The circadian variation of cardiovascular stress levels and reactivity: relationship to individual differences in morningness/eveningness.

Two studies assessed the circadian variation of cardiovascular responses to stress in healthy and coronary artery disease (CAD) populations. In within-subjects designs, stressors were administered to healthy male subjects and male CAD patients both in the morning and afternoon, and subjects were classified as either morning or evening types using the Morningness-Eveningness Questionnaire (Horne & Ostberg, 1976, International Journal of Chronobiology, 4, 97-110). No consistent circadian variation in blood pressure or heart rate responses was observed in the 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 cardiovascular levels during the morning session, and evening subjects exhibited higher levels during the afternoon session. Analyses of cardiovascular 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, preliminary analysis of myocardial wall function, an index of myocardial ischemia, did not reveal a significant interaction between morningness/eveningness and time of day, perhaps due to small sample size. The presence of differing circadian patterns in stress response based on individual 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.

Automated physical activity monitoring: validation and comparison with physiological and self-report measures.

Physical activity can be assessed via self-report, via physiological measures such as heart rate and oxygen uptake, or via automated monitor. An electronic accelerometer-based physical activity device (Actigraph) has been reported as an improvement over other activity measurement techniques in terms of utility and accuracy. Four studies provide systematic validation and reliability testing for this device and comparisons with other techniques for assessing daily activities. In the first study, the sensitivity of the Actigraph was determined for differentiating physical activities (walking, running, stair climbing, knee bends) versus sedentary activities (reading, typing, playing video games, and performing a mental arithmetic task). Fifteen healthy adults wore the Actigraph on their wrist during activities; oxygen uptake and heart rate were simultaneously recorded. Results revealed that the Actigraph significantly differentiated between the physical activities (p < .0001) and the sedentary activities (p < .0001). Actigraph counts also correlated significantly with oxygen uptake (r = .73) and heart rate (r = .71) during physical activities (r = .46) and sedentary activities (r = .35), respectively. Test-retest reliability was very high for 12 activities (r = .98). The high level of activity differentiation and strong relationship to oxygen uptake and heart rate suggest the usefulness of this device for behavioral and biomedical studies. However, these studies also indicate that the wrist may not always be the most adequate placement for indexing rate and intensity of daily activities and that further studies are needed to determine the optimal site of monitor attachment. Advantages and disadvantages of self-report, physiological, and automated measures of activity are discussed.

Cardiovascular reactivity and mental stress-induced myocardial ischemia in patients with coronary artery disease.

This report evaluates the relationships of hemodynamic reactivity and determinants of myocardial oxygen demand to myocardial ischemia during mental stress in coronary artery disease patients. Thirty-nine patients and 12 controls were studied by radionuclide ventriculography during three mental tasks (arithmetic, Stroop task, and simulated public speaking). Patients were subdivided into three groups based on the severity of ischemic wall motion responses to the mental stressors. Results revealed that systolic blood pressure (SBP) levels during the mental tasks and SBP reactivity (increases) to stress were highest for the severely ischemic group, lowest for controls, with the mild-moderate ischemic and nonischemic patients in between. Severely ischemic patients started out with lower double product (heart rate x SBP) levels, and reached higher levels during the Stroop and speech tasks. There were no reliable group effects for diastolic blood pressure, heart rate, or left ventricular end-diastolic volumes. Among severely ischemic patients, the most potent task in eliciting ischemia (the speech) was associated with higher cardiovascular levels and elicited greater heart rate, double product, and ventricular volume responses. The present data indicate a relationship between cardiovascular levels and reactivity and the magnitude of ischemia induced by mental stress.