123 Supporting A Learning System in Paediatric Emergency Pathways; Using Organisational Comparisons, Serious Incidents and Near Miss Events To Improve The Diagnosis And Treatment Of Testicular Torsion

Introduction

Scrotal pain is a common presentation to the emergency department requiring prompt investigation and management to identify testicular torsion. Using national data we aim to identify key suboptimal areas in the acute diagnosis and management of testicular torsion with a view to improving outcomes.

Method

A freedom of information request was made to all Trusts in England that manage testicular torsion. Serious Incidents (SI's) were analysed to see if those with Paediatric Emergency Departments fared better than those without. In addition, a qualitative thematic analysis of the NHS England Strategic Executive Information System database from 2007-2019 was undertaken, identifying common themes associated with orchidectomies and ‘near miss’ events in children.

Results

304 serious incidents were returned with 62 Orchidectomies and 242 Near Miss Events. Misdiagnosis of symptomatic testicle was not significant when comparing ED to specialists (OR = 1.46, p = 0.3842). Atypical presentation resulting in orchidectomy was significant when comparing ED to specialists (OR = 6, p = 0.0355). Near miss events are due to a variety of factors. There was no statistical significance in incidents when comparing ED's caring for all ages with Paediatric EDs U = 807.5, z = -1.124, p = 0.261.

Conclusions

There's a need for education in ED about atypical presentation of testicular torsion and examination of scrotum in cases of lower abdominal pain. It's also vital that specialist teams are cognisant of the standard operating procedures relevant to scrotal pain. Finally, there should be a drive for annual audit in Urology and ED units with regards to testicular torsion as SI's may be under-reported.

Some effects of melatonin and the control of its secretion in humans

Whether or not the pineal gland has a significant physiological role in humans is not known. There has nevertheless been speculation about the potential therapeutic use of melatonin (in view of its hypnotic and possible zeitgeber properties) in conditions such as insomnia and jet lag, and in shift-workers. Our work concerns the effects of melatonin administration in humans and the interactions between melatonin and other circadian variables. Chronic (one month), timed (1700 h), low-dose (2 mg daily) melatonin administration to normal subjects without environmental control consistently increased evening fatigue and slightly modified the 24 h prolactin rhythm without effect on cortisol, growth hormone, luteinizing hormone, thyroxine, testosterone or self-rated mood. In five out of 11 subjects the endogenous melatonin rhythm was advanced by one to three hours. During fractional desynchronization of circadian rhythms by increasing imposed 'day' length (26-29 h, 24 days, 500 lux), 5 mg melatonin per os at lights-out in two subjects resulted in better entrainment of the fatigue rhythm to the zeitgeber than in five out of six control subjects, without major consistent effects on other measured circadian variables. Using a new radioimmunoassay for 6-hydroxymelatonin sulphate (aMT6s), the major melatonin metabolite, we have shown that the urinary aMT6s rhythm is closely correlated to that of melatonin in plasma and is completely suppressed by an acute dose of atenolol (100 mg per os), a peripheral beta-adrenergic antagonist. During fractional desynchronization by increasing imposed 'day' length in one subject and decreasing imposed 'day' length in two subjects, the urinary aMT6s rhythm behaved similarly to that of core temperature. The results suggest that fatigue (or alertness) may be entrained by melatonin, but whether critical performance rhythms can be suitably manipulated remains to be clarified. It is likely that melatonin production is linked to the so-called 'strong' circadian oscillator.

Rest breaks and accident risk

Regular rest breaks are recommended to prevent accumulation of accident risk during sustained activities. We examined the effect of rest breaks on temporal trends in industrial accident risk, by assessment of accident records from a large engineering company, obtained over 3 years. In 2 h of continuous work, relative risk of an accident in the last half-hour of a shift was 2.08 (95% CI 1.73-2.43) higher than in the first half-hour. Trends in risk did not seem to differ between three 2-h work periods. Regular rest breaks seem to be an effective way to control accumulation of risk during industrial shift-work.

Can we predict perceived risk?

This paper examines the possibility that we may be able to use subjective measures of perceived risk in order to assess the relative safety of different shift systems. A large-scale survey of safety-critical engineers included three items relating to risk on each shift, namely alertness, likelihood of making a mistake and confidence in driving home after it. These three measures were found to load on a separate factor for each shift. Hierarchical regression analyses indicated that perceived night shift risk could be predicted on the basis of circadian type, the extent to which the engineers could control their work schedule, and a number of features of the scheduled shift system. In most cases the relationships observed were reasonably consistent with established trends in either performance capability or accident and injury frequency. However, there were exceptions to this indicating that results based on measures of perceived risk should be interpreted with the utmost caution.

The effect of a change in sleep-wakefulness timing, bright light and physical exercise interventions on 24-hour patterns of performance, mood and body temperature

Experiments consisting of baseline, bright light and physical exercise studies were carried out to compare the effect of a 9-hour delay in sleep-wakefulness timing, and the effects of bright light and physical exercise interventions on 24-hour patterns of performance, mood and body temperature were examined. Each study comprised a 24-hour constant routine at the beginning followed by 3 night shifts and 24-hour constant routine at the end. Performance on tasks differing in cognitive load, mood and body temperature was measured during each constant routine and the interventions were applied during the night shifts. The 24-hour pattern of alertness and performance on the tasks with low cognitive load in post-treatment conditions followed the change in sleep-wakefulness timing while more cognitively loaded tasks tended to show a reverse trend when compared to pre-treatment conditions. There was a phase delay around 4 hours in circadian rhythms of body temperature in post-treatment conditions.

Flexible work hours, health and well-being in the European Union: preliminary data from a SALTSA project

Demand for flexible work hours (FWH) is increasing in Europe aimed at increasing the number of production hours on one hand, and, on the other, reducing individual working hours and/or increasing autonomy and control on them. In view of the lack of knowledge of the effects of FWH on health and safety, we started a pilot project, funded by the Joint Programme for Working Life Research in Europe (SALTSA), aimed at: a) comparing the most relevant national legislation and how the EU Directive 93/104 "concerning certain aspects of working time" has been implemented in the member States; b) reporting prevalence and trend of FWH in Europe according to the three EU Surveys on Working Conditions carried out in the last decade; c) collecting practical examples of innovative FWH; d) evaluating their impact on health and safety in relation to work sectors, job demands, social life, aging and gender. Consequent actions are going to include information and consultancy for pertinent authorities and social parties involved, as well as training programmes for Union officials and similar groups concerning the organisation of FWH according to ergonomic principles.

Predicting shiftwork-related outcomes: shiftwork locus of control and circadian type

This research discusses the use and viability of the shiftwork locus of control construct alongside circadian type measures as a potential predictor of shiftwork-related outcomes. The shiftwork locus of control (SHLOC) scale, measures of circadian type and shiftwork-related outcome measures were completed by 100 shiftworkers on two occasions separated by seven months. The SHLOC scale measures shiftworkers' generalised beliefs about the levels of personal control they perceive in relation to four major functional domains commonly associated with shiftwork-related disruption. These domains include: sleep, social, health and work problems. The results of multivariate regression analysis showed the SHLOC scale to be predictive of the experience of shiftwork-related sleep and social-life problems while the circadian type measures were predictive of alertness at 7 months. The results suggest that a constellation of personality factors may be an important influence on an individual's tolerance to shiftwork.

Measurement properties of the Shiftwork Survey and Standard Shiftwork Index

The Shiftwork Survey (SS) was introduced, along with the Standard Shiftwork Index (SSI), to provide a set of standardized self-report measures to be used in shiftwork research. However, beyond the initial assessment, no attempt has been made to examine the measurement properties of these scales in an independent sample of shiftworkers. Our goal, therefore, was to examine the measurement properties of these scales in an industrial sample of primarily male shiftworkers (N = 370). We found that all scales had acceptable reliabilities (alphas). The confirmatory factor analyses revealed that the chronic fatigue, coping, job satisfaction, and sleep scales are the weakest psychometrically, and the anxiety, personality (extraversion, neuroticism), general health, and physical health scales are the strongest psychometrically. Using item response theory analyses, we found that the scales overall are generally adequate measures of their underlying constructs, although many items should be altered or omitted. Our results, however, are limited by reliance on a single sample.

Temperature profiles, and the effect of sleep on them, in relation to morningness-eveningness in healthy female subjects

There were 15 healthy female subjects, differing in their position on the "morningness-eveningness" scale, studied for 7 consecutive days, first while living a sedentary lifestyle and sleeping between midnight and 08:00 and then while undergoing a "constant routine." Rectal temperature was measured at regular intervals throughout this time, and the results were subjected to cosinor analysis both before and after "purification" for the effects of physical activity. Results showed that there was a phase difference in the circadian rhythm of core temperature that was associated with the morningness score, with calculations that "morning types" would be phased earlier than "evening types" by up to about 3 h. This difference in phase (which was also statistically significant when the group was divided by a median split into a "morning group" and an "evening group") could not be attributed to effects of waking activity and existed in spite of the subjects keeping the same sleep-wake schedule. Moreover, it persisted when the subjects' data had been purified and when the data were obtained from the constant routine. That is, there was an endogenous component to this difference in phase of the core temperature. The morning group also showed a greater fall of core temperature during sleep; this was assessed in two ways, the main one being a comparison of constant routine and nychthemeral data sets after correction for any effects of activity. Even though the morning group was sleeping at a later phase of their circadian temperature rhythm than was the evening group, neither group showed a fall of temperature due to sleep that varied with time elapsed since the temperature acrophase. It is concluded that another factor that differs between morning and evening types is responsible for this difference.

Effects of direction of rotation in continuous and discontinuous 8 hour shift systems

OBJECTIVES

Previous research has produced conflicting evidence on the relative merits of advancing and delaying shift systems. The current study assessed the effects of the direction of shift rotation within 8 hour systems, upon a range of measures including sleep, on shift alertness, physical health, and psychological wellbeing.

METHODS

An abridged version of the standard shiftwork index which included retrospective alertness ratings was completed by four groups of industrial shiftworkers on relatively rapidly rotating 8 hour systems (n=611). Two groups worked continuous systems that were either advancing or delaying; the other two groups worked discontinuous systems that were either advancing or delaying.

RESULTS

Few effects were found of direction of rotation on chronic measures of health and wellbeing, even when the systems incorporated "quick returns" (a break of only 8 hours when changing from one shift to another). This was despite the use of measures previously shown to be sensitive to the effects of a broad range of features of shift systems. However, advancing continuous systems seemed to be associated with marginally steeper declines in alertness across the shift (F (3,1080)=2.87, p<0.05). They were also associated with shorter sleeps between morning shifts (F (1,404)=4.01, p<0.05), but longer sleeps between afternoons (F (1,424)=4.16, p<0.05).

CONCLUSIONS

The absence of negative effects of advancing shifts upon the chronic outcome measures accorded with previous evidence that advancing shifts may not be as harmful as early research indicated. However, this interpretation is tempered by the possibility that difficult shift systems self select those workers most able to cope with their deleterious effects. The presence of quick returns in advancing continuous systems seemed to impact upon some of the acute measures such as duration of sleep, although the associated effects on alertness seemed to be marginal.

A comparison of some different methods for purifying core temperature data from humans

Nine healthy females were studied about the time of the spring equinox while living in student accommodations and aware of the passage of solar time. After 7 control days, during which a conventional lifestyle was lived under a 24h "constant routine," the subjects lived 17 x 27h "days" (9h sleep in the dark and 18h wake using domestic lighting, if required). Throughout the experiment, recordings of wrist activity and rectal (core) temperature were taken. The raw temperature data were assessed for phase and amplitude by cosinor analysis and another method, "crossover times," which does not assume that the data set is sinusoidal. Two different purification methods were used in attempts to remove the masking effects of sleep and activity from the core temperature record and so to measure more closely the endogenous component of this rhythm; these two methods were "purification by categories" and "purification by intercepts." The former method assumes that the endogenous component is a sinusoid, and that the masking effects can be estimated by putting activity into a number of bands or categories. The latter method assumes that a temperature that would correspond to complete inactivity can be estimated from measured temperatures by linear regression of these on activity and extrapolation to a temperature at zero activity. Three indices were calculated to assess the extent to which exogenous effects had been removed from the temperature data by these purification methods. These indices were the daily variation of phase about its median value; the ratio of this variation to the daily deviation of phase about midactivity; and the relationship between amplitude and the square of the deviation of phase from midactivity. In all cases, the index would decrease in size as the contribution of the exogenous component to a data set fell. The purification by categories approach was successful in proportion to the number of activity categories that was used, and as few as four categories produced a data set with significantly less masking than raw data. The method purification by intercepts was less successful unless the raw data had been "corrected" to reflect the direct effects of sleep that were independent of activity (a method to achieve this being produced). Use of this purification method with the corrected data then gave results that showed least exogenous influences. Both this method and the purification by categories method with 16 categories of activity gave evidence that the exogenous component no longer made a significant contribution to the purified data set. The results were not significantly influenced by assessing amplitude and phase of the circadian rhythm from crossover times rather than cosinor analysis. The relative merits of the different methods, as well as of other published methods, are compared briefly; it is concluded that several purification methods, of differing degrees of sophistication and ease of application to raw data, are of value in field studies and other circumstances in which constant routines are not possible or are ethically undesirable. It is also concluded that such methods are often somewhat limited insofar as they are based on pragmatic or biological, rather than mathematical, considerations, and so it is desirable to attempt to develop models based equally on mathematics and biology.

Diurnal variations in the mood and performance of highly practised young women living under strictly controlled conditions

The diurnal variation in a range of psychological functions and core body temperature were investigated in a series of studies involving a total of 24 highly practised young women who lived in a controlled environment and on a strictly regimented 24-hour routine for 6 or 7 days. Ten participants were exposed to the natural light/dark cycle (L/Dc) through windows, whereas the 14 remaining participants saw no daylight, but all had access to normal clock time. A battery of mood and performance tests was completed every 2 hours whilst awake (08:00-00:00), resulting in nine equally spaced measures per waking day. Average time of day (ToD) functions were calculated from the last 5 or 6 days spent in the controlled environment. Significant ToD effects were found for many of the variables taken although the nature of these effects differed across measures, with a 'post-lunch dip' being observed at 16:00 in some variables. Analysis of the standardized data established that all variables presented reliably different ToD functions to core body temperature, whilst factor analyses indicated possible relationships between the variables. It was concluded that those variables that exhibited diurnal variation showed trends that did not parallel those in core body temperature.

Estimates of the daily phase and amplitude of the endogenous component of the circadian rhythm of core temperature in sedentary humans living nychthemerally

Fifteen healthy female subjects were studied for eight days while living conventionally. Subjects were free to choose the ways they spent their time within a framework of regular times of retiring and rising; in practice, much of the waking time was spent in sedentary activities. Nine of the subjects were aware of the natural light-dark cycle, this approximating to a 12:12 L:D schedule at the time of year when the study took place. Before the study, subjects were assessed for their degree of "morningness" by questionnaire; throughout the study, they wore a rectal probe, and an activity meter on their non-dominant wrist. The timing (phase) and amplitude of the circadian rectal temperature rhythm were assessed on each day by cosinor analysis as well as by a method based on visual inspection of the data. These two parameters were also assessed after the temperature data for each day had been "purified" by a number of methods. From these results it was possible to investigate the effect of purification upon the amplitude of the circadian rhythm of temperature. Also, the day-by-day variability of phase, and the relationship between morningness and phase, were compared using these methods of phase estimation, and using cross-correlation between data sets from adjacent days; in all cases, raw and purified temperature data were used. There was a significantly greater amount of daily variation in phase using purified rather than raw data sets, and this difference was present with all methods of purification as well as with all methods for estimating phase. Purification decreased the amplitude of the circadian temperature rhythm by about 30%. Finally, there was a significant correlation between the morningness score of the subjects and the phase of the circadian temperature rhythm, the phase becoming earlier with increasing morningness; when this relationship was re-examined using purified data, it became more marked. These results reflect the masking effects exerted upon raw temperature data by lifestyle. The extent to which the purification methods enable the endogenous component of a circadian rhythm - and, by implication, the output of the endogenous circadian oscillator - to be estimated in subjects living normally is addressed.

Beyond the three-process model of alertness: estimating phase, time on shift, and successive night effects

This paper starts by summarizing the development and refinement of the additive three-process model of alertness first published by Folkard and Akerstedt in 1987. It reviews some of the successes that have been achieved by the model in not only predicting variations in subjective alertness on abnormal sleep-wake schedules but also in accounting for objective measures of sleep latency and duration. Nevertheless, predictions derived from the model concerning alertness on different shifts, and over successive night shifts, are difficult to reconcile with published data on accident risk. In light of this, we have examined two large sets of alertness ratings with a view to further refining the model and identifying additional factors that may influence alertness at any given point in time. Our results indicate that, at least for the range of sleep durations and wake-up times commonly found on rotating shift systems, we may assume the phase of the endogenous circadian component of alertness (process C) to be "set" by the time of waking. Such an assumption considerably enhanced the predictive power of the model and yielded remarkably similar phase estimates to those obtained by maximizing the post-hoc fit of the model. We then examined the manner in which obtained ratings differed from predicted values over a complete 8-day cycle of two, 12-h shift systems. This revealed a pronounced "first night compensation effect" that resulted in shift workers rating themselves as progressively more alert than would be predicted over the course of the first night shift. However, this appeared to be achieved only at the cost of lowered ratings on the second night shift. Finally, we were able to identify a "time on shift" effect whereby, with the exception of the first night shift, alertness ratings decreased over the course of each shift before showing a modest "end effect." We conclude that the identification of these additional components offers the possibility that in the future we may be able to predict trends in accident risk on abnormal sleep-wake schedules.

A process model of shiftwork and health

The authors developed and tested a process model of adaptation to shiftwork, which hypothesizes that various individual and situational variables influence the development of sleep and social and domestic disturbances. Both types of disturbances trigger various types of coping behavior, leading to several proximal outcomes. The end result is the development of chronic health problems in the form of digestive and cardiovascular symptoms. The model was tested with survey data collected from 2 samples of nurses (N = 1,532) in the United Kingdom and was cross-validated against a 3rd sample of industrial workers (N = 370). Results indicate support for the model across the 3 samples, although some sample-specific and subgroup effects were found. Results have direct implications for the development of shiftwork theory and interventions.

A process model of shiftwork and health

The authors developed and tested a process model of adaptation to shiftwork, which hypothesizes that various individual and situational variables influence the development of sleep and social and domestic disturbances. Both types of disturbances trigger various types of coping behavior, leading to several proximal outcomes. The end result is the development of chronic health problems in the form of digestive and cardiovascular symptoms. The model was tested with survey data collected from 2 samples of nurses (N = 1,532) in the United Kingdom and was cross-validated against a 3rd sample of industrial workers (N = 370). Results indicate support for the model across the 3 samples, although some sample-specific and subgroup effects were found. Results have direct implications for the development of shiftwork theory and interventions.

The effect of activity on the waking temperature rhythm in humans

Nine healthy female subjects were studied when exposed to the natural light-dark cycle, but living for 17 "days" on a 27h day (9h sleep, 18h wake). Since the circadian endogenous oscillator cannot entrain to this imposed period, forced desynchronization between the sleep/activity cycle and the endogenous circadian temperature rhythm took place. This enabled the effects of activity on core temperature to be assessed at different endogenous circadian phases and at different stages of the sleep/activity cycle. Rectal temperature was measured at 6-minute intervals, and the activity of the nondominant wrist was summed at 1-minute intervals. Each waking span was divided into overlapping 3h sections, and each section was submitted to linear regression analysis between the rectal temperatures and the total activity in the previous 30 minutes. From this analysis were obtained the gradient (of the change in rectal temperature produced by a unit change in activity) and the intercept (the rectal temperature predicted when activity was zero). The gradients were subjected to a two-factor analysis of variance (ANOVA) (circadian phase/ time awake). There was no significant effect of time awake, but circadian phase was highly significant statistically. Post hoc tests (Newman-Keuls) indicated that gradients around the temperature peak were significantly less than those around its trough. The intercepts formed a sinusoid that, for the group, showed a mesor (+/-SE) of 36.97 (+/-0.12) and amplitude (95% confidence interval) of 0.22 degrees C (0.12 degrees C, 0.32 degrees C). We conclude that this is a further method for removing masking effects from circadian temperature rhythm data in order to assess its endogenous component, a method that can be used when subjects are able to live normally. We suggest also that the decreased effect of activity on temperature when the endogenous circadian rhythm and activity are at their peak will reduce the possibility of hyperthermia.

Effect of sleep loss on core temperature when movement is controlled

Nine subjects were studied for 16 days in an isolation unit where they lived on normal time, working at a decision-making, computer-driven task during the daytime. Interspersed among these control days were three occasions when sleep was curtailed. Rectal temperature and activity (non-dominant wrist) were measured throughout. Any effects of sleep loss on core temperature and activity were assessed by comparing these variables on control days with values during the daytime immediately following sleep loss, and during the next (recovery) day. During the daytime following sleep loss, activity showed no significant changes. By contrast, core temperature was significantly lower, particularly after the night of complete sleep loss. On recovery days also, activity was not significantly changed from control days but core temperatures during work were significantly lower than on control days if there had been no sleep the previous night. These results indicate that the effects of sleep loss on core temperature can persist for at least 24 h, and that they occur in the absence of parallel changes in activity.

Distribution of rest days in 12 hour shift systems: impacts on health, wellbeing, and on shift alertness

OBJECTIVES

To investigate of the effects of distribution of rest days in 12 hour shift systems. Although several studies have examined the effects of compressing work schedules by comparing 8 and 12 hour shift systems, there is little published research examining the various forms of 12 hour shift system.

METHODS

An abridged version of the standard shiftwork index which included retrospective alertness ratings was completed by a large sample of industrial shiftworkers. The respondents worked 12 hour shift systems that either did or did not incorporate breaks of > 24 hours between the blocks of day and night shifts. For the purposes of the analysis, each of these two groups were further subdivided into those who started their morning shift at 0600 and those who started at 0700.

RESULTS

Systems which incorporated rest days between the day and night shifts were associated with slightly higher levels of on shift alertness, slightly lower levels of chronic fatigue, along with longer sleep durations when working night shifts and between rest days. Early changeovers were associated with shorter night sleeps between successive day shifts, but longer and less disturbed day sleeps between night shifts. These effects of changeover time were broadly in agreement with previous research findings.

CONCLUSIONS

The distribution of rest days in 12 hour shift systems had only limited effects on the outcome measures, although the few modest differences that were found favoured systems which incorporated rest days between the day and night shifts. It is conceded that the design of the study may have obscured some subtle differences between the shift systems. Nevertheless, it is concluded that the impact of distribution of rest days seems to be minor relative to previously found effects of other features of shift systems--for example, shift duration.

Diurnal trends in mood and performance do not all parallel alertness

OBJECTIVES

This study examined the hypothesis that alertness can be used to predict time-of-day effects on performance.

METHODS

For 6 or 7 days the volunteers (24, highly practiced young women) were required to retire to bed at 0000 and were awakened at 0800. A battery of mood and performance tests was completed every 2 hours while the women were awake; the result was 9 equally spaced measures per day. Measures of mood, serial reaction time, and memory scanning were recorded. Rectal temperature was recorded continuously.

RESULTS

After omitting the data from the first day to avoid any carry-over from the "first-night" effect on sleep, average time-of-day functions were calculated for each subject, for each variable, and were then z-transformed. Cross-correlations between the pooled time-of-day trends indicated that, while alertness was a reasonably good "predictor" of the simple perceptual-motor speed measures, it fared less well for some of the other measures. Two-way analyses of variance indicated that the time-of-day trend for all measures differed from that for alertness, although the magnitude of this difference varied substantially and, for some measures, was very largely due to the last reading of the day (0000).

CONCLUSION

It is clear from these results that, while alertness may successfully "predict" variations in some measures of performance capability, and especially those of simple perceptual motor speed, care should be exercised in extrapolating to other performance measures.

Shift length as a determinant of retrospective on-shift alertness

OBJECTIVES

This study examined the combined effects of shift length (8 versus 12 hours) and night-to-morning-shift changeover time (0600 versus 0700) on retrospective on-shift alertness ratings.

METHODS

An abridged version of the Standard Shiftwork Index, which included retrospective alertness ratings, was completed by 4 groups of industrial shift workers. Two groups worked 8-hour shift systems and started their morning shifts at either 0600 or 0700; the other 2 groups worked 12-hour systems, starting their day shifts at either 0600 or 0700.

RESULTS

The 8-hour workers reported considerably higher levels of alertness in the afternoon, while the 12-hour workers were more alert than the 8-hour workers in the morning and at 2200. Workers who started their shift around 0600 were less alert during the morning than those who started around 0700. The data suggested that the combined effects of working 8-hour shifts and starting the morning shift at around 0600 have particularly deleterious effects upon alertness.

CONCLUSIONS

Effects on alertness can be explained in terms of differences in elapsed time on duty, sleep duration, sleep disruption, and chronic fatigue. The findings of this study appear to contradict previous research demonstrating that the major deleterious effects of extended shifts and delayed changeovers upon alertness occur at night. However, it is acknowledged that the absence of a difference in alertness at night may have been due to floor effects. Nevertheless, the implications of the alertness ratings for performance and safety, particularly during the afternoon, should not be ignored.

Lack of evidence that feedback from lifestyle alters the amplitude of the circadian pacemaker in humans

Two groups of healthy subjects were studied indoors, first while living normally for 8 days (control section) and then for 18 x 27 h "days" (experimental section). This schedule forces the endogenous (body clock-driven) and exogenous (lifestyle-driven) components of circadian rhythms to run independently. Rectal temperature and wrist movement were measured throughout and used as markers of the amplitude of the circadian rhythm, with the rectal temperature also "purified" by means of the activity record to give information about the endogenous oscillator. Results showed that, during the experimental days, there were changes in the amplitude of the overt temperature rhythm and in the relative amounts of out-of-bed and in-bed activity, both of which indicated an interaction between endogenous and exogenous components of the rhythm. However, the amplitude and the amount of overlap were not significantly different on the control days (when endogenous and exogenous components remained synchronized) and those experimental days when endogenous and exogenous components were only transiently synchronized; also, the amplitudes of purified temperature rhythms did not change significantly during the experimental days in spite of changes in the relationship between the endogenous and exogenous components. Neither result offers support for the view that the exogenous rhythm alters the amplitude of oscillation of the endogenous circadian oscillator in humans.

Time of day effects in, and the relationship between, sleep quality and movement

The study aimed to measure the effects of a 27-h 'day' sleep-wake regime on actigraphic and subjective sleep variables, and to examine the relationships between these variables. Nine subjects spent 30 days and nights in the laboratory. After sleeping 8 h for each of 8 nights, the subjects had an imposed 27-h 'day', for 18 'days', remaining in bed for 9 h on each sleep period. Sleep periods therefore started 3 h later each day, although subjects' circadian rhythms stayed entrained to 24 h, because subjects were not isolated from the natural light-dark cycle. Time asleep, subjective sleep efficiency and subjective sleep quality, but not movement during sleep, were found to be significantly affected by time of going to bed. There were significant decreases in movement during recovery sleeps following each of two episodes of 26 h sleep deprivation. Over the study there were significant within-subject correlations between subjective sleep quality and subjective sleep efficiency (rav = 0.65), movement during sleep and subjective sleep efficiency (rav = -0.48), and movement during sleep and subjective sleep quality (rav = -0.26). We conclude that sleep movement, despite its low within- and between-subjects variability, is nevertheless a statistically reliable, but weak, indicator of subjective sleep efficiency and quality.

Industrial shift systems

This technical report describes the identification of shift systems worked by industrial shiftworkers in England, Scotland and Wales. A diverse range of shift systems were reported to be in operation across 27 industrial sectors. Companies employed up to 14 different shift systems at a particular site. The numbers of shiftworkers on a given shift schedule ranged from 1 to 2977. Most systems employed fewer than 100 people. The majority of rotas were regular, rotating systems. The most common shift durations were 8 or 12 h. Compared to earlier surveys of shiftwork prevalence in certain industries there appeared to be a substantial increase over the past 3 decades in the proportion of the workforce who work shifts. Information about the average numbers of hours worked per week on major system types is given. In addition, data for the range of shifts per cycle, the distribution of shifts and distributions of their start and end times are presented.

The impact of early and late shift changeovers on sleep, health, and well-being in 8- and 12-hour shift systems

The effects on industrial shift workers of the timing of the changeover from the night to morning shift and of the length of the shift were examined. Two groups changed over at 6 a.m. and worked either 8-hr or 12-hr shift systems; the other 2 groups changed over at 7 a.m., working either 8- or 12-hr systems. Night sleeps between consecutive shifts that started at 6 a.m. were shorter and more disrupted than those starting at 7 a.m. Day sleeps following night shifts that finished at 6 a.m. were longer and less disrupted than those finishing at 7 a.m. Early starts were associated with poorer psychological and physical health. These effects of changeover time are considered in relation to the circadian rhythms in sleep duration and propensity. Although several measures favored 12-hr shifts, physical health indicators appeared to favor 8-hr systems, especially in combination with late changeovers. However, the observed effects of shift length on chronic outcome measures are somewhat inconsistent with previous research findings.

Effects of the endogenous clock and sleep time on melatonin, insulin, glucose and lipid metabolism

This study was undertaken to determine whether the internal clock contributes to the hormone and metabolic responses following food, in an experiment designed to dissociate internal clock effects from other factors. Nine female subjects participated. They lived indoors for 31 days with normal time cues, including the natural light: darkness cycle. For 7 days they retired to bed from 0000 h to 0800 h. They then underwent a 26-h 'constant routine' (CR) starting at 0800 h, being seated awake in dim light with hourly 88 Kcal drinks. They then lived on an imposed 27-h day (18 h of wakefulness, 9 h allowed for sleep), for a total of 27 days. A second 26-h CR, starting at 2200 h, was completed. During each CR salivary melatonin and plasma glucose, triacylglycerol (TAG), non-essential fatty acids (NEFA), insulin, gastric inhibitory peptide (GIP) and glucagon-like peptide-1 (GLP-1) were measured hourly. Melatonin and body temperature data indicated no shift in the endogenous clock during the 27-h imposed schedule. Postprandial NEFA, GIP and GLP-1 showed no consistent effects. Glucose, TAG and insulin increased during the night in the first CR. There was a significant effect of both the endogenous clock and sleep for glucose and TAG, but not for insulin. These findings may be relevant to the known increased risk of cardiovascular disease amongst shift workers.

Light of domestic intensity produces phase shifts of the circadian oscillator in humans

Twelve subjects have been studied in a chamber that isolated them from external noise and lighting. After several control days, one group (n = 6) was subjected to 18 x 27-h 'days' and the other to 11 x 30-h 'days'. Sleep was in the dark, and awake times were spent in normal domestic lighting (150-500 lux). Rectal temperature and wrist actimetry were measured throughout, and the phase of the circadian oscillator was inferred from that of the temperature data, purified to remove direct effects of activity. During the experimental 'days' the rhythms showed a mean period of 24.4 h. A detailed examination of the phase shifts from one day to the next showed that small advances and delays were superimposed upon this drift. Moreover, the mean size and direction of these shifts depended upon the time of exposure to lighting relative to the temperature minimum, as would be predicted from a phase-response curve.

Work shift duration: a review comparing eight hour and 12 hour shift systems

OBJECTIVES

Shiftwork is now a major feature of working life across a broad range of industries. The features of the shift systems operated can impact on the wellbeing, performance, and sleep of shiftworkers. This paper reviews the current state of knowledge on one major characteristic of shift rotas-namely, shift duration. Evidence comparing the relative effects of eight hour and 12 hour shifts on fatigue and job performance, safety, sleep, and physical and psychological health are considered. At the organisational level, factors such as the mode of system implementation, attitudes towards shift rotas, sickness absence and turnover, overtime, and moonlighting are discussed.

METHODS

Manual and electronic searches of the shiftwork research literature were conducted to obtain information on comparisons between eight hour and 12 hour shifts.

RESULTS

The research findings are largely equivocal. The bulk of the evidence suggests few differences between eight and 12 hour shifts in the way they affect people. There may even be advantages to 12 hour shifts in terms of lower stress levels, better physical and psychological wellbeing, improved durations and quality of off duty sleep as well as improvements in family relations. On the negative side, the main concerns are fatigue and safety. It is noted that a 12 hour shift does not equate with being active for only 12 hours.

CONCLUSIONS

There can be considerable extension of the person's time awake either side of the shift. However, the effects of longer term exposure to extended work days have been relatively uncharted in any systematic way. Longitudinal comparative research into the chronic impact of the compressed working week is needed.

Black times: temporal determinants of transport safety

This paper is concerned with whether transport accident risk tends to peak at particular times, in relation to both time of day and time on task, and with the underlying causes of such peaks. Macro-analyses confirmed the presence of a clear circadian (ca 24 hour) rhythm in road accident risk with a major peak at ca 03:00 but suggested that this rhythm could not be entirely accounted for in terms of drivers falling asleep at the wheel. Sleep propensity clearly shows a pronounced circadian rhythm and performance efficiency in wakeful subjects shows a similar trend implying that the 03:00 road accident peak may simply reflect lowered performance capabilities. However, there are 'residual' peaks in accidents at certain times of day that are difficult to account for in terms of circadian rhythmicity. It is suggested that these may reflect a time on task effect which shows a pronounced, but transient, 2-4 hour peak in risk. Only when individuals had been on duty for 12 hours or more did the risk exceed that found during the 2-4 hour peak. While an explanation for this transient peak is offered, the underlying reason for it is, as yet, uncertain and clearly warrants investigation in view of its practical implications. It is concluded that there are 'black times' when accidents are far more likely and that there is a strong need to investigate possible countermeasures.

Models of shiftwork and health: an examination of the influence of stress on shiftwork theory

This paper critically reviews models of shiftwork and health and provides a historical overview of changes in the conceptualization of the association between them. Models are hypothetical and conceptually broad, becoming more so as they move away from linear, chronobiological to multidirectional, psychological conceptualizations. We attribute this tendency to the use of stress frameworks to explain the relationship between shiftwork and health. We assess the usefulness of stress as an explanatory concept in terms of how it affects shiftwork research and practice and make recommendations for future practice and theory development.

The three-process model of alertness and its extension to performance, sleep latency, and sleep length

This paper summarizes a mathematical/computer model for predicting alterness/performance in daily living. The model uses sleep data as input and contains a circadian and a homeostatic component (amount of prior wake and amount of prior sleep), which are summed to yield predicted alertness (on a scale between 1 and 16) as well as performance on monotonous tasks. The model includes an identification of levels at which the risk of performance/ alertness impairment starts, as well as prediction of sleep latency and time of awakening of sleep episodes. It is suggested that the model may be used to evaluate work/rest schedules in terms of sleep-related safety risks.

Complex interaction of the sleep-wake cycle and circadian phase modulates mood in healthy subjects

BACKGROUND

Several studies of healthy volunteers have revealed that subjective mood may vary with the duration of prior wakefulness and with the time of day. However, in these studies, the effects of extended wakefulness and circadian phase remained confounded, and the interaction of these 2 processes could not be assessed quantitatively.

METHODS

In the present study, a total of 24 healthy young subjects (16 men, 8 women) lived on a 30-hour sleep-wake schedule for 19 to 23 days or on a 28-hour sleep-wake schedule for 33 to 36 days; both schedules induced desynchrony between the subjects' sleep-wake cycle and their endogenous circadian pacemaker. Subjective mood was assessed by 2 types of visual analog scales, which were administered twice every 2 hours and every 20 minutes, respectively, during all scheduled wakefulness episodes. A circadian phase and an interval elapsed since awakening were attributed to each data point, and circadian and wake-dependent fluctuations of mood were assessed.

RESULTS

A significant variation of mood with circadian phase was observed, but no reliable main effect of the duration of prior wakefulness was found. A statistically significant interaction of circadian and wake-dependent fluctuations was evident; when the analysis was restricted to specific circadian phases, mood improved, deteriorated, or remained stable with the duration of prior wakefulness.

CONCLUSIONS

These results indicate that, in healthy young subjects, subjective mood is influenced by a complex and nonadditive interaction of circadian phase and duration of prior wakefulness. The nature of this interaction is such that moderate changes in the timing of the sleep-wake cycle may have profound effects on subsequent mood.

A preliminary investigation into individual differences in the circadian variation of meal tolerance: effects on mood and hunger

A forced desynchrony methodology was used to assess postprandial blood glucose in 9 female volunteers during a 3-h period following a mixed meal presented at four times of day (08:00, 14:00, 20:00, 02:00). The influence of time of day on the postmeal glucose responses was evaluated by calculating the area under the curve, largest increase, time taken to reach peak, and fasting level. Circadian variations in meal tolerance were found for the area under the curve and largest increase, responses were greater (indicating poorer meal tolerance) in the evening than the morning. Fasting blood glucose exhibited diurnal variation although in the opposite direction to meal tolerance; levels were higher in the morning than the evening. Time taken to reach peak levels was not modulated by circadian rhythmicity. Estimates of the timing of poorest meal tolerance and the magnitude of this intolerance were computed for each subject. Individual differences in the magnitude of meal intolerance were found to influence hunger and self-reported calmness. Subjects with good tolerance had rhythms in both calmness and hunger, which were not found in those with poor tolerance. Subjects with good tolerance also tended to rate themselves as feeling more calm. These mood and hunger effects may result from differences in insulin resistance, which is hypothesized to underlie the circadian variations in meal tolerance.

Comparison of eight and 12 hour shifts: impacts on health, wellbeing, and alertness during the shift

OBJECTIVES

The generally agreed view is that there is no ideal shift system, and that most systems will have both advantages and disadvantages. As such, attention has been placed on trying to identify good and bad features of shift systems, with a view to minimising the possible ill health as a consequence of shiftwork. The present study focuses on the duration of the shift and looks at the implications for individual health, wellbeing, and alertness during the shift of extending the shift from the traditional eight hours to 12.

METHODS

Two groups of chemical workers, one working 12 hour shifts and the other working eight hour shifts, took part. All completed a modified version of the standard shiftwork index (SSI), a set of self reported questionnaires related to health and wellbeing.

RESULTS

The two groups did not differ on most outcome measures, although the differences that did exist suggested advantages for the 12 hour shift workers over the eight hour shift workers; with the notable exception of rated alertness at certain times of day.

CONCLUSIONS

The results are explained in terms of the design of the 12 hour shift system and the specific sequencing of shifts that seem to minimise the potential for the build up of fatigue. Although the current data moderately favour 12 hour shifts, a cautionary note is sounded with regard to the implications of the alertness ratings for performance and safety.

The shape of the endogenous circadian rhythm of rectal temperature in humans

Fourteen healthy subjects have been studied in an isolation unit while living on a 30h "day" (20h awake, 10h asleep) for 14 (solar) days but while aware of real time. Waking activities were sedentary and included reading, watching television, and so forth. Throughout, regular recordings of rectal temperature were made, and in a subgroup of 6 subjects, activity was measured by a wrist accelerometer. Temperature data have been subjected to cosinor analysis after "purification," a method that enables the endogenous (clock-drive) and exogenous (activity-driven) components of the circadian rhythm to be assessed. Moreover, the protocol enables effects due to the circadian rhythm and time-since-waking to be separated. Results showed that the masking effects on body temperature exerted by the exogenous factors appeared to be less than average in the hours before and just after the peak of the endogenous temperature rhythm. This has the effect of producing a temperature plateau rather than a peak during the daytime. The implications of this for mental performance and sleep initiation are discussed.

The difference between activity when in bed and out of bed. III. Nurses on night work

Eight nurses have been studied during rest days and three successive night shifts. Measurements of wrist activity have been made and used to assess the extent to which the pattern of daily activity changes between control (rest) days and days involving night work. One analysis considered wrist activity during time spent in bed; this appears to decrease in parallel with the amount of time in bed that is lost during night work but, when this effect is corrected for, there is greater activity during time spent in bed in the daytime compared with control days (when time in bed is during the night). The dichotomy of activity (between lower values during time spent in bed and higher values when out of bed) also decreases if time in bed is during the daytime while on night shifts. These changes in the amount of wrist activity and the dichotomy between activity in and out of bed are related to the changed quality and quantity of sleep that has been measured by self-report questionnaires and the sleep EEG. It is concluded that results from wrist actimetry can provide valuable information regarding the process of adjustment to night work, and that its convenience (to subject and experimenter), coupled with the new analytical approaches described here, make it a viable method for field studies.

The difference between activity when in bed and out of bed. II. Subjects on 27-hour "days"

Nine healthy subjects have been studied while exposed to the normal alternation of light and dark, but with their sleep and activity pattern adjusted to a 27-h "day" for 17 imposed "days." Rectal temperature showed clearly the competing influences of 27-h and 24-h components, and these were separated by the method of "purification." The method indicated that the endogenous component had a constant amplitude throughout the experiment and remained entrained to solar (24-h) time; by contrast, the exogenous component followed the imposed 27-h "day" and increased rectal temperature in proportion to the amount of subjects' activity. Wrist movement was used to assess activity while in bed (attempting sleep) and out of bed (when naps were forbidden). While these results confirmed adherence of the subjects to the imposed 27-h "days," they also showed that the dichotomy between "out of bed" activity and "in bed" inactivity depended on the phase relationship between endogenous (24h) and exogenous (27h) components. Thus, the dichotomy was highest and was equal to that during control days (with a conventional 24-h life-style) when the two components were in phase and lowest when the solar and imposed day were in antiphase. This was due to changes in activity, both during time spent in bed and out of bed. We confirm that this protocol can produce valuable information about the properties of the circadian system in humans and the value of the process of purification of temperature data. We have established also that the very simple and noninvasive measurement of wrist movement, coupled with its use to calculate dichotomy indices, provides valuable information that both confirms and extends the results obtained from the more conventional (but also more invasive) measurement of rectal temperature.

Predicting sleep latency from the three-process model of alertness regulation

This paper presents a modification of the quantitative "three-process model of alertness regulation" to predict sleep latency in connection with irregular sleep/wake patterns. This model uses a circadian and a homeostatic component (sleep loss) that are summed to yield predicted alertness (on a scale of 1 to 20) across a specified time span. The timing of sleep from two studies of irregular sleep were used as input to the model. The predicted alertness at bedtime was regressed on empirical sleep latency from two studies. The maximum R2 (0.88) was reached for an exponential function, with the model acrophase set to 2048. The predictions were cross validated on another set of sleep latency data from an irregular sleep study and a maximum R2 of 0.65 was obtained. In both studies, the prediction from the model explained more variance that did self-rated alertness at bedtime. Cross validation was also carried out successfully with published data from two studies of shift work. It was concluded that sleep latency on irregular schedules may be predicted with accuracy from knowledge of the prior sleep/wake pattern. This may have practical consequences for rest/activity management.

The difference between activity when in bed and out of bed. I. Healthy subjects and selected patients

The activity records of five groups of healthy or ill subjects have been measured for 4-26 days by an accelerometer placed on the nondominant wrist. These data, together with a record of times retiring to/rising from bed, have been used to produce a series of dichotomy indices for comparing the amounts of activity when in bed and out of bed. Reliable differences between individuals were found, with healthy subjects showing a greater degree of dichotomy than one subject with delayed sleep phase syndrome or three subjects with colorectal cancer. The method is convenient for extended data collection and offers the possibility of describing an individual's activity profile in a variety of circumstances.

Predicting duration of sleep from the three process model of regulation of alertness

OBJECTIVES

Irregular working hours severely disturb sleep and wakefulness. This paper presents a modification of the quantitative (computerised) three process model of regulation of alertness to predict duration of sleep in connection with irregular sleep patterns.

METHODS

The model uses a circadian "C" (sinusoidal) and homeostatic "S" (exponential) component (the duration of previous periods awake and asleep), which are summed to yield predicted alertness (on a scale of 1-16). It assumes that waking from sleep will occur at a given alertness level (S' + C') when recuperation is complete. Variables of electroencephalographic duration of sleep from two studies of irregular sleep were used to model the S and C variables in a regression approach to maximise prediction. The model performance was cross validated against published field and laboratory data.

RESULTS

The model parameters were defined with a high degree of precision R2 = 0.99 and the validation yielded similar values R2 = 0.98-0.95, depending on the acrophase. The paper also describes a simplified graphical version of the computation model seen as a two dimensional duration of sleep nomogram.

CONCLUSION

The model seems to predict group means for duration of sleep with high precision and may serve as a tool for evaluating work and rest schedules to reduce risks of sleep disturbances.

Maintaining safety and high performance on shiftwork

This review of the shiftwork area focuses on aspects of safety and productivity. It discusses the situations in which shiftworker performance is critical, the types of problem that can develop and the reasons why shiftworker performance can be impaired. The review ends with a discnssion of the various advantages and disadvantages of several shift rotation systems, and of other possible solutions to the problem.