Vagal modulation of responses to mental challenge in posttraumatic stress disorder

Background: Studies of the autonomic nervous system in posttraumatic stress syndrome (PTSD) have focused on the sympathetic modulation of arousal and have neglected the parasympathetic contribution. This study addresses the parasympathetic control of heart rate in individuals who have survived traumatic events. Methods: Twenty-nine survivors, 14 with current PTSD and 15 without, participated in the study. The groups were comparable with regard to age, type of trauma, time since the latest traumatic event, and lifetime exposure to traumatic events. Electrocardiograms were recorded during rest and an arithmetic task. Heart period, respiratory sinus arrhythmia (RSA), and the amplitude the Traube-Hering-Mayer wave were quantified. Results: The groups did not differ on resting measures. During the arithmetic task, the past trauma group showed a significant increase in RSA (p < .007), whereas the PTSD group did not. In the past trauma group only, RSA and heart period were highly correlated (r = .75), thereby suggesting that the response to challenge was under vagal control. Conclusion: Trauma survivors who develop PTSD differ from those who do not in the extent to which their heat rate response to challenge is controlled by vagal activity. Responses to challenge in PTSD may be mediated by nonvagal, possibly sympathetic mechanism. Biol Psychiatr 2001;49:637-643 (C) 2001 Society of Biological Psychiatry.