Sympathetic influences on cardiac rate and contractility during acute stress in humans

Continuous real-time assessment of acute cognitive stress from cardiac mechanical signals captured by a skin-like patch

The inability to objectively quantify cognitive stress in real-time with wearable devices is a crucial unsolved problem with serious negative consequences for dementia and mental disability patients and those seeking to improve their quality of life. Here, we introduce a skin-like, wireless sternal patch that captures changes in cardiac mechanics due to stress manifesting in the seismocardiogram (SCG) signals. Judicious optimization of the device's micro-structured interconnections and elastomer integration yields a device that sufficiently matches the skin's mechanics, robustly yet gently adheres to the skin without aggressive tapes, and captures planar and longitudinal SCG waves well. The device transmits SCG beats in real-time to a user's device, where derived features relate to the heartbeat's mechanical morphology. The signals are assessed by a series of features in a support vector machine regressor. Controlled studies, compared to gold standard cortisol and following the validated imaging test, show an R-squared correlation of 0.79 between the stress prediction and cortisol change, significantly improving over prior works. Likewise, the system demonstrates excellent robustness to external temperature and physical recovery status while showing excellent accuracy and wearability in full-day use.

Exploring hazard anticipation and stress while driving in light of defensive behavior theory

In driving, poor hazard anticipation would provide drivers less time to prepare an appropriate response, increasing the urgency of the situation and generating more stress. Assuming this, the current study seeks to determine whether a predictable road hazard triggers hazard anticipation in drivers that can mitigate the ensuing stress response, and whether the stress response is influenced by driving experience. In a simulated road environment, a cue was used to trigger hazard anticipation, and a road hazard to induce a stress response. Heart rate, pupil diameter, driving speed, subjective stress, arousal, and negative emotions, were retrieved from 36 drivers who all faced the cue followed by the hazard (i.e. a predictable hazard), the cue only, and the hazard only. In the light of work on defensive behaviors, the findings indicate that a predictable hazard triggers hazard anticipation detectable via (1) freezing behavior-characterized by cardiac deceleration-(2) anticipatory pupil dilation and (3) anticipatory speed deceleration. The results also point to a beneficial role for hazard anticipation in reducing driver stress, as evidenced by reductions in peak heart rate levels, as well as in reported levels of stress and negative emotions. Finally, the findings showed an influence of driving experience on reported levels of stress. Overall, this study shows how previous work on defensive behaviors can be used to gain insight into the processes and driving behaviors involved in hazard anticipation and stress.

Effects of exercise anticipation on cardiorespiratory coherence

In this study, we explored the role of feedforward mechanisms in triggering cardiorespiratory adjustments before the onset of exercise. To isolate the feedforward aspects, we examined the effect of exercise anticipation on cardiorespiratory coherence. Twenty-nine healthy males (age = 18.8 [0.96] years) were subjected to bicycle (BE) and handgrip exercise (H) at two different intensities, viz., low and high. Bicycle exercise was performed in a unilateral (left- and right-sided) or bilateral mode, whereas handgrip was performed only in a unilateral mode. Single-lead ECG and respiratory rhythm, measured in the 5 min of anticipation phase before the onset of exercise, were used for analysis. Coherence was computed between ECG-derived instantaneous heart rate and respiratory signal. Average coherence in the high-frequency band (0.15-0.4 Hz) was used to estimate respiratory sinus arrhythmia (RSA). We found that coherence decreased with the anticipation of exercise relative to baseline (baseline = 0.54 [0.16], BE = 0.41 [0.12], H = 0.39 [0.12], p < 0.001). The decrease was greater for high intensity exercise (low = 0.42 [0.11], high = 0.37 [0.1], p < 0.001). The fall of coherence with intensity was stronger for bicycle exercise (BE: low = 0.44 [0.12], high = 0.37 [0.12], H: low = 0.4 [0.12], high = 0.37 [0.12], p = 0.00433). The expectation of bilateral exercise resulted in lower coherence compared to unilateral exercise (right-sided = 0.45 [0.16], left-sided = 0.4 [0.16], bilateral = 0.36 [0.15], unilateral vs. bilateral: p < 0.001), and the left-sided exercise had lower coherence compared to that of the right (left-sided vs. right-sided: p = 0.00925). Handgrip exercise showed similar trend (right-sided = 0.4 [0.15], left-sided = 0.37 [0.14], p = 0.0056). In conclusion, feedforward RSA adjustments in anticipation of exercise covaried with subsequent exercise-related features like intensity, muscle mass (unilateral vs. bilateral), and the exercise side (left vs. right). The left versus the right difference in coherence indicates autonomic asymmetry. Feedforward changes in RSA are like those seen during actual exercise and might facilitate the rapid phase transition between rest and exercise.

Comparison of TWA and PEP as indices of α2- and ß-adrenergic activation

RATIONALE

Pre-ejection period (PEP) and T-wave amplitude (TWA) have been used to assess sympathetic nervous system (SNS) activity. Here we report two single-blinded, placebo-controlled intravenous (IV) drug application studies in which we pharmacologically modified SNS activity with epinephrine (study 1) as well as dexmedetomidine (alpha2-agonist) and yohimbine (alpha2-antagonist) (study 2). Restricted heart rate (HR) intervals were analyzed to avoid confounding effects of HR changes.

OBJECTIVE

Study 1 served to replicate previous findings and to validate our approach, whereas study 2 aimed to investigate how modulation of central SNS activity affects PEP and TWA.

METHODS

Forty healthy volunteers (58% females) participated in study 1 (between-subject design). Twelve healthy men participated in study 2 (within-subject design). TWA and PEP were derived from ECG and impedance cardiography, respectively.

RESULTS

Epinephrine shortened PEP and induced statistically significant biphasic TWA changes. However, although the two alpha2-drugs significantly affected PEP as expected, no effects on TWA could be detected.

CONCLUSION

PEP is better suited to reflect SNS activity changes than TWA.

Temporal Analysis of Sequential Changes in Heart Rate Variability During Non-hypotensive Hypovolemia

INTRODUCTION

Haemorrhage is associated with changes in the cardiac autonomic drive which begins during early stages of mild haemorrhage. The knowledge of chronology of the autonomic changes at smaller timescale during the period of haemorrhage can help identify the primary autonomic parameter which signals the institution of cardiovascular reflex mechanisms.

AIM

To evaluate the heart rate variability in 2-min sequential segments with one minute overlap during and after the period of mild haemorrhage (450 ml) using blood donation as a model of acute blood loss.

METHODS

47 male blood donors who had volunteered for blood donation were recruited for the study. Continuous lead II ECG was recorded before the start of the blood donation (5 min), during the period of the blood donation (~ 5-7 min) and after blood donation (5 min). The parasympathetic and sympathetic drive to heart was estimated by measures of heart rate variability in time and frequency domain.

RESULTS

A significant decrease in the parameters assessing parasympathetic drive i.e., normalised High frequency (HFn) and NN50 (Number of pairs of adjacent NN intervals differing by more than 50 ms) and pNN50 (NN50 divided by the total number of all NN Intervals) was observed during blood donation at 3-5 min, as compared to baseline. An increase in parameters associated with sympathetic drive i.e., normalised low frequency (LFn) was observed only in the post donation period at 2-3 min. A significant rise in LF/HF ratio which is a marker of sympatho vagal balance was observed at 4-5 min during blood donation when compared to baseline.

CONCLUSION

The initial cardiac autonomic change during mild haemorrhage is withdrawal of parasympathetic drive, followed by an increase in sympathetic tone which occurs much later.

PPG neurons in the nucleus of the solitary tract modulate heart rate but do not mediate GLP-1 receptor agonist-induced tachycardia in mice

Objective

Glucagon-like peptide-1 receptor agonists (GLP-1RAs) are used as anti-diabetic drugs and are approved for obesity treatment. However, GLP-1RAs also affect heart rate (HR) and arterial blood pressure (ABP) in rodents and humans. Although the activation of GLP-1 receptors (GLP-1R) is known to increase HR, the circuits recruited are unclear, and in particular, it is unknown whether GLP-1RAs activate preproglucagon (PPG) neurons, the brain source of GLP-1, to elicit these effects.

Methods

We investigated the effect of GLP-1RAs on heart rate in anaesthetized adult mice. In a separate study, we manipulated the activity of nucleus tractus solitarius (NTS) PPG neurons (PPG^NTS) in awake, freely behaving transgenic Glu-Cre mice implanted with biotelemetry probes and injected with AAV-DIO-hM3Dq:mCherry or AAV-mCherry-FLEX-DTA.

Results

Systemic administration of the GLP-1RA Ex-4 increased resting HR in anaesthetized or conscious mice, but had no effect on ABP in conscious mice. This effect was abolished by β-adrenoceptor blockade with atenolol, but unaffected by the muscarinic antagonist atropine. Furthermore, Ex-4-induced tachycardia persisted when PPG^NTS neurons were ablated, and Ex-4 did not induce expression of the neuronal activity marker cFos in PPG^NTS neurons. PPG^NTS ablation or acute chemogenetic inhibition of these neurons via hM4Di receptors had no effect on resting HR. In contrast, chemogenetic activation of PPG^NTS neurons increased resting HR. Furthermore, the application of GLP-1 within the subarachnoid space of the middle thoracic spinal cord, a major projection target of PPG neurons, increased HR.

Conclusions

These results demonstrate that both systemic application of Ex-4 or GLP-1 and chemogenetic activation of PPG^NTS neurons increases HR. Ex-4 increases the activity of cardiac sympathetic preganglionic neurons of the spinal cord without recruitment of PPG^NTS neurons, and thus likely recapitulates the physiological effects of PPG neuron activation. These neurons therefore do not play a significant role in controlling resting HR and ABP but are capable of inducing tachycardia and so are likely involved in cardiovascular responses to acute stress.

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Activation of PPG neurons triggers increases in heart rate in mice.

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PPG neurons do not provide a tonic sympathetic drive to the heart.

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The tachycardic effect of systemic Ex-4 is not mediated by PPG neurons.

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GLP-1 receptor activation has a sympathoexcitatory effect that increases heart rate.

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Local activation of GLP-1R in the spinal cord is sufficient to elicit tachycardia.

Emotional and autonomic dysregulation in abstinent alcoholic men: An idiosyncratic profile?

Men who misuse alcohol tend to experience negative affect, which may entail difficulties in regulating emotions to cope effectively with stressful or anxiety-provoking situations, thus increasing the risk of alcohol relapse. This dysphoric state has been associated with alexithymia, which compromises an individual's abilities to acknowledge, recognize, and regulate emotional states. A physiological correlate of emotional regulation is autonomic flexibility, as shown by emotional dysregulation in men who misuse alcohol being correlated with reduced parasympathetic activation to control heart rate variability during stress and/or conflict situations. Hence, the main aim of this study was to investigate whether long-term abstinent alcoholic (LTAA) men exhibit higher levels of negative affect and sympathetic activation (cardiovascular and electrodermal) in response to acute standardized laboratory stress than non-alcoholic controls. In addition, we hypothesized that the higher the alexithymic traits, the greater would be the increase in negative affect and sympathetic activation in response to stress, especially in LTAAs. Our data demonstrated that LTAAs experienced slightly greater increases in anxiety, states of anger, and worsening of mood than controls. Moreover, they exhibited lower high-frequency heart rate variability, respiratory sinus arrhythmia values, shorter pre-ejection periods, and higher respiratory rates than controls. Finally, alexithymic traits imply greater worsening of mood and sympathetic predominance (shorter pre-ejection periods and smaller magnitude of response), with the associations being stronger in LTAAs. These findings indicate a different emotional and cardiovascular response to psychosocial stress in LTAA than non-alcoholic men. Improving our knowledge of the way this population reacts to stress may help identify risk factors for alcohol relapse.

Decreased Spontaneous Baroreflex Sensitivity as an Early Marker for Progression of Haemorrhage

INTRODUCTION

Blood donation provides an ideal setup for assessment of cardiovascular responses to mild hypovolemia for understanding the underlying mechanisms.

AIM

To evaluate cardiovascular responses in time and magnitude by estimating the spontaneous baroreflex sensitivity (BRS) during and after donation of 450 ml of blood.

METHODS

Continuous beat-to-beat blood pressure and lead II ECG was recorded before, during and after blood donation in 54 healthy volunteers (age 34.7 ± 5.08 years; weight 77.9 ± 8.20 kg), followed by offline analyses of baroreflex sensitivity.

RESULTS

The systolic, diastolic or mean blood pressures did not change during or after the blood donation. Decrease in pulse pressure and increase in heart rate was observed post donation. The spontaneous BRS decreased during [8.68 (6.038-12.69) ms/mmHg] and after blood donation [9.401 (6.396-11.59) ms/mmHg] as compared to the baseline [12.83 (6.884-18.18) ms/mmHg] with a significant decrease in α-HF on spectral analysis.

CONCLUSION

Mild blood loss (450 ml) results in non-hypotensive haemorrhage with a decrease in spontaneous BRS before the rise of heart rate during blood donation.

Cardiorespiratory interactions: Noncontact assessment using laser Doppler vibrometry

The application of a noncontact physiological recording technique, based on the method of laser Doppler vibrometry (LDV), is described. The effectiveness of the LDV method as a physiological recording modality lies in the ability to detect very small movements of the skin, associated with internal mechanophysiological activities. The method is validated for a range of cardiovascular variables, extracted from the contour of the carotid pulse waveform as a function of phase of the respiration cycle. Data were obtained from 32 young healthy participants, while resting and breathing spontaneously. Individual beats were assigned to four segments, corresponding with inspiration and expiration peaks and transitional periods. Measures relating to cardiac and vascular dynamics are shown to agree with the pattern of effects seen in the substantial body of literature based on human and animal experiments, and with selected signals recorded simultaneously with conventional sensors. These effects include changes in heart rate, systolic time intervals, and stroke volume. There was also some evidence for vascular adjustments over the respiration cycle. The effectiveness of custom algorithmic approaches for extracting the key signal features was confirmed. The advantages of the LDV method are discussed in terms of the metrological properties and utility in psychophysiological research. Although used here within a suite of conventional sensors and electrodes, the LDV method can be used on a stand-alone, noncontact basis, with no requirement for skin preparation, and can be used in harsh environments including the MR scanner.

The conditioning model of neurosis

The long-term persistence of neurotic symptoms, such as anxiety, poses difficult problems for any psychological theory. An attempt is made to revive the Watson-Mowrer conditioning theory and to avoid the many criticisms directed against it in the past. It is suggested that recent research has produced changes in learning theory that can be used to render this possible. In the first place, the doctrine of equipotentiality has been shown to be wrong, and some such concept as Seligman's “preparedness” is required, that is the notion that certain CS are biologically prepared to be more readily connected with anxiety responses than others. In the second place, the law of extinction has to be amended, and the law of incubation or enhancement added, according to which the exposure of the CS-only may, under certain specified conditions, have the effect of increasing the strength of the CR, rather than reducing it. The major conditions favouring incubation are (1) Pavlovian B conditioning, that is a type of conditioning in which the CR is a drive; (2) a strong UCS, and (3) short exposure of the CS-only.

Behavioural and cardiovascular responses during latent inhibition of conditioned fear: measurement by telemetry and conditioned freezing

This study assessed freezing behaviour and cardiovascular responses during the expression of latent inhibition of conditioned fear. Animals that were either repeatedly preexposed (PE) to a tone conditioned stimulus (CS) or naive to the tone (non-preexposed; NPE) subsequently experienced three presentations of the tone paired with footshock. Animals were tested 24 h later in the context of the footshock chamber, and on the following day, in the presence of the tone CS. Changes in heart rate and blood pressure were recorded by radio-telemetry. The PE rats spent more time freezing to the conditioned contextual cues and exhibited higher blood pressures during the last half of the context test session than did the NPE animals. During the tone test, the PE rats exhibited less conditioned freezing to the tone CS compared with the NPE animals, i.e. expression of the latent inhibition. This behavioural effect was associated with a significant increase in heart rate, but not blood pressure, in the PE but not the NPE animals. Our results suggest that the increased blood pressures of the PE rats during the context test directly reflect their greater fear of the conditioning context. In contrast, the increased heart rate response but decreased freezing shown by PE rats in response to the tone CS may be due to the fact that lower stress levels (e.g. PE condition) elicit sympathetically-mediated increases in heart rate, whereas higher stress levels (e.g. NPE condition) activate both sympathetic and parasympathetic systems, thus eliminating any CS-induced increase in heart rate in the NPE rats.

Predicting metabolic rate from heart rate in juvenile Steller sea lions Eumetopias jubatus

The validity of using heart rate to estimate energy expenditure in free-ranging Steller sea lions Eumetopias jubatus was investigated by establishing whether there is a relationship between heart rate (fH) and oxygen consumption rate ((O(2))) in captive sea lions while swimming and resting. Four trained Steller sea lions (2 males and 2 females; mass 87.4-194.4 kg; age 16 months-3 years) were each equipped with a datalogger and two dorsal subcutaneous electrodes to record electrocardiograms from which fH was calculated. (O(2)) (measured using open-circuit respirometry) was simultaneously recorded while the previously fasted animals were at rest within an enclosed dry metabolic chamber or while they swam in an enclosed swim mill against water currents of various speeds (0-1.5 m s(-1)). The mean regression equation describing the relationship between fH (beats min(-1)) and (O(2)) (ml h(-1) kg(-0.60)) for all four animals was (O(2)) =(71.3f(H)+/-4.3)-(1138.5+/-369.6) (means +/- S.E.M.) (r(2)=0.69, P<0.01). The relationship demonstrated between fH and (O(2)) while fasting suggests that heart rate can potentially be used to monitor energy consumption in free-ranging Steller sea lions. However, a short-term feeding experiment revealed no significant increase in heart rate following a 6 kg or 12 kg meal to match the observed increase in rate of oxygen consumption. This suggests that heart rate may not accurately reflect energy consumption during digestion events. Additional research should be conducted to further elucidate how the relationship between heart rate and oxygen consumption is affected by such factors as digestive state, stress and age.

Test-retest reliability of functional transcranial Doppler ultrasonography

The present study evaluates the reproducibility of lateralised blood flow velocity (BFV) changes measured with transcranial Doppler (TCD) ultrasonography during various cognitive paradigms. A total of 20 right-handed volunteers were confronted twice with 13 verbal and visuospatial tasks, with a time interval of 23 to 71 days. No statistically significant differences were found between the lateralisation indices (left BFV change minus right BFV change) on the first and second examinations. Lateralisation indices of eight tasks showed a significant test-retest reliability (r = 0.61 to 0.83). The reproducibility of cognitively induced lateralised BFV changes appears to be task-dependent. The possible influence from technical, physiological, and psychological factors is discussed. We conclude that functional neuroimaging studies based on blood flow data should preferably select cognitive paradigms that demonstrated sufficient test-retest reliability.

Transcranial Doppler ultrasonography monitoring of cerebral hemodynamics during performance of cognitive tasks: a review

The examination of blood flow velocity (BFV) changes during the performance of mental tasks is one of the applications of transcranial Doppler (TCD) ultrasonography. The purpose of this review is to summarize the results of the functional TCD literature, to investigate the effects of methodological differences between studies, and to provide guidelines for future research. It is concluded that larger series of more homogeneous groups concerning age and handedness, and stricter criteria for subject selection and laboratory setting are required. The implication of quantitative and qualitative performance measures and psychological parameters (motivation, anxiety, and task anticipation) could also yield important information. We recommend future agreement upon a more standardized methodology. TCD promises to be a useful tool to provide further insight into the cerebral organization and temporal reactivity of the human brain.

Conditioned fear-induced tachycardia in the rat: vagal involvement

The effects of conditioned fear on gross activity, heart rate, PQ interval, noradrenaline and adrenaline were studied in freely moving rats. Subcutaneous (s.c.) injections of atropine methyl nitrate (0.5 mg/kg) during rest resulted in a significant shortening of the PQ interval, indicating that the PQ interval can be used as a measure of vagal activity. Conditioned fear was induced by 10-min forced exposure to a cage in which the rat had previously experienced footshocks (5 x 0.5 mA x 3 s). In non-shocked controls, an increase in gross activity was found and a pronounced tachycardia, without changes in PQ interval. Conditioned fear rats showed immobility behaviour, associated with a less pronounced tachycardia and an increase in PQ interval. Noradrenaline was similarly increased in both groups, whereas adrenaline was increased in conditioned fear rats only. To further evaluate the role of the vagus, rats were exposed to conditioned fear after pre-treatment with atropine methyl nitrate (0.5 mg/kg, s.c.). Again, immobility was observed with a concomitant tachycardia, but without an increase in PQ interval. These results indicate that the autonomic nervous system is differentially involved in heart rate regulation in conditioned fear rats and in non-shocked controls: in non-shocked controls a predominant sympathetic nervous system activation results in an increase in heart rate, whereas in conditioned fear rats the tachycardiac response is attenuated by a simultaneous activation of sympathetic nervous system and parasympathetic nervous system.

Reproducibility of functional transcranial Doppler sonography in determining hemispheric language lateralization

BACKGROUND AND PURPOSE

Since functional transcranial Doppler ultrasonography (fTCD) allows convenient and fully automated quantification of language lateralization, it seems ideal for longitudinal studies of perfusion changes during deterioration as well as recovery of language functions. However, during serial examinations, the technical, stochastic, and physiological variabilities of cerebral blood flow velocities (CBFV) have to be considered. Therefore, before fTCD is accepted as a tool for evaluation of changes in lateralization in the diseased state, its reliability in healthy subjects needs to be determined.

METHODS

We performed fTCD during a word generation task based on a previously validated technique with automated calculation of the averaged CBFV differences in the middle cerebral arteries providing an index of lateralization (LI).

RESULTS

(1) The accuracy of the LI as assessed by the confidence interval was better than 1% of the mean hemispheric difference. (2) On repeated examination, LIs obtained from 10 subjects showed a high test-retest reproducibility (Pearson product moment correlation coefficient r = 0.95, P < 0.0001). (3) On 10 repeated assessments of LI in the same subject, no practice effects were detected.

CONCLUSIONS

Functional TCD is a suitable and very robust tool for the longitudinal quantitative measurement of cerebral language lateralization.

Vagal activation in novelty-induced tachycardia during the light phase in the rat

The effects of repeated exposure to a novel test box on cardiac and behavioral activities (locomotion, rearing, grooming, scanning, and immobility) were studied in rats tested during the dark phase ("dark" rats) or the light phase ("light" rats) of the lighting cycle, using a telemetry system for registration of ECGs during the first and fifth tests. Heart rate (HR) was used to monitor sympathetic and parasympathetic activity; the PQ interval was used to monitor parasympathetic activity. Behavior was videotaped simultaneously. In light rats, the first and fifth exposures to the test box resulted in higher increases of active behavior and HR than in dark rats, whereas the duration of the PQ interval of the ECG was increased in light rats only. This indicates that in the light phase novelty induces active behavior associated with an increase in both sympathetic and vagal outflow, whereas in the dark phase behavioral activation is predominantly associated with increased sympathetic activity, without appreciable changes in vagal outflow. In addition, light rats showed less active behavior during the fifth than during the first exposure, indicating behavioral habituation. This behavioral habituation to the test box in the light phase coincided with vagal habituation (a diminution of the PQ interval). The increase of the tachycardiac response during the fifth exposure as compared to the first exposure suggests that it is not likely that sympathetic outflow was part of the habituation process. In dark rats no behavioral or cardiac habituation was found.

Anticipatory EMG responses of pericranial muscles in relation to heart rate during a warned simple reaction time task

Obrist's cardiac-somatic coupling hypothesis predicts a widespread inhibition of heart rate and task-irrelevant muscle activity during expectancy situations. This hypothesis was tested by measuring heart rate and pericranial electromyographic (EMG) activity during a warned simple reaction time task with visual or auditory reaction signals and hand or foot responses. In each of three groups of 24 participants, EMG activity of three different facial, masticatory, or neck muscles was recorded. During the warning interval preceding the presentation of the reaction signal, masticatory and lower facial muscles predominantly showed a gradual inhibition in activity concomitant with heart rate deceleration. In contrast, two upper facial muscles showed increasing activity. Pericranial EMG responses were little affected by reaction signal modality and were independent of responding limb. Greater heart rate deceleration was associated with greater inhibition and weaker facilitation of EMG responses. The results suggest a functional role of inhibitory EMG responses in increasing the perceptual sensitivity to expected signals.

Speaking from the heart: cardiovascular components of stress rating changes and the relative reactivity of physiological and psychological variables

The first part of the experiment compared the relative reactivity of various cardiovascular measurements and self-reported assessment of mental arithmetic, an active coping stress task. It was found that the self-reported stress rating was more responsive (student's t = 9.4) than the physiological measurements. Among the cardiovascular indices, heart rate was the most responsive (student's t = 6.5), followed by the interval between R-wave and the maximal systolic pressure (student's t = 5.0). The second part of the study used a multiple regression to examine the cardiovascular components of change in stress rating following mental arithmetic. Both resting (psychophysiological "trait" variables) and change under stress (psychophysiological "state" variables) were used to predict change in stress rating. Stress rating increase were associated with greater maximal systolic pressure rate of rise (finger dP/dt) at baseline and less heart rate increase during mental arithmetic, yielding a multiple r of 0.67. The dual autonomic nature of active coping stress response is discussed. The shortcomings of using a correlate of a correlate are noted.

Heart rate changes following habituation testing of the motor response in normal human fetuses

We examined the heart rate (HR) response immediately following habituation testing in 54 normal human fetuses between 34 and 40 weeks of gestation to determine if cardiac self-regulation was a function of the rate of motor habituation. All fetuses received eight trials of a 1-s vibroacoustic stimulus (VAS) with a 10-s interstimulus interval. A score of 0-10 was assigned for each trial based on subjective assessment of intensity and duration of the fetal motor response. Motor habituation was evaluated in terms of the rate of response decrement over trials. For each fetus the average post-VAS HR was calculated in 1-min blocks for the first 7 min following habituation testing. When subjects were divided into slow and fast motor habituators, we found that fetuses who were slow habituators displayed a significantly greater increase in HR above baseline at each of the first 7 min following habituation testing as compared to fetuses whose motor response habituated more rapidly, F(1,52) = 4.88, P = 0.03. However, there was no difference between slow and fast motor habituators in the rate at which the HR returned toward prestimulus levels. To further examine these results, we divided the 54 fetuses into four groups based on the medians of the slope of the post-VAS HR regression line and the variability in HR about this line. We found that fetuses whose HR decreased slowly after habituation testing displayed significantly greater variability in their cardiac response as compared to fetuses whose HR decreased more rapidly (chi 2 = 4.74, P = 0.03).(ABSTRACT TRUNCATED AT 250 WORDS)

Generalization of cardiovascular response: supportive evidence for the reactivity hypothesis

Cardiovascular responses were monitored while 36 subjects completed a battery of laboratory stressors comprising mental arithmetic, a reaction time task, a speech task, and the forehead cold pressor. Inter-task consistency was assessed for each of 6 physiological parameters for all task pairings. Considerable inter-task consistency for reactivity scores was seen among the psychological stressors for all variables. The question of such consistency between the cold pressor and the psychological tasks was then addressed. The pattern of consistency was not as clear-cut in this case. For systolic blood pressure and pre-ejection period, reactivity scores to the cold pressor did not correlate with those to any of the psychological tasks. In contrast, cardiac output and total peripheral resistance responses showed considerable consistency. The importance of determining the nature of the relationship between psychological and physical stressors is discussed.

Cardiovascular reactivity to psychosocial stressors. A review of the effects of beta-blockade

Fifty-nine studies examining the effects of beta-blockers on cardiovascular reactivity to psychosocial stressors are reviewed. Across all classifications of beta-blockers, heart rate reactivity was reduced (p less than 0.0001), while there were no significant changes in either systolic or diastolic blood pressure reactivity. Nonselective beta-blockers were more often associated with a reduction in heart rate reactivity than selective blockers (p less than 0.05). There was no evidence that drug lipophilicity or intrinsic sympathomimetic activity differentially affected blood pressure or heart rate reactivity; nor was there evidence that the reactivity of hypertensive subjects was differentially affected by blockade compared to the reactivity of normotensive subjects. While beta-blockers are effective in reducing resting blood pressure, they are not effective agents in reducing blood pressure reactivity to mild psychosocial stressors.

Autonomic activity

A review such as this can do no more than provide an indication of the issues involved in using autonomic activity as a means of providing a "window on the brain." Several points arise. One of the most important is that of careful and appropriate use of techniques available. One well-known textbook of experimental psychology published some time ago advocated the use of two dimes applied to the palm of the hand for the measurement of electrodermal activity. It was this sort of recommendation that led to the use of psychophysiological measurement falling into disrepute. As indicated in the second section, it is important to understand fully the peripheral mechanisms involved before measurement of electrodermal activity can be usefully carried out. Appropriate use of silver/silver chloride electrodes and physiologically appropriate levels of saline in the electrolyte medium can lead to accurate and repeatable measurement where artefact is not carelessly introduced. Equally important is the context in which studies are carried out. The psychological invasiveness of the technique is important to recognize, and it is here that measurement of autonomic activity probably scores over other methods that are available insofar as very little restriction of the subject is required and the number of transducers that must be applied is minimal. The measurement of autonomic activity within the totality of the experimental context is all important. As an example Dawson and Schell investigated the SCR to words which had previously been associated with shock. When these words were presented to the ear to which attention was not directed in a dichotic listening paradigm, an SCR could be elicited although the subject was unaware of the presentation of the stimulus. The importance of the Dawson and Schell study was the care that they took to make sure that the subject really was unaware of the critical stimulus and had not momentarily switched attention from the attended ear. More important, their experiment, in contrast to some which had gone before, used a balanced design in which the critical stimuli were presented on different occasions to each ear. As a result of this it was found that critical stimuli, which were presented to the left ear, right hemisphere, gave rise to SCRs, even when the subject was not aware of their presentation, whereas stimuli presented to the right ear, left hemisphere elicited no response.(ABSTRACT TRUNCATED AT 400 WORDS)

Individual differences in resting heart rate and spontaneous electrodermal activity as predictors of attentional processes: effects on anticipatory heart rate deceleration and task performance

The present study was concerned with the question of whether tonic resting heart rate (HR) and resting spontaneous electrodermal activity account for the association between anticipatory HR deceleration and task performance in a choice reaction time (RT) task with a fixed foreperiod. The task employed (a varied mapping paradigm) differed from simple RT tasks especially with regard to processing and attention demands. Subjects were required to determine as quickly and accurately as possible whether a 'complex' probe, presented for 80 ms, was identical or not to one of two distinct memory items, presented at the onset of each trial. Reaction times as well as accuracy of responses were determined. Additionally, reaction time and error data were synthesized to obtain a joint measure of response behaviour. The results of the present study were indicative of a reliable anticipatory HR deceleration extended over the last seconds preceding the probe stimulus. In agreement with previous findings, the HR deceleration grew stronger over blocks of trials and was sensitive to detection requirements, i.e. probe complexity. Furthermore, HR deceleration was related to task performance. Subjects with stronger decelerations (below the median on mean deceleration) exhibited a more impulsive (fast-inaccurate) and subjects above the median a more reflective (slow-accurate) response style. The effect was mainly due to a significant difference in RT. Further results indicated that the relationship between anticipatory deceleration and RT performance was especially due to the response behaviour of one group of subjects. Subjects above the median of resting HR and resting spontaneous electrodermal activity behaved in a prominent reflective manner and also displayed the lowest foreperiod deceleration. Results were discussed in terms of differences in the regulation or control of attentional processes.

Individual differences in heart rate response during behavioral challenge

This program of experiments examined heart rate responses to mental arithmetic and a video game. Attention first focused on their metabolic relevance. Comparison with heart rate/oxygen consumption regression equations generated from isotonic exercise data revealed that the heart rate increases of certain individuals were considerably in excess of those necessitated by contemporary metabolic demand. Both temporal and intertask consistency of reaction were explored, and supportive evidence was obtained. The relationship between laboratory and real-world reactions was investigated, and preliminary evidence found suggesting that in-laboratory responses are indicative of responses to more naturalistic stressors. Finally, twin studies examining the genetic and environmental determinants of individual differences in heart rate change during the tasks revealed a substantial genetic component for these responses.

Cardiovascular regulation and lesions of the central nervous system

The central nervous system has an important role in the second-to-second regulation of cardiac activity and vasomotor tone. Central lesions that lead to a disturbance in autonomic activity tend to cause electrocardiographic and pathological evidence of myocardial damage, cardiac arrhythmias, and disturbances of arterial blood pressure regulation. To a great extent such cardiovascular disturbances result from alterations in sympathetic activity. Similar alterations in sympathetic activity can occur under conditions of emotional stress and precipitate cardiac arrhythmias that can themselves lead to the syndrome of sudden death. Experimental and clinical evidence suggests that central neural mechanisms may be involved in this important human syndrome, but no central lesion has yet been identified to account for it. Recent experimental evidence, derived from hypertension research, suggests that chemical disturbances in the central nervous system, without accompanying structural lesions, may be found to explain cardiovascular disturbances such as sudden death and hypertension.

Cardiac responses to psychological tasks: impedance cardiographic studies

In a series of studies, cardiac activity, assessed with an impedance cardiograph, was monitored as college students performed either a visual search or pursuit rotor task. Heart rate, systolic time intervals, stroke volume, cardiac output and the Heather (1969) index of contractility were measured before, during and after performance. In the first study, visual search did not affect the participants' (N = 44) level of cardiac output or their length of the pre-ejection period. It is likely that the lack of charge in cardiac output resulted from a fall in stroke volume and in the Heather index while the task was performed. Heart rate was most rapid during performance and emerged as the only measure affected by the withdrawal of monetary incentives for failure to solve the visual search problem. In the second study, 40 subjects performed a pursuit rotor task and increases in cardiac output as well as changes in all of the other cardiac measures occurred. The level of task difficulty influenced the extent of heart rate increases and stroke volume decreases during performance. An additional 20 male subjects participated in a third study in which the level of difficulty of the pursuit rotor task was signalled and the order of the levels of difficulty was balanced across trial blocks. Under these conditions, the changes in cardiac activity before, during and after performance were similar to those observed in the first two studies. Heart rate was the only measure sensitive to the level of task difficulty. In general, the findings underscore the sensitivity of heart rate to changes in subtle aspects of psychological situations. To enlist increases in cardiac output and inotropic parameters extensive alterations in behavioral state are required.