Generalization of cardiovascular response: supportive evidence for the reactivity hypothesis

Perfluoroalkyl substances (PFAS) and lead (Pb) as "cardiovascular disruptors" in 9-11-year-old children living in Syracuse, New York, United States

OBJECTIVE

Per- and polyfluoro-alkyl substances (PFAS) and lead (Pb) are ubiquitous environmental toxicants with apparent impact on cardiovascular disease (CVD) risk. As one possible mechanism for this increased risk, we have previously demonstrated an association between Pb exposure and heightened cardiovascular reactivity to acute psychological stress, a CVD risk factor. The present study expands this approach and considers both PFAS and Pb exposures (and the possible interaction).

METHODS

We assessed 14 serum PFAS and whole blood Pb concentrations in a sample of 9-11 year-old children (N = 291; 43.2% White, 56.8% Black; 53.5% female). We measured cardiovascular functioning at rest and during psychological stress as well as multiple indicators of subclinical CVD including resting blood pressure (BP), carotid-femoral pulse wave velocity (cfPWV), carotid intima-media thickness (cIMT), and left ventricular mass (LVM). Data analysis included general linear modeling as well as a non-parametric approach to study metal mixtures, specifically Bayesian Kernel Machine Regression (BKMR).

RESULTS

Significant interactions between different PFAS and with Pb suggest the importance of considering toxicant mixtures when assessing potential disruption of the cardiovascular system. The pattern of findings suggests that greater "vascular reactivity" (elevated BP and vascular resistance during acute psychological stress) was associated with higher concentrations of perfluorononanoic acid (PFNA), perfluorohexane sulfonate (PFHxS), and Pb, but only when perfluorooctanoic acid (PFOA) was concurrently elevated. With respect to subclinical outcomes, increasing perfluorodecanoic acid (PFDA) was associated with greater cIMT (β = 0.21, p = 0.010).

CONCLUSION

To our knowledge this is the first study to consider how PFAS exposures might affect cardiovascular functioning and subclinical disease. Although a complex pattern of associations emerged, it does appear that PFAS and Pb can be classified as "cardiovascular disruptors" in children. Further research is needed to replicate these novel findings and determine whether these disruptions produce future cardiovascular disease.

Socioeconomic status and hemodynamic recovery from mental stress

We assessed the changes in cardiac index and total peripheral resistance underlying blood pressure reactions and recovery from acute mental stress, in relation to socioeconomic status. A sample of 200 men and women aged 47-59 years was divided on the basis of occupation into higher, intermediate, and lower socioeconomic status groups. Blood pressure was monitored using the Portapres, and hemodynamic measures were derived by Modelflow processing of the arterial pressure waveform. Blood pressure increases during two stressful behavioral tasks were sustained by increases in cardiac index and total peripheral resistance. During the 45-min posttask recovery period, cardiac index fell below baseline levels, whereas peripheral resistance remained elevated. Peripheral resistance changes during recovery varied with socioeconomic status and blood pressure stress reactivity, with particularly high levels in reactive low status participants. Results are consistent with the hypothesis that disturbances of stress-related autonomic processes are relevant to the social gradient in cardiovascular disease risk.

Prostaglandin modulation of venoconstriction to physiological stress in normals and heart failure patients

Prostaglandins released from blood vessels modulate vascular tone, and inhibition of their production during exogenous infusions of catecholamines causes increased venoconstriction. To determine the influence of prostaglandin production on venoconstriction during physiological stimuli known to cause sympathetic activation, and to assess its importance in chronic heart failure (CHF), we studied 11 normal subjects (62 +/- 4 yr) and 14 patients with CHF (64 +/- 2 yr, left ventricular ejection fraction 23 +/- 1%, New York Heart Association classes II and III) (means +/- SE). Dorsal hand vein distension was measured during mental arithmetic (MA), cold pressor test (CPT), and lower body negative pressure (LBNP; -10 and -40 mmHg), with saline infusion in one hand and local indomethacin (cyclooxygenase inhibitor) infusion (3 microg/min) in the other. Acetylcholine (0.01-1 nmol/min) dilated veins preconstricted with PGF(2alpha) in normals but, consistent with endothelial dysfunction, barely did so in CHF patients (P = 0.001). Nonendothelial venodilation to sodium nitroprusside (0.3-10 nmol/min) was not different between normals and CHF patients. Resting venous norepinephrine levels were higher in CHF patients (2,812 +/- 420 pmol/l) than normals (1,418 +/- 145 pmol/l, P = 0.007). In normals, indomethacin caused increased venoconstriction to MA (from 4.9 +/- 1.5 to 19.2 +/- 4.5%, P = 0.022) and CPT (from 2.9 +/- 3.8 to 17.6 +/- 4.2%, P = 0.007). In CHF, indomethacin caused increased venoconstriction to MA (from 6.6 +/- 3.9% to 19.0 +/- 4.5%, P = 0.014), CPT (from 9.6 +/- 2.1% to 20.1 +/- 3.7%, P = 0.001), and -40 mmHg LBNP (from 10.7 +/- 3.0% to 23.2 +/- 3.8%, P = 0.041). Control responses for all tests were not different between normals and CHF patients. The effects of indomethacin on venoconstriction to MA and CPT were not different between normals and CHF patients, but venoconstriction to -40 mmHg LBNP was accentuated in CHF patients (P = 0.036). Inhibition of prostaglandins by indomethacin significantly enhances hand vein constriction to physiological stimuli in both normals and CHF patients, although a differential effect exists for LBNP.

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.

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.

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

Cardiovascular responses were examined in a community sample of 128 subjects, comprised of 58 African American and 70 Caucasian American men and women. Subjects completed a battery of laboratory stressors including mental arithmetic, reaction time, a speech task, and the cold pressor test. In addition to systolic and diastolic blood pressures, the underlying hemodynamic parameters of cardiac output and total peripheral resistance were assessed. In order to explore intertask consistency of response in both ethnic groups and both gender groups, correlational analyses were conducted separately for each group. For the psychological tasks, unanimously significant coefficients were observed. Intertask consistency between psychological tasks and the cold pressor was also considerable, but was somewhat less impressive (particularly for blood pressure) than that observed among the psychological tasks themselves. With regard to hemodynamic responses, cardiac output and total peripheral resistance demonstrated intertask consistency equal to, if not greater than, that shown by systolic and diastolic blood pressure, this consistency being evident for each ethnic and each gender group.

Consistency of children's hemodynamic responses to laboratory stressors

Hemodynamic responses to three standard laboratory stressors (i.e., postural change, video game, forehead cold) were evaluated in 341 children (170 males) who had a mean age of 11.2 +/- 2.6 years. Inter-task consistency was evaluated for five physiological parameters for all stressor pairings. Evidence of consistency in systolic and diastolic blood pressure, heart rate, cardiac output, and total peripheral resistance responses to all three stressors was observed. The highest and most consistent correlations across stressors were observed for cardiac output and total peripheral resistance responses. The need for clarification in the categorization of laboratory stressors used to measure reactivity is discussed.

Postural stability of hemodynamic responses during mental challenge

Laboratory stress testing is typically conducted while subjects are seated, whereas real-life stressors may often be encountered while standing. The present study of 20 healthy young men evaluated blood pressure and underlying hemodynamic adjustments to a standardized mental arithmetic task performed twice while seated and twice while standing. Blood pressure increased during mental arithmetic in both postures, but the underlying hemodynamic determinants of the pressor responses were different for the two postures. Augmented cardiac output was responsible for increasing blood pressure during seated task performance, whereas increased vascular resistance was the mechanism for the pressor response to the task performed while standing. Blood pressure and hemodynamic responses were reproducible subject characteristics for a given posture; test-retest correlations were significant for all cardiovascular measures. However, seated blood pressures responses were not significantly correlated with standing blood pressure responses. In contrast, significant between-posture correlations were found for cardiac output and vascular resistance responses. This preliminary evidence of postural stability of the hemodynamic determinants of blood pressure responses during stress is consistent with growing evidence that hemodynamic response tendencies are robust characteristics of reactivity. Ambulatory monitoring of hemodynamic response patterns during real-life stress may reveal more idiosyncratic profiles of stress reactivity than are displayed by blood pressure responses alone.

Temporal stability of task-induced cardiovascular, adrenergic, and psychological responses: the effects of race and hypertension

This study examined the test-retest reliability of task-induced responses of blood pressure, heart rate, norepinephrine, epinephrine, anger, and anxiety in 98 black and white normotensive and hypertensive individuals. Subjects completed three laboratory tasks (standing, mental arithmetic, and cold pressor) on two occasions 10 days apart. For all subjects, all baseline and test-retest correlation coefficients were significant (rs = .23-.71; median = .58). Baseline-adjusted (residual scores) reactivity test-retest correlation coefficients were consistently smaller (rs = .02-.55; median = .36). In contrast to the white hypertensives, white normotensives, and black normotensives, the black hypertensives showed no significant baseline-adjusted test-retest correlation coefficients (rs = -.21-.40; median = .12). Epinephrine responses revealed a significant session by race interaction; blacks had 20% higher mean values and whites had 10% lower mean values upon retesting. The data suggest that race and hypertension may interact to affect the temporal stability of task-induced responses to stressors.