Intertask consistency of hemodynamic responses to laboratory stressors in a biracial sample of men and women

OLD IDEAS, NEW DIRECTIONS: RE-EXAMINING THE PREDICTIVE UTILITY OF THE HEMODYNAMIC PROFILE OF THE STRESS RESPONSE IN HEALTHY POPULATIONS

The 'reactivity hypothesis' has a long and fruitful history in health psychology and behavioural medicine, with elements of its thesis taken as core and others lost in the plethora of research on its utility as a theory of psychosomatic disease. One such thesis is that the underlying hemodynamic profile of the stress response may be particularly revealing when detailing the impact of psychological stress on the development of cardiovascular disease. This paper re-examines old ideas surrounding the hemodynamic profile of the stress response, asking why its health-predictive properties were never fully explored. Further, this paper reviews the evidence that a vascular profile of stress responding may be especially predictive of disease development, particularly in the case of hypertension. In addition, measurement of hemodynamic profile as well as its known psychosocial moderators are reviewed including how examination of patterns of cardiovascular-stress response adaptation may extend the field. This paper highlights that the extension of the reactivity hypothesis to include both hemodynamic profile and patterns of cardiovascular stress-response adaptation may hold much explanatory power in detailing the impact of how stress responding and stress tolerance promotes disease development.

Differential Post-Exercise Blood Pressure Responses between Blacks and Caucasians

Post-exercise hypotension (PEH) is widely observed in Caucasians (CA) and is associated with histamine receptors 1- and 2- (H1R and H2R) mediated post-exercise vasodilation. However, it appears that blacks (BL) may not exhibit PEH following aerobic exercise. Hence, this study sought to determine the extent to which BL develop PEH, and the contribution of histamine receptors to PEH (or lack thereof) in this population. Forty-nine (22 BL, 27 CA) young and healthy subjects completed the study. Subjects were randomly assigned to take either a combined H1R and H2R antagonist (fexofenadine and ranitidine) or a control placebo. Supine blood pressure (BP), cardiac output and peripheral vascular resistance measurements were obtained at baseline, as well as at 30 min, 60 min and 90 min after 45 min of treadmill exercise at 70% heart rate reserve. Exercise increased diastolic BP in young BL but not in CA. Post-exercise diastolic BP was also elevated in BL after exercise with histamine receptor blockade. Moreover, H1R and H2R blockade elicited differential responses in stroke volume between BL and CA at rest, and the difference remained following exercise. Our findings show differential BP responses following exercise in BL and CA, and a potential role of histamine receptors in mediating basal and post-exercise stroke volume in BL. The heightened BP and vascular responses to exercise stimulus is consistent with the greater CVD risk in BL.

Cardiovascular reactivity in real life settings: measurement, mechanisms and meaning

Cardiovascular reactivity to stress is most commonly studied in the laboratory. Laboratory stressors may have limited ecological validity due to the many constraints, operating in controlled environments. This paper will focus on paradigms that involve the measurement of cardiovascular reactions to stress in real life using ambulatory monitors. Probably the most commonly used paradigm in this field is to measure the response to a specific real life stressor, such as sitting an exam or public speaking. A more general approach has been to derive a measure of CV variability testing the hypothesis that more reactive participants will have more variable heart rate or blood pressure. Alternatively, self-reports of the participants' perceived stress, emotion or demands may be linked to simultaneously collected ambulatory measures of cardiovascular parameters. This paper examines the following four questions: (1) What is the form and what are the determinants of stress-induced CV reactivity in real life? (2) What are the psychophysiological processes underlying heart rate and blood pressure reactivity in real life? (3) Does CV reactivity determined in the laboratory predict CV reactivity in real life? (4) Are ambulatory cardiovascular measures predictive of cardiovascular disease? It is concluded that the hemodynamic processes that underlie the blood pressure response can reliably be measured in real life and the psychophysiological relationships seen in the laboratory have been obtained in real life as well. Studies examining the effects of specific real life stressors show that responses obtained in real life are often larger than those obtained in the laboratory. Subjective ratings of stress, emotion and cognitive determinants of real life stress (e.g. demand, reward and control) also relate to real life CV responses. Surprisingly, ambulatory studies on real life cardiovascular reactivity to stress as a predictor of cardiovascular disease are rare. Measuring the CV response to stress in real life may provide a better measure of the stress-related process that are hypothesized to cause disease than is possible in the laboratory. In addressing these questions, below we review the studies that we believe are representative of the field. Therefore, this review is not comprehensive.

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.

Cardiovascular reactivity to psychological challenge: conceptual and measurement considerations

OBJECTIVE AND METHODS

This article is a selective review of recent findings bearing on the conceptualization and measurement of cardiovascular reactivity to psychological challenge, with a focus on several issues relevant to the reliability, content validity, construct validity, and criterion validity of these measures.

RESULTS AND CONCLUSIONS

With respect to reliability, use of standardized task demands and aggregated scores are associated with enhanced short-term reliability, but the long-term reliability of cardiovascular reactivity has not been sufficiently documented. With respect to content validity, existing evidence suggests that "vascular" or "cardiac" tasks may evoke responses that reflect similar distributions of individual difference, whereas associations between responses to "physical" and "psychological" tasks are modest. The evidence is not clear at present with respect to the importance of including affective or interpersonal stimuli as part of trait reactivity assessments. With respect to construct validity, existing data show that cardiovascular reactivity to psychological challenge is largely independent of standard measures of autonomic function. With respect to criterion validity, recent studies point to a number of methodological limitations that may have restricted our ability to detect lab-to-life generalizability of reactivity measures in the past. Continued progress in understanding and measuring reactivity as an individual difference dimension is essential in helping us to evaluate emerging evidence examining the relationship between reactivity and disease risk.

Temporal stability of psychophysiological response patterns: concepts and statistical tools

The specificity or patterning of psychophysiological responses to behavioral stimuli is of importance for basic and applied psychophysiological research. However, the statistical tools used to describe specificity are heterogenious and the attempts to describe temporal stability or reliability of such response profiles are even more complicated. The aim of this paper is to present an approach designed to clarify the relationships between different measures of temporal stability of specificity. This is done with a compilation of statistical measures based on variance components. This approach incorporates features of response specificity and reliability. Individual, situational and motivational response specificity are defined in a uniform way with respect to temporal stability. The use of the formulae is demonstrated with an empirical example. As is found in the research on single parameters, the profile reliability of level scores is higher than that of change scores. Furthermore, the stability of individual response patterns is dependent upon the question of whether the data is aggregated across situations or not. Situational response patterns are stable when the data is aggregated across subjects, whereas the stability is low without such aggregation. Issues of inconsistencies of variance estimates are addressed, and the relationships between temporal stability, consistency and covariation of physiological variables are discussed.

Reducing cardiovascular stress with positive self-stereotypes of aging

We examined whether aging self-stereotypes, or older individuals' beliefs about elderly people, can influence cardiovascular function. Older individuals were subliminally exposed to either positive or negative aging stereotypes. Then all participants faced mathematical and verbal challenges. Those exposed to the negative aging stereotypes demonstrated a heightened cardiovascular response to stress, measured by systolic blood pressure, diastolic blood pressure, and heart rate, compared with those exposed to positive aging stereotypes. The aging stereotypes appeared to influence the outcome variable of skin conductance in the same way. It appears that the negative aging stereotypes acted as direct stressors, whereas the positive aging stereotypes reduced cardiovascular stress. These findings indicate that negative aging stereotypes may contribute to adverse health outcomes in elderly persons without their awareness. The results also suggest that positive aging stereotypes could be used in interventions to reduce cardiovascular stress.

Stressor-induced alteration of cytokine production in multiple sclerosis patients and controls

OBJECTIVE

We administered an acute psychological stressor to multiple sclerosis (MS) patients and normal controls to determine whether differences in subjective and physiological responses to stress may underlie the susceptibility of MS patients to stress-related exacerbations.

METHOD

Twenty-five MS patients (18 female, 7 male) and 25 age- and gender-matched controls participated in the study. They were asked to give a 5-minute videotaped speech defending themselves in a hypothetical scenario in which they were wrongly accused of stealing. Subjective and autonomic responses were monitored, and blood was sampled at baseline, 5, 20, and 60 minutes after the stressor to assess mitogen-stimulated production of interleukin-1beta(IL-1beta), interleukin-4 (IL-4), tumor necrosis factor-alpha (TNF-alpha), and interferon-gamma (IFN-gamma).

RESULTS

MS patients and controls demonstrated similar subjective and physiological responses to the stressor that were independent of gender, mood, and disability status. The macrophage-derived cytokines IL-1beta and TNF-alpha were increased during the stressor, and remained elevated through 60 minutes. Th1 lymphocyte-derived IFN-gamma production also was increased at 5 and 60 minutes relative to baseline; however, there was no change in the Th2 lymphocyte-derived cytokine IL-4.

CONCLUSIONS

These results favor the hypothesis that MS patients do not differ in stress response from normal controls; however, psychological stress may enhance cellular immune responses that would be potentially harmful to MS patients.

Postural effects on hemodynamic response to interpersonal interaction

Laboratory studies of stress-induced cardiovascular reactivity have been conducted predominantly with participants in a seated posture. This procedure may contribute to limited laboratory-field generalization of cardiovascular response. The present study examined hemodynamic adjustments underlying pressor responses, in addition to heart rate and systolic time intervals, during seated and standing role-played, interpersonal interaction in 60 young adults. Irrespective of gender or race, blood pressure responses to the seated and standing interactions were comparable. However, seated interactions yielded a significantly greater increase in heart rate, shortened preejection period and decreased stroke index as compared to standing. Alternatively, interacting while standing yielded a significantly increased left ventricular ejection time and total peripheral resistance in comparison to sitting. These results suggest that hemodynamic adjustments during stressful interpersonal interaction vary as a function of posture, with somewhat greater cardiac influences apparent while seated and a more pronounced vascular response while standing.

Hemodynamic responses during psychological stress: Implications for studying disease processes

Investigation of the physiological correlates of psychological stress is of interest in relation to the putative impact of stress in the etiology of cardiovascular disease. Although the assessment of blood pressure and heart rate responses to psychological stress has been very informative, the addition of cardiac output measurement has added a further dimension to this research field. In recent studies, a more complete hemodynamic picture of the stress response has been documented in terms of cardiac output and systemic vascular resistance components of blood pressure changes. Different stressors have been shown to produce similar blood pressure increases due to quite different hemodynamic mechanisms. Furthermore, when faced with the same stressor, different individuals may exhibit pressor responses that are very different hemodynamically. There is growing evidence that these hemodynamic response patterns to psychological stress are stable individual traits. Response stability is a prerequisite for considering how stress-related hemodynamic changes may be implicated in the pathophysiology of cardiovascular diseases. Observations that hemodynamic response patterns in individuals at higher risk for the development of hypertension differ from those of lower risk individuals show that specific patterns of hemodynamic response are associated with disease processes. Although it is as yet unclear whether they represent markers or mechanisms. Overall. hemodynamic studies appear to he helping to refine our understanding of how stress can impact cardiovascular disease processes.

Comparison of cardiac versus vascular reactors and ethnic groups in plasma epinephrine and norepinephrine responses to stress

This study examined differences in plasma epinephrine (EPI) and norepinephrine (NOREPI) responses to stressors in 67 healthy African-American and Caucasian American men and women of the ages 18 to 49. Subjects were divided into three groups: (a) those who showed high blood pressure (BPI responses to stress associated with consistently high cardiac output (CO) increases with no substantial increases in total peripheral resistance (TPR), labeled cardiac reactors: (b) those with equally high BP increases associated with consistently higher TPR increases and lesser CO increases. labeled vascular reactors; (c) those who showed mixed hemodynamic responses or were low BP reactors. Ethnic and gender group differences in EPI and NOREPI responses were also examined. Cardiac reactors, vascular reactors and mixed + low reactors did not differ in EPI or NOREPI levels at baseline. During stressors, cardiac reactors showed greater increases in plasma EPI than vascular reactors or others during math, reaction time, and passive and active speech tasks: they also showed a weak trend toward greater NOREPI increases during these challenges as well. No differences were seen during the cold pressor: this stressor evoked the least change in EPI of all tasks, whereas the active speech elicited the greatest increases in both EPI and NOREPI of all tasks. Vascular reactors did not differ from mixed + low reactors in EPI or NOREPI reactivity, and men and women did not differ in EPI or NOREPI reactivity to any task. In contrast, Black subjects showed greater increases in NOREPI levels across all stressors compared to White subjects. These findings have implications for investigations of the role of sympathetic nervous system activity in the pathogenesis of hypertension in both African-American and Caucasian American populations.