TEMPORAL STABILITY OF HEART PERIOD VARIABILITY DURING A RESTING BASE-LINE AND IN RESPONSE TO PSYCHOLOGICAL CHALLENGE

Central to the psychophysiologic reactivity hypothesis of the etiology of coronary artery disease is the assumption that reactivity is an in dividual characteristic that is stable over time. Although heart rate (HR) and blood pressure reactivity appear to meet this criterion, temp oral stability of cardiac autonomic control as measured by analysis of heart period variability (HPV) has not been assessed. In this study, we tested the stability of HPV, measured in both the time and frequenc y domain, during a quiet, resting baseline and in response to 5-min me ntal arithmetic and reaction time tasks, in 20 normal subjects measure d in three testing sessions during a 9-month period. Stability, assess ed by the intraclass correlation coefficient (ICC), was excellent for resting baseline measures of HR and HPV, with ICCs of 0.68-0.86. Howev er, HR and HPV reactivity to either arithmetic or reaction time tasks generally was less stable, with ICCs of 0.17-0.73, in contrast to resu lts of previous studies demonstrating longterm stability of HR respons es to psychological challenge. Stability of aggregated reactivity scor es was only slightly improved. Whether for individual tasks or aggrega ted measures, reactivity of total and low-frequency measures of HPV wa s moderately stable but stability of high-frequency HPV reactivity was poor.