Post-lunch nap as a worksite intervention to promote alertness on the job.

A worksite study was conducted to examine whether a 15-min nap during a post-lunch rest period would affect subsequent alertness, performance, and nocturnal sleep in eight factory workers under a 3-week protocol. Subjects were asked to take the nap at 12:30 h on a reclining chair during the nap week, and to remain awake during the no-nap week. The order of these 2 weeks was counterbalanced between the subjects. During the third, follow-up week, each subject determined whether or not she/he would nap. Alertness on the job and nocturnal sleep were assessed using a sleep diary. Wrist activity was also recorded during sleep at night. Choice reaction time task (RT) was performed at 10:00 and 15:00 h every day of the nap week and every other day of the no-nap and follow-up weeks. Perceived alertness was significantly higher in the afternoon after nap than after no nap at the end of the week. Similar effects were observed during the follow-up week where almost half of the subjects napped. No significant differences between the three weeks were found for RT performance or nocturnal sleep. Workers' attitudes toward the nap were favourable. Although further intervention research is required, our results suggest that post-lunch napping may have the potential to promote daytime alertness at work.     

The use of prophylactic naps and caffeine to maintain performance during a continuous operation

After a normal baseline night of sleep and a morning of baseline test performance, 24 young adult male subjects returned to bed from 16:00-20:00 prior to a 24?h period of sleep loss. Twelve subjects received caffeine 200?mg at 01:30 and 07:30. Performance tests (correctly completed addition problems, vigilance sensitivity, and logical reasoning correct responses) all indicated maintenance of baseline performance levels in the caffeine group after administration of caffeine while performance declined in the placebo group. Similar results were found for the Multiple Sleep Latency Test and Oral Temperature, which both remained near baseline levels throughout the observation period in subjects receiving caffeine. The results indicated that the combination of a prophylactic nap and caffeine was more effective in maintaining nocturnal alertness and performance than was the nap alone. Of more interest was the fact that the group which was given the combination of nap and caffeine was able to maintain alertness and performance at very close to baseline levels throughout a 24?h period without sleep.     

The effect of night-time naps on recovery from fatigue following night work

Abstract

A questionnaire was performed in order to investigate the effect of naps during duty on recovery from fatigue. Studies were performed on 12 male computer operators in each of two chemical plants working a four-team three-shift system. In one of the plants, the shift workers were able to take a 2 h nap during the night shift (nap group). In the other plant, no nap was taken (no-nap group). Before and after the two consecutive night shifts, both the nap and no-nap groups greatly extended their night sleeps, but the daytime sleep taken by the no-nap group during this period was significantly longer than that of the nap group on both the first and second days. No significant difference was found when comparing the length of the day sleep of the no-nap group with the total sleeping time (night-time nap plus subsequent day sleep) of the nap group. Therefore a night-time nap enables part of the essential sleep to be taken in advance of the day sleep following night work. During night work, both tbe nap and no-nap groups exhibited an increase in the sleepiness scores and also in the subjective feelings of fatigue concerning the complaints related to drowsiness, dullness and difficulty in concentration. However, it was found that for the no-nap group these effects continued for a large part of the recovery period following night work. It can therefore be surmised that naps taken during night-time work can be to a certain extent aid recovery from the fatigue caused by that work.     

Innovative working schedule: introducing one short nap during the night shift

In order to test the possible long-term effects of the implementation of a short nap during night shifts, an experiment was conducted over a period of 1 year with 12 volunteer shiftworkers operating in an industrial plant. They were authorized, under certain conditions, to use individual sleeping areas, for a maximum of 1 hour, between 23h30 and 3h30. The participants were asked to fill in a short questionnaire every day during the entire study. The questions concerned the schedule of the main sleep period, the afternoon nap and the night-time nap, if any, as well as the evaluation of mood and the quality of work. This daily questionnaire was supplemented by an extensive questionnaire applied every 2 months in order to assess the main changes introduced in the life of the participants by this new working schedule. Results showed that this new organization introduced a general satisfaction about the quality and the easiness of the work at night. The vigilance level was considered to be higher during the hours following the nap. The efficacy of the nap time progressively increased for most subjects. The general quality of life improved for most subjects. While a few of them considered that falling asleep was less easy on the following morning at home, the statistical analysis did not show any detrimental effect of the short rest period on the length of the immediately consecutive main sleep period. However, different statistical analyses allow us to reveal significant differences between the main sleep durations following the night shift compared with those following both the afternoon shift and the resting period. The main sleep duration following the night shift was not statistically different from that of the morning shift. These results are very encouraging. A short nap during the night shift can be considered as a positive way to counteract the low level of vigilance that normally occurs during the late part of the night.     

Innovative working schedule: introducing one short nap during the night shift.

In order to test the possible long-term effects of the implementation of a short nap during night shifts, an experiment was conducted over a period of 1 year with 12 volunteer shiftworkers operating in an industrial plant. They were authorized, under certain conditions, to use individual sleeping areas, for a maximum of 1 hour, between 23h30 and 3h30. The participants were asked to fill in a short questionnaire every day during the entire study. The questions concerned the schedule of the main sleep period, the afternoon nap and the night-time nap, if any, as well as the evaluation of mood and the quality of work. This daily questionnaire was supplemented by an extensive questionnaire applied every 2 months in order to assess the main changes introduced in the life of the participants by this new working schedule. Results showed that this new organization introduced a general satisfaction about the quality and the easiness of the work at night. The vigilance level was considered to be higher during the hours following the nap. The efficacy of the nap time progressively increased for most subjects. The general quality of life improved for most subjects. While a few of them considered that falling asleep was less easy on the following morning at home, the statistical analysis did not show any detrimental effect of the short rest period on the length of the immediately consecutive main sleep period. However, different statistical analyses allow us to reveal significant differences between the main sleep durations following the night shift compared with those following both the afternoon shift and the resting period. The main sleep duration following the night shift was not statistically different from that of the morning shift. These results are very encouraging. A short nap during the night shift can be considered as a positive way to counteract the low level of vigilance that normally occurs during the late part of the night.     

Inversion of the Sleep Wakefulness Pattern: Effects on Circadian Variations in Psychophysiological Activation

Abstract

Thirty-six habitually dayworking railway repairmen were exposed to a 3 week period of nightwork. The subjects were studied with respect to circadian rhythms in catecholamine excretion, body temperature, subjective alertness and mood. For half the group the measurements covered one 24 h period before nightwork, the first week of night work, the third week of night work, and the first week after return to day work. For the other half measurements were made during the first and third day week after the night work. During day work weeks all variables exhibited pronounced circadian variation, peaking in the early afternoon, with the exception of body temperature which reached its maximum in the evening. During the first week of night work the day-oriented pattern of adrenaline excretion persisted but the mean 24 h level was increased and day sleep levels were very high. By the third week of night work thecircadian pattern had flattened out at a very low mean level. For noradrenaline excretion considerable adjustment (comparable to an inversion) to night work was seen with high night values. For body temperature, selfrated alertness and mood circadian functions flattened out during night work. It was concluded that all variables were strongly affected by the exposure to night work and that adrenaline excretion indicated a stress response of the organism. With reference to other studies it was also concluded that adrenaline excretion is not easily phase-shifted through a three week spell on night work, while noradrenaline in contrast appears to adjust very rapidly.     

Short nap versus short rest: recuperative effects during VDT work

The effects of a 20-min nap during 2 h of visual display terminal (VDT) work were examined. Ten young healthy adults took a 20-min nap or a 20-min rest 1 h after VDT work, followed by another 1 h of VDT work. A 20-min rest temporarily restored subjective sleepiness, but it deteriorated during the additional 1 h of work. In contrast, a 20-min nap maintained subjective alertness and performance level at a higher level and mental fatigue at a lower level for the additional 1 h of work. These results suggest that a short nap would be useful to both fatigue recovery and fatigue prevention during continuous VDT work. The present findings may provide a new work/rest strategy.     

Short nap versus short rest: recuperative effects during VDT work

The effects of a 20-min nap during 2 h of visual display terminal (VDT) work were examined. Ten young healthy adults took a 20-min nap or a 20-min rest I h after VDT work, followed by another 1 h of VDT work. A 20-min rest temporarily restored subjective sleepiness, but it deteriorated during the additional 1 h of work. In contrast, a 20-min nap maintained subjective alertness and performance level at a higher level and mental fatigue at a lower level for the additional 1 h of work. These results suggest that a short nap would be useful to both fatigue recovery and fatigue prevention during continuous VDT work. The present findings may provide a new work/rest strategy.     

Alertness of night nurses: two shift systems compared

The alertness of hospital trainee nurses during their night shift work was assessed by recording performance at night on an arousal-sensitive unprepared simple reaction time task. One group carried out a number of separate weeks on night shift throughout their three-year course. Here performance fell from first to seventh day of the week on night shift, implying progressive sleep deprivation. Another group covered their night work by a single three-month 'permanent' night shift of four (or three) nights on and three (or four) days off each week. Here initial performance level fell by the 45th night but had returned to normal by the last (90th) night. In both systems individuals varied considerably in their ability to maintain performance during sustained night work. These results strengthen the case for permanent night shifts, with careful selection of personnel, as a means of organizing night nursing in hospitals.     

Do subjective symptoms predict our perception of jet-lag?

A total of 39 subjects were studied after a flight from the UK to either Sydney or Brisbane (10 time-zones to the east). Subjects varied widely in their age, their athletic ability, whether or not they were taking melatonin, and in their objectives when in Australia. For the first 6 days after arrival, subjects scored their jet-lag five times per day and other subjective variables up to five times per day, using visual analogue scales. For jet-lag, the scale was labelled 0= no jet-lag to 10= very bad jet-lag; the extremes of the other scales were labelled ?5 and +5, indicating marked changes compared with normal, and the centrepoint was labelled 0 indicating ‘normal’. Mean daily values for jet-lag and fatigue were initially high (+ 3.65 ± 0.35 and + 1.55 ± 0.22 on day 1, respectively) and fell progressively on subsequent days, but were still raised significantly (p < 0.05) on day 5 (fatigue) or day 6 (jet-lag). In addition, times of waking were earlier on all days. By contrast, falls in concentration and motivation, and rises in irritability and nocturnal wakings, had recovered by day 4 or earlier, and bowel activity was less frequent, with harder stools, on days 1 and 2 only. Also, on day 1, there was a decrease in the ease of getting to sleep (? 1.33 ± 0.55), but this changed to an increase from day 2 onwards (for example, + 0.75 ± 0.25 on day 6). Stepwise regression analysis was used to investigate predictors of jet-lag. The severity of jet-lag at all the times that were measured was strongly predicted by fatigue ratings made at the same time. Its severity at 08:00 h was predicted by an earlier time of waking, by feeling less alert 30 min after waking and, marginally, by the number of waking episodes. Jet-lag at 12:00 and 16:00 h was strongly predicted by a fall of concentration at these times; jet-lag at mealtimes (12:00, 16:00 and 20:00 h) was predicted by the amount of feeling bloated. Such results complicate an exact interpretation that can be placed on an assessment of a global term such as jet-lag, particularly if the assessment is made only once per day.     

Cardio-respiratory performance of porters carrying loads on a treadmill

Four workers, accustomed to load carrying, carried loads (no load, 60, 80 and 100?kg) at 0·89 and 1·03?m s^?1 on a treadmill during the pre- and post-lunch period respectively, to obtain information regarding the degree of exhaustion from similar load carrying in their usual working situation. The rate of work is expressed in Watts. During pre- and post-lunch work there was a rise of 6 to 71 of pulmonary ventilation with each increment of 163 W. beyond the initial work level. The oxygen consumptions in the pre-lunch period were 15 to 27% higher, suggesting a greater anaerobic metabolism in the post-lunch period. The average work-pulse-rate varied from 116 to 162 beats min^?. Cardiac demand for a particular load is more or less constant, irrespective of time of day. During the pre-lunch period the work-pulse-sum was 78, 71, 65 and 54 beats per 163 W for respective four loads;-where-as in the post-lunch period, except the initial load, it varied only between 56 to 60 beats per 163 W. indicating a proportionate rise of pulse beats during post-lunch work. The 1st, 2nd and 3rd min recovery pulses of the 3rd and 4th loads were much beyond a level sustainable throughout the day. The recovery-pulse-sum varied from 39 to 104 beats and 36 to 117 beats min^? during the pre- and post-lunch period respectively, which were mostly beyond the permissible endurance limit. The oxygen-pulse for similar loads were 18 to 44% higher in the pre-lunch period, indicating better ability to work. To arrive at a reasonable load and rate of work, simple and multiple regression equations have been evolved. Indian workers may be allowed to work up to 1140 W (i.e. 50 to 55% of maximum oxygen uptake).     

The role of naps in alleviating sleepiness during an irregular sleep-wake schedule

Abstract

Four groups of four subjects have been studied in an isolation unit on an irregular schedule of sleep and waking. Sleep periods of 6h duration were taken at irregular times during the 9-day protocol; they were arranged such that the waking periods lasted 6, 12 or 18 h and were also in an irregular sequence. One-hour naps were taken after 6 and 12 h of waking if the next sleep was not due then. Just before either a nap or a full sleep, subjects assessed their sleepiness and, on rising, they assessed how well sleep had been initiated and maintained. A mathematical model was developed which enabled the effects upon sleepiness of circadian rhythmicity, of the length of the waking period since the last full sleep (time-since-sleep), and of the subjective value of the previous full sleep or nap to be independently quantified. Results showed that there was a tendency for sleepiness to increase, in some cases quite markedly, as the irregular schedule proceeded. There were also effects upon sleepiness due to circadian changes and the amount of time since the last full sleep. These two effects were similar in size and larger than the benefits to be derived from a previous nap or full sleep that had been assessed at the time as having been a good one. We conclude that one-hour naps can play a small role in decreasing an individual's sleepiness and suggest possible means by which their subjective value might be increased.     

The relationship between subjective and objective sleepiness and performance during a simulated night-shift with a nap countermeasure

The aim of the present study was to investigate the relationship between perceived and actual sleepiness and performance during a simulated night-shift that included a 30-min night-nap as an on-duty sleepiness countermeasure. Twenty-four healthy young adults (nine males, fifteen females) participated in a repeated measures design comprising two experimental conditions: no night-nap and 30-min night-nap. Both groups were given a 2-h prophylactic afternoon sleep opportunity (1500–1700 h). Measures of subjective sleepiness (Stanford Sleepiness Scale, Karolinska Sleepiness Scale and Visual Analogue Scale), objective sleepiness (sleep latency tests), objective performance (Symbol–Digit Substitution Task) and reaction time (Psychomotor Vigilance Task) were taken before the night-nap (0230 h) and at several intervals post-nap. Time–series correlation analyses indicated that subjective sleepiness was less correlated with objective sleepiness and objective performance when participants were given a 30-min night-nap. However subjective sleepiness and reaction time performance was strongly correlated in both conditions, and there was no significant difference between the nap and no-nap conditions. Consistent with previous research, results of the present study indicate that subjective and objective indicators of sleepiness and performance may not always correspond, and this relationship may be reduced by the inclusion of a night-nap.     

The relationship between subjective and objective sleepiness and performance during a simulated night-shift with a nap countermeasure

The aim of the present study was to investigate the relationship between perceived and actual sleepiness and performance during a simulated night-shift that included a 30-min night-nap as an on-duty sleepiness countermeasure. Twenty-four healthy young adults (nine males, fifteen females) participated in a repeated measures design comprising two experimental conditions: no night-nap and 30-min night-nap. Both groups were given a 2-h prophylactic afternoon sleep opportunity (1500-1700 h). Measures of subjective sleepiness (Stanford Sleepiness Scale, Karolinska Sleepiness Scale and Visual Analogue Scale), objective sleepiness (sleep latency tests), objective performance (Symbol-Digit Substitution Task) and reaction time (Psychomotor Vigilance Task) were taken before the night-nap (0230 h) and at several intervals post-nap. Time-series correlation analyses indicated that subjective sleepiness was less correlated with objective sleepiness and objective performance when participants were given a 30-min night-nap. However subjective sleepiness and reaction time performance was strongly correlated in both conditions, and there was no significant difference between the nap and no-nap conditions. Consistent with previous research, results of the present study indicate that subjective and objective indicators of sleepiness and performance may not always correspond, and this relationship may be reduced by the inclusion of a night-nap.     

Vigilance on the civil flight deck: incidence of sleepiness and sleep during long-haul flights and associated changes in physiological parameters

The study investigated sleepiness and sleep in aircrew during long-haul flights. The objectives were to identify loss of alertness and to recommend a practical approach to the design of an alerting system to be used by aircrew to prevent involuntary sleep. The flights were between London and Miami, covering both day- and night-time sectors, each with a duration of ~9 h. The subjects were 12 British Airways pilots. Various physiological variables were measured that could potentially be used to indicate the presence of drowsiness and involuntary sleep: brain electrical activity (electroencephalogram, EEG), eye movements via the electro-oculogram (EOG), wrist activity, head movements and galvanic skin resistance. The EEG and EOG identified sleepiness and sleep, as well as being potential measures on which to base an alarm system. Ten pilots either slept or showed evidence of sleepiness as assessed by the EEG and EOG. Many of the episodes of sleepiness lasted < 20 s, which could mean that the subjects were unaware of their occurrence and of the potential consequences on performance and vigilance. All physiological parameters showed changes during sleep, although only the EEG and EOG were modified by sleepiness. During sleep, skin resistance was increased, and wrist activity and head movements were absent for long periods. The study indicated that the measurement of eye movements (either alone or in combination with the EEG), wrist activity or head movement may be used as the basis of an alarm system to prevent involuntary sleep. Skin resistance is considered to be unsuitable, however, being related in a more general way to fatigue rather than to sleep episodes. The optimal way to monitor the onset of sleep would be to measure eye movements; however, this is not feasible in the flight deck environment at the present time due to the intrusive nature of the recording methodology. Wrist activity is therefore recommended as the basis of an alertness alarm. Such a device would alert the pilot after ~4–5 min of wrist inactivity, since this duration has been shown by the present study to be associated with sleep. The possibility that sleep inertia (reduced alertness immediately after awakening from sleep) could follow periods of sleep lasting 5 min needs to be considered. The findings reported here might be applicable to other occupational environments where fatigue and sleepiness are known to occur.     

Vigilance on the civil flight deck: incidence of sleepiness and sleep during long-haul flights and associated changes in physiological parameters

The study investigated sleepiness and sleep in aircrew during long-haul flights. The objectives were to identify loss of alertness and to recommend a practical approach to the design of an alerting system to be used by aircrew to prevent involuntary sleep. The flights were between London and Miami, covering both day- and night-time sectors, each with a duration of approximately 9 h. The subjects were 12 British Airways pilots. Various physiological variables were measured that could potentially be used to indicate the presence of drowsiness and involuntary sleep: brain electrical activity (electroencephalogram, EEG), eye movements via the electro-oculogram (EOG), wrist activity, head movements and galvanic skin resistance. The EEG and EOG identified sleepiness and sleep, as well as being potential measures on which to base an alarm system. Ten pilots either slept or showed evidence of sleepiness as assessed by the EEG and EOG. Many of the episodes of sleepiness lasted < 20 s, which could mean that the subjects were unaware of their occurrence and of the potential consequences on performance and vigilance. All physiological parameters showed changes during sleep, although only the EEG and EOG were modified by sleepiness. During sleep, skin resistance was increased, and wrist activity and head movements were absent for long periods. The study indicated that the measurement of eye movements (either alone or in combination with the EEG), wrist activity or head movement may be used as the basis of an alarm system to prevent involuntary sleep. Skin resistance is considered to be unsuitable, however, being related in a more general way to fatigue rather than to sleep episodes. The optimal way to monitor the onset of sleep would be to measure eye movements; however, this is not feasible in the flight deck environment at the present time due to the intrusive nature of the recording methodology. Wrist activity is therefore recommended as the basis of an alertness alarm. Such a device would alert the pilot after approximately 4-5 min of wrist inactivity, since this duration has been shown by the present study to be associated with sleep. The possibility that sleep inertia (reduced alertness immediately after awakening from sleep) could follow periods of sleep lasting 5 min needs to be considered. The findings reported here might be applicable to other occupational environments where fatigue and sleepiness are known to occur.     

Re-entrainment of Body Temperature in Experimental Shift-Work Studies

In a series of experimental shift work studies six subjects worked on continuous night shift for three weeks, four subjects worked on a 1-1-1 shift system (1st day morning shift, 2nd day afternoon shift, 3rd day night shift, 4th day off), and two subjects worked on an 2-2-2 shift system (the ‘metropolitan rota’). Rectal temperature was continuously recorded in each experiment.

The greatest changes in the circadian rhythm of body temperature occurred on the second night shift day, and during the first week of continuous night shift working. The changes involved both shifts in the phasing of the rhythm, and alterations in its form. The re-entrainment of the rhythm to its normal phasing took two or more days after two or more successive night shifts, but only one day after a single night shift. Considerable individual differences in the rhythm adjustment to night work were observed.

In a field validation of these findings, 34 shiftworkers in municipal gas and water supply undertakings measured their oral temperature every 2h both on and off duty. Although only very few temperature readings were obtained during sleep periods, the results confirmed, in general, those of the experimental studies.     

Performance and alertness on 8 h and 12 h rotating shifts at a natural gas utility

Abstract

An 8 h/5-7 day shift schedule was compared with a newly instituted 12 h/2-4 day schedule in this, our second worksite study of extended workshifts. Workers completed a performance/alertness test battery, and a questionnaire on sleep patterns and other personal habits, 2-4 times a week on all shifts. After 10 months adaptation to the 12 h shift schedule, there were decrements in performance/ alertness attributable to the extra 4 h on the extended shift. There were also reductions in sleep across the workweek which were most apparent on 12 h night shifts. The results are consistent with our first worksite study of 12 h shifts and indicate extra caution should be exercised when scheduling critical activities for extended workshifts, especially extended night shifts.     

Sleep schedules and peak times of oral temperature and alertness in morning and evening ‘types’

Abstract

The relation between circadian variables (oral temperature and subjective alertness) and sleep-awake schedules was explored as a function of a subjective preference index (Home and Ostberg 1976) which classifies subjects as ’morning’ or ‘evening’ type. Measurements of oral temperature and self-assessed alertness were obtained every 3 hours from rising time to bedtime over a 2 week period in 49 medical students. Sleep logs were kept by the students during the same period. Sleep schedules and alertness peak time, as well as the relative temporal location of alertness peak time and temperature peak time, differed in relation to the Home and Ostberg index. These results suggest that in normal conditions the coupling between temperature circadian rhythm and sleep-awake cycle differs in morning types and evening types.     

Do subjective symptoms predict our perception of jet-lag?

A total of 39 subjects were studied after a flight from the UK to either Sydney or Brisbane (10 time-zones to the east). Subjects varied widely in their age, their athletic ability, whether or not they were taking melatonin, and in their objectives when in Australia. For the first 6 days after arrival, subjects scored their jet-lag five times per day and other subjective variables up to five times per day, using visual analogue scales. For jet-lag, the scale was labelled 0 = no jet-lag to 10 = very bad jet-lag; the extremes of the other scales were labelled - 5 and + 5, indicating marked changes compared with normal, and the centrepoint was labelled 0 indicating 'normal'. Mean daily values for jet-lag and fatigue were initially high (+ 3.65 +/- 0.35 and + 1.55 +/- 0.22 on day 1, respectively) and fell progressively on subsequent days, but were still raised significantly (p < 0.05) on day 5 (fatigue) or day 6 (jet-lag). In addition, times of waking were earlier on all days. By contrast, falls in concentration and motivation, and rises in irritability and nocturnal wakings, had recovered by day 4 or earlier, and bowel activity was less frequent, with harder stools, on days 1 and 2 only. Also, on day 1, there was a decrease in the ease of getting to sleep (- 1.33 +/- 0.55), but this changed to an increase from day 2 onwards (for example, + 0.75 +/- 0.25 on day 6). Stepwise regression analysis was used to investigate predictors of jet-lag. The severity of jet-lag at all the times that were measured was strongly predicted by fatigue ratings made at the same time. Its severity at 08:00 h was predicted by an earlier time of waking, by feeling less alert 30 min after waking and, marginally, by the number of waking episodes. Jet-lag at 12:00 and 16:00 h was strongly predicted by a fall of concentration at these times; jet-lag at mealtimes (12:00, 16:00 and 20:00 h) was predicted by the amount of feeling bloated. Such results complicate an exact interpretation that can be placed on an assessment of a global term such as jet-lag, particularly if the assessment is made only once per day.