Predictability of repeated challenge: effects on cardiovascular activity in the type A (coronary prone) behavior...

Fifty-two healthy young adults classified either as Type A (coronary prone) or Type B were randomly assigned to a vigilance task during which observing responses produced targets according to either a predictable (i.e., fixed-interval 90-sec) or a nonpredictable (i.e., random-interval 90-sec) reinforcement schedule. During the task, blood volume pulse, interbeat interval, masseter (EMG) activity, and blood pressure were monitored. Transient peripheral vasomotor constriction and heart rate increases were initiated within an 8- to 12-sec period following target detection with the predictable schedule, with subjects evincing greater responsivity than their nonpredictable schedule counterparts. Type A subjects assigned to the random-schedule evinced significantly shorter heart rate and blood volume pulse response durations than did Type B subjects. Longer postevent EMG elevations were evidenced by subjects assigned to the predictable schedule. No significant blood pressure differences were found among the groups. The impact of challenge-contingent behavior on cardiovascular responsivity and the relevance of attentional processes to this relationship and to cardiovascular risk are discussed.