Significance of time awake for predicting pilots' fatigue on short-haul flights: implications for flight duty time regulations.

European regulations restrict the duration of the maximum daily flight duty period for pilots as a function of the duty start time and the number of scheduled flights. However, late duty end times that may include long times awake are not specifically regulated. In this study, fatigue levels in pilots finishing their duty late at night (00:00-01:59 hour) were analysed and compared with pilots starting their duty early (05:00-06:59 hour). Fatigue levels of 40 commercial short-haul pilots were studied during a total of 188 flight duty periods, of which 87 started early and 22 finished late. Pilots used a small handheld computer to maintain a duty and sleep log, and to indicate fatigue levels immediately after each flight. Sleep logs were checked with actigraphy. Pilots on late-finishing flight duty periods were more fatigued at the end of their duty than pilots on early-starting flight duty periods, despite the fact that preceding sleep duration was longer by 1.1 h. Linear mixed-model regression identified time awake as a preeminent factor predicting fatigue. Workload had a minor effect. Pilots on late-finishing flight duty periods were awake longer by an average of 5.5 h (6.6 versus 1.1 h) before commencing their duty than pilots who started early in the morning. Late-finishing flights were associated with long times awake at a time when the circadian system stops promoting alertness, and an increased, previously underestimated fatigue risk. Based on these findings, flight duty limitations should consider not only duty start time, but also the time of the final landing.

Effects of nocturnal aircraft noise on cognitive performance in the following morning: dose-response relationships in laboratory and field.

OBJECTIVE: Nocturnal aircraft noise disturbs sleep and impairs recuperation. We investigated in laboratory and field studies whether noise-induced sleep fragmentation is associated with performance impairments in a psychomotor vigilance task (PVT) and a memory search task. METHODS: In the laboratory, 112 participants were exposed to aircraft noise during 9 consecutive nights. In the field, 64 participants were examined during 9 consecutive nights in the vicinity of Cologne/Bonn airport. Reaction time, signal detection performance and subjective task load were recorded. RESULTS: Dose-response relationships showed significant, linear impairments in reaction times. In the laboratory, reaction time in PVT increased with 0.13 ms/dB equivalent noise level (LAeq) plus 0.02 ms/noise event. In the field study, reaction time increased with 0.3 ms/dB LAeq. Participants worked significantly less accurate after nocturnal noise exposure. CONCLUSION: Influences of LAeq and number of noise events on daytime performance were small but consistent and significant, stressing the potential public health impact of nocturnal noise exposure.

Performance impairment during four days partial sleep deprivation compared with the acute effects of alcohol and hypoxia.

OBJECTIVE: Subjects were exposed to cumulated partial sleep deprivation (psd), alcohol intake and hypoxia in a sequential design to examine the impact on neurobehavioral performance. METHODS: Sixteen healthy male volunteers were enrolled in this study and were exposed in turn, after adaptation and baseline measurements, to one day of periods of hypoxia, one day of alcohol intake and one day for recovering (with 8h time in bed TIB). Subsequently the exposition of those conditions is that the subjects spent 5h night restriction daily for four consecutive days, followed by two recovery days. Performance was tested five (or six) times per day with reaction time task (SRT) and unstable tracking task (UTT). RESULTS: The performance impairment showed to be cumulative in both tests over the four sleep deprivation days and differed significantly from baseline. Corresponding performance deficits under the influence of the stressors were for SRT: four days psd, 13% O(2) concentration and a blood alcohol concentration (BAC) of around 0.4-0.6 per thousand for UTT: four days psd, 13% O(2) concentration and a BAC of around 0.6 per thousand. One night of 8h sleep restored performance nearly to baseline level. CONCLUSIONS: A sleeping time of 5h per night for four consecutive days impairs performance in such a way that traffic safety may be compromised.

Pilot workload during approaches: comparison of simulated standard and noise-abatement profiles.

INTRODUCTION: A new noise-reduced landing approach was tested--a Segmented Continuous Descent Approach (SCDA)-with regard to the resulting workload on pilots. METHODS: Workload of 40 pilots was measured using physiological (heart rate, blood pressure, blink frequency, saliva cortisol concentration) and psychological (fatigue, sleepiness, tension, and task load) parameters. Approaches were conducted in A320 and A330 full-flight simulators during night shift. SCDA was compared to the standard Low Drag Low Power (LDLP) procedure as reference. RESULTS: Mean heart rate and blood pressure during the SCDA were not elevated, but were partly, even significantly, reduced (on average by 5 bpm and 4 mmHg from the flying captain). Cortisol levels did not change significantly with mean values of 0.9 to 1.2 ng ml(-1). Landing was the most demanding segment of both approaches as indicated by significant increases in heart rate and decreases in blink frequency. Subjective task load was low. DISCUSSION: Both approach procedures caused a similar workload level. Interpreting the results, methodological limitations have to be considered, e.g., the artificial and controlled airspace situation in the flight simulator. Nevertheless, it can be concluded that under these ideal conditions, the SCDA is operable without a higher workload for pilots compared to the common LDLP.

Partial sleep deprivation: impact on the architecture and quality of sleep.

OBJECTIVE: The study was aimed at the examination of the acute and cumulative impact of partial sleep deprivation (PSD) on architecture and quality of sleep, on circadian rhythm and on daytime fatigue. METHODS: Time in bed for 16 healthy male volunteers was reduced from 8 to 5h during four consecutive nights, followed by two recovery nights. This scheme matches the terms of service and sleep rhythms of rescue helicopter pilots in Germany. Polysomnography was recorded during each night, and motor activity and body core temperature were recorded continuously. Subjective sleep quality and alertness were acquired by questionnaires. RESULTS: In the course of PSD, electroencephalography (EEG) showed a reduction of S1 and S2 (p=0.039), whereas S3, S4 (0.024) and rapid eye movement (REM; p=0.030) sleep increased. Subjective sleep quality improved, while sleep need (p<0.001) and fatigue (p<0.001) deepened. These effects declined rapidly after one recovery night. CONCLUSIONS: PSD alters sleep and daytime alertness. The results indicate that not only slow wave sleep (SWS) but also REM is important for sleep. Sleep became more effective when wake periods and sleep latencies decreased, thereby improving subjective sleep quality. Sleepiness, sleep need and fatigue increased immediately and accumulated throughout the restricting procedure.

Chronobiotic effects of the melatonin agonist LY 156735 following a simulated 9h time shift: results of a placebo-controlled trial.

INTRODUCTION: The melatonin agonist LY 156735 (LY) is a new investigational drug under development to treat circadian rhythm disorders. The present study assessed the efficacy of LY to alleviate the symptoms of shift lag and to enhance readaptation of desynchronized circadian rhythms to a new time zone. SUBJECTS AND METHODS: Eight healthy male volunteers of age 25-35 yr participated in three identical trials of 13d duration in a temporal isolation unit separated by washout intervals. A high dose (HD) of 5 mg and a low dose (LD) of 0.5 mg of LY and placebo (PL) were administered double-blinded in a three-period cross-over design. Each trial consisted of an adaptation period, a pre-shift period for baseline measurements, a simulated 9h phase-advance shift, and a post-shift period for follow-up. The time shift was performed at 23:00h of day 6 by advancing the laboratory time to 08:00h of day 7. Double-blind study medication was administered at 14:30h on day 6, and at 22:30h on days 7-10. Subjective ratings of jet lag, alertness, tenseness, and daytime fatigue were assessed using visual analog scales (VAS) and standardized questionnaires. The objective markers of readaptation included core body temperature, wrist actigraphy, cortisol and electrolyte excretion, and a battery of computerized performance tests. RESULTS: HD but not LD enhanced the readaptation speed of all physiological rhythms investigated, as demonstrated by a significantly faster movement of acrophases towards the post-shift target time. HD (p = 0.05) significantly blunted the post-shift deterioration of performance in those tests that were sensitive to shift lag. Parameters of subjective well-being were not significantly affected by either dose. CONCLUSION: This pilot study demonstrates the chronobiotic efficacy of LY when taken at a dose of 5 mg/d.

Sleep deficit and stress hormones in helicopter pilots on 7-day duty for emergency medical services.

INTRODUCTION: Helicopter-based emergency medical services in Germany operate from sunrise to sunset, requiring up to 15.5 h of continuous duty during the summer months for pilots, who work for seven consecutive days. Because of concerns regarding the safety of this procedure with respect to pilot fatigue and stress, the German Ministry of Transport asked our laboratory to investigate the risks involved. METHODS: There were 13 pilots (mean age 38 yr) who were studied in the summer months for 2 d before, 7 d during, and 2 d after their duty cycle. Measured variables included sleep duration and quality, subjective fatigue, and heart rate, as well as 24-h excretion levels of stress hormones. RESULTS: During actual helicopter operations, maximum heart rates did not exceed 120 bpm. Over the 7-d duty period, mean sleep duration decreased from 7.8 h to 6 h or less, resulting in a cumulative sleep loss of about 15 h. Mean levels of excreted adrenalin, noradrenalin, and cortisol increased significantly by 50 to 80%; cortisol and noradrenalin excretion also remained elevated for the two post-duty days. CONCLUSIONS: Although the actual flights did not cause critical physiological responses, the acute and accumulated sleep deficit led to incomplete recuperation between duty hours and induced elevated stress indicators. It was, therefore, recommended that the duty cycle be amended as follows: 1.) enforce a 10-h rest period and at least an 8-h sleep opportunity per day; 2.) modify the duty period to allow no more than 3 consecutive rest periods of reduced sleep opportunities (8.5 h); and 3.) follow duty with several days that offer unrestricted sleep opportunities.