The Effects of Napping on Night Shift Performance February 2000 6
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DOT/FAA/AM-00/10 The Effects of Napping on Office of Aviation Medicine Washington, D.C. 20591 Night Shift Performance Pamela S. Della Rocco Carlos Comperatore Lynn Caldwell Crystal Cruz Civil Aeromedical Institute Federal Aviation Administration Oklahoma City, Oklahoma 73125 February 2000 Final Report This document is available to the public through the National Technical Information Service, Springfield, Virginia 22161. U.S. Department of Transportation Federal Aviation Administration NOTICE This document is disseminated under the sponsorship of the U.S. Department of Transportation in the interest of information exchange. The United States Government assumes no liability for the contents thereof. Technical Report Documentation Page 1. Report No. 2. Government Accession No. 3. Recipient's Catalog No. DOT/FAA/AM-00/10 4. Title and Subtitle 5. Report Date The Effects of Napping on Night Shift Performance February 2000 6. Performing Organization Code 7. Author(s) 8. Performing Organization Report No. Della Rocco, P.S., Comperatore, C., Caldwell, L., and Cruz, C. 9. Performing Organization Name and Address 10. Work Unit No. (TRAIS) FAA Civil Aeromedical Institute P.O. Box 25082 Oklahoma City, OK 73125 11. Contract or Grant No. 12. Sponsoring Agency name and Address 13. Type of Report and Period Covered Office of Aviation Medicine Federal Aviation Administration 14. Sponsoring Agency Code 800 Independence Ave., S.W. Washington, DC 20591 15. Supplemental Notes 16. Abstract This study represents a collaborative effort between the Federal Aviation Administration’s Civil Aeromedical Institute and the US Army Aeromedical Research Laboratory to investigate the effects of napping on the midnight shift as a potential countermeasure to sleepiness during the shift. The purpose of the present paper was to examine the patterns of performance degradation along with the subjective measures of mood, sleep quality, and sleepiness as a function of napping condition and time on task during the midnight shift. Sixty Air Traffic Control Specialists (ATCSs) were randomly assigned to one of the three midnight shift napping conditions: a long nap (LN) of 2 hours, a short nap (SN) of 45 minutes, and a no nap condition (NN). ATCSs completed a four-day protocol during which they worked three early morning shifts (0700-1500) followed by a rapid rotation to the midnight shift (2300-0700). Subjects completed three 1.5 hour test sessions (one session before the nap and 2 sessions after the nap) during the midnight shift involving two computer-based tasks: 1) the Air Traffic Scenarios Test (ATST), a task developed for selection of ATCSs, and 2) the Bakan, a test of vigilance. Data were analyzed using repeated measures analysis of variance and post-hoc multiple comparisons. Both cognitive performance and subjective measures of sleepiness supported the use of naps during the midnight shift. In fact, both the long nap of 2 hours and the short nap of 45 minutes resulted in better performance than no nap on the Bakan test at the end of the midnight shift. A dose-response relationship existed such that the long nap also resulted in better performance than the short nap. The ATST, on the other hand, was much less sensitive to differences in napping condition and even to the natural circadian trough, which would have been expected to affect all groups. Sleepiness ratings on the Stanford Sleepiness Scale suggested that, while sleepiness increased across the midnight shift for all groups, ratings were generally lower for the LN condition and were lower for males in the SN condition, when compared with the NN condition. The present study suggests that naps taken during the midnight shift could be useful as a countermeasure to performance decrement and sleepiness on the midnight shift. 17. Key Words 18. Distribution Statement Air Traffic Control Specialists, Naps, Shiftwork, Night Document is available to the public through the Shift, Performance, Vigilance, Sleepiness, Sleep Quality, National Technical Information Service, Mood Springfield, Virginia 22161 19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 22. Price Unclassified Unclassified 36 Form DOT F 1700.7 (8-72) Reproduction of completed page authorized i THE EFFECTS OF NAPPING ON NIGHT SHIFT PERFORMANCE Sleepiness on the first midnight shift of a work must change their sleep/wake schedule from day schedule is common among shiftworkers when their activity and night sleep to day sleep and night activity circadian rhythms are day-oriented. Effective coun- (Anch, Browman, Mitler, & Walsh, 1988). termeasures for sleepiness are important for employ- Research indicates that a major problem among ees in a safety critical job such as the Federal Aviation shift workers is disturbed sleep. Daytime sleep is Administration’s (FAA) Air Traffic Control Special- shorter than nighttime sleep and tends to be frag- ist (ATCS). The Human Factors Research Labora- mented (Torsvall, Akerstedt, Gillander, & Knutsson, tory (HFRL) at the Civil Aeromedical Institute 1989; Tilley, Wilkinson, Warren, Watson, & Drud, (CAMI) was asked by the Miami Air Route Traffic 1982). In addition, the order of slow wave sleep (SWS) Control Center to investigate sleepiness on the mid- and rapid eye movement (REM) sleep is disturbed, with night shift. They specifically requested information more REM sleep occurring at the beginning of the sleep about the possibility of using a scheduled nap as a period and more SWS occurring at the end, the opposite method to reduce sleepiness and maintain alertness of the natural SWS/REM pattern (Tilley et al., 1982). during this shift. Due to the disturbance in sleep, research shows that shift The shift schedules worked by ATCSs often mini- workers nap more frequently than daytime workers to mize the employee’s exposure to the midnight shift compensate for the sleep loss (cf Rosa, 1993; Akerstedt (Cruz & Della Rocco, 1995). ATCSs generally work & Torvsall, 1985). only one or two midnight shifts in a row. Thus, a Research also shows that night workers have in- circadian adaptation strategy of shifting the biological creased sleepiness during work, with most sleepiness clock to a night orientation is not practical in this occurring during the last half of the work shift population because of the time courses required to shift (Akerstedt, Torsvall, & Gillberg, 1982). This in- the clock to a night orientation and return back to a day crease in sleepiness during work leads to a decrease in orientation. An acutely administered coping strategy, performance (Mitler, Carskadon, Czeisler, Dement, such as scheduled napping, therefore, was a more rea- Dinges & Graeber, 1988), an increase in accidents sonable candidate for a sleepiness countermeasure. (Ribak, Ashkenazi, Klepfish, Avgar, Tall, Kallner & The purpose of this study was to determine the Noyman, 1983), and an increase in spontaneous naps effect of naps taken during a night shift on sleepiness on the job (Torsvall & Akerstedt, 1987; Torsvall et and performance after awakening and throughout al., 1989). According to a report by the Association of the duty hours following the nap. Issues related to Professional Sleep Societies’ Committee on Catas- sleep duration and sleep inertia were investigated. trophes, Sleep and Public Policy, heart attacks, ve- The study specifically compared two napping condi- hicular accidents, performance errors, and major tions, a Long Nap (2 hours) and a Short Nap (45 disasters are more likely to occur during the early minutes), to a No Nap condition. Performance was morning hours of shift work (Mitler et al., 1988). examined on two tasks, an air traffic scenarios task Other researchers have reported increased accidents (high workload) and a vigilance task (low workload). due to sleepiness in night workers (Hamelin, 1987; Ribak et al., 1983; Torsvall & Akerstedt, 1987). BACKGROUND Abuse of substances such as nicotine, caffeine, and other stimulants to help maintain alertness, and sleep- The problems associated with night and shift work ing pills to help obtain sleep also have been reported have been investigated by many researchers over the (cf Penn & Bootzin, 1990). past several years (Folkard, 1989; Wilkinson, 1992). According to Czeisler and his colleagues (Czeisler, These problems include physiological, psychologi- Kronauer, Allan, Duffy, Jewett, Brown & Ronda, cal, and social difficulties experienced by people who 1989; Czeisler, Johnson, Duffy, Brown, Ronda & 1 Kronauer, 1990), the problems associated with night taken before an extended sleep loss period, called work — sleep problems, fatigue and sleepiness, and “prophylactic naps”, will considerably attenuate the decreased performance — result from a desynch- decrease in performance during a night shift. ronization of the circadian cycle. Other problems in Length of nap. It is very difficult to compare many shift workers stem from the social and family disrup- of the nap studies due to variations in methodology, tions associated with shift work (Penn & Bootzin, however, most studies indicate that naps from 1 hour 1990). Workers desiring to spend time with family to 8 hours will improve performance and alertness and friends may not sleep when the opportunity during continuous operations (Bonnet, 1991). In a comes, leading to more fatigue and lack of sleep due study by Naitoh and colleagues (1982), subjects were to social and family activities. given a 3-hour nap after being awake for approxi- Because of the problems inherent with night work, mately 24 hours. After the nap, they were required to many interventions have been attempted to alleviate stay awake an additional 20 hours. Results indicated the ill effects. Some of the methods undertaken that this 3-hour nap reduced the decline in perfor- during the night shift to increase arousal and perfor- mance over the additional work period. mance include rest breaks, social activity during Another study (Lumley, Roehrs, Zorick, Lamphere, breaks, increasing task demands, feedback about work & Roth, 1986) deprived subjects of sleep for 24 performance, exercise, bright lights, and naps (Penn hours, after which a nap of either 15, 30, 60, or 120 & Bootzin, 1990; Bonnet, 1990).