The ensemble-averaged impedance cardiogram: an evaluation of scoring methods and interrater reliability

Cognitive conflict does not always mean high effort: Task difficulty's moderating effect on cardiac response

This article presents an experiment (N = 127 university students) testing whether the previously found impact of conflict primes on effort-related cardiac response is moderated by objective task difficulty. Recently, it has been shown that primed cognitive conflict increases cardiac pre-ejection period (PEP) reactivity-an index of effort intensity-during the performance of relatively easy tasks. This effect could be attributed to conflict-related negative affect. Consequently, as it has been shown for other types of negative affect, we expected conflict primes' effect to be task-context dependent and thus to be moderated by objective task difficulty. In a between-persons design, we manipulated conflict via embedded pictures of conflict-related vs. non-conflict-related Stroop items in a memory task. We expected primed conflict to increase effort in a relatively easy version of the task but to lead to disengagement when task difficulty was objectively high. PEP reactivity corroborated our predictions. Rather than always increasing effort, cognitive conflict's effect on resource mobilization was context-dependent and resulted in weak responses in a difficult task.

Action-orientation shields against primed cognitive conflict effects on effort-related cardiac response

This article presents a quasi-experiment (N = 79 university students) testing whether individual differences in action-state orientation moderate primed cognitive conflict's effects on sympathetically mediated cardiac response during task performance reflecting effort. Action control theory posits that action-oriented individuals are less receptive to distracting affective stimuli during goal pursuit than state-oriented individuals because action-orientation is related to higher volitional skills. Therefore, we expected that action-oriented individuals should be shielded against conflict primes' effect on effort-related responses in the cardiovascular system. By contrast, state-oriented individuals should be more sensitive to irrelevant negative affective stimulation and therefore mobilize higher resources under such conditions. Responses of the cardiac pre-ejection period (PEP) during a moderately difficult short-term memory task corroborated these predictions. The present findings provide the first evidence that individual differences in action-state orientation indeed moderate previously demonstrated cognitive conflict priming effects on effort-related cardiac response and extend recent findings on action shielding.

Is cognitive conflict really effortful? Conflict priming and shielding effects on cardiac response

Two experiments with N = 221 university students investigated the impact of primed cognitive conflict on effort assessed as cardiac response in tasks that were not conflict-related themselves. Manifest cognitive conflict in cognitive control tasks is confounded with objective response difficulty (e.g., in incongruent Stroop task trials). This makes conclusions about the effortfulness of cognitive conflict itself difficult. We bypassed this problem by administrating pictures of congruent versus incongruent Stroop task stimuli as conflict primes. As predicted, primed cognitive conflict increased cardiac pre-ejection period (PEP) responses in an easy attention task in Experiment 1. Accordingly, cognitive conflict itself is indeed effortful. This effect was replicated in an easy short-term memory task in Experiment 2. Moreover, as further predicted, the primed cognitive conflict effect on PEP reactivity disappeared when participants could personally choose task characteristics. This latter effect corresponds to other recent evidence showing that personal action choice shields against incidental affective influences on action execution and especially on effort-related cardiovascular response.

Individual differences in action‐state orientation moderate task difficulty effects on effort‐related cardiac response

A quasi experiment (N = 100 university students) tested whether individual differences in action-state orientation moderate task difficulty effects on resource mobilization assessed as cardiovascular response. According to action control theory, action-oriented individuals have higher self-regulation capacities in demanding situations than state-oriented persons. Action-orientated individuals should also self-generate positive affect in face of obstacles. Therefore, drawing on Wright's (1998) ability extension of motivational intensity theory and research on affective influences on effort-related cardiovascular response, we expected that action-orientation should lead to stronger effort-related cardiovascular responses in a difficult task, while state-orientation should do so in an easy task. Reactivity of cardiac pre-ejection period (PEP) during performance on a short-term memory task corroborated this hypothesis. The present findings provide the first evidence of a link between action-state orientation and effort-related responses in the cardiovascular system.

An Effective Method of Detecting Characteristic Points of Impedance Cardiogram Verified in the Clinical Pilot Study

Accurate and reliable determination of the characteristic points of the impedance cardiogram (ICG) is an important research problem with a growing range of applications in the cardiological diagnostics of patients with heart failure (HF). The shapes of the characteristic waves of the ICG signal and the temporal location of the characteristic points B, C, and X provide significant diagnostic information. On this basis, essential diagnostic cardiological parameters can be determined, such as, e.g., cardiac output (CO) or stroke volume (SV). Although the importance of this problem is obvious, we face many challenges, including noisy signals and the big variability in the morphology, which altogether make the accurate identification of the characteristic points quite difficult. The paper presents an effective method of ICG points identification intended for conducting experimental research in the field of impedance cardiography. Its effectiveness is confirmed in clinical pilot studies.

The Impact of Pain on Subsequent Effort and Cognitive Performance

Abstract. Theoretical accounts of pain and empirical evidence indicate that pain and cognitive control share common neurocognitive processes. Numerous studies have examined the interactions between pain and cognitive performance when they occur simultaneously, typically showing analgesic effects on task performance and impaired performance due to pain. However, the sequential impact of pain on cognitive control and effort remains less clear. This study investigated the influence of a first task, including painful vs. non-painful thermal stimuli, on effort-related cardiac response and performance in a subsequent moderately difficult cognitive task. Drawing on the hypothesis that experiencing pain should recruit cognitive resources (such as attention and working memory) and reduce perceived ability, we predicted lower task performance and/or stronger compensatory effort in the subsequent cognitive task after the painful than after the non-painful first task. Results support our predictions regarding the effect of pain on subsequent cognitive performance, which was moderately lower after the painful task. However, such a decrease in task proficiency was not associated with a comparable decrease in perceived capacity or increase in effort-related cardiac reactivity. Nevertheless, further correlational analyses indicated that effort and perceived capacity were significantly related to pain ratings. Moderate pain was associated with stronger effort during the cognitive task, whereas high pain led to disengagement, that is, a low effort. Moreover, in line with our predictions, higher pain ratings were associated with a lower self-reported capacity to perform the cognitive task. We discuss these findings regarding the relationship between effort and performance, the impact of fatigue on motivation, and interindividual variability in these after-effects.

Sympathetic involvement in time-constrained sequential foraging

Appraising sequential offers relative to an unknown future opportunity and a time cost requires an optimization policy that draws on a learned estimate of an environment’s richness. Converging evidence points to a learning asymmetry, whereby estimates of this richness update with a bias toward integrating positive information. We replicate this bias in a sequential foraging (prey selection) task and probe associated activation within the sympathetic branch of the autonomic system, using trial-by-trial measures of simultaneously recorded cardiac autonomic physiology. We reveal a unique adaptive role for the sympathetic branch in learning. It was specifically associated with adaptation to a deteriorating environment: it correlated with both the rate of negative information integration in belief estimates and downward changes in moment-to-moment environmental richness, and was predictive of optimal performance on the task. The findings are consistent with a framework whereby autonomic function supports the learning demands of prey selection.

RZ Interval as an Impedance Cardiography Indicator of Effort-Related Cardiac Sympathetic Activity

Research on effort and motivation commonly assesses how the sympathetic branch of the autonomic nervous system affects the cardiovascular system. The cardiac pre-ejection period (PEP), assessed via impedance cardiography, is a common outcome, but assessing PEP requires identifying subtle points on cardiac waveforms. The present research examined the psychometric value of the RZ interval (RZ), which has recently been proposed as an indicator of sympathetic activity, for effort research. Also known as the initial systolic time interval (ISTI), RZ is the time (in ms) between the ECG R peak and the dZ/dt Z peak. Unlike PEP, RZ involves salient waveform points that are easily and reliably identified. Data from two experiments evaluated the suitability of RZ for effort paradigms and compared it to a popular automated PEP method. In Studies 1 (n = 89) and 2 (n = 71), participants completed a standard appetitive task in which each correct response earned a small amount of cash. As expected, incentives significantly affected PEP and RZ in both experiments. PEP and RZ were highly correlated (all rs ≥ 0.89), and RZ consistently yielded a larger effect size than PEP. In Study 3, a quantitative synthesis of the experiments indicated that the effect size of RZ's response to incentives (Hedges's g = 0.432 [0.310, 0.554]) was roughly 15% larger than PEP's effect size (g = 0.376 [0.256, 0.496]). RZ thus appears promising for future research on sympathetic aspects of effort-related cardiac activity.

Associations between multisystem stress reactivity and peer nominated aggression in early childhood vary by sex

There is emerging evidence that the development of problematic aggression in childhood may be associated with specific physiological stress response patterns, with both biological overactivation and underactivation implicated. This study tested associations between sex-specific patterns of stress responses across the sympathetic nervous system (SNS) and hypothalamic-pituitary-adrenal (HPA) axis and peer nominations of aggression among 271 kindergarten children (Mean age = 5.32 years; 52% Female; 44% White). Upon entry to kindergarten, children participated in a multidomain standardized stress paradigm. Changes in pre-ejection period (PEP) and salivary cortisol were assessed. On a separate day, children provided peer ratings of physical and relational aggression in a standardized interview. As expected, there was a significant three-way interaction between PEP, cortisol reactivity, and sex, but only for physical aggression. Among boys, cortisol reactivity was positively associated with physical aggression only for those with higher SNS reactivity. Findings suggest that for boys, asymmetrical and symmetrical HPA/SNS reactivity may be associated with lower and higher risk for peer-directed physical aggression, respectively. Understanding the complex associations between multisystem physiology, child sex and peer-directed aggression in early childhood may offer insight into individual differences underlying the emergence of behavioral dysregulation in early peer contexts.

An open-source automated algorithm for removal of noisy beats for accurate impedance cardiogram analysis

OBJECTIVE

The impedance cardiogram (ICG) is a non-invasive sensing modality for assessing the mechanical aspects of cardiac function, but is sensitive to artifacts from respiration, speaking, motion, and electrode displacement. Electrocardiogram (ECG)-synchronized ensemble averaging of ICG (conventional ensemble averaging method) partially mitigates these disturbances, as artifacts from intra-subject variability (ISVar) of ICG morphology and event latency remain. This paper describes an automated algorithm for removing noisy beats for improved artifact suppression in ensemble-averaged (EA) ICG beats.

APPROACH

Synchronized ECG and ICG signals from 144 male subjects at rest in different psychological conditions were recorded. A 'three-stage EA ICG beat' was formed by passing 60-seconds non-overlapping ECG-synchronized ICG signals through three filtering stages. The amplitude filtering stage removed spikes/noisy beats with amplitudes outside of normal physiological ranges. Cross-correlation was applied to remove noisy beats in coarse and fine filtering stages. The accuracy of the algorithm-detected artifacts was measured with expert-identified artifacts. Agreement between the expert and the algorithm was assessed using intraclass correlation coefficients (ICC) and Bland-Altman plots. The ISVar of the cardiac parameters was evaluated to quantify improvement in these estimates provided by the proposed method.

MAIN RESULTS

The proposed algorithm yielded an accuracy of 96.3% and high inter-rater reliability (ICC > 0.997). Bland-Altman plots showed consistently accurate results across values. The ISVar of the cardiac parameters derived using the proposed method was significantly lower than those derived via conventional ensemble averaging method (p < 0.0001). Enhancement in resolution of fiducial points and smoothing of higher-order time derivatives of the EA ICG beats were observed.

SIGNIFICANCE

The proposed algorithm provides a robust framework for removal of noisy beats and accurate estimation of ICG-based parameters. Importantly, the methodology reduced the ISVar of cardiac parameters. An open-source toolbox has been provided to enable other researchers to readily reproduce and improve upon this work.

Automatic analysis of pre-ejection period during sleep using impedance cardiogram

The pre-ejection period (PEP) is a valid index of myocardial contractility and beta-adrenergic sympathetic control of the heart defined as the time between electrical systole (ECG Q wave) to the initial opening of the aortic valve, estimated as the B point on the impedance cardiogram (ICG). B-point detection accuracy can be severely impacted if ICG cardiac cycles corrupted by motion artifact, noise, or electrode displacement are included in the analyses. Here, we developed new algorithms to detect and exclude corrupted ICG cycles by analyzing their level of activity. PEP was then estimated and analyzed on ensemble-averaged clean ICG cycles using an automatic algorithm previously developed by the authors for the detection of B point in awake individuals. We investigated the algorithms' performance relative to expert visual scoring on long-duration data collected from 20 participants during overnight recordings, where the quality of ICG could be highly affected by movement artifacts and electrode displacements and the signal could also vary according to sleep stage and time of night. The artifact rejection algorithm achieved a high accuracy of 87% in detection of expert-identified corrupted ICG cycles, including those with normal amplitude as well as out-of-range values, and was robust to different types and levels of artifact. Intraclass correlations for concurrent validity of the B-point detection algorithm in different sleep stages and in-bed wakefulness exceeded 0.98, indicating excellent agreement with the expert. The algorithms show promise toward sleep applications requiring accurate and reliable automatic measurement of cardiac hemodynamic parameters.

An Open-Source Feature Extraction Tool for the Analysis of Peripheral Physiological Data

Electrocardiogram, electrodermal activity, electromyogram, continuous blood pressure, and impedance cardiography are among the most commonly used peripheral physiological signals (biosignals) in psychological studies and healthcare applications, including health tracking, sleep quality assessment, disease early-detection/diagnosis, and understanding human emotional and affective phenomena. This paper presents the development of a biosignal-specific processing toolbox (Bio-SP tool) for preprocessing and feature extraction of these physiological signals according to the state-of-the-art studies reported in the scientific literature and feedback received from the field experts. Our open-source Bio-SP tool is intended to assist researchers in affective computing, digital and mobile health, and telemedicine to extract relevant physiological patterns (i.e., features) from these biosignals semi-automatically and reliably. In this paper, we describe the successful algorithms used for signal-specific quality checking, artifact/noise filtering, and segmentation along with introducing features shown to be highly relevant to category discrimination in several healthcare applications (e.g., discriminating patterns associated with disease versus non-disease). Further, the Bio-SP tool is a publicly-available software written in MATLAB with a user-friendly graphical user interface (GUI), enabling future crowd-sourced modification to these tools. The GUI is compatible with MathWorks Classification Learner app for inference model development, such as model training, cross-validation scheme farming, and classification result computation.

Conscientiousness and Effort-Related Cardiac Activity in Response to Piece-Rate Cash Incentives

Although conscientiousness predicts many aspects of motivation, from delay of gratification to higher achievement, its relationship to responses to monetary incentives is surprisingly inconsistent. Several studies have found null or relationships between conscientiousness and behavioral performance in piece-rate, pay-for-performance tasks, in which people earn money for each unit of work completed. In the present study, we examined the role of conscientiousness in effort-related cardiac activity and behavioral performance during a pay-for-performance task. People worked on a self-paced, piece-rate cognitive task in which they earned 1 cent or 5 cents, manipulated within-person, for each correct response. Conscientiousness predicted greater physiological effort (i.e., shorter pre-ejection period [PEP] reactivity) as incentives increased but had no effect on behavioral performance. The findings suggest that conscientiousness is significantly related to effort for piece-rate tasks, and they reinforce a core idea in motivational intensity theory: effort, performance, and persistence are distinct outcomes that often diverge, so drawing conclusions about effort from performance can be complex.

Psychopathology, everyday behaviors, and autonomic activity in daily life: An ambulatory impedance cardiography study of depression, anxiety, and hypomanic traits

Discrepancies regarding the link between autonomic nervous system (ANS) activity and psychopathology may be due in part to inconsistent measurement of non-psychological factors, including eating, drinking, activity, posture, and interacting with others. Rather than sources of noise, behaviors like being active and being with others may be the behavioral pathways that connect psychopathology symptoms to autonomic activity. The present study examined whether behaviors mediate the association of depression, anxiety, and hypomanic traits with ANS by using experience sampling methodology and ambulatory impedance cardiography. Participants (n = 49) completed measures of affect and one day of experience sampling and ambulatory impedance cardiography. The association of hypomanic traits with heart rate variability and heart rate was mediated by physical activity, and social activity mediated the association of depressive symptoms and respiration. These results highlight the importance of considering the pathways between psychopathology and ANS and the mediating role that everyday behaviors play.

Get Going! Self-focused Attention and Sensitivity to Action and Inaction Effort Primes

Implicit action primes and inaction primes can directly affect effort in some circumstances. The present research examined if people high in trait self-focused attention were more strongly affected by action and inaction primes. Past work has found that self-focus makes people more likely to encode implicit primes as self-relevant, thus increasing the effects of primes. As a result, we expected that people high in trait self-focus would be more strongly affected when primed with action and inaction concepts. A group of young adults completed a self-paced parity task in which most trials primed words related to action or inaction. Effort was measured as baseline-to-task change in the cardiac pre-ejection period (PEP), a measure of sympathetic autonomic influence on the heart. Trait self-focus significantly interacted with the priming manipulation. People high in self-focus were more sensitive to the action primes, shown in greater PEP reactivity, but not to the inaction primes. The findings extend the growing literature on how priming influences effort and support models of how self-focused attention shapes motivational processes.

Toward a better noninvasive assessment of preejection period: A novel automatic algorithm for B-point detection and correction on thoracic impedance cardiogram

Impedance cardiography is the most common clinically validated, noninvasive method for determining the timing of the opening of the aortic valve, an important event used for measuring preejection period, which reflects sympathetic beta-adrenergic influences on the heart. Automatic detection of the exact time of the opening of the aortic valve (B point on the impedance cardiogram) has proven to be challenging as its appearance varies between and within individuals and may manifest as a reversal, inflection, or rapid slope change of the thoracic impedance derivative's (dZ/dt) rapid rise. Here, a novel automatic algorithm is proposed for the detection of the B point by finding the main rapid rise of the dZ/dt signal, which is due to blood ejection. Several conditions based on zero crossings, minima, and maxima of the dZ/dt signal and its derivatives are considered to reject any unwanted noise and artifacts and select the true B-point location. The detected B-point locations are then corrected by modeling the B-point time data using forward and reverse autoregressive models. The proposed algorithm is validated against expert-detected B points and is compared with different conventional methods; it significantly outperforms them by at least 54% in mean error, 30% in mean absolute error, and 27% in standard deviation of error. This algorithm can be adopted in ambulatory studies requiring beat-to-beat evaluation of cardiac hemodynamic parameters over extended time periods where expert scoring is not feasible.

On the implicit influence of pain cues on cognitive effort: Evidence from cardiovascular reactivity

To extend previous findings on the impact of implicit affect on behavior, two experiments investigated the influence of priming pain cues on cognitive effort. Effort was assessed as cardiovascular reactivity (PEP, SBP, DBP, and HR) during an easy or difficult cognitive task integrating briefly presented and masked pain-related words. The control condition included neutral words (Experiment 1) or anger-related words (Experiment 2). The pain primes were expected to increase the perceived difficulty of the task and to result in stronger effort during the easy task, compared to the control condition, and to lower effort during the difficult task, due to disengagement. Overall, cardiovascular reactivity of both experiments supported the predictions. Moreover, pain primes increased self-reported subjective difficulty. Finally, most participants could not report the content of the primes. Findings are discussed regarding the influence of implicit processes in pain experience and regarding the self-regulatory consequences of the influence of pain on effort mobilization.

Quantifying rapid changes in cardiovascular state with a moving ensemble average

MEAP, the moving ensemble analysis pipeline, is a new open-source tool designed to perform multisubject preprocessing and analysis of cardiovascular data, including electrocardiogram (ECG), impedance cardiogram (ICG), and continuous blood pressure (BP). In addition to traditional ensemble averaging, MEAP implements a moving ensemble averaging method that allows for the continuous estimation of indices related to cardiovascular state, including cardiac output, preejection period, heart rate variability, and total peripheral resistance, among others. Here, we define the moving ensemble technique mathematically, highlighting its differences from fixed-window ensemble averaging. We describe MEAP's interface and features for signal processing, artifact correction, and cardiovascular-based fMRI analysis. We demonstrate the accuracy of MEAP's novel B point detection algorithm on a large collection of hand-labeled ICG waveforms. As a proof of concept, two subjects completed a series of four physical and cognitive tasks (cold pressor, Valsalva maneuver, video game, random dot kinetogram) on 3 separate days while ECG, ICG, and BP were recorded. Critically, the moving ensemble method reliably captures the rapid cyclical cardiovascular changes related to the baroreflex during the Valsalva maneuver and the classic cold pressor response. Cardiovascular measures were seen to vary considerably within repetitions of the same cognitive task for each individual, suggesting that a carefully designed paradigm could be used to capture fast-acting event-related changes in cardiovascular state.

Patterns of brain and cardiovascular activation while solving rule-discovery and rule-application numeric tasks

It is known that solving mental tasks leads to tonic increase in cardiovascular activity. Our previous research showed that tasks involving rule application (RA) caused greater tonic increase in cardiovascular activity than tasks requiring rule discovery (RD). However, it is not clear what brain mechanisms are responsible for this difference. The aim of two experimental studies was to compare the patterns of brain and cardiovascular activity while both RD and the RA numeric tasks were being solved. The fMRI study revealed greater brain activation while solving RD tasks than while solving RA tasks. In particular, RD tasks evoked greater activation of the left inferior frontal gyrus and selected areas in the parietal, and temporal cortices, including the precuneus, supramarginal gyrus, angular gyrus, inferior parietal lobule, and the superior temporal gyrus, and the cingulate cortex. In addition, RA tasks caused larger increases in HR than RD tasks. The second study, carried out in a cardiovascular laboratory, showed greater increases in heart rate (HR), systolic blood pressure (SBP), diastolic blood pressure (DBP), and mean arterial pressure (MAP) while solving RA tasks than while solving RD tasks. The results support the hypothesis that RD and RA tasks involve different modes of information processing, but the neuronal mechanism responsible for the observed greater cardiovascular response to RA tasks than to RD tasks is not completely clear.

Mathematical detection of aortic valve opening (B point) in impedance cardiography: A comparison of three popular algorithms

The preejection period (PEP) is an index of left ventricle contractility widely used in psychophysiological research. Its computation requires detecting the moment when the aortic valve opens, which coincides with the B point in the first derivative of impedance cardiogram (ICG). Although this operation has been traditionally made via visual inspection, several algorithms based on derivative calculations have been developed to enable an automatic performance of the task. However, despite their popularity, data about their empirical validation are not always available. The present study analyzes the performance in the estimation of the aortic valve opening of three popular algorithms, by comparing their performance with the visual detection of the B point made by two independent scorers. Algorithm 1 is based on the first derivative of the ICG, Algorithm 2 on the second derivative, and Algorithm 3 on the third derivative. Algorithm 3 showed the highest accuracy rate (78.77%), followed by Algorithm 1 (24.57%) and Algorithm 2 (13.82%). In the automatic computation of PEP, Algorithm 2 resulted in significantly more missed cycles (48.57%) than Algorithm 1 (6.3%) and Algorithm 3 (3.5%). Algorithm 2 also estimated a significantly lower average PEP (70 ms), compared with the values obtained by Algorithm 1 (119 ms) and Algorithm 3 (113 ms). Our findings indicate that the algorithm based on the third derivative of the ICG performs significantly better. Nevertheless, a visual inspection of the signal proves indispensable, and this article provides a novel visual guide to facilitate the manual detection of the B point.

Do depressive symptoms "blunt" effort? An analysis of cardiac engagement and withdrawal for an increasingly difficult task

Research on depression and effort has suggested "depressive blunting"-lower cardiovascular reactivity in response to challenges and stressors. Many studies, however, find null effects or higher reactivity. The present research draws upon motivational intensity theory, a broad model of effort that predicts cases in which depressive symptoms should increase or decrease effort. Because depressive symptoms can influence task-difficulty appraisals-people see tasks as subjectively harder-people high in depressive symptoms should engage higher effort at objectively easier levels of difficulty but also quit sooner. A sample of adults completed a mental effort challenge with four levels of difficulty, from very easy to difficult-but-feasible. Depressive symptoms were assessed with the CESD and DASS; effort-related cardiac activity was assessed via markers of contractility (e.g., the cardiac pre-ejection period [PEP]) obtained with impedance cardiography. The findings supported the theory's predictions. When the task was relatively easier, people high in depressive symptoms showed higher contractility (shorter PEP), consistent with greater effort. When the task was relatively harder, people high in depressive symptoms showed diminished contractility, consistent with quitting. The results suggest that past research has been observing a small part of a larger trajectory of trying and quitting, and they illustrate the value of a theoretically grounded analysis of depressive symptoms and effort-related cardiac activity.

Preejection period can be calculated using R peak instead of Q

Preejection period (PEP) is a common measure of sympathetic nervous system activation in psychophysiological research, which makes it important to measure reliably for as many participants as possible. PEP is typically calculated as the interval between the onset or peak of the electrocardiogram Q wave and the impedance cardiography B point, but the Q wave can lack clear definition and even its peak is not visible for all participants. We thus investigated the feasibility of using the electrocardiogram R wave peak (Rpeak ) instead of Q because it can be consistently identified with ease and precision. Across four samples (total N = 408), young adult participants completed a variety of minimally metabolically demanding laboratory tasks after a resting baseline. Results consistently supported a close relationship between absolute levels of the Rpeak -B interval and PEP (accounting for approximately 90% of the variance at baseline and 89% during task performance, on average), but for reactivity values, Rpeak -B was practically indistinguishable from PEP (accounting for over 98% of the variance, on average). Given that using Rpeak rather than the onset or peak of Q saves time, eliminates potential subjectivity, and can be applied to more participants (i.e., those without a visible Q wave), findings suggest that Rpeak -B likely provides an adequate estimate of PEP when absolute levels are of interest and clearly does so for within-person changes.

Simultaneous acquisition of functional magnetic resonance images and impedance cardiography

While simultaneous acquisition of electrocardiography (ECG) data during MRI is a widely used clinical technique, the effects of the MRI environment on impedance cardiography (ICG) data have not been characterized. We collected echo planar MRI scans while simultaneously recording ECG and thoracic impedance using carbon fiber electrodes and customized amplifiers. Here, we show that the key changes in impedance (dZ/dt) and features of the ECG waveforms are not obstructed during MRI. We present a method for ensemble averaging ICG/ECG signals collected during MRI and show that it performs comparably with signals collected outside the MRI environment. These results indicate that ICG can be used during MRI to measure stroke volume, cardiac output, preejection period, and left ventricular ejection time.

Creative motivation: creative achievement predicts cardiac autonomic markers of effort during divergent thinking

Executive approaches to creativity emphasize that generating creative ideas can be hard and requires mental effort. Few studies, however, have examined effort-related physiological activity during creativity tasks. Using motivational intensity theory as a framework, we examined predictors of effort-related cardiac activity during a creative challenge. A sample of 111 adults completed a divergent thinking task. Sympathetic (PEP and RZ) and parasympathetic (RSA and RMSSD) outcomes were assessed using impedance cardiography. As predicted, people with high creative achievement (measured with the Creative Achievement Questionnaire) showed significantly greater increases in sympathetic activity from baseline to task, reflecting higher effort. People with more creative achievements generated ideas that were significantly more creative, and creative performance correlated marginally with PEP and RZ. The results support the view that creative thought can be a mental challenge.

Effort Deficits and Depression: The Influence of Anhedonic Depressive Symptoms on Cardiac Autonomic Activity During a Mental Challenge

Motivational approaches to depression emphasize the role of dysfunctional motivational dynamics, particularly diminished reward and incentive processes associated with anhedonia. A study examined how anhedonic depressive symptoms, measured continuously across a wide range of severity, influenced the physiological mobilization of effort during a cognitive task. Using motivational intensity theory as a guide, we expected that the diminished incentive value associated with anhedonic depressive symptoms would reduce effort during a "do your best" challenge (also known as an unfixed or self-paced challenge), in which effort is a function of the value of achieving the task's goal. Using impedance cardiography, two cardiac autonomic responses were assessed: pre-ejection period (PEP), a measure of sympathetic activity and our primary measure of interest, and respiratory sinus arrhythmia (RSA), a measure of parasympathetic activity. As expected, PEP slowed from baseline to task as anhedonic depressive symptoms increased (as measured with the DASS Depression scale), indicating diminished effort-related sympathetic activity. No significant effects appeared for RSA. The findings support motivational intensity theory as a translational model of effort processes in depression and clarify some inconsistent effects of depressive symptoms on effort-related physiology found in past work.

Gritty people try harder: grit and effort-related cardiac autonomic activity during an active coping challenge

Grit, a recently proposed personality trait associated with persistence for long-range goals, predicts achievement in a wide range of important life outcomes. Using motivational intensity theory, the present research examined the physiological underpinnings of grit during an active coping task. Forty young adults completed the Short Grit Scale and worked on a self-paced mental effort task. Effort-related autonomic nervous system (ANS) activity was assessed using impedance cardiography, which yielded measures of sympathetic activity (pre-ejection period; PEP) and parasympathetic activity (respiratory sinus arrhythmia; RSA). Multilevel models revealed that people high on the Perseverance of Effort subscale showed autonomic coactivation: both PEP and RSA became stronger during the task, reflecting higher activity of both ANS divisions. The Consistency of Interest subscale, in contrast, predicted only weaker sympathetic activity (slower PEP). Taken together, the findings illuminate autonomic processes associated with how "gritty" people pursue goals, and they suggest that more attention should be paid to the facets' distinct effects.

Alpha-adrenergic receptor gene polymorphisms and cardiovascular reactivity to stress in Black adolescents and young adults

Cardiovascular reactivity to stress and α-adrenergic receptor (α-AR) function may contribute to the development of hypertension. As Black Americans have an increased risk of hypertension, we evaluated associations between α(1A) -AR (Arg492Cys), α(2A) -AR (-1291C/G), and α(2B) -AR (Ins/Del301-303) gene variants and cardiovascular reactivity in 500 normotensive Black youth. Heart rate, preejection period, total peripheral resistance, and blood pressure were measured during cold and psychological stress. The Arg492Cys polymorphism in the α(1A) -AR gene was associated with heart rate reactivity to stress, but the association depended on sex. The -1291C/G promoter polymorphism in the α(2A) -AR gene was associated with vascular reactivity to stress; vasoconstriction increased as a linear function of the number of copies of the variant G allele. Thus, specific associations emerged between genetic variations in α-Ars and cardiovascular reactivity in young Blacks.

The Implicit “Go”

In this study, we examined the hypothesis that masked general action and inaction cues that are processed during a cognitive task directly mobilize effort exerted during the task. Participants were randomly assigned to an action-prime condition, an inaction-prime condition, or a control condition and performed a Sternberg short-term memory task. The intensity of effort the participants exerted during the task was estimated by measuring their heart responses (cardiac preejection period, PEP) during task performance. As expected, exposure to masked action cues resulted in stronger PEP reactivity than exposure to masked inaction cues. PEP reactivity in the control group fell in between reactivity when action cues were used and reactivity when inaction cues were used. Participants’ task performance revealed a corresponding pattern: Reaction times were the shortest in the action-prime condition, increased in the control condition, and increased further in the inaction-prime condition. These results show that masked action cues and inaction cues directly influence the intensity of effort exerted in the performance of a task.

Beta-adrenergic receptor gene polymorphisms and cardiovascular reactivity to stress in Black adolescents and young adults

Cardiovascular reactivity to stress and beta-adrenergic receptor (beta-AR) function may contribute to the development of hypertension. As Black Americans have an increased risk of hypertension, we evaluated associations between beta(1)-AR (Arg389Gly) and beta(2)-AR (Arg16Gly, Gln27Glu) gene variants and cardiovascular reactivity in 500 Black youth. Heart rate, preejection period, total peripheral resistance, and blood pressure reactivity were measured during cold and psychological stress. The Arg389Gly polymorphism in the beta(1)-AR was associated with preejection period reactivity in males but not in females. The Arg16Gly polymorphism in the beta(2)-AR was associated with diastolic blood pressure reactivity only during video game stress. An association between the Gln27Glu polymorphism in the beta(2)-AR and vascular reactivity depended on sex. Thus, specific patterns of associations emerged between genetic variations in beta-ARs and cardiovascular reactivity in young Blacks.

The heart contracts to reward: monetary incentives and preejection period

Wright's (1996) integration of motivational intensity theory (Brehm & Self, 1989) and Obrist's (1981) active coping approach predict that cardiovascular reactivity in active coping depends on the importance of success when task difficulty is unclear. Despite the support for this perspective, one of the basic hypotheses-the mediation of these effects by beta-adrenergic activity-has not been tested yet. To close this gap, participants worked on a delayed-matching-to-sample task and could earn either 1, 15, or 30 Swiss Francs for a successful performance. Results showed that preejection period reactivity-an indicator of beta-adrenergic impact on the heart-increased with increasing incentive value. Thus, this experiment closes a gap in the support of Wright's model by demonstrating that beta-adrenergic reactivity is associated with incentive value under conditions of unclear difficulty.

Task difficulty effects on cardiac activity

An experiment with 64 participants manipulated task difficulty and assessed cardiac reactivity in active coping over four levels of demand. Participants performed a memory task while preejection period, heart rate, and blood pressure were assessed. In accordance with the theoretical predictions of R. A. Wright's (1996) integration of motivational intensity theory (J. W. Brehm & E. A. Self, 1989) with Obrist's active coping approach (P. A. Obrist, 1981), preejection period and systolic blood pressure reactivity increased with task difficulty across the first three difficulty levels. On the fourth difficulty level-where success was impossible-reactivity of both preejection period and systolic blood pressure were low. These findings provide the first clear evidence for the notion of Wright's integrative model that energy mobilization in active coping is mediated by beta-adrenergic impact on the heart.

Where to B in dZ/dt

The B point on the impedance cardiograph waveform corresponds to the opening of the aortic valve and is an important parameter for calculating systolic time intervals, stroke volume, and cardiac output. Identifying the location of the B point is sometimes problematic because the characteristic upstroke that serves as a marker of this point is not always apparent. Here is presented a reliable method for B point identification, based on the consistent relationship between the R to B interval (RB) and the interval between the R-wave and the peak of the dZ/dt function (RZ). The polynomial function relating RB to RZ (RB = 1.233RZ - 0.0032RZ(2) - 31.59) accounts for 90%-95% of the variance in the B point location across ages and gender and across baseline and stress conditions. This relation affords a rapid approximation to B point measurement that, in noisy or degraded signals, is superior to visual B point identification and to a derivative-based estimate.

Reliability of cardiovascular reactivity to stress: Internal consistency

Research on the reliability of cardiovascular reactivity has focused on temporal stability and intertask consistency with only modest results. The present study evaluated the internal consistency reliability of cardiovascular reactivity in three large samples of adolescents and young adults (N=326, 136, and 142). Impedance cardiographic and blood pressure measures were recorded at rest and during standard laboratory stress tasks (math, video game, cold pressor). The reliability of cardiovascular reactivity within tasks, as assessed by Cronbach's alpha coefficient of internal consistency, ranged from alpha=.83 to .96 for 4-min to 5-min math tasks, and alpha=.65 to .94 for 3-min video game and cold pressor tasks. Although highly reliable within tasks, cardiovascular reactivity was less reliable across tasks, even within a single testing session. Possible reasons for the discrepancy between internal consistency and intertask consistency are discussed.

Sex differences in the hemodynamic responses to mental stress: Effect of caffeine consumption

The effect of caffeine on stress responses was compared in 25 men and 22 women in a 2-week placebo-controlled, double-blind, randomized crossover trial. On each week, participants abstained from all dietary sources of caffeine before undergoing a 6-h laboratory protocol under placebo or caffeine exposure followed by a 30-min mental stressor with blood pressure (BP) and cardiovascular hemodynamic assessments. On the placebo session, men and women showed a significant BP increase to stress, although women had significant cardiac responses whereas men had vascular responses. Caffeine ingestion before stress caused both men and women to have enhanced hemodynamic responses to the stressor associated with an increase in cardiac index and a drop in the peripheral resistance index. Caffeine enhances the cardiovascular fight-or-flight response pattern to stress in men and women.

Heritability of indices for cardiac contractility in ambulatory recordings

INTRODUCTION

Overactivity of the sympathetic nervous system (SNS) plays a pivotal role in the development of cardiovascular disease. This involvement suggests that the genetic susceptibility to adverse cardiovascular events may derive in part from individual differences in SNS activity.

METHODS AND RESULTS

To establish a genetic contribution to SNS activity, we measured sympathetic effects on cardiac contractility in 755 healthy adult twins and their singleton siblings. The preejection period (PEP) and the ratio of PEP to the left ventricular ejection time (PEP/LVET ratio) were derived from ambulatory recordings of the ECG and thorax impedance. During this type of prolonged recordings in a real life setting, the extent of cardiac sympathetic activity will vary with the demands of daily activities. Therefore, the genetic architecture of both indices was examined separately across three daytime periods (morning, afternoon, evening), and during nighttime sleep. Results showed significant genetic contribution to PEP (48-62%) over all daily periods. Heritability estimates for PEP/LVET ratio ranged between 35% and 58%. Cardiac sympathetic activity during the waking and sleep periods was largely influenced by genetic factors that were common to the entire 24-hour period. During sleep, additional genetic influences emerged that accounted for 8% of the variance in PEP.

CONCLUSION

Impedance-derived measures of sympathetic effects on cardiac contractility show substantial heritability across all periods of the day and during sleep.

Breast feeding, bottle feeding, and maternal autonomic responses to stress

OBJECTIVE

The aim of this study was to examine the effects of breast feeding on autonomic nervous system (ANS) response to stressors.

METHODS

Sympathetic and parasympathetic activities were examined before, during, and after standard laboratory stressors in women who were either exclusively breast feeding (n=14) or nonexclusively breast feeding (n=14), and in non-postpartum controls (n=15).

RESULTS

Mothers who breast fed exclusively showed greater levels of parasympathetic cardiac modulation and slower heart rate (HR) throughout the session and less HR increase and preejection period (PEP) shortening to mental arithmetic (MA) than did nonexclusive breast feeders and controls. Nonexclusive breast-feeders showed greater electrodermal reactivity to, and greater differences in skin conductance response (SCR) frequency between baseline and recovery from cold pressor (CP) than did either exclusive breast-feeders or controls. Sympathetic activity was negatively related to the number of breast feedings and positively related to bottle feedings.

CONCLUSION

Breast feeding shifts maternal ANS balance toward relatively greater parasympathetic and lesser sympathetic activity; the opposite occurs with bottle feeding. The frequency of feeding also is a critical factor in determining breast feeding effects on maternal ANS function.

Cardiovascular reactivity and adaptation to recurrent psychological stress: Replication and extension

We analyzed the effects of evaluative observation and baseline duration on cardiovascular reactivity and adaptation to recurrent psychological stress. Cardiovascular reactivity to mental arithmetic stress was assessed in college men and women (N=224) during two pretest tasks, a test task, and a posttest task. Participants were assigned randomly in a 2 x 2 design to manipulations of baseline duration before the test task (4 min vs. 12 min) and evaluative observation during the test task (observed vs. control). Repeated exposure to stress attenuated cardiac but not vascular reactivity. Evaluative observation disrupted cardiac adaptation, resulting in a resurgence of beta-adrenergic cardiac reactivity during the test task. Cardiac adaptation resumed fully during the posttest task. Baseline duration had no effect on reactivity. The results replicate and extend previous work, and support the dual process theory of habituation and sensitization.

Where to Q in PEP

The onset of ventricular depolarization defines the start of the preejection period (PEP), which is commonly used as an index of myocardial contractility and sympathetic control of the heart. Although the fiducial point for this onset has traditionally been the onset of the Q wave of the electrocardiogram, other measurement points have also been used in the literature, including the peak of the Q wave (i.e., the onset of the R wave). Conceptual, physiological, and empirical considerations addressing the reliability and validity of these alternative metrics support the application of the Q-wave peak/R-wave onset as the fiducial point for PEP measures.

Cardiovascular responses to physical and psychological stress in female alcoholics with transitory hypertension after early abstinence

BACKGROUND

Male alcoholic patients with acute withdrawal hypertension have shown exaggerated cardiovascular reactivity to stress after 3 to 4 weeks of abstinence, although resting blood pressures (BP) had returned to normal. Studies of this nature, however, have not been extended to women.

METHODS

In this study, 32 alcohol-dependent women, abstinent for 4 weeks, were compared with 16 healthy controls on cardiovascular hemodynamics during rest and in response to 2 moderately aversive stressors: isometric handgrip and a speech task. The alcoholics were placed according to withdrawal BP into transitory hypertensive (tHT; n = 16; BP >or=140/90 mm Hg) and normotensive (NT; n = 16; BP <140/90 mm Hg) subgroups.

RESULTS

During stress testing, the transitory hypertensive women had increased diastolic BP (p < 0.01), a higher peripheral resistance index (p < 0.05), and a reduced cardiac efficiency index (p < 0.03) relative to the normotensive and control subjects.

CONCLUSIONS

This cardiovascular pattern suggests that both cardiac and vascular functions were altered adversely in the transitory hypertensives. In contrast to men examined in previous studies, the transitory hypertensive women had no exaggeration of BP reactivity, but instead showed sustained alterations of resting cardiovascular function in relation to chronic alcohol consumption. Although the pattern of cardiovascular dysregulation seems to be different in female alcoholics than in males, it is consistent with studies showing that cardiovascular effects in women are more severe than in men and emerge at a lower threshold level of chronic drinking.

Cardiovascular reactivity to mental arithmetic and cold pressorin African Americans, Caribbean Americans, and white Americans

BACKGROUND

Caribbean Americans and African Americans, two of the largest Black ethnic groups in the United States, differ in cardiovascular-disease-related mortality rates.

PURPOSE

Cardiovascular reactivity to psychological stress may be an important marker or mediator of risk for cardiovascular disease development in Blacks in the United States, yet little attention has been paid to ethnicity among Blacks in reactivity research. This study examined cardiovascular reactivity to psychological stress in African American, Caribbean American, and White American participants.

METHODS

Forty-five women and 43 men performed mental arithmetic and hand cold pressor (CP) tasks.

RESULTS

Caribbean Americans displayed larger decreases in heart period variability during mental arithmetic than White Americans (p =.02). White Americans exhibited a pre-ejection period decrease, whereas African Americans and Caribbean Americans displayed pre-ejection period increases during CP (p =.023). African Americans exhibited greater decreases in interbeat interval during CP than White Americans (p =.013). Caribbean Americans displayed greater decreases in cardiac output than White Americans during CP (p =.009). White Americans exhibited significantly greater increases in systolic blood pressure than Caribbean Americans during CP (p =.014).

CONCLUSIONS

These findings suggest that differences in reactivity to psychological stress exist among Black ethnic groups in the United States and underscore the need to consider ethnicity as a factor in reactivity research with Black Americans.

Large-scale ensemble averaging of ambulatory impedance cardiograms

Impedance cardiography has been used increasingly to measure human physiological responses to emotional and mentally engaging stimuli. The validity of large-scale ensemble averaging of ambulatory impedance cardiograms was evaluated for preejection period (PEP), interbeat interval, and dZ/dt(min) amplitude. We tested whether the average of "classical" 60-sec ensemble averages across periods with fixed activity, posture, physical load, social situation, and location could be accurately estimated from a single large-scale ensemble average spanning these entire periods. Impedance and electrocardiograms were recorded for about 24-h from 21 subjects. Recordings were scored by seven raters, using both methods for each subject. Good agreement (average intraclass correlation coefficient was .91) between both ensemble averaging methods was found for all three cardiac function measures. The results indicate that for unambiguous ambulatory impedance cardiograms, large-scale ensemble averaging is valid, which makes measuring prolonged changes in cardiac sympathetic activity by measuring ambulatory PEP feasible even in large epidemiological samples.

Disinhibitory psychopathology in male adolescents: discriminating conduct disorder from attention-deficit/hyperactivity disorder through concurrent assessment of multiple autonomic states

T. P. Beauchaine recently proposed a model of autonomic nervous system functioning that predicts divergent patterns of psychophysiological responding across disorders of disinhibition. This model was tested by comparing groups of male adolescents with attention-deficit/hyperactivity disorder (ADHD) and attention-deficit/hyperactivity disorder plus conduct disorder (CD/ADHD) with controls while performing a repetitive motor task in which rewards were administered and removed across trials. Participants then watched a videotaped peer conflict. Electrodermal responding (EDR), cardiac pre-ejection period (PEP), and respiratory sinus arrhythmia (RSA) were monitored. Compared with controls, the ADHD and CD/ADHD participants exhibited reduced EDR. The CD/ADHD group was differentiated from the ADHD and control groups on PEP and from the control group on RSA. Findings are discussed in terms of the motivational and regulational systems indexed. Implications for understanding rates of comorbidity between CD and ADHD are considered.

Vagal rebound and recovery from psychological stress

OBJECTIVE

To characterize cardiovascular recovery and examine the possible relationship of vagal activity and reflexes to risk for heart disease.

METHODS

Subjects performed cold pressor and mental arithmetic tasks. Heart rate, heart period variability, and pre-ejection period were obtained for 1 minute before, during, and after each task (Experiment 1). In the second experiment, subjects performed a Stroop color-word task and a mental arithmetic task. Heart rate, heart period variability, blood pressure, and baroreflex sensitivity were obtained during the 5-minute baseline, task, and recovery periods (Experiment 2).

RESULTS

In Experiment 1, heart rate during recovery was lower than baseline despite continued pre-ejection period shortening, whereas recovery heart period variability was higher than baseline. In Experiment 2, blood pressure increased throughout the session. However, recovery heart rate after mental arithmetic was lower than baseline heart rate, and heart period variability was higher during both recovery periods than during baseline. Vagal rebound, a sharp increase in variability in the first minute of recovery, was reduced in men in Experiment 1 and in individuals with a family history of cardiovascular disease in Experiment 2 and was associated with degree of change in baroreflex sensitivity between task and rest.

CONCLUSIONS

Cardiovascular recovery from stress is associated with increased vagal modulation despite residual sympathetic activation. Vagal rebound may be involved in mechanisms resetting the baroreflex sensitivity at the onset and offset of stress. Diminished vagal rebound during recovery from stress is associated with standard risk factors for cardiovascular disease. The results support an association between attenuated vagal reflexes and risk for cardiovascular disease.

The effects of epinephrine administration on impedance cardiographic measures of cardiovascular function

The effects of epinephrine administration on cardiovascular function were examined in 26 men who were given a bolus injection of either 1:10,000 epinephrine hydrochloride or physiological saline. Impedance cardiographic and continuous blood pressure measures were recorded during a 2-min pre-injection baseline and in the post-injection period. Compared to a saline control, epinephrine elicited greater shortening of heart period, pre-ejection period, and the R-B interval; greater increases in cardiac output, stroke volume, dZ/dt amplitude, Heather Index, and systolic and diastolic pressures; and greater decreases in total peripheral resistance (all P < 0.05). Left ventricular ejection time and the Q-R interval were not affected. The results indicate that inotropic indices that are readily measured by impedance cardiography should be considered as important non-invasive indices of adrenergically mediated responses to stress.