Subsequent Night Shift Research Articles

Maternal Circadian Disruption from Shift Work and the Impact on the Concentration of Melatonin in Breast Milk.

Background and Objective: Melatonin in breast milk exhibits a 24-hour circadian rhythm, present in nighttime breast milk but nearly undetectable in daytime breast milk. Shift work can disrupt the circadian timing of individuals, evident in changes in melatonin in saliva and urine samples. However, it is unknown whether these changes are also reflected in breast milk from a shift working mother. The aim of this study was to investigate whether maternal circadian rhythm disturbance from shift work impacts the melatonin concentration in breast milk. Materials and Methods: Breast milk and saliva samples were collected from 11 shift working mothers at four timepoints across five consecutive days. This included during their day shift or nonworkdays to act as a control, night shift, subsequent night shifts and postnight shift. Where possible, pre- and postfeed collections were also undertaken. Samples were grouped into four-time intervals: 12-6:30 am, 7-11:30 am, 12-6:30 pm, 7-11:30 pm, and melatonin levels (picogram per milliliter) in the breast milk and saliva samples were analyzed. Results: There was a significant decrease in breast milk melatonin (p = 0.026) at the 12-6:30 am time interval on subsequent night shifts, compared with control days. However, there was no overall time and shift type interaction effect (p = 0.70). In addition, no observed difference in melatonin levels was found in saliva samples, or when comparing pre- and postfeed breast milk. Breast milk melatonin however was found to be significantly higher compared with saliva (p > 0.001), at all but one time interval. Conclusion: The findings suggest that there is a potential effect of maternal circadian rhythm disruption from shift work on breast milk melatonin levels. This is an important step in exploring the role of maternal circadian timing and the effect on breast milk composition. Expansion of this research and exploration of other circadian rhythm misalignment sleep disorders on breast milk is highly recommended.

Cognitive Impairments during the Transition to Working at Night and on Subsequent Night Shifts.

Demands of modern society force many work operations into the night when the internal circadian timekeeping system is promoting sleep. The combination of disturbed daytime sleep and circadian misalignment, which is common in overnight shift work, decreases cognitive performance, yet how performance may differ across multiple consecutive nights of shift work is not fully understood. Therefore, the primary aim of this study was to use a simulated night-shift protocol to examine the cognitive performance and ratings of sleepiness and clear-headedness across the hours of a typical daytime shift, a first night shift with an afternoon nap and extended wakefulness, and 2 subsequent overnight shifts. We tested the hypothesis that cognitive performance would be worse on the first night shift as compared with the baseline and subsequent nighttime shifts and that performance during nighttime shifts would be reduced as compared with the baseline daytime shift. Fifteen healthy adults (6 men) were studied in the 6-day in-laboratory protocol. Results showed that working during the night increased subjective sleepiness and decreased clear-headedness and performance on the Psychomotor Vigilance Task (i.e., slower median, fastest and slowest reaction times, and increased attentional lapses), Stroop color word task (decreased number of correct responses and slower median reaction time), and calculation addition performance task (decreased number attempted and correct). Furthermore, we observed limited evidence of sleepiness, clear-headedness, or performance adaptation across subsequent nights of simulated night work. Our findings demonstrate that night-shift work, regardless of whether it is the first night shift with a nap and extended wakefulness or subsequent night shifts, decreases performance and clear-headedness as compared with the day shift.

The Impact of Shift Work on Sleep, Alertness and Performance in Healthcare Workers

Shift work is associated with impaired alertness and performance due to sleep loss and circadian misalignment. This study examined sleep between shift types (day, evening, night), and alertness and performance during day and night shifts in 52 intensive care workers. Sleep and wake duration between shifts were evaluated using wrist actigraphs and diaries. Subjective sleepiness (Karolinska Sleepiness Scale, KSS) and Psychomotor Vigilance Test (PVT) performance were examined during day shift, and on the first and subsequent night shifts (3rd, 4th or 5th). Circadian phase was assessed using urinary 6-sulphatoxymelatonin rhythms. Sleep was most restricted between consecutive night shifts (5.74 ± 1.30 h), consecutive day shifts (5.83 ± 0.92 h) and between evening and day shifts (5.20 ± 0.90 h). KSS and PVT mean reaction times were higher at the end of the first and subsequent night shift compared to day shift, with KSS highest at the end of the first night. On nights, working during the circadian acrophase of the urinary melatonin rhythm led to poorer outcomes on the KSS and PVT. In rotating shift workers, early day shifts can be associated with similar sleep restriction to night shifts, particularly when scheduled immediately following an evening shift. Alertness and performance remain most impaired during night shifts given the lack of circadian adaptation to night work. Although healthcare workers perceive themselves to be less alert on the first night shift compared to subsequent night shifts, objective performance is equally impaired on subsequent nights.

Salivary levels of alpha-amylase are associated with neurobehavioral alertness during extended wakefulness, but not simulated night-shift work

Sleep loss is one of the most common causes of accidents and errors in operational environments. Currently, no single method satisfies all of the requisite criteria of an effective system for assessing the risk of injury prior to safety being compromised. Research has concentrated towards the development of a biomarker for individualized assessment of sleepiness-related deficits in neurobehavioral alertness, with salivary alpha-amylase (sAA) recently reported as a potential biomarker during acute total sleep deprivation. The present study extends on previous research by investigating the association between sAA and neurobehavioral alertness during simulated night-shift work, during individuals are required to work at night when biological processes are strongly promoting sleep and sleep during the day when endogenous processes are promoting wakefulness.In a laboratory-controlled environment, 10 healthy non-shift working males aged 24.7 ± 5.3 years (mean ± SD) underwent four consecutive nights of simulated night-shift work. Between 17:30–04:30 h participants provided saliva samples and completed a 3 min psychomotor vigilance test (PVT-B), 40 min simulated driving task, and 3 min digit symbol substitution test (DSST). Higher sAA levels were associated with faster response speed on the PVT-B, reduced lane variability on the simulated driving task, and improved information processing speed on the DSST during the first night-shift. There were no associations between sAA levels and performance outcomes during subsequent night-shifts. Findings indicate that the usability of sAA to assess the risk of neurobehavioral deficits during shift-work operations is limited. However, the robust circadian rhythm exhibited by sAA during the protocol of circadian misalignment suggests that sAA could serve as a potential circadian marker.

No first night shift effect observed following a nocturnal main sleep and a prophylactic 1-h afternoon nap

ABSTRACTNeurobehavioural impairment on the first night shift is often greater than on subsequent night shifts due to extended wakefulness. The aim of the study was to determine whether a 1-h afternoon nap prior to the first night shift is sufficient to produce neurobehavioural performance at levels comparable to the second night shift. Twelve male volunteers (mean age 22.9 years) participated in a laboratory protocol that simulated two 12-h night shifts. A nap preceded the first shift and a 7-h daytime sleep was scheduled between shifts. Neurobehavioural performance and subjective sleepiness measured across each night did not significantly differ between first and second shifts.

Use of an Appreciative Inquiry Approach to Improve Resident Sign-Out in an Era of Multiple Shift Changes

Resident duty hour restrictions have resulted in more frequent patient care handoffs, increasing the need for improved quality of residents' sign-out process. To characterize resident sign-out process and identify effective strategies for quality improvement. Mixed methods analysis of resident sign-out, including a survey of resident views, prospective observation and characterization of 64 consecutive sign-out sessions, and an appreciative-inquiry approach for quality improvement. Internal medicine residents (n = 89). An appreciative inquiry process identified five exemplar residents and their peers' effective sign-out strategies. Surveys were analyzed and observations of sign-out sessions were characterized for duration and content. Common effective strategies were identified from the five exemplar residents using an appreciative inquiry approach. The survey identified wide variations in the methodology of sign-out. Few residents reported that laboratory tests (13%) or medications (16%) were frequently accurate. The duration of observed sign-outs averaged 134 ±73s per patient for the day shift (6p.m.) sign-out compared with 59 ± 41s for the subsequent night shift (8p.m.) sign-out for the same patients (p = 0.0002). Active problems (89% vs 98%, p = 0.013), treatment plans (52% vs 73%, p = 0.004), and laboratory test results (56% vs 80%, p = 0.002) were discussed less commonly during night compared with day sign-out. The five residents voted best at sign-out (mean vote 11 ± 1.6 vs 1.7 ± 2.3) identified strategies for sign-out: (1) discussing acutely ill patients first, (2) minimizing discussion on straightforward patients, (3) limiting plans to active issues, (4) using a systematic approach, and (5) limiting error-prone chart duplication. Resident views toward sign-out are diverse, and accuracy of written records may be limited. Consecutive sign-outs are associated with degradation of information. An appreciative-inquiry approach capitalizing on exemplar residents was effective at creating standards for sign-out.

Impaired endothelial function in medical personnel working sequential night shifts

There is abundant and growing evidence that oxidative stress is an important factor in the propagation of endothelial dysfunction [1]. Recently, Hirsch, et al. reported that flow-mediate brachial artery dilation (FMD) is blunted in early compared to late morning postwaking hours, and independently predicts long-term adverse CVE in healthy subjects [2]. Transient endothelial dysfunction has been reported after mental and physical stress [3,4]. Most of the systemic processes that invoke endothelial dysfunction entail stress-induced activation of intracellular oxidative signaling, with secondary modulation of LDL oxidation, NO bioavailability, and vascular inflammatory gene expression [5]. We examined the effect of three sequential night shifts, with the accompanying inevitable stresses and lifestyle changes, on endothelial function by the FMD changes and the oxidative stress as the mechanism in apparently healthy medical personnel. The study group consisted of 22 healthy, female nurses (30.1± 4.1 years of age). None of the nurses had a history of coronary artery disease, diabetes mellitus, or hypertension. None of the nurses had a historyof usingherbalmedications or vitamins. The studywas approved by the Institutional Review Board of the Gwangju Veterans Hospital and all participants signed informed consent forms before the study. Endothelial function was examined twice in each subject: (1) on a regular workday (with no previous or subsequent night shift, and thus defined as the baseline measurement of FMD) and (2) after three sequential night shifts. All examinationswere performed in themorning (8 A.M.) under identical conditions in a temperature-controlled room. During the study, the participants in the no chocolate group were asked to substitute the chocolate with foods of similar energy and macronutrient composition. After the shift, nurses completed a questionnaire regarding the shift, including the number of hours slept, coffee consumption (number of cups drunk during the shift), and cigarette smoking. Endothelial function was examined non-invasively in the brachial artery using high-resolution ultrasound by standard methods (Sequoia 512; Acuson,Mountain View, CA, USA). The concentration of NOx (NO2 and NO3) was measured by using a nitrogen monoxide (NO) analyzer (model 7050; Antek Co., Guelph, Ontario, Canada). We calculated the concentration of NOx of the sample from a standardized curve, which was made by integrating values of a detector after injecting 50 μL of nitrous solution (1.63 nM,16.3 nM, and 163 nM) in theNO analyzer. The FMD (control and after three sequential night shifts) were compared using Student's t-test for paired data variance. Two tailed pb0.05 was considered significant. Systolic blood pressure at rest was slightly lower after the shift (from 105.00 ±8.89 to 102.50±9.11 beats/min, p=0.021), but there were no significant changes in diastolic blood pressure, heart rate, and BMI after 3 sequential night shifts compared with baseline measurements. The FMDwas significantly decreased after the sequential night shifts compared with baseline measurements (from 13.33±3.53% to 7.62±2.38%, pb0.001) (Fig. 1). There was no significant change in hsCRP after 3 sequential night shifts compared with baseline measurements. However, NOx was significantly decreased after 3 sequential night shifts compared with baseline measurements (from 176.1± 65.1 mmol/dL to 131.8±72.1 mmol/dL, p=0.033) (Fig. 1). By multivariate stepwise regression analysis, the decrease in FMD after shiftwork was independently related to a longer history of shift work (r=0.67, p=0.02). But, there was no correlation between changes in NOx and FMD before and after 3 sequential night shifts (r=−0.218, p=0.356). Our results are in agreement with a previous study which showed that working a 24-hour shift resulted in deterioration of the FMD [5]. Thus, night shift work might be a stressor that deteriorates the FMD, but the precise mechanism is unknown. We reasoned that oxidative stress might be the cause of endothelial dysfunction. One of the important results of production of oxygen radicals is reduced bioactivity by loss of NO. A decrease in the bioavailability of NO has important pathophysiologic effects in atherosclerosis, hypertension, and diabetic vascular disease [6]. Our study showed a significant

PARADOXICAL POST-EXERCISE RESPONSES OF ACYLATED GHRELIN AND LEPTIN DURING A SIMULATED NIGHT SHIFT

Approximately 10% of employees undertake night work, which is a significant predictor of weight gain, possibly because responses to activity and eating are altered at night. It is known that the appetite-related hormone, acylated ghrelin, is suppressed after an acute bout of exercise during the day, but no researcher has explored whether evening exercise alters acylated ghrelin and other appetite-related outcomes during a subsequent night shift. Six healthy men (mean ± SD: age 30 ± 8 yrs, body mass index 23.1 ± 1.1 kg/m2) completed two crossover trials (control and exercise) in random order. Participants fasted from 10:00 h, consumed a test meal at 18:00 h, and then cycled at 50% peak oxygen uptake or rested between 19:00–20:00 h. Participants then completed light activities during a simulated night shift which ended at 05:00 h. Two small isocaloric meals were consumed at 22:00 and 02:00 h. Venous blood samples were drawn via cannulation at 1 h intervals between 19:00–05:00 h for the determination of acylated ghrelin, leptin, insulin, glucose, triglyceride, and non-esterified fatty acids concentrations. Perceived hunger and wrist actimetry were also recorded. During the simulated night shift, mean ± SD acylated ghrelin concentration was 86.5 ± 40.8 pg/ml following exercise compared with 71.7 ± 37.7 pg/ml without prior exercise (p = 0.015). Throughout the night shift, leptin concentration was 263 ± 242 pg/ml following exercise compared with 187 ± 221 pg/ml without prior exercise (p = 0.017). Mean levels of insulin, triglyceride, non-esterified fatty acids, and wrist actimetry level were also higher during the night shift that followed exercise (p < 0.05). These data indicate that prior exercise increases acylated ghrelin and leptin concentrations during a subsequent simulated night shift. These findings differ from the known effects of exercise on acylated ghrelin and leptin during the day, and therefore have implications for energy balance during night work. (Author correspondence: c.j.morris@2006.ljmu.ac.uk).

Shaping the light/dark pattern for circadian adaptation to night shift work

This is the second in a series of simulated night shift studies designed to achieve and subsequently maintain a compromise circadian phase position between complete entrainment to the daytime sleep period and no phase shift at all. We predict that this compromise will yield improved night shift alertness and daytime sleep, while still permitting adequate late night sleep and daytime wakefulness on days off. Our goal is to delay the dim light melatonin onset (DLMO) from its baseline phase of ∼ 21:00 to our target of ∼ 3:00. Healthy young subjects ( n = 31) underwent three night shifts followed by two days off. Two experimental groups received intermittent bright light pulses during night shifts (total durations of 75 and 120 min per night shift), wore dark sunglasses when outside, slept in dark bedrooms at scheduled times after night shifts and on days off, and received outdoor light exposure upon awakening from sleep. A control group remained in dim room light during night shifts, wore lighter sunglasses, and had unrestricted sleep and outdoor light exposure. After the days off, the DLMO of the experimental groups was ∼ 00:00–1:00, not quite at the target of 3:00, but in a good position to reach the target after subsequent night shifts with bright light. The DLMO of the control group changed little from baseline. Experimental subjects performed better than control subjects during night shifts on a reaction time task. Subsequent studies will reveal whether the target phase is achieved and maintained through more alternations of night shifts and days off.

Usefulness of Temazepam and Zaleplon to Induce Afternoon Sleep

Insufficient daytime sleep may result in reduction of effectiveness and safety during overnight military missions. The usefulness of temazepam and zaleplon to optimize afternoon sleep and their effects on performance and alertness during a subsequent night shift were studied. In a randomized double-blind within-subjects design, 11 subjects took 20 mg of temazepam, 10 mg of zaleplon, or placebo before a 5:30-10:00 p.m. sleep period. Sleep length and quality were measured. Subjects were kept awake throughout the night while alertness, cognitive performance, and muscle power were repeatedly measured. Temazepam provided significantly longer and qualitatively better sleep than zaleplon or placebo. During the night, sleepiness increased and muscle power was impaired in all conditions. Better sleep was correlated with less sleepiness during the night. Temazepam is useful to optimize a 4.5-hour afternoon sleep before overnight missions. Irrespective of hypnotic treatment, sleepiness and fatigue increased during the night shift.