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Fatigue associated with shiftwork is a key contributor to human error in the workplace. One way to prevent fatigue-related errors from occurring is to identify fatigue in employees using fitness-for-duty measures. The Occupational Safety Performance Assessment Test (OSPAT), an unpredictable tracking task that measures hand-eye coordination, is currently being used as a fitness-for-duty measure in a variety of industries, but has not yet been validated as a test sensitive to the effects of fatigue. Consequently, the aim of this study was to systematically examine the impact of sustained wakefulness and time-of-day on OSPAT performance. Twenty individuals (10 male, 10 female), aged between 18-25 yr (M = 20.90, SD = 2.29) participated in the study, which was conducted in Australia. The study had a repeated measures design, whereby participants completed the OSPAT and measures of sustained attention (i.e., the psychomotor vigilance task: PVT), and subjective alertness (i.e., the Visual Analog Scale: VAS) every 2 h during 24 h of sustained wakefulness, beginning at 07:00h. Results revealed that VAS ratings of alertness, PVT performance, and OSPAT performance declined significantly as hours of wakefulness increased during the night-time (all p < .01). Furthermore, a positive correlation between OSPAT and PVT performance was observed (r = 0.40, p < .01). Overall, these findings suggest that OSPAT is sensitive to sustained wakefulness during the night-time, and builds the case for OSPAT being a suitable measure for determining fitness-for-duty in workplace environments.

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Short Communication

Changes in the Concentration of Urinary 6-sulphatoxymelatonin during a Week of Simulated Night Work

Gregory D. ROACH, Nicole LAMOND, Jill DORRIAN, Helen BURGESS, Alexandr ...

2005 Volume 43 Issue 1 Pages 193-196
Published: 2005
Released on J-STAGE: March 17, 2006

DOIhttps://doi.org/10.2486/indhealth.43.193

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The aim of the study was to examine the adaptation of participants to a common night work schedule using urinary 6-sulphatoxymelatonin (aMT6s) concentration as the circadian phase marker. Fifteen adults (7 male, 8 female, age = 21.9 yr) spent nine consecutive nights in the laboratory, including: (i) adaptation sleep, (ii) baseline sleep, and (iii) seven simulated night shifts (23:00-07:00 h) followed by daytime sleep. During the baseline and daytime sleeps, participants collected urine samples which were subsequently assayed for aMT6s. The concentration of aMT6s in urine for the first three day sleeps was significantly lower than for the baseline sleep, but there was no difference in aMT6s concentrations between any of the last three day sleeps and the baseline sleep. The data indicate that people may adapt to a pattern of work that includes seven consecutive night shifts if they adhere to a fixed sleep schedule, if their exposure to morning sunlight is minimised, and if they are provided with an ideal sleep environment.

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Field Reports

A National Sleep Foundation's Conference Summary: The National Summit to Prevent Drowsy Driving and a New Call to Action

Darrel DROBNICH

2005 Volume 43 Issue 1 Pages 197-200
Published: 2005
Released on J-STAGE: March 17, 2006

DOIhttps://doi.org/10.2486/indhealth.43.197

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On November 20-21, 2002, the National Sleep Foundation (NSF), a U.S.-based non-profit organization, and a coalition of other organizations, federal agencies and corporations convened a National Summit to Prevent Drowsy Driving at the National Academy of Sciences in Washington, DC. The Summit brought together experts in the fields of transportation, safety and health, sleep research, and communications as well as advocates to assist in the creation of a comprehensive national agenda to increase awareness about the dangers of drowsy driving. Recommendations from the Summit formed the basis of post-summit activities, including the development of a new Web site (www.drowsydriving.org) dedicated to the prevention of driver fatigue and a report, the National Action Plan to Prevent Drowsy Driving, which describes a series of action items for national, state and local initiatives in the areas of research, public policy, and educational programs.

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Improving Health, Safety, and Profits in Extended Hours Operations (Shiftwork)

Alex KERIN, Acacia AGUIRRE

2005 Volume 43 Issue 1 Pages 201-208
Published: 2005
Released on J-STAGE: March 17, 2006

DOIhttps://doi.org/10.2486/indhealth.43.201

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Circadian Technologies, Inc. (CIRCADIAN) is an international consulting firm that for over 20 yr has helped employees better cope with shiftwork, while ensuring their employers reduce costs and maximize profits. This paper describes two of the methods employed to reduce accidents, absenteeism, and turnover, while improving morale and productivity in extended hour operations (shiftwork). Shiftworkers rarely receive on-the-job training to help them cope better with the rigors of working nights, evenings, and early mornings. A pre- and post-training study by CIRCADIAN demonstrated improvements in health and fatigue indices, and an increase in daytime sleep length. Companies who provide shiftwork lifestyle training also have lower rates of absenteeism and turnover compared to companies that do not provide training. The second intervention described in this paper is a novel method of shift scheduling. There are thousands of potential schedules, so how does a company choose the best schedule for their facility? The answer lies in allowing employees to be involved in the process of selection. This results in a workforce that experiences less fatigue, turnover and absenteeism, and higher morale.

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The Napping Company: Bringing Science to the Workplace

William A. ANTHONY, Camille W. ANTHONY

2005 Volume 43 Issue 1 Pages 209-212
Published: 2005
Released on J-STAGE: March 17, 2006

DOIhttps://doi.org/10.2486/indhealth.43.209

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Increasing emphasis is currently being given to the importance of bringing knowledge gained from science into places where people live and work, in order to increase the impact science has on the general public's quality of life. Scientific findings about the positive impact of napping on mood and performance are an example of research generated knowledge that needs to be brought to the workplace. A major goal of the Napping Company (www.napping.com) is to bring the science of napping to the workers and the workplace so that employees and employers can act on this knowledge and change worker napping behavior and employer napping policies. The present paper overviews the challenges inherent in making scientific knowledge useful to how we live our lives. The Napping Company is guided by five principles of knowledge transfer in the company's attempts to disseminate and increase utilization of napping research. Examples are given to illustrate how the Napping Company has used these principles to bridge the gap between napping science and nap behavior and policies in the workplace.

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REGULAR ISSUES

Original Articles

The Effect of Heating on the Dissolution of Alkaline Earth Silicate Fibers in a Simple Amino Acid Solution and Water

Masato OHSAWA

2005 Volume 43 Issue 1 Pages 213-220
Published: 2005
Released on J-STAGE: March 17, 2006

DOIhttps://doi.org/10.2486/indhealth.43.213

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In order to evaluate the effect of pre-heating on biosolubility and water-resistance of alkaline earth silicate (AES) fibers in MgO-SrO-SiO₂ and MgO-CaO-SrO-SiO₂ compositions, dissolution experiments of the heat-treated (from 110°C to 1,260°C) AES fibers have been carried out in a glycine solution and in distilled water at 40°C for 50 h. The dissolution experiments show that the heat-treatment around 700°C has made the AES fibers more soluble in the glycine solution. This is due to the phase separation of the AES fibers resulting from the heat-treatment. Probably, alkaline earth-rich glassy phases formed by the phase separation facilitate the dissolution of the heat-treated AES fibers in the glycine solution. The heat-treatment around 700°C is possible to decrease the toxicity of the AES fibers further. Meanwhile, this heat-treatment around 700°C has given little effect on the dissolution of the AES fibers in the distilled water. This indicates that the resistance of the AES fibers to water or humidity remains unaffected by the heat-treatment. The water-resistance is a very useful property for MMVFs. This study suggests that the heat-treatment around 700°C is probably an useful treatment in order to enhance the total performance, biosolubility and water-resistance, of AES fibers.

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Evaluation of Whole-Body Vibration by the Category Judgment Method

Chikako KANEKO, Takahide HAGIWARA, Setsuo MAEDA

2005 Volume 43 Issue 1 Pages 221-232
Published: 2005
Released on J-STAGE: March 17, 2006

DOIhttps://doi.org/10.2486/indhealth.43.221

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The purpose of this research is to establish a scale for comfort with regard to whole-body vibration by the category judgment method. Experiments were conducted with random signals as stimuli. These stimuli consisted of three types of signal, namely stimulus F, with flat PSD (Power Spectrum Density) ranging from 1 to 100 Hz, stimulus H with PSD, which became 20 dB higher at 100 Hz than at 1 Hz, and stimulus L that had a PSD 20 dB lower at 100 Hz. These signals were modified by Wk frequency weighting in accordance with ISO 2631-1, and the R.M.S. values were adjusted to be equal. In addition, the signal levels were varied over a range of five steps to create 15 kinds of individual stimuli. The subjects sat on a flat, horizontal metal plate mounted directly on the vibrator and were exposed to vertical vibrations before being asked to choose a numerical category to best indicate their perceived level of comfort (or otherwise) during each stimulus. The creation of this assessment scale, including the aforementioned categories, enabled not only clarification of the relationship between the vibration stimuli and the degree of comfort but also discovery of the connection between the frequency-weighted R.M.S. acceleration and the corresponding categories representing each degree of comfort without overlap. Moreover, it became clear that the subjects' assessment of the degree of comfort perceived differed with differences in the vibration spectrum.

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Comparison of the Apparent Mass of the Seated Human Measured Using Random and Sinusoidal Vibration

Neil J. MANSFIELD, Setsuo MAEDA

2005 Volume 43 Issue 1 Pages 233-240
Published: 2005
Released on J-STAGE: March 17, 2006

DOIhttps://doi.org/10.2486/indhealth.43.233

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Exposure to whole-body vibration is generally accepted as being a risk factor for low back pain and therefore exposure to vibration should be minimised. The results of previous laboratory based research investigating the biomechanical response of the seated human to vibration has been used to develop models that can be used within tools that are capable of predicting the response of seats. Several studies in the literature have reported apparent masses of seated human subjects whilst exposed to either random or sinusoidal vibration. Although these studies have shown similar trends, there have been no systematic comparisons of apparent mass for the same subjects exposed to random and sinusoidal vibration. This paper reports a study where twelve male subjects were exposed to random whole-body vibration at 1.0 m/s² r.m.s. and to sinusoidal vibration at 1, 2, 4, 8, 16 and 32 Hz. The modulus of the apparent masses were nominally identical when measured using random or sinusoidal vibration. The phase of the apparent masses were similar at 1, 2 and 4 Hz, when measured using random or sinusoidal vibration, but showed consistent differences at 8, 16 and 32 Hz. As the results between experiments using different waveforms are similar, models derived from experimental work based on one type of stimulus could be applied in scenarios involving the other type of stimulus.

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Biodynamic Response at the Palm of the Human Hand Subjected to a Random Vibration

Ren G. DONG, Thomas W. McDOWELL, Daniel E. WELCOME

2005 Volume 43 Issue 1 Pages 241-255
Published: 2005
Released on J-STAGE: March 17, 2006

DOIhttps://doi.org/10.2486/indhealth.43.241

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This study investigated the biodynamic response (BR) distributed at the palm of the hand subjected to a random vibration. Twelve male subjects were used in the experiment. Each subject applied three coupling actions (grip-only, push-only, and combined grip and push) on a simulated tool handle at three different levels (50, 75, and 100 N) of palm force. This study found that the hand-arm system resonated mostly in the frequency range of 20 to 50 Hz, depending on the specific test treatment and individual characteristics. The maximum vibration power transmission through the palm occurred at the resonant frequency. Increasing the effective palm force generally increased the BR magnitude and resonant frequency. The apparent stiffness measured at the middle frequencies (80-100 Hz) is correlated to the BR in almost the entire frequency range (20-1,000 Hz). Under the same palm force, the push-only action corresponded to the highest BR values while the grip-only action generally produced the lowest values. Since the resonant frequency range matches the dominant vibration frequency range of many percussive tools, it is anticipated that the palm BR and vibration power transmission may have an association with vibration-induced injuries or disorders in the wrist-arm system among the workers using these tools.

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Relationship between Chest X-ray Findings and Pulmonary Function Tests in Dust Workers

Yoko TONORI, Masato NIITSUYA, Toshihiko SATO, Yumiko SUGIURA, Hitoshi ...

2005 Volume 43 Issue 1 Pages 256-266
Published: 2005
Released on J-STAGE: March 17, 2006

DOIhttps://doi.org/10.2486/indhealth.43.256

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Occupational injuries are decreasing due to the improvement in occupational management in the workplace in recent years. However, pneumoconiosis and its complications remain important occupational diseases. Based on the report ‘survey on classification for supervision of pneumoconiosis in Japan’ performed in 1994, this study compared age, number of years at the job and pulmonary function tests among work types, and examined the characteristics of cases in which pulmonary function results were worse than expected from the chest X-ray findings. In the comparison among work types, mean age was higher and %VC was lower among workers exposed to silica or asbestos, and FEV1.0% appeared to be lower among silica-exposed workers. Multiple regression analysis showed that silica or asbestos-exposed work environments strongly affected %VC. Some cases showed dissociation between the X-ray findings and pulmonary function tests, which appeared to be caused by certain types of work environments. In this study, all the subjects had findings of pneumoconiosis in their chest X-ray. It is necessary to perform a longitudinal survey on pneumoconiosis-free subjects to clarify the precise association of lung function tests with chest X-ray.

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