Race and cardiovascular reactivity. A replication

Children's, Adolescents', and Young Adults' Heart Rate Reactivity to, and Recovery from, a Brief Psychological Stressor

Heart rate reactivity to a 2 minute mental arithmetic stressor delivered under timed and competitive conditions and graded for age-related difficulty was collected on 148 males and 153 females grouped into five age cohorts ranging from 7 to 20 years. Data on resting heart rate, heart rate during the stressor period, and post-stressor recovery showed significant sex (females had higher heart rates) and age effects (there was a general decrease in heart rate with age). There were no significant interactions between age and sex. Mean heart rate reactivity also showed significant variation with age, but no significant differences between males and females, nor any significant interaction between age and sex. The age effect for heart rate reactivity appeared to be a result of the oldest age group having significantly greater increases in heart rate than all other age groups.

Effects of Maternal Cortisol during Pregnancy on Children's Blood Pressure Responses

BACKGROUND

It is well established that birth weight has an effect on subsequent blood pressure. Predominantly experimental studies have also reported effects of altered corticosteroid levels on subsequent cardiovascular responses. In the current study, we have examined the effects of both birth weight and maternal cortisol levels in a cohort of mothers and their pre-adolescent children.

PROCEDURE

A total of 216 women and their 7- to 9-year-old children comprised the cohort. The women had been assessed for plasma cortisol during the first (n = 71), second (n = 72) and third (n = 73) trimester. Maternal cortisol had been measured on a fasting sample taken between 9 and 11 a.m. The children's blood pressure and heart rate were recorded in the resting state, in response to a 10-min video game stress challenge and during recovery. Resting values, incremental responses to stress and recovery were evaluated.

OBSERVATION

Maternal cortisol levels increased with duration of pregnancy. There were inverse correlations between birth weight and all haemodynamic measures. The positive associations between maternal cortisol and children's haemodynamic measures were most evident in the first and second trimesters. Birth weight was inversely related to maternal cortisol. In multiple regression analyses, the effects of maternal cortisol were more consistent than those of birth weight.

CONCLUSION

Both birth weight and maternal cortisol are predictive of children's resting and stress-modulated haemodynamic measures. The effects of birth weight may partly mediate the effects of maternal cortisol.

Effects of maternal anxiety and depression during pregnancy in Chinese women on children's heart rate and blood pressure response to stress

Psychological disturbances, including anxiety and depression, are common during human pregnancy. Our objective was to determine whether these maternal disturbances influence cardiovascular responses of the offspring. The psychological status of 231 pregnant women was determined. Offspring (216) of these women were subsequently exposed to a video challenge stress when aged 7-9 years. Heart rate (HR) and blood pressure (BP) of the children were determined at rest, in response to video stress and during subsequent recovery. Children's resting and stress-induced increases in HR (bpm), systolic (SBP, mm Hg) and diastolic (DBP, mm Hg) BP were all greater in children whose mothers reported anxiety during pregnancy. Values (mean±s.d.) for resting HR, SBP and DBP were 75.15±5.87, 95.37±2.72 and 66.39±4.74 for children whose mothers reported no anxiety and an average of 81.62±6.71, 97.26±2.90 and 68.86±2.82 for children whose mothers reported anxiety at any level. Respective values for stress-induced increments in HR, SBP and DBP were 14.83.±2.14, 16.41±1.97 and 12.72±2.69 for children whose mothers reported no anxiety and 17.95±3.46, 18.74±2.46 and 14.86±2.02 for children whose mothers reported any level of anxiety. Effects of maternal depression were less consistent. The effects of maternal anxiety remained in multivariate analyses, which also included children's birth weight. The results indicate a long-term influence of maternal psychological status during pregnancy on the cardiovascular responses to stress among offspring. These effects may contribute to prenatal influences on subsequent health of the offspring.

Stress response and the adolescent transition: performance versus peer rejection stressors

Little is known about normative variation in stress response over the adolescent transition. This study examined neuroendocrine and cardiovascular responses to performance and peer rejection stressors over the adolescent transition in a normative sample. Participants were 82 healthy children (ages 7-12 years, n = 39, 22 females) and adolescents (ages 13-17, n = 43, 20 females) recruited through community postings. Following a habituation session, participants completed a performance (public speaking, mental arithmetic, mirror tracing) or peer rejection (exclusion challenges) stress session. Salivary cortisol, salivary alpha amylase (sAA), systolic and diastolic blood pressure (SBP, DBP), and heart rate were measured throughout. Adolescents showed significantly greater cortisol, sAA, SBP, and DBP stress response relative to children. Developmental differences were most pronounced in the performance stress session for cortisol and DBP and in the peer rejection session for sAA and SBP. Heightened physiological stress responses in typical adolescents may facilitate adaptation to new challenges of adolescence and adulthood. In high-risk adolescents, this normative shift may tip the balance toward stress response dysregulation associated with depression and other psychopathology. Specificity of physiological response by stressor type highlights the importance of a multisystem approach to the psychobiology of stress and may also have implications for understanding trajectories to psychopathology.

Hypertension in black people: study of specific genotypes and phenotypes will provide a greater understanding of interindividual and interethnic variability in blood pressure regulation than studies based on race

Hypertension is more frequent and more severe in some Black populations. Although many studies have focused on hypertension in black people in an attempt to understand the genetic and environmental factors that regulate blood pressure, this approach has not been productive. Study of the relationship between specific phenotypes and genotypes, both within and across ethnic groups, is more likely to advance our understanding of the regulation of blood pressure than studies focused on race and blood pressure.

The influence of gender and emotional versus instrumental support on cardiovascular reactivity in African-American adolescents

Research suggests that females seek out, prefer, and are more receptive to emotional support (encouragement), and that males seek out, prefer, and are more receptive to instrumental support (problem-solving). Thus, we hypothesized that boys would show lower blood pressure (BP) reactivity in response to instrumental than emotional or no support, and that girls would show lower BP reactivity in response to emotional than instrumental or no support. Forty-eight healthy African-American adolescents (50% males) participated in a role play conflict task and were randomized to receive either emotional, instrumental, or no support (presence only) from a confederate. Boys showed lower systolic blood pressure (SBP) reactivity in the instrumental than in the emotional or no support conditions and lower recovery SBP as compared to boys in the emotional or no support conditions. A similar pattern of results was demonstrated for diastolic blood pressure (DBP) reactivity. Girls, however, did not demonstrate lower BP reactivity in response to emotional as compared to instrumental support. These findings suggest that instrumental and emotional support differentially influence cardiovascular (CV) reactivity in African-American boys versus girls.

Role of cardiovascular reactivity to mental stress in predicting future hypertension

Hypertension (HT) has been known since times immemorial to be one of the major causes of morbidity and mortality. It contributes to atherosclerotic cardiovascular disease, increasing its risk 2-3 times and is also associated with dyslipidemia, insulin resistance, glucose intolerance and obesity (1). The age of onset of hypertension is now earlier than before, making it essential that early detection of people who could be future hypertensives is done. Therefore, cardiovascular reactivity to stress in predicting future hypertension becomes important. In this fast paced age most people are exposed to mental stress which is the most common and prevalent form of stress. Increase in blood pressure (BP) in response to emotional arousal is well known, but support for this hypothesis of reactivity in predicting future hypertension is limited. We are attempting here to put forth a review of the various endeavours done so far to support this hypothesis.

Socioeconomic status and blood pressure reactivity in healthy black adolescents

Adolescents in low-socioeconomic-status environments are more susceptible to illnesses, such as hypertension and cardiovascular diseases. This study examined the influence of both neighborhood- and family-level socioeconomic status (SES) on blood pressure (BP) reactivity in a healthy sample of 76 black adolescents. It was hypothesized that a higher level of parental education and/or income would reduce the elevated BP reactivity associated with living in poorer neighborhoods. Census-derived data were obtained using each participant's address. Neighborhood level of SES was based on percentage of households below the poverty line, female-headed households, owner-occupied housing, percentage vacant housing, and average number of persons per household. Family level of SES was based on self-reported level of parental education and annual family income. Adolescents participated in a competitive video game to establish their BP reactivity scores. As predicted, adolescents who lived in poorer neighborhoods had lower diastolic BPs if their parents were more (versus less) educated (P<0.05; 7+/-8 versus 13+/-6 mm Hg). Adolescents who lived in poorer neighborhoods also had significantly lower diastolic BP reactivity (P<0.05) if their family had a higher (versus lower) annual income (7+/-7 versus 12+/-8 mm Hg). These data are the first to demonstrate the buffering effect of family SES on the negative health consequences of living in low-SES neighborhoods in healthy black adolescents.

Race and sex differences in cardiovascular recovery from acute stress

To evaluate the effects of race and gender on recovery, i.e. the relative return to baseline after a stress challenge, cardiovascular and catecholamine measures were examined before, during and after two standardized laboratory stressors (a speaking and a mirror tracing task) in a group of 85 Black and White men and women (mean age 35.6 years, range 20 to 52). For the speech task, White men showed the least systolic (p < 0.025) and diastolic (p < 0.05) blood pressure recovery as compared to Black men and women. For the mirror star tracing task, total peripheral resistance (p < 0.03) recovery was least for Whites as compared to Blacks and heart rate (p < 0.04) recovery was least for White women as compared to Black women and men. There were no significant group effects in terms of catecholamine recovery from either task. The findings extend prior studies on race and gender by suggesting that these same characteristics affect recovery from stressors.

Hereditary intermediate phenotypes in African American hypertension

OBJECTIVE

Essential hypertension is a heterogeneous and multifactorial disorder and is at least twice as frequent among African Americans as in the general population. Inheritance of high blood pressure is complex, with the gene(s) responsible for hypertension still remaining elusive. A useful strategy for investigating the heritability of hypertension is to evaluate 'intermediate phenotypes'--simple Mendelian or monogenic traits that are associated with hypertension. These intermediate steps may identify potential pathophysiological factors that antedate the development of high blood pressure and suggest candidate genes. We are attempting to identify and characterize several such intermediate phenotypes, in particular as these might apply to hypertension in African Americans.

METHODS

We studied several physiological and biochemical candidate intermediate phenotypes in untreated black and white patients with essential hypertension and in their normotensive counterparts stratified by genetic risk of hypertension.

RESULTS AND CONCLUSIONS

Promising intermediate phenotypes, which may be useful for studies in African American families, include baroreceptor sensitivity to low and high pressure stimuli, cold pressor test responses, and biochemical markers such as plasma chromogranin A, dopamine-beta-hydroxylase and urinary kallikrein excretion. Identification of genes involved in complex traits such as hypertension may be facilitated by the intermediate phenotype approach, combined with recent advances in quantitative genetics and linkage mapping. Further studies are needed to pinpoint the nature of genes in African American hypertension.

Consistency of ethnic differences in children's pressor reactivity. 1987 to 1992

In this prospective investigation, all children enrolled in the public third-grade classrooms of an entire county (n = 474) had blood pressure measured both at rest and during a stressful television video game. Examinations were repeated in 4 subsequent years when cohort children as well as newly enrolled children were in grades 4, 5, 7, and 8. Both cross-sectional and longitudinal analyses indicated that black children demonstrated significantly greater systolic and diastolic pressor reactivity than white children. These data suggest that ethnic differences in children's pressor reactivity presage ethnic differences in adulthood hypertension.

Racial aspects of blood pressure in children and adolescents

The incidence, prevalence, and severity of essential hypertension are higher in minority adult populations, especially black Americans. Studies have not uniformly shown that black children and adolescents have higher blood pressure values than whites of the same age. The goal of this article is to review data available comparing minority and white populations. A section discussing studies addressing racial differences in related topics is included to demonstrate the existing fields of research that may not be familiar to the general pediatrician.

Ethnicity, pressor reactivity, and children's blood pressure. Five years of observations

During the 5 years of this investigation, resting blood pressure and pressor reactivity were measured in 292 white children and 46 black children in 1987, 1988, 1989, and 1991. In 1987, all children were in the third grade; in 1991, the children were in the seventh grade. Reactivity was assessed with a standardized psychological stressor, a television video game. Children displayed significant stability of absolute blood pressure and heart rate reactivity between grades 3 and 7. At all examinations, black children demonstrated blood pressure reactivity that was significantly greater in magnitude (both absolute level and change from resting measurements) than that of white children. Black children exhibited significantly greater heart rate reactivity only when defined as change from the resting measurements; absolute levels of heart rate reactivity were comparable for blacks and whites. For black children, blood pressure reactivity in 1987 was the strongest predictor of resting blood pressure (both systolic and diastolic) in 1991. Among white children, resting blood pressure was the strongest predictor of future resting blood pressure. Further research is needed to determine if ethnic differences in children's pressor reactivity are associated with ethnic differences in the prevalence of hypertension.

Myocardial and peripheral vascular responses to behavioral challenges and their stability in black and white Americans

The purpose of this study was to assess the short term stability of myocardial and peripheral vascular responses to behavioral challenges, and to compare the response patterns of Black and White men. Blood pressure and heart rate, as well as stroke volume, cardiac output, total peripheral resistance, and systolic time interval measures derived from the impedance cardiogram were obtained in 12 Black and 12 White men. These measures were taken prior to and during an evaluative speech stressor, a mirror star tracing task, and a forehead cold pressor test presented during two laboratory sessions scheduled two weeks apart. In general, total peripheral resistance and impedance-derived baseline measures showed acceptable reproducibility (G greater than .85). With a few exceptions, adequate reliability was also demonstrated for change (delta) scores. All tasks raised blood pressure responses above resting levels. Blacks demonstrated significantly greater increases in total peripheral resistance responses across tasks. Whites but not Blacks also revealed increases above baseline in cardiac output and contractility as estimated by the Heather Index. These findings are consistent with the view that Blacks show greater vascular responsiveness than Whites across a variety of tasks, but reveal less myocardial responsiveness.

Comparison of blood lipids and blood pressure in black and white collegiate male athletes

Blood lipids, lipoproteins, and blood pressure (BP) were examined in 74 black and 93 white male NCAA Division I-A collegiate football athletes. Subjects were involved in resistance training and anaerobic running and all ate at the same training table. All measurements were done in the morning following a 12 hour fast. No significant differences were found in mean systolic (128 mm Hg) or diastolic (77 mm Hg) BPs. Blacks and whites were similar in age, height, weight, V̇O_2max estimated from a 12 minute run test, total serum cholesterol, and low-density lipoprotein cholesterol (LDL-C). However, the black athletes had significantly (P < 0.01) lower serum triglycerides, total cholesterol to HDL-C ratio, and higher high-density lipoprotein cholesterol (HDL-C) compared to whites. In a subgroup of 34 subjects, there were no differences in dietary fat, carbohydrate, cholesterol, sodium, potassium, calcium, or fiber intake. These data suggest a race-related difference in some blood lipids-lipoproteins without a concomitant difference in BP within a group of young adult male athletes.

Whether to measure change from baseline or absolute level in studies of children's cardiovascular reactivity: a two-year follow-up

Blood pressure and heart rate were measured at rest and during a television video game in 399 healthy children. At the first assessment, children were in third grade and at the 2-year follow-up, they were in fifth grade. Children were classified according to race (black/white), gender (boy/girl), body mass index (light/heavy), and video game performance (low score/high score). Correlational analysis indicated that irrespective of the classification variable, absolute reactivity values, e.g., a heart rate of 110 bpm, tended to be more stable than change reactivity values, e.g., a heart rate change of 10 bpm. The greater stability of absolute values was most pronounced with systolic blood pressure. Absolute values were at least as stable as resting values and frequently demonstrated greater stability. Mean and maximal reactivities were correlated comparably. We conclude that children's reactivity is a stable characteristic and that, unless indicated by a priori hypotheses, the use of absolute values is preferable to the use of change values.

Children's cardiovascular reactivity: stability of racial differences and relation to subsequent blood pressure over a one-year period

After measuring blood pressure and heart rate at rest and during a video game procedure in 477 children enrolled in 3rd grade, 434 (91%) children had these measurements repeated a year later in 4th grade. Black children demonstrated greater blood pressure and heart rate reactivity than White children in both years, and an increase in heart rate reactivity from 3rd to 4th grade. Gender effects were inconsistent. Systolic and diastolic blood pressures during the video game were more highly correlated from year-to-year than were the resting measures. Regression analysis indicated that systolic reactivity was significantly related to subsequent systolic pressure at rest, particularly among Black girls. Diastolic reactivity was associated with subsequent resting diastolic pressure only among White children. Associations between reactivity and future blood pressure were independent of initial resting blood pressure. This study suggests that cardiovascular reactivity to psychological stress may be one important factor in future level of blood pressure and that the increased heart rate reactivity of Black children may be associated with the prevalence of hypertension among Black adults.

Racial and ethnic modifiers of the salt-blood pressure response

The relation between sodium and blood pressure is a centuries-old question. A substantial body of epidemiological and experimental data has accumulated that strongly implicates NaCl as having a causal role in the genesis of arterial hypertension. Prospective studies that have been performed in diverse populations that have manipulated NaCl exposure by diet or infusion have repeatedly documented an NaCl pressor effect. Further, similar studies in biracial populations have also demonstrated a greater prevalence of "salt sensitivity" in blacks compared with whites. The reasons for this observation are not entirely clear; however, intrinsic or hypertension-induced renal abnormalities that limit natriuretic capacity, reduced Na+,K(+)-ATPase pump activity, other membrane ion transport disturbances, differential exposure to psychological stressors, greater insulin resistance, and dietary factors (reduced Ca+ and K+ intake) have all been suggested as possibly playing a role. Salt sensitivity appears to be a widespread phenomenon. However, it is critically important to determine what factors account for racial differences in salt sensitivity. Moreover, the prevalence of salt sensitivity in the general population is unknown. Current definitions of salt sensitivity are varied and unidirectional. In comparison with bidirectional criteria (blood pressure increase with salt loading and blood pressure decrease with salt restriction), they are probably inadequate to identify salt-sensitive individuals who manifest less extreme blood pressure change after dietary sodium or plasma volume manipulations. More sensitive criteria for diagnosing salt sensitivity will facilitate a better understanding of racial and ethnic differences in the prevalence of salt sensitivity.

Effects of salt, race, and hypertension on reactivity to stressors

Blood pressure and heart rate reactivity to a psychological stressor and to a cold pressor test were examined in a group of 51 normotensive and 37 unmedicated hypertensive men. All were studied twice, once while the participants were maintained on a moderately high salt (200 meq sodium/day) diet and once while the participants were maintained on an extremely low salt (10 meq sodium/day) diet. Dietary salt had no effect on blood pressure or heart rate responses to the two stressors. The systolic and diastolic responses of the white participants to the psychological stressor were greater than those of the black participants (both p less than 0.05); however, there was no difference between blacks and whites in reactivity to the cold pressor challenge. As compared with the normotensive group, the hypertensive group reacted to the psychological stressor with increased responses in systolic blood pressure, diastolic blood pressure, and heart rate (all p less than 0.05). The hypertensive group also hyperresponded in terms of the systolic pressure response to the cold pressor task (p less than 0.05). Plasma norepinephrine and epinephrine responses were not significantly different across the two diets, races, or diagnoses.

Black-white differences in exercise blood pressure. The Lipid Research Clinics Program Prevalence Study

After exclusion of persons on blood pressure medication or with prevalent cardiovascular disease, we studied 83 black and 2,548 white men and 113 black and 1,519 white women 20-69 years old from the Lipid Research Clinics population sample who had performed a standardized treadmill exercise test. Resting systolic and diastolic blood pressures were similar in black and white men, but the diastolic pressure was significantly higher in black than in white women (81.4 vs 77.4 mm Hg). Body weight was higher in black than in white women, and reported physical activity was higher in black than in white men. The proportion of smokers was somewhat higher in blacks than in whites. During the treadmill exercise test with a modified Bruce protocol, mean systolic blood pressure at stage 2 was 174 mm Hg in black men and 166 mm Hg in white men (p less than 0.02), but stage 2 blood pressures did not differ between black and white women (153 and 152 mm Hg, respectively). Even after adjustments were made for levels of baseline characteristics (age, weight, resting systolic blood pressure, smoking, low density lipoprotein cholesterol, physical activity, and alcohol intake), black men responded with a 7-mm Hg higher systolic blood pressure during exercise than white men (p less than 0.01). Another new finding was a highly significant positive association between stage 2 systolic blood pressure and low density lipoprotein cholesterol in men. The findings suggest a higher systemic vascular resistance during exercise in the selected sample of black men, which is consistent with the higher incidence of hypertension in black men.

Autonomic function in hypertension. Are there racial differences?

Previous biochemical assessment of sympathetic nervous system activity including plasma catecholamines, plasma renin activity, and plasma dopamine-beta-hydroxylase levels has suggested racial differences in the contribution of the sympathetic nervous system to the pathogenesis or maintenance of hypertension. We, therefore, performed physiological and pharmacological studies in white and black subjects with essential hypertension and their age-matched normotensive counterparts to assess autonomic and sympathetic nervous system function. One hundred one male subjects (47 white hypertensive, 17 black hypertensive, 22 white normotensive, and 15 black normotensive subjects) were evaluated for baroreceptor reflex sensitivity to low-pressure (amyl nitrite inhalation) and high-pressure (phenylephrine infusion) stimuli; cold pressor test heart rate and blood pressure responses; and blood pressure response to phentolamine alpha-adrenergic blockade. Hypertensive subjects exhibited an increase in resting heart rate, a decrease in baroreceptor reflex sensitivity, and an exaggerated decline in mean arterial pressure in response to phentolamine. These abnormalities were present to a comparable degree in black and white hypertensive subjects. Cold pressor testing revealed greater increases in heart rate in blacks as compared with whites; however, this racial difference was present regardless of blood pressure status, occurring in black normotensive and black hypertensive subjects to a comparable degree. Cold pressor test blood pressure increments were similar in the four groups. We conclude that both white hypertensive and black hypertensive subjects demonstrate similar abnormalities in autonomic and sympathetic nervous system function including blunting of baroreceptor reflex sensitivity and an increased alpha-adrenergic receptor participation in blood pressure maintenance. The results do not suggest major racial differences in autonomic pathogenetic mechanisms in hypertension.