Toward a causal model of cardiovascular responses to stress and the development of cardiovascular disease

Anxiety Worsens Prognosis in Patients With Coronary Artery Disease

OBJECTIVES

This study examined the effect of anxiety on mortality and nonfatal myocardial infarction (MI) in patients with coronary artery disease (CAD).

BACKGROUND

Inconsistent data exist regarding the impact of anxiety on the prognosis of patients with CAD.

METHODS

The authors conducted a prospective cohort study at an outpatient cardiology clinic of 516 patients with CAD (mean age 68 years at entry, 82% male) by administering the Kellner Symptom Questionnaire annually. The primary outcome was the composite of nonfatal MI or all-cause mortality.

RESULTS

During an average follow-up of 3.4 years, we documented 44 nonfatal MIs and 19 deaths. A high cumulative anxiety score was associated with an increased risk of nonfatal MI or death. Comparing the highest to lowest tertile of anxiety score, the age-adjusted hazard ratio was 1.97 (95% confidence interval 1.03 to 3.78, p = 0.04). In a multivariate Cox model after adjusting for age, gender, education, marital status, smoking, hypertension, diabetes mellitus, previous MI, body mass index, and total cholesterol, each unit increase in the cumulative mean anxiety score was associated with increased risk of nonfatal MI or total mortality; the hazard ratio was 1.06 (95% confidence interval 1.01 to 1.12, p = 0.02).

CONCLUSIONS

A high level of anxiety maintained after CAD diagnosis constitutes a strong risk of MI or death among patients with CAD.

Forgiveness, health, and well-being: a review of evidence for emotional versus decisional forgiveness, dispositional forgivingness, and reduced unforgiveness

The extant data linking forgiveness to health and well-being point to the role of emotional forgiveness, particularly when it becomes a pattern in dispositional forgivingness. Both are important antagonists to the negative affect of unforgiveness and agonists for positive affect. One key distinction emerging in the literature is between decisional and emotional forgiveness. Decisional forgiveness is a behavioral intention to resist an unforgiving stance and to respond differently toward a transgressor. Emotional forgiveness is the replacement of negative unforgiving emotions with positive other-oriented emotions. Emotional forgiveness involves psychophysiological changes, and it has more direct health and well-being consequences. While some benefits of forgiveness and forgivingness emerge merely because they reduce unforgiveness, some benefits appear to be more forgiveness specific. We review research on peripheral and central nervous system correlates of forgiveness, as well as existing interventions to promote forgiveness within divergent health settings. Finally, we propose a research agenda.

Forgiveness, Health, and Well-Being: A Review of Evidence for Emotional Versus Decisional Forgiveness, Dispositional Forgivingness, and Reduced Unforgiveness

The extant data linking forgiveness to health and well-being point to the role of emotional forgiveness, particularly when it becomes a pattern in dispositional forgivingness. Both are important antagonists to the negative affect of unforgiveness and agonists for positive affect. One key distinction emerging in the literature is between decisional and emotional forgiveness. Decisional forgiveness is a behavioral intention to resist an unforgiving stance and to respond differently toward a transgressor. Emotional forgiveness is the replacement of negative unforgiving emotions with positive other-oriented emotions. Emotional forgiveness involves psychophysiological changes, and it has more direct health and well-being consequences. While some benefits of forgiveness and forgivingness emerge merely because they reduce unforgiveness, some benefits appear to be more forgiveness specific. We review research on peripheral and central nervous system correlates of forgiveness, as well as existing interventions to promote forgiveness within divergent health settings. Finally, we propose a research agenda.

Psychological factors associated with orofacial pains

This article develops the case for why trigeminal pain is a unique and challenging problem for clinicians and patients alike, and provides the reader with insights for effective trigeminal pain management based on an understanding of the interplay between psychologic and physiologic systems. There is no greater sensory experience for the brain to manage than unremitting pain in trigeminally mediated areas. Such pain overwhelms conscious experience and focuses the suffering individual like few other sensory events. Trigeminal pain often motivates a search for relief that can drain financial and emotional resources. In some instances, the search is rewarded by a treatment that immediately addresses an identifiable source of pain; in other cases, it can stimulate never-ending pilgrimages from one health provider to another.

Cardiovascular reactivity in hypertensives: differential effect of expressing and inhibiting emotions during moments of interpersonal stress

This study investigated cardiovascular reactivity of hypertensive adults during periods of emotional stress. Two types of instructions were given at different moments, to the same subject, either to express or to suppress feelings during role-play. Expressing, but not inhibiting, emotions elicited significantly higher reactivity during responding to negative scenes, followed by responding during the positive interactions. Blood pressure increases in both expressing and inhibiting conditions, were also found during the instruction periods. Results indicated that socially demanding situations represent a stressor whose effects may vary depending on whether or not respondents regulate expression of emotions. It is suggested that the difficulty in expressing emotions found in some hypertensive individuals may have the function of controlling or reducing blood pressure reactivity.

Symptoms of depression and cardiovascular reactions to acute psychological stress: evidence from a population study

Depression and exaggerated cardiovascular reactivity are considered risk factors for cardiovascular disease, possibly as a result of common antecedents, such as altered autonomic nervous system function. We examined the association between depressive symptomatology and cardiovascular reactions to psychological stress in 1608 adults (875 women) comprising 3 distinct age cohorts: 24-, 44-, and 63-year olds. Depression was assessed using the Hospital Anxiety and Depression Scale. Blood pressure and heart rate were measured at baseline and during the paced auditory serial arithmetic test. Depression scores were negatively associated with systolic blood pressure and heart rate reactions, after adjustment for likely confounders such as sex, cohort, occupational status, body mass index, stress task performance score, baseline cardiovascular activity, antidepressant, and antihypertensive medication. The direction of association was opposite to that which would be expected if excessive reactivity were to mediate the association between depression and cardiovascular disease outcomes or if they shared common antecedents.

Perceived Ethnic Discrimination in Relation to Daily Moods and Negative Social Interactions

Ethnic discrimination experienced in an interpersonal context has been identified as a stressor contributing to racial disparities in health. Exposure to racism may influence the way people view their ongoing experiences, making it more likely that individuals will appraise new situations as threatening and harmful, adding to their overall stress burden. A multiethnic sample of 113 adults completed a diary page every 30 min for one day. The diary inquired about moods and perceptions of social interactions. When controlling for personality characteristics, mixed models regression analyses indicated that baseline measures of ethnic discrimination (assessed with the Perceived Ethnic Discrimination Scale-Community Version) were positively associated with daily levels of anger and the intensity of participants' rating of routine social interactions as harassing, exclusionary, and unfair. These findings have implications for models of the contribution of psychosocial factors to racial disparities in health.

Predicting blood pressure and heart rate change with cardiovascular reactivity and recovery: results from 3-year and 10-year follow up

OBJECTIVES

We examined whether cardiovascular reactivity and recovery after laboratory-induced stress is useful in predicting 3-year and 10-year ambulatory blood pressure (BP) and heart rate (HR) among 330 initially normotensive individuals.

METHODS

At baseline, BP and HR measurements were recorded during three 5-minute laboratory challenges and three 5-minute recovery periods after each challenge. Measurements of systolic BP, diastolic BP, and HR were collected throughout this baseline protocol and also at 3-year and 10-year follow up by ambulatory monitoring.

RESULTS

After adjustment for traditional biologic predictors, reactivity was found to explain significant variance in follow-up data across all 3-year indices and two of the 10-year indices. Recovery, entered in a following step after reactivity, was found to explain additional significant variance across all 3-year indices but none of the 10-year indices. Family hypertension history data were not found to be significantly associated with reactivity or recovery nor were they predictive of longitudinal ambulatory data after adjustment for initial resting cardiovascular levels.

CONCLUSION

Overall, from a hierarchical regression model perspective, the data support the use of both reactivity and recovery in clinical predictions of proximal BP and HR and generally support the use of reactivity (but not recovery) in long-term BP predictions.

The effects of the spontaneous presence of a spouse/partner and others on cardiovascular reactions to an acute psychological challenge

The presence of supportive others has been associated with attenuated cardiovascular reactivity in the laboratory. The effects of the presence of a spouse and others in a more naturalistic setting have received little attention. Blood pressure and heart rate reactions to mental stress were recorded at home in 1028 married/partnered individuals. For 112 participants, their spouse/partner was present; for 78, at least one other person was present. Women tested with a spouse/partner present showed lower magnitude systolic blood pressure and heart rate reactivity than those tested without. Individuals tested with at least one nonspousal other present also displayed attenuated reactivity. This extends the results of laboratory studies and indicates that the spontaneous presence of others is associated with a reduction in cardiovascular reactivity in an everyday environment; spouse/partner presence would appear to be especially effective for women.

Cardiorespiratory fitness and laboratory stress: a meta-regression analysis

We performed a meta-regression analysis of 73 studies that examined whether cardiorespiratory fitness mitigates cardiovascular responses during and after acute laboratory stress in humans. The cumulative evidence indicates that fitness is related to slightly greater reactivity, but better recovery. However, effects varied according to several study features and were smallest in the better controlled studies. Fitness did not mitigate integrated stress responses such as heart rate and blood pressure, which were the focus of most of the studies we reviewed. Nonetheless, potentially important areas, particularly hemodynamic and vascular responses, have been understudied. Women, racial/ethnic groups, and cardiovascular patients were underrepresented. Randomized controlled trials, including naturalistic studies of real-life responses, are needed to clarify whether a change in fitness alters putative stress mechanisms linked with cardiovascular health.

Influence of apologies and trait hostility on recovery from anger

While there is growing evidence that quick recovery from stress is health-protective, relatively little is known about what factors affect recovery rates. We tested whether recovery from anger can be diffused with apologies. 184 participants performed a stress task involving verbal harassment and apologies. Participants were randomly assigned to one of four conditions: non-harassed control, good apology, pseudo-apology, or no apology. Measures of blood pressure and heart rate were taken at baseline, task and recovery periods. Participants scoring high in trait hostility displayed faster systolic blood pressure recovery when they received a genuine apology, but recovered more slowly when they received a pseudo-apology or no apology. Apologies did not influence subjective anger ratings. It was concluded that apologies may accelerate cardiovascular anger recovery among those with hostile personality predispositions.

The effects of effort-reward imbalance on inflammatory and cardiovascular responses to mental stress

OBJECTIVE

We examined the influence of effort-reward imbalance, a stressful feature of the work environment, on cardiovascular and inflammatory responses to acute mental stress.

METHODS

Ninety-two healthy men (mean age, 33.1 years) in full-time employment were recruited. Effort-reward imbalance was measured using a self-administered questionnaire. Blood, for the analysis of C-reactive protein (CRP) and von Willebrand factor (vWF) antigen, was sampled at baseline and 10 minutes after two mental stress tasks, whereas cardiovascular activity was measured throughout.

RESULTS

Plasma CRP and vWF were significantly elevated following the stress period, and cardiovascular activity was increased during and after both tasks (p < .001). Multiple linear regression analysis adjusted for age, body mass index, and baseline levels revealed that men with higher effort-reward imbalance demonstrated greater CRP and vWF responses to the stress tasks but blunted cardiovascular responses. Inflammatory and cardiovascular responses to stress appeared to be unrelated.

CONCLUSIONS

These findings suggest that the association between chronic work stress and cardiovascular disease risk may be mediated in part by heightened acute inflammatory responsivity. These responses appear not to result from differences in sympathoadrenal activation.

Rho kinase polymorphism influences blood pressure and systemic vascular resistance in human twins: role of heredity

The Rho/Rho kinase (ROCK) pathway is implicated in experimental hypertension. We, therefore, explored the role of ROCK2 genetic variation in human blood pressure (BP) regulation, exploiting the advantages of a human twin sample to probe heritability. The focus of this work is the common nonsynonymous variant at ROCK2: Thr431Asn. Cardiovascular and autonomic traits displayed substantial heritability (from approximately 33% to 71%; P<0.05). The Asn/Asn genotype (compared with Asn/Thr or Thr/Thr) was associated with greater resting systolic (P<0.001), diastolic (P<0.0001), and mean BP (P<0.0001); allelic variation at ROCK2 accounted for up to approximately 5% of BP variation (P<0.0001). Systemic vascular resistance was higher in Asn/Asn individuals (P=0.049), whereas cardiac output, large artery compliance, and vasoactive hormone secretion were not different. Coupling of the renin-angiotensin system to systemic resistance and BP was diminished in Asn/Asn homozygotes, suggesting genetic pleiotropy of Thr431Asn, confirmed by bivariate genetic analyses. The Asn/Asn genotype also predicted higher BP after environmental (cold) stress. The rise in heart rate after cold was less pronounced in Asn/Asn individuals, consistent with intact baroreceptor function, and baroreceptor slope was not influenced by genotype. Common genetic variation (Thr431Asn) at ROCK2 predicts increased BP, systemic vascular resistance (although not large artery compliance), and resistance in response to the endogenous renin-angiotensin system, indicating a resistance vessel-based effect on elevated BP. The results suggest that common variation in ROCK2 exerts systemic resistance-mediated changes in BP, documenting a novel mechanism for human circulatory control, and suggesting new possibilities for diagnostic profiling and treatment of subjects at risk of developing hypertension.

Prolonged stress-related cardiovascular activation: Is there any?

BACKGROUND

Prolonged physiological activation before or after stressors has gained recognition as a decisive element in theories that explain the link between stress and disease, specifically cardiovascular (CV) disease. This view is opposed to the conventional reactivity hypothesis that emphasizes responses during stressors.

PURPOSE

Prolonged activity has not often been an explicit research goal of real-life stress studies. Nevertheless, a growing number of these studies have provided evidence for prolonged activity, often as a secondary research goal.

METHODS

An overview of this evidence is lacking and is provided in this article.

RESULTS

The combined data from the reviewed studies suggest that discrete and chronic stress sources, as well as negative emotional episodes and dispositions, are related to prolonged CV activity of various durations, including sleep periods. On the other hand, evidence supporting the assumption that prolonged stress-related activation predicts disease is still very modest.

CONCLUSIONS

In this article we suggest that future research of prolonged activation should give priority to (a) the establishment of clear beginnings and endings of stressful events, (b) the prediction of disease by prolonged activation, and (c) potential psychological mediators of stress-related prolonged activation. These mediators may include, for example, worry and rumination, or other processes characterized by perseverative cognition, including unconscious processes.

The effects of sex and hormonal status on the physiological response to acute psychosocial stress

Whether one is male or female is one of the most important determinants of human health. While males are more susceptible to cardiovascular and infectious disease, they are outnumbered by women for many autoimmune disorders, fibromyalgia and chronic pain. Recently, individual differences in the physiological response to stress have emerged as a potentially important risk factor for these disorders. This raises the possibility that sex differences in prevalence of disease could at least in part be explained by sex differences in the nature of the physiological response to stress. In a psychophysiological laboratory, the autonomic nervous system response can be provoked by many different stressors including physical, mental and psychosocial tasks, while the hypothalamic-pituitary-adrenal axis (HPAA) response seems to be more specific to a psychosocial challenge incorporating ego involvement. The responses of both systems to different psychosocial challenges have been subject to extensive research, although in respect of sex differences the HPAA response has probably been more systematically studied. In this review, we focus on sex differences in HPAA and autonomic nervous system responses to acute psychosocial stress. Although some differences are dependent on the stressor used, the responses of both systems show marked and consistent differences according to sex, with the phase of the menstrual cycle, menopausal status and pregnancy having marked effects. Between puberty and menopause, adult women usually show lower HPAA and autonomic responses than men of same age. However, the HPAA response is higher in the luteal phase, when for example post stress free cortisol levels approach those of men. After menopause, there is an increase in sympathoadrenal responsiveness, which is attenuated during oral hormone replacement therapy, with most evidence suggesting that HPAA activity shows the same trends. Interestingly, pregnancy is associated with an attenuated response of the sympathoadrenal and HPAA systems at least as assessed by biochemical stimulation. It is likely that these sex differences in autonomic function are a result of estrogen exposure which attenuates sympathoadrenal responsiveness. The HPAA is however somewhat more complex and evidence now suggests the influence of other modifiers such as arginine vasopressin (AVP) and the regulation of circulating cortisol bioavailability by corticosteroid-binding globulin (CBG). The pronounced and multi-faceted sex differences in stress responsiveness suggest that they are a product of a strong evolutionary pressure. We hypothesise that this has to a great deal been driven by the need to protect the fetus from the adverse effects of maternal stress responses, in particular excess glucocorticoid exposure. Studying this hypothesis may have a fundamental impact on our understanding about how adult health is set during early life and how adult disease could be prevented in men and women.

The perseverative cognition hypothesis: a review of worry, prolonged stress-related physiological activation, and health

Perseverative cognition, as manifested in worry and rumination, is a common response to stress, but biopsychological models of stress and health have largely ignored it. These models have generally focused on physiological activation that occurs during stress and have insufficiently addressed effects that occur in anticipation of, or following, stressful events. We argue that perseverative cognition moderates the health consequences of stressors because it can prolong stress-related affective and physiological activation, both in advance of and following stressors. We review evidence that worry, rumination, and anticipatory stress are associated with enhanced cardiovascular, endocrinological, immunological, and neurovisceral activity. The findings yield preliminary support for our hypothesis, suggesting that perseverative cognition might act directly on somatic disease via enhance activation via the cardiovascular, immune, endocrine, and neurovisceral systems.

The importance of examining blood pressure reactivity and recovery in anger provocation research

OBJECTIVE

We investigated the moderating relationship of hostility on emotional and physiological arousal due to acute anger provocation; stress reactivity and recovery were measured.

METHOD

Forty-five participants completed a measure of trait hostility (CMHQ) and performed a mental arithmetic (serial 7s) task while receiving scripted comments at set intervals designed to provoke anger (harassment). The impact of trait hostility (high, medium or low) on arousal and recovery was examined.

RESULTS

Participants low in self-reported hostility showed greater HR reactivity to the task but recovered quickly. Participants high in hostility showed noticeably slower recovery in SBP maintained after task completion.

CONCLUSIONS

The findings underscore the importance of examining both reactivity and recovery data in anger provocation research because the apparent influence of trait hostility on cardiovascular functioning would have been missed if recovery had not been systematically studied.

Hemodynamic profile, compensation deficit, and ambulatory blood pressure

This study hypothesized that physiologically grounded patterns of hemodynamic profile and compensation deficit would be superior to traditional blood pressure reactivity in the prediction of daily-life blood pressure. Impedance cardiography-derived measures and beat-to-beat blood pressure were monitored continuously in 45 subjects during baseline and four tasks. Ambulatory blood pressure measures were obtained combining data from one work day and one off day. The mediating effects of gender and family history of hypertension were considered. Only gender was significantly associated with hemodynamic profile. Regression analysis indicated that typical reactivity measures failed to predict everyday life blood pressure. After controlling for gender and baseline blood pressure, hemodynamic patterns during specific tasks proved to be strong predictors, overcoming limitations of previous reactivity models in predicting real-life blood pressure.

Violence exposure and optimism predict task-induced changes in blood pressure and pulse rate in a normotensive sample of inner-city black youth

OBJECTIVE

This investigation examined the association of violence exposure (home and neighborhood) and optimism to task-induced changes in systolic blood pressure (SBP), diastolic blood pressure (DBP), and pulse rate (PR).

METHODS

Drawn from a larger investigation, the convenience sample for this study consisted of 172 normotensive black youth (mean age = 11.5 years, standard deviation = 1.3). Violence exposure and optimism were self-reported by participants, and task-induced changes in SBP, DBP, and PR were measured with an automated monitor during two sequentially administered digit-forward and digit-backward tasks.

RESULTS

Hierarchical regression analyses revealed that violence exposure was inversely related to task-induced changes in SBP (p = .010) and DBP (p = .005). Optimism was not an independent predictor of blood pressure or PR changes (p-s > .32). The final step of these hierarchical analyses indicated that the effects of violence exposure and optimism interacted to predict task-induced changes in SBP (p = .013) and PR (p = .003). Follow-up regression analyses indicated that violence exposure was inversely related to task-induced changes in SBP among participants high in optimism and was positively associated with PR reactivity in participants low in optimism.

CONCLUSIONS

The youth in this study have intact mechanisms for buffering blood pressure responses to violence exposure, especially those who are more optimistic about their future-a person factor whose moderating effects might wane with advancing age.

Sleep disturbances as predictors of hospitalization for back disorders-a 28-year follow-up of industrial employees

STUDY DESIGN

A prospective cohort study.

OBJECTIVE

To study the relationship of sleep disturbances with severe back disorders leading to hospitalization.

SUMMARY OF BACKGROUND DATA

Sleep disturbances are associated with persistent pain syndromes, but little is known about their relationship with back disorders.

METHODS

The first hospital admission for back disorders from 1973 to 2000 was studied in a cohort of metal industry workers (n = 902). The occurrence of sleep disturbances at baseline was categorized as: none; 1 type (either difficulties in falling asleep/waking up at night or nightmares); or both types. Cox proportional hazards regression was used to estimate the time between the assessment of risk factors and first hospital admission for back disorders.

RESULTS

Those individuals who had 1 type of sleep disturbance had a 2.1-fold (95% confidence interval 1.1-3.8) risk of back-related hospitalization, and those with both types of disturbance a 2.4-fold (1.2-4.6) risk, compared with those with no sleep disturbances. The hazard ratios were 2.1; 1.0-4.6 and 2.9; 1.2-7.1, respectively, when patients with chronic back disease or recurrent back symptoms at baseline were excluded from the analyses.

CONCLUSION

These findings suggest that sleep disturbances are predictive of hospitalization for back disorders. The mechanism underlying this association warrants further study.

Cardiovascular reactivity to and recovery from psychological challenge as predictors of 3-year change in blood pressure

The authors examined whether cardiovascular reactivity to and recovery from psychological challenge predict 3-year change in blood pressure (BP) among 216 initially normotensive, community-dwelling adults. Clinic BP assessments were conducted at baseline and follow-up. BP and heart rate (HR) readings were obtained before, during, and after 5 psychological tasks at baseline. Following adjustment for traditional predictors of BP and lifestyle factors, poorer systolic BP recovery across the tasks was associated with greater 3-year increases in clinic systolic and diastolic BP. Both diastolic BP recovery and HR recovery were also related to 3-year change in clinic BP, though cardiovascular reactivity measures were not. These findings suggest that the duration of stress-related cardiovascular responses may be important for predicting longitudinal changes in BP.

Social support versus social evaluation: unique effects on vascular and myocardial response patterns

OBJECTIVES

This study examined the effects of companion presence and evaluation on cardiovascular reactivity to an acute stressor.

METHODS

Eighty-two women completed a speech task in one of four conditions: with an evaluative companion present, with a nonevaluative companion present, alone while being evaluated by a companion with a video camera, or alone while the companion waited outside.

RESULTS

A significant interaction between companion condition and evaluative condition on systolic blood pressure was found; women who were evaluated while alone demonstrated significantly greater reactivity than did women who were in the nonevaluative alone condition. Furthermore, both potential for evaluation and the presence of a companion had important influences on hemodynamic parameters underlying the blood pressure response. Specifically, those in evaluative conditions showed greater myocardial responding than those in nonevaluative conditions and those in alone conditions showed greater vascular responding than did those with companions present. Taken together, those in the evaluative alone condition demonstrated systolic blood pressure responses reflecting both myocardial and vascular contributions.

CONCLUSIONS

Social support and social evaluation have unique effects on vascular and myocardial responding. The implications for future research include focus on the stress-buffering model of social support and the value of including impedance cardiography measures in investigations of cardiovascular functioning.

The role of angry rumination and distraction in blood pressure recovery from emotional arousal

OBJECTIVE

Cardiovascular recovery of prestress baseline blood pressure has been implicated as a possible additional determinant of sustained blood pressure elevation. We hypothesize that angry ruminations may slow the recovery process.

METHOD

A within-subjects design was used in which resting baseline blood pressure and heart rate measurements were assessed on 60 subjects, who then took part in two anger-recall tasks. After each task, subjects sat quietly and alone during a 12-minute recovery period randomized to with or without distractions. During baseline, task, and recovery, blood pressure was continuously monitored; during recovery, subjects reported their thoughts at five fixed intervals.

RESULTS

Fewer angry thoughts were reported in the distraction condition (17%) compared with no distraction (31%; p = .002); an interaction showed that this effect was largely the result of the two intervals immediately after the anger-recall task. Trait rumination interacted with distraction condition such that high ruminators in the no-distraction condition evidenced the poorest blood pressure recovery, assessed as area under the curve (p = .044 [systolic blood pressure] and p = .046 [diastolic pressure]).

CONCLUSIONS

People who have a tendency to ruminate about past anger-provoking events may be at greater risk for target organ damage as a result of sustained blood pressure elevations; the effect is exacerbated when distractions are not available to interrupt the ruminative process.

Expanding stress theory: prolonged activation and perseverative cognition

Several theories of the stress-disease link have now incorporated prolonged activation. This article argues that these theories still lack an important element, that is, the cognitive nature of the mechanism that causes stress responses to be sustained. The perception of stress and the initial response to it do not automatically lead to prolonged activation. The active cognitive representations of stressors need to be prolonged in order to extend their physiological concomitants. We call this mediating process perseverative cognition, and it is manifested in phenomena such as worry, rumination, and anticipatory stress. We summarize evidence suggesting that these phenomena are indeed associated with physiological activation, including cardiovascular, endocrinological and immunological parameters. This evidence is still far from sufficient, due to the many methodological insufficiencies in the studies involved. Nevertheless, it makes clear that cognitive phenomena characterized by perseverative cognition may be likely candidates to mediate the effects of stress sources on somatic disease. We also argue that there is a dearth of evidence supporting the role of prolonged activation. There are a limited number of studies demonstrating prolonged activity related to stressors and emotional episodes, and their methodologies often do not allow unambiguous conclusions. Even more important, the crucial assumption that prolonged activation actually leads to pathogenic states and disease has received hardly any attention yet and therefore is still largely unsupported. There are only a few studies that showed that anticipatory responses and slow recovery from stress predicted disease states.

Impact of chronic psychosocial stress on autonomic cardiovascular regulation in otherwise healthy subjects

Elevated psychosocial stress might favor the occurrence of cardiovascular disease; however, mechanisms are incompletely understood. We hypothesized that patients (n=126; 44+/-1 years of age) referred to an internal medicine clinic because of symptoms related to chronic psychosocial stress would demonstrate signs of autonomic dysregulation compared with controls (n=132; 42+/-1 years of age). We used autoregressive spectral analysis of RR interval variability to obtain indirect markers of sympathetic and of vagal (respectively, low-frequency and high-frequency components, both expressed in normalized units) oscillatory modulation of sinoatrial node, as well as of sympathetic vasomotor regulation (low-frequency component of systolic arterial pressure variability) and of cardiac baroreflex sensitivity (alpha-index). Higher values of systolic and diastolic arterial pressure (respectively, 124+/-1 versus 117+/-1 mm Hg and 80+/-1 versus 75+/-1 mm Hg; both P<0.001), altered markers of autonomic regulation (increased normalized low-frequency and reduced high-frequency component of RR variability, P<0.005; increased-low frequency component of systolic arterial pressure variability, P<0.002), and reduced baroreflex sensitivity (19.3+/-1.4 versus 23.0+/-2.0 ms/mm Hg; P<0.05) were observed in patients compared with controls. Autonomic responses to active standing were also blunted in stressed patients. Autonomic markers were significantly correlated to stress perception score and were capable of discriminating between controls and patients with a high degree of accuracy. Chronic real-life stress in humans appears associated to increased arterial pressure and to impaired autonomic regulation of cardiovascular functions. The combination of sympathetic predominance, vagal withdrawal, and blunted baroreflex sensitivity might represent a treatable mechanistic link between psychosocial factors and future incidence of hypertension.

Cardiovascular reactivity: mechanisms and pathways to cardiovascular disease

Researchers in physiology, psychology, and medicine have held the idea that risk for cardiovascular disease is increased by exaggerated responses to stress. Some epidemiological evidence supports this view and shows that exaggerated blood pressure responses to stress add to disease prediction beyond that provided by standard risk factors. Most studies of reactivity and disease risk have taken a correlational approach to the reactivity-disease relationship. This paper presents a model of central nervous system control over peripheral response systems that provides a way of designating three sources of exaggerated stress reactivity that may vary across individuals. The top level in the model consists of the limbic system and prefrontal cortex as interacting areas that form psychological stress responses. These frontal-limbic interactions are a means of translating experiential and affective processes into bodily responses. The middle level consists of hypothalamus and brainstem areas that translate descending influences into bodily outputs. Activation levels in these structures can lead to enhanced reactivity to many forms of challenge. The final level consists of the peripheral effectors that create the response itself; altered effector function can be a source of enhanced reactivity. Study designs that involve both psychological and physiological challenges and that take account of self-reports of affect and activation provide a basis for separating these sources of responsivity. This organization may provide useful insights into the sources of stress reactivity that characterize specific groups at risk and allow inferences as to the source of the disease pathophysiology.

Cardiovascular reactivity during dyadic social interaction: The roles of gender and dominance

The present study examined relationships among gender, trait dominance, and cardiovascular reactivity assessed during dyadic social interactions between same-gender and same-ethnicity participants. One-hundred sixty dyads, 76 comprised of African American participants and 84 comprised of European American participants, engaged in three 4-min discussions while their heart rate and blood pressure responses were assessed. All dyads were composed of unacquainted partners. Multilevel modeling for dyadic data revealed that trait dominance was significantly and positively associated with blood pressure reactivity during the discussions, but only among men who interacted with a highly dominant partner. The results of the present study add to the weight of the evidence identifying dominance as a social domain of significance for cardiovascular functioning, particularly among men. Potential reasons for gender-specific patterning are considered.

Sustained blood pressure increase after an acute stressor: the effects of the 11 September 2001 attack on the New York City World Trade Center

BACKGROUND

Effects of catastrophic stress on blood pressure are well documented, but usually few measurements were taken before the event occurred, and the people studied were directly involved or geographically close to the disaster. The impact of the 11 September 2001 (9/11) attacks in New York City had far greater reach, and has been sustained by subsequent events.

OBJECTIVE

To test the hypothesis that, after the 9/11 attacks, blood pressures in the population affected would be increased compared with that in both the preceding months and the same period during the previous year.

METHODS

We used data available from a current study of blood pressure in four sites in the USA that enabled us to examine them from two perspectives: a mixed (within and between groups) analysis that tested the overall differences in blood pressure before and after 9/11, and a within-subjects model to examine the more focused issue of individual change in blood pressure after 9/11. The blood pressures of 427 hypertensive individuals were telemonitored at four sites. An additional 101 patients had been monitored at two sites during the same period in the previous year.

RESULTS

Mean systolic blood pressure was significantly greater during the 2 months after 9/11, across the four sites, compared with that assessed during the previous 2 months (range of observed differences 1.7-3.8 mmHg). At the two sites for which data were available for the same period in the year 2000, there was also a significant effect for the same period during the preceding year for systolic blood pressure. However, at both these sites the effect at 2000 was significantly smaller than the effect at 2001. Blood pressure also generally increased among those individuals in whom monitoring overlapped the 9/11 event.

CONCLUSION

The World Trade Center attacks produced a substantial and sustained increase in blood pressure that appears to be independent of seasonal effects, and which has important implications for morbidity and financial burden. The ubiquitous continuing reference to the events in the news reports may contribute to the sustained effects.

A greater reduction in high-frequency heart rate variability to a psychological stressor is associated with subclinical coronary and aortic calcification in postmenopausal women

OBJECTIVE

Reduced cardiac parasympathetic activity, as indicated by a reduced level of clinic or ambulatory high-frequency heart rate variability (HF-HRV), is associated with an increased risk for atherosclerosis and coronary artery disease. We tested whether the reduction in HF-HRV to a psychological stressor relative to a baseline level is also associated with subclinical coronary or aortic atherosclerosis, as assessed by calcification in these vascular regions.

METHOD

Spectral estimates of 0.15 to 0.40 Hz HF-HRV were obtained from 94 postmenopausal women (61-69 years) who engaged in a 3-minute speech-preparation stressor after a 6-minute resting baseline. A median of 282 days later, electron beam tomography (EBT) was used to measure the extent of coronary and aortic calcification.

RESULTS

In univariate analyses, a greater reduction in HF-HRV from baseline to speech preparation was associated with having more extensive calcification in the coronary arteries (rho = -0.29, p = .03) and in the aorta (rho = -0.22, p = .06). In multivariate analyses that controlled for age, education level, smoking status, hormone therapy use, fasting glucose, high-density lipoproteins, baseline HF-HRV, and the stressor-induced change in respiration rate, a greater stressor-induced reduction in HF-HRV was associated with more calcification in the coronary arteries (B = -1.21, p < .05), and it was marginally associated with more calcification in the aorta (B = -0.92, p = .09).

CONCLUSION

In postmenopausal women, a greater reduction in cardiac parasympathetic activity to a psychological stressor from baseline may be an independent correlate of subclinical atherosclerosis, particularly in the coronary arteries.

Stimulated release of tissue plasminogen activator from artery wall sympathetic nerves: implications for stress-associated wall damage

Recurrent stress is clinically associated with early onset hypertension and coronary artery disease. A mechanism linking emotion to pathogenic remodeling of the artery wall has not been identified. Stress stimulates acute regulated release of tissue plasminogen activator (t-PA) into the circulation, which is presently attributed to the vascular endothelium. Sympathetic neurons also synthesize t-PA and axonally transport it to the arterial smooth muscle. Unlike release by the endothelium, a stress-stimulated sympathetic discharge would potentially accelerate degradation of the wall matrix by plasmin. To assess whether sympathetic axons are the principal source of acute stress-induced arterial release of t-PA, we compared the output from small densely innervated and large sparsely innervated isolated artery segments before and after sympathetic stimulation, and after ablations. Following phenylephrine infusion densely-innervated microvessels in uveal eyecups were released over 60-fold greater amounts of active t-PA per milligram than the sparsely innervated aorta; and ten-fold more than carotid artery segments. Mesenteric artery release was 4.8-fold greater than release by the carotid artery. In vivo, uveal release of t-PA increased more than three-fold within one minute following superior cervical sympathetic ganglion electrical stimulation, and after phenylephrine, or nicotine infusions of the anterior chamber. Circulating levels of t-PA fell 70% following chemical sympathectomy. We propose that sympathetic nerves are the primary source of stress-induced release of t-PA into and from the densely innervated resistance arteries and arterioles, where dysregulated plasmin-induced proteolysis could damage the wall matrix.

Life events and acute cardiovascular reactions to mental stress: a cohort study

OBJECTIVE

This study addressed the issue of whether frequent exposure to life events is associated with aggravation or blunting of cardiovascular reactions to acute mental stress.

METHODS

In a substantial cohort of 585 healthy young adults, systolic and diastolic blood pressure and pulse rate were recorded at rest and in response to a mental arithmetic stress task. Participants indicated, from a list of 50 events, those they had experienced in the last year.

RESULTS

There was an overall association between life events and blunted cardiovascular reactivity that was driven by variations in the frequency of exposure to desirable events. The total number of events and the number of personal events were negatively associated with systolic blood pressure and pulse rate reactions to acute stress, whereas the number of work-related events was negatively associated with diastolic blood pressure and pulse rate reactivity. The negative association between total events and systolic blood pressure reactivity was stronger for women than men, whereas men exposed to frequent undesirable events showed enhanced diastolic blood pressure reactivity. The blunting of pulse rate reactivity associated with frequent personal life events was evident particularly for those who had a relatively large number of close friends.

CONCLUSION

The nature and extent of the association between life events exposure and stress reactivity in young adults depends on the valence of the events together with the sex of the individual and their social network size.

Life events and hemodynamic stress reactivity in the middle-aged and elderly

Recent versions of the reactivity hypothesis, which consider it to be the product of stress exposure and exaggerated hemodynamic reactions to stress that confers cardiovascular disease risk, assume that reactivity is independent of the experience of stressful life events. This assumption was tested in two substantial cohorts, one middle-aged and one elderly. Participants had to indicate from a list of major stressful life events up to six they had experienced in the previous 2 years. They were also asked to rate how disruptive and stressful they were, at the time of occurrence and now. Blood pressure and pulse rate were measured at rest and in response to acute mental stress. Those who rated the events as highly disruptive at the time of exposure and now exhibited blunted systolic blood pressure reactions to acute stress. The present results suggest that acute stress reactivity may not be independent of stressful life events experience.

Cardiovascular reactivity in a simulated job interview: The role of gender role self-concept

This study investigated the relation of gender role self-concept (G-SC) to cardiovascular and emotional reactions to an ecologically relevant stressor in a sample of graduating male and female university students. Thirty-seven men and 37 women completed the Personal Attribute Questionnaire and worked on four tasks designed to reflect common features of a job interview. Blood pressure and heart rate were measured at baseline, during, and after each task; subjective stress was measured at baseline and after each task. Subjective and objective stress scores were averaged across tasks and analyzed by sex and G-SC (i.e., instrumentality, expressiveness). Results indicated that women as a group demonstrated greater emotional reactivity, but did not differ in their physiological reactions when compared to men. Regardless of sex, participants' instrumentality scores contributed significantly to the variation in subjective stress response: those scoring high on instrumentality reported less stress, but evidenced greater blood pressure reactivity than those scoring low on instrumentality. These results suggest that gender roles, particularly an instrumental self-concept, may play an important role in both subjective and objective reactions to an ecologically relevant stressor.

Is there a functional neural correlate of individual differences in cardiovascular reactivity?

OBJECTIVE

The present study tested whether individuals who differ in the magnitude of their blood pressure reactions to a behavioral stressor also differ in their stressor-induced patterns of functional neural activation.

METHODS

Sixteen participants (7 men, 9 women aged 47 to 72 years) were classified as high (n = 8) or low (n = 8) blood pressure reactors by the magnitude and temporal consistency of their systolic blood pressure (SBP) reaction to a Stroop color-word interference stressor. Both high and low SBP reactors completed this Stroop stressor while their task-related changes in blood pressure and functional neural activity were assessed in a blocked functional magnetic resonance imaging design.

RESULTS

In both high and low SBP reactors, the Stroop-stressor engaged the anterior cingulate, orbitofrontal, insular, posterior parietal, and the dorsolateral prefrontal regions of the cortex, the thalamus, and the cerebellum. Compared with low reactors, however, high reactors not only showed a larger magnitude increase in SBP to the Stroop stressor, but also an increased activation of the posterior cingulate cortex.

CONCLUSION

A behavioral stressor that is used widely in cardiovascular reactivity research, the Stroop stressor, engages brain systems that are thought to support both stressor processing and cardiovascular reactivity. Increased activation of the posterior cingulate, a brain region implicated in vigilance to the environment and evaluative emotional processes, may be a functional neural correlate of an individual's tendency to show large-magnitude (exaggerated) blood pressure reactions to behavioral stressors.

Psychological Stress Tasks in the Prediction of Blood Pressure Level and Need for Antihypertensive Medication: 9-12 Years of Follow-Up

Increased blood pressure (BP) reactivity to subtypes of psychological stimuli may differentially predict the development of future BP elevation or hypertension. The authors present the 9-12-year follow-up results of 82 (86%) of 95 male participants with different BP levels. They were healthy, untreated, and age-matched volunteers from a routine health checkup carried out on all 35-, 40-, and 45-year-olds from a medium-sized city. Intra-arterial systolic blood pressure (SBP) during the psychological tasks improved the prediction of future casual SBP and noninvasive 24-hr ambulatory SBP compared with predictions from casual diagnostic measurements. Diastolic blood pressure (DBP) was very useful when added to casual DBP in predicting the need for antihypertensive medication. Reactivity to active tasks especially predicts the need for antihypertensive medication.

Exaggerated Blood Pressure Responses During Mental Stress Are Prospectively Related to Enhanced Carotid Atherosclerosis in Middle-Aged Finnish Men

Background— Hemodynamic reactions to mental stress may contribute to atherosclerosis. We previously observed cross-sectional relationships between blood pressure reactions to a standardized stress battery and carotid intima-media thickness (IMT) in the Kuopio Ischemic Heart Disease (KIHD) study. These are the first prospective results on this relationship.

Methods and Results— Men from 4 age cohorts (42 to 60 years old at study onset) were challenged with a standardized mental stress battery, and heart rate and blood pressure reactions were assessed. Ultrasound measures of common carotid IMT were collected at this time and 7 years later as noninvasive markers of atherosclerosis. Data were collected from a sample of 756 men at both times. Systolic blood pressure reactions to mental stress at study onset were positively related to mean carotid IMT 7 years later (β=0.035, P =0.001, by blood pressure quartile, IMT=0.91, 0.93, 0.96, 1.00 mm) and to the progression of IMT (β=0.020, P =0.006, by blood pressure quartile, ΔIMT=0.08, 0.09, 0.11, 0.11 mm). Similar significant relations were shown for maximal IMT and plaque height. Diastolic blood pressure responses were less strongly related to carotid IMT than were systolic responses. Heart-rate responses were unrelated. Adjustment for standard risk factors did not substantially reduce the relation between systolic blood pressure reactivity and the progression of mean carotid IMT (standardized β=0.059, P =0.026), maximal carotid IMT (standardized β=0.084, P =0.006), or plaque height (standardized β=0.093, P =0.008).

Conclusions— The degree of systolic blood pressure reactivity to mental challenge is prospectively related to carotid IMT in middle-aged and older men, independent of known risk factors.

Functional allelic heterogeneity and pleiotropy of a repeat polymorphism in tyrosine hydroxylase: prediction of catecholamines and response to stress in twins

Tyrosine hydroxylase, the rate-limiting enzyme in catecholamine biosynthesis, has a common tetranucleotide repeat polymorphism, (TCAT)(n). We asked whether variation at (TCAT)(n) may influence the autonomic nervous system and its response to environmental stress. To understand the role of heredity in such traits, we turned to a human twin study design. Both biochemical and physiological autonomic traits displayed substantial heritability (h(2)), up to h(2) = 56.8 +/- 7.5% (P < 0.0001) for norepinephrine secretion, and h(2) = 61 +/- 6% (P < 0.001) for heart rate. Common (TCAT)(n) alleles, particularly (TCAT)(6) and (TCAT)(10i), predicted such traits (including catecholamine secretion, as well as basal and poststress heart rate) in allele copy number dose-dependent fashion, although in directionally opposite ways, indicating functional allelic heterogeneity. (TCAT)(n) diploid genotypes (e.g., [TCAT](6)/[TCAT](10i)) predicted the same physiological traits but with increased explanatory power for trait variation (in contrast to allele copy number). Multivariate ANOVA documented genetic pleiotropy: joint effects of the (TCAT)(10i) allele on both biochemical (norepinephrine) and physiological (heart rate) traits. (TCAT)(6) allele frequencies were lower in normotensive twins at genetic risk of hypertension, consistent with an effect to protect against later development of hypertension, and suggesting that the traits predicted by these variants in still-normotensive subjects are early, heritable, "intermediate phenotypes" in the pathogenetic scheme for later development of sustained hypertension. We conclude that common allelic variation within the tyrosine hydroxylase locus exerts a powerful, heritable effect on autonomic control of the circulation and that such variation may have implications in later development of cardiovascular disease traits such as hypertension.

Heart rate response is longer after negative emotions than after positive emotions

Summary. Recent ambulatory findings showing comparable cardiovascular effects of positive and negative emotions are not consistent with the assumed etiological role of negative affect in stress-related diseases. We tested the hypothesis that regardless of initial reactivity, responses associated with negative emotions would be prolonged compared to responses associated with positive emotions. During 8 h, 33 healthy subjects from a general population reported their emotional arousal, emotional valence and physical activity and recorded their heart rates (HR) after a beep at each 60th min ('initial HR'; T0), followed by two 'prolonged activation' recordings, respectively 5 min later (T1) and 10 min later (T2). While emotional arousal and activity predicted initial HR, prolonged activation at T1 was solely predicted by emotional valence (negative affect) at T0, independent of emotional recovery. The results lend support to the hypothesis that cardiovascular activation after negative emotions last longer than after positive emotions. This finding is consistent with the view that prolonged activation, and not so much reactivity, might be a mechanism underlying the etiological role of negative emotions ('stress') in somatic disease. Perseverative cognition (worry, rumination) might be responsible for this prolonged activation.

Applying latent growth curve modeling to the investigation of individual differences in cardiovascular recovery from stress

OBJECTIVE

This paper provides an introduction to latent growth curve (LGC) modeling, a modern method for analyzing data resulting from change processes such as cardiovascular recovery from stress. LGC models are superior to traditional approaches such as repeated measures analysis of variance and simple change scores.

METHODS

The basic principles of LGC modeling are introduced and applied to data from 167 men and women whose systolic blood pressure was assessed before, during, and after the cold pressor and evaluated speech stressors and who had completed the Cook-Medley Hostility Inventory.

RESULTS

The LGC models revealed that systolic blood pressure recovery follows a different nonlinear trajectory after speech relative to the cold pressor. The difference resulted not from the initial decline at the completion of the stressor, but from higher levels at the end of the stressor and slower rate of change in decline for the speech. Hostility predicted the trajectory for speech but not for cold pressor. This relationship did not differ as a function of gender, although men had larger systolic blood pressure responses than women to both stressors.

CONCLUSIONS

LGC modeling yields an understanding of the processes and predictors of change that is not attainable through traditional statistical methods. Although our application concerns cardiovascular recovery from stress, LGC modeling has many other potential applications in psychosomatic research.

Effects of acute stress, relaxation, and a neurogenic inflammatory stimulus on interleukin-6 in humans

Effects of three experimental manipulations: mental stress, relaxation, and a nociceptive inflammatory stimulus, capsaicin, on levels of interleukin-6 (IL-6) were examined. Fifty subjects were pre-trained in relaxation and then randomized to a stress (Stroop test), relaxation (tape), or control (video) manipulation. Subjects participated in an evening reactivity session including 20 min of stress, relaxation, or control followed by a capsaicin injection in the forearm. Cardiovascular variables and levels of IL-6 were measured before and after the manipulation, and at regular intervals up to 60 min post-capsaicin. Group assignment did not differentially affect change in IL-6 over time, either before or after capsaicin. Small but significant increases in IL-6 were seen at 60 min post-capsaicin. These findings suggest that an acute stress manipulation does not modulate IL-6 within this time frame. Although IL-6 did increase following a neurogenic inflammatory stimulus, it did so subsequent to the maximum flare, suggesting that flare mechanisms are independent of IL-6.

Parental history of hypertension and coping responses predict blood pressure changes in black college volunteers undergoing a speaking task about perceptions of racism

OBJECTIVE

This investigation explored the relationship of coping responses and parental history of hypertension to task-induced blood pressure changes.

MATERIALS AND METHODS

The sample consisted of 215 black college student volunteers (median age = 25.95 y). During the speaking task, participants responded to standardized questions about perceptions of intra-ethnic and inter-ethnic group racism. Systolic blood pressure and diastolic blood pressure were measured via an automated blood pressure monitor. Usual ways of coping with intra-ethnic group racism were assessed with the COPE Scale, and parental history of hypertension (PHH) was self-reported by participants.

RESULTS

Findings from the final step of hierarchical general linear models indicated that the main effect of emotion-focused coping was negatively associated with diastolic blood pressure (p = 0.02) and systolic blood pressure (p = 0.002) changes. Further, these analyses revealed that PHH interacted: (1) with the coping responses of planning (p = 0.007) and denial (p = 0.002) to predict changes in systolic blood pressure and (2) with the planning coping response to predict diastolic blood pressure changes (p = 0.02). The direction of these effects indicated that among participants who were high in these coping responses, participants who also had a positive PHH had larger blood pressure changes. Regression analyses also revealed that PHH interacted with the cognitive coping response (p = 0.01) to predict changes in systolic blood pressure. The direction of this effect indicated that among participants who were low in this coping response, participants who also had a positive PHH had larger systolic blood pressure changes.

CONCLUSION

This study highlights the importance of examining the joint contribution of biological and psychosocial parameters to blood pressure reactivity in blacks.

Psychophysiological reactivity: mechanisms and pathways to cardiovascular disease

OBJECTIVE

This article examines possible sources of heightened psychophysiological reactivity in relation to risk for hypertension and coronary artery disease. The idea that exaggerated reactions to psychological stress may predict greater risk for future disease has some support in the psychosomatic and behavioral medicine literature. However, the pathways by which exaggerated reactivity could arise in a given person and the implications of different sources of reactivity for potential disease relationships have received little attention.

METHODS

This topic is approached through a selective literature review and by means of a neurophysiologically based model of individual differences in physiological reactivity. Temperament characteristics, cognitive processes, neurophysiology, and peripheral physiology are used to indicate three levels that could contribute to exaggerated physiological reactivity.

RESULTS

At the top level in the model, activity of the frontal cortex and limbic system establish cognitive-emotional sources of activation that may underlie exaggerated physiological reactivity. In the absence of these influences, large responses may be more likely when exaggerated subcortical response tendencies are present via the hypothalamus or brain stem. Finally, peripheral alterations may account for larger reactions in persons who have otherwise normal emotional and hypothalamic and brainstem response tendencies. Cognitive-emotional and hypothalamic-brainstem sources of altered reactivity may cause or aggravate disease. In contrast, altered peripheral reactivity suggests that a pathophysiologic process may be present, serving as a marker for disease.

CONCLUSIONS

These three levels of analysis allow for organization of existing data in the area of cardiovascular reactivity and for planning future studies in a hypothesis-building framework.

Cardiovascular reactivity: status quo and a research agenda for the new millennium

This article introduces a series of articles that assess the present status of the cardiovascular reactivity construct as well as the progress that has been made since a critical review of the reactivity literature by Pickering and Gerin was published in 1990.