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

Two-year stability of individual differences in (para)sympathetic and HPA-axis responses to public speaking in childhood and adolescence

Long-term stability of individual differences in stress responses has repeatedly been demonstrated in adults, but few studies have investigated the development of stability in adolescence. The present study was the first to investigate the stability of individual differences in heart rate, parasympathetic (RMSSD, pNN50, HF), sympathetic (LF/HF, SC), and HPA-axis (salivary cortisol) responses in a youth sample (8-19 years). Responses to public speaking were measured twice over 2 years. Stability was moderate for absolute responses and task delta responses of HR, RMSSD, pNN50, and HF. Stability was lower for SC and task delta responses of LF/HF and cortisol. Anticipation delta responses showed low stability for HR and cortisol. The latter was moderated by age or puberty, so that individual differences were more stable in more mature individuals. The results support the suggestion that stress responses may be reset during adolescence, but only for the HPA axis.

Physiological reactivity, social support, and memory in early childhood

The interactive effects of physiological reactivity and social support on children's memory were examined. Four- to 6-year-olds completed a laboratory protocol during which autonomic responses and salivary cortisol were measured. Memory was assessed shortly afterward and 2 weeks later. During the second interview, children were questioned by a supportive or nonsupportive interviewer. Few significant relations emerged between reactivity and children's short-term memory. Following a 2-week delay, cortisol reactivity was associated with poorer memory and autonomic reactivity was associated with increased accuracy among children questioned in a supportive manner but decreased accuracy among children questioned in a nonsupportive manner. Results question traditional conceptualizations of reactivity as a risk factor and instead suggest that reactivity may only confer risk in certain environmental contexts.

Modes of cardiovascular regulation during middle childhood

Obtaining meaningful baseline measures of children's cardiovascular activity (CVA) has been difficult because of constraints inherent to laboratory procedures that are used to assess individual differences in response to stress. To circumvent these problems, we performed repeated baseline measures of pulse rate (PR) and blood pressure for 174 children (aged 7-10 yr) in their natural school setting throughout 2 1-week periods. In addition, experimental assessments of cardiovascular reactivity (CVR) were conducted after each baseline period while children participated in a challenging cognitive task. Multivariate analyses of physiological indices revealed three primary styles of cardiovascular functioning. Two of them, characterizing children either with high PR and low blood pressure or conversely with low PR and high blood pressure, have already been described in the research literature. However, analyses also revealed a third group of children (48% of the subjects) who had both low PR and low blood pressure. Findings indicate developmental differences in cardiovascular regulation and highlight the need to consider both variations in baseline CVA as well as in CVR when examining children's physiological adaptation in everyday settings.

Four-year stability of cardiovascular reactivity to psychological stress

The 4-year stability of cardiovascular responses to laboratory psychological stress (mental arithmetic) was examined in 75 adults. The stability coefficients were .76 for heart rate (HR) change and .81 for absolute HR, .66 for systolic blood pressure (SBP) change and .52 for absolute SBP, .16 for diastolic blood pressure (DBP) change and .27 for absolute DBP. Males had greater SBP and DBP reactivity than females in the first session, but this reactivity decreased by the 4-year follow-up session (which was not the case for women).

Laboratory reactivity models as predictors of ambulatory blood pressure and heart rate

We attempted to validate the usefulness of the laboratory reactivity paradigm by examining responses to three distinct lab tasks and an overall lab average as predictors for ambulatory blood pressure. Subjects were 126 university students. We assessed ambulatory blood pressure, heart rate and perceived distress during an 8-hr working day. In the lab, all subjects responded to three standardized 5-min tasks: isometric handgrip, mental arithmetic, and a structured discussion of a recent interpersonal conflict situation. The analyses used absolute task levels, change scores, a composite index of reactivity, and a mean value for all obtained lab measures. Task levels correlated significantly with means of the ambulatory cardiovascular indices; the scores ranged from 0.35 to 0.49 for SBP, from 0.45 to 0.58 for DBP, and from 0.57 to 0.65 for HR. Only the DBP change score associated with the discussion task correlated with the ambulatory mean. The correlations between lab task levels and ambulatory measures were strongest for the discussion task and the composite score; the task level for the math task was consistently the weakest predictor of ambulatory activity. When lab resting values were forced into a step-wise multiple regression as step one, only the response to the discussion added significantly (3% each for SBP and DBP) to the variance in ambulatory pressure that was not already explained by resting values. The overall lab mean for SBP was a better predictor of the ambulatory mean than was any combination of resting values and reactivity indices.

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.

Alternate cardiovascular baseline assessment techniques: vanilla or resting baseline

The accurate evaluation of cardiovascular reactions to psychological challenge requires stable baselines against which change can be evaluated. When more than one challenge is employed, the recovery of this baseline becomes important in order to avoid carryover effects. Resting periods, even those of 20 min or more, do not guarantee baseline stability. We compared a 20-min resting condition and a new form of baseline condition in 48 college men using video tasks as the psychological challenges. The new form was a minimally demanding color detection task, termed the "vanilla" baseline condition. A 10-min version and a 20-min version of this condition were tested. Comparisons to 10-min resting baselines were made using our prior work and values from the literature. Vanilla baseline conditions were shown to be equal to or better than resting baseline conditions using criteria of between- and within-baseline stability, amplitude and significance of responsivity, and generalizability between sessions on separate days. Ten-minute resting baselines also showed acceptable stability, questioning the value of lengthy baselines. The good performance of the 10-min vanilla baseline in initial and replication samples supported its utility for estimating baselines for many purposes.

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.