***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: OBJECTIVE To determine the specific effects of working long hours in surgery  and potential cardiac stress in the individual surgeon by measuring heart rate variability ( HRV ) . DESIGN , SETTING , AND PARTICIPANTS This prospect i ve study measured HRV before , during , and after a 24-hour shift in a st and ardized resting period of 10 minutes . Measurements were repeated over 10 shifts for each participant . Eight surgeons from a high-volume inner-city surgery department took part in the study . MAIN OUTCOME MEASURES Time and frequency domain parameters of HRV as parameters of cardiac stress and correlations with perceived stress and fatigue on a visual analog scale . RESULTS Perceived fatigue increased over 24 hours ( P < .001 ) , whereas stress levels decreased slightly ( P = .06 ) . Time domain parameters of HRV increased from before the shift to after the shift ( st and ard deviation of normal to normal intervals , square root of the mean normal to normal interval , and percentage of adjacent pairs of normal to normal intervals differing by more than 50 milliseconds : all P < .01 ) , denoting more cardiac relaxation . Both the low- and high-frequency components increased ( P = .04 and P < .001 , respectively ) , showing a heightened activity of the autonomic nervous system . CONCLUSIONS Measurements of HRV during a 24-hour surgical shift did not show an increase in cardiac stress concerning time domain parameters despite intense workloads for a median of 20 hours . Frequency components increased in parallel , though , suggesting alterations in sympathovagal balance . Perceived stress levels correlated with HRV , whereas fatigue did not . Further studies on occupational stress and its cardiac effects in surgeons are needed Background Low heart rate variability ( HRV ) is associated with a higher risk of death in patients with heart disease and in elderly subjects and with a higher incidence of coronary heart disease ( CHD ) in the general population . Methods and Results We studied the predictive value of HRV for CHD and death from several causes in a population study of 14 672 men and women without CHD , aged 45 to 65 , by using the case-cohort design . At baseline , in 1987 to 1989 , 2-minute rhythm strips were recorded . Time-domain  measures of HRV  were determined in a r and om sample of 900 subjects , for all subjects with incident CHD ( 395 subjects ) , and for all deaths ( 443 subjects ) that occurred through 1993 . Relative rates of incident CHD and cause-specific death in tertiles of HRV were computed with Poisson regression for the case-cohort design . Subjects with low HRV had an adverse cardiovascular risk profile and an elevated risk of incident CHD and death . The increased risk of death could not be attributed to a specific cause and could not be explained by other risk factors . Conclusions Low HRV was associated with increased risk of CHD and death from several causes . It is hypothesized that low HRV is a marker of less favorable health The objective of this study was to establish the separate associations between parasympathetic modulations of the heart [ evaluated through heart rate ( HR ) variability ( HRV ) indexes and postexercise HR recovery ( HRR ) indexes ] with cardiorespiratory fitness and training load . We have measured cardiorespiratory fitness through peak oxygen consumption ( Vo2 max ) and estimated weekly training load with the Baecke sport score in 55 middle-aged individuals ( 30.8 + /- 1.8 yr , body mass index 24.5 + /- 0.4 kg/m2 ) . HRV indexes were analyzed at rest under controlled breathing , and HRR was estimated from HR curve fitting after maximal exercise or from measurements of the number of beats recovered at 60 s after exercise . Multiple linear regressions were used to investigate the separate relationships between vagal-related HRV indexes and Vo2 max and Baecke scores . On the basis of their Vo2 max and Baecke scores , subjects were classified as fit or unfit and as low trained ( LT ) or moderately trained ( MT ) , which yielded four groups : UnfitLT , UnfitMT , FitLT , and FitMT . Vagal-related HRV indexes were positively correlated with Vo2 max ( P < 0.05 ) but not with Baecke scores . In contrast , HRR indexes were related to Baecke scores ( P < 0.05 ) but not with Vo2 max . FitLT and FitMT had significantly higher ( P < 0.05 ) normalized vagal-related HRV indexes than UnfitLT and UnfitMT , but HRR did not change . Moderate training was associated with significantly lower HRR indexes both in UnfitMT and FitMT compared with UnfitLT and FitLT , but there was no difference in vagal-related HRV indexes . These results indicate that vagal-related HRV indexes are related more to cardiorespiratory fitness , whereas HRR appears to be better associated with training load Objective : Everyday stressors elicit adaptive changes in the hypothalamic-pituitary-adrenal ( HPA ) axis and the autonomic nervous system . Data on the relationship between these two systems under real-life conditions are sparse . We , therefore , sought to examine the association between HRV and salivary cortisol , which were recorded simultaneously in a stress-exposed , prospect i ve , occupational cohort . Methods : The study population comprised 88 nurses . We recorded heart rate ( HR ) and HRV  during 301 working shifts . Participants provided salivary cortisol sample s at the beginning of their work shift and every 2 hours thereafter . Sample s were collected during three investigation periods spread over 9 months . Change scores for cortisol were calculated as deviations from the expected circadian baseline . Change scores from the gr and diurnal mean in the time domain-based root mean square of successive differences served to index alterations in HRV . To account for the temporal delay between changes in HR/HRV and changes in salivary cortisol , the latter were compared with the changes in HR/HRV observed 15 minutes to 45 minutes before the cortisol sampling . Results : During periods of high stress as indexed by high cortisol levels , we found significant associations between cortisol levels and HR ( r = .48 , p < .001 ) and HRV ( r = −.28 , p = .05 ) . However , during low stress periods , these associations were attenuated and became nonsignificant . Conclusions : These data suggest a relative independence in the regulation of the HPA axis and the autonomic nervous system in response to everyday stressors but synchrony of both systems in highly stressful situations . ANS = autonomic nervous system ; bpm = beats per minute ; CV = coefficient of variation ; HPA = hypothalamic-pituitary-adrenal ; HRV = heart rate variability ; RMSSD = root mean square of successive differences ; CI = confidence interval Aims /hypothesisCurrently , three categories of cardiovascular autonomic nervous function measures are used : classic Ewing-test measures , measures of heart-rate variability ( HRV ) , and measures of baroreflex sensitivity ( BRS ) . Little is known about the agreement between these measures , and reference and reproducibility values for these measures have not been reported within the same group . Methods As part of the Hoorn Study , 631 subjects aged 50 to 75 participated in a study of autonomic nervous function . Cardiac cycle duration ( RR interval ) and continuous finger arterial pressure  were measured under three conditions : during spontaneous breathing , during six deep breaths over 1 min , and during an active change in position from lying to st and ing . From these readings , ten measures of autonomic function were assessed ( mean  heart rate , three Ewing test measures  , five HRV measures  and one  BRS measure ) . Results Regression analysis in a healthy subgroup ( n=191 ) showed sex differences for two of the ten measures and seven measures decreased with age . Therefore , appropriate age-specific and sex-specific reference values were calculated . Reproducibility ( n=39 ) of most measures was moderate , with a reliability coefficient of around 50 % . Agreement between the measures of autonomic nervous function varied greatly , between 0 % and 87 % . The HRV-power ratio measure and the blood pressure changes in the lying-to-st and ing test showed the lowest agreement with all other measures . Conclusion /InterpretationThis study provides age-specific and sex-specific reference values for a wide range of different autonomic function measures in an elderly population . Agreement among the different measures varied widely and reproducibility was only moderate Abstract Objective : To examine the association between work stress , according to the job strain model and the effort-reward imbalance model , and the risk of death from cardiovascular disease . Design : Prospect i ve cohort study . Baseline examination in 1973 determined cases of cardiovascular disease , behavioural and biological risks , and stressful characteristics of work . Biological risks were measured at 5 year and 10 year follow up . Setting : Staff of a company in the metal industry in Finl and . Participants : 812 employees ( 545 men , 267 women ) who were free from cardiovascular diseases at baseline . Main outcome measure : Cardiovascular mortality 1973 - 2001 from the national mortality register . Results : Mean length of follow up was 25.6 years . After adjustment for age and sex , employees with high job strain , a combination of high dem and s at work and low job control , had a 2.2-fold ( 95 % confidence interval 1.2 to 4.2 ) cardiovascular mortality risk compared with their colleagues with low job strain . The corresponding risk ratio for employees with effort-reward imbalance ( low salary , lack of social approval , and few career opportunities relative to efforts required at work ) was 2.4 ( 1.3 to 4.4 ) . These ratios remained significant after additional adjustment for occupational group and biological and behavioural risks at baseline . High job strain was associated with increased serum total cholesterol at the 5 year follow up . Effort-reward imbalance predicted increased body mass index at the 10 year follow up . Conclusions : High job strain and effort-reward imbalance seem to increase the risk of cardiovascular mortality . The evidence from industrial employees suggests that attention should be paid to the prevention of work stress Study Design . A 3-year prospect i ve cohort study among 1334 workers was conducted . Objective . To determine whether the work-related psychosocial factors of quantitative job dem and s , conflicting job dem and s , skill discretion , decision authority , supervisor support , coworker support , and job security are risk factors for neck pain . Summary of Background Data . Among the various risk factors for neck pain , work-related psychosocial factors play a major role . Previous studies on risk factors for neck pain often had a cross-sectional design , and did not take both physical and psychosocial factors into account . Methods . At baseline , data on work-related psychosocial factors were collected by means of a question naire . During the 3-year follow-up period , data on the occurrence of neck pain were collected by means of postal question naires . Individuals without neck pain at baseline were selected for the analyses . Cox regression analysis was applied to examine the relation between the work-related psychosocial factors and the cumulative incidence of neck pain . Adjustments were made for various physical factors and individual characteristics . Results . The analysis included 977 patients . Altogether , 141 workers ( 14.4 % ) reported that they had experienced neck pain at least once during the 3-year follow-up period . The relation of neck pain to high quantitative job dem and s ( relative risk [ RR ] , 2.14 ; 95 % confidence interval [ CI ] , 1.28–3.58 ) and low coworker support ( RR , 2.43 ; 95 % CI , 1.11–5.29 ) was statistically significant . An increased risk was found for low decision authority in relation to neck pain ( RR , 1.60 ; 95 % CI , 0.74–3.45 ) , but this relation was not statistically significant . Conclusions . High quantitative job dem and s and low coworker support are independent risk factors for neck pain . There are indications that another risk factor for neck pain is low decision authority A robust method is presented for  electrocardiogram (ECG)-based estimation of the respiratory frequency during stress testing . Such ECGs contain highly nonstationary noise and exhibit changes in QRS morphology which , when combined with the dynamic nature of the respiratory frequency , make most existing methods break down . The present method exploits the oscillatory pattern of the rotation angles of the heart 's electrical axis as induced by respiration . The series of rotation angles , obtained from least-squares loop alignment , is subject to power spectral analysis and estimation of the respiratory frequency . Robust techniques are introduced to h and le the nonstationary properties of exercise ECGs . The method is evaluated by means of both simulated signals , and  ECG/airflow signals recorded from 14 volunteers and 20 patients during stress testing . The result ing respiratory frequency estimation error is , for simulated signals , equal to 0.5 % /spl plusmn/ 0.2 % , mean /spl plusmn/ SD ( 0.002 /spl plusmn/ 0.001 Hz ) , whereas the error between respiratory frequencies of the ECG-derived method and the airflow signals is 5.9 % /spl plusmn/ 4 % ( 0.022 /spl plusmn/ 0.016 Hz ) . The results suggest that the method is highly suitable for analysis of noisy ECG signals recorded during stress testing BACKGROUND Job strain has been linked to increased risk of cardiovascular diseases . In modern media work , time pressures , rapidly changing situations , computer work and irregular working hours are common . Heart rate variability ( HRV ) has been widely used to monitor sympathovagal balance . Autonomic imbalance may play an additive role in the development of cardiovascular diseases . AIMS To study the effects of work dem and s and job control on the autonomic nervous system recovery among the media personnel . METHODS From the cross-sectional postal survey of the employees 
    Output:
    
The main finding was that heightened occupational stress was found associated with lowered HRV , specifically with reduced parasympathetic activation .
Reduced parasympathetic activation was seen as decreases in RMSSD and HF power , and increase in LF/HF ratio .