***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: BACKGROUND It is unclear from prior reports whether the relationships between self-ratings of anxiety or emotional stress and parasympathetic nervous system components of heart rate variability are independent of personality and cardiorespiratory fitness . We examined those relationships in a clinical setting prior to a st and ardized exercise test . METHODS AND RESULTS Heart rate variability ( HRV ) was measured during 5 min of supine rest among 92 healthy men ( N=52 ) and women ( N=40 ) who had above-average cardiorespiratory fitness as indicated by peak oxygen uptake measured during grade -incremented treadmill exercise . HRV data sets were decomposed into low-frequency ( LF ; 0.05 - 0.15 Hz ) and high-frequency ( HF ; 0.15 - 0.5 Hz ) components using spectral analysis . Self-ratings of trait anxiety and perceived emotional stress during the past week were also assessed . CONCLUSIONS There was an inverse relationship between perceived emotional stress during the past week and the normalized HF component of HRV ( P=0.038 ) . This indicates a lower cardiac vagal component of HRV among men and women who perceived more stress . That relationship was independent of age , gender , trait anxiety , and cardiorespiratory fitness . It was also independent of heart rate ; mean arterial blood pressure ; and respiration rate , factors which can influence HRV and might be elevated among people reporting anxiety and perceived stress . We conclude that vagal modulation of heart period appears to be sensitive to the recent experience of persistent emotional stress , regardless of a person 's level of physical fitness and disposition toward experiencing anxiety The aim of the present study was to investigate the effect of vagal tone on performance during executive and non-executive tasks , using a working memory and a sustained attention test . Reactivity to cognitive tasks was also investigated using heart rate ( HR ) and heart rate variability ( HRV ) . Fifty-three male sailors from the Royal Norwegian Navy participated in this study . Inter-beat-intervals were recorded continuously for 5 min of baseline , followed by r and omized presentation of a working memory test ( WMT ) based on Baddeley and Hitch 's research ( 1974 ) and a continuous performance test ( CPT ) . The session ended with a 5-min recovery period . High HRV and low HRV groups were formed based on a median split of the root mean squared successive differences during baseline . The results showed that the high HRV group showed more correct responses than the low HRV group on the WMT . Furthermore , the high HRV group showed faster mean reaction time ( mRT ) , more correct responses and less error , than the low HRV group on the CPT . Follow-up analysis revealed that this was evident only for components of the CPT where executive functions were involved . The analyses of reactivity showed a suppression of HRV and an increase in HR during presentation of cognitive tasks compared to recovery . This was evident for both groups . The present results indicated that high HRV was associated with better performance on tasks involving executive function BACKGROUND Although heart rate variability ( HRV ) has been found to be associated with increased mortality in the elderly , the association of HRV and cognitive function and activity of daily living ( ADL ) capacity in the very elderly are not clear . METHODS A sample of very elderly people ( N = 138 ) , aged 75 years and older , living in Urausu , Hokkaido , participated in this study . Participants were classified into three groups : normal , borderline , and dementia . Time and frequency domain measures of HRV were compared with behavioral and cognitive functions . RESULTS HRV components , except for the LF/HF ratio , did not correlate with age in the very elderly . The LF component showed a statistically significant correlation with all the variables of behavioral functions . Most HRV components showed statistically significant and positive correlations with the flexibility of the back . The LF and LF/HF ratio were significantly lower in the dementia group than in the normal group . CONCLUSION Although the meaning of the LF component is still controversial , we foundadefinite relationship between the LF component and behavioral functions . A positive relationship between most HRV components and the flexibility of the back may suggest that reduced flexibility leads to deteriorated cardiopulmonary function and reduced HRV . A further prospect i ve study is needed to examine whether HRV and neurobehavioral functions are independent predictors of morbidity and mortality in very elderly people Background : To examine the relationship between reduced heart rate variability ( HRV ) and cognitive function in middle-aged adults in the general population . Methods : HRV , in both time and frequency domains , and cognitive functioning were measured twice in 5,375 male and female participants of the UK Whitehall II study ( mean ages = 55 and 61 years , respectively ) .  Logistic regression was used to model associations between HRV and cognition [ short-term verbal memory , reasoning ( Alice Heim 4-I ) , vocabulary , phonemic and semantic fluency ] . Cross-sectional associations were assessed at both waves , and longitudinal associations were measured as changes in cognition over the 5-year follow-up . Results : No consistent associations were found in men or women , either in the cross-sectional , prospect i ve or the longitudinal analyses of declines in cognition . Conclusion : Reduced cardiovascular autonomic function does not contribute to cognitive impairment in this middle-aged population . Further studies are needed to verify the potential role of HRV measures in predicting the degeneration of cognitive function at older ages Objective To evaluate the relationship between the autonomic nervous system basal state and performance in decision-making tasks . Background The link between performance in decision-making tasks and acute changes in autonomic parameters during their execution has been extensively investigated . However , there is lacking evidence regarding the relationship between decision making and basal autonomic state . Methods Resting autonomic nervous system activity in 18 healthy individuals was assessed by means of heart rate variability ( HRV ) analysis before conducting 3 different decision-making tasks : an ambiguous one , the Iowa Gambling Task ; a test that assesses risk-taking behavior , the Game of Dice Task ; and a test that assesses reversal learning behavior , the Reversal Learning Task . The tasks were administered in a r and om manner . Results There was a direct correlation between the Iowa Gambling Task net score and the resting low frequency HRV ( r=0.73 ; P<0.001 ) , which is strongly influenced by sympathetic activity . No correlations were found between HRV and the Game of Dice Task net score or the Reversal Learning Task last error trial . Conclusions The results are compatible with the idea that a higher basal activation of autonomic nervous system is beneficial for subsequent decision-making process Abstract The aim of the present study was to investigate the relationship between resting heart rate variability ( HRV ) and cognitive functions during threat of shock . A Continuous Performance Task and a Working Memory Task were used to measure cognitive functions .  Sixty-five male participants from the Royal Norwegian Navy participated .  HRV was measured during baseline , test conditions and recovery . Participants were r and omly assigned into non-threat and threat groups . Based on the median split of the high frequency ( HF ) spectral power , groups were divided into two additional groups . Overall , the high HRV participants showed superior performance on cognitive tasks independent of non-threat or threat conditions . During threat condition the low HRV group showed improved performance . Thus , individuals with high HRV were more stress tolerant and resilient in the face of environmental changes . The results from the study might have implication s with regard to performance in operational setting s , but also for other fields of psychological research such as individual differences , anxiety and coping This paper reports an investigation of forearm blood flow and cardiac responses to high intensity auditory stimulation . Blood was assessed in terms of forearm girth ( FG ) using a strain gauge , and since this technique had not been used previously , a preliminary study was conducted to vali date the measure . In Experiment 1 ( N = 24 ) , subjects performed either a fast- or slow-paced mental arithmetic task .  The data indicated that the strain gauge technique differentiated periods of rest from arithmetic stress and produced results comparable with those obtained using limb volume plethysmography . In Experiment 2 ( N = 24 ) , subjects received eight presentations of either a 60 dB or a 110 dB white noise stimulus at r and omly ordered intervals of 35 , 40 , 45 and 50 sec ; stimulus rise time was 50 msec and the duration 1 sec. Both groups displayed short-latency ( i.e. within 10 beats poststimulus ) cardiac accelerative responses which habituated over trials . In addition , the 110dB group displayed a long-latency ( 19.9 sec ) accelerative response of approximately 25 beats per min and this was accompanied by an increase in FG . These responses occurred only following the first stimulus presentation , and analysis of the EKG T-wave amplitude suggested that the cardiac response was mediated sympathetically . These results are discussed in terms of conceptions of the startle and defence responses in man and the fight/flight reaction in animals Objective : To investigate the cross-sectional and longitudinal associations of 10-second heart rate variability ( HRV ) with various domains of cognitive function in older participants at risk of cardiovascular disease . Methods : We studied 3,583 participants , mean age of 75.0 years , who were enrolled in the Prospect i ve Study of Pravastatin in the Elderly at Risk . From baseline 10-second ECGs , st and ard deviation of normal-to-normal intervals was calculated as the index of HRV . Four cognitive domains were assessed at baseline and repeated during a mean follow-up period of 3.2 years . Results : Lower HRV at baseline was associated with worse performance in reaction time ( mean difference between low third vs high third of HRV = 1.96 seconds , 95 % confidence interval [ CI ] 0.20 to 3.71 ) and processing speed ( −0.57 digits coded , 95 % CI −1.09 to −0.05 ) . During follow-up , participants with lower HRV had a steeper decline in processing speed ( mean annual change between low third vs high third of HRV = −0.16 digits coded , 95 % CI −0.28 to −0.04 ) . There was no difference in annual changes of reaction time or immediate and delayed memory among HRV thirds during follow-up . All these associations remained unchanged after adjustment for medications , cardiovascular risk factors , and comorbidities . Conclusions : Participants with lower 10-second HRV have worse performance in reaction time and processing speed and experience steeper decline in their processing speed , independent of medications , cardiovascular risk factors , and comorbidities 
    Output:
    
Results : Both increased sympathetic activity and decreased parasympathetic activity seem to be associated with a worse performance in the cognitive domains considered , in the absence of dementia and severe cardiovascular diseases or other medical and psychiatric diseases .
Conclusion : The results highlight the influence of the autonomic nervous system ( ANS ) in cognitive functioning .
Despite these limits , HRV could be considered a promising early biomarker of cognitive impairment in population s without dementia or stroke .