Heart rate variability and endothelial function after sleep deprivation and recovery sleep among male shift and non-shift workers

Effects of two 15-min naps on the subjective sleepiness, fatigue and heart rate variability of night shift nurses

The purpose of this study was to examine the effects of two 15-min naps on nurses who work at night in a three-shift system. Of the 15 nurses who were included as study subjects on a night shift, eight took two short naps (the Nap condition), and seven worked without taking a nap (the No-nap condition) during the night shift. We measured sublingual temperature and the bispectral index (BIS), obtained heart rate and heart rate variability measures from an electrocardiogram (ECG), and evaluated sleepiness and fatigue levels every hour using the Visual Analog Scale (VAS). Both subjective sleepiness and fatigue increased between 4:00 and 5:00, with no significant differences observed between the two groups. However, the low- to high-frequency ratio (LF/HF) in the Nap condition group was found to be significantly lower than in the No-nap condition group. Furthermore, a sudden, brief increase in HF values was observed in the No-nap condition group in the morning. The results of this study suggest that taking two short naps may effectively reduce tension and prevent a brief increase in HF values by suppressing sympathetic nervous activity in the morning.

Circadian adaptation to night shift work influences sleep, performance, mood and the autonomic modulation of the heart

Our aim was to investigate how circadian adaptation to night shift work affects psychomotor performance, sleep, subjective alertness and mood, melatonin levels, and heart rate variability (HRV). Fifteen healthy police officers on patrol working rotating shifts participated to a bright light intervention study with 2 participants studied under two conditions. The participants entered the laboratory for 48 h before and after a series of 7 consecutive night shifts in the field. The nighttime and daytime sleep periods were scheduled during the first and second laboratory visit, respectively. The subjects were considered "adapted" to night shifts if their peak salivary melatonin occurred during their daytime sleep period during the second visit. The sleep duration and quality were comparable between laboratory visits in the adapted group, whereas they were reduced during visit 2 in the non-adapted group. Reaction speed was higher at the end of the waking period during the second laboratory visit in the adapted compared to the non-adapted group. Sleep onset latency (SOL) and subjective mood levels were significantly reduced and the LF∶HF ratio during daytime sleep was significantly increased in the non-adapted group compared to the adapted group. Circadian adaptation to night shift work led to better performance, alertness and mood levels, longer daytime sleep, and lower sympathetic dominance during daytime sleep. These results suggest that the degree of circadian adaptation to night shift work is associated to different health indices. Longitudinal studies are required to investigate long-term clinical implications of circadian misalignment to atypical work schedules.

Effect of nighttime aircraft noise exposure on endothelial function and stress hormone release in healthy adults

AIMS

Aircraft noise disturbs sleep, and long-term exposure has been shown to be associated with increases in the prevalence of hypertension and an overall increased risk for myocardial infarction. The exact mechanisms responsible for these cardiovascular effects remain unclear.

METHODS AND RESULTS

We performed a blinded field study in 75 healthy volunteers (mean age 26 years), who were exposed at home, in random order, to one control pattern (no noise) and two different noise scenarios [30 or 60 aircraft noise events per night with an average maximum sound pressure level (SPL) of 60 dB(A)] for one night each. We performed polygraphy during each study night. Noise caused a worsening in sleep quality (P < 0.0001). Noise60, corresponding to equivalent continuous SPLs of 46.3 dB (Leq) and representing environmental noise levels associated with increased cardiovascular events, caused a blunting in FMD (P = 0.016). As well, although a direct comparison among the FMD values in the noise groups (control: 10.4 ± 3.8%; Noise30: 9.7 ± 4.1%; Noise60: 9.5 ± 4.3%, P = 0.052) did not reach significance, a monotone dose-dependent effect of noise level on FMD was shown (P = 0.020). Finally, there was a priming effect of noise, i.e. the blunting in FMD was particularly evident when subjects were exposed first to 30 and then to 60 noise events (P = 0.006). Noise-induced endothelial dysfunction (ED) was reversed by the administration of Vitamin C (P = 0.0171). Morning adrenaline concentration increased from 28.3 ± 10.9 to 33.2 ± 16.6 and 34.1 ± 19.3 ng/L (P = 0.0099). Pulse transit time, reflecting arterial stiffness, was also shorter after exposure to noise (P = 0.003).

CONCLUSION

In healthy adults, acute nighttime aircraft noise exposure dose-dependently impairs endothelial function and stimulates adrenaline release. Noise-induced ED may be in part due to increased production in reactive oxygen species and may thus be one mechanism contributing to the observed association of chronic noise exposure with cardiovascular disease.

Diurnal 24-Hour Rhythm in Ambulatory Heart Rate Variability during the Day Shift in Rotating Shift Workers

Circadian variation in cardiac autonomic nervous system activity and behavior during the day shifts of shift workers has not hitherto been clarified. This study examined diurnal 24-h variation in heart rate variability (HRV), sleep-wake cycle, physical activity, and food intake during the day shift in rotating shift workers. The subjects were female nurses and caregivers working at a health care facility (14 day workers and 13 rotating shift workers). Each subject was asked to undergo 24-h electrocardiograph and step count recordings. Coarse graining spectral analysis was used for approximately 10-min segments of HRV (600 beats) to derive the total power (TOT: >0.04 Hz), integrated power in the low-frequency (LF: 0.04-0.15 Hz) and high-frequency (HF: >0.15 Hz) ranges, the ratio of HF power to TOT (HF nu), and the ratio of LF power to HF power (LF/HF). Double cosinor analysis was used to obtain 24-h and 12-h period variations in variables of HRV and physical activity. While no difference was found in the acrophases of either period for step counts or in the 12-h period of HRV variables between the groups, the acrophases of the 24-h period for HRV variables were delayed by 1.3 to 5.5 h in rotating shift workers, and their differences in HF power, HF nu, and LF/HF reached a significant level ( p < 0.05). On the days of the experiment, retiring time, waking up time, total time in bed, sleep efficiency, and mealtimes and energy intake for each diet did not differ between the groups. These results suggest that there is a possibility of an abnormal phase angle between circadian variation in cardiac autonomic nervous system activity and the sleep-wake cycle during the day shift in shift workers.

Effects of implementing an ergonomic work schedule on heart rate variability in shift-working nurses

OBJECTIVES

The aim of this study was to compare the psychophysiological strain related to a conventional shift schedule and new ergonomically improved two- and three-shift schedules using heart rate variability (HRV) analysis. The specific aim was to determine whether the introduced ergonomic shift arrangement had any positive effects on the psychophysiological strain such as increased HRV or decrease in the sympathovagal balance of the autonomic nervous system (ANS).

METHODS

Questionnaire data and 24-hour HRV recordings were gathered from 48 female shift-working nurses once while working the conventional shift schedule (baseline) and again after one year working an ergonomic shift schedule during the morning shift.

RESULTS

Comparisons between conventional and ergonomic shift schedules (baseline and follow-up, respectively) revealed significant differences in frequency-domain parameters. Implementing an ergonomic shift schedule resulted in decreased normalized low frequency (LF) power, increased normalized high frequency (HF) power, and decreased LF/HF ratio at the beginning of the shift. Furthermore, at baseline, mean RR interval, root mean square of successive RR interval differences (RMSSD) and normalized HF power were increased at the end of the shift compared with the values at the beginning of the morning shift. In contrast, at the follow-up, LF power was increased between the end and beginning of the morning shift.

CONCLUSIONS

The psychophysiological strain measured by HRV analysis was lower at the beginning of the work shift for the ergonomic shift schedules compared with the conventional schedule. This indicates that an ergonomic shift schedule may have a positive effect on the ANS recovery occurring between successive work shifts.

Anti-clockwise rotating shift work and health: would you prefer 3-shift or 4-shift operation?

BACKGROUND

We explored the association between work schedules involving nightshifts and selected measures of health and whether these associations differed among those working in either 3- or 4-shift cycles.

METHODS

Employees at a German industrial company who worked on a fixed daytime schedule or on one involving nightshifts were invited to participate in this cross-sectional study. Work schedules involving a nightshift were organized into either 3 or 4 shifts rotated anti-clockwise on a weekly basis. Health characteristics included a range of clinical and physiological measures and self-reported data on stress and sleep quality. We assessed the independent association of work schedules involving any nightshift and these health characteristics in separate regression analyses, adjusting for age, gender, smoking, and alcohol consumption.

RESULTS

Nightshift work (N = 133) in general and 3-shift-work (N = 53) in particular was associated with decreased sleep quality (P < 0.001). Compared to those working daytime (N = 632), employees working on a 3-shift cycle had higher adjusted odds of meeting the definition of metabolic syndrome (OR = 2.56 [1.38, 4.75]). Employees working 4-shift cycles were somewhat less likely to have metabolic syndrome (OR = 1.22 [0.73, 2.05]) and had higher parasympathetic activity measured by heart rate variability (OR = 2.20 [1.04, 4.63]).

CONCLUSIONS

Our data suggest important relationships between shift schedule and a selected group of objective and subjective health measures. Additional research that further clarifies potential mechanisms underlying these relationships is needed.

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.

Noisy and individual, but doable: shift-work research in humans

Working around the clock is common for many occupations, as diverse as nurses, truck drivers, physicians, steel workers, and pilots. Each shift-work profession is individual in more aspects than just work hours and individual work scenarios, each posing a different impact on the health of workers. Related health problems in shift workers, therefore, are also diverse and encompass sleep problems, metabolic and cardiovascular system disturbances, as well as cancer. Little is known about how all these individual factors influence a shift worker's health status, partly because many shift-work studies show inconsistent results. In addition, these individual factors create many methodological difficulties for researchers who investigate such work scenarios. This chapter presents examples from our laboratory and field studies of shift workers, which emphasize the importance of taking individual circumstances into account. Both study approaches, laboratory and field based, are needed to fully account for the difficulties that shift-work studies pose on both workers and researchers. Finally, understanding the mechanisms that underpin interindividual differences in response to shift work will advance our understanding of how to design better and healthier shift-work schedules in the future.

Differences in heart rate variability of female nurses between and within normal and extended work shifts

The aim of this study was to investigate differences in heart rate variability (HRV) reflecting the function of autonomic nervous system (ANS) and psycho-physiological strain associated with normal and extended work shifts in nursing work. Complete data were available from 51 female nurses with a mean age of 40 yr, and based on two comparable 36-h HRV measurements supplemented with a questionnaire. Time-domain (meanRR, SDNN, RMSSD) and frequency-domain (LF power, HF power) parameters represented the HRV data, and were analyzed by linear mixed models. The differences between the compared work shifts were minor, revealing mainly increased sympathetic activity at the beginning of the normal work shift. The HRV parameters detected significant differences between work and leisure-time during the normal and extended work shifts in female nurses. During work shifts, an increase in sympathetic and a decrease in parasympathetic control of HRV was observed when compared to the leisure-time situation. Older subjects had overall lower HRV than younger subjects indicating increased sympathetic activation of ANS, especially during work. HRV parameters revealed significant differences between work, leisure-time and sleep of female nurses, but there were few differences between normal and extended work shifts in HRV parameters. This lack of differences between work shifts may be a consequence of the adaptation of nurses to the extended shifts or the more flexible organization of work duties possible during extended work shifts.

Protective effect of metoprolol on arrhythmia and heart rate variability in healthy people with 24 hours of sleep deprivation

PURPOSE

Sleep deprivation, which is a strong stressor, can greatly affect the cardiovascular system of rescue workers. This study aimed to investigate the effect of 24-h sleep deprivation on heart rate variability (HRV) in young healthy people and the protective effect of metoprolol on arrhythmia.

METHODS

Sixty young, healthy subjects (6 women and 54 men), aged 25 ± 4.5 years, were enrolled in this study. All participants received 24-h continuous ambulatory electrocardiogram monitoring. Arrhythmia, time, and frequency domain parameters were analyzed in subjects at the following three stages: normal sleep stage, sleep deprivation stage, and metoprolol treatment before sleep deprivation stage.

RESULTS

After 24-h sleep deprivation, the high frequency (HF) of HRV was significantly decreased (p < 0.05), low frequency (LF) was remarkably increased (p < 0.05), and LF/HF was significantly increased compared with those in normal sleep (p < 0.05). Some subjects presented with mild palpitation due to premature atrial complexes and premature ventricular complexes. At the metoprolol treatment stage, compared with the sleep deprivation stage, LF and LF/HF were significantly reduced, HF of HRV was elevated (p < 0.05), and the total amount of premature atrial and ventricular complexes was decreased.

CONCLUSION

The underlying mechanism of arrhythmia and HRV alteration after 24-h sleep deprivation could be attributable to lower vagal activity and elevated sympathetic activity. Metoprolol improves the change in autonomic nervous system activity after 24-h sleep deprivation, which may be responsible for its protective role on arrhythmia in healthy subjects undergoing sleep deprivation.