STUDY OBJECTIVES:This paper aims to determine whether experimental arousals from sleep delay the sleep related fall in cardiovascular activity in healthy adults. DESIGN:We report the results of 2 studies. The first experiment manipulated arousals from sleep in young adults. The second compared the effect of frequent arousals on young and middle-aged adults. The influence of arousals were assessed in 2 ways; (1) the fall in cardiovascular activity over sleep onset and the early sleep period, and (2) the underlying sleep levels during the sleep periods in between arousals. SETTING:Both experiments were conducted in the sleep laboratory of the Department of Psychology, The University of Melbourne, Australia. PARTICIPANTS:There were 5 male and 5 female healthy individuals in each experiment between the ages of 18-25 years (Experiment 1) and 38-55 years (Experiment 2). INTERVENTIONS:Participants in Experiment 1 were aroused by auditory stimuli every (i) 2 min, (ii) 1 min, and (iii) 30 sec of sleep for 90 min after the first indication of sleep. In a control condition, participants slept undisturbed for one NREM sleep cycle. Experiment 2 compared the control with the 30-sec condition in the young adults and in an additional group of middle-aged adults. MEASUREMENTS AND RESULTS:The dependent variables were blood pressure (BP) and heart rate (HR). In Experiment 1, sleep fragmentation at higher frequencies retarded the fall in BP over sleep onset but did not affect the underlying sleep levels. Experiment 2 showed that there were no age differences on the effect of arousals on changes in BP and HR during sleep. CONCLUSIONS:This paper supports the hypothesis that repetitive arousals from sleep independently contribute to elevations in BP at night.