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.

Effects of Self-Deception, Social Desirability, and Repressive Coping on Psychophysiological Reactivity to Stress

This study examined the relationship between psychophysiological reactivity to stress and three measures of defensiveness (self-deception, social desirability, and repressive coping). Physiological and psychological responses were recorded while subjects engaged in two consecutive, difficult mental arithmetic tasks. As expected, individuals high in self-deception appraised an upcoming novel mental arithmetic task as less threatening and were less psychophysiologically reactive during the task than low self-deceivers. In contrast, there were no effects for social desirability on task appraisal, but individuals high in social desirability were more physiologically reactive during the task. There were no effects for repressive coping, operationalized using a social desirability/anxiety typology, that were not accounted for by social desirability alone. The possible mechanisms underlying these effects are discussed.

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.

Initial experience with conivaptan use in critically ill infants with cardiac disease

OBJECTIVE

Arginine vasopressin (AVP) is the primary regulator of free water retention through its interactions with the AVP type 2 receptor (V(2)). As opposed to the natriuresis and diuresis that occur with loop and thiazide diuretics, conivaptan is an AVP V(1A)/V(2) receptor antagonist, which enhances free water excretion while minimizing sodium loss. We report our preliminary experience with conivaptan to promote diuresis in infants with functional or structural cardiac disease.

METHODS

A retrospective cohort study was conducted of infants who had received conivaptan from August 2007 to January 2008. A loading dose of conivaptan (0.3-0.6 mg/kg) was followed by a continuous infusion of 0.01-0.02 mg/kg/hr for 24 hours. Sodium, potassium, chloride, blood urea nitrogen (BUN), creatinine, bicarbonate, and urine output were measured prior to the start of conivaptan and at 24 hours after initiation of the infusion.

RESULTS

Conivaptan was administered intravenously on 6 occasions to 5 patients with hypervolemic hyponatremia. Patients ranged in age from 8 to179 days, and body weight ranged from 3 to 4.12 kg. Mean sodium concentration increased from 130.17 ± 1.94 mEq/L to 133.67 ± 3.88 mEq/L (p=0.048), and median urine output increased from 4.15 to 5.05 mL/kg/hr (p=0.286). No significant changes were noted in serum potassium, bicarbonate, creatinine, or BUN. No adverse effects were noted during conivaptan infusion.

CONCLUSION

Intravenous conivaptan is effective for increasing serum sodium levels and may be a potential adjuvant to enhance diuresis in children with cardiac disease. Given the potential benefits of conivaptan compared to diuretic therapy, with all their potential complications, prospective trials are warranted.

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.

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.

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.

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.

Child abuse potential in at-risk African American mothers: the role of life experience variables

The effects of life experience variables on child abuse potential were evaluated in 95 prospectively recruited African American mothers 1 month postpartum. All participants had used opiates or cocaine during pregnancy and were considered high risk for child maltreatment. Abuse potential was assessed with the Child Abuse Potential Inventory, a widely used and psychometrically sound measure with demonstrated predictive validity. Conceptually relevant measures of life experiences and demographic data were obtained from hospital records, maternal self-report, and clinician-administered interviews. Hierarchical multiple regression analysis indicated that exposure to violence in the family of origin and lifetime use of illicit substances made significant independent contributions to the prediction of child physical abuse potential, even after maternal age and current socioeconomic status were controlled for.

Psychophysiological correlates of narcissistic traits in women during active coping

Two dimensions of narcissism were related to psychophysiological responses to stress in 50 young women. Cardiovascular, electrodermal, task performance, and stress appraisal measures were recorded during rest, mental arithmetic, and a computerized Thematic Apperception Test (Murray, 1943). The Egocentricity and Alienation scales of the Bell Object Relations and Reality Testing Inventory (Bell, 1995) served as measures of overt/inflated and covert/deflated narcissism. Egocentricity correlated consistently with heightened preejection period reactivity, whereas Alienation correlated consistently with diminished electrodermal reactivity (all p < .05). Multivariate analyses supported specific relationships between Egocentricity and preejection period hyperreactivity, and between Alienation and electrodermal hyporeactivity. These results have implications for narcissism, cardiovascular disease risk, and a variety of psychiatric disorders.

Breast-feeding and maternal cardiovascular function

Two studies examined the effects of breast-feeding on maternal cardiovascular function. In the first experiment, groups of breast-feeding and bottle-feeding women were compared on preejection period (PEP), heart rate (HR), cardiac output (CO), and total peripheral resistance (TPR) recorded for 1-min periods before and during standard laboratory stressors. Compared with bottle-feeders, breast-feeders had higher CO throughout the session, and greater decreases in CO and increases in TPR during cold pressor. In the second experiment, HR and blood pressure (BP) were compared before and after one breast-feeding and one bottle-feeding session in a within-subjects design. Both feeding methods increased BP but decreased HR, and systolic BP was higher for the breast-feeding than the bottle-feeding condition. Both studies support the notion that breast-feeding alters maternal cardiovascular function, possibly through the actions of oxytocin.

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.

Childhood physical abuse, personality, and adult relationship violence: a model of vulnerability to victimization

An association between childhood physical abuse and current relationship violence was observed in a sample of 56 young adult women, suggesting that childhood physical abuse may be a unique risk factor for victimization in intimate adult relationships. Aspects of personality and interpersonal functioning that reflect extreme doubt about one's interpretation and understanding of interpersonal events, and an inability to make sensible causal connections between people's thoughts, feelings, and actions largely mediated this link. Implications for intervention and directions for future research are discussed.

Psychophysiological characteristics of narcissism during active and passive coping

This study provides the first psychophysiological analysis of narcissism by measuring autonomic responses during active and passive anticipatory coping in 40 undergraduate men who scored high or low on the Narcissistic Personality Inventory (NPI). Compared to the low NPI group, the high NPI group showed greater preejection period (PEP) shortening, cardiac deceleration, and skin conductance response (SCR) habituation during anticipation of an aversive stimulus (p < .02). As expected, SCR and PEP reactivity were greater during active than passive coping. In the case of PEP, this effect emerged only in the low NPI group; the high NPI group showed the greatest PEP reactivity during the first task, regardless of coping demands. These data support hypothesized relationships among narcissism, psychopathy, and psychological predictors of cardiovascular disease, and suggest that a psychobiological dimension may underlie important features of narcissism.

Consistency of hemodynamic responses to cold stress in adolescents

Laboratory research on hypertension often is performed with cold stress to elicit vasoconstriction and increases in blood pressure. Several studies have shown that cardiovascular responses to the cold pressor test predict the development of hypertension. We extended this research by comparing cardiovascular responses to a traditional forehead cold pressor test and a naturalistic whole-body cold exposure. We evaluated blood pressure and impedance cardiographic measures of cardiac output and total peripheral resistance in healthy black (n=69) and white (n=47) adolescents (mean age, 14.7 years) during forehead cold pressor (3 degrees C to 4 degrees C) and passive whole-body exposure to a cold chamber (8 degrees C to 10 degrees C). Both tasks elicited increases in vascular resistance and blood pressure, but forehead cold elicited an increase in cardiac output, whereas whole-body cold elicited a decrease in cardiac output (P<0.05). Consistent with previous research, there was a tendency toward greater vasoconstrictive reactivity to cold stress in blacks than in whites, particularly during whole-body cold exposure (P<0.05). Cardiovascular reactivity correlated significantly between tasks, but substantial intertask consistency occurred only for cardiac and vascular reactivity in male subjects (r>0.30) but not in female subjects (r<0.15). These gender differences might reflect diminished adrenergic receptor function in female subjects. We conclude that whole-body cold exposure offers a viable, relatively naturalistic alternative to traditional cold pressor tests for the assessment of cardiovascular reactivity.

Cardiovascular reactivity and adaptation to recurrent psychological stress: the moderating effects of evaluative observation

The impact of evaluative observation on cardiovascular reactivity and adaptation to recurrent psychological stress was evaluated in 162 undergraduate men and women. All participants performed three mental arithmetic tasks with or without evaluative observation. Impedance cardiographic, blood pressure, task performance, and stress appraisal measures were recorded for each task. Evaluative observation moderated the effects of task repetition on cardiac reactivity but not vascular reactivity. The introduction of evaluative observation disrupted cardiac adaptation, resulting in a resurgence of beta-adrenergic cardiac reactivity (p < .005), whereas the removal of evaluative observation promoted cardiac adaptation. Evaluative observation also increased stress appraisals and slowed task performance. The results support the dual process theory of habituation, rather than stimulus comparator theory, but only partially support cognitive appraisal theory.

Racial differences in hemodynamic responses to environmental thermal stress among adolescents

BACKGROUND

Previous studies by our laboratory and others have shown that blood pressure (BP) responses to many short-term laboratory stressors are greater in black than in white children. We sought to determine the cardiac and vascular contributions to these differences in BP reactivity and whether racial differences in vascular reactivity involve excessive vasoconstriction or deficient vasodilation.

METHODS AND RESULTS

We evaluated BP, heart rate, and impedance cardiographic measures of preejection period (PEP) and total peripheral resistance (TPR) in healthy black (n=76) and white (n=60) adolescents (mean age, 14.8 years) during passive exposure to a vasoconstrictive cold chamber (8 degrees C to 10 degrees C) and a vasodilatory heat chamber (40 degrees C to 42 degrees C). Results indicated greater decreases in PEP and increases in TPR in blacks than whites during cold exposure (P<0.05) but no group differences during heat exposure. Covariance analyses indicated that the racial differences during cold exposure probably reflected greater beta-adrenergic cardiac reactivity and alpha-adrenergic vasoconstrictive reactivity in blacks than whites.

CONCLUSIONS

Blacks and whites exhibited comparable myocardial and vasodilatory responses to heat stress, but blacks exhibited heightened myocardial and vasoconstrictive reactivity to cold stress. These results suggest that the locus of racial differences in vascular reactivity involves vasoconstrictive rather than vasodilatory function. The pattern of racial differences during cold stress raises the possibility that both myocardial and vasoconstrictive mechanisms may contribute to the increased risk of hypertension in blacks.

Cardiovascular reactivity and adaptation to recurrent psychological stress: effects of prior task exposure

The effects of prior task exposure on cardiovascular reactivity to stress were examined in two experiments by randomly assigning participants to repeated exposure groups that performed mental arithmetic pretest and test tasks versus delayed exposure groups that performed only the test task after prolonged rest. Impedance cardiographic and blood pressure measures were recorded continuously from 60 undergraduate men in Experiment 1 and 112 undergraduate men and women in Experiment 2. Task repetition attenuated cardiovascular reactivity and improved task performance in repeated exposure groups (p < .001), suggesting an integrated process of behavioral adaptation. During the test task, delayed exposure groups showed greater cardiac reactivity (p < .01), but not vascular reactivity, than repeated exposure groups. Thus, cardiac reactivity varied as a specific function of prior task exposure, whereas vascular reactivity varied as a general function of time.

Rorschach assessment of malevolence in sexually abused girls

Clinical samples of sexually abused and nonabused girls were compared on COP/AG, a proposed Rorschach index of malevolence. Defined as the co-occurrence of COP and AG in a single response, this variable is introduced as a Rorschach analog of a measure of malevolence devised for use with narrative material. Sexually abused girls scored significantly higher on COP/AG than did nonabused girls (p < .01), with no group differences emerging for either COP or AG alone. These findings provide empirical support for the salience of malevolence in the interpersonal perceptions and expectancies of victims of childhood sexual abuse. Clinical implications and directions for future research are discussed.

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.

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

The interrater reliability and concurrent validity of two methods of scoring the ensemble-averaged impedance cardiogram were evaluated. Impedance cardiographic and electrocardiographic signals were recorded from 40 undergraduate men and women during a baseline rest period and a vocal mental arithmetic task period. Recordings were scored by four rates using a conventional method, involving ensemble averaging after careful editing of beat-to-beat waveforms, and a streamlined method, involving ensemble averaging without beat-to-beat editing. Intraclass correlations for interrater reliability exceeded .92, whereas intraclass correlations for concurrent validity exceeded .97, indicating excellent agreement between rates and scoring methods for all cardiac measures. The streamlined method was significantly faster than the conventional method. The results indicate that variations in beat-to-beat editing do not constitute a serious source of error in the ensemble-averaged impedance cardiogram and support the interrater reliability and concurrent validity of the two scoring methods.

Object relations of sexually and physically abused female children: a TAT analysis

Selected Thematic Apperception Test (Murray, 1943) stories of 17 sexually abused, 15 physically abused, and 15 nonabused but distressed clinical comparison subjects were analyzed using the Social Cognition and Object Relations Scales (Westen, Lohr, Silk, Kerber, & Goodrich, 1985). Results revealed significant differences in overall object relations between the abused and nonabused children both on mean scores, reflecting lower levels of typical functioning, and on frequency of Level 1 scores, indicating a propensity for more grossly pathological functioning. Further comparisons between sexual and physical abuse victims revealed differential impairments in the capacity to invest in relationships and moral standards. Diagnostic and theoretical implications are discussed.

Object relations and physical abuse: a TAT analysis

Selected Thematic Apperception Test (Murray, 1943) stories of 39 physically abused children and a clinical group of 39 children with no recorded history of abuse were examined using the Social Cognition and Object Relations Scales (Westen, Lohr, Silk, Kerber, & Goodrich, 1985). As predicted, a history of physical abuse was associated with a more malevolent object world; a lower level capacity for emotional investment in relations and moral standards; and less accurate, complex, and logical attributions of causality in understanding human interaction. These impairments in object relations were manifest both as a typical level of functioning and as a propensity for more grossly pathological functioning. Results are discussed in terms of clinical and theoretical implications.

Cardiorespiratory response under combined psychological and exercise stress

The effects of combined physical and psychological stress on cardiovascular and respiratory responses were examined. Thirty-six undergraduate men performed a mental arithmetic task and moderate aerobic exercise, separately and in combination, while physiological measures were recorded continuously using electrocardiography, impedance cardiography, and respiratory gas analysis techniques. Cardiovascular responses during the combination of exercise and mental arithmetic stress were greater than those during either stressor alone, indicating that exercise did not mask the increases in cardiovascular performance evoked by psychological stress. In contrast, respiratory responses to the combined stressor were greater than those during isolated mental arithmetic, but less than those during isolated exercise. Thus the results indicate that physical and psychological stress exert a synergistic impact on cardiac performance, but not necessarily on respiratory performance. The results are consistent with the notion that the cardiovascular response to acute psychological stress exceeds concurrent metabolic demands.

Object relations of sexually abused female subjects: a TAT analysis

TAT stories of 17 sexually abused female subjects and a clinical group of 25 female subjects with no documented history of sexual abuse were analyzed using the Object Relations and Social Cognition Scoring System (Western, Lohr, Silk, Kerber, & Goodrich, 1985). Subjects ranged in age from 5 to 16 years. As predicted, mean scores on a measure of overall object relations were significantly different between groups. Specifically, the mental representations of subjects in the abuse group were characterized by more primitive and simple characterizations of people, more negative and punitive affect in their perceptions of the interpersonal world, an inability to invest in people and relationships in other than need-gratifying ways, and an inability to make sensible attributions of self and others. Abuse subjects also produced more pathological responses overall than did their nonabuse counterparts, indicating a tendency toward more extreme and immature functioning. These group differences were independent of any contribution of age and a measure of verbal productivity. Treatment and diagnostic implications are discussed.

Attitude accessibility as a moderator of autonomic reactivity during decision making

Attitude functionality was assessed in 2 experiments examining attitude accessibility as a moderator of physiological responses during decision making. In Study 1, experimental Ss but not controls rehearsed attitudes toward novel objects (abstract paintings). Subsequently, all Ss made rapid preference judgments for pairs of the paintings. In Study 2, attitudes were rehearsed by all Ss toward 1 of 2 mutually exclusive sets of abstract paintings. During the subsequent decision-making task, half the Ss made rapid pairwise preference judgments for rehearsed abstract paintings and half for pairs from the unrehearsed set. Autonomic measures were recorded continuously throughout both experiments. As predicted, in both experiments less autonomic reactivity was evident during the criterion pairwise preference task for groups for whom attitude rehearsal was relevant to the criterion task.

Affect intensity and cardiac arousal

Relationships between affect intensity and basal, evoked, and perceived cardiac arousal were investigated in 3 experiments. Affect intensity was assessed using Larsen and Diener's (1987) Affect Intensity Measure (AIM). Cardiac arousal was evoked with exercise in the 1st study and with mental arithmetic in the 2nd and 3rd. Perceived cardiac arousal was measured under optimal conditions using a standard heartbeat discrimination procedure. Women as a group scored higher on the AIM. Affect intensity was unrelated to basal or evoked cardiac arousal and was negatively related to perceived cardiac arousal in all 3 studies. Data suggest that affect intensity, although unrelated to actual physiological arousal, is negatively related to the accuracy with which individuals perceive their own arousal. Results are discussed within the context of an expanded arousal-regulation model (Blascovich, 1990).

Affect intensity and cardiac arousal

Relationships between affect intensity and basal, evoked, and perceived cardiac arousal were investigated in 3 experiments. Affect intensity was assessed using Larsen and Diener's (1987) Affect Intensity Measure (AIM). Cardiac arousal was evoked with exercise in the 1st study and with mental arithmetic in the 2nd and 3rd. Perceived cardiac arousal was measured under optimal conditions using a standard heartbeat discrimination procedure. Women as a group scored higher on the AIM. Affect intensity was unrelated to basal or evoked cardiac arousal and was negatively related to perceived cardiac arousal in all 3 studies. Data suggest that affect intensity, although unrelated to actual physiological arousal, is negatively related to the accuracy with which individuals perceive their own arousal. Results are discussed within the context of an expanded arousal-regulation model (Blascovich, 1990).

Electrodermal lability and myocardial reactivity to stress

The relationship between electrodermal lability and myocardial reactivity to stress was examined in male undergraduates, who were classified as electrodermally labile (n = 19) or stabile (n = 19) based on the frequency of nonspecific skin conductance responses at rest. Heart rate, pre-ejection period, cardiac output, and skin conductance responses were recorded at rest, during task instructions, and during two mental arithmetic tasks that varied in level of difficulty. As predicted, labiles exhibited greater myocardial reactivity to the task instructions and the tasks than did stabiles, with more persistent group differences emerging for pre-ejection period and cardiac output than for heart rate. The group differences did not vary as a function of task difficulty, but did decline over time. These results support a positive relationship between electrodermal lability and beta-adrenergic myocardial reactivity to stress, particularly under conditions of task novelty or uncertainty, and suggest that electrodermal lability is related fundamentally to arousal and reactivity processes.

Presence of human friends and pet dogs as moderators of autonomic responses to stress in women

Autonomic responses were measured while 45 adult women performed a standard experimental stress task in the laboratory with only the experimenter present and 2 weeks later at home in the presence of a female friend, pet dog, or neither. Results demonstrated that autonomic reactivity was moderated by the presence of a companion, the nature of whom was critical to the size and direction of the effect. Ss in the friend condition exhibited higher physiological reactivity and poorer performance than subjects in the control and pet conditions. Ss in the pet condition showed less physiological reactivity during stressful tasks than Ss in the other conditions. The results are interpreted in terms of the degree to which friends and pets are perceived as evaluative during stressful task performance. Physiological reactivity was consistent across the laboratory and field settings.

Presence of human friends and pet dogs as moderators of autonomic responses to stress in women

Autonomic responses were measured while 45 adult women performed a standard experimental stress task in the laboratory with only the experimenter present and 2 weeks later at home in the presence of a female friend, pet dog, or neither. Results demonstrated that autonomic reactivity was moderated by the presence of a companion, the nature of whom was critical to the size and direction of the effect. Ss in the friend condition exhibited higher physiological reactivity and poorer performance than subjects in the control and pet conditions. Ss in the pet condition showed less physiological reactivity during stressful tasks than Ss in the other conditions. The results are interpreted in terms of the degree to which friends and pets are perceived as evaluative during stressful task performance. Physiological reactivity was consistent across the laboratory and field settings.

An evaluation of the ensemble averaged impedance cardiogram

The ensemble averaged impedance cardiogram was evaluated during rest and during vocal mental arithmetic stress in samples of female (n = 17) and male (n = 40) undergraduates. Measures of myocardial performance determined from ensemble averaged signals were compared to those determined by simple beat-to-beat averaging over 60-s and 20-s sampling intervals. In addition, the influence of cardiac interval variability on dZ/dt amplitude measures was assessed. As expected, measures derived by the two averaging techniques corresponded closely, with correlations ranging from r = 0.882 to r = 1.000 for the 60-s sampling intervals, and from r = 0.726 to r = 1.000 for the 20-s sampling intervals. Inverse relationships of comparable magnitude were found between cardiac interval variability and dZ/dt amplitude measures determined by both averaging techniques, suggesting that these relationships did not result simply from artifacts introduced by the ensemble averaging technique. The results support the validity of ensemble averaging as a method for deriving impedance cardiographic measures of myocardial performance.

Methodological guidelines for impedance cardiography

Impedance cardiography was introduced over 20 years ago as a noninvasive and unobtrusive technique for measuring systolic time intervals and cardiac output. Although our understanding of the physiological events reflected in the impedance cardiogram has become more refined, the technique's theoretical basis remains somewhat controversial and acceptance of its validity has relied heavily upon empirical validation. Largely as a consequence of this status, there have been inadequate grounds on which to develop sound methodological standardization. Currently, the methodological approaches that have been most frequently adopted may be viewed as representing the standard. The various aspects of impedance methodology are discussed, and alternative approaches described, with the objective of providing an informed basis for choosing among these methodological alternatives. It is recommended that studies utilizing impedance cardiography should be reported with clear and detailed methodological description. This should help clarify the extent to which methodological differences may underlie any discrepant research observations, as well as facilitate the emergence of improved methodological standards.