***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: Central withdrawal of parasympathetic cardiac control and increased respiratory frequency represent two important determinants of reduced respiratory-related heart rate variability ( HRV ) . However , studies are missing to disentangle their relative contribution during mental stress . Healthy subjects ( n=10 ) and type 2 diabetic patients ( n=8 ) , the latter with evidence of cardiac autonomic neuropathy , participated in this study . Using an intra-individual approach , high-frequency ( hf ) HRV was assessed for spontaneous ( during rest and mental stress ) and paced breathing ( 0.15 , 0.2 , 0.25 , 0.3 , 0.35 , 0.4 and 0.45 Hz ; r and omized sequence ) . Mental stress was induced by a challenging reaction time task . Effects of respiratory frequency on hf HRV were individually predicted by paced breathing data . Mental stress decreased hf HRV ( p<.001 ) , and increased respiratory frequency ( p=.01 ) . Individual prediction of hf HRV by stress respiratory frequency result ed in lower values ( p=.02 ) than observed during rest , indicating that respiratory stress effects were sufficient to reduce hf HRV . However , observed hf HRV values during stress were even lower ( p<.001 ) . These results indicate that hf HRV reductions during stress can only partly be explained by concomitant respiratory frequency changes . This effect is detectable in healthy subjects and in patients with evidence of diabetic cardiac autonomic neuropathy The effects of exercise on subsequent psychophysiological responses to mental stress were assessed in a study of 30 normotensive male volunteers . Participants were r and omly allocated to three experimental conditions--20-min exercise at 100 Watts ( high exercise ) , 20-min exercise at 25 Watts ( low exercise ) , or 20-min no exercise ( control ) . After a recovery period of 20 min , all subjects performed a mental arithmetic task for four 5-min trials . Blood pressure and heart rate were monitored continuously using a Finapres , and respiration and electrodermal activity were also recorded . Baroreceptor reflex control of heart rate was assessed using power spectrum analysis . Exercise produced consistent increases in systolic blood pressure , heart rate , and subjective tension , together with reductions in systemic resistance and baroreflex sensitivity . The systolic and diastolic blood pressure and heart rate reactions to mental arithmetic were significantly blunted in the high exercise compared with control conditions , with the low exercise group showing an intermediate pattern . Subjective responses to mental stress were unaffected by prior exercise . The pattern of hemodynamic response was not a result of changes in baroreflex sensitivity . The mechanisms underlying this result are discussed in relation to the discrepancies between subjective and physiological responses to mental stress , and the implication s for the use of exercise in stress management This study tested various sources of changes in respiratory sinus arrhythmia ( RSA ) .  Twenty-two healthy participants participated in three experimental conditions ( mental stress , relaxation , and mild physical exercise ) that each consisted of three breathing parts ( normal breathing , breathing compressed room air , and breathing compressed 5 % CO2-enriched air ) . Independent contributions to changes in RSA were found for changes in tonic vagal modulation of heart rate , central respiratory drive ( i.e. , PaCO2 ) , respiratory depth , and respiratory frequency . The relative contributions to changes in RSA differed for mental stress and physical exercise . It is concluded that uncorrected RSA will suffice to index within-subject changes in tonic vagal modulation of heart rate in most situations . However , if the central respiratory drive is expected to change , RSA should ideally be corrected for changes in PaCO2 , respiratory depth , and respiratory frequency The sensitivity of physiological measures to mental workload was investigated in a flight simulator . Twelve pilots had to fly through a tunnel with varying levels of difficulty . Additionally , they had to perform a memory task with four levels of difficulty . The easiest memory task was combined with the easiest tunnel task and the most difficult memory task with the most difficult tunnel task . Between the tunnel tasks , subjects had to fly a pursuit task in which a target jet had to be followed . Rest periods before and after the experiment were used as a baseline for the physiological measures . Mental workload was measured with heart period , continuous blood pressure , respiration and eye blinks . Several respiratory parameters , heart rate variability , blood pressure variability and the gain between systolic blood pressure and heart period ( modulus ) were scored . All measures showed differences between rest and flight , and between the pursuit and the tunnel task . Only heart period was sensitive to difficulty levels in the tunnel task . Heart rate variability increased when respiratory activity around 0.10 Hz increased , which occurred often . The modulus was hardly influenced by respiration and therefore appears to be a better measure than heart rate variability . Among the respiratory parameters , the duration of a respiratory cycle was the most sensitive to changes in workload . The time in between two successive eye blinks ( blink interval ) increased and the blink duration decreased as more visual information had to be processed . Increasing the difficulty of the memory task led to a decrement in blink interval , probably caused by subvocal activity during rehearsal of target letters . The data show that physiological measures are sensitive to mental effort , whereas rating scales are sensitive to both mental effort and task difficulty To investigate the functional neuroanatomy of voluntary respiratory control , blood O2 level-dependent functional magnetic resonance imaging was performed in six healthy right-h and ed individuals during voluntary hyperpnea . Functional images of the whole brain were acquired during 30-s periods of spontaneous breathing alternated with 30-s periods of isocapnic hyperpnea [ spontaneous vs. voluntary : tidal volume = 0.5 + /- 0.01 vs. 1.3 + /- 0.1 ( SE ) liters and breath duration = 4.0 + /- 0.4 vs. 3.2 + /- 0.4 ( SE ) s ] . For the group , voluntary hyperpnea was associated with significant ( P < 0.05 , corrected for multiple comparisons ) neural activity bilaterally in the primary sensory and motor cortices , supplementary motor area , cerebellum , thalamus , cau date nucleus , and globus pallidum . Significant increases in activity were also identified in the medulla ( corrected for multiple comparisons on the basis of a small volume correction for a priori region of interest ) in a superior dorsal position ( P = 0.012 ) . Activity within the medulla suggests that the brain stem respiratory centers may have a role in mediating the voluntary control of breathing in humans Olfactory perception and related emotions are largely dependent on inspiration . We acquired simultaneous respiration and electroencephalographic recordings  during pleasant odour and unpleasant odour stimulation .  We sought to identify changes in respiratory pattern , inspiratory-related potentials and location of dipoles estimated from the potentials . Electroencephalographic recording was triggered by inspiration onset . Respiratory frequency decreased at pleasant odour recognition , and it increased at unpleasant odour detection and recognition . O2 consumption records showed that these changes were not due to metabolic dem and . During olfactory stimulation , inspiratory phase-locked alpha oscillation ( I-alpha ) was found in the averaged potential triggered by inspiration onset . I-alpha was observed at both pleasant odour and unpleasant odour detection and recognition , but it was not seen in the inspiration-triggered potentials of normal air breathing . Electroencephalographic dipole tracing identified the location of dipoles from the I-alpha in the limbic area and the cortex ; the entorhinal cortex , hippocampus , amygdala , premotor area and centroposterior orbitofrontal cortex subserve odour detection , and the rostromedial orbitofrontal cortex subserves odour recognition . We suggest that the I-alpha in our study originated from the olfactory cortex in the forebrain and was phase-locked to inspiration The level of expertise of an operator may significantly influence his/her psychophysiological response to high task dem and . A naive individual may invest considerable mental effort during performance of a difficult task and psychophysiological reactivity will be high compared to the psychophysiological response of a highly skilled operator . A study on multitasking performance was conducted to investigate the interaction between learning and task dem and on psychophysiological reactivity . Thirty naive participants performed high and low dem  and versions of the Multi-attribute Task Battery ( MATB ) over a learning period of 64 min . High and low task dem and setting were preset via a pilot study . Psychophysiological variables were collected from four channels of  EEG ( Cz , P3 , P4 , Pz ) , ECG , EOG and respiration rate to measure the impact of task dem and and learning . Several variables were sensitive to the task dem and manipulation but not time-on-task , e.g. , heart rate , Theta activity at parietal sites . The sensitivity of certain variables to high dem and was compromised by skill acquisition , e.g. , respiration rate , suppression of alpha activity . A sustained learning effect was observed during the high dem and condition only ; multiple regression analyses revealed that specific psychophysiological variables predicted learning at different stages on the learning curve . The implication s for the sensitivity of psychophysiological variables are discussed The purpose of the current study was to vali date the change in thoracic impedance ( dZ ) derived respiratory signal obtained from four spot electrodes against incidental spirometry . Additionally , a similar validation was performed for a dual respiratory belts signal to compare the relative merit of both methods . Participants were 38 healthy adult subjects ( half male , half female ) . Cross- method comparisons were performed at three ( paced ) respiration frequencies in sitting , supine and st and ing postures . Multilevel regression was used to examine the within- and between-subjects structure of the relationship between spirometric volume and the respiratory amplitude signals obtained from either dZ or respiratory belts . Both dZ derived respiratory rate and dual belts derived respiratory rate accurately reflected the pacing frequencies . For both methods , fixed factors indicated acceptable but posture-specific regression on spirometric volume . However , r and om factors indicated large individual differences , which was supported by variability of gain analyses . It was concluded that both the dZ and dual belts methods can be used for measurement of respiratory rate and within-subjects , posture-specific , changes in respiratory volume . The need for frequent subject-specific and posture-specific calibration combined with relatively large measurement errors may strongly limit the usefulness of both methods to assess absolute tidal volume and minute ventilation in ambulatory design Background Exaggerated cardiovascular and neuroendocrine responses to mental stress may enhance cardiovascular disease risk , Coronary heart disease and hypertension increase in prevalence with advancing age , whereas the excess male/female ratio declines in later middle age . Psychosocial factors may contribute to these changing risk profiles . The hypothesis that cardiovascular and neuroendocrine stress responses are associated with age and gender differences in cardiovascular disease risk was tested . Method 132 healthy men and women from younger ( 30–40 years ) and older ( 55–65 years ) age b and s were selected at r and om from general practice lists . They performed a series of mental stress tests during which blood pressure , heart rate , cardiovascular baroreflex sensitivity , Cortisol , respiration patterns and electrodermal activity were monitored . A submaximal exercise test was performed and psychological characteristics were assessed by question naire . Results At rest , systolic and diastolic blood pressure was higher in men than in women , while cardiac baroreflex sensitivity was greater in younger than in older participants . Blood pressure responses to tasks were substantial , with changes from the baseline averaging 18.6/8.11 , 26.0/13.5 and 40.7/19.0 mmHg for computerized problem solving , mirror drawing and speech tasks , respectively . Men and women in the older age b and did not differ from each other in blood pressure , heart rate or baroreflex sensitivity responses . Systolic blood pressure responses ( mean ± SEM ) were larger in older than in younger women ( mean peak difference 6.87 ± 2.67 mmHg ) , and in the younger male compared with the younger female groups ( mean peak difference 7.20 ± 2.97 mmHg ) . Diastolic blood pressure and heart rate responses to mental stress were larger in younger than in older age participants of both sexes . Baroreflex sensitivity was inhibited during behavioural tasks , with significantly greater suppression in younger than in older groups ( 5.28 ± 0.52 and 2.62 ± 0.35 ms/mmHg , respectively ) . Cortisol responses were greater in men than in women , but did not vary with age . Across the entire sample , systolic blood pressure responsivity was negatively related to the expression of anger . Among older men , heightened blood pressure responses were associated with elevated fasting low-density lipoprotein cholesterol levels , and with lower concentrations of high-density lipoprotein cholesterol . Conclusions Systolic blood pressure stress responsivity increases with age in women but not in men . Other data do not support the notion that stress responsivity mediates age and gender differences in cardiovascular disease risk . However , in middle-aged men , exaggerated cardiovascular stress responsivity is associated with an unfavourable risk profile It is well established that pacemaker neurons in the brainstem provide automatic control of breathing for metabolic homeostasis and survival . During waking spontaneous breathing , cognitive and emotional dem and s can modulate the intrinsic brainstem respiratory rhythm . However the neural circuitry mediating this modulation is unknown . Studies of supra-pontine influences on the control of breathing have implicated limbic/paralimbic-bulbar circuitry , but these studies have been limited to either invasive surgical electrophysiological methods or neuroimaging during substantial respiratory provocation . Here we probed the limbic/paralimbic-bulbar circuitry for respiratory-related neural activity during unlabored spontaneous breathing at rest as well as during a challenging cognitive task ( sustained r and om number generation ) . Functional magnetic resonance imaging ( fMRI ) with simultaneous physiological monitoring ( heart rate , respiratory rate , tidal volume , end-tidal CO(2 ) ) was acquired in 14 healthy 
    Output:
    
The available results show that respiratory behavior generally reflects cognitive processing and that distinct parameters differ in sensitivity : While mentally dem and ing episodes are clearly marked by faster breathing and higher minute ventilation , respiratory amplitude appears to remain rather stable .
The present findings further indicate that total variability in respiratory rate is not systematic ally affected by cognitive load whereas the correlated fraction decreases .
In addition , we found that cognitive load may lead to overbreathing as indicated by decreased end-tidal CO2 but is also accompanied by elevated oxygen consumption and CO2 release .