On the nature of cardiovascular activation at an arousal from sleep

STUDY OBJECTIVES: The intent of the study was to explore the nature and function of the cardiovascular activation response that occurs at an arousal from sleep. DESIGN: Four experiments were conducted. The first compared the pattern of physiologic response to orienting and startle stimuli and arousal from sleep. The second and third measured the amplitude of the cardiovascular arousal response as a function of the trait of fearfulness and the threat value of the arousing stimulus, respectively. The final experiment assessed the effect of arousal duration. SETTING: The experiments were conducted in the sleep laboratory of the Department of Psychology, University of Melbourne. PARTICIPANTS: A total of 42 (24 women and 18 men) healthy individuals between the ages of 18 and 24 participated in the experiments. INTERVENTIONS: The experiments manipulated the stimuli to which participants were exposed (orienting and startle stimuli and arousal from sleep), the threat value of stimuli used to arouse participants from sleep, and individual differences in fearfulness. MEASUREMENTS AND RESULTS: The major dependent variables were heart rate, blood pressure, and a measure of peripheral vasoconstriction (digital pulse volume). In addition, in the first study, the galvanic skin response and orbicularis oculi electromyographic activity were measured. Experiment 1 showed that the pattern of physiologic response at an arousal from sleep differed, with a substantially larger cardiovascular component, from responses to orienting and startle stimuli. Experiments 2a and 2b indicated that the magnitude of the cardiovascular response at an arousal was unrelated to either individual differences in fearfulness or differences in the threat value of arousing stimuli. The final experiment showed that the cardiovascular response at an arousal was not a return to waking levels of activity but, rather, was a transient activation response. CONCLUSIONS: The study supported the view that the cardiovascular activation response at an arousal from sleep is a transient, reflex-like response that is different from the response that occurs during normal wakefulness.