Effects of shift work on QTc interval and blood pressure in relation to heart rate variability

Objectives: There is evidence that shift work contributes to excess cardiovascular mortality. The purpose of this study was to determine the effects of shift work on heart rate-corrected QT (QTc) and blood pressure in relation to heart rate variability (CV_RR). Methods: The study population consisted of 153 male shiftworkers and 87 male day workers who were employed at a copper-smelting plant. The QTc interval, total power spectral density (t-PSD) of 100 RR intervals, PSDs with frequencies of 0.01 Hz–0.15 Hz and 0.15 Hz–0.40 Hz (PSD_LF and PSD_HF), CV_RR, low frequency (LF) component variability and high frequency (HF) component variability (CCV_LF and CCV_HF) and %LF (PSD_LF/(PSD_LF+PSD_HF) ·100) were measured (LF and HF components are thought to reflect the sympathetic and parasympathetic activities, respectively). Results: The QTc interval was significantly longer in the shiftworkers than in the day workers, although there was no significant difference in systolic or diastolic blood pressure between the two groups. Also, the CCV_LF and log(PSD_LF) were significantly depressed in the shiftworkers. In the day workers, the QTc interval was significantly related to the CV_RR, log(t-PSD), CCV_HF, log(PSD_HF),%LF, and log(LF/HF ratio) (partial correlation coefficient r=–0.305, –0.377, –0.312, –0.355, 0.297, and 0.277, respectively). In the shiftworkers only two relations of the QTc interval to non-specific CV_RR and log(t-PSD) were significant. Conclusion: The clear association between long QTc interval and reduced parasympathetic activity observed in the day workers did not exist in the shiftworkers. Rather, the shiftworkers had a selective reduction in sympathetic drive, which may have compensated for prolonged QTc interval due to shift work. On the other hand, the impact of shift work on hypertension remains unclear, although reduced sympathetic drive in the shiftworkers may explain the absence of differences in blood pressure between shiftworkers and day workers to some extent.     

Effects of shift work on 24-hour ambulatory blood pressure and its variability among Japanese workers

OBJECTIVES: This study examined the effects of rotating shift work on blood pressure in a comparison of ambulatory blood pressure and long-term changes in blood pressure between shift and day workers. METHODS: Ambulatory blood pressure was measured for 24-hour periods at an interval of 30 minutes for 27 shift workers and 26 day workers when they worked during the day. Blood pressure was compared between these 2 groups of workers for 4 time categories (awake, sleep, nonwork awake, and work periods). Their long-term blood pressures, recorded in annual surveys, were reviewed for long-term changes. These comparisons were adjusted for the effects of body mass index, alcohol intake, anger expression, and physical activity. RESULTS: On the average, sleep time was shorter and the anger-in (ie, anger suppressed) score was higher for the shift workers than for the day workers, but body mass index and alcohol intake did not differ between the 2 groups. Even after adjustment for these co-variables, the mean systolic blood pressure during the 24-hour, awake, and work periods were higher among the shift workers than among the day workers. The 24-hour standard deviations of the systolic blood pressures were also higher for the shift workers than for the day workers. Among the shift workers, but not among the day workers, a significant long-term increase was observed in systolic blood pressure measured in the annual surveys. CONCLUSIONS: These results suggest that shift work may increase systolic blood pressure levels among Japanese men.     

Job strain in relation to ambulatory blood pressure, heart rate, and heart rate variability among female nurses

OBJECTIVE: This study examined the effects of exposure to job strain on independent predictors of cardiovascular disease (ambulatory blood pressure, heart rate, and heart rate variability). METHODS: The participants comprised a homogeneous group of 159 healthy female nurses [mean age 35.9 (SD 8.5) years]. The choice of this population minimized variance attributable to gender, socioeconomic status, and work characteristics. Job demands, decision latitude, and social support were measured with the Karasek job content questionnaire, which was administered twice with an average interval of 12.2 months. The nurses' scores for job demands and decision latitude on both occasions were used to define their job-strain category. Ambulatory blood pressure, heart rate, and heart rate variability were assessed on a workday and a day of leisure. RESULTS: No effect on the ambulatory levels of blood pressure, heart rate, or heart rate variability was found for job strain by itself or in interaction with social support. In addition, job strain was not associated with differences in short-term or long-term physiological recovery during sleep after a workday or a day of leisure. High job demand was associated with higher systolic blood pressure at work and with higher diastolic blood pressure at work, but the latter association was found only when decision latitude was concurrently high, rather than low. CONCLUSIONS: High job strain among young female nurses is not associated with an unfavorable ambulatory cardiovascular profile. The robust effect of job strain on male health appears to be less apparent for women.     

Changes in frequency of premature complexes and heart rate variability related to shift work

OBJECTIVES—To investigate whether an increased risk of cardiovascular disease might be caused by increased arrhythmogeneity and by unfavourable changes in autonomic cardiac control the changes in the occurrence of premature complexes (PVCs) and in heart rate variability (HRV) were studied in subjects who started to work in shifts.
METHODS—1 Year changes in frequency of PVCs and HRV were measured in 49 shift workers and 22 control subjects working in daytime. All respondents were starting in a new job in integrated circuit or waste incinerator plants.
RESULTS—The incidence of PVC increased significantly in shift workers over the 1 year follow up, compared with daytime workers. The frequency of ventricular extrasystoles increased in 48.9% of the shift workers, and in 27.3% of the daytime workers. The Spearman correlation coefficient between the number of nights worked and the change in PVCs was 0.33 (p=0.004). A small non-significant unfavourable change in HRV was found in both the shift and daytime workers.
CONCLUSIONS—A change in arrhythmogeneity, but not in cardiac autonomic control, might explain the increased risk of cardiovascular disease in shift workers.


Keywords: arrhythmia; heart rate; shift work     

Effects of passive smoking on heart rate variability, heart rate and blood pressure: an observational study

BACKGROUND: Exposure to environmental tobacco smoke (ETS) has been shown to increase the risk for cardiovascular diseases and death, and autonomic dysfunction (specifically, reduced heart rate variability (HRV)) is a predictor of increased cardiac risk. This study tests the hypothesis that ETS exposure reduces HRV in the general population and discusses possible pathways. METHODS: This cross-sectional study was conducted between 2001 and 2003 and is part of the SAPALDIA (Swiss Cohort Study on Air Pollution and Lung Diseases in Adults) study. The analysis included 1218 randomly selected non-smokers aged 50 and above who participated in 24-h electrocardiogram recordings. Other examinations included an interview, investigating health status (especially respiratory and cardiovascular health and health relevant behaviours and exposure to ETS) and measurements of blood pressure, body height and weight. RESULTS: Subjects exposed to ETS at home or at work for more than 2 h/day had a difference of -15% in total power (95%CI: -26 to -3%), low frequency power (-28 to -1%), low/high frequency ratio (-26 to -3%) and -18% (-29 to -4%) in ultralow frequency power of HRV compared with subjects not exposed to ETS at home or work. We also found a 2.7% (-0.01 to 5.34%) higher heart rate during the recording in exposed subjects. CONCLUSIONS: Exposure to ETS at home and work is associated with lower HRV and with higher heart rate in an ageing population. Our findings suggest that exposure to ETS increases cardiac risk through disturbances in the autonomic nervous system.     

Napping during the night shift and recovery after work among hospital nurses

OBJECTIVE:

To analyze the association between the length of napping during the night shift and the recovery after work among nurses.

METHOD:

Cross-sectional epidemiological study involving 1940 nurses from 18 public hospitals in the City of Rio de Janeiro. A multidimensional and self-applied questionnaire was used with information about health, sociodemographic and occupational characteristics, health-related behaviors and housework. Multiple logistic regression was applied to identify the association, adjusted for confounding variables.

RESULTS:

The gross analyses showed 44%, 127% and 66% higher chances of a high level of recovery after work for nurses who sleep up to two hours, between 2.1 and 3 hours and 3.1 hours or more, respectively, when compared to the nurses who do not sleep. After adjusting for confounding variables, the association only continues significant for the group that sleeps 2.1 to 3 hours during the night shift (OR=1.79; 95%CI=1.33-2.41).

CONCLUSION:

The association between the length of napping and the high level of recovery after work, confirmed in the present results, can be included in the studies that aim to support more appropriate policies aimed at improving the workers'' work, life and health conditions, not only in nursing, but night-shift workers in general.     

Effects of 2-hour nighttime nap on melatonin concentration and alertness during 12-hour simulated night work

A nighttime nap is expected to mitigate melatonin suppression during night work by blocking light input to the retina, but it is unclear. In the present study, we investigated the effects of a nap break on melatonin level, subjective sleepiness, and vigilance performance during simulated night work. Eleven healthy young males (mean ± SD age: 22.2 ± 4.1 years) participated in counterbalanced crossover design experiments with two conditions (nap vs. no nap). The subjects performed 12-hour simulated night work from 21:00 to 09:00 h (illuminance: ∼500 lx). Subjects with a nap condition took a nap for 2 hours in a dark room from 03:00, while subjects with a no nap condition continued the simulated night work. The results showed that immediately after the 2-h nap break, the melatonin level at 05:00 h temporarily recovered from light-induced melatonin suppression during the simulated night work but significantly suppressed again at 07:00 and 09:00 h. Subjective alertness and vigilance performance were impaired immediately after the nap break but subsequently enhanced. The results suggest that a single nap break for 2 hours could be a strategy to enhance alertness during the last part of night shift but inadequate for mitigating melatonin suppression.     

Sleep,sleepiness and need for recovery of industrial employees after a change from an 8- to a 12-hour shift system

Employees often prefer 12-hour work shifts but they can increase sleepiness and injury risk. We assessed whether sleep, sleepiness, satisfaction and need for recovery changed after changing from an 8-hour to a 12-hour shift system. The participants were 178 employees of the paper, pulp and chemical industries. Using a quasi-experimental controlled intervention design, 83 employees, who changed from an 8-hour shift schedule to a 12-hour shift schedule were compared to those who remained in the 8-hour shift schedule (n=95). Participants filled in a survey on sleep, sleepiness, satisfaction and need for recovery at baseline and 9–12 months after the shift schedule change. We used generalized estimation equation models adjusted for age, sex, shift work experience in years and baseline shift system. Sleep length was longer in the 12-hour shift schedule before the first morning shift and between morning shifts. Sleepiness during morning shifts was less frequent and satisfaction with the shift system was more prevalent in the 12-hour shift schedule. Also, perceived negative associations of the current shift system with work-life balance were less common in the 12-hour shift schedule. The differences found between the shift systems were minor and the results did not indicate significant disadvantages of the 12-hour fast forward-rotating shift system.     

60例老年2型糖尿病患者心率变异性及血压变异性分析

目的 本研究旨在探索老年男性2型糖尿病患者心率变异性及血压变异性的变化.方法 入选人群均为老年男性,共100例,其中对照组（A组）40例,2型糖尿病组（B组）60例.进行24小时动态心电图及24小时动态血压监测.收集其HRV时域指标、BP及BPV长时变异性指标,之后进行对比分析,了解老年男性2型糖尿病患者心率变异性及血压变异性的变化.结果 与对照组相比,2型糖尿病组HRV时域指标减少（P＜0.05）;与对照组相比,2型糖尿病组BPV增大（dSBPSD、dSBPCV等,P〈0.05）.结论 老年2型糖尿病患者组HRV时域指标减少及BPV增大,提示其心脏自主神经功能受损.这对患者病情的严重程度、治疗、预后进行判断、指导和评估是具有重要价值的.     

Experimental shift work studies of permanent night,and rapidly rotating,shift systems

Summary The effects of permanent night and rapidly rotating shift systems on the daily course of body temperature were examined in an experimental situation.In the first series of tests 4 subjects worked on night shift for 3 successive weeks. A further 4 subjects worked on rapidly rotating shift systems; 2 subjects on a 1 - 1 - 1 - system (first day early shift, 2nd day late shift, 3rd day night shift, 4th day free), and 2 subjects on a 2 - 2 - 2 -system (metropolitan rota).Only slight changes in the daily course of rectal temperature were found with single night shifts. The greatest changes in the circadian rhythm occurred during the first week of night shifts. p]Even after 21 consecutive night shifts we failed to find complete inversion of the daily course of body temperature.In view of these test results rapidly rotating shift systems would seem to be advisable.     

Experimental shift work studies of permanent night,and rapidly rotating,shift systems

Summary In connection with experimental shift work 20 volunteers were examined while working on different rapidly or slowly rotating shift systems. Sleep was analysed over a total of 112 days.Sleep was disturbed by childrens' noise or traffic noise. Sleep duration and sleep quality were particularly badly affected by noise with a high information value (childrens' noise).The ultradian rhythmicity of sleep did not appear to be disrupted by the change from day to night work.There were no significant differences between morning sleep and afternoon sleep after night work.In the laboratory experiments with fixed sleep durations, no separate effects on sleep quality could be established for different shift systems.     

Heart rate during work and heart rate variability during the following night: a day-by-day investigation on the physical activity paradox among blue-collar workers

Objectives:Contrary to leisure-time physical activity, occupational physical activity (OPA) may have harmful health effects, called the physical activity paradox. A proposed mechanism is that OPA can elevate the heart rate (HR) for several hours per day. We aimed to investigate the association between the mean intensity of OPA and HR variability (HRV) indices the following night.Methods:Three cohorts (NOMAD, DPhacto, and Physical Workload and Fitness) involving blue-collar workers from different sectors were merged in this study. HR monitors (Actiheart) recorded 24-hour inter-beat intervals (IBI) for up to four consecutive days. The relative intensity of the mean HR during work was estimated by HR reserve (%HRR), and time-domain indices of HRV were analyzed during the following night. Data were analyzed using a multilevel growth model to test the association between mean %HRR during work and HRV indices at night in a day-by-day analysis adjusted for age, BMI, alcohol consumption, smoking, and occupation.Results:The dataset included a sample of 878 Danish blue-collar workers, with a mean %HRR during work of 31%, and 42% worked at an intensity ≥30%HRR. The multilevel model showed negative within- and between-subject associations between %HRR during work and HRV indices at night.Conclusions:Our results indicate a higher %HRR during work to associate with lower HRV indices the following night and a higher HR, reflecting an imbalanced autonomic cardiac modulation. This finding supports a high mean HR during work to be a potential underlying mechanism for the harmful health effect of OPA.     

Diurnal variations of blood pressure in shift workers during day and night shifts

Summary The dependence of blood pressure upon internal rhythms and the short-term effects of shift rota on the blood pressure were investigated in shift workers. Blood pressure was measured every 30 min using automatic recorders for 24 h in 17 physically working men in a chemical factory during their morning and night shifts. Mean 24-h blood pressures were identical in the morning and night shifts. There were no differences of the mean blood pressure between the respective sleeping phases or between the working periods. The amplitudes of circadian blood pressure variations were equal. There was a phase difference of 8 h corresponding to the lag between the working periods. At this 8-h lag the hourly means of the 24-h blood pressure were closely correlated (r = 0.69). Comparisons of 24-h blood pressure profiles during the first and last days of a night shift week showed that the effects of night work on the blood pressure were already fully developed within the first 24h (r = 0.86). Thus the diurnal variations of the blood pressure are determined by the working and sleeping periods and largely independent of endogenous rhythm. There is no short-term alteration of the mean 24-h blood pressure after shift rota.     

Excessive fatigue and weight gain among cleanroom workers after changing from an 8-hour to a 12-hour shift.

OBJECTIVES: This study attempted to clarify the health effects of implementing a 12-hour shift in place of the traditional 8-hour shift in work in a clean room in an electronic parts producing factory. METHODS: Health-check records during a year or longer before and after the shift change were reviewed regarding subjective symptoms, height, body weight, and blood pressure for 189 male workers who had moved to a 12-hour shift and for 16 male workers who remained on an 8-hour shift. RESULTS: The workers changing to a 12-hour shift showed significant increases in subjective symptoms, particularly psychological symptoms defined as related to fatigue and bodyweight gain, 1 kg on average, in the year after the shift change. Increased symptoms and body weight remained high even another year later. The workers remaining in the 8-hour shift did not show significant changes in symptoms or body weight during the observation. No changes in blood pressure were observed in relation to the shift move. CONCLUSIONS: The results suggested that implementing a 12-hour shift caused marked psychological fatigue and unhealthy weight gain among some cleanroom workers and that the adaptation to the new work shift did not seem easy for these workers. Working in a clean room can be considered a job in which special caution is needed regarding increased fatigue when a compressed working schedule is implemented. Attention should also be paid to possible weight gain among persons working 12-hour shifts.     

Relationship between intensity of night shift work and antioxidant status in blood of nurses

Purpose

Light-at-night exposure can disrupt the human circadian rhythm via clock gene expressions. The circadian rhythm influences antioxidant enzymes’ activity and cellular mRNA levels of these enzymes. The employees working based on a shift system adjust to the changes occurring both on the cell level and on the level of the whole organism. Therefore, a question should be answered whether shift work disturbs oxidant–antioxidant balance and/or generates oxidative stress.

Methods

A cross-sectional study was conducted among nurses selected from the Local Registry of the Chamber of Nurses and Midwives in Lodz: 359 nurses worked daily only and 349 working rotating night shifts. These two groups differed significantly in respect of age (p < 0.0001), menopausal status (p < 0.0001), and current smoking habit (p = 0.02). The average total work duration was significantly shorter (12.4 years) in nurses working currently rotating night shifts who worked significantly longer on night shifts than day-workers (26.6 years).

Results

We found statistically significant higher red blood cell glutathione peroxidase in nurses working on night shifts (21.0 ± 4.6 vs. 20.0 ± 5.0 U/g Hb, p < 0.009) after adjusting for age, oral contraceptive hormone use, smoking, and drinking alcohol during last 24 h. Statistically significant lower vitamin A and E levels were found in the premenopausal women working in rotating system (0.690 ± 0.238 vs. 0.786 ± 0.262 μg/ml, p < 0.0001 for vitamin A and 10.93 ± 4.15 vs. 12.78 ± 4.75 μg/ml, p < 0.0001 for vitamin E). The marker of lipid peroxidation (TBARS concentration) was significantly lower in the premenopausal nurses than postmenopausal ones working day shifts only (2.06 ± 0.76 vs. 2.21 ± 0.80 nmol/ml, p < 0.038). We observed that erythrocyte GSH-Px activity rose statistically significant in nurses working more night shifts per month (p < 0.01).

Conclusions

The results quoted above seem to support the existence of an association between light-at-night exposure and blood glutathione peroxidase activity in female shift workers. Nevertheless, in order to explain the mechanisms of this association, we need more studies.     

Gender and night work: sleep, daily life and the experiences of night shift workers

This paper deals with the impact of night work from a gender perspective, through a field study at a factory employing men and women on the night shift. It is based on data for hours of sleep over the course of several weeks, socio-demographic data, and job information, using a semi-structured interview. The methodology includes chronobiological aspects of sleep (mainly quantitative data) and workers' discourse concerning gender-related experiences in the day-to-night switch. Despite gender issues and differences in daily life, the switch is perceived quite vividly by both men and women, permeating several aspects of life, like health, leisure, studies, and intimate personal relations. Quantitative sleep analysis showed more severe effects of night work on women, especially those with children. Such sleep patterns were associated with different expectations among men and women, revealing gender issues that are essential for understanding the reality of individuals who work odd hours.     

A comparison of heart rate during rest and work in shift workers with different work styles

To determine if the type of work performed should be considered in research on shift work and cardiovascular disease, we compared the heart rates, total number of steps walked, and blood pressures of 12 shift workers on the same rotating 3-shift schedule in a pulp and paper mill. Six workers were selected from the paper manufacturing section (group 1) and six workers from the chemical products section (group 2). Average heart rate (in beats per min) monitored during duty time was 84.3 in group 1 and 87.4 in group 2. Average heart rate during work was not significantly higher than that during rest in both groups 1 (work 85.8, rest 75.3) and 2 (work 87.9, rest 83.1). There was no significant difference in the total number of steps walked. A non-significant decrease in systolic blood pressure value was found in group 1 compared with that in group 2. Although future studies will be needed to explain the relation between different work styles and their effects on the health of shift workers, our results suggest no significant difference in heart rates among workers engaged in different kinds of work on the same shift work schedule.     

Effect of forward rapidly rotating shift work on circadian rhythms of arterial pressure, heart rate and oral temperature in air traffic controllers

Twenty-four-hour records of arterial pressure (AP), heart rate(HR), oral temperature (OT) and physical and mental performancewere obtained in air traffic controllers during morning (n=16),afternoon (n=17) and night (n=19) shifts. Data were analyzedby the cosinor method. The results obtained during the morningshift were as follows (mesor/amplitude/;acrophase): systolicAP (mm Hg)—113.6/10.0/16:03 h; diastolic AP—71.1/8.2—15:19h; mean AP—85.6/8.8/15:41 h; HR (beats/min)—77.5/8.9/16:00h; OT (dg C)—36.71/0.21/15:49 h; right-hand grip strength(kg)—49.8/2.0/17:43 h; left-hand grip strength—46.1/2.0/16.08h; mental performance (calculations/min)—14.9/1.1/16:39h. During the night shift either no change of the circadianacrophases (HR, right-hand grip strength) or acrophase delaysranging from about 2 h (systolic AP, OT, mental performance)up to 3 h (diastolic and mean AP, left-hand grip strength) wereobserved. Our data suggest that the shift system studied doesnot significantly alter the circadian rhythms, and does notinduce a desynchronization, particularly as concerns arterialpressure and oral temperature.     

The effect of maternal fish oil supplementation during the last trimester of pregnancy on blood pressure, heart rate and heart rate variability in the 19-year-old offspring

Studies in experimental animals and human subjects have suggested that intake of n-3 fatty acids in early life can affect cardiovascular risk factors in adult life. Therefore, the aim of the present study was to investigate the effect of fish oil (FO) supplementation during the third trimester of pregnancy on blood pressure (BP), heart rate (HR) and HR variability (HRV) in the 19-year-old offspring. The study was based on follow-up of a randomised, controlled trial from 1990, in which 533 pregnant women were randomised to FO, olive oil (OO) or no oil (NO) during the last trimester of pregnancy. The offspring was invited to a physical examination including BP, HR and HRV measurements. A subgroup consisting of the offspring of mothers with a low baseline fish intake also had 24?h HRV determined. The OO group was used as reference and multiple linear regression modelling was used to compare the FO and OO groups. A total of 180 of the offspring from the FO and OO groups agreed to participate in the study (45?%). The adjusted difference between the FO and OO groups was 2 (95?% CI -?1, 4)?mmHg in systolic and 1 (95?% CI 0, 3)?mmHg in diastolic BP. The difference in HR was 1 (95?% CI -?2, 4). Also, HRV indices did not differ significantly between groups. Hence, FO supplementation during late pregnancy was not associated with offspring BP, HR and HRV during adolescence.