Effects of shift schedules on fatigue and physiological functions among firefighters during night duty

Influence of Night Shift Work on Heart Rate Variability in an Age- and Gender-Matched Study Group

Regular and long-term shift work is associated with a number of chronic diseases. There is some evidence that shift work also has an influence on the autonomous nervous system. Studies that have examined the effect of shift work on heart rate variability (HRV) have not taken into account age and gender. Therefore, the aim of this study was to investigate the influence of night shift based on 24 h long-term analyses carried out on non-night shift days with a matched control group for age and gender. In total, 172 (128 male, 44 female) healthy shift night workers were compared with subjects from a non-night shift worker group at a ratio of 1:1, forming matched pairs based on the subjects' sex and age. HRV parameters were analyzed based on 24 h ECG recording. An analysis of the HRV parameters showed only a small difference but without statistical significance between the two groups with regard to all of the HRV parameters examined (SDNN, RMSSD, NN50, pNN50, VLF, LF, HF, LF/HF, DFA1, and DFA2). An analysis of the subgroup of subjects who had only worked night shifts for a minimum of 10 or 20 years, with the respective pairs matched by age and gender, did not reveal any significant differences between the HRV parameters of employees working night shifts and those not working night shifts. Taking into account qualitative aspects of HRV analysis, this study was thus able to show that working night shifts for many years may not have as big an influence on HRV as had been assumed so far.

Strategies that nurses working irregular night shifts use to improve sleep quality: A qualitative study among good and poor sleepers

AIMS

To assess the sleep strategies that nurses working irregular night shifts use to improve their sleep quality, and to compare the strategies of good and poor sleepers to determine whether the differences between the two groups could provide insights into possible effective strategies.

DESIGN

A qualitative descriptive study.

METHODS

The study was conducted from September 2019 to January 2020. Thirty-four nurses working irregular night shifts participated; 17 were classified as good sleepers and 17 as poor sleepers based on the Sleep-Wake Experience List, a validated self-report instrument that measures one's sleep quality. Interviews were conducted using open questions to explore strategies around the night-shift set. The interviews were analysed using thematic analysis.

FINDINGS

Both groups described similar and different strategies that help them work and sleep well during and after night shifts. However, good sleepers mentioned a greater number of strategies and seemed to have thought about them more than poor sleepers. The most common strategies were having a clear structure, being organized-especially regarding sleeping time-maintaining a daily routine and adjusting their sleep environment.

CONCLUSION

Healthcare institutions should consider offering education and training programs aimed at empowering nurses who work irregular night shifts. These programs should provide nurses with various sleep strategies to enhance their sleep quality and overall well-being.

IMPLICATIONS FOR THE PROFESSION

Nurses working irregular night shifts can possibly enhance their sleep quality by making personalized plans, for example, including a clear day structure, or an optimized sleep environment.

IMPACT

The study focused on how nurses working night shifts could possibly enhance their sleep quality. The findings highlight the importance of providing nurses with diverse sleep strategies to improve sleep quality, helping them to identify what works best for them and consistently apply these strategies.

REPORTING METHOD

The Consolidated Criteria for Reporting Qualitative Research guidelines were followed.

PATIENT OR PUBLIC CONTRIBUTION

Nurses working irregular night shifts at Maastricht University Medical Center in Maastricht, the Netherlands, who agreed to participate in the study, engaged in a discussion to assess the relevance of sleep quality to their work. They were also encouraged to share their perspectives during the interviews.

Inappropriate timing of salt intake increases the risk of heat-related illness: An observational study

The importance of salt intake in preventing heat-related illness (HRI) is well established, however, the specific method of ingestion has not been sufficiently studied. This study, therefore, aimed to investigate the optimal timing of salt intake to prevent HRI during hot outdoor work. We recruited 28 healthy male firefighters working at a fire department in Japan. They were provided a questionnaire to complete before and after receiving training in the summer season. We assessed their salt intake as before, during, and after training or none. In addition, they completed a brief self-administered diet history questionnaire to evaluate their daily salt and alcohol intake. HRI was determined through subjective and objective symptoms listed in the questionnaire, and environmental data were obtained from a national database. Subsequently, factors related to HRI were determined using a logistic regression model. The mean age of the participants was 31.0 ± 7.7 years. The study was performed within 250 working days, and we detected 28 HRI symptoms (11.2%). The median alcohol intake was 25.6 g/day when calculated according to the actual work system. Logistic mixed effect model analysis revealed that salt intake before training (OR: 5.893, 95% CI: 1.407-24.675), and salt intake before and during training (OR: 22.889, 95% CI: 4.276-122.516) were positively associated with HRI symptoms. The results indicate that inappropriate timing of salt intake increases the risks of HRI. Thus, a timely intake of salt in adequate amounts may be important in preventing these risks.

An Examination of Subjective and Objective Measures of Stress in Tactical Populations: A Scoping Review

Persons working in tactical occupations are often exposed to high-stress situations. If this stress is to be measured, an understanding of the stress outcomes used in these occupations is needed. The aim of this review was to capture and critically appraise research investigating subjective and objective outcome measures of physiological stress in tactical occupations. Several literature databases (PubMed, EMBASE, EBsco) were searched using key search words and terms. Studies meeting inclusion criteria were critically evaluated and scored by two authors using the Joanne Briggs Institute (JBI) critical appraisal tool. Of 17,171 articles, 42 studies were retained. The Cohen's Kappa agreement between authors was 0.829 with a mean JBI Score of included studies of 8.1/9 ± 0.37 points. Multiple subjective and objective measures were assessed during a variety of high-stress tasks and environments across different occupations, including police officers, emergency service personnel, firefighters, and soldiers in the military. Common objective outcomes measures were heart rate, cortisol, and body temperature, and subjective measures were ratings of perceived exertion, and the Self Trait Anxiety Inventory. Often used in combination (i.e., subjective and objective), these outcome measures can be used to monitor stressors faced by tactical personnel undergoing on-the-job training.

Wilderness First Responder Medical Clearance - A Scoping Review with Recommendations

BACKGROUND AND PURPOSE

Due to environmental extremes, as well as the nature of the work itself, wilderness first responders are at risk of incurring medical events in the line of duty. There currently do not exist standardized and scientifically supported methods to screen for a wilderness first responder's risk of incurring a medical event.

METHODS

We performed multiple scoping reviews using PubMed and CINAHL. The reviews covered six medical screening criteria based on previous recommendations from the National Fire Protection Association (NFPA) and the US Forest Service, and we grouped our reviews into two categories: articles that addressed objective screening criteria, and articles that addressed subjective findings with the first responder.

RESULTS

Of the objective criteria, our reviews identified 21 articles addressing the ability to screen for risk of incurring a medical event by evaluation of a first responder's heart rate, 12 by blood pressure assessment, and 56 by assessment of body temperature. Of the subjective criteria we identified 19 articles focused on self-assessment, 34 articles on the use of standardized tools to assess for fatigue and sleepiness, and two articles on assessment of a first responder's urine to determine level of dehydration. We also identified seven additional articles through a hand search. Overall, there were 151 articles identified in our scoping reviews. These articles were largely of low quality, consisting mostly of case series without comparison groups.

CONCLUSION

There is a dearth of high-quality research into the medical assessment of first responders. We recommend that this paper, and measures discussed within it, be used as a starting point in the development of an evidence-based assessment protocol for wilderness first responders. We also recommend the development of a national database of medical events incurred by wilderness first responders to facilitate higher-quality research of screening protocols in this community.

The effect of extended shift work on autonomic function in occupational settings: A systematic review and meta-analysis

OBJECTIVE

To examine the effect of 24-h shift work on autonomic nervous system function via heart rate variability (HRV) methodologies.

METHODS

Electronic databases (indexed in either PubMed, MEDLINE, CINAHL, SPORTDiscus, or OpenDissertations) were searched from January 1964 to March 2023. A modified Downs and Black checklist was used for assessing methodological quality and the Grading of Recommendation, Assessment, Development, and Evaluation (GRADE) approach was used to evaluate the quality of evidence. Study design, study population, study sample, shift work description, and assessment of HRV metrics and methods were extracted from each study.

FINDINGS

A total of 58 478 study articles were identified, of which 12 articles met inclusion criteria. Sample sizes varied from eight to 60 participants, with the ratio of low- to high-frequency HRV (LF/HF) as the most common frequency-domain variable reported. Of the nine included studies that observed LF/HF, three (33.3%) demonstrated a significant increase after 24-h shift work. Moreover, of the five studies that reported HF, two (40%) noted a significant decrease after 24-h shift work. When observing risk of bias, two (16.6%) studies were low quality, five (41.7%) were moderate quality, and five (41.7%) were high quality.

INTERPRETATION

There were inconsistent findings demonstrating an effect of 24-h shift work on autonomic function, with a suggested shift away from parasympathetic dominance. Discrepancies in HRV methodologies, such as the duration of recordings and hardware used for measurement, may have contributed to the disparity in findings. In addition, differences in roles and responsibilities across occupations may explain the incongruence in findings across studies.

A Systematic Review of Heart Rate Variability as a Measure of Stress in Medical Professionals

Understanding the physiological effects of responding to crises is a critical component in understanding how to manage and prepare medical professionals to be crisis responders. Heart rate variability (HRV) is the variation in rate between a succession of R-R intervals. This variation is not only affected by physiological processes such as respiration or metabolic rate but is also directly controlled by the autonomic nervous system. As such, heart rate variability has been proposed as a noninvasive tool to measure the physiological stress response. The aim of this systematic review is to consolidate heart rate variability literature in the context of medical emergencies to determine if heart rate variability changes predictably from baseline when responding to medical crises. This may demonstrate utility as an objective, noninvasive measure of stress response. A systematic literature review of six databases yielded 413 articles, 17 of which met our inclusion criteria of being written in English, measuring HRV in healthcare providers, and measuring HRV in real or simulated medical resuscitations or procedures. Articles were then analyzed using the Grades of Recommendation, Assessment, Development, and Evaluation (GRADE) scoring system. Out of the 17 articles reviewed, 11 demonstrated statistically significant results showing heart rate variability responding in a predictable manner to stress. Three articles utilized a medical simulation as the stressor, six used medical procedures, and eight used medical emergencies encountered during clinical work. Overall, a predictable trend in heart rate variability metrics of standard deviation from the mean value of normal-to-normal (N-N) intervals (SDNN), root mean square of the successive differences (RMSSD), mean number of times per time interval in which the change in successive normal sinus (N-N) intervals exceeds 50 ms (PNN50), low frequency % (LF%), and low-frequency-to-high-frequency ratio (LF/HF) was observed when responding to stress. This systematic literature review showed that heart rate variability among healthcare providers responding to stressful scenarios follows a predictable pattern of change and expands our understanding of the physiology of stress in healthcare providers. This review supports the use of HRV to monitor stress during high-fidelity simulation to ensure that appropriate physiological arousal is achieved during the training of medical personnel.

Fatigue sensitivity and mental health among trauma-exposed firefighters

Background

Firefighters are faced with numerous work-related demands and stressors, including exposure to potentially traumatic events, and are thus at an increased risk for poor mental health outcomes. To better understand the mental health of trauma-exposed firefighters, the current study sought to examine the association of fatigue sensitivity with posttraumatic stress disorder (PTSD), anxiety, and depressive symptom severity in a cross-sectional study design.

Methods

Participants included 107 (M _age = 40.8 years; SD _age = 8.95; age range: 21-67 years; 95.0% male) trauma-exposed firefighters.

Results

Findings from the current study indicated that fatigue sensitivity was a statistically significant clinical correlate of PTSD, anxiety, and depressive symptom severity. The statistically significant incremental effects were small to medium across the mental health variables, but evident after accounting for years in the fire service, sleep quality, and trauma load.

Conclusions

The present data provide initial empirical evidence for the role of fatigue sensitivity in terms of a broad range of mental health indices among trauma-exposed firefighters.

Physiological Demands of Basic Fire Management Tasks in Members of the Canadian Armed Forces: A Pilot Study

INTRODUCTION

Members of the Canadian Armed Forces (CAF) are required to meet the minimum standards of the Fitness for Operational Requirements of CAF Employment (FORCE) job-based simulation test (JBST) and must possess the capacity to perform other common essential tasks. One of those tasks is to perform basic fire management tasks during fire emergencies to mitigate damage and reduce the risk of injuries and/or death until professional firefighters arrive at the scene. To date however, the physiological demands of common firefighting tasks have mostly been performed on professional firefighters, thus rendering the transferability of the demands to the general military population unclear. This pilot study aimed to quantify, for the first time, the physiological demands of basic fire management tasks in the military, to determine if they are reflected in the FORCE JBST minimum standard. We hypothesized that the physiological demands of basic fire management tasks within the CAF are below the physiological demands of the FORCE JBST minimum standard, and as such, be lower than the demands of professional firefighting.

MATERIALS AND METHODS

To achieve this, 21 CAF members (8 females; 13 males; mean [SD] age: 33 [10] years; height: 174.5 [10.5] cm; weight: 85.4 [22.1] kg, estimated maximal oxygen uptake [$\dot V$O2peak]: 44.4 (7.4) mL kg-1 min-1) participated in a realistic, but physically demanding, JBST developed by CAF professional firefighting subject matter experts. The actions included lifting, carrying, and manipulating a 13-kg powder fire extinguisher and connecting, coupling, and dragging a 38-mm fire hose over 30 m. The rate of oxygen uptake ($\dot V$O2), heart rate, and percentage of heart rate reserve were measured continuously during two task simulation trials, which were interspersed by a recovery period. Rating of perceived exertion (6-no exertion; 20-maximal exertion) was measured upon completion of both task simulations. Peak $\dot V$O2 ($\dot V$O2peak) was estimated based on the results of the FORCE JBST.

RESULTS

The mean (SD) duration of both task simulation trials was 3:39 (0:19) min:s, whereas the rest period in between both trials was 62 (19) minutes. The mean O2 was 21.1 (4.7) mL kg-1 min-1 across trials, which represented 52.1 (12.2) %$\dot V$O2peak and ∼81% of the FORCE JBST. This was paralleled by a mean heart rate of 136 (18) beats min-1, mean percentage of heart rate reserve of 61.2 (10.8), and mean rating of perceived exertion of 11 ± 2. Other physical components of the JBST consisted of lifting, carrying, and manipulating a 13-kg load for ∼59 seconds, which represents 65% of the load of the FORCE JBST. The external resistance of the fire hose drag portion increased up to 316 N, translating to a total of 6205 N over 30 m, which represents 96% of the drag force measured during the FORCE JBST.

CONCLUSIONS

Our findings demonstrate that the physiological demands of basic fire management tasks in the CAF are of moderate intensity, which are reflected in the CAF physical fitness standard. As such, CAF members who achieve the minimum standard on the FORCE JBST are deemed capable of physically performing basic fire management tasks during fire emergencies.

Monitoring stress and allostatic load in first responders and tactical operators using heart rate variability: a systematic review

BACKGROUND

Awareness of the cumulative stress placed on first responders and tactical operators is required to manage acute fatigue, which can impair occupational performance, and may precipitate negative chronic health outcomes. The aim of this review was to investigate the utility of heart rate variability (HRV) to monitor stress and allostatic load among these populations.

METHODS

A systematic search of Academic Search Complete, MEDLINE complete, PsycINFO, SPORTDiscus and Scopus databases was conducted. Eligibility criteria: original peer reviewed research articles, written in English, published between 1985 and 2020, using human participants employed as a first responder or tactical operator, free from any psychological disorder.

RESULTS

Of the 360 articles screened, 60 met the inclusion criteria and were included for full text assessment. Articles were classified based on single or repeated stressor exposure and the time of HRV assessment (baseline, during stressor, post stressor). Singular stressful events elicited a reduction in HRV from baseline to during the event. Stressors of greater magnitude reduced HRV for extended durations post stressor. Lower resting HRV was associated with lower situational awareness and impaired decision-making performance in marksmanship and navigation tasks. There were insufficient studies to evaluate the utility of HRV to assess allostatic load in repeated stressor contexts.

CONCLUSION

A reduction in HRV occurred in response to acute physical and cognitive occupational stressors. A slower rate of recovery of HRV after the completion of acute occupational stressors appears to occur in response to stressors of greater magnitude. The association between lower HRV and lower decision-making performance poses as a useful tool but further investigations on within subject changes between these factors and their relationship is required. More research is required to investigate the suitability of HRV as a measure of allostatic load in repeated stress exposures for fatigue management in first responder and tactical operators.

Using Ecological Momentary Assessment to Examine the Effects of Duty Status on Acute Stress and Tiredness in Firefighters: A Pilot Study

OBJECTIVE

Characterize firefighters' acute stress and tiredness by duty status (ie, "off night/day," "on night/day").

METHODS

Thirty nine career firefighters completed three, eight-day smartphone-based ecological momentary assessment periods with seven surveys per day assessing stress and tiredness. Mixed-effects location scale models examined duty status effects on stress and tiredness.

RESULTS

Firefighters' lowest stress and tiredness levels were when off-duty (β = 16.27 and β = 24.71, respectively) and their highest levels were when on-duty (β = 24.47 and β = 32.18, respectively). Within-subject effects of duty status accounted for a larger proportion of variability in stress and tiredness for all duty types, except for stress when "on-duty night/off-duty day."

CONCLUSIONS

Firefighters had more similar stress and tiredness outcomes when they were on-duty and less similar outcomes when off-duty. This could be due to firefighters having more similar experiences when they are on- versus off-duty.

Comparison of Cortisol level by Shift Cycle in Korean Firefighters

(1) Study Objectives: By investigating the change of cortisol levels during shift cycles among professional firefighters in Korea, this study aims to evaluate the difference between individuals' stress response and the recovery of their circadian rhythm after working night shifts. (2) Methods: A total of 325 shift firefighters, who were working in 3, 6, 9, or 21 day cycles, participated in the study. Their urinary and serum cortisol levels were measured during the day (09-18), during the night (18-09), and every 24 h (09-09) per shift cycle, and adjustments were made for confounding factors. (3) Results: Serum cortisol levels were significantly increased after working during the night or for 24 h compared with that of working throughout the day. However, whether working night or 24 h shifts, the serum cortisol levels were undoubtedly different based on the 3, 6, 9, or 21 day cycles. In all shift cycles, the urinary cortisol level decreased during the night or throughout the 24 h shifts compared with sleeping during this time, but this was considered to be significantly applicable only to those working in 21 day cycles. Additionally, in serial measurements, the recovery of urinary cortisol secretion after a night or 24 h shift was successful for individuals working in 9 day cycles, but the recovery was delayed for those working in 6 or 21 day cycles. (4) Conclusions: After analyzing the urine cortisol levels, the study indicates that only subjects working in 9 day cycles fully recovered their circadian rhythm while those working in 6 day or 21 day cycles did not completely recover. Therefore, it is important to recognize how stressful night shifts can be, and it is crucial to enhance firefighters' current shift cycles in order to allow sufficient recovery of their circadian rhythm as well as the prevention of disrupting their circadian rhythm after working at night. Further research is necessary to take into account the amount of work load, the challenges of being sleep deprived, and the individual's capacity to overcome sleepiness.

The Effect of Various Hot Environments on Physiological Responses and Information Processing Performance Following Firefighting Activities in a Smoke-Diving Room

Background

Fire service workers often implement multiple duties in the emergency conditions, with such duties being mostly conducted in various ambient temperatures.

Methods

The aim of the current study was to assess the firefighters' physiological responses, information processing, and working memory prior to and following simulated firefighting activities in three different hot environments. Seventeen healthy male firefighters performed simulated firefighting tasks in three separate conditions, namely (1) low heat (LH; 29–31°C, 55–60% relative humidity), (2) moderate heat (MH; 32–34°C, 55–60% relative humidity), and (3) severe heat (SH; 35–37°C, 55–60% relative humidity). It took about 45–50 minutes for each firefighter to finish all defined firefighting activities and the paced auditory serial addition test (PASAT).

Results

At the end of all the three experimental conditions, heart rate (HR) and tympanic temperature (TT) increased, while PASAT scores as a measure of information processing performance decreased relative to baseline. HR and TT were significantly higher at the end of the experiment in the SH (159.41 ± 4.25 beats/min; 38.22 ± 0.10°C) compared with the MH (156.59 ± 3.77 beats/min; 38.20 ± 0.10°C) and LH (154.24 ± 4.67 beats/min; 38.17 ± 0.10°C) conditions (p < 0.05). There was no significant difference in PASAT scores between LH and MH (p > 0.05). Nonetheless, there was a measurable difference in PASAT scores between LH and SH (p < 0.05).

Conclusion

These consequences demonstrate that ambient temperature is effective in raising the physiological responses following firefighting activities. It is therefore argued that further increase of ambient temperature can impact firefighters' information processing and working memory during firefighting activity.

Arterial stiffness, oxidative stress, and smoke exposure in wildland firefighters

OBJECTIVES

To assess the association between exposure, oxidative stress, symptoms, and cardiorespiratory function in wildland firefighters.

METHODS

We studied two Interagency Hotshot Crews with questionnaires, pulse wave analysis for arterial stiffness, spirometry, urinary 8-iso-prostaglandin F2α (8-isoprostane) and 8-hydroxy-2'-deoxyguanosine (8-OHdG), and the smoke exposure marker (urinary levoglucosan). Arterial stiffness was assessed by examining levels of the aortic augmentation index, expressed as a percentage. An oxidative stress score comprising the average of z-scores created for 8-OHdG and 8-isoprostane was calculated.

RESULTS

Mean augmentation index % was higher for participants with higher oxidative stress scores after adjusting for smoking status. Specifically for every one unit increase in oxidative stress score the augmentation index % increased 10.5% (95% CI: 2.5, 18.5%). Higher mean lower respiratory symptom score was associated with lower percent predicted forced expiratory volume in one second/forced vital capacity.

CONCLUSIONS

Biomarkers of oxidative stress may serve as indicators of arterial stiffness in wildland firefighters.

Very Long (> 48 hours) Shifts and Cardiovascular Strain in Firefighters: a Theoretical Framework

Shift work and overtime have been implicated as important work-related risk factors for cardiovascular disease (CVD). Many firefighters who contractually work on a 24-hr work schedule, often do overtime (additional 24-hr shifts) which can result in working multiple, consecutive 24-hr shifts. Very little research has been conducted on firefighters at work that examines the impact of performing consecutive 24-hr shifts on cardiovascular physiology. Also, there have been no standard field methods for assessing in firefighters the cardiovascular changes that result from 24-hr shifts, what we call “cardiovascular strain”. The objective of this study, as the first step toward elucidating the role of very long (> 48 hrs) shifts in the development of CVD in firefighters, is to develop and describe a theoretical framework for studying cardiovascular strain in firefighters on very long shifts (i.e., > 2 consecutive 24-hr shifts). The developed theoretical framework was built on an extensive literature review, our recently completed studies with firefighters in Southern California, e-mail and discussions with several firefighters on their experiences of consecutive shifts, and our recently conducted feasibility study in a small group of firefighters of several ambulatory cardiovascular strain biomarkers (heart rate, heart rate variability, blood pressure, salivary cortisol, and salivary C-reactive protein). The theoretical framework developed in this study will facilitate future field studies on consecutive 24-hr shifts and cardiovascular health in firefighters. Also it will increase our understanding of the mechanisms by which shift work or long work hours can affect CVD, particularly through CVD biological risk factors, and thereby inform policy about sustainable work and rest schedules for firefighters.

Delinking resident duty hours from patient safety

Patient safety is a powerful motivating force for change in modern medicine, and is often cited as a rationale for reducing resident duty hours. However, current data suggest that resident duty hours are not significantly linked to important patient outcomes. We performed a narrative review and identified four potential explanations for these findings. First, we question the relevance of resident fatigue in the creation of harmful errors. Second, we discuss factors, including workload, experience, and individual characteristics, that may be more important determinants of resident fatigue than are duty hours. Third, we describe potential adverse effects that may arise from--and, therefore, counterbalance any potential benefits of--duty hour reductions. Fourth, we explore factors that may mitigate any risks to patient safety associated with using the services of resident trainees. In summary, it may be inappropriate to justify a reduction in working hours on the grounds of a presumed linkage between patient safety and resident duty hours. Better understanding of resident-related factors associated with patient safety will be essential if improvements in important patient safety outcomes are to be realized through resident-focused strategies.

The effects of a self-selected nap opportunity on the psychophysiological, performance and subjective measures during a simulated industrial night shift regimen

This study compared the effects of a 1 h self-selected recovery period to those of a standard night shift arrangement (with a total break time of 1-h) over a simulated three-day night shift schedule in a laboratory setting. Results showed that the inclusion of the flexible nap scheme resulted in higher performance output, improvements in physiological strain responses and reduced sleepiness during each night shift and generally over the three-night cycle. Certain variables also revealed the impact of napping compared with the standard rest break condition on the circadian rhythm. The sleep diary records show that the inclusion of the current intervention did not significantly reduce daytime recovery sleep. The results suggest that the potential benefits of flexible napping may outweigh the logistical effort it requires in a workplace environment.

PRACTITIONER SUMMARY

Consensus on appropriate napping strategies for shift work remains a challenge. This simulated night shift laboratory study sought to determine the effects of a 1-h self-selected nap opportunity relative to a normal shift set-up. The nap improved performance and decreased sleepiness, without affecting daytime sleep.

A Comparison of the Effects of Fixed- and Rotating-Shift Schedules on Nursing Staff Attention Levels

Purpose:

Sleep deficit affects neurobehavioral functioning, reduces attention and cognitive function, and negatively impacts occupational safety. This study investigated selective attention levels of nursing staff on different shifts.

Methods:

Using a prospective, randomized parallel group study, selective attention was measured using the d2 test in 62 nursing staff in a medical center in Taiwan.

Findings:

There were significant differences in selective attention indicators (E%) between the fixed-day-shift group (control group) and rotating-shift group (experimental group): The percentage of errors (E%) for night-shift workers in the rotating-shift group was higher than that of fixed-day-shift workers, while the total number of items scanned minus error (TN − E) and concentration performance (CP) scores were higher for fixed-day-shift workers. Within the experimental group, the error rate on night shift was 0.44 times more than that on day shift and .62 times more than on evening shift; the TN-E on night shift was 38.99 items less than that on day shift, and the CP was 27.68 items less on night shift than on day shift; indicating that staff on the night shift demonstrated poorer speed and accuracy on the overall test than did the staff on day shifts.

Conclusions:

Inadequate sleep and a state of somnolence adversely affected the attention and operation speed of work among night-shift workers. More than 2 days off is suggested when shifting from the night shift to other shifts to provide adequate time for circadian rhythms to adjust.

Sleep Quality in Nurses

The study investigated the number of days off nurses working night shifts need to recover their sleep quality to the level of daytime workers during their days off. This study included 30 day-shift nurses and 32 night-shift nurses. It was conducted as a randomized clinical trial in the medical and surgical wards of a medical center in northern Taiwan in May and June 2010 using sleep diaries and sleep parameters collected by actigraphy on different workdays and days off. On workdays, the night-shift group had significantly less total sleep time (TST) on Day 5 and significantly lower sleep efficiency (SE) on Day 3 than the day-shift group. TSTs of the two groups on days off were higher than those on workdays. On the 4th consecutive day off, higher TST, a decrease in WASO, and an increase in SE suggests that the night-shift group had recovered their sleep quality to the level of the day-shift group on their days off. The SE of the night-shift group exceeded that of the day-shift group after the 4th consecutive day off, though the difference was not statistically significant in the present study. Based on these data, it is recommended that night-shift workers arrange a period of at least 4 days off after 5 consecutive night shifts and at least 5 days off if the staff who have previously worked night shifts are being assigned a set of different shifts.

Activity-rest schedules in physically demanding work and the variation of responses with age

Workers in physically demanding occupations require work breaks to recover from exertion. In a laboratory setting, we investigated the impact of ergometer cycling for 7 h in two conditions with an identical total break time but with two different activity-rest schedules. We hypothesised that more frequent but shorter breaks lead to less psychophysical strain and its effects than do less frequent but longer breaks, particularly for older workers. Twenty-nine participants representing three different age groups were tested in both conditions. Heart rate, perceived exertion/tension and feelings of fatigue were assessed and used as dependent variables. Results indicate no general activity-rest differences as well as no age-related differences of break effects under the condition of subjectively equal straining load. However, heart rate was found to be lower at some measurement points in the frequent-short-break condition and perceived exertion was lower in the infrequent-long-break condition.

PRACTITIONER SUMMARY

Design of activity-rest schedules in physically demanding occupations is a key issue in the prevention of strain and hence of interest to ergonomists. Our study suggests that breaks during physically demanding work have the same effect if they are frequent and short or infrequent and long, regardless of age.

Physiological and psychological impacts on male medical interns during on-call duty

This study aimed to explore the physiological and psychological impacts on male medical interns during on-call duty (OCD). A prospective study of 13 medical interns was carried out using repeated testing during an on-call internal medicine and a duty-free course. There are 10 OCDs per month and each duty is composed of 33.5 consecutive work hours followed by 2 duty-free days for a time period of 3 months. Spectral analysis of R-R intervals was performed to evaluate the participants' heart rate variability. Among the three main spectral components distinguished, a high-frequency (HF) component of 0.15-0.4 Hz and a low-frequency component (LF) of 0.04-0.15 Hz were analyzed. The ratio of LF and HF (LF/HF) was also calculated. Reduced LF/HF, which suggests reduced cardiac sympathetic modulation, was found during duty night work. Increased HF was identified during the first sleep after OCD, which corresponded to the sleepiness scales. The OCD causes temporary emotional influence by the findings of higher anxiety and depression scores. In addition, inattention and impulsiveness, as represented by the continuous performance test score and lower nocturnal sympathetic modulation, were found, which indicated the differences between the internal medicine course and duty-free course. Our study suggests that 10 stressful on-call duties monthly result in reduced sympathetic modulation during duty night work, high anxiety and depression state, and a persistent inattention.

The effect of shift rotation on employee cortisol profile, sleep quality, fatigue, and attention level: a systematic review

BACKGROUND

Disrupted circadian rhythm, especially working night duty together with irregular sleep patterns, sleep deprivation, and fatigue, creates an occupational health risk associated with diminished vigilance and work performance.

PURPOSE

This study reviewed the effect of shift rotations on employee cortisol profile, sleep quality, fatigue, and attention level.

METHODS

Researchers conducted a systematic review of relevant articles published between 1996 and 2008 that were listed on the following databases: SCOPUS, OVID, Blackwell Science, EBSCO Host, PsycINFO, Cochrane Controlled Trials Register, and CEPS. A total of 28 articles were included in the review.

RESULTS

Previous research into the effects of shift work on cortisol profiles, sleep quality, fatigue, and attention used data assessed at evidence Levels II to IV. Our systematic review confirmed a conflict between sleep-wake cycle and light-dark cycle in night work. Consequences of circadian rhythm disturbance include disruption of sleep, decreased vigilance, general feeling of malaise, and decreased mental efficiency. Shift workers who sleep during the day (day sleepers) experience cortisol secretion increases, which diminish the healing power of sleep and enjoy 1 to 4 hours less sleep on average than night sleepers. Sleep debt accumulation results in chronic fatigue. Prolonged fatigue and inadequate recovery result in decreased work performance and more incidents. Rotation from day shift to night shift and its effect on shift workers was a special focus of the articles retained for review.

CONCLUSIONS

Disturbed circadian rhythm in humans has been associated with a variety of mental and physical disorders and may negatively impact on work safety, performance, and productivity.

The effects of sleep deprivation on dissociable prototype learning systems

BACKGROUND

The cognitive neural underpinnings of prototype learning are becoming clear. Evidence points to 2 different neural systems, depending on the learning parameters. A/not-A (AN) prototype learning is mediated by posterior brain regions that are involved in early perceptual learning, whereas A/B (AB) is mediated by frontal and medial temporal lobe regions.

STUDY OBJECTIVES

To investigate the effects of sleep deprivation on AN and AB prototype learning and to use established prototype models to provide insights into the cognitive-processing locus of sleep-deprivation deficits.

DESIGN

Participants performed an AN and an AB prototype learning task twice, separated by a 24-hour period, with or without sleep between testing sessions.

PARTICIPANTS

Eighteen West Point cadets participated in the sleep-deprivation group, and 17 West Point cadets participated in a control group.

MEASUREMENTS AND RESULTS

Sleep deprivation led to an AN, but not an AB, performance deficit. Prototype model analyses indicated that the AN deficit was due to changes in attentional focus and a decrease in confidence that is reflected in an increased bias to respond non-A.

CONCLUSIONS

The findings suggest that AN, but not AB, prototype learning is affected by sleep deprivation. Prototype model analyses support the notion that the effect of sleep deprivation on AN is consistent with lapses in attentional focus that are more detrimental to AN than to AB. This finding adds to a growing body of work that suggests that different performance changes associated with sleep deprivation can be attributed to a common mechanism of changes in simple attention and vigilance.

The effects of sleep deprivation on information-integration categorization performance

BACKGROUND

Sleep deprivation is a serious problem facing individuals in many critical societal roles. One of the most ubiquitous tasks facing individuals is categorization. Sleep deprivation is known to affect rule-based categorization in the classic Wisconsin Card Sorting Task, but, to date, information-integration categorization has not been examined.

STUDY OBJECTIVES

To investigate the effects of sleep deprivation on information-integration category learning.

DESIGN

Participants performed an information-integration categorization task twice, separated by a 24-hour period, with or without sleep between testing sessions.

PARTICIPANTS

Twenty-one West Point cadets participated in the sleep-deprivation group and 28 West Point cadets participated in a control group.

MEASUREMENTS AND RESULTS

Sleep deprivation led to an overall performance deficit during the second testing session-that is, whereas participants allowed to sleep showed a significant performance increase during the second testing session, sleepless participants showed a small (but nonsignificant) performance decline during the second testing session. Model-based analyses indicated that a major contributor to the sleep-deprivation effect was the poor second-session performance of a subgroup of sleep-deprived participants who shifted from optimal information-integration strategies at the end of the first session to less-optimal rule-based strategies at the start of the second session. Sleep-deprived participants who used information-integration strategies in both sessions showed no drop in performance in the second session, mirroring the behavior of control participants.

CONCLUSIONS

The findings suggest that the neural systems underlying information-integration strategies are not strongly affected by sleep deprivation but, rather, that the use of an information-integration strategy in a task may require active inhibition of rule-based strategies, with this inhibitory process being vulnerable to the effects of sleep deprivation.

An ERP examination of the different effects of sleep deprivation on exogenously cued and endogenously cued attention

BACKGROUND

Behavior and neuroimaging studies have shown selective attention to be negatively impacted by sleep deprivation. Two unresolved questions are (1) whether sleep deprivation impairs attention modulation of early visual processing or of a later stage of cognition and (2) how sleep deprivation affects exogenously versus endogenously driven selective attention.

STUDY OBJECTIVES

To investigate the time course and different effects of sleep deprivation on exogenously and endogenously cued selective attention.

DESIGN

Participants performed modified Attention Network Tests (ANTs) using exogenously and endogenously cued targets to index brain networks underlying selective attention. Target-locked event-related potentials (ERPs) were recorded as participants performed the Attention Network Tests on 2 days separated by 24 hours of total sleeplessness.

PARTICIPANTS

Fourteen US Military Academy cadets and 12 US Army soldiers from the Ironhorse Brigade, Ft. Hood, Texas.

MEASUREMENT AND RESULTS

For both Attention Network Tests, sleep deprivation led to slowed response times, decreased accuracy rates, a diminished positive P3 (450- to 550-ms) ERP component, and an enhanced P2 (312- to 434-ms) ERP component. In contrast, the parietal N1 (157- to 227-ms) ERP response was reduced with sleep deprivation for endogenously, but not exogenously, cued targets. These sleep deprivation-related effects occurred in the context of typical behavior and ERP patterns expected in a cued spatial-attention task.

CONCLUSIONS

These findings suggest that as little as 24 hours of sleep deprivation affects both early and late stages of attention selection but affects endogenously driven selective attention to a greater degree than it does exogenously driven selective attention.

Heart rate variability in occupational health --a systematic review

This systematic review evaluates and summarizes the evidence of association between work-related factors and heart rate variability (HRV) in workers. We reviewed English articles indexed in MEDLINE under the key words: work, worker, occupational, industrial, and heart rate variability. Studies were included if one or more of the dependent variables was one of the time- or frequency-domain indexes of HRV [standard deviation of all normal-to-normal (NN) intervals (SDNN), mean of the 5-min standard deviations of NN intervals calculated over several hours (SDNN index), the root mean squared differences of successive NN intervals (RMSSD), integrated spectral powers of high (HF, > 0.15 Hz) and low frequency (LF, 0.04-0.15 Hz) HRV, and the LF/HF ratio] as recommended by the European Society of Cardiology and the North American Society of Pacing Electrophysiology. Physical and chemical work environments (i.e. exposure to occupational toxicants and hazardous environments), psychosocial workload (i.e. job stressors), and working time (i.e. shift work) had been examined and identified as having associations with low HF power. These findings may indicate that research into parasympathetic nervous system activity should be focused to protect cardiovascular health at work. We also propose the use of very low and ultralow frequency HRV components in autonomic research for workers' health.

Arrhythmias and increased neuro-endocrine stress response during physicians' night shifts: a randomized cross-over trial

AIMS

To evaluate the effects of a 24 h (h) physicians on-call duty (OCD) ('night shift') on 24 h electrocardiogram (ECG), heart rate variability, blood pressure (BP), and various biochemical serum and urine 'stress markers' compared with a 'regular' day at work.

METHODS AND RESULTS

The study was designed as a prospective randomized cross-over trial with each physician completing a 24 h (h) OCD and a 24 h control period including a regular 8 h non-OCD. Thirty healthy physicians with a median age of 33.5 years (range 29.0-45.0) were analysed. Twenty-four hours ECG and BP monitoring were performed and participants were instructed to fill out an event diary and perform a 24 h urine collection. Furthermore, blood was drawn before and after OCD and control day. Twenty-four hours ECG showed a higher rate of ventricular premature beats (VPB) during early morning hours (VPB 0-6 h, 0.5 vs. 0.0, P = 0.047) and increased low-frequency normalized units (29.3 vs. 25.5, P = 0.050) during night shift when compared with respective control night at home. During OCD, BP monitoring revealed a greater diastolic BP throughout 24 h (83.5 vs. 80.2 mmHg, P = 0.025) as well as during night-time (75.4 vs. 73.0, P = 0.028) associated with a higher rate of systolic BP more than 125 mmHg during sleep time. Tumour necrosis factor alpha concentrations increased significantly during night shift (0.76 vs. 0.05 pg/mL, P = 0.045). Urinary noradrenaline excretion was greater during OCD when compared with control day (46.0 vs. 36.0 microg/24 h, P = 0.007).

CONCLUSION

Our results highlight the association of OCD with an increased risk profile for cardiovascular disease. In addition to the acute effects observed, frequent night-calls over a longer period possibly elicit sustained alterations in cardiovascular homeostasis.

Twenty-four-hour shift work, depressive symptoms, and job dissatisfaction among Japanese firefighters

BACKGROUND

The influence of a 24-hr shift-work burden on firefighters' mental health has not been fully investigated. The purpose of this study is to clarify the relationships between specific workload items among firefighters engaged in 24-hr shift work and job stress as estimated by the generic job-stress questionnaire on depressive symptoms and job dissatisfaction from the National Institute for Occupational Safety and Health (NIOSH).

METHOD

The subjects were 1,301 firefighters. The questionnaire covered age, gender, job type, job class, marital status, smoking and drinking habits, number of attendances, turnout time, extra work hours, average nap-time, the Center for Epidemiologic Studies Depression Scale (CES-D), and questions from the NIOSH generic job-stress questionnaire, including those on job satisfaction.

RESULTS

In multivariate logistic regression analyses, a model that included all variables except the measures from the NIOSH generic job-stress questionnaire showed that shorter nap-time had significant higher odds ratios (ORs) for depressive symptoms and job dissatisfaction, but the significances disappeared in a fully adjusted model. In fully adjusted logistic regression analyses, low quantitative workload, low variance in workload, high intra- and intergroup conflict, low social support from a supervisor, high role conflict and ambiguity, and low self-esteem had significant higher ORs for depressive symptoms and/or job dissatisfaction.

CONCLUSIONS

Amount of workload, variance in workload, intra- and intergroup conflict, social support from a supervisor, role conflict and ambiguity, and self-esteem were significantly related to depressive symptoms and/or job dissatisfaction among Japanese firefighters. Moreover, inadequate nap-time may affect their mental health.

What do we know about ageing at work? Evidence-based fitness for duty and health in fire fighters

This study sought to collect evidence on age and workability in fire fighters, using systematic international literature searches, interviews, and secondary analyses from Dutch fire fighter studies. Recent decades have witnessed growing demands on fire fighters, who face peak task demands during duty. Older Dutch fire fighters experience greater emotional and mental demands than their younger colleagues. Huge inter-individual variation emerged in task performance with over six-fold differences in time-on-tasks and the percentage heart rate reserve between and within age groups. However, no age-effect was observed in lifting capacity during simulations. Compared to their youngest colleagues, older Dutch fire fighters face a six-fold increase in the risk of health complaints. The international literature lacks psychological age effects studies. Semi-functional tests, (e.g. exercise stress testing or push-ups) do not predict workability. Regular screening of fire fighters, using multi-modal functional tests that closely simulate real job activities, is recommended.

Impact of nap length, nap timing and sleep quality on sustaining early morning performance

The study examined how nap length, nap timing and sleep quality affect early morning performance (6:00 to 8:00). Twelve students participated in a simulated nightshift schedule (22:00 to 8:00) where the length and timing of nocturnal naps were manipulated (0:00-1:00, 0:00-2:00, 4:00-5:00 and 4:00-6:00). A performance test battery was administered consisting of a psychomotor vigilance test, a logical reasoning test, and a visual analogue scale for subjective fatigue and sleepiness. The results showed that a 120-min nap sustained early morning performance better than a 60-min nap. Taking a nap earlier or later did not affect the neurobehavioral performance tests, although participants slept more efficiently during naps later in the night shift. A negative effect of a nocturnal nap during the night shift on subsequent daytime and nocturnal sleep was not observed in the sleep architecture. It still remains unclear whether slow wave sleep plays an important role in sustaining early morning performance. In terms of work safety and sleep health, the results suggest that a longer and later nap is beneficial during night shifts.

Job stress and depressive symptoms among Japanese fire fighters

BACKGROUND

Associations between job stresses, as assessed by theoretical job stress model and depressive symptoms among fire fighters have not been fully investigated. The purpose of this study is to clarify the factors of job stress that influence the depressive symptoms in Japanese fire fighters.

METHODS

The subjects involved 1,672 fire fighters from a local government. The questionnaire comprised age, gender, job type, job class, martial status, smoking, and drinking habit, the Center for Epidemiologic Studies Depression Scale (CES-D), and The National Institute for Occupational Safety and Health (NIOSH) generic job questionnaire.

RESULTS

A group showing depressive symptoms (CES-D > or = 16) included 373 subjects (22.3%). In a multivariate logistic regression analysis, high variance in workload, high intergroup conflict, high role conflict, and low self-esteem had significantly higher odds ratio for depressive symptoms.

CONCLUSIONS

High variance in workload, high intergroup conflict, high role conflict, and low self-esteem were significantly related to depressive symptoms among Japanese fire fighters. Further prospective studies are needed to clarify the influence of these stress factors on other health outcomes, and to elucidate whether alleviation of these stress factors improve the mental health among fire fighters.

A systematic review of the neurobehavioural and physiological effects of shiftwork systems

Shiftwork is a common experience for many workers. There are a wide range of shift systems in use, with a number of general approaches and myriad variations of each one. Many aspects of shift systems have been studied, but attempts to reach definitive conclusions about appropriate designs have been hampered by a number of methodological issues. The aim of this systematic review was to provide evidence-based recommendations on the effect of various shift systems on neurobehavioural and physiological functioning and to identify areas which are lacking in appropriate evidence. Two main aspects of shift design were able to be considered-the direction of shift rotation and extended shift length (mainly 12-h shifts). Other areas for which there was at least one relevant paper of adequate methodology were the use of naps during night shifts, the starting time of shifts, and several other specific shift issues. Overall, the review found there is insufficient evidence to support definitive conclusions regarding any of these factors. However, the analysis provides support for the use of forward rotating shift systems in preference to backward rotating shift systems, at last as far as 8-h shifts are concerned. There are many unanswered questions in shift design. For these questions to be answered, it is important that the methodological shortcomings present in most of the studies published to date be overcome.