Anxiety and heart rate variability before sleep indicate chronic stress in students

The purpose of the present study was to investigate the effect of chronic stress on the first-night effect in terms of autonomic nervous system activity and anxiety. Participants (N = 11; M age = 20.3 yr., SD = 0.47) included six with high stress (High stress group) and five with low stress (Low stress group), for whom all EEG data were available from three consecutive nights. Heart rate variability was calculated using the MemCalc method. The ratio of low to high frequency of heart rate variability before sleep onset in the High stress group on the first night indicated significantly higher activities than the ratio before sleep onset in the Low stress group. No significant difference in sleep latency was found between the two groups. However, the High stress group was more aware of anxiety than was the Low stress group, and the former estimated more subjective difficulty in falling asleep. These results suggest that measuring LF/HF before sleep may constitute a new way to assess chronic stress.     

Mental load,heart rate and heart rate variability

Summary Several investigators have shown that diminished sinus arrhythmia can be seen as an indication of increased mental load. The present experiment deals with the influence of different levels of mental load, operationalized as the number of binary choices per minute, on the regularity of the heart rate. Also we investigated the influence of four different rest conditions on the regularity of the heart rate.The results show that sinus arrhythmia scores differentiate significantly between several levels of mental load, but heart frequency appeared to be an even better indicator.No significant differences were found between the four rest conditions. Stability over three subsequent measurement sessions was satisfactory, and reliability within the measurement periods was very high.

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Zusammenfassung Mehrere Forscher haben gezeigt, daß abnehmende Sinusarrhythmie betrachtet werden kann als ein Indikator zunehmender mentaler Belastung.In der vorliegenden Untersuchung handelt es sich um den Einfluß verschiedener Niveaus der mentalen Belastung, operationalisiert als die Zahl der binären Wahlen pro Minute, auf die Regelmäßigkeit der Herzfrequenz.Außerdem untersuchten wir den Einfluß vier verschiedener Ruhezustände auf die Regelmäßigkeit der Herzfrequenz.Die Ergebnisse zeigen, daß auf Grund Sinusarrhythmiedaten differenziert werden kann zwischen verschiedenen Niveaus mentaler Belastung, aber die Herzfrequenz erweist sich sogar als ein besserer Indikator.Man stellte keine signifikanten Unterschiede zwischen den vier verschiedenen Ruhezuständen fest.Die Stabilität während drei verschiedener Meßperioden war befriedigend, und die Zuverlässigkeit der Messungen (reliability) innerhalb der Meßperioden war sehr groß.

     

Rhythmic organization of heart rate in breast-fed and bottle-fed newborn infants

Heart rates and behavioural states of 14 breast-fed and 14 bottlefed newborn infants were assessed every 30 seconds for 2 continuous hours. The 240 observations of heart rate were treated as time-series data and spectrum-analysed for behavioural rhythmicities. Of the 28 infants, 25 showed reliable cycles in heart rate; 22 of the 25 infants showed a dominant frequency with a 30–60 min periodicity, one that approximates the basic-rest activity cycle (BRAC). In addition to this basic cycle, additional higher frequency cycles in long-term heart rate variability were evident in the spectra of many infants. Breast-fed newborns had greater numbers of reliable cycles in heart rate than bottle-fed newborns. Further, breast-fed newborns had lower overall mean heart rates and lower mean heart rates in Quiet and Active Sleep states than bottle-fed newborns. Bottle-fed newborns were observed more often in Quiet Sleep than breast-fed newborns. Without knowledge of the specific mechanisms causing these behavioural differences, the results of this study suggest that the context in which breast-feeding occurs results in a more complex and energy-efficient pattern of behavioural organization than the context of bottle-feeding.     

Human visual evoked responses are related to heart rate.

The purpose of the present experiment was to determine the relation between changes in heart rate and averaged evoked potentials. Sixteen male subjects with variable heart rates received 50 flashes of light during fast heart beats, 50 during slow heart beats, and 50 during midrange heart rate level. Evoked responses were recorded from the scalp overlying the right and left occipital lobes. Heart rate, respiration, eye movements, and cephalic blood flow were also recorded. The results indicated that spontaneous changes in heart rate are related to changes in visual evoked responses and that this relation differs for the two cerebral hemispheres. Furthermore, cephalic pulse amplitude was largest following slow heart beats and smallest following fast heart beats, which suggests that changes in heart rate are related to changes in cerebrovascular as well as electrocortical activity. The results are discussed in terms of formulations derived from behavioral studies regarding the relation between cardiovascular activity and attentional processes.     

An on-line program to calculate respiratory sinus arrhythmia amplitude

A variety of evidence shows that the amplitude of respiratory sinus arrhythmia (RSA)—the peak-to-peak variations in heart rate caused by respiration—is a valid and reliable index of para-sympathetic cardiac control. An on-line program to calculate RSA amplitude on a breath-by-breath basis is described. The validity of the RSA amplitude values obtained through the computer pro-gram were tested in two studies. From the first one, the correlations between RSA amplitude and a set of cardiorespiratory variables, under both rest and auditory stimulation conditions, are reported. In the second study, the effect of atropine administration on the RSA amplitude, under both rest and mental load conditions, was examined. The results of both studies are con-gruent with predictions and suggest the usefulness of the software.     

Cognitive reappraisal increases heart rate variability in response to an anger provocation

Adaptive self-regulatory responses to negative events are associated with good mental health, social functioning, and physical health. Two forms of emotion regulation that have received attention within the context of anger are cognitive reappraisal and expressive suppression. Research suggests that greater heart rate variability (HRV) is a physiological indicator of adaptive emotion regulation and decreased mental load. In the present experiment, we recorded HRV while 131 undergraduate women viewed an anger-inducing video of a fellow student arguing for a position counter to that of the participant on an important political issue. Immediately prior to viewing, participants were instructed to reappraise, suppress their emotions, or simply watch the video as normal. Participants in the reappraisal condition showed increased HRV whereas those in the suppression and control condition showed no such increase. These results provide support for increased HRV as a biological correlate of adaptive emotion regulation. One implication is that cognitive reappraisal might afford greater autonomic flexibility when an individual is confronted with anger-inducing events.     

Matters of the variable heart: respiratory sinus arrhythmia response to marital interaction and associations with marital quality

Maintenance of relationship quality requires self-regulation of emotion and social behavior, and women often display greater effort in this regard than do men. Furthermore, such efforts can deplete the limited capacity for self-regulation. In recent models of self-regulation, resting level of respiratory sinus arrhythmia, quantified as high-frequency heart rate variability (HF-HRV), is an indicator of self-regulatory capacity, whereas transient increases in HF-HRV reflect self-regulatory effort. To test these hypotheses in marriage, 114 young couples completed measures of marital quality and a positive, neutral, or negative initial marital task, preceded and followed by resting baseline assessments of HF-HRV. Couples then discussed a current marital disagreement. Resting HF-HRV was correlated with marital quality, suggesting that capacity for self-regulation is associated with adaptive functioning in close relationships. For women but not men, the negative initial task produced a decrease in resting HF-HRV. This effect was mediated by the husbands' negative affect response to the task and their ratings of wives as controlling and directive. When the subsequent disagreement discussion followed the negative initial task, women displayed increased HF-HRV during the discussion but a decrease when it followed the neutral or positive task. The valence of the initial task had no effect on men's HF-HRV during disagreement. Negative marital interactions can reduce women's resting HF-HRV, with potentially adverse health consequences. Women's reduced health benefit from marriage might reflect the depleting effects on self-regulatory capacity of their greater efforts to manage relationship quality.     

Variable heart rate and a flexible mind: Higher resting-state heart rate variability predicts better task-switching

The neurovisceral integration model proposes that heart rate variability (HRV) is linked to prefrontal cortex activity via the vagus nerve, which connects the heart and the brain. HRV, an index of cardiac vagal tone, has been found to predict performance on several cognitive control tasks that rely on the prefrontal cortex. However, the link between HRV and the core cognitive control function “shifting” between tasks and mental sets is under-investigated. Therefore, the present study tested the neurovisceral integration model by examining, in 90 participants, the relationship between vagally mediated resting-state HRV and performance in a task-switching paradigm that provides a relatively process-pure measure of cognitive flexibility. As predicted, participants with higher resting-state HRV (indexed both by time domain and frequency domain measures) showed smaller switch costs (i.e., greater flexibility) than individuals with lower resting-state HRV. Our findings support the neurovisceral integration model and indicate that higher levels of vagally mediated resting-state HRV promote cognitive flexibility.     

Respiratory sinus arrhythmia in response to fear-relevant and fear-irrelevant stimuli

Heart period variability and heart rate were studied in 15 women and 15 men while they were viewing negatively (snakes/spiders), neutrally (scenic views), and positively (cats and kittens/puppies and dogs) valenced films. Time-frequency analyses of the heart period variability power spectrum in the high frequency region (0.12-0.4 Hz), reflecting respiratory sinus arrhythmia (RSA), were carried out during 5 minutes in each condition. The main finding showed that RSA-magnitude (high frequency power) was inversely related to emotional valence: lowest magnitudes were found in response to positive films, and highest magnitude to negative films. The findings were interpreted as reflecting motor or behavioral inhibition, and increased attention to negatively valenced, stimuli.     

Facets of psychopathy, heart rate variability and cognitive function

The aim of the present study was to investigate whether the four facets of Hare's Psychopathy Checklist-Revised (PCL-R; Hare, 1991; Bolt, Hare, Vitale, & Newman, 2004) were related to physiological and cognitive mechanisms. Fifty-three male prisoners participated in this study. Physiological responses were measured as heart rate variability (HRV) and heart rate (HR). Cognitive functions were measured using a continuous performance test (CPT; California Computerized Assessment Package, Abbreviated version) and a working memory test (WMT); based on Baddeley & Hitch (1974). The regression analysis of the HRV revealed that the interpersonal facet explained most of the variance during baseline (28%), CPT (16%), and WMT (12%). This was also true for the HR data during baseline (28%), CPT (20%), WMT (10%), and recovery (13%). The antisocial facet explained 10% of the variance only during baseline. Subjects scoring high compared to low on the interpersonal facet also showed better cognitive functioning. The study suggests that the different facets were differently associated with both physiological and cognitive functions.     

Contact-free measurement of heart rate, respiration rate, and body movements during sleep

We describe a noncontact method for the ambulant measurement of basic sleep physiology parameters in humans, particularly for field studies involving sleep research and sleep disturbances. This method traces the body movements, respiration, and heart action of a person at rest or asleep on a bed, using four high-resolution force sensors installed under the bedposts. The recoil movement of the body at each heartbeat, known as the cardioballistic effect, as well as the lifting and lowering of the thorax, while breathing, causes very small shifts of the center of gravity of the bed and the subject. These shifts are reflected in the altering force distributions across the four sensors. Cardiac and respiratory parameters and the subject’s movement activity can be calculated from the sensor signals. Neither electrodes nor other kinds of transducers are in direct contact with the subject, which is the main advantage of this technique over conventional methods. Laboratory experiments were carried out to estimate validity and practicability. The method has been found to be adequate, especially for automated and unattended sleep-data collection over long periods of time.     

Field validity of heart rate variability metrics produced by QRSTool and CMetX

Interest in heart rate variability (HRV) metrics as markers of physiological and psychological health continues to grow beyond those with psychophysiological expertise, increasing the importance of developing suitable tools for researchers new to the field. Allen, Chambers, and Towers (2007) developed QRSTool and CMetX software as simple, user-friendly tools that can be used to compute metrics of HRV. In the present study, the authors examined the field validity of these software tools-that is, their validity when used by nonexperts. In a lab with extensive expertise in psychopathology but not psychophysiology, ECG data were obtained from 63 undergraduates at baseline and during a stressor and then processed using QRSTool and CMetX to produce the 10 HRV indices described in Allen et al. (2007). The indices displayed factor structures and patterns of changes from baseline to stressor that were similar to findings from Allen et al. and consistent with how indices of parasympathetic and sympathetic activity should behave. Results support the field validity of QRSTool and CMetX, suggesting that they are useful for nonexperts in psychophysiology interested in measuring HRV. (PsycINFO Database Record (c) 2012 APA, all rights reserved).     

Relationship between heart rate variability and cognitive function during threat of shock

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 randomly 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 implications with regard to performance in operational settings, but also for other fields of psychological research such as individual differences, anxiety and coping.     

Approximate entropy and point correlation dimension of heart rate variability in healthy subjects

The contribution of nonlinear dynamics to heart rate variability in healthy humans was examined using surrogate data analysis. Several measures of heart rate variability were used and compared. Heart rates were recorded for three hours and original data sets of 8192 R-R intervals created. For each original data set (n=34), three surrogate data sets were made by shuffling the order of the R-R intervals while retaining their linear correlations. The difference in heart rate variability between the original and surrogate data sets reflects the amount of nonlinear structure in the original data set. Heart rate variability was analyzed by two different nonlinear methods, point correlation dimension and approximate entropy. Nonlinearity, though under 10 percent, could be detected with both types of heart rate variability measures. More importantly, not only were the correlations between these measures and the standard deviation of the R-R intervals weak, the correlation among the nonlinear measures themselves was also weak (generally less than 0.6). This suggests that in addition to standard linear measures of heart rate variability, the use of multiple nonlinear measures of heart rate variability might be useful in monitoring heart rate dynamics.     

A MATLAB toolbox for correcting within-individual effects of respiration rate and tidal volume on respiratory sinus arrhythmia during variable breathing

Respiratory sinus arrhythmia (RSA) is a common estimator of vagal outflow to the heart, dependent on parasympathetic activity. During variable breathing, both respiration rate and tidal volume contribute substantially to within-individual RSA variance. A respiratory control method allows for within-individual correction of the time-domain index of RSA. rsaToolbox is a set of MATLAB programs for scoring respiration-corrected RSA using measurements of cardiac interbeat intervals, respiratory-cycle times, and tidal volumes, recorded at different paced-breathing frequencies. The within-individual regression of RSA divided by tidal volume upon total respiratory cycle time is then used to estimate the baseline vagal tone for each breath of a given total respiratory-cycle time. During a subsequent analysis, the difference between the observed RSA (divided by the tidal volume at each breath) and the RSA divided by the tidal volume that was predicted by the baseline equation serves as an estimate of changes in vagal tone. rsaToolbox includes a graphical user interface for intuitive handling. Modular implementation of the algorithm also allows for flexible integration within other analytic strategies or for batch processing.     

Low heart rate variability is not caused by typical neuroleptics in schizophrenia patients

Both elevated cardiovascular mortality and low cardio-vagal (parasympathetic) heart rate variability (HRV)--a risk factor for postmyocardial infarction--are reported in schizophrenia (SZ). Since a number of medications have strong effects of cardiac conductivity, we thought it important to examine if typical neuroleptic medications might also affect HRV. We examined cardiac vagal activity during both neuroleptic treatment and a drug-free condition in seven SZ patients who were participating in a pilot double-blind, crossover study of placebo and haloperidol treatment. Twenty-four-hour Holter electrocardiograms were analyzed for high frequency HRV, quantitated as the percent of successive normal interbeat intervals greater than 50 milliseconds (PNN50), which is a good index of parasympathetic cardiac modulation. The patients showed unchanged PNN50 (8.4+/-9.5 versus 8.3+/-10.5; t=.22, df=6, P=.5) between the haloperidol treatment and drug-free conditions. Despite the elapsed time, change in medication, and altered clinical state, the PNN50s were highly correlated (Spearman r=.98, P=.000). SAPS positive symptom scores declined with treatment from 12.8+/-6.5 to 8.5+/-3.5; paired t=3.26: df=6; P=.01. PNN50s were significantly associated with positive (r=-.86, df=6, P=.012) and negative symptom scores (r=-.87, df=6, P=.01). We found low cardiovagal modulation in medication-free SZ patients that was associated with core SZ symptoms and was unchanged by haloperidol and benztropine treatment. The reduced HRV in SZ patients at baseline may render them at greater cardiovascular risk than healthy subjects when treated with medications having strong cardiovascular effects.     

Forebrain mechanisms related to internal inhibition and sleep

In experiments performed on cats and monkeys over the past nine years a “forebrain inhibitory system” has been investigated through recording of neurophysiologic, behavioral, reflexive and intracellular parameters. This forebrain system is capable of expressing its inhibitory influences widely throughout the body, and on both somatic and visceral mechanisms. Electrical stimulation within this system has been shown to: a) suppress ongoing behavior, synchronize the EEG and induce the initial stages of sleep. These behavioral effects could be conditioned to indifferent stimuli. Other studies have shown that lesions within this system result in marked alterations in sleep patterns and in behavioral hyperactivity,b) Inhibit remarkably monosynaptic and polysynaptic reflexes in the brain stem and at cervical and lumbosacral levels of the spinal cord.c) Induce hyperpolarizing potentials within motoneurons of the final common path. Cl infusion caused the hyperpolarization to change to depolarization. Studies of the “forebrain inhibitory system” indicate that at least in part it is a descending system involving both multisynaptic (loop) pathways and direct pathways. It is felt that descending circuits from the forebrain to inhibitory centers in the medulla are responsible for the effects observed at the final common paths from stimulation in the forebrain. It has been found that behaviorally, reflexively and intracellularly, the “forebrain inhibitory system” acts generally in opposition to the reticular activating system of the brain stem, and that the achievement of an organism’s overt behavioral patterns depends on the functional state of both systems.     

Approximate entropy and point correlation dimension of heart rate variability in healthy subjects.

The contribution of nonlinear dynamics to heart rate variability in healthy humans was examined using surrogate data analysis. Several measures of heart rate variability were used and compared. Heart rates were recorded for three hours and original data sets of 8192 R-R intervals created. For each original data set (n = 34), three surrogate data sets were made by shuffling the order of the R-R intervals while retaining their linear correlations. The difference in heart rate variability between the original and surrogate data sets reflects the amount of nonlinear structure in the original data set. Heart rate variability was analyzed by two different nonlinear methods, point correlation dimension and approximate entropy. Nonlinearity, though under 10 percent, could be detected with both types of heart rate variability measures. More importantly, not only were the correlations between these measures and the standard deviation of the R-R intervals weak, the correlation among the nonlinear measures themselves was also weak (generally less than 0.6). This suggests that in addition to standard linear measures of heart rate variability, the use of multiple nonlinear measures of heart rate variability might be useful in monitoring heart rate dynamics.