***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 : Conventional pulmonary rehabilitation programs improve exercise tolerance but have no effect on pulmonary function in patients with chronic obstructive pulmonary disease ( COPD ) . The role of controlled breathing using respiratory biofeedback during rehabilitation of patients with COPD remains unclear . Objectives : To compare the effects of a conventional 4-week pulmonary rehabilitation program with those of rehabilitation plus controlled breathing interventions . Methods : A r and omized controlled trial was performed . Pulmonary function ( FEV1 ) , exercise capacity ( 6-min walking distance , 6MWD ) , health-related quality of life ( chronic respiratory question naire , CRQ ) and cardiac autonomic function ( rMSSD ) were evaluated . Results : Forty COPD patients ( mean ± SD age 66.1 ± 6.4 , FEV1 45.9 ± 17.4 % predicted ) were r and omized to rehabilitation ( n = 20 ) or rehabilitation plus controlled breathing ( n = 20 ) . There were no statistically significant differences between the two groups regarding the change in FEV1 ( mean difference –0.8 % predicted , 95 % CI –4.4 to 2.9 % predicted , p = 0.33 ) , 6MWD ( mean difference 12.2 m , 95 % CI –37.4 to 12.2 m , p = 0.16 ) , CRQ ( mean difference in total score 0.2 , 95 % CI –0.1 to 0.4 , p = 0.11 ) and rMSSD ( mean difference 2.2 ms , 95 % CI –20.8 to 25.1 ms , p = 0.51 ) . Conclusions : In patients with COPD undergoing a pulmonary rehabilitation program  , controlled breathing using respiratory biofeedback has no effect on exercise capacity , pulmonary function , quality of life or cardiac autonomic function OBJECTIVE Non-invasive mechanical ventilation ( NIMV ) has the potential to improve sympathovagal control of heart rate . The aim of this study was to investigate the acute effects of NIMV on heart rate variability ( HRV ) in chronic obstructive pulmonary disease ( COPD ) patients with hypercapnic respiratory failure ( HRF ) . METHODS In this prospect i ve study 28 COPD patients ( 64+/-10 years ) with HRF underwent electrocardiographic Holter monitorization .  Both time domain ( TD ) and frequency domain ( FD ) means of HRV analysis were measured for two hours before and during NIMV application . For the TD , mean-RR , SDNN , SDANN , SDNN index , RMSSD , pNN50 and HRV triangular index were measured . For FD , high frequency ( HF ) and low frequency ( LF ) were detected . To compare HRV parameters before and during bi-level positive airway pressure ( BiPAP ) application ; paired sample t test was used for normally distributed variables and Wilcoxon signed rank test was used for the variables that were not normally distributed . Pearson correlation test was used to analyze the correlation between HRV and blood gas parameters during BiPAP application . RESULTS High frequency power of HRV ( 39 ( 18 - 65 ) ms2 vs. 28 ( 12 - 50 ) ms2 , p<0.05 ) , HRV triangular index ( 9 ( 3 - 17 ) units vs. 6 ( 2 - 13 ) units , p<0.05 ) and pNN50 ( 59 % ( 13 - 110 ) vs. 42 % ( 5 - 84 ) , p<0.05 ) , were higher during NIMV than before noninvasive mechanical ventilation . CONCLUSIONS We think that NIMV may improve heart rate variability indices of parasympathetic modulation of heart rate in COPD cases with HRF and decrease arrhythmic potential Background and Purpose — The baroreceptor reflex arc is important in the short-term regulation of the cardiovascular system , and small studies have reported impaired cardiac baroreceptor sensitivity ( BRS ) after acute stroke . However , the prognostic significance of impaired BRS is uncertain . Methods — One hundred twenty-four patients underwent simultaneous ECG and noninvasive beat-to-beat blood pressure ( BP ) monitoring within 72 hours of neuroradiologically confirmed acute ischemic stroke . Cardiac BRS was assessed from the combined & agr;-index by means of power spectral analysis techniques . Baseline data for acute stroke patients were compared with those of a control group matched for age , sex , and casual BP . Patients were followed up for a median of 1508 days ( range , 9 to 2656 days ) , and outcome was compared between patients with and without impaired BRS . Results — Median BRS values were significantly lower in stroke patients than in controls ( 5 [ interquartile range , 3.5 to 7.4 ] versus 6.2 [ interquartile range , 4.5 to 8.3 ] ms/mm Hg;P = 0.04 ) . Sixty-one ( 33 male ) patients ( mean age , 70.2 [ SD 10.5 ] years ) had impaired BRS ( ≤5.0 ms/mm Hg ) compared with 63 ( 35 male ) patients ( mean age , 70.6 [ SD 11.7 ] years ) without impaired BRS ( > 5.0 ms/mm Hg ) . Stroke patients with impaired BRS values had a significantly poorer prognosis ( 28 % versus 8 % mortality rate during the follow-up period ) although there were no differences in age , stroke severity , stroke type , or casual or 24-hour BP parameters between the 2 groups . Conclusions — Impaired cardiac BRS is associated with increased long-term mortality after acute ischemic stroke , irrespective of age , sex , stroke type , and BP . This may reflect cardiac arrhythmias , but the mechanisms underlying this association are unknown , although therapies that improve cardiac BRS after stroke warrant further investigation Objectives Chronic obstructive pulmonary disease ( COPD ) is associated with cardiac autonomic nervous system dysregulation . This study evaluates the effects of interval hypoxic training on cardiovascular and respiratory control in patients with mild COPD . Methods In 18 eucapnic normoxic mild COPD patients ( age 51.7 ± 2.4 years , mean ± SEM ) , r and omly assigned to either training or placebo group , and 14 age-matched healthy controls ( 47.7 ± 2.8 years ) , we monitored end-tidal carbon dioxide , airway flow , arterial oxygen saturation , electrocardiogram , and continuous noninvasive blood pressure at rest , during progressive hypercapnic hyperoxia and isocapnic hypoxia to compare baroreflex sensitivity to hypoxia and hypercapnia before and after 3 weeks of hypoxic training . In double-blind fashion , both groups received 15 sessions of passive intermittent hypoxia ( training group ) or normoxia ( placebo group ) . For the hypoxia group , each session consisted of three to five hypoxic ( 15–12 % oxygen ) periods ( 3–5 min ) with 3-min normoxic intervals . The placebo group inhaled normoxic air . Results Before training , COPD patients  showed depressed baroreflex sensitivity , as compared with healthy individuals , without evident chemoreflex abnormalities . After training , in contrast to placebo group , the training group showed increased ( P < 0.05 ) baroreflex sensitivity up to normal levels and selectively increased hypercapnic ventilatory response ( P < 0.05 ) , without changes in hypoxic ventilatory response . Conclusion Eucapnic normoxic mild COPD patients already showed signs of cardiovascular autonomic abnormalities at baseline , which normalized with hypoxic training . If confirmed in more severe patients , interval hypoxic training may be a therapeutic strategy to rebalance early autonomic dysfunction in COPD patients Background —It is well established that a depressed baroreflex sensitivity may adversely influence the prognosis in patients with chronic heart failure ( CHF ) and in those with previous myocardial infa rct ion . Methods and Results —We tested whether a slow breathing rate ( 6 breaths/min ) could modify the baroreflex sensitivity in 81 patients with stable ( 2 weeks ) CHF ( age , 58±1 years ; NYHA classes I [ 6 patients ] , II [ 33 ] , III [ 27 ] , and IV [ 15 ] ) and in 21 controls .  Slow breathing induced highly significant increases in baroreflex sensitivity , both in controls ( from 9.4±0.7 to 13.8±1.0 ms/mm Hg , P < 0.0025 ) and in CHF patients ( from 5.0±0.3 to 6.1±0.5 ms/mm Hg , P < 0.0025 ) , which correlated with the value obtained during spontaneous breathing ( r = + 0.202 , P = 0.047 ) . In addition , systolic and diastolic blood pressure decreased in CHF patients ( systolic , from 117±3 to 110±4 mm Hg , P = 0.009 ; diastolic , from 62±1 to 59±1 mm Hg , P = 0.02 ) . Conclusions —These data suggest that in patients with CHF  , slow breathing , in addition to improving oxygen saturation and exercise tolerance as has been previously shown , may be beneficial by increasing baroreflex sensitivity BACKGROUND The chronic obstructive pulmonary disease ( COPD ) is associated with the strength and resistance decreasing in addition to the dysfunction on autonomic nervous system ( ANS ) . The aerobic training isolated or in association with the resistance training showed evidence of beneficial effects on an autonomic modulation of COPD ; however , there are no studies addressing the effect of isolated resistance training . AIMS This study aims at investigating the influence of resistance training on an autonomic modulation through heart rate variability ( HRV ) , functional capacity and muscle strength in individuals with COPD . DESIGN Clinical series study . SETTING Out patients . POPULATION The study involved 13 individuals with COPD . METHODS The experimental protocol was composed by an initial and final evaluation that consisted in autonomic evaluations ( HRV ) , cardiopulmonary functional capacity evaluation ( 6-minute walk test ) and strength evaluation ( dynamometry )  in addition by the resistance training performed by 24 sessions lasted 60 minutes each one and on a frequency of three times a week . The intensity was determined initially with 60 % of one maximum repetition and was progressively increased in each five sessions until 80 % . RESULTS The HRV temporal and spectral indexes analysis demonstrates improvement of autonomic modulation , with significant statistical increases to sympathetic and parasympathetic components of ANS representing by SDNN , LF and HF . In addition , it was observed significant statistical increases to shoulder abduction and knee flexion strength and functional capacity . CONCLUSION The exclusive resistance training performed was able to positively influence the autonomic modulation ; in addition it promoted benefits on cardiorespiratory functional capacity and strength benefits in individuals with COPD . CLINICAL REHABILITATION IMPACT This study could contribute to clinical and professionals research ers that act with COPD , even though the resistance component of pulmonary rehabilitation presents consensual benefits on several healthy indicators parameters . There is no evidence about the effects on HRV before . Moreover , this study showed , on clinical practice , the HRV uses as an ANS activity on sinus node evaluation and highlights further importance on scientific context To investigate the distribution of heart rate variability ( HRV ) spectral power in an unselected sample of the population , and to ascertain the population correlates of HRV , we examined 1,984 healthy persons , aged 45 to 64 years , r and omly selected from the Atherosclerosis Risk in Communities ( ARIC ) study cohort .  Resting , supine , 2-minute , beat-to-beat heart rate data were collected between 7 A.M. and 12 noon . The race- and sex-adjusted geometric means of low-frequency component ( LF , 0.025 to 0.15 Hz ) were 4.00 and 3.13 (beats/min)2 ; of high-frequency component ( HF , 0.16 to 0.35 Hz ) , 1.65 and 1.21 (beats/min)2 ; and of the HF/LF ratio , 0.41 and 0.39 , for 45-to-54 and 55-to-64 years age groups , respectively ( test of mean difference by age , p < 0.01 , p < 0.01 , and p = 0.11 for LF , HF , and HF/LF ratio , respectively ) . Comparing black with white examinees , the age- and sex-adjusted geometric means of LF were 3.06 and 3.70 (beats/min)2 ; of HF , 1.66 and 1.36 (beats/min)2 ; of HF/LF , 0.54 and 0.37 , respectively ( test of mean difference by race , p < 0.01 , p < 0.01 , and p < 0.01 ) . The age- and race-adjusted geometric means of LF for women and men were 3.12 and 4.10 (beats/min)2 ; of HF , 1.46 and 1.38 (beats/min)2 ; and of HF/LF , 0.47 and 0.34 , respectively ( test of mean difference , p < 0.01 , p = 0.34 , and p < 0.01 ) . We conclude that HRV spectral indexes are associated with age , race , and sex 
    Output:
    
The results of the studies review ed showed a strong level of evidence to support the impairment of heart rate variability in the time domain .
A similar evidence level was also found to support impairment in baroreceptor sensitivity and muscle sympathetic nerve activity .
Furthermore , this review identified physical activity level , muscle function , and circadian rhythm as the major influencing factors ( strong evidence ) of autonomic function in subjects with COPD .
However , no definite conclusion could be reached for factors such as dyspnea , anxiety , body composition , pulmonary function , age , breathing frequency , ventilatory effort , quality of life , and disease severity due to limited , conflicting , or lack of existing evidence .