Impedance cardiography was introduced over 20 years ago as a noninvasive and unobtrusive technique for measuring systolic time intervals and cardiac output. Although our understanding of the physiological events reflected in the impedance cardiogram has become more refined, the technique's theoretical basis remains somewhat controversial and acceptance of its validity has relied heavily upon empirical validation. Largely as a consequence of this status, there have been inadequate grounds on which to develop sound methodological standardization. Currently, the methodological approaches that have been most frequently adopted may be viewed as representing the standard. The various aspects of impedance methodology are discussed, and alternative approaches described, with the objective of providing an informed basis for choosing among these methodological alternatives. It is recommended that studies utilizing impedance cardiography should be reported with clear and detailed methodological description. This should help clarify the extent to which methodological differences may underlie any discrepant research observations, as well as facilitate the emergence of improved methodological standards.

Cardiovascular reactivity to stress may have a pathophysiological role in neurogenic hypertension. We studied the value of measuring blood pressure change during standardized mental and physical challenges to prediction of resting blood pressure status 6.5 years later among 206 middle-aged adults and their 164 children, with the latter group originally being tested while enrolled in elementary through high school. After adjustment for age, resting blood pressure, and body mass index at study entry, as well as length of follow-up, larger systolic and diastolic blood pressure responses to a combination of mental and physical challenges were associated with higher subsequent resting diastolic blood pressure 6.5 years later among adults. Among boys, but not among girls, larger systolic and diastolic blood pressure responses to challenge were associated with higher subsequent resting blood pressure. These data suggest that people who are at high risk for elevated blood pressure might have an exaggerated stress-induced cardiovascular response at a younger age.

This study was designed to examine the hypothesis that certain behavioral demands may tend to trigger sympathetic mechanisms which result in metabolically excessive cardiac output elevations. Oxygen consumption and cardiac output adjustments during a contrived reaction‐time shock‐avoidance task were compared to a cold pressor test in healthy young male adults. The linear cardiac output/oxygen consumption relationship generated by performance on a graded exercise task was used to assess the metabolic appropriateness of cardiac output adjustments to the reaction‐time task and cold pressor. The reaction‐time task was generally found to evoke metabolically excessive increases in cardiac output, while cardiac output adjustments to cold pressor were more consistent with changes in metabolic demands. However, the tasks were associated with similar heart rate responses, with a significant attenuation in stroke volume during cold pressor accounting for the differential alterations in cardiac output. This finding suggests a limited reliability for heart rate as an index of cardiac performance. The effects of propranolol, which was employed to evaluate the role of sympathetic influences, indicated that beta‐adrenergic mechanisms were responsible for mediating the cardiac output response to the reaction‐time task, but only partially contributed to the cold pressor response. Post‐hoc analyses of individual differences in cardiovascular reactivity to the reaction‐time task suggest that, for hyperreactive individuals, the coping responses evoked by this task may lead to tissue overperfusion with oxygen, thereby providing a stimulus for autoregulatory vascular reflexes which may be associated with the etiology of hypertensive disease.

Exaggerated cardiovascular reactivity to psychological stress is a potential pathophysiological mechanism linking behavior and cardiovascular disease. Because of the recognized gender differences in incidence of cardiovascular disease, potential gender differences in cardiovascular reactivity to laboratory stressors have been evaluated. The current study examined the cardiovascular responses of a total of 42 young women (N = 22) and men (N = 20) undergoing a laboratory protocol including the following: a nonverbal math task, a mirror tracing task, the Stroop Color-Word interference task, and an isometric handgrip task. In addition to the assessment of heart rate and blood pressure, cardiac output, stroke volume, total peripheral resistance and preejection period were assessed by impedance cardiography. A number of personality characteristics that vary in prevalence by gender were also measured to evaluate their ability to explain potential gender differences in cardiovascular responses. Results indicated that men responded with greater total peripheral resistance and systolic and diastolic blood pressure responses than did women on a subset of tasks, whereas women exhibited larger increases in heart rate on a subset of tasks. Thus, men were more likely to be "vascular" reactors, with women being more likely to be "cardiac" reactors. Personality characteristics did differ between men and women, but did not explain significant variance in the gender differences in cardiovascular responses. We conclude that additional studies should focus on experimental manipulations of potential physiological mechanisms responsible for these differences, such as reproductive hormones.

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The objectives of the present study were threefold: (a) to compare the patterns of hemodynamic responding of children and adolescents during behavioral challenges, (b) to examine whether previously reported cardiovascular reactivity differences between Black and White children are dependent on pubertal status, and (c) to assess whether gender differences in hemodynamic response reported for adults is similar in children. One hundred fifty-nine children (ages 8-10 years) and adolescents (ages 15-17 years), equally divided along gender and racial lines, participated in a laboratory protocol consisting of a reaction time task, a mirror tracing task, a cold forehead challenge, and a stress interview. Results indicated that adolescents responded with greater beta-adrenergic activation than did children and that gender differences in reactivity often reported for adults emerged more clearly in the adolescents than in the children. This study failed to replicate prior findings of greater vasoconstrictive responses in Black children as compared with White children.

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This study adds to the pediatric literature documenting an association between cardiovascular reactivity to stress and subsequent risk for hypertension. It is the first to show that impedance-derived measures of myocardial function during stress are related to future blood pressure levels.