An adaptive-duration version of the PVT accurately tracks changes in psychomotor vigilance induced by sleep restriction

Occupational and Driving Challenges Within Sleep Medicine

Shift work is a necessity for a society that requires 24/7 services. However, working around the clock can cause a misalignment with our sleep-wake cycle, resulting in sleepiness, impaired cognition and poor health. Due to the prevalence of shift work within safety-critical contexts, there is a need to further understand the causes and consequences of non-typical work on sleep, wellbeing, health and safety, as well as ways to effectively reduce this risk. Furthermore, disorders such as obstructive sleep apnoea, which is the most prevalent medical cause of sleepiness, compound the adverse health and safety consequences of shift work. This article provides an overview of some of the key occupational and sleep health challenges related to shift work: accurate measurement of sleepiness, mitigation, long-term sustainability and work/life balance. We conclude by proposing four directions for future work in this area to consider, with the overall aim of improving the sleep, health and wellbeing of the shift-working population.

Objective alertness, rather than sleep duration, is associated with burnout and depression: A national survey of Japanese physicians

Approximately 40% of Japanese physicians report working more than 960 hr of overtime annually, with 10% exceeding 1860 hr. To protect their health, annual overtime limits went into effect in 2024. The objective of this study was to investigate associations of self-reported sleep duration with psychological health and objective alertness. This was a cross-sectional National Survey for The Work Style Reform of Long Working Physicians. Physicians self-reported daily sleep duration, burnout (Abbreviated Maslach Burnout Inventory), depression (Center for Epidemiologic Studies Depression Scale) and traffic accidents. Alertness was then evaluated using the brief Psychomotor Vigilance Test. Of 20,382 physicians invited, 1226 completed the survey and brief Psychomotor Vigilance Test. Daily sleep duration was inversely associated with weekly work hours (β = -5.4; 95% confidence interval -6.8 to -4.0, p < 0.0001). Sleep duration < 6 hr and ≥ 8 hr per day was associated with slower responses on the brief Psychomotor Vigilance Test (adjusted p < 0.05). An additional 10 hr worked per week was associated with a 0.40 point (95% confidence interval 0.08-0.72) increase in burnout severity and a 1.7% (95% confidence interval 0.1-3.3%) increase in odds of reporting a traffic accident. Increased brief Psychomotor Vigilance Test lapses, indicating lower alertness, were associated with worse symptoms of depression (β = 0.23 points; 95% confidence interval 0.14-0.31, p < 0.0001) and burnout (β = 0.25 points; 95% confidence interval 0.13-0.36, p < 0.0001). This study emphasizes the importance of sufficient sleep to maintain alertness, and supports limiting work hours for Japanese physicians to protect psychological health. Performance on the brief Psychomotor Vigilance Test may be a useful indicator of psychological health.

Safety and effectiveness of acute intermittent hypoxia during a single treatment at different hypoxic severities

PURPOSE

Examine the cardiovascular, muscular function, cognitive, and neural plastic responses to determine the safety and effectiveness of acute Intermittent hypoxia (AIH) at a low, high, and control fractional inspired oxygen (FiO2) dosage METHODS: Thirteen human participants performed 30-min of AIH in 60-s intervals at FiO2's of 0.21 (AIH21), 0.15 (AIH15), and 0.09 (AIH9). Heart rate variability (root mean squared of successive differences; RMSSD), heart rate, oxygen saturation (SpO2), blood pressure, muscular strength, neuromuscular activation, cerebral hemodynamic responses, cognition, symptomology, and brain-derived neurotrophic factor (BDNF) responses were measured before (Pre-AIH), after (post-AIH), and at 20-min of recovery (Recovery-AIH) RESULTS: There were no differences between AIH protocols for heart rate, RMSSD, blood pressure, or SpO2. Muscular strength improved Post-AIH for AIH15 (10 %) and AIH9 (14 %) and remained elevated (6 %) at Recovery-AIH. Neuromuscular activation increased Pre-AIH to Post-AIH for AIH15 (10 %) and AIH9 (11 %). Cerebral hemodynamic responses were not impacted between conditions. Both AIH15 and AIH9 increased BDNF Post-AIH (62 %) and Recovery-AIH (63 %) CONCLUSION: Acute intermittent hypoxia is generally safe and effective at producing neural plastic responses, but further examination of co-occurring cardiovascular diseases is needed. This study provides safety focused findings which will widen the adoption and refinement of AIH protocols.

Fluctuation in cortical excitation/inhibition modulates capability of attention across time scales ranging from hours to seconds

Sustained attention, as the basis of general cognitive ability, naturally varies across different time scales, spanning from hours, e.g. from wakefulness to drowsiness state, to seconds, e.g. trial-by-trail fluctuation in a task session. Whether there is a unified mechanism underneath such trans-scale variability remains unclear. Here we show that fluctuation of cortical excitation/inhibition (E/I) is a strong modulator to sustained attention in humans across time scales. First, we observed the ability to attend varied across different brain states (wakefulness, postprandial somnolence, sleep deprived), as well as within any single state with larger swings. Second, regardless of the time scale involved, we found highly attentive state was always linked to more balanced cortical E/I characterized by electroencephalography (EEG) features, while deviations from the balanced state led to temporal decline in attention, suggesting the fluctuation of cortical E/I as a common mechanism underneath trans-scale attentional variability. Furthermore, we found the variations of both sustained attention and cortical E/I indices exhibited fractal structure in the temporal domain, exhibiting features of self-similarity. Taken together, these results demonstrate that sustained attention naturally varies across different time scales in a more complex way than previously appreciated, with the cortical E/I as a shared neurophysiological modulator.

Camera-Position-Robust Drowsiness Estimation Based on Rotated-Facial-Video Augmentation

This paper proposes a camera-position-robust drowsiness estimation system that utilizes head-pose information and estimation models trained on the basis of rotated-facial-video augmentation. From original single-view training data collected by a camera placed at a specific position, a face rotation technology is applied in the generation of images by cameras placed at different positions. Integration of the estimate by a model trained with original data and the estimate by a model trained with rotated data increases drowsiness estimation robustness even when eye-openness features used for drowsiness estimation change depending on camera position. Drowsiness estimation evaluations were performed using test data collected by three cameras placed at different positions. In the normalized mean absolute error for the test data captured from below the face, which was only barely included in the original training data, a significant relative superiority of 6.2-9.0% was achieved by the proposed method employing rotated data over that achieved by a conventional method not employing rotated data.

Implementation of a psychomotor vigilance test to investigate the effects of driving fatigue on oil and gas truck drivers' performance

Introduction

Driving fatigue has been shown to increase the risk of accidents and potentially fatal crashes. Fatigue is a serious risk that some drivers do not take seriously. Previous studies investigated the effects of driving fatigue in the Malaysian oil and gas transportation industry by employing survey questionnaires. However, they did not explain the behavior of fatigue. Besides, these results required validation by a more reliable method that can describe how fatigue occurs.

Methods

Thus, in this study, we used the Psychomotor Vigilance Test (PVT-192) and a short survey to address driving fatigue behavior and identify the influences of driving fatigue on driving performance in real life (on the road) with actual oil and gas tanker drivers. The total participants in the experimental study were 58 drivers.

Results

For the analysis, a Wilcoxon Signed Ranks Test, Z value and Spearman's rho were used to measure the significant difference between the pre and post-tests of PVT and the correlation between the fatigue variables and driving performance.

Discussion

During the experiment's first and second days, this study's results indicated that driving fatigue gradually escalated. Likewise, there was a negative correlation based on the test of the relationship between the PVT data and the driving performance survey data. Additionally, the drivers suffer from accumulative fatigue, which requires more effort from the transportation company management to promote the drivers awareness of fatigue consequences.

Evaluation of Correlation between Psychomotor Vigilance Task Scores and Drowsiness Estimation Levels Obtained from Facial Videos

This paper reports the results of an experiment to evaluate the relationship between results obtained with a drowsiness estimation system we have developed using facial videos and those obtained with the Psychomotor Vigilance Task (PVT), which is a standard index of sleepiness used in sleep medicine. The correlation between PVT scores and the output of the drowsiness estimation system, which outputs drowsiness levels from assigned facial expressions, was calculated using data from 30 subjects. The Spearman's correlation coefficients between the drowsiness estimation results and the PVT mean response time, the slowest 10% response time, and the number of lapses were 0.36 (p <0.001), 0.43 (p <0.001), and 0.40 (p <0.001), respectively. Since this experiment showed a correlation between the drowsiness estimation results and those with PVT, it would seem possible to make specific interventions based on drowsiness estimation results learned from ground-truth drowsiness levels. Such estimation results could help prevent accidents resulting from drowsiness or insufficient vigilance while driving or working.

PERCLOS-based technologies for detecting drowsiness: current evidence and future directions

Drowsiness associated with sleep loss and circadian misalignment is a risk factor for accidents and human error. The percentage of time that the eyes are more than 80% closed (PERCLOS) is one of the most validated indices used for the passive detection of drowsiness, which is increased with sleep deprivation, after partial sleep restriction, at nighttime, and by other drowsiness manipulations during vigilance tests, simulated driving, and on-road driving. However, some cases have been reported wherein PERCLOS was not affected by drowsiness manipulations, such as in moderate drowsiness conditions, in older adults, and during aviation-related tasks. Additionally, although PERCLOS is one of the most sensitive indices for detecting drowsiness-related performance impairments during the psychomotor vigilance test or behavioral maintenance of wakefulness test, no single index is currently available as an optimal marker for detecting drowsiness during driving or other real-world situations. Based on the current published evidence, this narrative review suggests that future studies should focus on: (1) standardization to minimize differences in the definition of PERCLOS between studies; (2) extensive validation using a single device that utilizes PERCLOS-based technology; (3) development and validation of technologies that integrate PERCLOS with other behavioral and/or physiological indices, because PERCLOS alone may not be sufficiently sensitive for detecting drowsiness caused by factors other than falling asleep, such as inattention or distraction; and (4) further validation studies and field trials targeting sleep disorders and trials in real-world environments. Through such studies, PERCLOS-based technology may contribute to preventing drowsiness-related accidents and human error.

Anhedonia modulates benzodiazepine and opioid demand among persons in treatment for opioid use disorder

Background

Benzodiazepine (BZD) misuse is a significant public health problem, particularly in conjunction with opioid use, due to increased risks of overdose and death. One putative mechanism underlying BZD misuse is affective dysregulation, via exaggerated negative affect (e.g., anxiety, depression, stress-reactivity) and/or impaired positive affect (anhedonia). Similar to other misused substances, BZD consumption is sensitive to price and individual differences. Although purchase tasks and demand curve analysis can shed light on determinants of substance use, few studies have examined BZD demand, nor factors related to demand.

Methods

This ongoing study is examining simulated economic demand for alprazolam (among BZD lifetime misusers based on self-report and DSM-5 diagnosis; n = 23 total; 14 male, 9 female) and each participant's preferred-opioid/route using hypothetical purchase tasks among patients with opioid use disorder (n = 59 total; 38 male, 21 female) who are not clinically stable, i.e., defined as being early in treatment or in treatment longer but with recent substance use. Aims are to determine whether: (1) BZD misusers differ from never-misusers on preferred-opioid economic demand, affective dysregulation (using questionnaire and performance measures), insomnia/behavioral alertness, psychiatric diagnoses or medications, or urinalysis results; and (2) alprazolam demand among BZD misusers is related to affective dysregulation or other measures.

Results

Lifetime BZD misuse is significantly (p < 0.05) related to current major depressive disorder diagnosis, opioid-negative and methadone-negative urinalysis, higher trait anxiety, greater self-reported affective dysregulation, and younger age, but not preferred-opioid demand or insomnia/behavioral alertness. Alprazolam and opioid demand are each significantly positively related to higher anhedonia and, to a lesser extent, depression symptoms but no other measures of negative-affective dysregulation, psychiatric conditions or medications (including opioid agonist therapy or inpatient/outpatient treatment modality), or sleep-related problems.

Conclusion

Anhedonia (positive-affective deficit) robustly predicted increased BZD and opioid demand; these factors could modulate treatment response. Routine assessment and effective treatment of anhedonia in populations with concurrent opioid and sedative use disorder may improve treatment outcomes.

Clinical trial registration

https://clinicaltrials.gov/ct2/show/NCT03696017, identifier NCT03696017.

A Field Study on Safety Performance of Apron Controllers at a Large-Scale Airport Based on Digital Tower

The innovative concept of digital tower provides a new solution for reducing the construction and operation costs of airports with adverse natural environments, poor intervisibility conditions, or sparse traffic. However, it leads to changes in the situational awareness of air traffic controllers and to challenges in safety performance. To research the safety performance of apron controllers at a large-scale airport applying a digital tower, a field study was conducted at Baiyun International Airport in Guangzhou, China. In this study, we established a comprehensive index system from the perspective of situational awareness, which provided measurements on the areas of interests, gaze and physiological features, and vigilance of controllers. Three modules were compared: a physical tower module, a digital tower module with a large panoramic screen, and a digital tower module with a small panoramic screen. The differences in the safety performances of apron controllers are discussed in two aspects: adaptability and reliability. The results indicated that the apron controllers at the three modules performed different cognition patterns, but similar cognition effort was paid toward maintaining performance. Furthermore, the significant vigilance decrement of controllers exists between after-duty and before-duty, but with no significant difference among the three modules. In conclusion, apron controllers at a large-scale airport could obtain effective safety performances based on a digital tower that were no less than those from a physical tower.

Test-retest reliability of the 5-minute psychomotor vigilance task in working-aged females

BACKGROUND

The psychomotor vigilance task (PVT) is a commonly used test that effectively assesses neurobehavioral alertness. The originally developed PVT is 10 minutes in duration, which presents practical and logistical issues, particularly when administered to large samples or on a repetitive basis. More recently the PVT has been used in both 3- and 5-minute formats. While both of these durations have been shown to be field sensitive to identify impairments from sleep- and fatigue-related interventions, the 5-minute version has been suggested to be more valid than the 3-minute. However, while these have shown field-validity in a number of working populations, there is a paucity of data reporting the test-retest reliability statistics of the 5-minute PVT, particularly in working-aged females. The purpose of the study was to examine the test-retest reliability of a comprehensive set of PVT variables for the 5-minute PVT in a population of working-aged females (20-63 years).

NEW METHOD

Participants reported to the laboratory on two separate days and performed a 5-minute PVT on each occasion. Outcome measures included the mean reaction time (MRT), fastest and slowest 10% of reaction times (F10RT% and S10RT%, respectively), standard deviation of reaction times (SDRT) as well as error-based metrics including major and minor lapses, anticipations, and false starts. In addition, total errors (ERR) were computed as a composite of all types of errors. Reliability statistics were reported as intraclass correlation coefficients (ICCs), standard error of measurement (SEM, SEM%), and minimal difference to be considered real (MD, MD%). Systematic error was also evaluated between sessions.

RESULTS

Overall high reliability was shown for the MRT (ICC = 0.79, SEM% = 4.14%) and F10RT% (ICC = 0.83, SEM% = 4.43%) variables, with moderate relative reliability (based on ICCs) for the false starts, ERR, and sleepiness scale (ICC = 0.50 - 0.70) variables but these all exhibited poor absolute reliability (based on SEM% values of 32.60 - 168.69%). Poor relative reliability was found for the SDRT and S10RT% variables (ICCs < 0.50) but the S10RT% variable had good absolute reliability (SEM% = 7.12%). The minor and major lapses and anticipations variables had too few of event occurrences for a confident determination of the reliability.

CONCLUSIONS

The finding that the MRT variable displayed systematic error (P = 0.01) indicating that a learning curve may have been present, but the F10RT% did not show systematic error, suggests the F10RT% may be the most reliable PVT variable in a 5-minute duration test. These findings provide researchers and practitioners with reliability statistics that may help in determining which variable(s) to use, and which to avoid when specifically conducting 5-minute PVT assessments, particularly in a population of working-aged females. These results suggest that the 5-minute PVT can be used in place of the 10-minute version, if used appropriately.

Effect of moderate and Severe Hypoxic exposure coupled with fatigue on psychomotor vigilance testing, muscle tissue oxygenation, and muscular performance

PURPOSE

The purpose of this study is to examine the effects of fatigue on muscular performance, oxygenation saturation, and cognition following acute hypoxic exposure at Normoxia, Moderate Hypoxia (MH), and Severe Hypoxia (SH).

METHODS

Twelve males performed 3 sets of leg extensions to failure under Normoxia (FiO2: 21%), MH (Fi02: 15.4%), and SH (Fi02: 12.9%). Heart rate, peripheral oxygenation saturation, total saturation index, psychomotor vigilance testing reaction time, psychomotor vigilance error rate, maximum strength, and repetitions to failure were measured throughout each visit.

RESULTS

The primary findings indicated that MH and SH resulted in significant decreases in psychomotor vigilance test performance (MH: 388.25-427.17 ms, 0.41-0.33 error rate; SH: 398.17-445.42 ms reaction time, 0.25-1.00 error rate), absolute muscle tissue oxygen saturation (Abs-StO2) (MH:67.22% compared to SH:57.56%), but similar muscular strength, heart rate, and patterns of muscle tissue oxygen saturation responses (StO2%) during fatigue when compared to Normoxia. There was an acute decrease in the ability to remain vigilant and/or respond correctly to visual stimuli as indicated by the worsened reaction time (PVTRT) during MH (FiO2: 15.4%) and increased PVTRT and error rate (PVTE) during SH (FiO2: 12.9%) conditions.

CONCLUSIONS

Acute hypoxic exposure in the current study was not a sufficient stimuli to elicit hypoxic-related changes in HR, muscular strength (1-RM), or repetitions to failure. The SpO2 responses were hypoxic-level dependent with increasing levels of hypoxia resulting in greater and more sustained reductions in SpO2. The combined SpO2 and StO2 responses at MH and SH suggested a balance between the muscles metabolic demand remaining lower than the muscle oxygen diffusion capacity. During the SH condition, Abs-StO2 suggested greater metabolic stress than Normoxia and MH conditions during the fatiguing leg extensions. The patterns of responses for StO2% during the three sets of leg press to failure indicated that exercise is a more potent influencer to muscle oxygenation status than hypoxic conditions (FiO2: 15.4 and 12.9%).

Effects of a snack on performance and errors during a simulated 16-h night shift: A randomized, crossover-controlled, pilot study

BACKGROUND

Night shift workers might not eat due to their busy schedules during the night shift. However, food may not only satisfy hunger, but also affect performance and errors. The aim of this study was to clarify the effect of a snack on performance and errors during 2-day, 16-h, simulated night shifts.

METHODS

A randomized, repeated-measure, crossover study was performed to investigate subjective and cognitive performance in 15 healthy female adults (mean age, 21.7 years) after they consumed a snack (352 kcal) during a simulated night shift (16:00 to 09:00) from October to November 2018. The participants were kept awake from waking up in the morning to the next day at 09:00. Subjects were tested for performance on the Uchida-Kraepelin test, as well as for subjective feeling, body temperature, psychomotor vigilance test, and heart rate variability, before and after they consumed the snack. One day before the experiment, all participants wore an actigraphy monitoring device to determine their sleep state.

RESULTS

There was no difference between having (Snack condition) and not having (Skipping condition) the snack in sleep states the day before the experiment. On the day of the experiment, between 16:00 and 09:00, subjective sleepiness, fatigue, and body temperature were not different between the two conditions. Subjects maintained performance on the Uchida-Kraepelin test and showed a significant improvement in false starts on the psychomotor vigilance test, the primary outcome measure, in the Snack condition compared with the Skipping condition. The Snack condition was also associated with decreased high-frequency power, a decreased low-frequency power/high-frequency power ratio, and increased heart rate in the vagally mediated heart rate variability indices, which may reflect a higher ability to modulate cognitive and behavioral processes.

CONCLUSIONS

These results suggest that providing a snack to shift workers during night shifts might improve work safety and efficiency.

A Broader Application of the Detection Response Task to Cognitive Tasks and Online Environments

OBJECTIVE

The present research applied a well-established measure of cognitive workload in driving literature to an in-lab paradigm. We then extended this by comparing the in-lab version of the task to an online version.

BACKGROUND

The accurate and objective measurement of cognitive workload is important in many aspects of psychological research. The detection response task (DRT) is a well-validated method for measuring cognitive workload that has been used extensively in applied tasks, for example, to investigate the effects of phone usage or passenger conversation on driving, but has been used sparingly outside of this field.

METHOD

The study investigated whether the DRT could be used to measure cognitive workload in tasks more commonly used in experimental cognitive psychology and whether this application could be extended to online environments. We had participants perform a multiple object tracking (MOT) task while simultaneously performing a DRT. We manipulated the cognitive load of the MOT task by changing the number of dots to be tracked.

RESULTS

Measurements from the DRT were sensitive to changes in the cognitive load, establishing the efficacy of the DRT for experimental cognitive tasks in lab-based situations. This sensitivity continued when applied to an online environment (our code for the online DRT implementation is freely available at https://osf.io/dc39s/), though to a reduced extent compared to the in-lab situation.

CONCLUSION

The MOT task provides an effective manipulation of cognitive workload. The DRT is sensitive to changes in workload across a range of settings and is suitable to use outside of driving scenarios, as well as via online delivery.

APPLICATION

Methodology shows how the DRT could be used to measure sources of cognitive workload in a range of human factors contexts.

Response speed measurements on the psychomotor vigilance test: how precise is precise enough?

STUDY OBJECTIVES

The psychomotor vigilance test (PVT) is frequently used to measure behavioral alertness in sleep research on various software and hardware platforms. In contrast to many other cognitive tests, PVT response time (RT) shifts of a few milliseconds can be meaningful. It is, therefore, important to use calibrated systems, but calibration standards are currently missing. This study investigated the influence of system latency bias and its variability on two frequently used PVT performance metrics, attentional lapses (RTs ≥500 ms) and response speed, in sleep-deprived and alert participants.

METHODS

PVT data from one acute total (N = 31 participants) and one chronic partial (N = 43 participants) sleep deprivation protocol were the basis for simulations in which response bias (±15 ms) and its variability (0-50 ms) were systematically varied and transgressions of predefined thresholds (i.e. ±1 for lapses, ±0.1/s for response speed) recorded.

RESULTS

Both increasing bias and its variability caused deviations from true scores that were higher for the number of lapses in sleep-deprived participants and for response speed in alert participants. Threshold transgressions were typically rare (i.e. <5%) if system latency bias was less than ±5 ms and its standard deviation was ≤10 ms.

CONCLUSIONS

A bias of ±5 ms with a standard deviation of ≤10 ms could be considered maximally allowable margins for calibrating PVT systems for timing accuracy. Future studies should report the average system latency and its standard deviation in addition to adhering to published standards for administering and analyzing the PVT.

Tracking intermediate performance of vigilant attention using multiple eye metrics

Vigilance deficits account for a substantial number of accidents and errors. Current techniques to detect vigilance impairment measure only the most severe level evident in eyelid closure and falling asleep, which is often too late to avoid an accident or error. The present study sought to identify ocular biometrics of intermediate impairment of vigilance and develop a new technique that could detect a range of deficits in vigilant attention (VA). Sixteen healthy adults performed well-validated Psychomotor Vigilance Test (PVT) for tracking vigilance attention while undergoing simultaneous recording of eye metrics every 2 hours during 38 hours of continuous wakefulness. A novel marker was found that measured VA when the eyes were open-the prevalence of microsaccades. Notably, the prevalence of microsaccades decreased in response to sleep deprivation and time-on-task. In addition, a novel algorithm for detecting multilevel VA was developed, which estimated performance on the PVT by integrating the novel marker with other eye-related indices. The novel algorithm also tracked changes in intermediate level of VA (specific reaction times in the PVT, i.e. 300-500 ms) during prolonged time-on-task and sleep deprivation, which had not been tracked previously by conventional techniques. The implication of the findings is that this novel algorithm, named "eye-metrical estimation version of the PVT: PVT-E," can be used to reduce human-error-related accidents caused by vigilance impairment even when its level is intermediate.

The effect of one-night sleep deprivation on cognitive functions in healthy young adults

INTRODUCTION

The effects of acute sleep deprivation on cognitive function have not been clearly elucidated. The purpose of this study was to evaluate changes in cognitive function in healthy adults after one night of sleep deprivation.

MATERIAL AND METHODS

Twenty-one healthy young adults (aged 18-30 years) underwent assessment of cognitive functions before and after one night of total sleep deprivation and an age- and gender-matched control group was assessed before and after a normal night sleep. Cognitive functions were assessed using the Montreal cognitive assessment (MOCA) and trail making test (TMT) parts A and B.

RESULTS

General linear model repeated measures demonstrated an insignificant effect for time × group (sleep deprivation) interaction for MOCA, TMT Part A, and TMT Part B scores after one-night sleep deprivation (p>.05 for all).

CONCLUSION

A single night of sleep deprivation, which can be inevitable in modern society, had no significant effect on cognitive performance in healthy adults.

Workers’ Aging Management—Human Fatigue at Work: An Experimental Offices Study

The aging issue in the work context is becoming a significant element of the future sustainability of service and industrial companies. It is well known that with increasing worker age the problem of maintaining the performance and the safety level when fatigue increases is a crucial point, and fatigue increases with the age. Due to social and political developments, especially in Western countries, the retirement age is increasing and companies operate with a higher workforce mean age. Therefore, the problem of recognizing and measuring fatigue has become a key aspect in the management of aging. Note that in the scientific engineering field, the problem of fatigue evaluation when a worker is performing his/her work activities is an important issue in the industrial and service world and especially in the context of the researchers that are investigating the human reliability assessment. As it is clear from the literature, the industrial operations management are suffering from some misleading concepts that only the medicine scientific context can clarify. Therefore, the aim of this paper is to define what are the open issues and the misleading concepts present in the classical fatigue evaluation methods, and second to define two experimental curves of fatigue that will help the decision makers to minimize the impact of fatigue on the workers, thus maximizing the sustainability of the working tasks assigned. This aim is achieved by examining the medical literature about the measurement of a particular kind of fatigue related to the circadian cycle, i.e., the cognitive one; after that, a survey about the possible technologies for measurements is performed. On the basis of technology selection, an experiment on real work activities is performed and some remarkable results about the fatigue in the workers observed and the technology use and its limitations are defined.

Enhancing Slow Oscillations and Increasing N3 Sleep Proportion with Supervised, Non-Phase-Locked Pink Noise and Other Non-Standard Auditory Stimulation During NREM Sleep

PURPOSE

In non-rapid eye movement (NREM) stage 3 sleep (N3), phase-locked pink noise auditory stimulation can amplify slow oscillatory activity (0.5-1 Hz). Open-loop pink noise auditory stimulation can amplify slow oscillatory and delta frequency activity (0.5-4 Hz). We assessed the ability of pink noise and other sounds to elicit delta power, slow oscillatory power, and N3 sleep.

PARTICIPANTS AND METHODS

Participants (n = 8) underwent four consecutive inpatient nights in a within-participants design, starting with a habituation night. A registered polysomnographic technologist live-scored sleep stage and administered stimuli on randomized counterbalanced Enhancing and Disruptive nights, with a preceding Habituation night (night 1) and an intervening Sham night (night 3). A variety of non-phase-locked pink noise stimuli were used on Enhancing night during NREM; on Disruptive night, environmental sounds were used throughout sleep to induce frequent auditory-evoked arousals.

RESULTS

Total sleep time did not differ between conditions. Percentage of N3 was higher in the Enhancing condition, and lower in the Disruptive condition, versus Sham. Standard 0.8 Hz pink noise elicited low-frequency power more effectively than other pink noise, but was not the most effective stimulus. Both pink noise on the "Enhancing" night and sounds intended to Disrupt sleep administered on the "Disruptive" night increased momentary delta and slow-wave activity (ie, during stimulation versus the immediate pre-stimulation period). Disruptive auditory stimulation degraded sleep with frequent arousals and increased next-day vigilance lapses versus Sham despite preserved sleep duration and momentary increases in delta and slow-wave activity.

CONCLUSION

These findings emphasize sound features of interest in ecologically valid, translational auditory intervention to increase restorative sleep. Preserving sleep continuity should be a primary consideration if auditory stimulation is used to enhance slow-wave activity.

The Effects of Fatigue on Cognitive Performance in Police Officers and Staff During a Forward Rotating Shift Pattern

Background

Few studies have examined the effects of a forward rotating shift pattern on police employee performance and well-being. This study sought to compare sleep duration, cognitive performance, and vigilance at the start and end of each shift within a three-shift, forward rotating shift pattern, common in United Kingdom police forces.

Methods

Twenty-three police employee participants were recruited from North Yorkshire Police (mean age, 43 years). The participants were all working the same, 10-day, forward rotating shift pattern. No other exclusion criteria were stipulated. Sleep data were gathered using both actigraphy and self-reported methods; cognitive performance and vigilance were assessed using a customized test battery, comprising five tests: motor praxis task, visual object learning task, NBACK, digital symbol substitution task, and psychomotor vigilance test. Statistical comparisons were conducted, taking into account the shift type, shift number, and the start and end of each shift worked.

Results

Sleep duration was found to be significantly reduced after night shifts. Results showed a significant main effect of shift type in the visual object learning task and NBACK task and also a significant main effect of start/end in the digital symbol substitution task, along with a number of significant interactions.

Conclusion

The results of the tests indicated that learning and practice effects may have an effect on results of some of the tests. However, it is also possible that due to the fast rotating nature of the shift pattern, participants did not adjust to any particular shift; hence, their performance in the cognitive and vigilance tests did not suffer significantly as a result of this particular shift pattern.

Do different salience cues compete for dominance in memory over a daytime nap?

Information that is the most salient and important for future use is preferentially preserved through active processing during sleep. Emotional salience is a biologically adaptive cue that influences episodic memory processing through interactions between amygdalar and hippocampal activity. However, other cues that influence the importance of information, such as the explicit direction to remember or forget, interact with the inherent salience of information to determine its fate in memory. It is unknown how sleep-based processes selectively consolidate this complex information. The current study examined the development of memory for emotional and neutral information that was either cued to-be-remembered (TBR) or to-be-forgotten (TBF) across a daytime period including either napping or wakefulness. Baseline memory revealed dominance of the TBR cue, regardless of emotional salience. As anticipated, napping was found to preserve memory overall significantly better than remaining awake. Furthermore, we observed a trending interaction indicating that napping specifically enhanced the discrimination between the most salient information (negative TBR items) over other information. We found that memory for negative items was positively associated with the percentage of SWS obtained during a nap. Furthermore, the magnitude of the difference in memory between negative TBR items and negative TBF items increased with greater sleep spindle activity. Taken together, our results suggest that although the cue to actively remember or intentionally forget initially wins out, active processes during sleep facilitate the competition between salience cues to promote the most salient information in memory.

An on-road study of sleepiness in split shifts among city bus drivers

Bus drivers often work irregular hours or split shifts and their work involves high levels of stress. These factors can lead to severe sleepiness and dangerous driving. This study examined how split shift working affects sleepiness and performance during afternoon driving. An experiment was conducted on a real road with a specially equipped regular bus driven by professional bus drivers. The study had a within-subject design and involved 18 professional bus drivers (9 males and 9 females) who drove on two afternoons; one on a day in which they had driven early in the morning (split shift situation) and one on a day when they had been off duty until the test (afternoon shift situation). The hypothesis tested was that split shifts contribute to sleepiness during afternoon, which can increase the safety risks. The overall results supported this hypothesis. In total, five of the 18 drivers reached levels of severe sleepiness (Karolinska Sleepiness Scale ≥8) with an average increase in KSS of 1.94 when driving in the afternoon after working a morning shift compared with being off duty in the morning. This increase corresponded to differences observed between shift workers starting and ending a night shift. The Psychomotor Vigilance Task showed significantly increased response time with split shift working (afternoon: 0.337s; split shift 0.347s), as did the EEG-based Karolinska Drowsiness Score mean/max. Blink duration also increased, although the difference was not significant. One driver fell asleep during the drive. In addition, 12 of the 18 bus drivers reported that in their daily work they have to fight to stay awake while driving at least 2-4 times per month. While there were strong individual differences, the study clearly showed that shift-working bus drivers struggle to stay awake and thus countermeasures are needed in order to guarantee safe driving with split shift schedules.

Preferential consolidation of emotionally salient information during a nap is preserved in middle age

Sleep preferentially preserves aspects of memory that are most salient and valuable to remember at the expense of memory for less relevant details. Daytime naps and nocturnal sleep enhance this emotional memory trade-off effect, with memory for emotional components correlated with slow-wave sleep during the day and rapid eye movement sleep overnight. However, these studies have primarily sampled from young adult populations. Sleep and memory are altered by middle age, and the aim of the present study was to examine how age affects sleep-based mechanisms of emotional memory prioritization, using a daytime nap protocol to compare young to middle-aged adults. In both age groups, a nap soon after encoding scenes that contained a negative or neutral object on a neutral background led to superior retention of emotional object memory at the expense of memory for the related backgrounds. Sleep spindle activity during slow-wave sleep was related to memory for this emotionally salient information across the age range.

Interindividual variability in neurobehavioral response to sleep loss: A comprehensive review

Stable trait-like responding is well established for neurobehavioral performance measures across repeated exposures to total sleep deprivation and partial chronic sleep restriction. These observed phenotypes are task-dependent, suggesting that there are distinct cognitive profiles of responding with differential vulnerability to sleep loss within the same individual. Numerous factors have been investigated as potential markers of phenotypic vulnerability to the effects of sleep loss but none fully account for this phenomenon. Observed interindividual differences in performance during extended wakefulness may be driven by underlying deficits in the wake-promoting system resulting in greater performance instability due to failure to counteract increased homeostatic pressure. Further work would benefit from a systems approach to the study of interindividual vulnerability in which behavioral, neurobiological, and genetic data are integrated in a larger framework delineating the relationships between genes, proteins, neurobiology, and behavior.

The psychomotor vigilance test: a comparison of different test durations in elite athletes

The 10-min Psychomotor Vigilance Test (PVT-10) is regarded as the gold-standard for assessing vigilant attention following sleep loss; however, other studies have investigated whether shorter versions of the test elicit similar results to the PVT-10. The present study compared the PVT-10 with 3-min (PVT-3) and 5-min (PVT-5) versions of the test in elite female basketball players. Athletes performed all three tests in the morning and evening for seven consecutive days. Response speed (mean reciprocal reaction time; mean 1/RT), number of errors and number of lapses were determined for each test and time point. The PVT-3 elicited significantly faster response speeds than the other two tests (p < 0.01), while the PVT-5 and PVT-10 were not different. The PVT-10 resulted in more lapses than the PVT-5, followed by the PVT-3, with all tests being significantly different to each other (p < 0.01). In conclusion, while the PVT-5 and PVT-10 were generally similar for response speed, the PVT-3 did not produce results comparable with the PVT-10 for response speed, lapses or errors, and should therefore not be used interchangeably. Further research is required to determine whether the shorter tests are a suitable replacement for the PVT-10 in professional basketball players.

3-minute smartphone-based and tablet-based psychomotor vigilance tests for the assessment of reduced alertness due to sleep deprivation

The psychomotor vigilance test (PVT) is widely used to measure reduced alertness due to sleep loss. Here, two newly developed, 3-min versions of the psychomotor vigilance test, one smartphone-based and the other tablet-based, were validated against a conventional 10-min laptop-based PVT. Sixteen healthy participants (ages 22-40; seven males, nine females) completed a laboratory study, which included a practice and a baseline day, a 38-h total sleep deprivation (TSD) period, and a recovery day, during which they performed the three different versions of the PVT every 3 h. For each version of the PVT, the number of lapses, mean response time (RT), and number of false starts showed statistically significant changes across the sleep deprivation and recovery days. The number of lapses on the laptop was significantly correlated with the numbers of lapses on the smartphone and tablet. The mean RTs were generally faster on the smartphone and tablet than on the laptop. All three versions of the PVT exhibited a time-on-task effect in RTs, modulated by time awake and time of day. False starts were relatively rare on all three PVTs. For the number of lapses, the effect sizes across 38 h of TSD were large for the laptop PVT and medium for the smartphone and tablet PVTs. These results indicate that the 3-min smartphone and tablet PVTs are valid instruments for measuring reduced alertness due to sleep deprivation and restored alertness following recovery sleep. The results also indicate that the loss of sensitivity on the 3-min PVTs may be mitigated by modifying the threshold defining lapses.

Using interstimulus interval to maximise sensitivity of the Psychomotor Vigilance Test to fatigue

There is some evidence that short interstimulus intervals (ISIs) on the Psychomotor Vigilance Test (PVT) are associated with longer and more varied reaction times (RTs). Preparation processes may impede RT following short ISIs, resulting in additional unexplained variance. The aims of this study were to investigate whether there is an effect of ISI on RT and errors within the PVT, and whether such an effect changes with three elements of fatigue: time of day, prior wake and time on task. Twelve male participants completed 49 PVTs across 7× 28h periods of forced desynchrony. For analysis, RTs, reciprocal reaction times (1/RT), false starts and lapse responses within each 10min session were assigned to a 1-s ISI group, a 2-min time of task group, a 2.5-h PW level and a 60° phase of the circadian rhythm of core body temperature (as a measure of time of day). Responses following short ISIs (2-5s) were significantly slower and more varied than responses following longer ISIs (5-10s). The likelihood of a lapse was also higher for short ISIs, while the probability of a false start increased as a function of ISI. These effects were independent of the influences of time of day, prior wake and time on task. Hence, mixed model ANOVAs comprising only long ISIs (5-10s) contained stronger effect sizes for fatigue than a model of all ISIs (2-10s). Including an ISI variable in a model improved the model fit and explained more variance associated with fatigue. Short ISIs resulted in long RTs both in the presence and absence of fatigue, possibly due to preparation processes or ISI conditioning. Hence, omitting short ISI trials from RT means or including an ISI variable in analysis can reduce unwanted variance in PVT data, improving the sensitivity of the PVT to fatigue.

The influence of vibration on seated human drowsiness

Although much is known about human body vibration discomfort, there is little research data on the effects of vibration on vehicle occupant drowsiness. A laboratory experimental setup has been developed. Vibration was applied to the volunteers sitting on the vehicle seat mounted on the vibration platform. Seated volunteers were exposed to a Gaussian random vibration, with 1-15 Hz frequency bandwidth at 0.2 ms(-2) r.m.s., for 20-minutes. Two drowsiness measurement methods were used, Psychomotor Vigilance Test (PVT) and Karolinska Sleepiness Scale (KSS). Significant changes in PVT (p<0.05) and KSS (p<0.05) were detected in all eighteen volunteers. Furthermore, a moderate correlation (r>0.4) was observed between objective measurement (PVT) and subjective measurement (KSS). The results suggest that exposure to vibration even for 20-minutes can cause significant drowsiness impairing psychomotor performance. This finding has important implications for road safety.

Infant sleep and feeding patterns are associated with maternal sleep, stress, and depressed mood in women with a history of major depressive disorder (MDD)

Our goal was to examine associations of infant sleep and feeding patterns with maternal sleep and mood among women at risk for postpartum depression. Participants were 30 women (age ± SD = 28.3 ± 5.1 years) with a history of MDD (but not in a mood episode at enrollment) who completed daily sleep diaries, wore wrist actigraphs to estimate sleep, and had their mood assessed with the Hamilton Depression Rating Scale (HAM-D-17) during four separate weeks of the perinatal period (33 weeks pregnancy and weeks 2, 6, and 16 postpartum). They logged their infants' sleep and feeding behaviors daily and reported postnatal stress on the Childcare Stress Inventory (CSI) at week 16. Mothers' actigraphically estimated sleep showed associations with infant sleep and feeding patterns only at postpartum week 2. Shorter duration of the longest infant-sleep bout was associated with shorter maternal sleep duration (p = .02) and lower sleep efficiency (p = .04), and maternal sleep efficiency was negatively associated with the number of infant-sleep bouts (p = .008) and duration of infant feeding (p = .008). Neither infant sleep nor feeding was associated with maternal sleep at 6 or 16 weeks, but more disturbed infant sleep and more frequent feeding at 6 weeks were associated with higher HAM-D scores at 6 and 16 weeks and higher CSI scores. Sleep in the mother-infant dyad is most tightly linked in the early postpartum weeks, but mothers continue to experience disturbed sleep and infant sleep and feeding behaviors continue to be associated with mothers' depressive symptoms and stress ratings as long as 16 weeks postpartum. These data imply that interventions designed to improve maternal sleep and postpartum mood should include both mothers and infants because improving infant sleep alone is not likely to improve maternal sleep, and poor infant sleep is linked to postpartum depression and stress.

Effects of a single night of postpartum sleep on childless women's daytime functioning

STUDY OBJECTIVES

The maternal postpartum period is characterized by sleep fragmentation, which is associated with daytime impairment, mental health disturbances, and changes in melatonin patterns. In addition to sleep fragmentation, women undergo a complex set of physiological and environmental changes upon entering the postpartum period, confounding our understanding of effects of postpartum sleep disturbance. The primary study aim was to understand the basic impact of a single night of postpartum-like sleep fragmentation on sleep architecture, nocturnal melatonin levels, mood, daytime sleepiness, and neurobehavioral performance.

MEASUREMENTS AND RESULTS

For one week prior to entry into the laboratory, eleven healthy nulliparous women kept a stable sleep-wake schedule (verified via actigraphy). Participants contributed three consecutive nights of laboratory overnight polysomnography: (1) a habituation/sleep disorder screening night; (2) a baseline night; and (3) a sleep fragmentation night, when participants were awakened three times for ~30min each. Self-reported sleep quality and mood (Profile of Mood States survey) both decreased significantly after sleep fragmentation compared to baseline measurements. Unexpectedly, daytime sleepiness (Multiple Sleep Latency Test) decreased significantly after sleep fragmentation. Experimental fragmentation had no significant effect on time spent in nocturnal sleep stages, urinary 6-sulfatoxymelatonin concentration, or psychomotor vigilance test performance. Participants continued to provide actigraphy data, and daily PVTs and self-reported sleep quality assessments at home for one week following sleep fragmentation; these assessments did not differ from baseline values.

CONCLUSIONS

While there were no changes in measured physiological components of a single night of postpartum-like experimental sleep fragmentation, there were decreases in self-reported measures of mood and sleep quality. Future research should examine the effects of multiple nights of modeling postpartum-like sleep fragmentation on objective measures of sleep and daytime functioning.

Development and Validation of the Cognition Test Battery for Spaceflight

BACKGROUND

Sustained high-level cognitive performance is of paramount importance for the success of space missions, which involve environmental, physiological, and psychological stressors that may affect brain functions. Despite subjective symptom reports of cognitive fluctuations in spaceflight, the nature of neurobehavioral functioning in space has not been clarified.

METHODS

We developed a computerized cognitive test battery (Cognition) that has sensitivity to multiple cognitive domains and was specifically designed for the high-performing astronaut population. Cognition consists of 15 unique forms of 10 neuropsychological tests that cover a range of cognitive domains, including emotion processing, spatial orientation, and risk decision making. Cognition is based on tests known to engage specific brain regions as evidenced by functional neuroimaging. Here we describe the first normative and acute total sleep deprivation data on the Cognition test battery as well as several efforts underway to establish the validity, sensitivity, feasibility, and acceptability of Cognition.

RESULTS

Practice effects and test-retest variability differed substantially between the 10 Cognition tests, illustrating the importance of normative data that both reflect practice effects and differences in stimulus set difficulty in the population of interest. After one night without sleep, medium to large effect sizes were observed for 3 of the 10 tests addressing vigilant attention (Cohen's d = 1.00), cognitive throughput (d = 0.68), and abstract reasoning (d = 0.65).

CONCLUSIONS

In addition to providing neuroimaging-based novel information on the effects of spaceflight on a range of cognitive functions, Cognition will facilitate comparing the effects of ground-based analogues to spaceflight, increase consistency across projects, and thus enable meta-analyses.

Adverse Effects of Daylight Saving Time on Adolescents' Sleep and Vigilance

STUDY OBJECTIVES

Daylight saving time (DST) has been established with the intent to reduce energy expenditure, however unintentional effects on sleep and vigilance have not been consistently measured. The objective of this study was to test the hypothesis that DST adversely affects high school students' sleep and vigilance on the school days following its implementation.

METHODS

A natural experiment design was used to assess baseline and post-DST differences in objective and subjective measures of sleep and vigilance by actigraphy, sleep diary, sleepiness scale, and psychomotor vigilance testing (PVT). Students were tested during school days immediately preceding and following DST.

RESULTS

A total of 40 high school students were enrolled in this study; 35 completed the protocol. Sleep duration declined by an average of 32 minutes on the weeknights post-DST, reflecting a cumulative sleep loss of 2 h 42 min as compared to the baseline week (p = 0.001). This finding was confirmed by sleep diary analyses, reflecting an average sleep loss of 27 min/night (p = 0.004) post-DST. Vigilance significantly deteriorated, with a decline in PVT performance post-DST, resulting in longer reaction times (p < 0.001) and increased lapses (p < 0.001). Increased daytime sleepiness was also demonstrated (p < 0.001).

CONCLUSION

The early March DST onset adversely affected sleep and vigilance in high school students resulting in increased daytime sleepiness. Larger scale evaluations of sleep impairments related to DST are needed to further quantify this problem in the population. If confirmed, measures to attenuate sleep loss post-DST should be implemented.

A new likelihood ratio metric for the psychomotor vigilance test and its sensitivity to sleep loss

The Psychomotor Vigilance Test (PVT) is a widely used assay of behavioural alertness sensitive to the effects of sleep loss and circadian misalignment. However, there is currently no accepted PVT composite outcome metric that captures response slowing, attentional lapses and compensatory premature reactions observed typically in sleep-deprived subjects. We developed a novel likelihood ratio metric (LRM) based on relative frequency distributions in 50 categories of reaction times (RT) and false starts in alert and sleep-deprived subjects (acute total sleep deprivation: n = 31 subjects). The LRM had the largest effect size both in a 33-h total sleep deprivation protocol [1.96; 95% confidence interval (CI): 1.61-2.44; followed by response speed 1/RT, effect size 1.93, 95% CI: 1.55-2.65] and in a chronic partial sleep restriction protocol (1.22; 95% CI: 0.96-1.59; followed by response speed 1/RT, effect size 1.21, 95% CI: 0.94-1.59; 5 nights at 4 h sleep per night; n = 43 subjects). LRM scores correlated highly with response speed (R(2 ) = 0.986), and less well with five other common PVT outcome metrics (R(2 ) = 0.111-0.886). In conclusion, the new LRM is a sensitive PVT outcome metric with high statistical power that takes subtle sleep loss-related changes in the distribution of reaction times (including false starts) into account, is not prone to outliers, does not require baseline data and can be calculated and interpreted easily. Congruence between LRM and PVT response speed and their similar effect size rankings support the use of response speed as the primary, most sensitive and most parsimonious standard PVT outcome metric for determining neurobehavioural deficits from sleep loss.

Sleepiness and Safety: Where Biology Needs Technology

Maintaining human alertness and behavioral capability under conditions of sleep loss and circadian misalignment requires fatigue management technologies due to: (1) dynamic nonlinear modulation of performance capability by the interaction of sleep homeostatic drive and circadian regulation; (2) large differences among people in neurobehavioral vulnerability to sleep loss; (3) error in subjective estimates of fatigue on performance; and (4) to inform people of the need for recovery sleep. Two promising areas of technology have emerged for managing fatigue risk in safety-sensitive occupations. The first involves preventing fatigue by optimizing work schedules using biomathematical models of performance changes associated with sleep homeostatic and circadian dynamics. Increasingly these mathematical models account for individual differences to achieve a more accurate estimate of the timing and magnitude of fatigue effects on individuals. The second area involves technologies for detecting transient fatigue from drowsiness. The Psychomotor Vigilance Test (PVT), which has been extensively validated to be sensitive to deficits in attention from sleep loss and circadian misalignment, is an example in this category. Two shorter-duration versions of the PVT recently have been developed for evaluating whether operators have sufficient behavioral alertness prior to or during work. Another example is online tracking the percent of slow eyelid closures (PERCLOS), which has been shown to reflect momentary fluctuations of vigilance. Technologies for predicting and detecting sleepiness/fatigue have the potential to predict and prevent operator errors and accidents in safety-sensitive occupations, as well as physiological and mental diseases due to inadequate sleep and circadian misalignment.

Sleepiness and Safety: Where Biology Needs Technology

Maintaining human alertness and behavioral capability under conditions of sleep loss and circadian misalignment requires fatigue management technologies due to: (1) dynamic nonlinear modulation of performance capability by the interaction of sleep homeostatic drive and circadian regulation; (2) large differences among people in neurobehavioral vulnerability to sleep loss; (3) error in subjective estimates of fatigue on performance; and (4) to inform people of the need for recovery sleep. Two promising areas of technology have emerged for managing fatigue risk in safety-sensitive occupations. The first involves preventing fatigue by optimizing work schedules using biomathematical models of performance changes associated with sleep homeostatic and circadian dynamics. Increasingly these mathematical models account for individual differences to achieve a more accurate estimate of the timing and magnitude of fatigue effects on individuals. The second area involves technologies for detecting transient fatigue from drowsiness. The Psychomotor Vigilance Test (PVT), which has been extensively validated to be sensitive to deficits in attention from sleep loss and circadian misalignment, is an example in this category. Two shorter-duration versions of the PVT recently have been developed for evaluating whether operators have sufficient behavioral alertness prior to or during work. Another example is online tracking the percent of slow eyelid closures (PERCLOS), which has been shown to reflect momentary fluctuations of vigilance. Technologies for predicting and detecting sleepiness/fatigue have the potential to predict and prevent operator errors and accidents in safety-sensitive occupations, as well as physiological and mental diseases due to inadequate sleep and circadian misalignment.

Sleep disturbance and neurobehavioral performance among postpartum women

STUDY OBJECTIVES

Sleep disturbances cause neurobehavioral performance and daytime functioning impairments. Postpartum women experience high levels of sleep disturbance. Thus, the study objective was to describe and explore the relation between neurobehavioral performance and sleep among women during the early postpartum period.

DESIGN

Longitudinal field-based study.

PARTICIPANTS

There were 70 primiparous women and nine nulliparous women in a control group.

INTERVENTIONS

None.

METHODS AND RESULTS

During their first 12 postpartum weeks, 70 primiparous women wore continuous wrist actigraphy to objectively monitor their sleep. Each morning they self-administered the psychomotor vigilance test (PVT) to index their neurobehavioral performance. Nine nulliparous women in a control group underwent the same protocol for 12 continuous weeks. Postpartum PVT mean reciprocal (1/RT) reaction time did not differ from that of women in the control group at postpartum week 2, but then worsened over time. Postpartum slowest 10% 1/RT PVT reaction time was significantly worse than that of women in the control group at all weeks. Despite improvements in postpartum sleep, neurobehavioral performance continued to worsen from week 2 through the end of the study. Across the first 12 postpartum weeks, PVT measures were more frequently associated with percent sleep compared with total sleep time, highlighting the deleterious consequences of sleep disruption on maternal daytime functioning throughout the early postpartum period.

CONCLUSIONS

Worsened maternal neurobehavioral performance across the first 12 postpartum weeks may have been influenced by the cumulative effects of sleep disturbance. These results can inform future work to identify the particular sleep profiles that could be primary intervention targets to improve daytime functioning among postpartum women, and indicate need for further research on the effectiveness of family leave policies. The time when postpartum women return to control-level daytime functioning is unknown.

Sleepiness, long distance commuting and night work as predictors of driving performance

Few studies have examined the effect of working night shift and long distance commuting. We examined the association between several sleep related and demographic variables, commuting distance, night work and use of mobile phones on driving performance. We used a prospective design to recruit participants and conducted a telephone survey (n = 649). The survey collected demographic and journey details, work and sleep history and driving performance concerning the day the participant was recruited. Participants also completed the Karolinska Sleepiness Scale and the Epworth Sleepiness Scale. Night workers reported significantly more sleepiness, shorter sleep duration and commuting longer distances. Seven variables were significant predictors of lane crossing. The strongest predictor was acute sleepiness (OR = 5.25, CI, 1.42–19.49, p<0.01) followed by driving ≥150 kms (OR = 3.61, CI, 1.66–7.81, p<0.001), obtaining less than 10 hours sleep in the previous 48 hours (OR = 2.58, CI, 1.03–6.46, p<0.05), driving after night shift (OR = 2.19, CI, 1.24–3.88, p<0.001), being <43 years old (OR = 1.95, CI, 1.11–3.41, p<0.05) and using mobile phones during the journey (OR = 1.90, CI, 1.10–3.27, p<0.05). Sleep related variables, long-distance commuting and night work have a major impact on lane crossing. Several interventions should be considered to reduce the level of sleepiness in night workers.