***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 In a study of the effectiveness of systematic relaxation training alone or combined with biofeedback in the treatment of  hypertension in pregnancy , 60 women were seen weekly for 6 weeks . 18 were given relaxation therapy alone ( group A ) , 18 relaxation plus biofeedback ( group B ) , and there were 24 controls . Whereas two-thirds of the control group had to be admitted to hospital during their pregnancies , less than a third of each experimental group had to be admitted . The experimental groups also had significantly lower systolic and diastolic blood pressure than the control group . There were no significant differences between groups A and B in hospital admission rates or blood-pressure measurements Matched groups of primigravid women received one of three antenatal training programmes : normal antenatal classes , normal classes plus electromyography biofeedback relaxation training , or normal classes plus skin-conductance biofeedback relaxation training . Myographic training was found to be effective within conventional antenatal constraints , whereas skin-conductance training was not . The women reported use of biofeedback training and related skills to be of some benefit during early labour . However , no difference between effectively trained electromyographic , ineffectively trained skin-conductance and control groups was found on labour and delivery performance measures OBJECTIVE Prenatal distress has been linked to pregnancy complications and poor offspring 's health , despite the fact that longitudinal assessment s of various stress dimensions are still lacking . Hence , we aim ed to assess perceived stress over the course of pregnancy . Moreover , we examined whether social support and coping styles are linked to prenatal stress trajectories . METHODS Data from 543 women participating in the PRINCE ( Prenatal Identification of Children Health ) study , a prospect i ve population -based cohort study , was used for the present analyses . Once per trimester the women completed question naires regarding different psychometric measures , including the  Perceived Stress Scale ( PSS ) . Linear mixed regression models were used to examine perceived stress development longitudinally and to relate social support and coping styles to stress trajectories during pregnancy . RESULTS A significant decrease of perceived stress was observed over the course of pregnancy . Stratifying the study sample according to parity , women delivering their first child had continuously lower perceived stress scores compared to women having already one or more children , and a significant decrease during pregnancy was exclusively observed in primiparous women . Both , positive coping strategies and higher perceived and received social support were independently associated with lower perceived stress , while evasive coping strategies were associated with higher levels of perceived stress . CONCLUSION Our study reveals stress perception trajectories during pregnancies in primi- and multiparous women . Our findings underscore the need for intervention strategies aim ing to improve social support and positive coping strategies especially in multiparous women in order to reduce the risks for adverse pregnancy outcomes Acute psychosocial stress is typically investigated in laboratory setting s using protocol s with distinctive characteristics . For example , some tasks involve the action of speaking , which seems to alter Heart Rate Variability ( HRV ) through acute changes in respiration patterns . However , it is still unknown which task induces the strongest subjective and autonomic stress response . The present cross-over r and omized trial sought to investigate the differences in perceived stress and in linear and non-linear analyses of HRV between three different verbal ( Speech and Stroop ) and non-verbal ( Montreal Imaging Stress Task ; MIST ) stress tasks , in a sample of 60 healthy adults ( 51.7 % females ; mean age = 25.6 ± 3.83 years ) . Analyses were run controlling for respiration rates . Participants reported similar levels of perceived stress across the three tasks . However , MIST induced a stronger cardiovascular response than Speech and Stroop tasks , even after controlling for respiration rates . Finally , women reported higher levels of perceived stress and lower HRV both at rest and in response to acute psychosocial stressors , compared to men . Taken together , our results suggest the presence of gender-related differences during psychophysiological experiments on stress . They also suggest that verbal activity masked the vagal withdrawal through altered respiration patterns imposed by speaking . Therefore , our findings support the use of highly-st and ardized math task , such as MIST , as a valid and reliable alternative to verbal protocol s during laboratory studies on stress A study of the effects of biofeedback on the pain of childbirth was conducted . Forty primigravidae were r and omly assigned to either an experimental group or a control group . The experimental group was given a series of training sessions in biofeedback and used biofeedback equipment during labor . All subjects were monitored during the labor and delivery period for their reports of pain using a visual analogue scale ( VAS ) and a verbal descriptor scale ( VDS ) . Results showed that women using biofeedback during childbirth reported significantly lower pain : from admission to labor and delivery ( p less than 0.05:VDS ; p less than 0.01:VAS ) , at delivery ( p less than 0.005:VDS ) , and 24-hr postpartum ( p less than 0.01:VDS ) . Also , women in the biofeedback group labored an average of 2 hr less and used 30 % fewer medications . The results of this study suggest that EMG biofeedback may be effective in reducing levels of acute pain experienced by childbearing women The aim of this study was to investigate cardiac functional status in pregnancy using a comprehensive approach taking into account the simultaneous changes in loading and geometry , as well as maternal age and anthropometric indices . This was a prospect i ve cross-sectional study of 559 nulliparous pregnant women assessed at 4 time points during pregnancy and at 1 year postpartum . All women underwent conventional echocardiography and tissue Doppler velocities and strain rate analysis at multiple cardiac sites . Mean arterial pressure and total vascular resistance index significantly decreased ( both P<0.001 ) during the first 2 trimesters of pregnancy and increased thereafter . Stroke volume index and cardiac index showed the opposite trend compared with mean arterial pressure and total vascular resistance index ( both P<0.05 ) . Myocardial and ventricular function were significantly enhanced in the first 2 trimesters but progressively declined thereafter . By the end of pregnancy , significant chamber diastolic dysfunction and impaired myocardial relaxation was evident in 17.9 % and 28.4 % of women , respectively , whereas myocardial contractility was preserved . There was full recovery of cardiac function at 1 year postpartum . Cardiovascular changes during pregnancy are thought to represent a physiological adaptation to volume overload . The findings of a drop in stroke volume index , impaired myocardial relaxation with diastolic dysfunction , and a tendency toward eccentric remodeling in a significant proportion of cases at term are suggestive of cardiovascular maladaptation to the volume-overloaded state in some apparently normal pregnancies . These unexpected cardiovascular findings have important implication s for the management of both normal and pathological pregnancy states 1 . The effect of a variation in inspiration and expiration times on heart rate variability was studied in 12 healthy subjects ( mean age 30±6 years ; five females ) This investigation assessed the efficacy of a biobehavioral intervention in the adjunctive treatment of mild pregnancy-induced hypertension ( PIH ) , a potentially serious complication of pregnancy in which normotensive women develop hypertension , proteinuria , and edema of unknown etiology late in gestation . Forty-five women with symptoms of PIH were r and omly assigned to one of three treatment conditions : bed rest alone ( the most common obstetrical treatment ) , bed rest with individualized compliance enhancement training , or a four-session biobehavioral treatment consisting of bed rest , compliance enhancement training , and individualized thermal biofeedback-assisted relaxation training . Results indicated that while blood pressure for the bed rest and compliance enhancement groups continued to rise and pose an increasing health risk to maternal and fetal well-being , subjects in the biobehavioral group maintained their blood pressure at a significantly lower , and presumably safer , level . The biobehavioral treatment is hypothesized to affect blood pressure levels in subjects with mild PIH through the mediation of the sympathetic nervous system , decreasing peripheral vascular resistance and cardiac output . The results of this investigation suggest that the biobehavioral intervention may be an effective adjunct to bed rest in the treatment of mild PIH remote from term PURPOSE This study was conducted to investigate the effectiveness of pelvic floor muscle exercise using biofeedback and electrical stimulation after normal delivery . METHODS The subjects of this study were 49 ( experimental group : 25 , control group : 24 ) postpartum women who passed 6 weeks after normal delivery without complication of pregnancy , delivery and postpartum . The experimental group was applied to the pelvic muscle enforcement program by biofeedback and electrical stimulation for 30 minutes per session , twice a week for 6 weeks , after then self-exercise of pelvic floor muscle was done 50 - 60 repetition per session , 3 times a day for 6 weeks . Maximum pressure of pelvic floor muscle contraction ( MPPFMC ) , average pressure of pelvic floor muscle contraction ( APPFMC ) , duration time of pelvic floor muscle contraction ( DTPFMC ) and the subjective lower urinary symptoms were measured by digital perineometer and Bristol Female Urinary Symptom Question naire and compared between two groups prior to trial , at the end of treatment and 6 weeks after treatment . RESULTS The results of this study indicated that MPPFMC , APPFMC , DTPFMC were significantly increased and subjective lower urinary symptoms were significantly decreased after treatment in the experimental group than in the control group . CONCLUSIONS This study suggested that the pelvic floor muscle exercise using biofeedback and electrical stimulation might be a safer and more effective program for reinforcing pelvic floor muscle after normal delivery BACKGROUND Several parameters of heart rate variability ( HRV ) have been shown to predict the risk of sudden cardiac death ( SCD ) in cardiac patients . There is consensus that risk prediction is increased when measuring HRV during specific provocations such as orthostatic challenge . For the first time , we provide data on reproducibility of such a test in patients with a history of acute coronary syndrome . METHODS Sixty male patients ( 65 ± 8 years ) with a history of acute coronary syndrome on stable medication were included .  HRV was measured in supine ( 5 min ) and st and ing ( 5 min ) position on 2 occasions separated by two weeks . For risk assessment relevant time-domain [ st and ard deviation of all R-R intervals ( SDNN ) and root mean squared st and ard differences between adjacent R-R intervals ( RMSSD ) ] , frequency domain [ low-frequency power ( LF ) , high-frequency power ( HF ) and LF/HF power ratio ] and short-term fractal scaling component ( DF1 ) were computed . Absolute reproducibility was assessed with the st and ard errors of the mean ( SEM ) and 95 % limits of r and om variation , and relative reproducibility by the intraclass correlation coefficient ( ICC ) . RESULTS We found comparable SEMs and ICCs in supine position and after an orthostatic challenge test . All ICCs were good to excellent ( ICCs between 0.636 and 0.869 ) . CONCLUSIONS Reproducibility of HRV parameters during orthostatic challenge is good and comparable with supine position Abstract Objective : We sought to characterise the influence of an antenatal exercise programme on ECG-derived cardiac variables . Methods : Fifity-one healthy pregnant women were recruited and r and omly assigned ( 2 × 2 × 2 design ) to an exercise group or a control group . Exercising groups attended weekly classes from the 20th week of pregnancy onwards . Cardiovascular assessment s ( heart rate variabiliy ( HRV ) , QT , and the QT variability index ( QTVI ) ) were performed at 12–16 , 26–28 , 34–36 weeks and 12 weeks following birth , during supine rest and exercise conditions . Results : Advancing gestation was associated with an increased maternal heart rate ( p = 0.001 ) , shorter QT interval ( p = 0.003 ) , diminished HRV ( p = 0.002 ) and increased QTVI ( p = 0.002 ) . Each of these changes was reversed within 12 weeks postpartum ( p < 0.004 ) . The 
    Output:
    
The major findings of this review can be described as follows : ( a ) HRVBF and psychological stress in peripartum women are related concepts , ( b ) peripartum women who completed HRVBF report a reduction in stress compared with participants who did not receive HRVBF , and ( c ) there is currently no information on the effectiveness of HRVBF on psychological stress in the first and early second trimester of pregnancy .
Overall , this systematic review of the literature provides objective evidence that HRVBF may be a potential beneficial adjuvant treatment for stress management in peripartum women