THE CIRCADIAN VARIATION OF CARDIOVASCULAR STRESS LEVELS AND REACTIVITY - RELATIONSHIP TO INDIVIDUAL-DIFFERENCES IN MORNINGNESS-EVENINGNESS

Two studies assessed the circadian variation of cardiovascular respons es to stress in healthy and coronary artery disease (CAD) populations. In within-subjects designs, stressors were administered to healthy ma le subjects and male CAD patients both in the morning and afternoon, a nd subjects were classified as either morning or evening types using t he Morningness-Eveningness Questionnaire (Home & Ostberg, 1976, Intern ational Journal of Chronobiology, 4, 97-110). No consistent circadian variation in blood pressure or heart rate responses was observed in th e aggregate sample of either healthy subjects or CAD patients. However , there were significant interactions between circadian type and time of day. In both populations, morning subjects exhibited higher cardiov ascular levels during the morning session, and evening subjects exhibi ted higher levels during the afternoon session. Analyses of cardiovasc ular reactivity revealed less consistent evidence for this interaction . Self-reports of stress revealed interactions between time of day and morningness/eveningness only in the CAD sample. In CAD patients, prel iminary analysis of myocardial wall function, an index of myocardial i schemia, did not reveal a significant interaction between morningness/ eveningness and time of day, perhaps due to small sample size. The pre sence of differing circadian patterns in stress response based on indi vidual differences in morningness/eveningness is discussed in terms of its methodological implications for psychophysiological research and in terms of the role of stress as an acute trigger of CAD.