This pilot study was conducted to determine what affects the cardiovascular reactivity of different people. Variables such as the order of stress-inducing and relaxing activities, performing multiple tasks on different days, personality, familial history of diseases, and general health were investigated as to their effects, if any, on cardiovascular reactivity.

Ten healthy, normal male subjects, aged 18 - 33 years, volunteered to be subjected to studies on three experimental days, the first one being for gathering information. On the second and third days, the subjects performed the following activities: mental arithmetic, numeric repetition, 10 breaths-per-minute (bpm) paced-breathing, and normal breathing, with 12-minute periods of rest before and after each activity. EKG, blood pressure, and respiration measurements were recorded from each subject throughout the entire 90-minute sessions.

Results from the statistical analysis showed that the vagal tone readings for the normal breathing activity were affected by the subject's depression state, the order of the activities, performing multiple tasks on different days (session), and the interaction of depression and order or session. Readings for both the mental arithmetic and numeric repetition activities were only affected by the subject's depression state. No factors affected the readings for the 1 O-bpm paced breathing activity. Other factors did not provide insight to the differences in vagal tone readings between subjects. Further study, preferably with more subjects, is needed to substantiate these results.