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Psychosomatic Medicine 62:760-767 (2000)
© 2000 American Psychosomatic Society

ORIGINAL ARTICLES

The Effects of Life Events on Cardiovascular Reactivity to Behavioral Stressors As a Function of Socioeconomic Status, Ethnicity, and Sex

Linda Musante, PhD, Frank A. Treiber, PhD, Gaston Kapuku, MD, PhD, Donna Moore, MD, Harry Davis, MS and William B. Strong, MD

From the Georgia Institute for Prevention of Human Diseases and Accidents (F.A.T., G.K., D.M., H.D., W.B.S.), Department of Pediatrics (F.A.T., D.M., W.B.S.), Department of Psychiatry (F.A.T.), and Office of Biostatistics (H.D.), Medical College of Georgia, Augusta, Georgia; and Department of Psychology (L.M.), University of Tampa, Tampa, Florida.

Address reprint requests to: Frank A. Treiber, PhD, Georgia Prevention Institute Bldg., HS 1640, Medical College of Georgia, Augusta, GA 30912. Email: ftreiber{at}mail.mcg.edu


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 METHODS
 RESULTS
 DISCUSSION
 ACKNOWLEDGMENTS
 REFERENCES
 
OBJECTIVE: The purposes of this study were 1) to examine the effects of stressful life events on cardiovascular reactivity to acute laboratory stressors in youth and 2) to determine whether these effects varied as a function of socioeconomic status, ethnicity, and/or sex.

METHODS: Four hundred eighty-three youths (mean age = 16.7 years; 249 Caucasian Americans [126 males, 123 females] and 234 African Americans [109 males, 125 females]) completed the Adolescent Resources Challenge Scale (ARCS), a measure of stressful life events, and underwent two laboratory stressors (a car-driving simulation and the Social Competence Interview) during which blood pressure, heart rate, cardiac output, and total peripheral resistance were assessed.

RESULTS: Youths who reported high levels of stressful life events showed smaller increases in blood pressure (both systolic and diastolic) and heart rate to the car-driving simulation but larger increases in cardiac output in response to the Social Competence Interview than did youths who reported low levels of stressful life events. The effect of stressful life events on cardiovascular reactivity was not moderated by sex, ethnicity, or socioeconomic status. Higher family socioeconomic status was associated with greater blood pressure, heart rate, and cardiac output increases in response to the Social Competence Interview.

CONCLUSIONS: The attenuating effects of stressful life events on cardiovascular reactivity in response to car-driving simulation in youths are consistent with an inoculation effect, whereas the potentiating impact of stressful life events on reactivity observed during the social stressor interview is compatible with a possible cost of coping effect.

Key Words: cardiovascular reactivity • life events, • adolescence • inoculation.

Abbreviations: ARCS = Adolescent Resources Challenges Scale; BMI = body mass index; BP = blood pressure; CO = cardiac output; CV = cardiovascular; CVD = cardiovascular disease; CVR = cardiovascular reactivity; DBP = diastolic blood pressure; HR = heart rate; MAP = mean arterial pressure; SBP = systolic blood pressure; SCI = Social Competence Interview; SES = socioeconomic status; TPR = total peripheral resistance.


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
METHODS
 RESULTS
 DISCUSSION
 ACKNOWLEDGMENTS
 REFERENCES
 
Excessive CVR to stress has been implicated as playing a role in the development of CVD (for review, see Ref. 1). Because the pathogenesis of CVD has its origins in childhood (2), CVR is receiving greater attention in child health research. CVR to acute laboratory stress in youth has been shown to be stable over 1- to 6-year intervals and predictive of later preclinical manifestations of CVD risk, including increased resting BP and left ventricular mass (for review, see Ref. 3). Given that CVR in childhood seems to be a stable individual difference characteristic and to be associated with future indices of CV function, research has begun to focus on potential moderator variables that have been associated with CVR in adults.

The purpose of the present study was to examine the potential moderating effects of frequent and/or ongoing stressful life events on CVR to acute laboratory challenge. Stressful life events can be defined as situational occurrences that most individuals would perceive as threatening, challenging, or requiring effort at adaptation without regard to personal coping resources. Individuals exposed to frequent or ongoing stressful life events may exhibit persistent psychological and physiological changes that may adversely affect health, including development of CVD (4, 5). Stressful life events (eg, family disorganization, parental depression, financial problems, and major illness or death of family member) have been prospectively associated with indices of poor health in child and adolescent populations, including streptococcal infection, respiratory disease, incidence of infectious illness, and major and minor injury (6–9). However, few pediatric studies have examined whether the experience of stressful life events affects the magnitude of CVR to acute laboratory challenge.

Experience with stressful life events could theoretically be predicted to either augment or attenuate responses to acute laboratory challenge. Ongoing or chronic stressful life events may result in an "allostatic load," which culminates in a chronic state of physiological arousal that compromises the individual’s ability to cope with additional stress (5). This model has received some support in studies showing that frequent stressful life experiences have produced persistent physiological arousal that may further escalate during acute stress (10, 11). For instance, youths experiencing allostatic load due to high household density exhibited increased CVR to behavioral and cognitive stress (12). On the other hand, it could be argued that experience with stressful life events "inoculates" the individual against exaggerated physiological increases to transient laboratory challenge. Eysenck (13) cited support for this model with a variety of human and animal studies showing that attenuated responsiveness to stressors as a result of repeated exposure to stress.

Results of adult studies on the relationship between stressful life events and CVR have been inconsistent, with some studies finding positive relationships (14–18) and others finding inverse (18–21) or no relationships (22, 23). To our knowledge, only four published studies have examined this issue in youths, and the results are similarly inconclusive. Providing evidence of inoculation effects, Liang et al. (24) found that self-reports of life stress (ie, family dysfunction and neighborhood crime) were associated with smaller increases in MAP and HR to scanning, forehead cold pressure, and social stressor interview laboratory stressors in a small sample of Caucasian American adolescent boys. Similarly, Boyce and Chesterman (25) found that increases in HR and MAP in response to video, mental arithmetic, and forehead cold pressure stressors were greater in a sample of Caucasian American adolescent boys who reported fewer stressful positive and negative life events (eg, parents’ divorce, death of friend, or relocation). On the other hand, as noted above, Johnston-Brooks et al. (12) found larger increases in BP and HR responses to mental arithmetic and computer game stress among boys who were exposed to chronic environmental stress. In the most comprehensive youth study to date, Matthews et al. (26) obtained measures of CVR by means of impedance cardiography and found that youth who reported a recent important or ongoing stressful life event (eg, living with abusive boyfriend or father arrested for spouse abuse) showed larger increases in DBP and TPR in response to four laboratory stressors (ie, cold pressure, reaction time, mirror tracing, and SCI) than did those without such stress. These results were not moderated by personality traits (ie, hostility, anger, or anxiety) or by sociodemographic variables (ie, sex and ethnicity).

It is difficult to directly compare the results of these four youth studies because they used different laboratory stressors, relatively small samples (with the exception of Ref. 26), and different operational definitions of stressful life events. Given these inconsistent findings, further examination of whether stressful life events augment or attenuate CVR to laboratory stressors is warranted. To investigate this issue, we assessed the frequency of stressful life events in a large sample of youths using an instrument specifically designed for use with youths and examined CVR to two laboratory tasks that provided active behavioral challenge.

In addition to investigating the general impact of stressful life events on CVR to laboratory stress in youth, we examined whether this relationship varied as a function of sex, ethnicity, and/or SES. The potential moderating effects of ethnicity and sex were examined because these sociodemographic variables have been associated with both the magnitude of CVR to acute laboratory stress and CVD risk. African American youths and adults typically show greater vasoconstriction-mediated BP reactivity to laboratory stressors than Caucasian Americans (for reviews, see Refs. 3 and 27). Similarly, by adolescence males typically exhibit greater BP reactivity than females, which seems to be due to greater vasoconstrictive responsivity (27). African Americans and males are also at higher CV risk than their Caucasian and female counterparts (28). However, three of the four youth studies that assessed the relationship between stressful life events and CVR tested only Caucasian American males. Matthews et al. (26) found in subsidiary analyses that neither sex nor ethnicity affected the relationship between self-reported background stress and CVR to a battery of acute stressors, but this issue warrants further investigation.

An extensive body of research has shown a strong inverse relationship between SES and all-cause morbidity and mortality from numerous diseases, including CVD, in adults (for review, see Ref. 29). One explanation for this relationship is that high SES serves to buffer the individual against the psychosocial stressors, discrimination, injustices, and prejudice that are encountered more frequently in lower SES environments (30). In many previous studies ethnicity has been either confounded with SES or statistically controlled for, although separate examination of ethnicity and SES is clearly warranted (31). Anderson and Armstead (32) proposed that the experience of SES might vary by ethnicity; hence, it may influence the nature of the relationship between stressful life events and CVR. Kessler and Neighbors (33) found that African Americans of low SES perceived more stress in their lives than did Caucasian Americans of low SES or other ethnicity/SES groups. With respect to CVR, Armstead et al. (34) found that African American women of low SES were more reactive to a stressful laboratory interview than African American women of high SES. However, SES was unrelated to reactivity in Caucasian American women. Given the potential importance of SES on CVR, separate aggregated measures of neighborhood and family SES were included in the present study, which provided the opportunity to examine the separate and combined effects of ethnicity and SES on CVR as a function of stressful life events.


   METHODS
TOP
 ABSTRACT
 INTRODUCTION
 METHODS
RESULTS
 DISCUSSION
 ACKNOWLEDGMENTS
 REFERENCES
 
Participants
Participants were 483 children and adolescents (mean age = 16.7 years; 249 Caucasian Americans [126 males, 123 females] and 234 African Americans [109 males, 125 females]). Subjects were recruited by means of family CV health history questionnaires obtained from a screening of public school children in kindergarten through grade 8 in Augusta, Georgia. A random sample of youths stratified by ethnicity and sex who had a physician- or hospital record–verified family history of either essential hypertension and/or premature myocardial infarction was recruited to participate in ongoing longitudinal studies of the development of biobehavioral risk factors for CVD (35, 36). This was the seventh annual evaluation, during which measures of lifestyle behaviors, coping styles, CVR to laboratory stressors, and measures of overall CV health were obtained. Ethnicity was based on parental classification as follows: 1) African American if identified as African American, black, or negro and not of Hispanic descent or 2) Caucasian American if identified as Caucasian or white and not of Native American or Hispanic descent. All subjects were overtly healthy and free of any acute or chronic illness based on parental report with the exception of 22 subjects who were taking prescribed medications for asthma, allergies, attention deficit disorder with hyperactivity, type II diabetes mellitus, or birth control.

Hemodynamic Monitoring Equipment
Hemodynamic parameters assessed in the study were SBP, DBP, CO, HR, and TPR. CO was assessed with a noninvasive thoracic electrical bioimpedance monitor (NCCOM-3 model 6, Bo-Med Medical Manufacturing, Ltd., Irvine, CA), which has been validated by simultaneous CO values derived from oximetric measurements using the Fick equation (37) and used in other CVR studies (35, 36, 38). A detailed description of the methodology is available in Braden et al. (37).

Blood pressure was measured with a Dinamap adult/pediatric vital signs monitor (model 1846SX, Critikon, Inc., Tampa, FL). The Dinamap has been validated for use during rest and reactivity evaluations (39). CO was calculated by the NCCOM-3 while the Dinamap was inflating and calculating blood pressures. TPR (ie, [(SBP + 2 x DBP)/3]/CO) was derived by using concurrently measured BP and CO values.

Acute Laboratory Stressors
Subjects participated in a battery of laboratory stressors, which included postural change followed by three stressors (ie, supine cycle ergometry, car-driving simulation, and a social stressor interview) presented in a counterbalanced order. Only the car-driving simulation and social stressor interview data were selected for analyses in the present study because effects of stressful life events would more likely be manifested in response to these behavioral challenges.

Car-Driving Simulation.
The car-driving stressor is described in detail elsewhere (36). Briefly, the stressor is a virtual-reality car-driving simulation ("Need for Speed," Pioneer Productions and Electronic Arts, Inc., Burnaby, Canada) that is played using a Panasonic Real 3DO interactive multiplayer (model FZ-1, Matsushita Electric Corporation of America, Secaucus, NJ) interfaced with a Kaiser Electro-Optics Vision Immersion headset (model 500, Kaiser Aerospace and Electronics Co., Carlsbad, CA).

The head-mount display weighs 24 oz, is fully adjustable for head size and interpupillary distance, and has full-color, multiple active matrix liquid-crystal display (LCDs) containing 360,000 color elements. The Panasonic 3DO system uses a handheld control pad to steer, accelerate, and decelerate the vehicle. The participant drove a Porsche 911 for 10 minutes on a coastal highway with the goal of beating the opponent (a Lamborghini) to the finish line. Real-time visual and auditory stimuli were provided throughout the game. The participant attempted to keep the car on the road without crashing and also monitored a radar detector to avoid being stopped by police. If the game ended prematurely as a result of either crashing three times or receiving three speeding tickets, it was restarted and continued until the 10-minute period ended. Hemodynamic responses were recorded at minutes 1, 3, 5, 7, and 9.

Social Competence Interview.
The SCI (40) is a 10-minute structured interview in which the participant discussed a recently experienced stressful situation chosen from a list of problems concerning school, family, friends, work, money, and/or neighborhood-related stress. The interviewer encouraged the subject to reconstruct the situation, including his or her thoughts and emotions and attempts to resolve the issue. Hemodynamic responses were recorded at minutes 1, 3, 5, 7, and 9.

Assessment of SES
The measures selected to assess neighborhood and family SES have been used in several recent pediatric health studies (41–43). Neighborhood SES was calculated using each subject’s mailing address and 1990 census tract block group data. Data included level of educational attainment, median household income, median monthly rent or mortgage, average home value, percentage below poverty level, percentage unemployed, and percentage of single women with children (the last three measures were reverse scored). All measures were transformed to Z scores, and an average neighborhood SES Z score was calculated.

The Four-Factor Index of Social Status (44) was used as the index of family SES. A score was calculated on the basis of the educational attainment and occupational level of the parents. Scores ranged from 8 to 66, with higher scores representing higher family SES.

Assessment of Life Events
The ARCS is a self-report scale that assesses whether the respondent has experienced any of 35 stressful events during the past 12 months (C. K. Ewart, unpublished). The scale lists stressful life experiences from the neighborhood environment (eg, "I saw or heard people my age or older fighting on the street where I live" and "I saw or heard someone dealing drugs in my neighborhood"), family (eg, family members abused alcohol or drugs), and peer environment (eg, "I argued or had problems with my boyfriend/girlfriend" and "my friends got drunk or used drugs"). This scale was chosen because 1) it was designed specifically for use with adolescent populations and 2) it assesses the accumulation of life events rather than single discrete stressors, a strategy recommended in stress assessment (45). Total ARCS scores have acceptable test-retest reliability over 4 years (r = 0.49) (C. K. Ewart, unpublished). Evidence of construct validity of the scale is noted in significant correlations between total scores and measures of risk-taking behavior (r = 0.37), depression (r = 0.36), general negative affect (r = 0.44), and reports of illness and injury (r = 0.40) and negative correlations with self-esteem and social support (r = 0.25) (C. K. Ewart, unpublished). With respect to the current study, the total ARCS scale had an internal consistency of 0.74 (Cronbach’s {alpha}). Although there were differences by ethnicity and/or sex in proportions endorsing several individual items, there were no overall significant differences in total score by ethnicity, sex, or their interaction (all p values > .07).

Experimental Procedure
After participants (and their parent(s) if under 18 years of age) signed an informed consent agreement, anthropometric measures were obtained. Participants were then fitted with an appropriately sized BP cuff on the right arm, and two sets of electrodes (one current emitting, one sensing) interfaced with the bioimpedance monitor were positioned 5 cm apart at the level of the xiphoid notch in the midaxillary line and at the angle of the jaw on each side of the neck.

Participants were then placed in a supine position on a standard hospital bed and asked to relax as completely as possible for 15 minutes. Resting hemodynamics were measured at 11, 13, and 15 minutes. The two stressors described above were then presented. All were conducted with the participant in a supine position and were presented within each ethnicity and sex group in a block randomized order. Each stressor was followed by a recovery period of at least 5 minutes until BP returned to within 5 mmHg of the initial supine baseline readings. After completion of the last recovery period, participants were debriefed and paid $50 for their participation.

Data Reduction
Data were reduced by computing mean scores for hemodynamic responses during the supine baseline period. Mean supine scores were then subtracted from peak scores during each of the stressors, and the resulting change scores were used as an index of reactivity.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 METHODS
 RESULTS
DISCUSSION
 ACKNOWLEDGMENTS
 REFERENCES
 
Table 1 presents anthropometric characteristics, resting hemodynamics, and ARCS scores by SES, ethnicity, and sex groups. A series of 2 x 2 (ethnicity by sex) analyses of variance were conducted to assess whether anthropometric characteristics (age, height, weight, BMI), SES, and ARCS scores differed by ethnicity and/or sex. African American participants were older (p < .04), heavier (p < .001), and had a higher BMI (p < .0001) and lower SES (p < .0001) than Caucasian American participants. Males were taller (p < .0001) and heavier (p < .01) and had a lower BMI (p < .02) than females.


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  		Table 1. Unadjusted and Adjusted Meansa (SDs) of Anthropometrics and Resting Hemodynamics by Ethnicity and Gender
 
All subjects who smoked (N = 42) were asked to refrain from smoking for 4 hours before the evaluation. However, the validity of self-reported compliance is questionable. In addition, 22 subjects were taking prescribed medications that could potentially affect hemodynamic function. The data of the individuals who smoked and/or took medications (N = 60) were removed, and analyses were conducted again. The pattern of significant findings remained unchanged. Thus, the results presented below involve the entire sample.

Effects of Stressful Life Events, SES, Ethnicity, and Sex on Resting Hemodynamics
A multivariate analysis of covariance using a general linear models approach was conducted on the supine resting hemodynamic variables using age, BMI, neighborhood SES, family SES, and ARCS scores as covariates and ethnicity and sex as independent variables. The interactions of ethnicity and sex with each other, with ARCS scores, and with SES were also included in the model. After multivariate testing, univariate analyses of covariance were conducted using the same general linear models approach on each dependent variable separately. Only those covariates and main and interaction effects significant in the multivariate model were used in the univariate analyses.

At the multivariate level, age, BMI, SES, ARCS scores, ethnicity, sex, and the ethnicity-by-SES interaction were significant (all p values < .05). At the univariate level, the ethnicity-by-SES interaction was significant only for resting HR, which indicated that among Caucasian Americans, those from a lower family SES tended to have a higher resting HR, whereas the opposite was the case among African Americans.

With respect to sex and ethnicity differences for the remaining resting hemodynamics, males had higher resting SBP (p < .0001) and TPR (p < .0001). Females had higher resting DBP (p < .002), HR (p < .0001), and CO (p < .0001). African Americans had higher resting SBP (p < .0001), DBP (p < .0001), and TPR (p < .0001), and Caucasian Americans had higher CO (p < .02). ARCS effects were noted for resting hemodynamics such that those with higher ARCS scores had lower resting SBP and HR (both p values < .03). For SES, those from lower family SES environments had higher resting DBP than those from higher SES environments (p < .003).

Effects of Stressful Life Events, SES, Ethnicity, and Sex on CVR
Multivariate analyses were conducted using a general linear models approach. First, the reactivity scores were regressed on their corresponding initial baseline resting values. The residual scores were then used as the dependent variables in multivariate analyses with BMI, age, family SES, and neighborhood SES as covariates. Sex, ethnicity, and the order in which the stressors were given were used as fixed effects. In addition, to test the equality of slopes assumption, cross-product terms for each covariate with the fixed effects and their interactions were included in the multivariate analyses. Multivariate analyses were then conducted, and a backward elimination procedure was used to remove the term with the highest p value within each level of interaction. This process was repeated until the only terms remaining in the model were statistically significant ({alpha} = 0.05) or were components of a statistically significant interaction. The final model was then used in a subsequent univariate analysis with each of the reactivity scores as a dependent variable and with the initial baseline resting value as the first covariate. This final model from the multivariate analyses included the following effects: sex-by-order of stressor interaction, sex-by-age interaction, sex, ethnicity, order of stressor presentation, BMI, ARCS score, and family SES.

Car-Driving Simulation
As shown in Table 2, initial baseline levels of SBP, DBP, HR, and CO were significant predictors of their respective CVR measures for car driving such that higher baseline levels were associated with lower CVR (all p values < .02). Higher ARCS scores were also associated with lower SBP, DBP, and HR reactivity (all p values < .01). Ethnicity effects revealed that African Americans exhibited greater HR and CO reactivity than Caucasian Americans (both p values < .05). An age effect for HR reactivity indicated that older subjects were less reactive (p < .05). Greater adiposity (ie, BMI) was associated with lower TPR reactivity (p < .02). Finally, a sex-by-age interaction was noted for SBP reactivity such that overall males were more reactive than females and older males were more reactive than younger males, whereas the opposite was the case among females (p < .01).


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  		Table 2. Models Predicting CVR to Car Driving and SCI
 
Social Stressor Interview
Similar to car driving simulation, SBP, DBP, HR, and CO were significantly inversely related to their respective CVR measures for the SCI (all p values < .001). Higher family SES was associated with greater SBP, DBP, HR, and CO reactivity (all p values < .05). Higher ARCS scores were associated with greater CO reactivity (p < .05). Ethnicity main effects indicated that Caucasian Americans exhibited greater DBP, HR, and TPR reactivity (p values < .01). Sex and age effects for DBP were qualified by a sex-by-age interaction (p < .05) such that males, in general, were more reactive and older males were more reactive than younger males, whereas older females were slightly less reactive than younger females. A sex-by-age interaction (p < .04) was also observed for SBP such that older males were more reactive than younger males, whereas there was little difference by age among females. A sex-by-order interaction (p < .02) was also observed for SBP reactivity such that males exhibited greater reactivity than females overall and displayed the greatest reactivity when car driving preceded the SCI. Females showed greater reactivity when the social stressor preceded the car driving. A sex-by-order interaction for TPR indicated that males were more reactive than females overall and when car driving preceded the SCI, where as females were unaffected by order of stressor (p < .04). Lower adiposity (ie, BMI) was associated with greater HR and TPR reactivity (both p values < .001).


   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 METHODS
 RESULTS
 DISCUSSION
ACKNOWLEDGMENTS
 REFERENCES
 
The purposes of the present study were 1) to examine the effects of stressful life events on CVR to acute laboratory stress in youths and 2) to determine whether these effects varied by ethnicity, sex, and/or SES. The results showed an inverse relationship such that youths, irrespective of ethnicity or sex, who reported high levels of stressful life events showed smaller BP (both SBP and DBP) and HR increases in response to the car-driving simulation than did youths who reported low levels of life stress. These findings are consistent with several other studies in which higher levels of environmental stress exposure (eg, family dysfunction, job strain, and self-reported stressful life events) were associated with attenuated CVR in adults (18–21). On the other hand, a greater number of stressful life events were associated with increased CO reactivity to the SCI.

Our results for car driving are consistent with an inoculation effect, whereby repeated exposure to stressful stimuli can result in a decrease in physiological responsivity to stress over time (13). A review of the childhood resiliency literature indicates that youths who live in stress-filled environments develop adaptive cognitive and behavioral coping skills if provided adequate social support (46). It is thus possible that youths in the present study who reported experiencing stressful life events have developed adaptive coping strategies that subsequently reduced their CV responses to acute laboratory challenge. This may explain the inconsistency between our results and those of Matthews et al. (26), who found greater CVR in youths who reported a single ongoing stressful event but no effects on CVR in youths who reported having resolved a significant life stressor. The youths who showed augmented CVR in that study may have been those who reported an ongoing life stressor with which they had not yet successfully coped, hence the lack of an "inoculation" effect.

On the other hand, youth who reported higher levels of stressful life events exhibited greater CO reactivity to the SCI. These findings are consistent with several adult studies in which chronic stress (eg, job strain, high-density neighborhoods; see Refs. 4, 14, and 16) was associated with exaggerated CVR to a variety of laboratory stressors. Collectively, these findings could be interpreted within an allostatic load model, similar to the Johnston-Brooks et al. (12) findings, which were framed in terms of allostatic load (ie, increased household density) being associated with increased CVR to laboratory stressors in boys.

Several ethnicity differences were observed in response to the stressors. African Americans exhibited greater CO and HR reactivity to the car-driving simulation and greater DBP and TPR reactivity to the SCI. These findings are generally consistent with those of previous youth studies, in which African Americans have frequently exhibited greater BP responsivity to a variety of stressors, including video game challenge, cold stimulation, and dynamic exercise. In many cases, the increased BP was due to a greater increase or less attenuation of vasoconstrictive tone (for review, see Ref. 3).

Interestingly, several sex-by-order interactions were observed for the SCI. If the car-driving stressor preceded the interview, males exhibited higher SBP and TPR reactivity. These findings suggest that even though the protocol ensured subjects returned to baseline levels, there was a differential carryover effect, possibly due to anticipatory anxiety. Thus, future studies should balance the order of stressor presentation within relevant groupings (eg, sex and ethnicity), as was done in the present study. Also, studies should test for possible differential carryover effects by testing the order-by-grouping interaction terms.

Contrary to expectation, SES did not have a buffering effect on the relationship between stressful life events and CVR. In fact, family SES was positively associated with increased BP, CO, and HR reactivity to the SCI. Few youth studies have examined the impact of SES on CVR, and the findings have been mixed. Similar positive relationships have been observed in several studies (41, 42), whereas other studies have revealed inverse relationships (43). Discrepancies in findings to date may be partially attributable to methodological differences, including variability of subject characteristics, choice of stressors, and selection of SES measures. Future studies need to evaluate the impact of other social resources, including perceived social status, social support networks, and other potential moderators of relationships between SES and CVR to acute stress.

Strengths of the present study include the use of a standardized instrument designed specifically for use with adolescents that assesses stressful life events over many domains, a large and sociodemographically diverse sample, and use of two realistic challenging behavioral laboratory stressors. Weaknesses include a lack of evaluation of subjects’ perceptions of various dimensions of life stress (eg, valence, controllability, and duration), which recently have been found to influence CVR (18, 21), valence of the acute stressor and the participant’s abilities to cope with the life stressors, and acute stressors that could result in either an inoculation or exacerbation effect on CVR. The inconsistent findings with respect to life events and CVR between the car-driving and the SCI stressors could in part be related to these factors. Future CVR studies may benefit from following Lazarus and Folkman’s (47) model of coping, in which life events are interpreted in light of the individual’s perceptions of various dimensions of life stress and acute stress as well as his or her personal coping resources (eg, religiosity, social support, coping styles, and perceived social status), which collectively may influence the CVR to acute stress.


   ACKNOWLEDGMENTS
TOP
 ABSTRACT
 INTRODUCTION
 METHODS
 RESULTS
 DISCUSSION
 ACKNOWLEDGMENTS
REFERENCES
 
This research was supported by the National Institutes of Health (Grants HL35073 and HL41781).

Received for publication December 29, 1998.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 METHODS
 RESULTS
 DISCUSSION
 ACKNOWLEDGMENTS
 REFERENCES
 

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